MIMO broadcast channels with cooperation among densely clustered receivers

While channel state information (CSI) at the transmitter is critical to the system capacity of multiple input multiple output (MIMO) broadcast channels, its acquisition is practically intricate. This paper exploits the benefit of receiver cooperation to render it unnecessary to acquire CSI at the transmitter. As a fundamental question, how many downlink transmission bits can one bit of receiver cooperation buy? In this paper, the quantitative relationship between the cooperation multiplexing gain and the cooperation rate R with compress-and-forward strategy is established. It is proved that if R is scaled at the rate of α log₂ γ, where γ is the signal-to-noise ratio (SNR and α ϵ [0, 1] is the scaling factor, a multiplexing gain of 1+ α (K - 1) can be achieved, where K is the number of cooperating receivers. a ≥ 1 yields full multiplexing gain. Moreover, analysis result shows that benefitting from the dense clustering feature, each receiver consumes negligible cooperation power compared to the downlink data transmission.