A simple transmission scheme to cancel co-channel interference within a cell in IEEE 802.16j relay networks

In IEEE 802.16j-based relay networks, frequency reuse by RS(Relay Station)s and BS(Base Station) is considered as a way to improve the frequency utilization. However, since the same frequency band is used by RSs and BS, MS located in the middle between neighboring transmitting stations suffer severe interference or even outage. This co-channel interference within a cell is a major bottleneck in providing uniform QoS(Quality of Service) to all the MSs regardless of their locations. We propose a simple and effective solution to this problem. When two or three transmitting stations interfere with each other at the receiving MSs considerable (beyond given thresholds), we require the transmitting stations to transmit the signals again (shifted by 180 for the two stations or shifted by 120 and 240 degrees for the three stations). The receiving MSs combine these retransmitted signals with original signals to cancel the co-channel interference. Transmitting the same signals two of three times incurs overhead in terms of resources. However, we derive thresholds which determine whether our scheme is beneficial or not to individual MSs. Since our scheme is used only for the chosen MSs, it improves known schemes with frequency reuse in terms of throughput and fairness. Our scheme excels the known schemes (orthogonal allocation and the overlapped allocation) by 113% and 34.1, respectively, in terms of throughput. Fairness is also improved by 60.5% against the overlapped allocation scheme.