Windowed OFDM for small-cell 5G uplink

We consider one of the most interesting candidates for the 5G transceiver system, the windowed OFDM, and we carry out an evaluation of the spectral efficiency that can be achieved in the uplink of small but crowded cells by means of a time-frequency multiple-access scheme. Our analysis is first carried out in the absence of multiple-access interference in order to determine a performance upper bound and to gain more insights about the role of the system parameters. The main contribution of the paper is constituted by the evaluation of the achievable spectral efficiency as a function of the most important transceiver parameters, and above all by the number of subcarriers assigned to each active mobile terminal. In particular, we show that, unlike the downlink scenario, the spectral efficiency in multiple access is not optimized by choosing the cyclic prefix length to be just larger than the multipath delay spread, but increasing it much more, especially when the number of adjacent subcarriers assigned to each terminal is small.