We investigate the spectral efficiency of large-array systems serving a single-antenna user in cellular frequencies, using full digital or hybrid analog-digital beamforming in frequency division duplexing (FDD) or time division duplexing (TDD) mode. We consider downlink transmission in time-frequency coherent channel blocks, containing both the pilots and data. Considering FDD and taking the pilot overhead into account, we show that hybrid beamforming provides better spectral efficiency performance than full digital beamforming, mainly in cases with high mobility and many antenna elements. We also optimize the number of used radio chains for hybrid beamforming in FDD and show it is possible to achieve comparable spectral efficiency as with full digital beamforming in TDD.
['Daniel C. Araujo', 'Eleftherios Karipidis', 'André L. F. de Almeida', 'João Cesar M. Mota']
Improving spectral efficiency in large-array FDD systems with hybrid beamforming