Cross-layer adaptive design for the frame length of IEEE 802.11 networks

In this paper, we study the cross-layer (between MAC and PHY) design problem for IEEE 802.11 wireless networks. It is focused on the design of the optimal length of the frame body. The following results are obtained: 1) The optimal length of the frame body in logarithmic scale, expressed as log L_f,opt, can be coarsely approximated by a linear function of the signal-to-noise power ratio (SNR) E_b/N₀ (in dB) and finely approximated by a second-order polynomial of E_b/N₀; 2) The coefficients of the aforementioned approximation functions depend only on the data transmission rate and other parameters specified in the protocol, and they do not depend on the access mechanisms; 3) The number of active nodes has little effect on L_f,opt, especially in the range of both low and high SNR; 4) The system throughput is sensitive to the length of the frame body L_f when the SNR is low, while it is insensitive to L_f in a considerably large neighborhood of L_f,opt when the SNR is high; and 5) Fragmentation can always increase the system throughput, but the increasing rate is conspicuous only in the low SNR regime.