Analysis of Linear Precoding Techniques for OFDMA Systems

This paper investigates the performance of linearly precoded OFDMA systems. Based on the pairwise error probability (PEP) analysis, a new design criterion, namely, the good shaping criterion, is introduced. Existing precoding techniques are discussed and an ad-hoc constellation shaping strategy is presented in order to satisfy the proposed criterion. Since maximum-likelihood (ML) detection has the ability to exploit the diversity achieved with the most effective spreading matrices, small size precoders are considered to keep the complexity reasonable. Simulation results have shown that linear precoding recovers most of the frequency diversity loss that is inherent to OFDMA. Moreover it is observed that simple constellation shaping strategies may be effective for small sizes of precoders.