Wireless Ad Hoc and Sensor Networks

Distributed Fair Scheduling in Wireless Ad Hoc and Sensor Networks 335TABLE 7.1G4-SSN CapabilitiesIc @ 3.3V[mA]FlashMemory[bytes]RAM[bytes]ADC SamplingRate [kHz] Form-Factor MIPSG4-SSN 35 128k 8448 100 @ 10/12-bit 100-pin LQFP 100The former include strain gauges, accelerometers, thermocouples, andgeneral A/D sensing. The latter include analog filtering, compact flash (CF)memory interfacing, and 8-bit data processing at a maximum of 100 MIPS.7.5.3 G4-SSN CapabilitiesThe abilities of the UMR and SLU motes nodes are shown in Table 7.1.As seen in the table, the G4-SSN provides powerful 8-bit processing, asuitable amount of RAM, and a low-power small form-factor. Anotherstrong point of the G4-SSN is the available code space found on the SiliconLaboratories C8051F12x variant.ADFS requires that the sensor nodes are synchronized. For this reason,a test was performed on the G4-SSN real-time clock (RTC) capabilities.Experimentation consisted of a statistical analysis of the RTC accuracy.Extended use of the RTC without resynchronization can cause drift tooccur, and this drift must be quantified to provide a confidence measureof the RTC. A 32.768-kHz quartz crystal is used to feed a timer on the8051 and is used at the time-base of the RTC. The RTC was allowed torun for 10 min, and the results are tabulated in Table 7.2.As seen in Table 7.2, the RTC has a drift error of around a ∫ sec over 10min; this translates to 3.5 sec/h. In the context of this application, this driftis acceptable as the RTC will be synchronized with the BS every 30 sec.7.5.4 Hardware ResultsIn this section, hardware implementation results are shown. Using the802.15.4 standard with 250kbps RF data bandwidth, the scheduling algorithmTABLE 7.2G4-SSN RTC Drift Testing ResultsTest Time[min]t[sec]Variance[µ-sec]Mean[sec]STD[sec]Error[sec]10 0.05 50.45 0.0504 0.007 0.515