Hybrid antenna array for mmWave massive MIMO

This chapter introduces the massive hybrid array architecture, where antenna elements are grouped into multiple analog subarrays, and a single digital signal is received from or sent to each subarray. It provides an affordable and spatially feasible solution for millimeter-wave (mmWave) massive array, and can achieve comparable performance with a full digital array thanks to the temporal and spatial sparsity of mmWave propagation channels. This chapter starts by presenting the hybrid array architecture, highlighting two typical configurations of interleaved and localized arrays. It then presents four optional hardware implementations of this architecture. Array construction is then discussed through quasi-Yagi antenna arrays and stacked patch antenna with perpendicular feed substrate. Two prototypes, developed by CSIRO and Samsung, are also introduced. After reviewing the hardware development, this chapter further discusses signal processing techniques for hybrid arrays, with focus on angle-of-arrival estimation, single-user line-of-sight multiple-input multiple-output and its capacity, and spatial division multiple access techniques. Overall, this chapter shows that massive hybrid array is a very promising technique for 5G mmWave cellular communications, with vast open research challenges.