A Low-Complexity CDD-Based Frequency Selective Scheduling with Efficient Feedback for Downlink OFDMA Systems

Cyclic-delay diversity (CDD) based frequency-selective scheduling is an effective technique to increase system capacity with low complexity. By increasing the channels´ frequency selectivity with cyclic delays, the merit of multi-user diversity can be exploited more effectively in the system. This paper aims to optimize the design of the CDD-aided frequency-selective scheduling for downlink OFDMA systems. First, a low-complexity search of CD-values is proposed that results in a higher system capacity than the existing methods. Second, a new feedback method is proposed based on the principle of proportional-fair, where users who currently enjoy more downlink source are allotted less uplink resource for feedback. The method is shown to provide a better tradeoff between system capacity and fairness than the traditional methods, under a fixed feedback overhead. The effectiveness of the proposed method is verified by extensive computer simulations.