Achievable rates with quantised channel state information in a multiple-access channel with one cognitive transmitter

The authors investigate the achievable rates of a multiple-access channel with one cognitive transmitter in a fading channel. The cognitive transmitter uses dirty-paper coding to mitigate the known interference. They assume partial transmit channel state information which is obtained through a quantised limited feedback. In this model, the receiver sends as feedback only a finite number of bits describing the fading coefficients. Numerical results show that different quantisation schemes must be used for different transmitters (cognitive and non-cognitive) in order to maximise their rates. Also, the number of quantisation bits allocated to each channel coefficient (i.e. the channels from the non-cognitive and cognitive transmitters to the receiver), for a fixed total feedback bits, can affect the achievable rates of the transmitters, and even for each channel coefficient, how to dedicate the considered quantisation bits between the coefficient magnitude and phase can have substantial effects on the rate.