Analysis of transmit beamforming and fair OFDMA scheduling

Abstract

Two promising candidates for beyond 3 generation (B3G) and 4G communication standards are multiple input multiple output (MIMO) and orthogonal frequency division multiple access (OFDMA) systems. OFDMA is a new technique that enables multiple users to transmit parallel data streams, allowing a much higher data rate than conventional systems, such as time division multiple access (TDMA) or code division multiple access (CDMA). Another research topic involving MIMO systems use antenna arrays at both the transmitter and the receiver. By using multiple antennas, the transmitter can adapt to the channel as it varies across time. This is accomplished by using a codebook of beamforming vectors which are known to both the transmitter and receiver. As the receiver acquires information about the channel, it calculates which beamforming vector matches the channel the best. The receiver then sends back the index of that vector to the transmitter. The symbol being transmitted is multiplied by the beamforming vector and sent over the channel, this is known as transmit beamforming (TB). Transmit beamforming can not only increase performance in wireless MIMO systems, but also add increased performance when put in combination with other MIMO systems like spatial multiplexing and space time codes. TB has advantages over other MIMO schemes because by measuring the channel, one can use adaptive modulation techniques to achieve a coding gain not obtainable without channel state information (CSI). Past research assumed the feedback channel was error free and had no delay. This isolated the effects of finite rate feedback. We assume there is delay in the