BER Fairness and PAPR Study of Interleaved OFDMA System

For an OFDMA system, the role of interleavers is analyzed to ensure fairness of BER performance among the active users and investigate their respective PAPR properties. In this paper, the authors consider a generic system and show that for a slowly changing multipath channel, individual user’s BER performance can vary, implying that the propagation channel effect is unfairly distributed on the users. Applying different types of frequency interleaving mechanisms, the authors demonstrate that random interleaving can ensure BER fairness on an individual user basis but the associated system overhead for de-interleaving is very high. In this context, the authors introduce the application of cyclically shifted random interleaver and demonstrate its effectiveness in achieving BER fairness (dispersion in individual users BER reduced by 94% compared to no interleaving at 20dB SNR) with little system overhead. The authors also explore the comparative performance of different interleavers for scenarios with varying number of total subcarriers and subcarriers per user. Based on the scenario specific results, the authors conclude that for a heavily loaded system, i.e., relatively low number of subcarriers per user, cyclically shifted random interleavers can effectively ensure uniform performance among active users with reduced system complexity and manageable PAPR.