Patent ID: 8891598

Claim:
A communication device having a receive path comprising: a number M antennas and respective radio modules, wherein the M antennas and respective radio modules support N×N multiple-input multiple-output (MIMO) transmissions and receptions, wherein M≧N; a processor operable in a baseband domain and configured to perform a self-calibration procedure by which a correction factor is computed for a channel reciprocity level, determined by said self-calibration procedure; a plurality of switches in each one of said radio modules configured to change the receive path for regular MIMO operation or during said self-calibration procedure; a digital attenuator configured to adjust calibration signals in the baseband domain; and a low noise amplifier (LNA), wherein there are multiple receive paths and at least one path loss included in the receive path between one of the M antennas used for receiving and the LNA, wherein the M antennas are configured to alternate transmitting and receiving periods on a single channel according to a time division duplex (TDD) communication protocol, wherein the M antennas are configured to define phases employed in MIMO transmission and selected using information measured at the communication device during receiving periods based on the channel reciprocity level, wherein the digital attenuator is further configured to digitally attenuate the calibration signal by an amount that is sufficient to prevent the LNA in the path undergoing calibration from saturating, wherein the communication device is further operable to perform the self-calibration procedure in which one antenna/radio (i) acts as a transmitter and the other antenna/radio (j) acts as the receiver during the self-calibration procedure, the self-calibration procedure comprising: performing the following for each of two antennas/radios (i and j): emitting a first calibration signal with a signal strength equivalent to a signal strength used during regular MIMO operation, the receiver using one receive path with some path loss to prevent the LNA from saturation and recording a received calibration signal R a — ji ; transmitting a second calibration signal that is digitally attenuated, the receiver continually employing the same one receive path used in said emitting step and recording a received calibration signal R b — ji ; transmitting a third calibration signal that is digitally attenuated, the receiver switch selecting the receive path used for regular MIMO operation and recording a received calibration signal R c — ji ; and reversing roles of transmitter and receiver for the two selected antennas/radios to repeat said self-calibration procedure and recording the measured calibrated signals: R a — ij , R b — ij , and R c — ij .