Speaker: V. Vignesh Kumar (EE13S074)
In a multipoint to point link, where multiple streams from geographically separated points co-existing in time and frequency are jointly detected, the relative powers at which the signals are received play an important role in deciding the sum rate. Unlike Rayleigh fading, where decreasing the power of any of the streams will result only in decrease in the sum rate, Rician fading exhibits an interesting behaviour where one can actually improve the sum rate by decreasing the power of one or more of the transmitted streams. This gives rise to the possibility of power efficient communications under Rician channel conditions. In this work, we discuss a power control scheme where the receiver, based on the present received powers and k-factor, feeds back the optimal powers to be transmitted so that the total transmitted power is minimized without any loss in the sum rate. It can be shown that by employing such a power control scheme, considerable amount of power can be saved on the transmit side, paving way to greener communications, for LoS or near LoS links.
In a similar setup where multiple streams are jointly detected, and two or more of the streams see a block faded channel, randomly phase rotating the constellation points of all the streams at the transmitter end provides an improvement in block error rate and helps achieve a performance close to the case where a single stream is transmitted without any co-channel interference. This kind of precoding scheme does not require any channel statistics at the transmitter and the overhead involved in communicating the random sequence is also minimal making it practically viable in interference limited scenarios where multiple streams are jointly detected. The performance of this scheme is analysed in various scenarios.