Space-time trellis codes (STTC) versus beam pattern scanning (BPS)

Two transmit diversity techniques, space-time trellis coding (STTC) and beam pattern scanning (BPS) (also called beam pattern oscillation) are compared. In the recently introduced BPS, controlled time varying weight vectors are applied to the base station antenna array elements. This creates a small movement in the antenna array pattern directed toward the desired user. In rich scattering environments, this small beam pattern movement creates an artificial fast fading channel. The receiver is designed to exploit time diversity benefits created by the fast fading channel. Via the application of simple combining techniques, the error-probability performance and the network capacity can be significantly improved with minimal cost and complexity. We conduct a comparison between Tarokh´s π/4-QPSK, 4-states, 2 b/s/Hz STTC and BPS π/4-QPSK, 2 b/s/Hz schemes in terms of their complexity and antenna physical dimension, network capacity (in term of number of users), frame-error-rate (FER) performance, and their relative spectrum efficiency. Network capacity and FER performance simulations are generated and compared. BPS achieves a higher network capacity and FER performance with a smaller antenna dimension and complexity (especially for wideband systems) with minimal cost to spectrum efficiency. This identifies the BPS technique as a promising scheme for future wireless communications.