In the IEEE 802.15.4a amendment, an ultra-wideband (UWB) physical layer (PHY) based on an impulse radio signaling scheme using band-limited pulses is specified. Furthermore, the format of an UWB frame is described, consisting of three major components: the Synchronization Header Preamble (SHR), the PHY Header (PHR) and the Physical Layer Service Data Unit (PSDU). The SHR preamble that is being added prior to the PHR could be used to aid receiver algorithms that perform packet synchronization.
Ultra wideband (UWB) systems have received great attention recently due to their distinctive advantages over conventional narrowband systems. First, they have low sensitivity to severe multipath fading and jamming. Second, they enable accurate positioning and ranging. Third, they coexist well with current wireless systems and have low probability of intercept. Fourth, they provide good flexibility to trade off between data rate and power consumption.
In practice, the receiver needs to know the timing information of the received signal to accomplish demodulation. The procedure that estimates the timing information is referred to as the synchronization. In this procedure, the receiver has to search all possible positions in order to find the location where the received signal can be recovered with maximal energy. Performing synchronization is especially difficult in UWB systems due to the large search space, which mainly results from the very fine resolution of the timing uncertainty region and the long spreading code.
Synchronization algorithms can be used to determine three sampling positions: first, the pulse-level position, i.e. the position where the pulses appear in pulse duration; second, the code-level position, i.e. the position where pulses start to be combined to form one symbol; third, the bit-level position, i.e. the position where the data payload effectively starts. The offsets between the sampling position and the ideal position are referred to as the pulse-, code-, and bit-level offsets, respectively.
In literature, there are two possible acquisition strategies searching for the pulse- and code-level positions: either searching first for the pulse-level position afterwards for the code-level position, or jointly searching for both positions. The first strategy in principle requires a smaller search space compared with the second strategy as the searching of two positions is decoupled. However, this strategy suffers from a poor energy accumulation when searching for the pulse-level position. This is undesirable for ultra-low power systems where the transmit power is very small for an isolated pulse. In addition, this first strategy requires a longer preamble as the two positions are searched sequentially.
Synchronization algorithms are for example known from WO-A-96/41432 and US-A-2004/136439.
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