-49-scattering can cause rapid changes in received power levels over small distances. This is because the power level is the sum from signals coming from a number of different paths and the phases of those paths are random, sometimes adding and sometimes subtracting. As the mobile unit moves, the contributions along various paths change. 10.7 Open-loop power control depends solely on the mobile unit, with no feedback from the BS, and is used in some SS systems. Closed loop power control adjusts signal strength in the reverse (mobile to BS) channel based on some metric of performance in that reverse channel, such as received signal power level, received signal-to-noise ratio, or received bit error rate. 10.8 The mean rate of calls is the number of calls attempted in a unit time, so its dimensions are calls per second or a similar dimension. Traffic intensity is a normalized version of mean rate of calls, and equals the average number of calls arriving during the average holding period. Thus, traffic intensity is
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