A study of transmit beamforming combined with space-time coding in the correlated fading channels

Abstract

Recently, there have been enormous researches on multiple-input multiple-output (MIMO) deploying multiple antennas at transmitter and receiver sides, which can be widely classified into beamforming and space-time coding (STC). The former generates specific beam targeted to serving user to accomplish array gain or SNR gain while the latter exploits independent multiple paths between each transmit-receive antenna pair to obtain spatial multiplexing and/or spatial diversity such as vertical Bell Lab layered space time (V-BLAST), space-time block coding (STBC), and double space-time transmit diversity (D-STTD). It is well known that the antenna spacing in the beamforming systems is required to be narrow, but that in the STC systems should be enough wide to be uncorrelated between each path. In outdoor environment, however, it is not easy to secure the independence of each path for STC due to spatial limitation for deploying a large number of antennas and relatively insufficient scatters. In this respect, transmit beamforming combined with V-BLAST and Alamouti``s STBC has been developed, which generates independent and power-concentrated beam paths in order to attain array gain as well as spatial multiplexing gain and/or spatial diversity gain by employing a uniform-linear array (ULA). In this thesis, we extensively and rigorously investigate the transmit beamforming systems with quasi-orthogonal STBC (QO-STBC), and D-STTD. Furthermore, beamforming group selection scheme for the case combined with V-BLAST, beam shuffling and beam selection schemes for the case combined with QO-STBC and D-STTD are proposed to improve spatial diversity gain with no additional radio frequency (RF) chains in an economical manner. Especially, the simplified algorithm for the beam shuffing and the beam selection in the case combined with D-STTD is presented in comparison with the conventional antenna shuffling and selection schemes.