llular transceiver with a WiFi (802.11 a and g) transceiver in terms of peak to average ratio (PAR), peak to mean ratio, whether the radio channels are full or half-duplex and the power-control dynamic range. The use of OFDM in 802.11 a and g delivers some significant benefits in terms of channel resilience and ISI performance (a constant and relatively low symbol rate) but the cost is a substantial envelope variation on the composite modulated waveform (although the example Table 3.16 Typical 802.11 a and g and b receive sensitivity Data rate 54 Mbps (a and g) 11 Mbps (b) 5.5 Mbps (b) 2 Mbps (b) 1 Mbps (b) Typical sensitivity (dBm) -75 dBm -85 dBm -88 dBm - -89 dBm -92 dBm Claimed max sensitivity - -101 dBm Making Telecoms Work Table 3.17 Linearity comparisons between cellular and WiFi (OFDM) Generation System PAR (dB) PMR (dB) Duplex Power control (dB) 25 dB ETACS 25 dB J TACS 25 dB 30 dB 30 dB US TDMA 30 dB Half/Full 35 dB 80 dB 80 dB (Re199) 17 dB >20 dB 30 dB of 20 dB peak to mean is a worst-case condition with all 52 subcarriers lining up over a symbol period). This requires additional linearity from the PA, which is difficult to realise in a power-efficient manner. In contrast, Bluetooth 2.0 EDR (which uses GFSK, four-phase DQPSK or optionally eight- phase DPSK) is arguably more power efficient. GSM, PDC, TDMA and EDGE are described as half-duplex in that they don't transmit and receive at the same time (except theoretically for EDGE Class 13 through 18) but they still have an RF duplex separation between transmit and receive that translates directly into an improved sensitivity figure. WiFi is half-duplex in that it uses the same RF channel that is time division duplexed to separate the uplink and downlink. This means the sensitivity will always be less than a full duplexed cellular system using separate RF channels for the uplink and downlink. This matters because sensitivity is part of the link budget and the link budget determines coverage (range) and capacity. On this basis it could be argued that WiF