Sum Rate Analysis of a Reduced Feedback OFDMA Downlink System Employing Joint Scheduling and Diversity

We consider joint scheduling and diversity to enhance the benefits of multiuser diversity in an orthogonal frequency-division multiple access (OFDMA) downlink system. The OFDMA spectrum is assumed to consist of N_RB resource blocks and the reduced feedback scheme consists of each user feeding back channel quality information (CQI) for only the best-N_FB resource blocks. Assuming largest normalized CQI scheduling and a general value for N_FB, we develop a unified framework to analyze the sum rate of the system for both the quantized and nonquantized CQI feed- back schemes. Based on this framework, we provide closed-form expressions for the sum rate for three different multiantenna transmitter schemes; transmit antenna selection (TAS), orthogonal space time block codes (OSTBC) and cyclic delay diversity (CDD). Furthermore, we approximate the sum rate expression and determine the feedback ratio (N_FB/N_RB) required to achieve a sum rate comparable to the sum rate obtained by a full feedback scheme.