+ 0.2x receive X 0.2x sleep Watts 0.6 x2 + 0.2x 0.8 + 0.2x 0.9 X 0.2 X 0.04 Total 1.54 watts Table 3.21 Sensitivity gains Received signal level dBm Industry norm 11 Mbps 5.5 Mbps 2 Mbps 1 Mbps Data rate achieved Atheros 6 Mbps 1 Mbps 250 kbps 5 Atheros is now owned by Qualcomm. Interrelationship of the Physical Layer with Other Layers of the OSI Model Table 3.22 Path loss and distance Path loss -88 and -89 dBm the packet error rate triggers a change of modulation scheme which reduces the throughput from 5.5 to 2 Mbps. As with LTE, an increase in sensitivity in the user device will delay the point at which additional error coding and/or a lower-order modulation is needed. But one of the areas of particular interest for cellular operators is how LTE compares with WiFi both in terms of peak data rate and the throughput power budget for local connectivity (a few metres from the base station). On a like for like basis assuming similar TX power levels in a similar channel (20 MHz at 2.4 GHz or 20 MHz at 2.6 GHz) and a similar distance from the base station then the peak data rate and average data throughputs should be similar. LTE replaces the OFDM used on the WiFi link with an OFDM-related modulation and multiplexing scheme described as single carrier frequency division multiple access (SC- FDMA). This reduces the envelope variation on the modulated waveform that at least in theory should allow the TX path to be marginally more efficient. However, it can be said that this 'improvement' is only from an onerous 12 dB or 16x to an only slightly less onerous 10 dB or 10x. The relative performance will also depend on whether LTE is used in TDD or FDD mode and what band is used for local connectivity, but the assumption would be 2.6 GHz versus 2.4 GHz or 5 GHz for the WiFi connection. An alternative is to use LTE TDD devices that have been developed for the China market. However, if operators are aspiring to use LTE as an alternative to WiFi for example in femtocells then any noticeable performance advantage will probably n