 milliwatts 30 milliwatts 20 milliwatts 5 milliwatts 1 milliwatt 100 microwatts easier to do measurement reporting with WiFi than it is with cellular (which uses a different radio channel on the uplink and downlink each with different propagation properties). However, it is all very well collecting this information but then you have to decide what to do with it. There has not been much point up to now in doing power control with best-effort data. If the RX level is good then you just send the data faster using higher-order modulation and/or with reduced channel coding. Voice, video and/or voice and video combined are, however, different in that they occupy periodic bandwidth with typically a longer (more persistent) session length. If the user is close to the base station then it is worth reducing power to a level at which packet error rates can be kept above the coding threshold of the channel encoder and the error threshold of the source decoder. Reducing the TX power helps reduce battery drain on the uplink but also tends to improve receive sensitivity SO the downlink usually benefits as well but care needs to be taken to make sure the power control doesn't take up more bandwidth and/or power than it saves. The range of RSSI measurement in a 802.11 transceiver is typically 60 dB. The range of power control is typically either 20 or 30 dBm as shown in Table 3.14. This is less than you find in a wide-area radio interface (35 dB for EDGE, 80 dB for 1XEV or Rel 99 UMTS) but still potentially useful. The usefulness depends (as with handover algorithms) on how mobile the user is likely to be. Table 3.15 is taken from a University research project on mobility thresholds. 4 It assumes two users a certain distance apart with one of the users walking away from the other user at 1.5 m (metres) per second. The closer the distance between the two transceivers the faster the rate of change in terms of required output power. For example, at a distance of 9 m, walking 2 m away (just over a second of elapsed time) results in a