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ENHANCED IEEE 802.11 MAC PROTOCOL FOR AD HOC NETWORKS
ALCATEL


In contrast to pure ad hoc networks, we are focusing more on networks where a bunch of access points (AP) is connected to the access server (AS), which in turn is connected to the Internet. Wireless terminals (WT) in the coverage of this APs can connect directly to it and therefore to the Internet. Other WTs which are not within the coverage of the access point have to use the multi\u2013hop capability of other WTs or VAPs to reach the wired access point. We favor this network scenario in contrast to pure ad hoc networks, because it allows a larger variety of services (all provided by the Internet). A pure ad hoc network is always characterized by a limited set of services. Therefore, we think that the focused scenario described before has more relevance for a sophisticated business model. The question arises how a multi\u2013hop network can be realized. Multi\u2013hop networks based on IEEE802.11 do not perform well because of the RTS/CTS scheme used. All Papers known to the authors focus on transmission on one channel, i.e., one collision domain, and lead to poor system performance. The upcoming IEEE802.11a offers higher data rates than IEEE802.11b, but this will not increase the multi\u2013hop performance significantly since the problem lies in the MAC design. IEEE802.11a allows the use of multiple orthogonal channels. On each channel a maximum of eight different data rates (6,9,12,18,24,36,48, and 54 Mbit/s) are available using different modulation and coding schemes. The problem to be solved in this scenario is still the management of the channels used. We advocate the use of a common signaling channel for the task of assigning channels among WTs.

Our approach separates the RTS/CTS signaling from the data exchange including the acknowledgment packet. By means of this separation all wireless nodes are forced to listen to one domain, on which the channel assignment process takes place. After a four way RTS/CTS handshake, the data transmission occurs on a dedicated channel. Due to this new scheme, collisions are reduced. The common signaling channels helps also find the appropriate node for routing
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