In an Orthogonal Frequency Division Multiplexing (OFDM) system, downlink beamforming can be implemented either before IDFT (frequency domain) or after IDFT (time domain) module in a base station transmitter. This paper compares Pre-IDFT downlink beamforming with Space-Time Block coded and Space-Frequency block coded transmit diversity schemes for 4×1 downlink multi-user OFDM (OFDM-TDMA and OFDMA) systems. The study is performed for indoor micro and pico cells and urban macro cells. Regardless of the multiple access schemes, it is found that beamforming always performs better in outdoor environment, where angular spread is lower, thus spatial correlation is higher.
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