Bridging the Gap Between CP-OFDM and ZP-OFDM for the Provision of Ultra-Low Latency Services in 5G

In this paper, we introduce and characterize a new filter bank multicarrier (FBMC) architecture, based on flexible zero padding (FZP), suitable for applications obeying stringent latency requirements. FZP conveniently distributes zeros between transmit (Tx) and receive (Rx) waveforms, and covers cyclic prefix (CP) and zero padding (ZP) as special extremal cases, providing, in this way, a bridge between classical CP-orthogonal frequency division multiplexing (OFDM) and ZP-OFDM. It has the merit of being the only possible architecture that guarantees optimum confined and autonomous transmission and reception of each OFDM symbol within the symbol period, leading to a minimized latency. We assess the best achievable signal-to-interference-plus-noise-ratio (SINR) performances, of all possible FBMC configurations, obeying the FZP architecture, through a systematic optimization of their Tx and Rx waveforms, using the ping-pong optimized pulse shaping (POPS) algorithm. We also assess the whole communication link performance, in terms of raw and coded bit error rate (BER), for several representative FZP configurations. It turns out that the medium alternative between CP and ZP, which evenly distributes FZP between the Tx and Rx waveforms, does not provide a significant improvement in signal-to-interference ratio (SIR) and BER, for slightly time dispersive channels, but brings more robustness to time synchronization errors. The conducted study shows that conventional CP-OFDM remains an interesting alternative since it leads to an insignificant degradation in SIR, compared to the optimal FZP configuration, while providing a decorrelated noise at the receiver, beneficial for short coded packets.