Download or read book Collision Recovery Techniques for Wireless LANS written by Samuel Michael Keene and published by . This book was released on 2009 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: The fields of networks and wireless communications are merging, giving birth to the field of wireless networks. Each of these fields brings with them their own assumptions. The field of networks assumes that a collision equals total packet loss. The field of wireless communications assumes that all interference is stationary. In wireless networks, both of these assumptions are false, yet they remain in most protocol designs. We challenge both of these assumptions, and investigate how the physical layer can cooperate with higher layers to resolve the problem of collisions in a new way. We first investigate fundamentally what happens when a collision occurs. We discover that, for the majority of cases, only a small number of bits are corrupted. This invalidates the 'collision equals total packet loss' assumption made by upper layer protocols. Furthermore, due to their bursty nature, we see that collisions introduce non-stationary impairments at the physical layer. To resolve these problems, we begin by deriving a physical layer algorithm that can identify which bits have been corrupted by collision. This algorithm accurately locates all collision induced errors when the channel signal to noise ratio is high enough for reliable communication. By leveraging this algorithm, we can produce a wide range of benefits for all layers of the protocol stack. For example, at the data link layer, by providing collision location information, we can enhance forward error correcting codes so that they may effectively completely remove the collision, saving a packet that would otherwise be discarded. We will show that a large percentage of packets that would ordinarily be discarded are in fact recoverable by applying this technique. At the medium access layer, we may use the collision location to improve performance of ARQ protocols and also to improve signal to noise ratio estimation. Finally, we may provide accurate feedback to the transport layer, informing it about the cause of packet failure, so that the transmission rate can be adjusted appropriately.