Throughput of Wlan with TDMA and Superimposed Transmission with Resource and Traffic Constraints

For a specific high-throughput wireless local area network system based on OFDM we study the sum rate of multiple access with time multiplexing or superimposed transmission (TDMA, SUP). In allocating resources we consider a minimum granularity, i.e., size of the smallest unit that a user can be allotted. We further assume packet switched traffic with most traffic carried by only a few large packets and relatively little data carried by a large number of small packets. We show and quantify that given the granularity and traffic constraints the sum rate may be drastically reduced compared to the unconstrained case. This happens whenever mapping (small) packets to resource units (OFDM symbols) incurs matching losses. As these losses are highest in TDMA, it suffers most. Moreover, we show that allowing more users to be active helps to maintain a high throughput in SUP only. Our analysis and results apply to scenarios with the described features where the transmitters know the average channel statistics, the receiver has perfect channel state information and the total received power is the same in all schemes