Abstract-This paper presents performance analysis of Layered Random Beamforming (LRB) -MIMO-OFDMA employing various resource scheduling algorithms with feedback reduction in a realistic outdoor environment. LRB enables the exploitation of spatial multi-user diversity gain, spatial multiplexing capacity gain and layer spatial multi-user diversity gain, which is achieved by enabling the multiplex of data transmitted simultaneously to different destinations. Unlike a conventional beamforming system, an LRB system only requires an effective signal to interference and noise ratio (ESINR) based numerical data rate as feedback from every spatial layer of the MIMO channel and thus has potentially lower feedback requirements than a system which requires feedback of more detailed channel information. By combining the LRB technique with OFDMA, LRB-OFDMA can achieve an additional spectral multi-user diversity gain compared to the single carrier LRB system. Various scheduling algorithms are proposed for LRB-OFDMA and they show a trade-off between maintaining fairness and minimising delay. The performance of LRB-OFDMA is evaluated using some well-established statistical channel models as well as a propagation modeling tool, which represents a realistic outdoor environment.Index Terms-Layered Random Beamforming, MIMO-OFDMA, Multi-user Diversity, Scheduling Algorithm.
I. INTRODUCTIONESEARCH on future generation cellular systems has focused on supporting multi-user transmission and providing higher data rates and spectral efficiency. An OFDMA system is one of the most promising PHY and multiple access candidates for future communication systems [1]. For example, the WiMAX standard (802.16) uses OFDMA as the air interface [2] and the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) has already assumed that the downlink of the air interface would be OFDMA based [3]. Performance can be further improved by employing MIMO. Eigenbeamforming [4][5] is a capacity achieving transmission scheme that utilises singular value decomposition (SVD) and requires full channel state information (CSI) at the transmitter. However, this feedback amount increases with the product of the numbers of transmit and receive antennas.In a multi-user environment, there is likely to be at least one mobile station (MS) whose channel is near its peak at one time and/or frequency, provided different MSs experience independent fading channels. Application of a randomly generated beamforming pattern at the transmitter to achieve Opportunistic Beamforming is proposed in [6] and it can effectively exploit multi-user diversity in combination with transmit beamforming to attain the coherent beamforming capacity and only requires the feedback of signal to noise ratio (SNR) (no spatial information is required). By combining the opportunistic beamforming concept and SVD technique, [7] and [8] extend this theory to a single carrier MIMO system and develop the Random Beamforming (RB) and Layered Random Beamforming (LRB) techniques respectively. RB is ca...