Massive Access with Channel Statistical Information

In this chapter, we study the problem of massive access in the 5G cellular IoT, where the channels are fast-varying. To address the challenging issue of channel state information (CSI) acquisition and beam design for a massive number of IoT devices over fast time-varying fading channels, we design a non-orthogonal beamspace multiple access framework. In particular, the user equipments (UEs) are non-orthogonal not only in the temporal-frequency domain, but also in the beam domain. We analyze the performance of the proposed non-orthogonal beamspace multiple access scheme, and derive an upper bound on the weighted sum rate in terms of channel conditions and system parameters. For further improving the performance, we propose three non-orthogonal beam construction methods with different beamspace resolutions. Finally, extensively simulation results show the performance gain of the proposed non-orthogonal beamspace multiple access scheme over the baseline ones.