Dynamic Rate Switching; Media Access - Black Box LW0050A Manual

PRO 11 SERIES WIRELESS ETHERNET
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Common Coverage Area
Figure C-4. The Common Coverage Area of a Multi-cell Structure.
C.4 Dynamic Rate Switching
The data rate of each station is automatically adjusted according to the received
signal quality. Performance (throughput) is maximized by increasing the data rate
and decreasing re-transmissions. This is very important for mobile applications
where the signal quality fluctuates rapidly, but less important for fixed outdoor
installations where signal quality is stable.
C.5 Media Access
When many users are located in the same area, performance becomes an issue. To
address this issue, wireless LANs use the Carrier Sense Multiple Access (CSMA)
algorithm with a Collision Avoidance (CA) mechanism in which each unit senses
the medium before it starts to transmit.
If the medium is free for several microseconds, the unit can transmit for a limited
time. If the medium is busy, the unit will back off for a random time before it
senses again. Since transmitting units compete for air time, the protocol should
ensure equal fairness between the stations.
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