i is not particularly spectrally efficient. The additional linearity needed also means it is not particularly power efficient when compared to legacy cellular or Bluetooth systems. 3.6.6 WiFi's Spectral-Efficiency and Power-Efficiency Limitations So the WiFi PHY is arguably less spectrally efficient and less power efficient than cellular and probably less spectrally efficient and certainly less power efficient than Bluetooth. The WiFi contention optimised MAC when used for connection orientated time-bounded traffic is arguably less efficient than existing connection optimised MACS used in cellular and Bluetooth voice applications. 3.6.7 Why WiFi for IP Voice and Video? IP voice, IP video and IP voice and video are all potentially supportable on WiFi radio systems but require careful implementation in terms of PHY management (channel reuse) and MAC management (the cosharing of common bandwidth between time-bounded voice and best-effort data). Interrelationship of the Physical Layer with Other Layers of the OSI Model Whether WiFi is efficient or not when compared to other options is to an extent irrelevant if costs are sufficiently low to drive adoption though an inefficient PHY and MAC will always have a cost in terms of additional battery drain. The addition of OFDM increases processing overhead in the receive chain (the cost of the receiver FFT) and processing overhead in the TX chain (the inverse FFT). The additional linearity implied by the envelope of the composite waveform also reduces TX power efficiency when compared to other radio systems. However, OFDM is really the only way to realise data rates in the region of tens of Mbps (direct sequence spread spectrum starts to run into jitter problems at these higher speeds and you need the OFDM multiplex to slow the symbol rate down in order to control ISI and increase multipath resilience). In the longer term, WiFi with MIMO (multiple input multiple output) is one way of getting speeds of the order of 100 Mbps or more (the other way is to deploy in the 60-GHz b