Comparison of Multi-user Timing Offset Resilient Uplink OFDMA Schemes with Optimal Power Control
Abstract-We propose a new Ad hoc OFDMA(Orthogonal Frequency Division Multiple Access) scheme with greatly enhanced tolerance of timing offset among the nodes. In terms of data frame structure, the proposed scheme is similar to code spread OFDMA or MC DS CDMA. The main different aspect is that we employ a cyclic extended PSW (Properly Scrambled Walsh-Hadamard) code as the spreading sequences for the Ad hoc nodes. Exploiting the property that PSW code has zero correlation despite ±1 chip timing offset, the proposed Ad hoc OFDMA achieves internode- interference free performance with the timing offset up to ±1 OFDM symbol duration. In contrast, the other existing schemes in comparison undergo severe performance degradation even with small timing offset under multipath fading channel.