While the transition to digital television is currently happening in most countries around the world, there has been increasing interest recently in enhancing the spectrum usage efficiency especially in TV bands via cognitive radio based access where the bandwidth is reused on a non-interfering basis. The wideband and weak signal characteristic of leaky coaxial cable (LCX) is attractive for cognitive radio systems, however, its capacity has never been assessed in this type of application. In this study, we evaluate the ergodic capacity performance of LCX for a cognitive radio based system coexisting with TV transmission. Based on measured data, the channel capacity was first computed by suboptimal constant power allocation. Then, water filling technique was used to compensate for the variations in the channel and the interference caused by the TV signal in occupied bands. Finally, the results showed that LCX can provide a capacity of about 20 Mb/s in a typical UHF channel within the 20 dB interference protection limit for digital television. However, the LCX system cannot satisfy the 51 dB interference protection limit for analog television in both VHF and UHF channels.
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