A large-system analysis of the imperfect-CSIT Gaussian broadcast channel with a DPC-based transmission strategy

The Gaussian broadcast channel (GBC) with K transmit antennas and K single-antenna users is considered for the case in which the channel state information is obtained at the transmitter via a finite-rate feedback link of capacity r bits per user. The throughput (i.e., the sum-rate normalized by K) of the GBC is analyzed in the limit as K ¿ ¿ with r/K ¿ r¿. Considering the transmission strategy of zeroforcing dirty paper coding (ZFDPC), a closed-form expression for the asymptotic throughput is derived. It is observed that, even under the finite-rate feedback setting, ZFDPC achieves a significantly higher throughput than zeroforcing beamforming. Using the asymptotic throughput expression, the problem of obtaining the number of users to be selected in order to maximize the throughput is solved.