Overhearing packet transmissions to reduce preamble overhead and improve throughput in IEEE 802.11 networks

While there has been a significant increase in the data rate carrying capacity of the physical medium of Wi-Fi in recent years, there has not been a proportionate increase in the application layer throughput. The primary cause for this are overheads such as those of the preamble, acknowledgement, and channel access present in the packet data communication. This paper is a proof of concept for a novel method to increase the data throughput by cutting down preamble overheads. The preamble is present in the beginning of the packet for the purposes of packet detection, automatic gain control, channel estimation and phase error correction. In 802.11, a receiver estimates the channel response afresh for every received packet using its preamble and forgets this channel estimate thereafter. This necessitates the need for a large preamble to be sent with every packet. In our method, a node remembers channel estimates from preambles of packets transmitted (to itself or to any other node) in the recent past (within a coherence time), which it reuses for future received packets. This allows transmitters to reduce the size of the preambles of some packets significantly, thereby improving throughput. We validate our method through detailed physical layer simulations of 802.11n in matlab and show that we can shorten the preamble by as much as 16's for 2×2 MIMO which would bring down the preamble overhead by as much as 50%.