Wireless communication systems and methods for long-code communications for regenerative multiple user detection involving matched-filter outputs

[0001] This application claims the benefit of priority of (i) U.S. Provisional Application Serial No. 60/275,846 filed Mar. 14, 2001, entitled Improved Wireless Communications Systems and Methods; (ii) U.S. Provisional Application Serial No. 60/289,600 filed May 7, 2001, entitled Improved Wireless Communications Systems and Methods Using Long-Code Multi-User Detection and (iii) U.S. Provisional Application Serial Number. 60/295,060 filed Jun. 1, 2001 entitled Improved Wireless Communications Systems and Methods for a Communications Computer, the teachings all of which are incorporated herein by reference.

[0002] The invention pertains to wireless communications and, more particularly, by way of example, to methods and apparatus providing multiple user detection for use in code division multiple access (CDMA) communications. The invention has application, by way of non-limiting example, in improving the capacity of cellular phone base stations.

[0003] Code-division multiple access (CDMA) is used increasingly in wireless communications. It is a form of multiplexing communications, e.g., between cellular phones and base stations, based on distinct digital codes in the communication signals. This can be contrasted with other wireless protocols, such as frequency-division multiple access and time-division multiple access, in which multiplexing is based on the use of orthogonal frequency bands and orthogonal time-slots, respectively.

[0004] A limiting factor in CDMA communication and, in particular, in so-called direct sequence CDMA (DS-CDMA) communication, is the interference between multiple cellular phone users in the same geographic area using their phones at the same time, which is referred to as multiple access interference (MAI). Multiple access interference has an effect of limiting the capacity of cellular phone base stations, driving service quality below acceptable levels when there are too many users.

[0005] A technique known as multi-user detection (MUD) is intended to reduce multiple access interference and, as a consequence, increases base station capacity. It can reduce interference not only between multiple transmissions of like strength, but also that caused by users so close to the base station as to otherwise overpower signals from other users (the so-called near/far problem). MUD generally functions on the principle that signals from multiple simultaneous users can be jointly used to improve detection of the signal from any single user. Many forms of MUD are discussed in the literature; surveys are provided in Moshavi, Multi-User Detection for DS-CDMA Systems, IEEE Communications Magazine (October, 1996) and Duel-Hallen et al, Multiuser Detection for CDMA Systems, IEEE Personal Communications (April 1995). Though a promising solution to increasing the capacity of cellular phone base stations, MUD techniques are typically so computationally intensive as to limit practical application.

[0006] An object of this invention is to provide improved methods and apparatus for wireless communications. A related object is to provide such methods and apparatus for multi-user detection or interference cancellation in code-division multiple access communications.

[0007] A further related object is to provide such methods and apparatus as provide improved short-code and/or long-code CDMA communications.

[0008] A further object of the invention is to provide such methods and apparatus as can be cost-effectively implemented and as require minimal changes in existing wireless communications infrastructure.

[0009] A still further object of the invention is to provide methods and apparatus for executing multi-user detection and related algorithms in real-time.

[0010] A still further object of the invention is to provide such methods and apparatus as manage faults for high-availability.

[0011] Wireless Communication Systems And Methods For Long-code Communications For Regenerative Multiple User Detection Involving Implicit Waveform Subtraction

[0012] The foregoing and other objects are among those attained by the invention which provides, in one aspect, an improved spread-spectrum communication system of the type that processes one or more spread-spectrum waveforms, e.g., a CDMA transmissions, each representative of a waveform received from, or otherwise associated with, a respective user (or other transmitting device). The improvement is characterized by a first logic element, e.g., operating in conjunction with a wireless base station receiver and/or modem, that generates a residual composite spread-spectrum waveform as a function of a composite spread-spectrum waveform and an estimated composite spread-spectrum waveform. It is further characterized by one or more second logic elements that generate, for at least a selected user (or other transmitter), a refined matched-filter detection statistic as a function of the residual composite spread-spectrum waveform generated by the first logic element and a characteristic of an estimate of the selected user's spread-spectrum waveform.

[0013] Related aspects of the invention as described above provide a system as described above in which the first logic element comprises arithmetic logic that generates the composite spread-spectrum waveform based on a relation

[0014] wherein

[0015] r_res⁽ⁿ⁾t is the residual composite spread-spectrum waveform,

[0016] rt represents the composite spread-spectrum waveform,

[0017] {circumflex over (r)}⁽ⁿ⁾t represents the estimated composite spread-spectrum waveform,

[0018] t is a sample time period, and

[0019] n is an iteration count,

[0020] The estimated composite spread-spectrum waveform, according to further related aspects, can be pulse-shaped and based on estimated complex amplitudes, estimated symbols, and codes encoded within the user waveforms.

[0021] Still further aspects of the invention provide improved spread-spectrum communication systems as described above in which the one or more second logic elements comprise rake logic and summation logic, which generate the refined matched-filter detection statistic for at least the selected user based on a relation

[0022] wherein

[0023] A_k⁽ⁿ⁾² represents an amplitude statistic,

[0024] {circumflex over (b)}_k⁽ⁿ⁾m represents a soft symbol estimate for the k^th user for the m^th symbol period,

[0025] y_res.k⁽ⁿ⁾m represents a residual matched-filter detection statistic for the k^th user, and

[0026] n is an iteration count.

[0027] Further related aspects of the invention provide improved systems as described above wherein the refined matched-filter detection statistics for each user is iteratively generated. Related aspects of the invention provide such systems in which the user spread-spectrum waveform for at least a selected user is generated by a receiver that operates on long-code CDMA signals.

[0028] Further aspects of the invention provide a spread spectrum communication system, e.g., of the type described above, having a first logic element which generates an estimated composite spread-spectrum waveform as a function of estimated user complex channel amplitudes, time lags, and user codes. A second logic element generates a residual composite spread-spectrum waveform a function of a composite user spread-spectrum waveform and the estimated composite spread-spectrum waveform. One or more third logic elements generate a refined matched-filter detection statistic for at least a selected user as a function of the residual composite spread-spectrum waveform and a characteristic of an estimate of the selected user's spread-spectrum waveform.

[0029] A related aspects of the invention provides such systems in which the first logic element generates the estimated re-spread waveform based on a relation ${}^{\left(n\right)}\left[t\right]=\underset{k=1}{\overset{K_v}{}}\underset{p=1}{\overset{L}{}}\underset{r}{}\left[t-{\hat{}}_{\mathrm{kp}}^{\left(n\right)}-{\mathrm{rN}}_c\right]{\hat{a}}_{\mathrm{kp}}^{\left(n\right)}{c}_k\left[r\right]{\hat{b}}_k^{\left(n\right)}\left[r/N_k\right]$

[0030] wherein

[0031] K_v is a number of simultaneous dedicated physical channels for all users,

[0032] t is a discrete-time delta function,

[0033] _kp^(a) is an estimated complex channel amplitude for the p^th multipath component for the k^th user,

[0034] c_kr represents a user code comprising at least a scrambling code, an orthogonal variable spreading factor code, and a j factor associated with even numbered dedicated physical channels,

[0035] {circumflex over (b)}_k⁽ⁿ⁾m represents a soft symbol estimate for the k^th user for the m^th symbol period,

[0036] {circumflex over ()}_kp⁽ⁿ⁾ is an estimated time lag for the p^th multipath component for the k^th user,

[0037] N_k is a spreading factor for the k^th user,

[0038] t is a sample time index,

[0039] L is a number of multi-path components.,

[0040] N_c is a number of samples per chip, and

[0041] n is an iteration count.

[0042] Related aspects of the invention provide systems as described above wherein the first logic element comprises arithmetic logic that generates the estimated composite spread-spectrum waveform based on the relation

[0043] ${\hat{r}}^{\left(n\right)}\left[t\right]=\underset{r}{}g\left[r\right]{}^{\left(n\right)}\left[t-r\right],$

[0044] wherein

[0045] {circumflex over (r)}⁽ⁿ⁾t represents the estimated composite spread-spectrum waveform,

[0046] gt represents a raised-cosine pulse shape.

[0047] Related aspects of the invention provide such systems that comprise a CDMA base station, e.g., of the type for use in relaying voice and data traffic from cellular phone and/or modem users. Still further aspects of the invention provide improved spread spectrum communication systems as described above in which the user waveforms are encoded using long-code CDMA protocols.

[0048] Still other aspects of the invention provide methods multiple user detection in a spread-spectrum communication system paralleling the operations described above.

[0049] Wireless Communication Systems And Methods For Long-code Communications For Regenerative Multiple User Detection Involving Matched-filter Outputs

[0050] Further aspects of the invention provide an improved spread spectrum communication system, e.g., of the type described above, having first logic element operating in conjunction with a wireless base station receiver and/or modem, that generates an estimated composite spread-spectrum waveform as a function of user waveform characteristics, e.g., estimated complex amplitudes, time lags, symbols and code. The invention is further characterized by one or more second logic elements that generate for at least a selected user a refined matched-filter detection statistic as a function of a difference between a first matched-filter detection statistic for that user and an estimated matched-filter detection statisticthe latter of which is a function of the estimated composite spread-spectrum waveform generated by the first logic element.

[0051] Related aspects of the invention as described above provide for improved wireless communications wherein each of the second logic elements generate the refined matched-filter detection statistic for the selected user as a function of a difference between (i) a sum of the first matched-filter detection statistic for that user and a characteristic of an estimate of that user's spread-spectrum waveform, and (ii) the estimated matched-filter detection statistic for that user based on the estimated composite spread-spectrum waveform.

[0052] Further related aspects of the invention provide systems as described above in which the second logic elements comprise rake logic and summation logic which generates refined matched-filter detection statistics for at least a selected user in accord with the relation

[0053] wherein

[0054] A_k⁽ⁿ⁾² represents an amplitude statistic,

[0055] {circumflex over (b)}_k⁽ⁿ⁾m represents a soft symbol estimate for the k^th user for the m^th symbol period,

[0056] y_k⁽ⁿ⁾m represents the first matched-filter detection statistic,

[0057] y_est,k⁽ⁿ⁾m represents the estimated matched-filter detection statistic, and

[0058] n is an iteration count.

[0059] Other related aspects of the invention include generating the refined matched-filter detection statistic for the selected user and iteratively refining that detection statistic zero or more times.

[0060] Related aspects of the invention as described above provide for improved wireless communications methods wherein an estimated composite spread-spectrum waveform is based on the relation $y_{\mathrm{est},k}^{\left(n\right)}\left[m\right]\mathrm{Re}\left\{\underset{p=1}{\overset{L}{}}{\hat{a}}_{\mathrm{kp}}^{\left(n\right)H}\frac{1}{2N_k}\underset{r=0}{\overset{N_k-1}{}}{\hat{r}}^{\left(n\right)}\left[{\mathrm{rN}}_c+{\hat{}}_{\mathrm{kp}}^{\left(n\right)}+{\mathrm{mT}}_k\right]c_{\mathrm{km}}^{*}\left[r\right]\right\},$

[0061] wherein

[0062] L is a number of multi-path components,

[0063] _kp⁽ⁿ⁾ is an estimated complex channel amplitude for the p^th multipath component for the k^th user,

[0064] N_k is a spreading factor for the k^th user,

[0065] {circumflex over (r)}⁽ⁿ⁾t represents the estimated composite spread-spectrum waveform,

[0066] N_c is a number of samples per chip,

[0067] {circumflex over ()}_kp⁽ⁿ⁾ is an estimated time lag for the p^th multipath component for the k^th user,

[0068] m is a symbol period,

[0069] T_k is a data bit duration,

[0070] n is an iteration count, and

[0071] c_kmr represents a user code comprising at least a scrambling code, an orthogonal variable spreading factor code, and aj factor associated with even numbered dedicated physical channels.

[0072] Wireless Communication Systems And Methods For Long-code Communications For Regenerative Multiple User Detection Involving Pre-maximal Combination Matched Filter Outputs

[0073] Still further aspects of the invention provide improved-spread spectrum communication systems, e.g., of the type described above, having one or more first logic elements, e.g., operating in conjunction with a wireless base station receiver and/or modem, that generate a first complex channel amplitude estimate corresponding to at least a selected user and a selected finger of a rake receiver that receives the selected user waveforms. One or more second logic elements generate an estimated composite spread-spectrum waveform that is a function of one or more complex channel amplitudes, estimated delay lags, estimated symbols, and/or codes of the one or more user spread-spectrum waveforms. One or more third logic elements generate a second pre-combination matched-filter detection statistic for at least a selected user and for at least a selected finger as a function of a first pre-combination matched-filter detection statistic for that user and a pre-combination estimated matched-filter detection statistic for that user.

[0074] Related aspects of the invention provide systems as described above in which one or more fourth logic elements generate a second complex channel amplitude estimate corresponding to at least a selected user and at least selected finger.

[0075] Still further aspects of the invention provide systems as described above in which the third logic elements generate the second pre-combination matched-filter detection statistic for at least the selected user and at least the selected finger as a function of a difference between (i) the sum of the first pre-combination matched-filter detection statistic for that user and that finger and a characteristic of an estimate of the selected user's spread-spectrum waveform and (ii) the pre-combination estimated matched-filter detection statistic for that user and that finger.

[0076] Related aspects of the invention as described above provide for the first logic elements generating a complex channel amplitude estimated corresponding to at least a selected user and at least a selected finger of a rake receiver that receives the selected user waveforms based on a relation ${\hat{a}}_{\mathrm{kp}}^{\left(n\right)}\underset{s}{}w\left[s\right]\frac{1}{N_p}\underset{m=0}{\overset{N_p-1}{}}{y}_{\mathrm{kp}}^{\left(n\right)}\left[m+\mathrm{Ms}\right]b_k^{\left(n\right)}\left[m+\mathrm{Ms}\right]$

[0077] wherein

[0078] _kp⁽ⁿ⁾ is a complex channel amplitude estimate corresponding to the p^th finger of the k^th user,

[0079] ws is a filter,

[0080] N_p is a number of symbols,

[0081] y_kp⁽ⁿ⁾m is a first pre-combination matched-filter detection statistic corresponding to the p^th finger of the k^th user for the m^th symbol period,

[0082] M is a number of symbols per slot,

[0083] {circumflex over (b)}_k⁽ⁿ⁾m represents a soft symbol estimate for the k^th user for the m^th symbol period,

[0084] m is a number symbol period index,

[0085] s is a slot index, and

[0086] n is an iteration count.

[0087] Further related aspects of the invention as described above provide for one or more second logic elements, each coupled with a first logic element and using the complex channel amplitudes generated therefrom to generate an estimated composite re-spread waveform based on the relation ${}^{\left(n\right)}\left[t\right]=\underset{k=1}{\overset{K_v}{}}\underset{p=1}{\overset{L}{}}\underset{r}{}\left[t-{\hat{}}_{\mathrm{kp}}^{\left(n\right)}-{\mathrm{rN}}_c\right]{\hat{a}}_{\mathrm{kp}}^{\left(n\right)}{c}_k\left[r\right]{\hat{b}}_k^{\left(n\right)}\left[r/N_k\right],$

[0088] wherein

[0089] K_v is a number of simultaneous dedicated physical channels for all users,

[0090] t is a discrete-time delta function,

[0091] _kp⁽ⁿ⁾ is an estimated complex channel amplitude for the p^th multipath component for the k^th user,

[0092] c_kr represents a user code comprising at least a scrambling code, an orthogonal variable spreading factor code, and a j factor associated with even numbered dedicated physical channels,

[0093] {circumflex over (b)}_k⁽ⁿ⁾m represents a soft symbol estimate for the k^th user for the m^th symbol period,

[0094] {circumflex over ()}_kp⁽ⁿ⁾ is an estimated time lag for the p^th multipath component for the k^th user,

[0095] N_k is a spreading factor for the k^th user,

[0096] t is a sample time index,

[0097] L is a number of multi-path components.,

[0098] N_c is a number of samples per chip, and

[0099] n is an iteration count.

[0100] Further related aspects of the invention provide systems as described above in which the second logic element comprises arithmetic logic that generates the estimated composite spread-spectrum waveform based on a relation

[0101] ${\hat{r}}^{\left(n\right)}\left[t\right]=\underset{r}{}g\left[r\right]{}^{\left(n\right)}\left[t-r\right]$

[0102] wherein

[0103] {circumflex over (r)}⁽ⁿ⁾t represents the estimated composite spread-spectrum waveform,

[0104] gt represents a pulse shape.

[0105] Still further related aspects of the invention provide systems as described above in which the third logic elements comprise arithmetic logic that generates the second pre-combination matched-filter detection statistic based on the relation

[0106] wherein

[0107] y_kp⁽ⁿ¹⁾m represents the pre-combination matched-filter detection statistic for the p^th finger for the k^th user for the m^th symbol period,

[0108] _kp⁽ⁿ⁾ is the complex channel amplitude for the p^th finger for the k^th user,

[0109] {circumflex over (b)}_k⁽ⁿ⁾m represents a soft symbol estimate for the k^th user for the m^th symbol period,

[0110] y_kp⁽ⁿ⁾m represents the first pre-combination matched-filter detection statistic for the p^th finger for the k^th user for the m^th symbol period,

[0111] y_est,kp⁽ⁿ⁾m represents the pre-combination estimated matched-filter detection statistic for the p^th finger for the k^th user for the m^th symbol period, and

[0112] n is an iteration count.

[0113] Still further aspects of the invention provide methods of operating multiuser detector logic, wireless base stations and/or other wireless receiving devices or systems operating in the manner of the apparatus above. Further aspects of the invention provide such systems in which the first and second logic elements are implemented on any of processors, field programmable gate arrays, array processors and co-processors, or any combination thereof. Other aspects of the invention provide for interatively refining the pre-combination matched-filter detection statistics zero or more time.

[0114] Other aspects of the invention provide methods for an improved spread-spectrum communication system as the type described above.

[0115] A more complete understanding of the invention may be attained by reference to the drawings, in which:

[0116] FIG. 1 is a block diagram of components of a wireless base-station utilizing a multi-user detection apparatus according to the invention.

[0117] FIG. 2 is a detailed diagram of a modem of the type that receives spread-spectrum waveforms and generates a baseband spectrum waveform together with amplitude and time lag estimates as used by the invention.

[0118] FIGS. 3 and 4 depict methods according to the invention for multiple user detection using explicitly regenerated user waveforms which are added to a residual waveform.

[0119] FIG. 5 depicts methods according to the invention for multiple user detection in which user waveforms are regenerated from a composite spread-spectrum pulsed-shaped waveform.

[0120] FIG. 6 depicts methods according to the invention for multiple user detection using matched-filter outputs where a composite spread-spectrum pulse-shaped waveform is rake-processed.

[0121] FIG. 7 depicts methods according to the invention for multiple user detection using pre-maximum ratio combined matched-filter output, where a composite spread-spectrum pulse-shaped waveform is rake-processed.

[0122] FIG. 8 depicts an approach for processing user waveforms using full or partial decoding at various time-transmission intervals based on user class.

[0123] FIG. 9 depicts an approach for combining multi-path data across received frame boundaries to preserve the number of multi user detection processing frame counts.

[0124] FIG. 10 illustrates the mapping of rake receiver output to virtual to preserve spreading factor and number of data channels across multiple user detection processing frames where the data is linear and contiguous in memory.

[0125] FIG. 11 depicts a long-code loading implementation utilizing pipelined processing and a triple-iteration of refinement in a system according to the invention; and

[0126] FIG. 12 illustrates skewing of multiple user waveforms.

[0127] Code-division multiple access (CDMA) waveforms or signals transmitted, e.g., from a user cellular phone, modem or other CDMA signal source, can become distorted by, and undergo amplitude fades and phase shifts due to phenomena such as scattering, diffraction and/or reflection off buildings and other natural and man-made structures. This includes CDMA, DS/CDMA, IS-95 CDMA, CDMAOne, CDMA2000 1X, CDMA2000 1xEV-DO, WCDMA (or UTMS), and other forms of CDMA, which are collectively referred to hereinafter as CDMA or WCDMA. Often the user or other source (collectively, user) is also moving, e.g., in a car or train, adding to the resulting signal distortion by alternately increasing and decreasing the distances to and numbers of building, structures and other distorting factors between the user and the base station.

[0128] In general, because each user signal can be distorted several different ways en route to the base station or other receiver (hereinafter, collectively, base station), the signal may be received in several components, each with a different time lag or phase shift. To maximize detection of a given user signal across multiple tag lags, a rake receiver is utilized. Such a receiver is coupled to one or more RF antennas (which serve as a collection point(s) for the time-lagged components) and includes multiple fingers, each designed to detect a different multipath component of the user signal. By combining the components, e.g., in power or amplitude, the receiver permits the original waveform to be discerned more readily, e.g., by downstream elements in the base station and/or communications path.

[0129] A base station must typically handle multiple user signals, and detect and differentiate among signals received from multiple simultaneous users, e.g., multiple cell phone users in the vicinity of the base station. Detection is typically accomplished through use of multiple rake receivers, one dedicated to each user. This strategy is referred to as single user detection (SUD). Alternately, one larger receiver can be assigned to demodulate the totality of users jointly. This strategy is referred to as multiple user detection (MUD). Multiple user detection can be accomplished through various techniques which aim to discern the individual user signals and to reduce signal outage probability or bit-error rates (BER) to acceptable levels.

[0130] However, the process has heretofore been limited due to computational complexities which can increase exponentially with respect to the number of simultaneous users. Described below are embodiments that overcome this, providing, for example, methods for multiple user detection wherein the computational complexity is linear with respect to the number of users and providing, by way of further example, apparatus for implementing those and other methods that improve the throughput of CDMA and other spread-spectrum receivers. The illustrated embodiments are implemented in connection with long-code CDMA transmitting and receiver apparatus; however those skilled in the art will appreciate that the methods and apparatus therein may be used in connection with short-code and other CDMA signalling protocols and receiving apparatus, as well as with other spread spectrum signalling protocols and receiving apparatus. In these regards and as used herein, the terms long-code and short-code are used in their conventional sense: the former referring to codes that exceed one symbol period; the latter, to codes that are a single symbol period or less.

[0131] Five embodiments of long-code regeneration and waveform refinement are presented herein. The first two may be referred to as a base-line embodiment and a residual signal embodiment. The remaining three embodiments use implicit waveform subtraction, matched-filter outputs rather than antenna streams and pre-maximum ratio combination of matched-filter outputs. It will be appreciated by those skilled in the art, that other modifications to these techniques can be implemented that produce the like results based on modifications of the methods described herein.

[0132] FIG. 1 depicts components of a wireless base station 100 of the type in which the invention is practiced. The base station 100 includes an antenna array 114, radio frequency/intermediate frequency (RF/IF) analog-to-digital converter (ADC), multi-antenna receivers 110, rake modems 112, MUD processing logic 118 and symbol rate processing logic 120, coupled as shown.

[0133] Antenna array 114 and receivers 110 are conventional such devices of the type used in wireless base stations to receive wideband CDMA (hereinafter WCDMA) transmissions from multiple simultaneous users (here, identified by numbers 1 through K). Each RF/IF receiver (e.g., 110) is coupled to antenna or antennas 114 in the conventional manner known in the art, with one RF/IF receiver 110 allocated for each antenna 114. Moreover, the antennas are arranged per convention to receive components of the respective user waveforms along different lagged signal paths discussed above. Though only three antennas 114 and three receivers 110 are shown, the methods and systems taught herein may be used with any number of such devices, regardless of whether configured as a base station, a mobile unit or otherwise. Moreover, as noted above, they may be applied in processing other CDMA and wireless communications signals.

[0134] Each RF/IF receiver 110 routes digital data to each modem 112. Because there are multiple antennas, here, Q of them, there are typically Q separate channel signals communicated to each modem card 112.

[0135] Generally, each user generating a WCDMA signal (or other subject wireless communication signal) received and processed by the base station is assigned a unique long-code code sequence for purpose of differentiating between the multiple user waveforms received at the basestation, and each user is assigned a unique rake modem 112 for purpose of demodulating the user's received signal. Each modem 112 may be independent, or may share resources from a pool. The rake modems 112 process the received signal components along fingers, with each receiver discerning the signals associated with that receiver's respective user codes. The received signal components are denoted here as r_kqt denoting the channel signal (or waveform) from the k^th user from the q^th antenna, or r_kt denoting all channel signals (or waveforms) originating from the k^th user, in which case r_kt is understood to be a column vector with one element for each of the Q antennas. The modems 112 process the received signals r_kt to generate detection statistics y_k⁽⁰⁾m for the k^th user for the m^th symbol period. To this end, the modems 122 can, for example, combine the components r_kqt by power, amplitude or otherwise, in the conventional manner to generate the respective detection statistics y_k⁽⁰⁾m. In the course of such processing, each modem 112 determines the amplitude (denoted herein as a) of and time lag (denoted herein as ) between the multiple components of the respective user channel. The modems 112 can be constructed and operated in the conventional manner known in the art, optionally, as modified in accord with the teachings of some of the embodiments below.

[0136] The modems 112 route their respective user detection statistics y_k⁽⁰⁾m, as well as the amplitudes and time lags, to common user detection (MUD) 118 logic constructed and operated as described in the sections that follow. The MUD logic 118 processes the received signals from each modem 112 to generate a refined output, y_k⁽¹⁾m, or more generally, y_k⁽ⁿ⁾m, where n is an index reflecting the number of times the detection statistics are iteratively or regeneratively processed by the logic 118. Thus, whereas the detection statistic produced by the modems is denoted as y_k⁽⁰⁾m indicating that there has been no refinement, those generated by processing the y_k⁽⁰⁾m detection statistics with logic 118 are denoted y_k⁽⁰⁾m, those generated by processing the y_k⁽¹⁾m detection statistics with logic 118 are denoted y_k⁽²⁾m, and so forth. Further waveforms used and generated by logic 118 are similarly denoted, e.g., r⁽ⁿ⁾t.

[0137] Though discussed below are embodiments in which the logic 118 is utilized only once, i.e., to generate y_k⁽¹⁾m from y_k⁽⁰⁾m, other embodiments may employ that logic 118 multiple times to generate still more refined detection statistics, e.g., for wireless communications applications requiring lower bit error rates (BER). For example, in some implementations, a single logic stage 118 is used for voice applications, whereas two or more logic stages are used for data applications. Where multiple stages are employed, each may be carried out using the same hardware device (e.g., processor, co-processor or field programmable gate array) or with a successive series of such devices.

[0138] The refined user detection statistics, e.g., y_k⁽¹⁾m or more generally y_k⁽ⁿ⁾m, are communicated by the MUD process 118 to a symbol process 120. This determines the digital information contained within the detection statistics, and processes (or otherwise directs) that information according to the type of user class for which the user belongs, e.g., voice or data user, all in the conventional manner.

[0139] Though the discussion herein focuses on use of MUD logic 118 in a wireless base station, those skilled in the art will appreciate that the teachings hereof are equally applicable to MUD detection in any other CDMA signal processing environment such as, by way of non-limiting example, cellular phones and modems. For convenience, such cellular base stations other environments are referred to herein as base stations.

[0140] Referring to FIG. 2, modem 112 receives the channel-signals rt 112 from the RF/IC receiver (FIG. 1). The signals are first input into a searcher receiver 212. The searcher receiver analyzes the digital waveform input, and estimates a time offset {circumflex over ()}_kp⁽ⁿ⁾ for each signal component (e.g. for each finger). As those skilled in the art will appreciate, the hat or symbol denotes estimated values. The time offset for each antenna channel is communicated to a corresponding rake receiver 214.

[0141] The rake receiver receivers 214 receive both the digital signals rt from the RF/IF receivers, and the time offsets, {circumflex over ()}_kp⁽ⁿ⁾. The receivers 214 calculate the pre-combination matched-filter detection statistics, y_kp⁽⁰⁾m, and estimate signal amplitude, _kp⁽ⁿ⁾, for each of the signals. The amplitudes are complex in value, and hence include both the magnitude and phase information. The pre-combination matched-filter detection statistics, y_kp⁽⁰⁾m, and the amplitudes _kp⁽ⁿ⁾ for each finger receiver 212, are routed to a maximal ratio combining (MRC) 216 process and combined to form a first approximation of the symbols transmitted by each user, denoted y_k⁽⁰⁾m. While the MRC 216 process is utilized in the illustrated embodiment, other methods for combining the multiple signals are known in the art, e.g., optimal combining, equal gain combining and selection combining, among others, and can be used to achieve the same results.

[0142] At this point, it can be appreciated by one skilled in the art that each detection statistic, y_k⁽⁰⁾m, contains not only the signal originating from user k, but also has components (e.g., interference and noise) that have originated in the channel (e.g., the environment in which the signal was propagated and/or in the receiving apparatus itself). Hence, it is further necessary to differentiate each user's signal from all others. This function is provided by the multiple user detection (MUD) card 118.

[0143] The methods and apparatus described below provide for processing long-code WCDMA at sample rates and can be introduced into a conventional base station as an enhancement to the matched-filter rake receiver. The algorithms and processes can be implemented in hardware, software, or any combination of the two including firmware, field programmable gate arrays (FPGAs), co-processors, and/or array processors.

[0144] The following discussion illustrates the calculations involved in the illustrated multiple user detection process. For the following discussion, and as can be recognized by one skilled in the art, the term physical user refers to an actual user. Each physical user is regarded as a composition of virtual users. The concept of virtual users is used to account for both the dedicated physical data channels (DPDCH) and the dedicated physical control channel (DPCCH). There are 1N_dk virtual users corresponding to the k^th physical user, where N_dk is the number of DPDCHs for the k^th user.

[0145] As one with ordinary skill in the art can appreciate, when long-codes are used, the base-band received signals, rt,, which is a column vector with one element per antenna, can be modeled as: $\begin{array}{cc}r\left[t\right]=\underset{k=1}{\overset{K_v}{}}\underset{m}{}{\tilde{s}}_{\mathrm{km}}\left[t-{\mathrm{mT}}_k\right]b_k\left[m\right]+w\left[t\right]& \left(1\right)\end{array}$

[0146] where t is the integer time sample index, K_v is the number of virtual users, T_kN_kN_c is the channel symbol duration, which depends on the user spreading factor, N_k is the spreading factor for the k^th virtual user, N_c is the number of samples per chip, wt is receiver noise and other-cell interference, {tilde over (s)}_kmt is the channel-corrupted signature waveform for the k^th virtual user over the m^th symbol period, and b_km is the channel symbol for the k^th virtual user over the m^th symbol period.

[0147] Since long-codes extend over many symbol periods, the user signature waveform and hence the channel-corrupted signature waveform vary from symbol period to symbol period. For L multi-path components, the channel-corrupted signature waveform for the k^th virtual user is modeled as, $\begin{array}{cc}{\tilde{s}}_{\mathrm{km}}\left[t\right]=\underset{p=1}{\overset{L}{}}{a}_{\mathrm{kp}}{s}_{\mathrm{km}}\left[t-{}_{\mathrm{kp}}\right]& \left(2\right)\end{array}$

[0148] where _kp are the complex multi-path amplitudes. The amplitude ratios _k are incorporated into the amplitudes _kp. One skilled in the art will see that if k and l are virtual users corresponding to the DPCCH and the DPDCHs of the same physical user, then, aside from scaling by _k and _l, the amplitudes _kp and _lp are equal. This is due to the fact that the signal waveforms for both the DPCCH and the DPDCH pass through the same channel.

[0149] The waveform s_kmt is referred to as the signature waveform for the k^th virtual user over the m^th symbol period. This waveform is generated by passing the code sequence C_kmn through a pulse-shaping filter gt, $\begin{array}{cc}{s}_{\mathrm{km}}\left[t\right]=\underset{r=0}{\overset{N_k-1}{}}g\left[t-{\mathrm{rN}}_c\right]c_{\mathrm{km}}\left[r\right]& \left(3\right)\end{array}$

[0150] where gt is the raised-cosine pulse shape. Since gt is a raised cosine pulse as opposed to a root-raised-cosine pulse, the received signal rt represents the baseband signal after filtering by the matched chip filter. The code sequence c_kmrc_krmN_k represents the combined scrambling code, orthogonal variable spreading factor (OVSF) code and j factor associated with even numbered DPDCHs.

[0151] The received signal rt which has been match-filtered to the chip pulse is next match-filtered by the user long-code sequence filter and combined over multiple fingers. The resulting detection statistic is denoted here as y_lm, the matched-filter output for the l^th virtual user over the m^th symbol period. The matched-filter output y_lm for the l^th virtual user can be written, $\begin{array}{cc}{y}_l\left[m\right]\mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^H\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}r\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]\right\}& \left(4\right)\end{array}$

[0152] where {circumflex over ()}_lq^H is the estimate of _lq^H, and {circumflex over ()}_lq is the estimate of _lq.

[0153] Because of the extreme computational complexity of symbol-rate multiple user detection for long-codes, it is advantageous to resort to regenerative multiple user detection when long-codes are used. Although regenerative multiple user detection operates at the sample rate, for long-codes the overall complexity is lower than with symbol-rate multiple user detection. Symbol-rate multiple user detection requires calculating the correlation matrices every symbol period, which is unnecessary with the signal regeneration methods described herein.

[0154] For regenerative multiple user detection, the signal waveforms of interferers are regenerated at the sample rate and effectively subtracted from the received signal. A second pass through the matched filter then yields improved performance. The computational complexity of regenerative multiple user detection is linear with the number of users.

[0155] By way of review, the implementation of the regenerative multiple user detection can be implemented as a baseline implementation. Referring back to the received signal, rt $\begin{array}{cc}\begin{array}{c}r\left[t\right]=\underset{k=1}{\overset{K_v}{}}\underset{m}{}\underset{p=1}{\overset{L}{}}{a}_{\mathrm{kp}}{s}_{\mathrm{km}}\left[t-{}_{\mathrm{kp}}-{\mathrm{mT}}_k\right]b_k\left[m\right]+w\left[t\right]\\ =\underset{k=1}{\overset{K_v}{}}{r}_k\left[t\right]+w\left[t\right]\end{array}{r}_k\left[t\right]\underset{m}{}\underset{p=1}{\overset{L}{}}{a}_{\mathrm{kp}}{s}_{\mathrm{km}}\left[t-{}_{\mathrm{kp}}-{\mathrm{mT}}_k\right]b_k\left[m\right]& \left(5\right)\end{array}$

[0156] For the baseline implementation, all estimated interference is subtracted yielding a cleaned-up signal {circumflex over (r)}_l⁽ⁿ¹⁾t as follows: $\begin{array}{cc}{\hat{r}}_l^{\left(n+1\right)}\left[t\right]=r\left[t\right]-\underset{\underset{k1}{k=1}}{\overset{K_v}{}}{r}_k^{\left(n\right)}\left[t\right]{\hat{r}}_k^{\left(n\right)}\left[t\right]\underset{m}{}\underset{p=1}{\overset{L}{}}{\hat{a}}_{\mathrm{kp}}^{\left(n\right)}{s}_{\mathrm{km}}\left[t-{\hat{}}_{\mathrm{kp}}^{\left(n\right)}-{\mathrm{mT}}_k\right]b_k^{\left(n\right)}\left[m\right]& \left(6\right)\end{array}$

[0157] The implementation represented by Equation (6) corresponds to a total subtraction of the estimated interference. One skilled in the art will appreciate that performance can typically be improved if only a fraction of the total estimated interference is subtracted (i.e., partial interference subtraction), this owing to channel and symbol estimation errors. Equation (6) is easily modified so as to incorporate partial interference cancellation by introducing a multiplicative constant of magnitude less than unity to the sum total of the estimated interference. When multiple cancellation stages are used the optimum value of this constant is different for each stage.

[0158] The above equations are implemented in the baseline long-code multiple user detection process 118 as illustrated in FIG. 3. The receiver base-band signal rt 122 is input to the rake receiver cards 112 (i.e., one rake receiver for each user) as described above. Each of the rake receivers 112 processes the base-band signal rt 122 and outputs the first approximation of the transmitted symbol, y_k⁽⁰⁾m 304 for each user k (e.g., user 1 through user K), as well as the estimated amplitude _kp⁽⁰⁾, time lag {circumflex over ()}_kp⁽⁰⁾ and user code 306. For ease of notation, here, the superscript refers to the n^th regeneration iteration. Hence, for example, _kp⁽⁰⁾ refers to the base-band because no iterations have been performed.

[0159] The y_k⁽⁰⁾m 304 output from the rake receiver 112 is input into a detector which outputs hard or soft symbol estimates {circumflex over (b)}_k⁽⁰⁾m used to cancel the effects of multiple access interference (MAI). One skilled in the art will appreciate that many different detectors may be used, including the hard-limiting (sign function) detector, the null-zone detector, the hyperbolic tangent detector and the linear-clipped detector, and that soft detectors (all but the first listed above) typically yield improved performance.

[0160] The outputs from the rake receivers 112 and the soft symbol estimates are input into a respreading process 310 which assembles an estimated spread-spectrum waveform corresponding to the selected user but without pulse shaping. The re-spread signals are input into the raised-cosine filter 312 which produces an estimate of the received spread-spectrum waveform for the selected user.

[0161] The raised-cosine pulse shaping process accepts the signals from each of the respread processes (e.g., one for each user), and produces the estimated user waveforms {circumflex over (r)}_k⁽ⁿ⁾t. Next, the waveforms {circumflex over (r)}_k⁽ⁿ⁾t are further processed in a series of summation processes 314, 316, 318 to determine each user's cleaned-up signal {circumflex over (r)}_l⁽ⁿ¹⁾t according to the above equation (6).

[0162] Therefore, for example, to determine the signal corresponding to the 1^st user, the base-band signal rt 122 from the RF/IF receivers 110 containing information from all simultaneous users is reduced by the estimated signals {circumflex over (r)}_k⁽ⁿ⁾t for all users except the 1^st user. After the subtraction of the {circumflex over (r)}_k⁽ⁿ⁾t signals (e.g., {circumflex over (r)}₂⁽ⁿ⁾t through {circumflex over (r)}_Kv⁽ⁿ⁾t as illustrated), the remainder signal contains predominately the signal for the 1st user. Hence, the summation function 314, applies the above equation (6) to produce the cleaned up signal {circumflex over (r)}₁⁽ⁿ¹⁾t. This process is performed for each simultaneous user.

[0163] The output from the summation processes 314, 316, 318 is supplied to the rake receivers 320 (or re-applied to the original rake receivers 112). The resulting signal produced by the rake receivers 320 is the refined matched-filter detection statistic y_k⁽¹⁾m. The superscript (1) indicates that this is the first iteration on the base-band signal. Hence, the base-line long-code multiple user detection is implemented. As illustrated, only one iteration is performed, however, in other embodiments, multiple iterations may be performed depending on limitations (e.g., computational complexity, bandwidth, and other factors).

[0164] It can be appreciated by one skilled in the art that the above methods are limited by bandwidth and computational complexity. Specifically, for example, if K128 , i.e., there are 128 simultaneous users for this implementation, the total bisection bandwidth is 998.8 Gbytes/second, determined with the following assumption, for example:

[0165] The computational complexity is calculated in terms of billion operations per second (GOPS), and is calculated separately for each of the processes of re-spreading, raised-cosine filtering, interference cancellation (IC), and the finger receiver operations. The re-spread process involves amplitude-chip-bit multiply-accumulate operations (macs). Assuming, for example, that there are only four possible chips and further that the amplitude chip multiplications are performed via a table look-up requiring zero GOPS, then the re-spread computational complexity is the (amplitude-chip)(bit macs). Therefore, the re-spread computational cost (in GOPS) is:

[0166] Based on the same assumptions, the raised-cosine filter requires:

[0167] The computational cost of the IC process is

[0168] Finally, the computational complexity for the rake receiver processes is:

[0169] Summing the separate computational complexities for each of the above processes yields the following results:

	Process	GOPS
	Re-Spread	31.5
	Raised Cosine Filtering	1,132.5
	IC	2,013.3
	Finger Receivers	62.9
	TOTAL	3,240.2

[0170] However, both the bandwidth and computation complexity are reduced by employing a residual-signal implementation as now described. The bandwidth can be reduced by forming the residual signal, which is the difference between the received signal and the total (i.e., all users and all multi-paths) estimated signal. Then, the cleaned-up signal {circumflex over (r)}_l⁽ⁿ¹⁾t expressed in terms of the residual signal is: $\begin{array}{cc}\begin{array}{c}{\hat{r}}_l^{\left(n+1\right)}\left[t\right]=r\left[t\right]-\underset{\underset{kl}{k=1}}{\overset{K_v}{}}{\hat{r}}_k^{\left(n\right)}\left[t\right]\\ ={\hat{r}}_l^{\left(n\right)}\left[t\right]+r\left[t\right]-\underset{k=1}{\overset{K_v}{}}{\hat{r}}_k^{\left(n\right)}\left[t\right]\\ ={\hat{r}}_l^{\left(n\right)}\left[t\right]+r_{\mathrm{res}}^{\left(n\right)}\left[t\right]\end{array}{r}_{\mathrm{rest}}^{\left(n\right)}\left[t\right]r\left[t\right]-{\hat{r}}^{\left(n\right)}\left[t\right]r^{\left(n\right)}\left[t\right]\underset{k=1}{\overset{K_v}{}}{r}_k^{\left(n\right)}\left[t\right]& \left(7\right)\end{array}$

[0171] This implementation is illustrated in FIG. 4. One skilled in the art can recognize that through the point of determining the output from the raised-cosine filters, the residual signal implementation is identical with that above illustrated within FIG. 3. It is at this point, the residual signal implementation varies as now described.

[0172] A summation process 402 calculates r_res⁽ⁿ⁾t according to equation (7) above by accepting the base-band signal rt and subtracting the signal {circumflex over (r)}⁽ⁿ⁾t (i.e., the output from all of the raised-cosine filters 310).

[0173] Differing from the baseline implementation, here, a first summation process 402 is performed by subtracting from the baseband signal rt 122 the output from each raised-cosine pulse shaping process 310. This produces the residual signal r_res⁽ⁿ⁾t corresponding to the base-band signal and the total (e.g., all users in all multi-paths) estimated signal.

[0174] The residual signal r_res⁽ⁿ⁾t is supplied to a further summation process for each user (e.g., 404) where the output from that user's raised-cosine pulse shaping process 312 is added to the r_res⁽ⁿ⁾t signal as described in above equation (7), thus determining the cleaned-up signal {circumflex over (r)}_l⁽ⁿ¹⁾t for each user.

[0175] Next, as with the baseline implementation, the cleaned-up signal {circumflex over (r)}_l⁽ⁿ¹⁾t for each user is supplied to a rake receiver 320 (or reapplied to 112) for processing into the resultant y_l⁽ⁿ¹⁾m detection statistics ready for processing by the symbol processor 120.

[0176] One skilled in the art can recognize that both the bandwidth and computational complexity is improved (i.e., lowered) for this implementation compared with the base-line implementation described above. Specifically, continuing with the assumptions used in determining the bandwidth and computational complexity as above and applying those assumptions to the residual-signal implementation, the bandwidth can be estimated as follows:

[0177] The computational complexity for each of the processes is as follows: the re-spreading and raised-cosine are the same as with the baseline implementation.

[0178] For the IC processes, the computational complexity is:

[0179] Finally, the finger receiver processes are the same as with the base-line implementation above. Therefore, summing the separate computational complexities for each of the above processes yields the following results:

	Process	GOPS
	Re-Spread	31.5
	Raised Cosine Filtering	1,132.5
	IC	47.2
	Finger Receivers	62.9
	TOTAL	1,274.1

[0180] Therefore, both the bandwidth and computational complexity is improved, however, it can be recognized by one skilled in the art that even with such improvement, the computational complexity may be a limiting factor.

[0181] Further improvement is possible and is now described within in the following three embodiments, although other embodiments can be recognized by one skilled in the art. One improvement is to utilize a implicit waveform subtraction rather than the explicit waveform subtraction described for use with both the baseline implementation and the residual long-code implementation above. A considerable reduction in computational complexity results if the individual user waveforms are not explicitly calculated, but rather implicitly calculated.

[0182] The illustrated embodiment utilize implicit waveform subtraction by expanding on equation (7) above, and using approximations as shown below in equation (8). $\begin{array}{cc}\begin{array}{c}{y}_l^{\left(n+1\right)}\left[m\right]\mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)H}\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{\hat{r}}_l^{\left(n+1\right)}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(n\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]\right\}\\ =\mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)H}\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{\hat{r}}_l^{\left(n\right)}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(n\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]\right\}+\\ \mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)H}\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{r}_{\mathrm{res}}^{\left(n\right)}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(n\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]\right\}\\ =\mathrm{Re}\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)H}\frac{1}{2N_l}\underset{n=0}{\overset{N_{l-1}}{}}[\underset{m^{}}{}\underset{q^{}=1}{\overset{L}{}}{\hat{a}}_{{\mathrm{lq}}^{}}^{\left(n\right)}{s}_{{\mathrm{lm}}^{}}[{\mathrm{nN}}_c+\\ {\hat{}}_{\mathrm{lq}}^{\left(n\right)}-{\hat{}}_{{\mathrm{lq}}^{}}^{\left(n\right)}+\left(m-m^{}\right)T_l]{\hat{b}}_l^{\left(n\right)}\left[m^{}\right]]c_{\mathrm{lm}}^{*}\left[n\right]\}+y_{\mathrm{res},l}^{\left(n\right)}\left[m\right]\\ \mathrm{Re}\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)H}\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}\left[\underset{q^{}=1}{\overset{L}{}}{\hat{a}}_{{\mathrm{lq}}^{}}^{\left(n\right)}{s}_{\mathrm{lm}}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(n\right)}-{\hat{}}_{{\mathrm{lq}}^{}}^{\left(n\right)}\right]\right]\\ c_{\mathrm{lm}}^{*}\left[n\right]\}{\hat{b}}_l^{\left(n\right)}\left[m\right]+y_{\mathrm{res},l}^{\left(n\right)}\left[m\right]\\ =\mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}\underset{q^{}=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)H}{\hat{a}}_{{\mathrm{lq}}^{}}^{\left(n\right)}\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{s}_{\mathrm{lm}}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(n\right)}-{\hat{}}_{{\mathrm{lq}}^{}}^{\left(n\right)}\right]c_{\mathrm{lm}}^{*}\left[n\right]\right\}\\ {\hat{b}}_l^{\left(n\right)}\left[m\right]+y_{\mathrm{res},l}^{\left(n\right)}\left[m\right]\\ \mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)H}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)}\right\}{b}_l^{\left(n\right)}\left[m\right]+y_{\mathrm{res},l}^{\left(n\right)}\left[m\right]\\ A_l^{\left(n\right)2}{\hat{b}}_l^{\left(n\right)}\left[m\right]+y_{\mathrm{res},l}^{\left(n\right)}\left[m\right]\end{array}& \left(8\right)\end{array}$ $A_l^{\left(n\right)2}\mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)H}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)}\right\}$ $y_{\mathrm{res},l}^{\left(n\right)}\left[m\right]\mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)H}\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{r}_{\mathrm{res}}^{\left(n\right)}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(n\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]\right\}$

[0183] The two approximations used, as indicated within equation (8), include neglecting inter-symbol interference terms for the user of interest, and further, neglecting cross-multi-path interference terms for the user of interest. Because the user of interest term has a strong deterministic term, the omission of these low-level random contributions is justified. These contributions could be included in a more detailed embodiment without incurring excessive increases in computational complexity. However, implementation computational complexity would increase somewhat. Such an embodiment may be appropriate for high data-rate, low spreading factor users where inter-symbol and cross multi-path term are larger.

[0184] A noteworthy aspect of equation (8) above is that the rake receiver operation on the estimated user of interest signal {circumflex over (r)}_l⁽ⁿ⁾t can be calculated analytically. Thus, the signal need not be explicitly formed, but rather, the corresponding contribution is added after the rake receiver operation on the residual signal alone. Now referring to FIG. 5, this implicit waveform subtraction implementation is illustrated.

[0185] One skilled in the art can glean from the illustration that separate re-spreading and raised-cosine processing is no longer performed on each individual user signal, but rather, is performed only once on the baseband composite re-spread signal ⁽ⁿ⁾t. Thus, the re-spread process 312 accumulates the composite signal ⁽ⁿ⁾t based on the amplitudes _kp ⁽ⁿ⁾, time lags {circumflex over ()}_kp⁽ⁿ⁾ and user codes. The output from the re-spreading process produces another composite signal {circumflex over (r)}⁽ⁿ⁾t 502 as described below and in equation (9).

[0186] At this point, it is of note that a substantial reduction in computational complexity accrues due to not having to explicitly calculate the individual user estimated waveforms. As illustrated in FIG. 5, the individual user waveforms are not required, hence, the composite signal ⁽ⁿ⁾t 502 representing the sum of all estimated user waveforms can be formed by calculating this composite waveform first without performing the raised-cosine filtering process on each individual waveform. Only one filtering operation need be performed, which represents a substantial reduction in computational complexity.

[0187] The form of ⁽ⁿ⁾t is as follows: $\begin{array}{cc}{}^{\left(n\right)}\left[t\right]=\underset{k=1}{\overset{K_v}{}}\underset{p=1}{\overset{L}{}}\underset{r}{}\left[t-{\hat{}}_{\mathrm{kp}}^{\left(n\right)}-{\mathrm{rN}}_c\right]{\hat{a}}_{\mathrm{kp}}^{\left(n\right)}{c}_k\left[r\right]{\hat{b}}_k^{\left(n\right)}\left[r/N_k\right]{\hat{r}}^{\left(n\right)}\left[t\right]=\underset{r}{}g\left[r\right]{}^{\left(n\right)}\left[t-r\right]& \left(9\right)\end{array}$

[0188] Now that an understanding of the composite waveform ⁽ⁿ⁾t is accomplished, referring back to FIG. 5, this waveform is transformed into {circumflex over (r)}(n)t via the raised-cosine pulse shaping filter 312. From here, a summation process 506 subtracts {circumflex over (r)}⁽ⁿ⁾t from the base-line waveform rt producing the residual waveform r_res⁽ⁿ⁾t as shown above (e.g., in equation (7)).

[0189] Unlike the residual signal implementation described above, here, the r_res⁽ⁿ⁾t is applied directly to the rake receivers 506 (or reapplied to the rake receivers 112) for each user together with the user code for that user. The output from each rake receiver is applied to a summation process, where the A₁⁽ⁿ⁾²{circumflex over (b)}_l⁽ⁿ⁾m values are added to the rake receiver output as described above in equation (8) producing the y_l⁽ⁿ¹⁾m detection statistics suitable for symbol processing 120.

[0190] The computational complexity of this embodiment is reduced as now described. The re-spread processing and rake receiver computational costs are the same as with the previous implementations. However, the raise-cosine filtering and interference cancellation computational cost is now:

[0191] For the raised-cosine filtering,

[0192] 3.84 Mchips/sec/antenna/multiple user detection stage8 samples/chip2 antennas1 multiple user detection stage6 ops/sample (complex addition then realcomplex mac)24 taps (using symmetry)8.8 GOPS

[0193] The computational cost of the IC process is

[0194] 3.84 Mchips/sec/antenna/multiple user detection stage8 samples/chip2 antennas1 multiple user detection stage2 ops/sample/waveform addition (complex add)1 waveform addition0.123 GOPS

[0195] Summing the separate computational complexities for each of the above processes yields the following results:

	Process	GOPS
	Re-Spread	31.5
	Raised Cosine Filtering	8.8
	IC	0.1
	Finger Receivers	62.9
	TOTAL	103.3

[0196] Another embodiment using matched-filter outputs rather than antenna streams is now presented. This embodiment follows from equation (8) above where the rake receiver outputs are: $\begin{array}{cc}{y}_{\mathrm{res},l}^{\left(n\right)}\left[m\right]\mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)}\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{r}_{\mathrm{res}}^{\left(n\right)}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(n\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]\right\}& \left(10\right)\end{array}$

[0197] and further user equation (7) above, equation (10) can be re-written as: $\begin{array}{cc}\begin{array}{c}{y}_{\mathrm{res},l}^{\left(n\right)}\left[m\right]\mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)H}\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{r}_{\mathrm{res}}^{\left(n\right)}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(n\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]\right\}\\ =\mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)H}\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}r\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(n\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]\right\}-\\ \mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)H}\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{\hat{r}}^{\left(n\right)}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(n\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]\right\}\\ =y_l^{\left(n\right)}\left[m\right]-\mathrm{Re}\begin{array}{c}\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)H}\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{\hat{r}}^{\left(n\right)}[{\mathrm{nN}}_c+\\ {\hat{}}_{\mathrm{lq}}^{\left(n\right)}+{\mathrm{mT}}_l]c_{\mathrm{lm}}^{*}\left[n\right]\}\end{array}\end{array}& \left(11\right)\end{array}$

[0198] and then, combining equation (11) with equation (8) yields: $\begin{array}{cc}{y}_l^{\left(n+1\right)}\left[m\right]=A_l^{\left(n\right)2}{b}_l^{\left(n\right)}\left[m\right]+y_l^{\left(n\right)}-\mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{\left(n\right)H}\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{\hat{r}}^{\left(n\right)}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(n\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]\right\}& \left(12\right)\end{array}$

[0199] This embodiment improves the above approaches in that the antenna streams do not need to be input into the multiple user detection process, however, it is not possible to re-estimate the channel amplitudes.

[0200] Referring to FIG. 6, an illustration of the matched-filter output embodiment is illustrated. As illustrated, the processing of the baseband rt waveform is accomplished as described in FIG. 5 above, and further, ⁽ⁿ⁾t is determined in accordance with equation (9) and is applied to the raised-cosine pulse shaping process 602.

[0201] Differing from the above embodiment, however, there is no summation process before applying {circumflex over (r)}⁽ⁿ⁾t of the second rake receiver process 604. Rather, {circumflex over (r)}⁽ⁿ⁾t is applied directly to the rake receiver process 604. The output from the rake receivers 604 is subtracted 606 from the output y_l⁽ⁿ⁾m from the first rake receivers 112. This difference is then added to the A_l²²{circumflex over (b)}_l⁽ⁿ⁾m value to produce y_l⁽ⁿ¹⁾m. This process is described within the above equations (11) and (12).

[0202] The computational complexity is reduced because there is no longer an explicit interference canceling (IC) operation, and thus, the interference canceling computational cost is zero. The rake receiver computational cost is half the previous embodiment's value because now the re-estimate of the amplitudes cannot be performed, and there is no need to cancel interference on the dedicated physical control channel (DPCCH). Therefore, the computational cost is:

	Process	GOPS
	Re-Spread	31.5
	Raised Cosine Filtering	8.8
	IC	0.0
	Finger Receivers	31.5
	TOTAL	71.8

[0203] Another embodiment using matched-filter outputs obtained before the maximal ratio combination (MRC) is now described. The pre-MRC rake matched-filter outputs can be described as: $\begin{array}{cc}{y}_{\mathrm{lq}}^{\left(0\right)}\left[m\right]=\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}r\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(0\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]& \left(13\right)\end{array}$

[0204] The same detection statistics based on the cleaned up signal {circumflex over (r)}_l⁽ⁿ¹⁾t is $\begin{array}{cc}{y}_{\mathrm{lq}}^{\left(n+1\right)}\left[m\right]=\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{\hat{r}}_l^{\left(n+1\right)}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(0\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]& \left(14\right)\end{array}$

[0205] Now from Equation (7),

[0206] Hence the first-stage pre-MRC matched-filter outputs can be re-written: $\begin{array}{cc}\begin{array}{c}{y}_{\mathrm{lq}}^{\left(n+1\right)}\left[m\right]=\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{\hat{r}}_l^{\left(n+1\right)}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(0\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]\\ =\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{\hat{r}}_l^{\left(n\right)}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(0\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]+\\ \frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}r\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(0\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]-\\ \frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{\hat{r}}^{\left(n\right)}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(0\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]\\ ={\hat{a}}_{\mathrm{lq}}^{\left(n\right)}{\hat{b}}_l^{\left(n\right)}\left[m\right]+y_{\mathrm{lq}}^{\left(n\right)}\left[m\right]-y_{\mathrm{est},\mathrm{lq}}^{\left(n\right)}\left[m\right]\end{array}{y}_{\mathrm{est},\mathrm{lq}}^{\left(n\right)}\left[m\right]\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{\hat{r}}^{\left(n\right)}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(0\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]& \left(16\right)\end{array}$

[0207] where the following approximation has been used, $\begin{array}{cc}{y}_{\mathrm{lq},1}^{\left(n+1\right)}\left[m\right]\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}{\hat{r}}_l^{\left(n\right)}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}^{\left(0\right)}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]{\hat{a}}_{\mathrm{lq}}^{\left(n\right)}{\hat{b}}_l^{\left(n\right)}\left[m\right]& \left(17\right)\end{array}$

[0208] Given the pre-MRC matched-filter outputs the re-estimated channel amplitudes are $\begin{array}{cc}{\hat{a}}_{\mathrm{lq}}^{\left(n+1\right)}\underset{s}{}w\left[s\right]\frac{1}{N_p}\underset{m=0}{\overset{N_p-1}{}}{y}_{\mathrm{lq}}^{\left(n+1\right)}\left[m+\mathrm{Ms}\right]{\hat{b}}_l^{\left(n\right)}\left[m+\mathrm{Ms}\right]& \left(18\right)\end{array}$

[0209] wherein

[0210] ws is a filter,

[0211] N_p is a number of symbols, and

[0212] M is a number of symbols per slot,

[0213] and the post-MRC matched-filter outputs are then $\begin{array}{cc}{y}_l^{\left(n+1\right)}\left[m\right]\mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{{\left(n+1\right)}^H}{y}_{\mathrm{lq}}^{\left(n+1\right)}\left[m\right]\right\}& \left(19\right)\end{array}$

[0214] This embodiment is illustrated in FIG. 7. Here, the y_lq⁽⁰⁾m detection statistics are produced as with the above embodiments, however, before being applied to the MRC, the estimated amplitude _lq⁽⁰⁾ is determined first. Next, the MRC produces the y_l⁽⁰⁾m detection statistics which are from the amplitudes _lq⁽⁰⁾ and the pre-combination matched-filter detection statistics y_lq⁽⁰⁾m as in Equation (19) above.

[0215] The {circumflex over (r)}t waveform is applied (or reapplied) to a rake receiver 704. The output from the rake receiver 704 is subtracted 706 from the y_lq⁽⁰⁾m detection statistics. Next, the difference from the subtraction 706 is summed 708 with the _lq⁽⁰⁾{circumflex over (b)}_l⁽⁰⁾m value, thus producing y_lq⁽¹⁾m in accordance with equation (19) above.

[0216] After n iterations are performed, the y_lq⁽ⁿ⁾ detection statistics for each of the users corresponding to each antenna has been determined. The detection statistics for each user, y_l⁽ⁿ⁾ is next determined via estimating the complex amplitudes 710 across the Q channels for that user, and performing a maximum ratio combination 712 using those amplitudes.

[0217] It is helpful to understand that although the computational complexity increased, here, it is possible to re-estimate channel amplitudes, and hence, cancel interference on the dedicated physical control channels (DPCCH). The computational complexity of this embodiment is:

	Process	GOPS
	Re-Spread	31.5
	Raised Cosine Filtering	8.8
	IC	0.0
	Finger Receivers	62.9
	TOTAL	103.2

[0218] which is still within a practical range.

[0219] Therefore, as shown in all the embodiments above, and other non-illustrated embodiments, methods for performing multiple user detection are illustrated.

[0220] Turning now to software implementations for the above, one of several implementations is designed to allow full or partial decoding of users at various transmission time intervals (TTIs) within the multiple user detection (MUD) iterative loop. The approach, illustrated in FIG. 8, allows users belonging to different classes (e.g., voice and data) to be processed with different latencies. For example, voice users could be processed with a 10ms latency 802, whereas data users could be process with an 80ms latency 804. Alternately, voice users could be processed with a 20ms latency 806 or a 40ms latency 808, so as to include voice decoding in the MUD loop. Other alternatives are possible depending on the implementation and limitations of the processing requirements.

[0221] If a particular data user is to be processed with an 80ms latency 804 so as to include the full turbo decode within the MUD loop then the input channel bit-error rate (BER) pertaining to these users might be extraordinarily high. Here, the MUD processing might be configured so as to not include any cancellation of the data users within the 10ms latency 802. These data users would then be cancelled in the 20ms latency 806 period. For this cancellation it could be opted to perform MUD only on data users. The advantage of canceling the voice users in the first latency range (e.g., first box) would still benefit the second latency range processing.

[0222] Alternately, the second box 806 could perform cancellation on both voice and data users. The reduced voice channel bit-error rate would not benefit the voice users, whose data has already been shipped out to meet the latency requirement, but the reduced voice channel BER would improve the cancellation of voice interference from the data users. In the case that voice and data users are cancelled in the second box 806, another, possible configuration would be to arrange the boxes in parallel. Other reduced-latency configurations with mixed serial and parallel arrangements of the processing boxes are also possible.

[0223] Depending on the arrangement chosen, the performance for each class of user will vary. The approach above tends to balance the propagation range for data and voice users, and the particular arrangement can be chosen to tailor range for the various voice and data services.

[0224] Each box is the same code but configured differently. The parameters that differ are:

[0225] N_FRAMES_RAKE_OUTPUT;

[0226] Decoding to be performed (e.g. repetition decoding, turbo decoding, and the like);

[0227] Classes of users to be cancelled;

[0228] Threshold parameters.

[0229] The pseudo code for the software implementation of one long-code multiple user detection processing box is as follows:

	Initialize
	Zero data
	Generate OVSF codes
	Generate raised cosine pulse
	Allocate memory
	Open rake output files
	Open mod output files
	Align mod data
	Main Frame Loop
	Determine number of physical users
	Read_in_rake_output_records (N frames)
	Reformat_rake_output_data (N frames at a time)
	for stage 1 : N_stages
	Perform appropriate decoding(SRD, turbo, and
	the like, depending on TTI)
	Perform_long_code_mud
	end
	Free memory

[0230] The following four functions are described below:

[0231] Read_in_rake_output_records;

[0232] Reformat_rake_output_data

[0233] Perform appropriate decoding(SRD, turbo, and the like, depending on TTI);

[0234] Perform_long_code_mud.

[0235] The Read_in_rake_output_records function performs:

[0236] Reading in data for each user; and

[0237] Assigning data structure pointers.

[0238] The rake data transferred to MUD is associated with structures of type Rake_output_data_type. The elements of this structure are given in Table 1. There is a parameter N_FRAMES_RAKE_OUTPUT with values 1, 2, 4, 8 that specifies the number of frames to be read-in at a time. The following table tabulates the Structure Rake_output_buf_type elements:

	Element Type	Name
	unsigned long	Frame_number
	unsigned long	physical_user_code_number
	int	physical_user_tfci
	int	physical_user_sf
	int	physical_user_beta_c
	int	physical_user_beta_d
	int	N_dpdchs
	int	compressed_mode_flag
	int	compressed_mode_frame
	int	N_first
	int	TGL
	int	slot_format
	int	N_rake_fingers
	int	N_antennas
	unsigned long	mpath_offsetN_ANTENNAS
	unsigned long	tau_offset
	unsigned long	y_offset
	COMPLEX*	mpathN_ANTENNAS
	unsigned long*	tau_hat
	float *	y_data

[0239] It is helpful to describe several structure elements for a complete understanding. The element slot_format is an integer from 0 to 11 representing the row in the following table (DPCCH fields), 3GPP TS 25.211. By way of non-limiting example, when slot_format3, it maps to the fourth row in the table corresponding to slot format 1 with 8 pilot bits and 2 TPC bits. The offset values (e.g. tau_offset) give the location in memory relative to the top of the structure where the corresponding data is stored. These offset values are used for setting the corresponding pointers (e.g. tau_hat). For example, if Rbuf is a pointer to the structure then:

[0240] is used to set the tau_hat pointer.

[0241] The rake output structure associated data (mpath, tau_hat and y_data) is ordered as follows:

[0242] where

[0243] nantenna index (0: Na1)

[0244] qfinger index (0: L1)

[0245] sslot index (0: Nslots1)

[0246] msymbol index (0:149)

[0247] jbit index (0: J1)

[0248] dDPDCH index (1: Ndpdchs)

[0249] NaN_ANTENNAS

[0250] LN_RAKE_FINGERS_MAX

[0251] NslotsN_SLOTS_PER_FRAME15

[0252] J256/SF

[0253] M1J*Ndpdchs.

[0254] The memory required for the rake output buffers is dominated by the y-data memory requirement. The maximum memory requirement for a user is Nsym*(164*6) floats per frame, where Nsym150 is the number of symbols per frame. This corresponds to 1 DPCCH at SF 256 and 6 DPDCHs at SF 4. If 128 users are all allocated to this memory then possible memory problems arise. To minimize allocation problems, the following table gives the maximum number of user that the MUD implementation will be designed to handle at a given SF and Ndpdchs.

		Number	Bits per	Mean bits
SF	Ndpdchs	users	symbol	per symbol
256	1	256	2	4.0
128	1	192	3	4.5
64	1	128	5	5.0
32	1	96	9	6.8
16	1	64	17	8.5
8	1	32	33	8.3
4	1	16	65	8.1
4	2	12	129	12.1
4	3	8	193	12.1
4	4	4	257	8.0
4	5	3	321	7.5
4	6	2	385	6.0

[0255] In the proceeding table, the Bits per symbol1(256/SF)*N_DPDCHs, Mean bits per symbol (Number users)*(Bits per symbol)/128, and NdpdchsNumber DPDCHs.

[0256] From the above table it is noted that the parameter specifying the mean number of bits per symbol be set to MEAN_BITS_PER_SYMBOL16. The code checks to see if the physical users specifications are consistent with this memory allocation. Given this specification, the following are estimates for the memory required for the rake output buffers.

Data	Type	Size	Count	Count	Bytes
Rake_output_buf	Structure	88	1	1	88
mpath	COMPLEX	8	Lmax * Nslots * Na	240	1,920
tau	int	4	Lmax	8	32
y	float	4	Nsym * Nbits	2400	9,600
ylq	COMPLEX	8	Nsym * Nbits * Lmax * Na		307,200
	Total bytes per user per frame	318,840
	Total bytes for 128 users and 9 frames	367 Mbytes

[0257] Where Count is the per physical user per frame, assuming numeric values based on:

	Lmax N_RAKE_FINGERS_MAX 8
	Nslots N_SLOTS_PER_FRAME 15
	Na N_ANTENNAS 2
	Nsym N_SYMBOLS_PER_FRAME 150
	Nbits MEAN_BITS_PER_SYMBOL 16

[0258] The location of each structure is stored in an array of pointers

[0259] where Frame_idx varies from 0 to N_FRAMES_RAKE_OUTPUT inclusive. Frame 0 is initially set with zero data. After all frames are processed, the structure and data corresponding to the last frame is copied back to frame 0 and N_FRAMES_RAKE_OUTPUT new structures and data are read from the input source.

[0260] The Reformat_rake_output_data function performs:

[0261] Combining of multi-path data across frame boundaries;

[0262] Determines number of rake fingers for each MUD processing frame

[0263] Filling virtual-user data structures

[0264] Separates DPCHs into virtual users

[0265] Determines chip and sub-chip delays for all fingers

[0266] Determines the minimum SF and maximum number of DPDCHs for each user

[0267] Reformats user b-data to correspond to the minimum SF

[0268] Reformats rake data to be linear and contiguous in memory.

[0269] Interference cancellation is performed over MUD processing frames. Due to multi-path and asynchronous users, the MUD processing frame will not correspond exactly with the user frames. MUD processing frames, however, are defined so as to correspond as closely as possible to user frames. It is preferable for MUD processing that the number of multi-path returns be constant across MUD processing frames. The function of multi-path combining is to format the multi-path data so that it appears constant to the long-code MUD processing function. Each time after NN_FRAMES_RAKE_OUTPUT frames of data is read from the input source the combining function is called.

[0270] FIG. 9 shows a hypothetical set of multi-path lags corresponding to several frames of user data 902. Also shown are the corresponding MUD processing frames 904. Notice that MUD processing frame k overlaps with user frames k1 and k. For example, processing frame 1 906 overlaps with user frame 0 908, and further, overlaps with user frame 1 910. The MUD processing frame is positioned so that this is true for all multi-paths of all users. A one-symbol period corresponds to a round trip for a 10 km radius cell. Hence even large cells are typically only a few symbols asynchronous.

[0271] The multi-path combining function determines all distinct delay lags from user frames k1 and k. Each of these lags is assigned as a distinct multi-path associated with MUD processing frame k, even if some of the distinct lags are obviously the same finger displaced in delay due to channel dynamics. The amplitude data for a finger that extends into a frame where the finger wasn't present is set to zero. The illustrated thin lag-lines (e.g., 912) represent finger amplitude data that is set to zero. After the tentative number of fingers is assessed in this way, the total finger energy that falls within the MUD processing frame is assessed for each tentative finger and the top N_RAKE_FINGERS_MAX fingers are assigned. In the assignment of fingers the finger indices for fingers that were active in the previous MUD processing frame are kept the same so as not to drop data.

[0272] The user SF and number of DPDCHs can change every frame. It is helpful for efficient MUD processing that the user SF and number of DPDCHs be constant across MUD processing frames. This function, Reformat_rake_output_data formats the user b-data so that it appears constant to the long-code MUD processing function. Each time after NN_FRAMES_RAKE_OUTPUT frames of data is read from the input source this function is called. The function scans the N frames of rake output data and determined for each user the minimum SF and maximum number of DPDCHs. Virtual users are assigned according to the maximum number of DPCHs. If for a given frame the user has fewer DPCH the corresponding b-data and a-data are set to zero.

[0273] Note that this also applies to the case where the number of DPDCHs is zero due to inactive users, and also to the case where the number of DPCHs is zero due to compressed mode. It is anticipated that the condition of multiple DPDCHs will not often arise due to the extreme use of spectrum. If for a given frame the SF is greater than the minimum the b-data is expanded to correspond to the lower SF. That is, for example, if the minimum SF is 4, but over some frames the SF is 8, then each SF-8 b-data bit is replicated twice so as to look like SF-4 data. Before the maximum ration combination (MRC) operation the y-data corresponding to expanded b-data is averaged to yield the proper SF-8 y-data.

[0274] FIG. 10 shows how rake output data is mapped to (virtual) user data structures. Each small box (e.g., 1002) in the figure represents a slot's-worth of data. For DPCCH y-data or b-data, for example, each box would represent 150 values. Data is mapped so as to be linear in memory and contiguous frame to frame for each antenna and each finger. The reason for this mapping is that data can easily be accessed by adjusting a pointer. A similar mapping is used for other data except the amplitude data, where it would be imprudent to attempt to keep the number of fingers constant over a time period of up to 8 frames. For the virtual-user code data there are generally 38,400 data items per frame; and for the b-data and y-data there are generally 150256/SF data items per frame.

[0275] Note that for pre-MRC y-data, the mapping is linear and contiguous in memory for each antenna and each finger. Each DPCH is mapped to a separate virtual user data structure. The initial conditions data (frame 0 1004) is initially filled with zero data (except for the codes). After frame N data is written, this data is copied back to frame 0 1004, and the next frame of data that is written is written to frame 1 1006. For all data types the 0-index points to the first data item written to frame 0 1004. For example, the initial-condition b-data (frame 0) for an SF 256 virtual user is indexed b0, b1, . . . , b149, and the b-data corresponding to frame 1 is b150, b151, . . . , b299.

[0276] Four indices are of interest: chip index, bit index, symbol index, and slot index. The chip index r is always positive. All indices are related to the chip index. That is, for chip index r we have

[0277] Chip indexr

[0278] Bit indexr/Nk

[0279] Symbol indexr/256

[0280] Slot indexr/2560

[0281] where Nk is the spreading factor for virtual user k.

[0282] The elements for the (virtual) user data structures are given in the following table along with the memory requirements.

Element Type	Name	Bytes	Bytes
int	Dpch_type	4	4
int	Sf	4	4
int	log2Sf	4	4
float	Beta	4	4
int	Mrc_bit_idx	4	4
int	N_bits_per_dpch	4	4
int	N_rake_fingersNf	4*8	32
int	Chip_idx_rsLmax	4*8	32
int	Chip_idx_dsLmax	4*8	32
int	Delay_lagLmax	4*8	32
int	finger_idx_max_lag	4	4
int	Chip_delayLmax	4*8	32
int	Sub_chip_delayLmax	4*8	32
COMPLEX	axcodeNfNaLmaxNslots * 24	8*8*2*8*15*2*4	122880
COMPLEX	a_hat_dsNfNaLmaxNslots * 2	8*8*2*8*15*2	30720
COMPLEX*	mf_ylqNaLmax	4*2*8	64
COMPLEX*	mud_ylqNaLmax	4*2*8	64
float*	mf_y_data	4	4
float*	mud_y_data	4	4
char*	mf_b_data	4	4
char*	mud_b_data	4	4
char*	mod_b_data	4	4
char	CodeNchips * (1Nf)	1*38400*9	345600
COMPLEX	mud_ylq_saveNaLmax	8*2*8	128
int	Mrc_bit_idx_save	4	4
float	Repetition_rate	4	4
COMPLEX1,2	mf_ylqNaLmaxNbits1 * (1 Nf)	8*2*8*1200*9	1382400
COMPLEX1,2	mud_ylqNaLmaxNbits1 *(1Nf)	8*2*8*1200*9	1382400
float1,2	mf_y_dataNbits1 * (1Nf)	4*1200*9	43200
float1,2	mud_y_dataNbits1 * (1Nf)	4*1200*9	43200
char(1,2)	mf_b_dataNbits1 * (1Nf)	1*1200*9	10800
char(1,2)	mud_b_dataNbits1 * (1Nf)	1*1200*9	10800
char(1,2)	mod_b_dataNbits1 * (1Nf)	1*1200*9	10800
Total			3,383,304
x 256 v-users			866 Mbytes
OLD:
COMPLEX	CodeNchips * 2	8*38400*2	614400
where the following notations are defined:
1 - Associated data, not explicitly part of structure
2 - Based on 8 bits per symbol on average
Lmax N_RAKE_FINGERS_MAX 8
Na N_ANTENNAS 2
Nslots N_SLOTS_PER_FRAME 15
(Nbitsmax1 N_BITS_PER_FRAME_MAX_1 9600)
Nchips N_CHIPS_PER_FRAME 38400
Nf N_FRAMES_RAKE_OUTPUT 8
Nbits1 MEAN_BITS_PER_FRAME_1 150*4.25 640.

[0283] Each user class has a specified decoding to be performed. The decoding can be:

[0284] None

[0285] Soft Repetition Decoding (SRD)

[0286] Turbo decoding

[0287] Convolutional decoding.

[0288] All decoding is Soft-Input Soft-Output (SISO) decoding. For example, an SF 64 voice user produces 600 soft bits per frame. Thus 1,200 soft bits per 20 ms transmission time intervals (TTIs) are produced. These 1,200 soft bits are input to a SISO de-multiplex and convolution decoding function that outputs 1,200 soft bits. The SISO de-multiplex and convolution decoding function reduces the channel bit error rate (BER) and hence improve MUD performance. Since data is linear in memory no reformatting of data is necessary and the operation can be performed in-place. If further decoders are included, reduced complexity partial-decode variants can be employed to reduce complexity. For turbo decoding, for example, the number of iterations may be limited to a small number.

[0289] The Long-code MUD performs the following operations:

[0290] Respread

[0291] Raised-Cosine Filtering

[0292] Despread

[0293] Maximal-Ratio Combining (MRC).

[0294] The re-spread function calculates rt given by $\begin{array}{cc}\left[t\right]\underset{k=0}{\overset{K_v-1}{}}\underset{p=0}{\overset{L-1}{}}\underset{r}{}\left[t-{\hat{}}_{\mathrm{kp}}-{\mathrm{rN}}_c\right]{\hat{a}}_{\mathrm{kp}}\left[r/2560\right]c_k\left[r\right]{\hat{b}}_k\left[r/N_k\right]& \left(20\right)\end{array}$

[0295] The function rt is calculated over the interval t0:Nf*M*Nc1, where M38400 is the number of chips per frame and Nf is the number of frames processed at a time. The actual function calculated is

[0296] which represents a section of the waveform of length Nchips chips, and the calculation is performed for m0:Nf*M*Nc/Nchips1. The function is defined (and allocated) for negative indices (Lg1): 1, representing the initial conditions which are set to zero at start-up. The parameter Lg is the length of the raised-cosine filter discussed below.

[0297] Note that every finger of every user adds one and only one non-zero contribution per chip within this interval corresponding to chip indices r. Given the delay lag tlq for the qth finger of the lth user we can determine which chip indices r contribute to a given interval. To this end define

[0298] The first definition defines t as belonging to the nth chip interval; the second is a decomposition of the delay lag into chip delay and sub-chip delay. Given the above we can solve for r and q using

[0299] Notice that chip indices r as given above can be negative. In the implementation the pointers _kp, c_k and {circumflex over (b)}_k point to the first element of frame 1 1006 (FIG. 10).

[0300] The repeated amplitude-code multiplies are avoided by using: $\begin{array}{cc}{\left(\hat{a}c\right)}_{kp}\left[s\right]\left[c_k\left[r\right]\right]{\hat{a}}_{\mathrm{kp}}\left[s\right]c_k\left[r\right]{\left(\hat{a}c\right)}_{kp}\left[s\right]\left[c\right]\{\begin{array}{c}{\hat{a}}_{\mathrm{kp}}\left[s\right]\left(+1+j\right),c=0\\ {\hat{a}}_{\mathrm{kp}}\left[s\right]\left(-1+j\right),c=1\\ {\hat{a}}_{\mathrm{kp}}\left[s\right]\left(-1-j\right),c=2\\ {\hat{a}}_{\mathrm{kp}}\left[s\right]\left(+1-j\right),c=3\end{array}{c}_k\left[r\right]\{\begin{array}{c}0,c_k\left[r\right]=+1+j\\ 1,c_k\left[r\right]=-1+j\\ 2,c_k\left[r\right]=-1-j\\ 3,c_k\left[r\right]=+1-j\end{array}& \left(24\right)\end{array}$

[0301] The raised-cosine filtering operation applied to the re-spread signal rt produces an estimate of the received signal given by: $\begin{array}{cc}\hat{r}\left[t\right]=\underset{t^{}=0}{\overset{L_g-1}{}}g\left[t^{}\right]\left[t-t^{}\right]& \left(25\right)\end{array}$

[0302] where

[0303] gt is the raised-cosine pulse and

[0304] t0:Nc*Nchips1

[0305] t'0:Lg1

[0306] LgNsamplesrc (length of raised-cosine filter)

[0307] For example, if an impulse at t0 is passed through the above filter the output is gt. The position of the maximum of the filter then specifies the delay through filter. The delay is relevant since it specifies the synchronization information necessary for subsequent despreading. The raised cosine filter is calculated over the time period n(n1:n2 )/Nc, where Nc is the number of samples per chip, and time is in chips. Note that nl is negative, and the position of the maximum of the filter is at n0. The length of the filter is then Lgn2n1, and the maximum occurs at sample nl. The delay is thus nl samples, and the chip delay is n1/Nc chips. For simplicity of implementation n I is required to be a multiple of Nc.

[0308] The de-spread operation calculates the pre-MRC detection statistics corresponding to the estimate of the received signal: $\begin{array}{cc}{y}_{\mathrm{est},\mathrm{lq}}^{\left(1\right)}\left[m\right]\frac{1}{2N_l}\underset{n=0}{\overset{N_l-1}{}}\hat{r}\left[{\mathrm{nN}}_c+{\hat{}}_{\mathrm{lq}}+{\mathrm{mT}}_l\right]c_{\mathrm{lm}}^{*}\left[n\right]& \left(26\right)\end{array}$

[0309] Prior to the MRC operation, the MUD pre-MRC detection statistics are calculated according to:

[0310] These are then combined with antenna amplitudes to form the post-MRC detection statistics: $\begin{array}{cc}{y}_l^{\left(1\right)}\left[m\right]\mathrm{Re}\left\{\underset{q=1}{\overset{L}{}}{\hat{a}}_{\mathrm{lq}}^{{\left(1\right)}^H}{y}_{\mathrm{lq}}^{\left(1\right)}\left[m\right]\right\}& \left(28\right)\end{array}$

[0311] Multiuser detection systems in accord with the foregoing embodiments can be implemented in any variety of general or special purpose hardware and/or software devices. FIG. 11 depicts one such implementation. In this embodiment, each frame of data is processed three times by the MUD processing card 118 (or, MUD processor for short), although it can be recognized that multiple such cards could be employed instead (or in addition) for th is purposed During the first pass, only the control channels are respread which the maximum ratio combination (MRC) and MUD processing is performed on the data channels. During subsequent passes, data channels are processed exclusively, with new y (i.e., soft decisions) and b (i.e., hard decisions) data being generated as shown in the diagram.

[0312] Amplitude ratios and amplitudes are determined via the DSP (e.g., element 900, or a DSP otherwise coupled with the processor board 118 and receiver 110), as well as certain waveform statistics. These values (e.g., matrices and vectors) are used by the MUD processor in various ways. The MUD processor is decomposed into four stages that closely match the structure of the software simulation: Alpha Calculation and Respread 1302, raised-cosine filtering 1304, de-spreading 1306, and MRC 1308. Each pass through the MUD processor is equivalent to one processing stage of the implementations discussed above. The design is pipelined and parallelized. In the illustrated embodiment, the clock speed can be 132 MHz resulting in a throughput of 2.33 ms/frame, however, the clock rate and throughput varies depending on the requirements. The illustrated embodiment allows for three-pass MUD processing with additional overhead from external processing, resulting in a 4-times real-time processing throughput.

[0313] The alpha calculation and respread operations 1302 are carried out by a set of thirty-two processing elements arranged in parallel. These can be processing elements within an ASIC, FPGA, PLD or other such device, for example. Each processing element processes two users of four fingers each. Values for b are stored in a double-buffered lookup table. Values of and j are pre-multiplied with beta by an external processor and stored in a quad-buffered lookup table. The alpha calculation state generated the following values for each finger, where subscripts indicate antenna identifier:

[0314] These values are accumulated during the serial processing cycle into four independent 8-times oversampling buffers. There are eight memory elements in each buffer and the element used is determined by the sub-chip delay setting for each finger.

[0315] Once eight fingers have been accumulated into the oversampling buffer, the data is passed into set of four independent adder-trees. These adder-trees each termination in a single output, completing the respread operation. The four raised-cosine filters 1304 convolve the alpha data with a set of weights determined by the following equation: $g_{\mathrm{rc}}\left(t\right)=\frac{\sin \left(\frac{1}{t}\right)\cos \left(\frac{1}{T}\right)}{\frac{1}{t}\left(1-{\left(2\frac{1}{T}\right)}^2\right)}$

[0316] The filters can be implemented with 97 taps with odd symmetry. The filters illustrated run at 8-times the chip rate, however, other rates are possible. The filters can be implemented in a variety of compute elements 220, or other devices such as ASICs, FPGAs for example.

[0317] The despread function 1306 can be performed by a set of thirty-two processing elements arranged in parallel. Each processing element serially processes two users of four fingers each. For each finger, one chip value out of eight, selected based on the sub-chip delay, is accepted from the output of the raised-cosine filter. The despread state performs the following calculations for each finger (subscripts indicate antenna): $\begin{array}{c}{y}_0=\underset{0}{\overset{\mathrm{SF}-1}{}}C{r}_0+\mathrm{jC}{\mathrm{jr}}_0\\ {\mathrm{jy}}_0=\underset{0}{\overset{\mathrm{SF}-1}{}}C{\mathrm{jr}}_0-\mathrm{jC}{r}_0\\ y_1=\underset{0}{\overset{\mathrm{SF}-1}{}}C{r}_1+\mathrm{jC}{\mathrm{jr}}_1\\ {\mathrm{jy}}_1=\underset{0}{\overset{\mathrm{SF}-1}{}}C{\mathrm{jr}}_1-\mathrm{jC}{r}_1\end{array}$

[0318] The MRC operations are carried out by a set of four processing elements arranged in parallel, such as the compute elements 220 for example. Each processor is capable of serially processing eight users of four fingers each. Values for y are stored in a double-buffered lookup table. Values for b are derived from the MSB of the y data. Note that the b data used in the MUD stage is independent of the b data used in the respread stage. Values of and j< are pre-multiplied with by an external processor and stored in a quad-buffered lookup table. Also, (²j²) for each channel is stored in a quad-buffered table.

[0319] The output stage contains a set of sequential destination buffer pointers for each channel. The data generated by each channel, on a slot basis, is transferred to the crossbar (or other interconnect) destination indicated by these buffers. The first word of each of these transfers will contain a counter in the lower sixteen bits indicating how many y values were generated. The upper sixteen bits will contain the constant value 0AA55. This will allow the DSP to avoid interrupts by scanning the first word of each buffer. In addition, the DSP_UPDATE register contains a pointer to single crossbar location. Each time a slot or channel data is transmitted, an internal counter is written to this location. The counter is limited to 10 bits and will wrap around with a terminal count value of 1023.

[0320] The method of operation for the long-code multiple user detection algorithm (LCMUD) is as follows. Spread factor for four-channels requires significant amount of data transfer. In order to limit the gate count of the hardware implementation, processing an SF4 channel can result in reduced capability.

[0321] A SF4 user can be processed on certain hardware channels. When one of these special channels is operating on an SF4 user, the next three channels are disabled and are therefore unavailable for processing. This relationship is as shown in the following table:

SF4 Chan	Disabled Channels	SF4 Chan	Disabled Channels
0	1, 2, 3	32	33, 34, 35
4	5, 6, 7	36	37, 38, 39
8	9, 10, 11	40	41, 42, 43
12	12, 14, 15	44	45, 46, 47
16	17, 18, 19	48	49, 50, 51
20	21, 22, 23	52	53, 54, 55
24	25, 26, 27	56	57, 58, 59
28	29, 30, 31	60	61, 62, 63

[0322] The default y and b data buffers do not contain enough space for SF4 data. When a channel is operating on SF4 data, the y and b buffers extend into the space of the next channel in sequence. For example, if channel 0 is processing SF data, the channel 0 and channel 1b buffers are merged into a single large buffer of 040 32-bit words. The y buffers are merged similarly.

[0323] In typical operation, the first pass of the LCMUD algorithm will respread the control channels in order to remove control interference. For this pass, the b data for the control channels should be loaded into BLUT while the y data for data channels should be loaded into YDEC. Each channel should be configured to operate at the spread factor of the data channel stored into the YDEC table.

[0324] Control channels are always operated at SF 256, so it is likely that the control data will need to be replicated to match the data channel spread factor. For example, each bit (b entry) of control data would be replicated 64 times if that control channel were associated with an SF 4 data channel.

[0325] Each finger in a channel arrives at the receiver with a different delay. During the Respread operation, this skew among the fingers is recreated. During the MRC stage of MUD processing, it is necessary to remove this skew and realign the fingers of each channel. This is accomplished in the MUD processor by determining the first bit available from the most delayed finger and discarding all previous bits from all other fingers. The number of bits to discard can be individually programmed for each finger with the Discard field of the MUD-PARAM registers. This operation will typically result in a short first slot of data. This is unavoidable when the MUD processor is first initialized and should not create any significant problems. The entire first slot of data can be completely discarded if short slots are undesirable.

[0326] A similar situation will arise each time processing is begun on a frame of data. To avoid losing data, it is recommended that a partial slot of data from the previous frame be overlapped with the new frame. Trimming any redundant bits created this way can be accomplished with the Discard register setting or in the system DSP. In order to limit memory requirements, the LCMUD FPGA processes one slot of data at a time. Doubling buffering is used for b and y data so that processing can continue as data is streamed in. Filling these buffers is complicated by the skew that exists among fingers in a channel.

[0327] FIG. 12 illustrates the skew relationship among fingers in a channel and among the channels themselves. The illustrated embodiment allows for 20 us (77.8 chips) of skew among fingers in a channel and certain skew among channels, however, in other embodiments these skew allowances vary.

[0328] There are three related problems that are introduced by skew: Identifying frame & slot boundaries, populating b and y tables and changing channel constants. Because every finger of every channel can arrive at a different time, there are no universal frame and slot boundaries. The DSP must select an arbitrary reference point. The data stored in b & y tables is likely to come from two adjacent slots.

[0329] Because skew exists among fingers in a channel, it is not enough to populate the b & y tables with 2,560 sequential chips of data. There must be some data overlap between buffers to allow lagging channels to access old data. The amount of overlap can be calculated dynamically or fixed at some number greater than 78 and divisible by four (e.g. 80 chips). The starting point for each register is determined by the Chip Advance field of the MUDPARAM register.

[0330] A related problem is created by the significant skew among channels. As can be seen in FIG. 12, Channel 0 is receiving Slot 0 while Channel 1 is receiving Slot 2. The DSP must take this skew into account when generating the b and y tables and temporally align channel data.

[0331] Selecting an arbitrary slot of data from a channel implies that channel constants tied to the physical slot boundaries may change while processing the arbitrary slot. The Constant Advance field of the MUDPARAM register is used to indicate when these constants should change. Registers affected this way are quad-buffered. Before data processing begins, at least two of these buffers should be initialized. During normal operation, one additional buffer is initialized for each slot processed. This system guarantees that valid constants data will always be available.

[0332] The following two tables shown the long-code MUD FPGA memory map and control/status register:

Start Addr	End Addr	Name	Description
0000_0000	0000_0000	CSR	Control & Status Register
0000_0008	0000_000C	DSP_UPDATE	Route & Address for DSP updating
0001_0000	0001_FFFF	MUDPARAM	MUD Parameters
0002_0000	0002_FFFF	CODE	Spreading Codes
0003_0000	0004_FFFF	BLUT	Respread: b Lookup Table
0005_0000	0005_FFFF	BETA_A	Respread: Beta * a_hat Lookup Table
0006_0000	0007_FFFF	YDEC	MUD & MRC: y Lookup Table
0008_0000	0008_FFFF	ASQ	MUD & MRC: Sum a_hat squared LUT
000A_0000	000A_FFFF	OUTPUT	Output Routes & Addresses

[0333]

Bit	31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16
Name	Reserved
R/W	RO
Reset	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X	X
Bit	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Name	Reserved	YB	CBUF	A1	A0	R1	R0	Lst	Rst
R/W	RO	RO	RO	RO	RO	Rw	Rw	Rw	Rw
Reset	X	X	X	X	X	X	X	0	0	0	0	0	0	0	0	0