Microwave Radio System With Software Configuration of Operating Parameters

A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.

This invention relates to microwave radios and in particular to a microwave radio wherein the operating parameters of the radio are software controlled.

Microwave radios are well known and are commonly used for line of sight communication systems. Microwave signals are typically transmitted from a transmitting antenna along a straight line to a receiving antenna optically visible from the transmitting antenna. Typically, the antenna is mounted on the top of a tower and is driven by what is called an "outdoor unit" which includes an IF processor and an outdoor control module. Should any of the operating parameters of the outdoor unit (which is often called the RF assembly and is located outdoors on top of the tower) be required, a technician must climb the tower and physically adjust the unit. This is sometimes difficult and often dangerous. Accordingly, there is a need for a better way of controlling the operating parameters of the RF assembly associated with the microwave transmission system.

In accordance with this invention, a software controlled radio system is provided which allows the RF assembly to be remotely controlled by software associated with the transmission system. For example, the transmit power associated with the transmission system is controlled by software as required to reflect allowed changes in channel capacity (i.e. bit rate) and/or availability. Availability is generally defined in the microwave art as the amount of time on average over a year that a link (made up of a transmitter and a receiver) will operate at this defined level of performance. Performance, in this context, is defined as an error rate such as 10.sup.-6 (i.e. one error in one million bits). As a measure of comparison, no noise is audible at an error rate of approximately 10.sup.-3.

In accordance with this invention, the RF assemblies in both the transmitter and the receiver associated with a transmission link can each be controlled in terms of output power (and other parameters) by use of telemetry data to change the software which controls the operations of the transmitter and the receiver.

This invention will be more fully understood in light of the following detailed description taken together with the drawings.

FIG. 1 illustrates in schematic block diagram form a radio link in accordance with this invention comprising two terminals, terminal 100A and terminal 100B.

FIG. 2 illustrates the outdoor portion of a terminal which in turn is part of the complete radio system.

FIG. 3 illustrates in more detail the structure shown in schematic block diagram form in FIG. 2.

FIG. 4 illustrates a control portion of the outdoor equipment used for controlling the output power from the outdoor equipment radio in response to telemetry data signals from the indoor equipment.

FIGS. 5a and 5b illustrate the relationship between the control voltage and the power output of the output amplifier of the outdoor equipment radio.

FIG. 6 illustrates the detail of the signal processing module.

The outdoor equipment which is the main RF portion of the radio (i.e. which transmits signals at the gigahertz frequencies commonly used in microwave systems) has in its output transmitting stage, an amplifier, the output power of which can be controlled using a DC control voltage. In accordance with this invention, this DC control voltage is derived from a digital value stored in memory within the microcomputer in the outdoor equipment and this digital value stored in memory is converted to an analog control voltage using a digital-to-analog (D to A) converter in the outdoor equipment. The digital value that is stored in that memory location in turn is based in part on a telemetry signal from the indoor equipment microprocessor which communicates to the outdoor equipment microprocessor via a telemetry link between the indoor and the outdoor equipment. The digital value is stored in nonvolatile memory to allow data recovery after a power loss. Thus equipment always powers up in the state in which it last operated before power down. In accordance with this invention, the digital value representing output power can be changed under the control of the software to reflect a new output power to be used by the transmitter. So by altering a parameter on the indoor equipment, that parameter is communicated to the outdoor equipment which in turn adjusts the output power. Furthermore, because each indoor equipment at either end of the link can communicate over the peer channel which is on the service channel which is multiplexed into the aggregate data stream, it is also possible to adjust the power at the remote end of the link from the local end of the link. This is a major advantage in field installations where, for example, a change in the availability is required dictating an increase in output power. A change in availability can therefore be done from either end of the link without having to recover the outdoor equipment. One advantage of this invention is that if a change in bit rate from, for example, 1 slot of 2 megabits through to 4 slots of 2 megabits is required, for a given availability this would require a 6 db change in output power. All of the radios on the market at present would require recovery (i.e. removal from site and return to an appropriate facility for adjustment) and manipulation to adjust the outdoor equipment directly to implement this change whereas in accordance with this invention, the adjustments can be configured using radio telemetry from either end of the link. A further advantage that comes from the use of telemetry to adjust the outdoor equipment parameters occurs when network management is provided. In accordance with this invention, all of the parameters in the radio are available and configurable using network management. It is also possible to adjust the power output and therefore the availability of the equipment by the network management system.

One particular implementation that is being used employs a linear voltage regulator type circuit which has been fabricated using discrete components and an operational amplifier. The setpoint value for the operational amplifier is derived from the D to A converter which in turn derives its output voltage from a code stored in a particular memory location.

In one embodiment an operational amplifier includes a pass transistor to provide the available power dissipation within the equipment. The output voltage from the operational amplifier is referenced closed-loop back to the input voltage to that operational amplifier. Typically zero (0) to five (5) volts are produced from the D to A converter. For a 38 gigahertz embodiment, the D to A converter output is scaled to 0 to 5.7 volts which corresponds to the range of values from the minimum output power to the maximum output power required to be available from the transmitter.

In one embodiment, the microprocessor in the outdoor equipment monitors a number of functions, such as, for example, temperature. In this embodiment the curve of output power versus bias voltage is corrected for temperature. As is shown in FIG. 5a, the relationship between output power and control voltage is nonlinear over the range of 0 to 5 volts. However, this nonlinear relationship has some temperature dependency, as is shown in FIG. 5a. Using the microprocessor, the actual value for the control voltage that is set onto the output stage is a function of the desired value plus some correction factor to take account the nonlinearity of the transfer characteristic of FIG. 5a. The outdoor equipment radios can actually have an interface in dbm; that is the output power of the radio can be set to a given value in dbm, such as to minus 20 dbm which in turn is turned into a voltage. That voltage is then curve corrected and temperature corrected to set the output power value on the output stage. As shown in FIG. 5b, this output power is linearly related to the selected input power.

In accordance with the present invention, two transceivers 100A and 100B (FIG. 1) exchange information over a wireless channel 110. Transceivers 100A and 100B are of identical construction. Therefore, the following description of transceiver 100A is applicable to transceiver 100B.

Transceiver 100A includes an indoor unit 102A and an outdoor unit 104A which are connected by a cable 106A. Outdoor unit 104A is typically placed outdoors in a position such that a parabolic antenna 108A is facing a parabolic antenna 108B of transceiver 100B. As such, outdoor unit 104A is generally not easily and comfortably accessed by technicians who periodically monitor and adjust operating parameters of outdoor unit 104A. In accordance with the present invention, outdoor unit 104A is controlled by indoor unit 102A through cable 106A which supports a telemetry channel as described in greater detail below.

Outdoor unit 104A includes an IF processor (IFP) 112A and an outdoor control module (OCM) 114A. Outdoor control module 114A controls the operation of outdoor unit 104A and is described in greater detail below. IF processor 112A processes information received from and transmits information to an (RFP) processor 116A of indoor unit 102A through cable 106A using conventional frequency division multiplex techniques. IF processor 112A and RF processor 116A transfer information using any one of a number of standard techniques. In one embodiment, the well-known BISYNC protocol is used.

In addition to RF processor 116A, indoor unit 102A includes a signal processing module (SPM) 118A, a front panel interface (FPI) 120A, and a power supply control module (PSC) 122A. Signal processing module 118A contains logic, which is described in greater detail below and which sends messages to and receives messages from outdoor control module 114A through RF processor 116A, cable 106A, and IF processor 112A. In response to messages received from signal processing module 118A, outdoor control module 114A controls the operation of outdoor unit 104A and sends messages to signal processing module 118A regarding the operation of outdoor unit 104A.

A technician has easy and comfortable access to indoor unit 102A because indoor unit 102A is typically placed indoors. A technician can control outdoor unit 104A through a front panel (not shown), which is connected through front panel interface 120A. In response to signals generated by the front control panel which are transmitted by front panel interface 120A to signal processing module 118A, signal processing module 118A forms a message indicating a change in transmit power and sends the message through RF processor 116A and cable 106A to outdoor unit 104A. Outdoor unit 104A responds to this message by amending a digital value stored in nonvolatile memory, which digital value controls the output power of the signal transmitted by outdoor unit 104.

Outdoor unit 104A is shown in greater detail in FIG. 2. Cable 106A supports the following. DC power from indoor unit 102A, a receive IF carrier signal from outdoor unit 104A to indoor unit 102A, a transmit IF carrier signal from indoor unit 102A to outdoor unit 104A, a telemetry channel from indoor unit 102A to outdoor unit 104A, and a telemetry channel from outdoor unit 104A to indoor unit 102A. IF processor 112A transmits to an amplifier module 202 the transmit IF carrier signal. Amplifier module 202 amplifies and translates the frequency of the transmit IF carrier signal and transmits the IF carrier signal to a millimeter wave block 206. Millimeter wave block 206 then converts the transmit IF carrier signal to a microwave frequency (such as 23, 38 or 50 gigahertz) and transmits the microwave signal through antenna 108A. As described in more detail below, outdoor control module 114A controls the power of the microwave transmit carrier signal broadcast by millimeter wave block 206 through a voltage applied through a line 210.

A microwave frequency receive carrier signal is received through antenna 108A by millimeter wave block 206. Millimeter wave block 206 then transmits the signal to a down converter 208 which converts the microwave frequency receive signal to an intermediate frequency. The intermediate frequency is then transmitted to IF processor 112A which then transmits the IF receive carrier signal to indoor unit 102A (FIG. 1). Both amplifier module 202 (FIG. 2) and down converter 208 are controlled by a synthesizer 204. Synthesizer 204 controls, in a well known manner, the carrier signal transmitted from amplifier module 202 to millimeter wave block 206 and thus the frequency ultimately transmitted by millimeter wave block 206. Millimeter wave block 206 includes a frequency tripler 302 (FIG. 3) which triples the frequency of the carrier signal received from amplifier module 202 (FIG. 2). Naturally a frequency tripler is not essential to the invention. Rather, a doubler, a quadrupler or a straight amplifier could be used instead of a tripler, depending on the desired output frequency.

Similarly, down converter 208 translates the frequency of the received microwave carrier signal using synthesizer 204. Synthesizer 204 also converts the received microwave carrier signal, which has been reduced to an intermediate frequency by down converter 208, to be processed by an IF processor 112A.

IF processor 112A transmits to outdoor control module 114A the telemetry signal received from indoor unit 102A.

Outdoor control module 114A is shown in greater detail in FIG. 4. Outdoor control module 114A includes a microprocessor 402 which receives signals from IF processor 112A (FIG. 2). Microprocessor 402 is connected through a bus to a memory 404 and a non-volatile memory 406. Memory 404 can be, for example, random accessible memory (RAM), read only memory (ROM), programmable read only memory (PROM), or flash memory. Memory 404 includes firmware 408 which is executed by microprocessor 402 using conventional techniques. One embodiment of firmware 408 is included as Appendix A which is incorporated herein by reference. Nonvolatile memory 406 includes a datum 410 which represents the power in dbm of the microwave frequency signal transmitted by millimeter wave block 206 (FIG. 2).

In a process described more completely below, firmware 408 retrieves from nonvolatile memory 406 datum 410 and supplies to microprocessor 402 digital data representing a voltage to be applied to tripler 302 (FIG. 3) to cause millimeter wave block 206 to transmit a microwave frequency carrier signal at the particular power represented by datum 410 (FIG. 4). Microprocessor 402 supplies that digital data to a digital-to-analog converter 414 which then applies to line 210 a control voltage specified by the digital data received by digital-to-analog converter 414.

The voltage applied to line 210 by digital-to-analog converter 414 is supplied to tripler 302 (FIG. 3). In one embodiment, tripler 302 is available from Milliwave of Sacramento, Calif. The tripler produces a signal at a power level which is controlled by the voltage on line 210. Thus, firmware 408 (FIG. 4) uses datum 410 to control the power of microwave frequency carrier signals transmitted by millimeter wave block 206 (FIG. 2) through antenna 108A.

Datum for 410 represents the output power from the transmitter and that datum can be changed, in accordance with this invention, by a new datum sent over the telemetry channel to the outdoor equipment from the indoor equipment.

FIG. 5A illustrates the nonlinear relationship between the transmitted power output from the transmitter and the control voltage applied on line 210 (FIG. 4) to the triplet 302 (FIG. 3). As shown in FIG. 5A, the transmitted power output (in dbm) varies non-linearly with control voltage. As the control voltage varies over its expected range from 0 to 5.7 volts, the output power rises approximately linearly and then rises between approximately 1 to 3 volts at an ever increasing rate as the voltage increases until in the range from 3 to approximately 5 volts, the output power rises at decreasing rates until it becomes almost constant with increasing voltage in excess of approximately 5.2 volts. Note that the relationship between transmitted power output and the control voltage is temperature dependent. The lower the temperature, the higher the output power for a given control voltage. In accordance with one embodiment of this invention, datum 410, which can comprise a series of look up tables, allows the correct look up table to be selected corresponding to the relationship between transmitted power output as a function of control voltage.

FIG. 5B illustrates a linearized relationship between output power and dbm and the power level selected in dbm. As shown in FIG. 5B, this relationship is truly linear with the power level selected matching exactly the power output from the transmitter.

In an alternative embodiment, one look up table is provided showing the relationship between the desired transmitter power output and the control voltage and a correction factor is then generated based upon the measured ambient temperature. This correction factor then allows the particular datum 410 to be corrected to give the desired power output in accordance with the curve shown in FIG. 5a for the given temperature. This correction can be made as frequently as desired during the operation of the microwave system to take into account changes in ambient temperature.

As shown in FIG. 3, the output control voltage on line 210 is transmitted to provide the bias setting for amplifier 306. Amplifier 306 is part of tripler 302 which produces an output signal three times the frequency of the input signal. Tripler 302 includes tripling circuit 305, which can be anyone of a number of well known tripling circuits, which basically receives an input signal at a first frequency and produces an output signal at a frequency three times the frequency of the input signal. In one embodiment, tripler 305 is purchased from Milliwave Corporation in Sacramento, Calif. However, any other commercially available tripler could be used for this function. Input signal to tripler 305 is derived from amplifier module 202 (see FIG. 2). Amplifier module 202 includes a mixer 301 which mixes an input signal from IFP 112A (FIG. 2) with the signal from s synthesizer 204 (FIG. 2). Synthesizer 204 provides a frequency reference signal to be used in modulator 301 to translate the information bearing signal from IFP 112A up to the frequency of the input signal to be provided to tripler 302. The output signal from modulator 301 is transmitted through bandpass filter 302 having center frequency typical of 13 gigahertz in one embodiment. From bandpass filter 302 the 13 gigahertz signal is transmitted to amplifier 303 and then through another bandpass filter 304 having the same center frequency. Filter 304 is provided to limit noise. Output signal from filter 304 is then transmitted as the input signal to tripler 302. Within tripler 302 tripling element 305 triples the frequency of this signal to 39 gigahertz. The 39 gigahertz signal output from tripler 305 is passed through amplifier 306, the power level of which is controlled by the analog control signal on control line 210. The output signal from amplifier 306 is then transmitted through one or more bandpass filters and passed to an antenna corresponding, for example to antenna 108A in FIG. 1 for transmission.

While one embodiment of this invention has been described, other embodiments of this invention will be obvious in view of the above description. Parameters other than the output power can be controlled, for example, by telemetry data signals provided under the control of the software. Output frequency, muting of the transmitter, and testing can, for example, be implemented under control of the software.

The power of the signal transmitted by outdoor unit 104A through antenna 108A is controlled by signal processing module 118A of indoor unit 102A according to signals received through a maintenance port 124A. A personal computer or similar device (not shown) is connected to maintenance port 124A and transmits to signal processing module 118A a change power message. A change power message is a message according to the message format described more completely below which is a command to outdoor unit 104A to change the power at which signals are transmitted through antenna 108A.

Signal processing module 118A is shown in more detail in FIG. 6. Signal processing module 118A includes a microprocessor 602 which is connected through a bus to memory 606 and nonvolatile memory 608. Memory 606 includes firmware 610 which is executed by microprocessor 602. Microprocessor 602 is connected through a UART 604 to maintenance port 124A.

Microprocessor 602 retrieves from UART 604 characters which collectively form messages received by signal processing module 118A through maintenance port 124A. Messages are transferred through maintenance port 124A using conventional techniques.

Firmware 610 receives through maintenance port 124A and through UART 604 a change power message. Once a complete change power message is received, firmware 610 sends the change power message through a UART 612 to RF processor 116A (FIG. 1). In one embodiment, microprocessor 602 (FIG. 6) is the 80C196 microprocessor available from Intel Corporation of Santa Clara, Calif. and UART 612 is built into microprocessor 602.

In one embodiment, messages transferred between signal processing module 118A (FIG. 1) and outdoor control module 114A are of the following format. Messages begin with a synchronization byte which is followed by a single byte OP code. The single byte OP code identifies the operation to be performed in response to the message. Following the OP code is a single byte which defines the length of the message. The length of the message ranges from 0 to 255 bytes. Following the length byte are a number of data bytes equal to the value of the length byte. For example, if the length byte is 0, the length byte is followed by no data bytes. Similarly, if the length byte is equal to 10, the length byte is followed by 10 data bytes. Following the data bytes is a single checksum byte.

A change power message is a message whose OP code identifies the message as an instruction to change power. In a change power message, the length byte has a value of 2 and is followed by two data bytes. The first data byte identifies a subcommand and the second byte identifies a power setting value. Subcommands of a change power message include set, read, and store. The second byte is ignored unless the change power message has a subcommand of set.

The change power command is received by firmware 408 (FIG. 4) of outdoor control module 114A as described more completely above. Firmware 408 compares the OP code byte of the message to an OP code identifying a change power message to thereby determine that the received message is a change power message. Firmware 408 then determines which subcommand is identified by the first byte of the data field. If the subcommand is set, firmware 408 applies the value of the second byte of the data field to digital-to-analog converter 414. If the first byte of the data field of the change power message is a store subcommand, firmware 408 stores the value applied to digital-to-analog converter 414 as datum 410 and nonvolatile memory 406. If the first byte of the data field of the change power message is a read subcommand, firmware 408 builds a reply message with a single data byte whose value is the value that is applied to the input of digital-to-analog converter 414 and sends the message back to signal processing module 118A. Thus, the power of signals transmitted through antenna 108A by outdoor control module 114A is controlled in response to a message received from signal processing module 118A of indoor unit 102A.

In addition to receiving change power messages through maintenance port 124A, signal processing module 118A can receive change power messages from signal processing module 118B of indoor unit 102B of transceiver 100B. A pier channel is included in the IF carrier signal broadcast between RF processor 116B of indoor 102B and RF processor 116A of indoor unit 102A through outdoor units 104A and 104B and wireless channel 110. Transceiver 100B changes the power at which outdoor unit 104A of transceiver 100A transmits signals by building a change power message as described above. The change power message is transmitted to indoor unit 102A through the pier channel and received by RF processor 116A. RF processor 116A transmits the change power message to signal processing module 118A. Firmware 610 (FIG. 6) of signal processing module 118A receives the change power message and forwards the change power message to outdoor control module 114A (FIG. 1) in the manner described above. In the manner described more completely above, outdoor control module 114A changes the power with which signals are transmitted through antenna 108A in accordance with the received change power message. Thus, using the principles of the present invention, the power of signals transmitted by one transceiver is controlled by a second transceiver.

One embodiment of firmware 408 (FIG. 4) of outdoor control module 114A is created by compiling the source code of Appendix A and linking the resulting object code using the C compiler and linker, respectively, available from Franklin Corporation of San Jose, Calif. for use with the 8552 microprocessor. In this same embodiment, microprocessor 402 of outdoor control module 114A is the 8552 microprocessor available from Franklin Corporation.

One embodiment of firmware 610 (FIG. 6) of signal processing module 118A is created by compiling the source code of Appendix B and linking the resulting object code using the C compiler and linker, respectively, available from Intel Corporation of Santa Clara, Calif. for use with the 80C196 microprocessor. In this same embodiment, microprocessor 602 of signal processing module 118A is the 80c196 microprocessor available from Intel Corporation.

A second embodiment of firmware 408 (FIG. 4) of outdoor control module 114A is created by compiling the source code of Appendix C and linking the resulting object code using the C compiler and linker, respectively, available from Franklin Corporation of San Jose, Calif. for use with the 8552 microprocessor.

A second embodiment of firmware 610 (FIG. 6) of signal processing module 118A is created by compiling the source code of Appendix D and linking the resulting object code using the C compiler and linker, respectively, available from Intel Corporation of Santa Clara, Calif. for use with the 80c196 microprocessor.

The embodiments described above are illustrative only and are not limiting. Instead, the scope of the present invention is limited only by the claims which follow. ##SPC1##