 would further reduce session duty cycles by increasing DC power drain. This would effectively invalidate any business plans predicated on the use of mobile or portable equipment. 15.14 Uneconomic Network Density as a Function of Transceiver TX and RX Inefficiency Unless white-space devices somehow escape the fundamental laws of physics, it will be hard to realise transmission or receive efficiency across the required operational bandwidth. The lack of consistent channel pairing would make an FDD band plan problematic, SO the assumption has to be that this would be a TDD interface. This will result in additional loss of receive sensitivity particularly when devices need to transmit and receive at the same time. This will compromise the measurement capabilities of the devices (see spectrum sensing above) but additionally implies a network density that would be unlikely to be cost economic. Mesh networks are not a solution. (See the section on signalling efficiency above.) TDD also implies a loss of capacity over extended distances, a function of the time-domain guard band overhead needed to accommodate round-trip delay. This implies a relatively dense network topology. Note that TV receivers are inherently insensitive due to their need to tune over an extended frequency range. This does not matter if signals are being received through a high-gain roof- mounted antenna but it does matter for devices with internal antennas and/or for devices used at ground level. White-space devices will be used typically at ground level and may or may not have internal antennas. They will need to tune across similar bandwidths but additionally have to generate transmit power for the uplink, not something a television has to do. This will result in further receive desensitisation that will translate into lower downlink data rates and/or denser more costly networks. 15.15 Cognitive Radios Already Exist - Why Not Extend Them into White-Space Spectrum? Cognitive radios already exist in mass market applications. DECT cordless phones are