Comparison of Multi-user Timing Offset Resilient Uplink OFDMA Schemes with Optimal Power Control

We investigate the channel capacity of two kinds of uplink OFDMA (Orthogonal Frequency Division Multiple Access) schemes, i.e., ZCZ (Zero Correlation Zone) code time-spread OFDMA and sparse SC-FDMA (Single Carrier Frequency Division Multiple Access) which are robust to access timing offset (TO) among users. For the practical condition, we consider not only the TO among users but also the PAPR (peak to average power ratio) which is a major issue of uplink OFDMA. In the case with TOs in arrival times among users, the amplified user´s signal by power control affect the distortion of other user´s signal. Meanwhile, amplified signal by simply considering distance between user and base station might be distorted due to the limit of amplifier and thus the performance might degrade. In order to achieve the maximum channel capacity, we investigate the combinations of optimized power control so called ASF (Adaptive Scaling Factor) by numerical simulations. We check that the channel capacity with optimized power control by ASF increases compared to the case without ASF i.e., ASF=1. From the simulation, in the case of high signal to noise ratio (SNR), ZCZ code time-spread OFDMA achieves higher channel capacity compared to sparse block SC-FDMA. On the other hand, in the case of low SNR, the sparse block SC-FDMA achieves better performance compared to ZCZ time-spread OFDMA.