Capacity bounds for downlink channels with peak power constraints and causal relay networks

Abstract

Capacity characterization of communication channels and systems is a fundamental problem in information theory. In most network models, the general capacities are still unknown. In this thesis, we focus on some bounds on the capacity. Specifically, we show inner bounds on the capacity for a multiple antenna broadcast channel with a per-antenna peak power constraint, and outer bounds on the capacity for a causal relay network. For inner bounds, a new achievable scheme is introduced which is suitable for the channel with peak power constraint based on dirty-tape coding (DTC). Also, we provide two outer bounds for relay networks with causal relays, where the transmit signals of relays depend on the current received symbol as well as on the past received symbols.

First, we consider a Gaussian multiple-input single-output (MISO) broadcast channel with a per-antenna peak power constraint (simply peak power constraint). It is more realistic to consider the peak power constraint on each transmit antenna because in many practical implementations each antenna is equipped with its own power amplifier. Assuming the perfect knowledge of the channel state information (CSI) at the transmitter, we propose an achievable scheme using DTC. The ideal dirty-paper coding (DPC), which is a capacity-achieving scheme for the Gaussian multiple-input multiple-output (MIMO) broadcast channel, cannot be used for our model because its optimal input distribution is Gaussian and thus the peak power constraint is violated. On the other hand, the channel input of DTC is uniformly distributed in a fixed range, which helps to control the peak power of the transmit signal easily. We also present an algorithm that finds capacity-achieving beamforming vector and power allocation factors under a per-antenna average power constraint and use the optimized parameters in the proposed scheme. Simulation results show that the proposed scheme provides gains of 2.7dB over a non-DTC scheme based on minimum ...