Performance Bounds for Coherent Chirp Synthesis in Multiband Signals

Radio-based position estimation is severely affected by multipath radio propagation. A sufficiently large signal bandwidth allows for a separation of the line-of-sight signal component from the multipath components and ensures, therefore, accurate positioning. This paper investigates the possibility of combining multiple, consecutively transmitted subband signals into a combined signal with a scaled-up effective bandwidth. The Cramer-Rae lower bound (CRLB) is derived for this time-of-arrival-estimation problem in order to analyze its scaling behavior. It is found that an overlap of the subband signals in the frequency domain can be exploited to increase the effective signal bandwidth. However, this method is only effective in presence of multipath propagation, it does not yield any gain in AWGN channels without multipath. Theoretical results are validated by means of computer simulations for chirp-based radio signals.