Hz) Chip rate (kcps) Modulation Bit rate (kbps) Symbol rate (ksps) Symbols 868/915 868-868.6 Binary 902-928 Binary 2400-2483.5 Offset-QPSK 16-ary orthogonal CHAPTER 5.2 Short-range wireless applications and technologies (offset quadrature phase shift keying) with half-sine wave pulse shaping is essentially equivalent to a form of frequency shift keying, MSK (minimum shift keying). It is fairly easy to generate and has a relatively narrow bandwidth for the given chip rate. This latter feature allows a large number of nonoverlapping channels that can be used, with proper upper layer software, on the crowded 2.4 GHz band to avoid interference. Figure 5.2-23 Cluster-tree topology. Other physical layer characteristics of Zigbee are output power and receiver sensitivity. The devices must be capable of radiating at least -3 dBm although output coordinator, in addition to any specific application it may may be reduced to the minimum necessary in order to have, is to initiate, terminate, or route communication limit interference to other users. Maximum power is around the network. It also provides synchronization determined by the regulatory authorities. While much services. In a star network, each device communicates higher powers are allowed, it may not be practical to directly with the coordinator. The coordinator must be transmit over, say 10 dBm, because of absolute limits on a FFD, and the others can be FFDs or RFDs. Relatively spurious radiation and the general objective of low-cost simple applications, like PC peripherals and toys, would and low-power consumption. Minimum receiver sensi- typically use the star topology. tivity for the 868/915 MHz physical layer is specified as In the peer-to-peer topology, any device can commu- -92 dBm and -85 dBm on 2.4 GHz. These limits are for nicate with any other device as long as it is in range. RFDs a packet error rate of one percent. cannot participate, since an RFD can only communicate with a FFD. More complicated structures can be set up Device types and topologies as a 