Multi- Channel Broadband Re-configurable RF Front End for Software Defined Radio / Cognitive Radio

[0001] The present application is based on, and claims priority from, IN Application Number 3076/CHE/2012, filed on 27 Jul. 2012, the disclosure of which is hereby incorporated by reference herein.

[0002] This embodiment relates to radio frequency front-end design more particularly to a Multi-channel broadband re-configurable RF Front End for Software Defined Radio and Cognitive Radio.

[0003] Studies conducted by regulatory bodies in various countries have revealed that most of the radio frequency spectrum is inefficiently utilized. Allocation of fixed spectrum (assigned to specific services) prevents rarely used frequencies from being used by unlicensed users, even when there is no threat of interference at all with any of the assigned services

[0004] Advances in the wireless technology along with the development of analog and digital electronics have led to the emergence of wide range of wireless and radio access technologies. There is a huge demand for the availability of spectrum with the increased number of applications in the wireless communications space. With the existing radio frequency spectrum, being pushed to its boundaries there is a limitation on the spectrum availability.

[0005] To address spectrum scarcity issue and to satisfy the increased demand of applications new methods are needed for efficient and intelligent use of spectrum.

[0006] Wireless communication systems like cognitive radios are working towards allowing the wide frequency spectrum to be shared thus enabling efficient radio spectrum utilization. Cognitive radio devices use dynamic spectrum management system and can identify available/idle frequencies/frequency bands the spectrum that can be used for communications. Multiple cognitive radio systems generally share information to find vacant spectrum bands.

[0007] For cognitive radios to succeed, it is essential that they must be software defined, capable of operating on a broader frequency range, have better interference management, strong spectrum sensing and also have re-configurability in terms of operating parameters like frequency, input/output power, receiver sensitivity, bandwidth and so on based on the radio environment. Broad frequency range of operation (for spectrum sensing, interference management and communication) and reconfigurabilty of operating parameters depends on the design of the RF front end.

[0008] Accordingly, the embodiment provides a multichannel broadband re-configurable RF front-end system for software-defined radios/cognitive radios with multiple channels operating on broad frequency range. Each transceiver channel is capable of performing transmitter function and/or receiver function. Each channel contains an RF transmitter, a RF receiver, a control and monitoring section, and a reference switching section, a Transmit/Receiver switch and a power supply and conditioning circuit. The RF transmitter up converts baseband signal to a RF signal. The RF receiver converts the received RF signal from antenna in to the baseband signal using double/dual conversion. One receiver of one transceiver channel is dedicated for sensing of spectrum holes if used for cognitive radio application. Each transceiver channel is reconfigurable across a range of operating parameters. The parameters are reconfigured using a control and monitoring section, which has controller for sending and receiving reconfiguration information. The reference switching section provides said reference frequency-to-frequency synthesizers in channel. A Transmit/Receiver switch is used to operate/perform a channel in TDD or FDD mode of operation.

[0009] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

[0017] The embodiments herein, the various features, and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0018] Referring now to the drawings, and more particularly to FIGS. 1 through 6, where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.

[0019] FIG. 1 illustrates a block diagram of multichannel broadband reconfigurable RF front end, according to the embodiments as disclosed herein. The Multi Channel Broadband Reconfigurable RF Front End consists of the multiple channels and consists of RF receivers (down converters) 102, RF Transmitters (Up converters) 101, control and Monitoring Section (Controller) 104, Optional Internal Reference (105), reference switching section 106, Tx/Rx switches 108 and power supply/power supply and conditioning circuitry 107.

[0020] Each channel can operate from 400 MHz to 6000 MHz. Each channel comprises of RF-transmitter 101/up converter, RF receiver 102/down converter, master controller 104 and its associated circuitry. Each channel will get a common reference from reference and switching circuitry 106. The reference could be internally generated through internal reference 105 or can be externally supplied. Each broadband RF transceiver channel is connected to broadband antennas through TX/RX switch 108. Depending on the position of the TX/RX switch 108, the channel works at the TDD (Time Division Duplex) mode or FDD (Frequency Division Duplex) mode. The selection of the operating mode is controlled from the baseband unit. The individual blocks of the system are powered by power supply and conditioning circuitry 107. In the multichannel RF front end, one receiver in one channel works as a “sensing channel” for sensing the environment and other channels are used for the communication at broad frequency range. Although in FIG. 1 only depicted four channels and associated control section is depicted in practice it but can be applied to multiple channels (more than 4). The RF receiver 102 and RF transmitter 101 contains appropriate modulators, demodulators, local oscillators and so on for operation.

[0021] FIG. 2 is a block diagram of receiver section in a multichannel broadband reconfigurable RF front end, according to the embodiments disclosed herein. The broadband, reconfigurable RF receiver comprises of two quadrature demodulators 201, broadband local oscillator circuitry 202, fixed frequency local oscillator circuitry 206, low noise amplifiers 205, RF variable attenuators, RF Power detection circuitry 203, and control and monitoring circuitry (not shown in figure). The received signal from antenna is fed to the broadband re-configurable RF receiver. The receiver can work at the TDD (Time Division Duplex) mode or FDD (Frequency Division Duplex) mode using the switch as shown in FIG. 2. The broadband re-configurable RF receiver provides the appropriate amplification to the input signal; using the low noise amplifier 205, gain blocks and digital attenuators. Amplified input signal is down converted into baseband signal using dual conversion. During reception, to avoid the desensitization of receiver, received RF signal in the range 400 MHz to 6000 MHz is first down converted into 70 MHz I/Q signal. The local oscillator frequency is generated by the synthesizer circuitry. Two different synthesizers are used in the receiver. Two LO signals are sent to the two different demodulators. At first conversion, the quadrature demodulator 201 converts the input RF frequency signal into First IF (say 70 MHz signal). At second conversion, the first IF is further down converted into zero IF or low IF signal (say 0 MHz to 22 MHz) using another quadrature demodulator 207. Local oscillator signals for the first quadrature demodulator 201 (First LO) are generated using broadband LO circuitry 202. The local oscillator signal for the second quadrature modulator 207 (Second LO) is constant/fixed frequency and generated by fixed frequency LO circuitry 206. Multiple power detection circuitry are used for precise power detection and thus for precise automatic gain control (AGC). The power detection circuitry 203 comprising an ultra high bandwidth, high directivity coupler and power detector. The reference signal required for generating the local oscillator signals is provided using reference generating circuitry. The controlling and re-configuring are done by the control and monitoring circuitry. The re-configurability in terms of operating frequency is provided by changing the Local oscillator signal (from the broadband local oscillator circuitry, First LO 202) to the quadrature demodulator 201. The frequency is re-configurable or changeable in precise steps (say in the order of 100 KHz). The re-configurability in terms of input power dynamic range is provided by selecting the appropriate amplification path (out of the four (N) paths) using automatic gain control (AGC) mechanism. The receiver is re-configurable/changeable to the input power level in precise steps (say in the order of 1 dB). The receiver can operate over a broad frequency range (say from 400 MHz to 6000 MHz) and can support broad input power dynamic range (say average input power from −80 dBm to +0dBm). The receiver is reconfigurable to any frequency within the frequency range of operation and can be configured to any input power within the input power dynamic range. The receiver section has been described in patent application 2433/CHE/2012.

[0022] FIG. 3 is a block diagram of transmitter section in a multichannel broadband reconfigurable RF front end, according to the embodiments disclosed herein. The transmitter unit is implemented based on direct conversion architecture. The broadband, reconfigurable RF transmitter comprises of quadrature modulator 301, broadband local oscillator circuitry 302, RF amplifiers, RF variable attenuators, RF Power detection circuitry 303, and control and monitoring circuitry. The baseband signal with Q channels and I is fed to the wideband quadrature modulator 301. The local oscillator signal for the quadrature modulator 301 is generated using broadband Local oscillator circuitry 302. The low power RF signal generated by quadrature modulator 301 is subjected to required amplification and attenuation 305 and filtered 304 to provide the required output power. The re-configurability in terms of operating frequency is provided by changing the local oscillator signal (from the broadband local oscillator circuitry 302) to the quadrature modulator 301. The re-configurability in terms of output power is provided by selecting the appropriate amplification path (out of the three (N) paths) and appropriate DVA settings in the corresponding path. The frequency is re-configurable or changeable in precise steps (say in the order of 100 KHz). The output power is re-configurable and changeable in precise steps (say in the order of 1 dB). Multiple power detection sections are used for precise power detection and thus for precise automatic power control (APC) and Automatic Gain Control (AGC) with precise output power level. Plurality of power detection circuitry is placed into the chain. Multiple power detection circuits output signal sends to the controller, where it is matches with desired output signal power level, by which can get accurate and precise output power. The power detection circuitry 303 comprising an ultra high bandwidth, high directivity coupler and power detector. The reference signal required for generating the local oscillator signal is provided using reference generating circuitry. The controlling and re-configuring are done by the control and monitoring circuitry. The channel can also work at the TDD (Time Division Duplex) mode or FDD (Frequency Division Duplex) mode using the switch as shown in FIG. 3. The detailed description of the transmitter is provided in 2434/CHE/2012, the description of which is included herein by reference.

[0023] FIG. 4 is a block diagram of the broadband local oscillator section used in a multichannel broadband reconfigurable RF front end, according to the embodiments disclosed herein. In each channel, two broadband local oscillators are used; wherein one LO is present in the RF transmitter 101 and the second LO is present in the RF receiver 102. The receiver also comprises of a fixed frequency oscillator for down conversion of received signal. A frequency synthesizer 401 is used to produce the desired range of frequencies. Reference frequency generated by the reference generating section is for the frequency synthesizer 401. Synthesizer 401 receives commands from the control and monitoring circuitry and accordingly generates a broadband local oscillator frequency. To achieve the broadband operation, the LO section comprises two frequency selection paths. The path 1 is to generate the portion of the entire frequency range that the frequency synthesizer could support. The path 2 comprises a frequency multiplier to cover the remaining portion of the frequency range and that the frequency synthesizer could not support. Appropriate amplification and filtering is provided in both paths to achieve required LO power level and with adequate harmonic rejection. Appropriate path will be selected using RF switches, which receives the commands from control and monitoring circuitry. The detailed description of the LO is provided in 2433/CHE/2012 and 2434/CHE/2012, the description of which are included herein by reference.

[0024] FIG. 5 is a block diagram of the reference section used in a multichannel broadband reconfigurable RF front end, according to the embodiments disclosed herein. The reference section produces the required reference signal for the frequency synthesizer in the RF receiver 102 and RF transmitter 101 for all the channels to produce the corresponding LO signal. The reference section produces the number of coherent signals say at 10 MHz frequency. The reference section provides the coherent reference signals using clock buffers 503 to all synthesizers in the RF front-end unit and to the other section modules (like baseband unit) for synchronization purpose. By default, the system operates with internal reference frequency 501 that is generated by the TCXO/OCXO. In the presence of the external reference frequency 502 of say 10 MHz with adequate power level internal reference will be switched off and external reference is given to all frequency synthesizers in transmitter as well as in receiver section.

[0025] FIG. 6 is a block diagram of the control and monitoring section used in a multichannel broadband reconfigurable RF front end, according to the embodiments disclosed herein. The control and monitoring section reports the health status of the RF transmitter to the base band unit. The control and monitoring interface section contains a microcontroller 600 and its associated circuitry.

[0026] The baseband unit sends commands, like frequency setting, attenuation setting, to the controller section (Master controller) of the RF Frontend. The Control section processes it and modifies it suitably according to the up convertor 601 and down converters 602 and then sends it to the controllers (slave controllers) in the respective Tx and Rx. The slave controllers could have direct interface to the baseband unit also. This master controller 600 receives instruction from the baseband unit (BBU) through an interface (say SPI) for a required frequency (within the frequency range of operation) and required output power (within the output power dynamic range) for each channel.

[0027] The RF front end can suitably work in receiver mode for say =80 dBm to 0 dBm average input power and in transmit mode for say −70 dBm to +10 dBm average output power. The RF front end can suitably be used up to 12 dB crest factor signal. The multichannel broadband reconfigurable RF front end is well suited for cognitive application: with multiple channels, with broadband nature of front end, plurality of communication standards can be supported and with re-configurability of variable power levels and frequency range can be supported.

[0028] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.