Blind synchronization in asynchronous UWB networks based on the transmit-reference scheme

Abstract

Ultra-wideband (UWB) wireless communication systems are based on the transmission of extremely narrow pulses, with a duration inferior to a nanosecond. The application of transmit reference (TR) to UWB systems allows to side-step channel estimation at the receiver, with a tradeoff of the effective transmission bandwidth, which is reduced by the usage of a reference pulse. Similar to CDMA systems, different users can share the same available bandwidth by means of different spreading codes. This allows the receiver to separate users, and to recover the timing information of the transmitted data packets. The nature of UWB transmissions-short, burst-like packets-requires a fast synchronization algorithm, that can accommodate several asynchronous users. Exploiting the fact that a shift in time corresponds to a phase rotation in the frequency domain, a blind and computationally effcient synchronization algorithm that takes advantage of the shift invariance structure in the frequency domain is proposed in this paper. Integer and fractional delay estimations are considered, along with a subsequent symbol estimation step. This results in a collision-avoiding multiuser algorithm, readily applicable to a fast acquisition procedure in a UWB ad hoc network.

Signal model and receiver algorithms for a transmit-reference ultra-wideband communication system

“…The performance of the iterative receiver is as good and occasionally much better than the matched-filter and the BMSR. Additional work shows that joint timing acquisition and detection based on this model is fairly straightforward [15]. Future work will provide a multiuser analysis, and pay attention to interchip interference.…”

“…Even synchronization is not needed in the analog domain; this can be done in the DSP based on the received data model [15]. With times oversampling of the integrator output, there is no loss of information.…”

“…In this receiver model, is measured, is known (user code), is known (delay code), and is known and data independent (this assumes synchronization; without synchronization an unknown number of zero rows are stacked on top but this can be estimated and resolved, see [15]). and are unknown (channel correlation coefficients), and is the data symbol to be detected.…”

“…The channel autocorrelation function defined in (6) depends on both the physical channel response and the transmitted UWB pulse . With the physical channel model in (15), the effective channel response is…”

“…In this section, we will study the expected value and variance of these parameters under certain statistical assumptions of the physical channel. We consider a multipath channel model, where the physical channel impulse response is modeled as a sum of discrete delta pulses (15) where are ray amplitudes, and are their corresponding arrival times. Generally, these parameters are considered as random variables with different statistical assumptions depending on the specific channel model.…”