Partially coherent signal combination for impulse radio synchronisation

Impulse radio ultra-wideband offers the potential of high data rate communication and accurate ranging with low power. However, synchronisation of impulse radio systems is known to be difficult. To be able to detect pulses with low energy, the receiver needs to combine multiple pulses. Traditionally, coherent and non-coherent signal combination are used. The vectorial sum of the samples used for coherent combination suppresses the noise but also leads to signal degradation when frequency offset is present. Non-coherent combination sums the magnitude of the samples. It is not affected by frequency offset but is more susceptible to noise. This paper proposes a novel method where sets of coherently combined samples are added non-coherently. This hybrid method, called partial coherence, improves synchronisation performance compared to the non-coherent method even in the presence of frequency offset.