Opportunistic Auto Rate (OAR) is an opportunistic media access protocol for multi-rate IEEE 802.11. With OAR, nodes with good channel conditions are granted access to the channel for a duration that allows multiple packet transmissions vs. a single packet when the nodes access the channel at the base rate. Consequently, by exploiting inherent variations in channel conditions, nodes will transmit more data during epochs of high-quality channels thereby increasing the total throughput of all users. Moreover, OAR ensures that all nodes, regardless of their channel condition, access the channel for a time-share equal to that achieved with single-rate IEEE 802.11.
Although OAR does not depend on the underlying
multi-rate protocol, the NS implementation of OAR provided here
utilizes RBAR as a starting point. The NS extensions include RNG
implementation of RBAR and OAR for ns-2.1b7.
The implementation of Ricean Fading Model is based on CMU additions to NS to handle Ricean and Rayleigh fading(under Downloads). Although the CMU implementation results in an accurate simulation of the wireless channel for each individual flow, the fading components of channels for different flows are identical, a scenario not encountered in practice. This arises due to the fact that the index into the pre-computed channel table (used to look-up the components of fading envelope) is chosen based on the simulator's time instant, which is identical for all flows. To more realistically model the wireless channel for multiple users we modified the implementation such that channel lookup indexes are a function of the flow and time.
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