Optimal bit allocation of limited rate feedback for cooperative jamming

In this paper, we investigate bit allocation schemes with limited rate feedback for cooperative jamming. In addition to the transmitter and receiver, we assume a passive eavesdropper and cooperative jammer are present. In order to achieve a secure communications link against the eavesdropper, the transmitter and jammer require channel state information (CSI) to be fed back to them from the receiver. Assuming feedback channels with a maximum sum feedback rate constraint, the receiver must allocate the total number of bits available to quantize the CSI between the transmitter and jammer. This requires the receiver to balance the need for a strong channel from the transmitter against the need for the jammer to accurately null the receiver and reduce the resulting interference. We propose an optimal bit allocation strategy for this problem using mean-squared error as the performance metric, and we use simulation examples to illustrate its advantage over a non-optimized feedback allocation.