Channel Setup
Access point coverage and comparison

Figure illustrates that, as a client roams away from the access point, the transmission signals between the two attenuate (weaken). Rather than decreasing reliability, the AP shifts to a slower data rate, which gives more accurate data transfer. This is called data rate or multi-rate shifting. As a client moves away from an 802.11b access point, the data rate will go from 11 Mbps, to 5.5Mbps, to 2 Mbps, and, finally, to 1 Mbps. This happens without losing the connection, and without any interaction from the user. The same thing occurs with 802.11a. However, as Figure shows, the data rates step down from 54 Mbps. Figure also shows the approximate distances from the AP, for each data rate.

The Cisco Aironet 2.4 GHz radio delivers 100 mW of output and offers a high degree of receiver sensitivity. The 5 GHz client radio has a 20 mW transmit power and the 5 GHz access point has a 40 mW transmit power. It is possible to adjust the power level down, to create pico-cells, or smaller coverage cells. This would be done, for example, to prevent the coverage area of one AP from extending too far into the coverage area of another AP.


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