Wideband communication with high-dimensional arrays: New results and transceiver architectures

Wideband high-dimensional antenna arrays are expected to play a key role in future 5G wireless systems. Due to narrow beamwidths, phased array/beamforming methods are the natural choice for design and analysis of high-dimensional MIMO systems. However, conventional methods are based on the narrowband assumption which is violated as the bandwidth and array dimension increase. In this paper we revisit the use of high-dimensional arrays in line-of-sight single-input multiple-output (SIMO) systems. We develop a channel model that reveals coupling between the spatial and temporal dimensions that is not captured by conventional separable models. We then apply beamspace MIMO (B-MIMO) theory - system representation with respect to orthogonal spatial beams - to analyze system performance. Our analysis reveals a key dispersion factor Δ ch that captures the impact of array dimension and bandwidth on performance. We show that Δ ch characterizes the magnitude of the coupled signal dispersion in spatial angle and time. This leads to new B-SIMO transceivers that use on the order of Δ ch beams to deliver near-optimal performance with dramatically low complexity compared to the optimal receiver. We present results that demonstrate the significant losses incurred by phased array receivers, and the near-optimal performance of low-complexity B-SIMO transceivers. Extension of the new wideband LoS SIMO model to MISO, MIMO, and multipath scenarios is outlined.