how power consumption is distributed in a lap top between the computer functions and WiFi connectivity functions, in this case, 802.11g. Table 3.18 Power-consumption comparisons Lap Top WLAN Card WLAN Host Total Making Telecoms Work Table 3.19 RF power budget 2 watts 0.9 watts Listen 0.8 watts Sleep 40 milliwatts Note this includes the RF power budget and directly related IP uplink and downlink packet processing overheads. Table 3.19 shows the RF power budget. The RF power consumed including TX and RX efficiency loss is a function of the duty cycle An example is given in Table 3.20 with a duty cycle that yields an average power consump- tion of 1.54 watts. It might be considered that 1.54 watts is inconsequential, but in practice there is a further 2.85 watts of associated CPU power totalling 4.389 watts. 4 watts represents a 20 to 30% reduction in battery duty cycle, four hours is reduced to three hours. Note that the typical peak power requirement is 20 watts for a lap top, 10 to 15 watts for larger than smart-phone device, 5 to 10 watts for a smart phone and sub-5 watts for a basic phone. The RF power budget (including related processor overheads) of a smart phone is likely to be higher than 30% due to the additional signalling load incurred by mobile applications. Table 3.21 shows typical WiFi throughput against received signal level. The table shows an Atheros5 implementation where higher throughputs have been achieved at these levels, the difference being the improved sensitivity in the Atheros front end. Table 3.22 shows the relationship between the link budget and the path loss which will determine the coverage radius from the base station. There are several points to make here. Theoretically, in a noise-limited channel a 3-dB increase in power or the equivalent increase in sensitivity translates into the error rate drop- ping a thousand fold. However, as can be seen in the industry standard example, between Table 3.20 Assumed uplink duty cycles TCP Uplink power consumption Duty cycle 0.6x TX + 2x listen 