On Downlink Transmission Without Transmit Channel State Information and With Outage Constraints

Abstract

This paper investigates downlink transmission over a quasi-static fading Gaussian broadcast channel (BC), to model delay-sensitive applications over slowly time-varying fading channels. System performance is characterized by the outage capacity region. In contrast to most previous work, here the problem is studied under the key assumption that the transmitter knows only the probability distributions of the fading coefficients, not their realizations. For scalar-input channels, two coding schemes are studied. The first scheme is called blind dirty paper coding (B-DPC), which utilizes a robustness property of dirty paper coding to perform precoding at the transmitter. The second scheme is called statistical superposition coding (S-SC), in which each receiver adaptively performs successive decoding with the process statistically governed by the realized fading. Both B-DPC and S-SC schemes achieve the outage capacity region, which dominates the outage rate region of time-sharing, irrespective of the particular fading distributions. The S-SC scheme can be extended to BCs with multiple transmit antennas.