Transmit Antenna Selection and OSTBC in adaptive multiuser OFDMA systems with different user priorities and imperfect CQI

Abstract

In this paper, an adaptive multiuser OFDMA system in the downlink with multiple antennas at the transmitter and the receivers is investigated which serves two sets of users differing in their priority regarding channel access. At the transmitter either Transmit Antenna Selection (TAS) or Orthogonal Space Time Block Coding (OSTBC) is performed. In addition, Maximum Ratio Combining (MRC) is performed at each receiver side. A Weighted Proportional Fair Scheduling (WPFS) approach is applied using the different user priorities and the instantaneous Signal-to-Noise-Ratios (SNRs) of the corresponding equivalent Single Input Single Output (SISO) channels of the users as Channel Quality Information (CQI) to allocate the different subcarriers to the different users. These CQI values are assumed to be imperfect due to time delays and estimation errors. The joint impact of imperfect CQI and user priority on the system performance is analytically investigated for both transmission schemes. Numerical results show that serving users with different priorities comes at the expense of reduced system data rate and less robustness against imperfect CQI. Furthermore, it is beneficial to switch from TAS to OSTBC in scenarios for fast varying channels due to the additional exploitation of spatial diversity applying OSTBC.