Joint Flock based Quantization and Antenna Combining Approach for MCCDMA Systems with Limited Feedback

The multi-carrier code division multiple access (MCCDMA) is a strong candidate to facilitate multi-user (MU) multi input multi output (MIMO) communication for the current and next generation wireless mobile system. An orthogonal frequency division multiplexing (OFDM) based MCCDMA system with limited feedback channel is considered for reducing channel state information (CSI) feedback load. The residual multi user interference (MUI) inevitably comes with multiuser signals on each subcarrier of OFDM due to limited feedback and increases as large number of users is simultaneously active since it is related to the number of subcarriers and multiple antenna. The efficient quantization of CSI is the vital solution in order to break the interference limitation to increase the user capacity of MCCDMA system. The joint flock based quantization and antenna combining approach is proposed to make quantization on flock basis which exploits flock of correlated subcarriers and stick together with combining process of multiple antenna signals for reducing the CSI feedback bits with minimum quantization error. For this, the minimum angular distance criterion is developed based on upper bounded throughput loss to find the reliable representative quantization vector for the flock which is feedback to the transmitter with minimum bits and enable the efficient antenna combining jointly to yield the unique effective channel for multiple antennas at the receiver. The simulation result shows that the proposed scheme achieves significant performance improvement in terms of quantization error and throughout compared to conventional schemes with the reduced feedback load and similar order of complexity (O (N)). The result also shows that it can support more number of users due to increased MUI mitigation efficiency.