Wireless Ad Hoc and Sensor Networks

286 Wireless Ad Hoc and Sensor NetworksTABLE 6.4G4-SSN CapabilitiesI c @ 3.3 V[mA]Flash Memory[bytes]RAM[bytes]ADC SamplingRate [kHz] Form-Factor MIPSG4-SSN 35 128k 8448 100 @ 10/12-bit 100-pin LQFP 1006.11.1.3 ADF7020 ISM Band TransceiverADF7020 ISM band transceiver is used as the physical layer for the implementationof the DAPC protocol. The major advantage given by theADF7020 is the freedom in controlling various physical layer properties,including operating frequency, output power, data rate, and modulationscheme. These features are essential in evaluating new wireless protocols,which require physical level access (Table 6.5). In the implementation ofDAPC, direct access RSSI reading and output power are used. In addition,the low power consumption of this transceiver is suitable for embeddedsensor network applications.6.11.1.4 LimitationsHardware implementation of any algorithm is constrained by the limitationsof the hardware. With a single-chip software layered architecture, the microprocessormust simultaneously handle data communication with radio transceivers,internal processing, and applications. Therefore, the 8-bit processingpower limits the data rate at which the radio transceivers can operate. Currently,a maximum data rate of 48 kbps has been successfully tested. Quantizationis another issue faced in hardware and cannot be avoided.Quantization means that the hardware does not provide enough precision asdesired by the algorithm, such as in calculation, A/D or digital-to-analogconverter. In the implementation of the DAPC, the signal strength reading isonly accurate up to 0.5 dB and power control is limited to 0.3-mW steps.These limitations must be treated to reduce the effects on the algorithm.TABLE 6.5AD7020 CapabilitiesFeatureFrequency bandsData ratesOutput powerRSSIModulationPower consumptionCapabilities431 MHz ~ 478 MHz and 862 MHz ~ 956 MHz0.15 kbps to 200 kbps16–+13 dBm in 0.3 dBm steps6-bit digital readbackFSK, ASK, GFSK19 mA in receive, 28 mA in transmit (10 dBm)