Short-range wireless applications and technologies CHAPTER 5.2 d2 as a function of d1 is found as follows, using power Power control in dBm: Limiting transmitter power to the maximum required 1. PRWF = PWF - 10log(Kdl'); for a satisfactory level of performance will reduce inter- ference to collocated networks. Power control is man- PRBT = PBT - 10log(Kd2') datory for Class 1 Bluetooth systems, where maximum power is 100 mW. The effect of the power on the in- 2. = PRWF - PRBT = terference radius is evident in equation (5.2.1). For ex- PBT + 10log(Kd2') ample, in a Bluetooth piconet established between devices located over a spread of distances from the 3. (CIcc - PWF+PBT)/10r=log(d2/d1) master, the master will use only the power level needed to communicate with each of the slaves in the network. 4. d2 : d1 10(Clcc-Pwy+Psy)/(10-r) Lack of power control would mean that all devices would (5.2.1) communicate at maximum power and the collocated Wi-Fi system would be exposed to a high rate of inter- As an example, the interfering area radius d2 is now fering Bluetooth packets. calculated from equation (5.2.1) using the following system parameters: CIcc = 10 dB, PWF = 13 dBm, PBT = 0 dBm, Adaptive frequency hopping r = 2 (free space) Wi-Fi and Bluetooth share approximately 25 percent Solving equation (5.2.1): d1 X .71 of the total Bluetooth hop-span of 80 MHz. Probably the most effective way to avoid interference between the In this case, if a Wi-Fiterminal is located 15 meters from two systems is to restrict Bluetooth hopping to the an access point, for example, all active Bluetooth devices frequency range not used by Wi-Fi. When there is no within a distance of 10.6 meters from it have the potential coordination or cooperation between collocated net- of interfering. Only co-channel interference is considered. works, the Bluetooth piconet master would have to sense Adjacent channel interference, if significant, would in- the presence of Wi-Fi transmissions and modify the fre- crease packet error probability because many