Interference Analysis and Filter Parameters Optimization for Uplink Asynchronous F-OFDM Systems

Filtered-orthogonal frequency division multiplexing (F-OFDM) is a candidate for 5G new waveform, which has flexible numerologies to support various scenarios and can combat interference of multi-users effectively with filters. However, although longer filter length and higher roll-off factor can suppress out of band radiation, inter-symbol interference (ISI) and inter-carrier interference (ICI) will increase at the same time. Meanwhile, the wider guard band reduce inter-user interference (IUI) at the cost of higher spectrum occupancy. To meet target bit error rate (BER) requirements of all users and maximize the spectrum efficiency, a filter parameter and guard bandwidth optimization model was proposed to design related parameters dynamically for uplink asynchronous F-OFDM system, where users are allocated with different numerologies. We present a detailed theoretical derivation on ISI, ICI, and IUI for BER calculation, and the theoretical derivation of IUI in multi-user scenario with different subcarrier spacing between users is first presented. The formulated problem is proved to be a non-convex NP hard problem and Imperialist Competitive Algorithm (ICA) is applied for a desirable solution. The simulation results show that the theoretical derivations are valid and the proposed filter parameter and guard bandwidth optimization model can achieve higher spectrum efficiency than the fixed filter parameters in F-OFDM while outperforms traditional OFDM.