Performance Issues With IEEE802.11 in Ad Hoc Networking. 汇报人：曾苗祥. 作者： Claude Chaudet. introduction. Background :
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DIFS(Distributed interframe space):the aim is to insure that the channel is idle.
The author classified the presented performance into 3 categories:
The 802.11 DCF mechanisms that prevent an emitter from accessing the radio medium in normal conditions can be classified in three categories:
A and E are totally independent.
This can be happen when flows are emitted at a low throughput or there is a obstacles block the line of sight between A and E.
Result: the pair (C ,D)expect no more than 15% of the medium capicity.While the (A,B)and (E,F) share the others.
Throughput for the three pair configuration with different packet size
A and C are independent but both communicate with B
This can be happen either when flows are emitted at a low
throughput and emitters are distant enough or if obstacles
block the line of sight between A and C.
Result: the throughput of each emitter increases with the packet size, but the ratio between the two emitters’s throughout remains the same: B sends around seven times more packets than A.
Large EIFS problem
The RTS-CTS exchange can solve hidden node situation and result in fair medium access in the long term , but the behavior of the medium access is unfair in the short term
This can be happen either when flows are emitted at a low throughput and emitters are distant enough , or if obstacles block the line of sight between the emitters.
Hidden node scenario
The overall used bandwidth decreases with low-speed communication links or high-speed communication links with obstacles making A and D independent.
Small EIFS problem
This configuration happens as soon as two mobiles not in communication range wish to communicate and routing is involved
: different chain length
Throughput for chain configuration
: six hops,with and without RTS/CTS