Optimized Signal Acquisition for Low-Complexity and Low-Power IR-UWB Transceivers

Impulse-based ultra-wideband systems are appealing for low-power short-range communications as they can benefit from duty-cycled low-complexity analog architectures. Low-power receivers correlate in the analog domain and sample only at the pulse repetition frequency. However, achieving acquisition with such a receiver requires an efficient search strategy, as digital post-processing (equalization) of the signal is not possible. Moreover, as we target a network of ultra-low-power sensors which can only send a few pulses and do not implement receiver functionality in order to sustain ARQ protocols, the receiving base station has extra constraints on synchronization performance and maximal preamble length. This paper describes and optimizes a strategy compliant with that scenario, including pulse position and spreading code phase acquisition, end-of-preamble detection, and derivation of the corresponding detection thresholds. Based on a 300-bit preamble, it works within 1.5 dB of ideal synchronization on AWGN. EOP detection is analyzed, showing that a PN sequence of length 7 is sufficient, and also proposing optimal receive filters for EOP sequences defined in IEEE 802.15.4a. Finally, we show that on fading channels, the error floor coming from missed acquisitions can be removed by simply changing the detection threshold.