System and method for antenna diversity using equal power joint maximal ratio combining

Abstract

An equal gain composite beamforming technique which includes the constraint that the power of the signal output by each antenna is the same, and is equal to the total power of the transmit signal divided by the number N of transmit antennas from which the signal is to be transmitted. By reducing output power requirements for each power amplifier, the silicon area of the power amplifiers are reduced by as much as N times (where N is equal to the number of transmit antennas) relative to a non-equal gain composite beamforming technique.

What is claimed is: 
     
       1. A wireless communication device, comprising:
 a plurality of N antennas; and 
 a baseband processor configured to determine a receive weight vector of a plurality of complex receive antenna weights for each of the plurality of N antennas, the receive antenna weights applied to a received baseband signal; 
 compute a transmit weight vector by computing a conjugate of the receive weight vector, the transmit weight vector comprising a complex transmit antenna weight for each of plurality of N antennas of the communication device, wherein each complex transmit antenna weight has a magnitude and a phase whose values may vary with frequency across a bandwidth of the baseband signal, thereby generating a plurality of N transmit signals each of which is weighted across the bandwidth of the baseband signal to be transmitted from corresponding ones of the plurality of N antennas to a second communication device, wherein the magnitude of the complex transmit antenna weight associated with each antenna is such that the power to be output at each antenna is the same and is equal to the total power to be output by all of the N antennas divided by N and such that the sum of the power at each corresponding frequency across the plurality of transmit signals is equal to a constant; 
 apply the transmit weight vector to a baseband signal for transmission via the plurality of N antennas; and 
 update the transmit weight vector by repeating the determining of the receive weight vector and computing of the transmit weight vector each time signals are received to update the transmit weight vector. 
 
     
     
       2. The device of  claim 1 , wherein the bandwidth of the baseband signal comprises K plurality of frequency sub-bands, and the magnitude of the complex transmit antenna weights associated with each of the plurality of N antennas is such that the power to be output by each antenna is the same and is equal to 1/(KN) of the total power to be output for all of the K frequency sub-bands of the communication device. 
     
     
       3. The device of  claim 2 , further comprising a baseband memory configured to store, for each of the N antennas, complex transmit antenna weights for a subset of the K frequency sub-bands or sub-carriers. 
     
     
       4. The device of  claim 3 , wherein the baseband processor and the stored subset of complex transmit antenna N and weights generate therefrom the complete set of antenna weights for all of the K frequency sub-bands or sub-carriers using interpolation techniques. 
     
     
       5. The device of  claim 1 , wherein the receive weight vector, the transmit weight vector and the baseband signal of the are applied to each of K frequency sub-bands of the baseband signal that correspond to sub-carriers of a multi-carrier baseband signal or synthesized frequency sub-bands of a single carrier baseband signal. 
     
     
       6. A wireless communication device comprising:
 a plurality of N antennas; and   a processor configured to produce a weight for each of the plurality of N antennas for use in beamforming; wherein the processor is further configured to determine a total transmit power; wherein the processor is configured to divide the total transmit power by N; wherein the processor is further configured to produce a multi-carrier signal for transmission; wherein the multi-carrier signal is weighted for each antenna per the produced weight and a power applied to each of the N antennas for the weighted multi-carrier signal is equal to the total transmit power divided by N.   
     
     
       7. The wireless communication device of claim 6 wherein the beamforming is used for multiple input multiple output. 
     
     
       8. The wireless communication device of claim 6 wherein the multi-carrier signal is an orthogonal frequency division multiplex signal. 
     
     
       9. The wireless communication device of claim 6 wherein the multi-carrier signal has a plurality of K subcarriers; wherein a power applied to each of the K subcarriers per antenna is equal to the total transmit power divided by KN. 
     
     
       10. A method comprising:
 producing, by a wireless communication device, a weight for each of a plurality of N antennas for use in beamforming;   determining, by the wireless communication device, a total transmit power;   dividing, by the wireless communication device, the total transmit power by N;   producing, by the wireless communication device, a multi-carrier signal for transmission;   weighting, by the wireless communication device, the multi-carrier signal for each antenna per the produced weight; and   applying, by the wireless communication device, a power to each of the N antennas so that the weighted multi-carrier signal for that antenna is equal to the total transmit power divided by N.   
     
     
       11. The method of claim 10 wherein the beamforming is used for multiple input multiple output. 
     
     
       12. The method of claim 10 wherein the multi-carrier signal is an orthogonal frequency division multiplex signal. 
     
     
       13. The method of claim 10 wherein the multi-carrier signal has a plurality of K subcarriers; wherein a power applied to each of the K subcarriers per antenna is equal to the total transmit power divided by KN.