Preamble Design for Channel Estimation in OFDM/OQAM Cooperative Systems

Preamble design for LS channel estimation in OFDM/OQAM cooperative systems is investigated in this paper. A simple but important setup is considered, consisting of a pair of single-antenna terminals (source and destination) assisted in their communication by an AF relay and following a well-established two-phase transmission protocol. The so-called sparse preamble case (i.e., pilot tones surrounded by nulls) was recently addressed and the optimal design - in the sense of minimum MSE subject to transmit energy constraints - was shown to coincide with the one for CP-OFDM, thus resulting in no performance gains from the adoption of OFDM/OQAM. In order to complete this study and exhibit the possibilities of OFDM/OQAM to outperform CPOFDM, the so-called full preamble design (i.e., with all tones carrying pilot symbols) is addressed in this paper. The results are in line with the corresponding design for single-link systems, where the interference among pilots is positively exploited to provide significant performance gains over CP-OFDM. As a byproduct, the solution for cooperative CP-OFDM is also given, through its connection to OFDM/OQAM. The presented simulation results corroborate the analysis, demonstrating superior performance over CP-OFDM for both mildly and highly frequency selective channels and at practical SNR values.