Adaptive Design for the Packet Length of IEEE 802.11n Networks

In this paper, we investigate how various kinds of design parameters in IEEE 802.11n wireless networks affect the system throughput. It is focused on the design of the optimal packet length from the viewpoint of cross-layer interaction between the MAC and PHY. The following results are obtained: I) The optimal packet length in logarithmic scale, expressed as log Lp,opt , can be finely approximated by a second-order polynomial of the signal-to-noise ratio (SNR); 2) The coefficients of the aforementioned approximation function depend on the data transmission rate and other parameters specified in the protocol, but it does not depend on the type of the MAC access mechanisms; 3) The number of active nodes has little effect on Lp,opt, especially when the SNR is low; 4) The system throughput is sensitive to the packet length Lp when the SNR is low, while it is insensitive to Lp in a considerably large neighborhood of Lp,opt when the SNR is high; and 5) Aggregation can always increase the system throughput. Particularly, when the SNR is low, the increasing rate of the system throughput with the number of subframes is remarkably high. Therefore, in the low SNR regime, making the packet length adaptive to the channel SNR and increasing the number of subframes are essential to improve the system performance.

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