A 2-Dimensional Transmit Beamforming Method: Performance Results for Slow Fading Channels

Abstract

The main concern in slow fading channels is that the coded symbols can not be sent over multiple fades of the channel, because when they are transmitted across all strong and weak subchannels of a multiple-input multiple-output (MIMO) channel, the weak subchannels play the major role in the degradation of the total performance of the channel. In this paper, we propose a 2-dimensional transmit beamforming (2-DTBF) method that enables us to code across the two strongest subchannels of a MIMO channel, and by combining Alamouti space-time coding with this method, we are able to utilize both spatial multiplexing and diversity. We will show that the spectral efficiency of the proposed scheme is greater than that of orthogonal space-time block codes (OSTBCs) and is equal to those of quasi-OSTBCs (QOSTBCs) and space-time trellis codes (STTCs) for the same number of transmit antennas. We will also illustrate that the proposed scheme has better bit error rate (BER) performance than OSTBCs and QOSTBCs and has better frame error rate (FER) performance than STTCs at asymptotically low signal-to-noise ratio (SNR) regime.