Codebook based beamforming and multiuser scheduling scheme for mmWave outdoor cellular systems in the 28, 38 and 60GHz bands

In this paper a 3D ray tracing tool is developed for mmWave outdoor environments. Coverage analysis and system performance is performed for a small cell system at 60GHz. Peak throughputs beyond 3Gbps and cell edge throughputs in excess of 500Mbps are demonstrated at 98% of the mobile test locations. Analogue codebook based beamforming is applied. The analysis of the statistical angular spread at the mobiles is shown to be clustered; leading to many users selecting the similar analogue beamforming code which results is high levels of co-channel interference. It is often assumed that the use of analogue beamforming implies a single beam pattern pointing in a specific direction to support a single user. In this case users that cannot be spatially separated must be scheduled in different time slots. However, due to the clustered aspect of the users' angle spreads, those with the same beam code can still be scheduled in the same time slot using different frequency channels via a single RF chain. The paper analyses a scheduling scheme based on this concept. The same scheduling scheme is applied to systems operating at 28, 38 and 60GHz where different numbers of frequency channels are available. Different user densities and street scenarios are studied. The 60GHz scheme make use of 4 frequency channels and is shown to double the system throughput compared to operation at 28GHz band using a single frequency channel. Finally, the optimal number of RF chains required at the base station is analysed. This is shown to be a critical design issue for mmWave cellular systems.