OFDM Pulse Shaping for use in 5G Systems

Currently new waveforms spectrally more efficient than the Orthogonal Frequency Division Multiplexing (OFDM) modulation are being studied by recent research projects for the development of the 5G physical layer. Although OFDM has powerful features such as implementation flexibility and robustness against channel selectivity and intersymbol interference (ISI), its use is not certain in the new emerging communication systems mainly due to its carrier frequency offset sensitivity, very large dynamic amplitude range, and high-power spectral sidelobes around active subcarriers eventually generating out-ofband emissions (OOBE) which in some cases cause intercarrier interference (ICI) among channels. These drawbacks limit its use in heterogeneous and densed 5G networks and in fragmented spectrum and cognitive radio scenarios where flexible use of spectrum is very important. This paper presents the analysis of the time-domain windowing technique applied to OFDM (WOFDM) to deal with the OFDM OOBE problem. The effect of windowing is analytically derived and constraints are given on the window formats to guarantee the non significant signal-tointerference power ratio (SIR) and BER degradations caused by ISI and ICI. Numerical simulations are elaborated for a scenario based on 5-MHz 3GPP Long-Term Evolution (LTE) and multipath channel.