Effect of opportunistic scheduling on the quality of service perceived by the users in OFDMA cellular networks

Our objective is to analyze the impact of fading and opportunistic scheduling on the quality of service perceived by the users in an orthogonal frequency-division multiple access cellular network. To this end, assuming Markovian arrivals and departures of customers that transmit some given data volumes, as well as some temporal channel variability (fading), we study the mean throughput that the network offers to users in the long run of the system. Explicit formulas are obtained in the case of allocation policies, which may or may not take advantage of the fading, called respectively opportunistic and non-opportunistic. The main practical results of the present work are the following: Firstly, we evaluate for the non-opportunistic allocation the degradation due to fading compared to additive white Gaussian noise (AWGN; that is, a decrease of at least 13% of the throughput). Secondly, we evaluate the gain induced by the opportunistic allocation. In particular, when the traffic demand per cell exceeds some value (about 2 Mbits/s in our numerical example), the gain induced by opportunism compensates the degradation induced by fading compared to AWGN.