In this paper, theoretical limits on time delay estimation are studied forultra-wideband (UWB) cognitive radio systems. For a generic UWB spectrum withdispersed bands, the Cramer-Rao lower bound (CRLB) is derived for unknownchannel coefficients and carrier-frequency offsets (CFOs). Then, the effects ofunknown channel coefficients and CFOs are investigated for linearly andnon-linearly modulated training signals by obtaining specific CRLB expressions.It is shown that for linear modulations with a constant envelope, the effectsof the unknown parameters can be mitigated. Finally, numerical results, whichsupport the theoretical analysis, are presented.
展开▼
