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On the Bit Error Rate of OFDMA Employing Short Cyclic Prefix and Maximal Ratio Combining

Abstract:

Orthogonal frequency division multiple access (OFDMA) has been chosen as the fourth generation (4G) standard and also in the first releases of fifth generation (5G) mobile systems. Unfortunately, OFDMA uses a cyclic prefix that requires an increase in bandwidth and transmission power. In practical systems, there is no need to maintain a bit error rate (BER) lower than that required by a service. Hence, it is possible to reduce the cyclic prefix duration and maintaining an adequate performance. In this sense, in this work, the BER of OFDMA systems that employ a cyclic prefix shorter than the channel delay spread is evaluated. In addition, an antenna array at reception is considered. Diversity signals are combined employing maximal-ratio-combining (MRC). Assuming that noise plus intersymbol interference plus intercarrier interference can be modeled as a zero-mean Gaussian random variable, a closed form expression to calculate the BER for M-QAM modulations is derived. Simulation results show that our theoretical expression behaves as a lower bound, which becomes more accurate as the cyclic prefix duration tends to the channel delay spread.