d time coincidence of control applications, it will not fit all of them, and will not the transmission of one system and reception of the necessarily take advantage of all the possibilities of the other, it's possible for an error to occur. Whether it does unlicensed device regulations. Its declared maximum or not depends on the relative signal strengths of the range of some 50 to 75 meters will fall short of the re- desired and undesired signals. These in turn depend on quirements of many systems. Given the meager maxi- the radiated power outputs of the transmitters and the mum power allowed, greater range means reduced distance between them and the receiver. When two bandwidth and reduced data rate. In fact, a great many of terminals are very close (on the order of centimeters), the applications envisaged by Zigbee can get by very well interference may occur even when the transmitting fre- with data rates of hundreds or a few thousand bits per quency is outside the bandwidth of the affected receiver. second, and by matching receiver sensitivity to these Bluetooth and Wi-Fi systems are not synchronous and rates, ranges of hundreds of meters can be achieved. interference between them has to be quantified statisti- One partial answer to the range question is the de- cally. We talk about the probability of a packet error of ployment of the Zigbee network in a cluster-tree con- one system caused by the other system. The consequence figuration, as previously described. Adjacent nodes serve of a packet error is that the packet will have to be as repeaters SO that large areas can be covered, as long as retransmitted once or more until it is correctly received, CHAPTER 5.2 Short-range wireless applications and technologies BLUETOOTH PICONET WI-FI WI-FI TIME -- ms BLUETOOTH Figure 5.2-26 Importance of relative terminal location. Figure 5.2-25 Wi-Fi and Bluetooth spectrum occupation. than Bluetooth, typically 20 mW compared to 1 mW. which causes a delay in message throughput. Voice Bluetooth Class 1 systems may transmit u