Multiple Access Using MSE-OFDM

In this paper we propose a new multiple access scheme using multi-symbol encapsulated orthogonal frequency division multiplexing (MSE-OFDM). MSE-OFDM is a bandwidth efficient OFDM scheme, where a number of OFDM symbols are grouped together as a frame and protected by one single cyclic prefix. We wish to explore a multiple access MSE-OFDM, where each symbol of the frame is from a different user. Performance analysis of multi-user MSE-OFDM in AWGN and multipath fading channels has been done and the effects of carrier frequency offset and timing offset on its performance have been studied for downlink channel. The signals from multiple users are assumed to be synchronous in the downlink and the channel conditions are also assumed to be similar for each user. The multiple access interference (MAI) should be minimum if the orthogonality of subcarriers is maintained. However, due to carrier frequency offset and symbol timing misalignment, the orthogonality between users may be destroyed resulting in MAI. The MAI has been analyzed for the proposed scheme and can be reduced by using suitable methods for frequency and time synchronization. Expressions for probability of error for multi-user MSE-OFDM in presence of inter-channel interference (ICI) and inter-symbol interference (ISI) have been derived. Both analysis and simulation results are found to be in close agreement.