Abstract:

In medium access control (MAC) method design,the effective management of co-channel interference (CCI) among multiple concurrent transmissions is critical to enhancing a system’s spectrum efficiency (SE).The main idea of existing interference management (IM) methods is to make multiple signals orthogonal to each other during their transmissions.However,in the multi-user multiple input multiple output (MU-MIMO) system,the numbers of transmitters and receivers and their antenna settings highly restrict the number of orthogonal concurrent data transmissions that the system can support.To remedy such deficiency,this paper proposes a relaxed orthogonal precoder based multiple access (ROPMA) method for MU-MIMO downlink transmission.By introducing an orthogonal amplitude tuning function to adjust the precoder’s amplitude in a symbol duration,and then using the adjusted precoder for signal processing and transmission,the requirement of strict orthogonality of multi-user signals in the spatial domain can be relaxed to the orthogonality in the sense of correlation.Accordingly,the receiver employs correlation based desired signal detection;by exploiting the orthogonality of amplitude tuning functions,the influence of the CCI can be eliminated at the decision time.Our simulation results have shown that the proposed method can significantly increase the number of users that the system can accommodate and improve the system’s SE without consuming the extra spectrum resource.

Key words: multiple access, co-channel interference, interference management, precoding, orthogonal function