The wide choices of deployment parameters in next generation wireless communication systems, such as flexible bandwidth allocation, synchronous/asynchronous modes, FDD/TDD, full/half duplex, and configurable cyclic prefix duration, etc., present significant challenges in preamble and system acquisition design. This paper addresses these challenges, as well as the solutions provided by the 3GPP2 Ultra Mobile Broadband (UMB) standard. The proposed preamble design facilitates the maximal flexibility of the system configuration and yet has low overhead, low acquisition latency, and low complexity. Although the design is discussed under the UMB context, it also serves as a preamble design paradigm for an OFDMA communication system in general.

In this paper, we investigate the timing acquisition problem for transmitted reference (TR) ultra-wideband systems employing direct-sequence (DS) spreading. We show that a two-level DS signaling helps in achieving good acquisition performance. We propose a two-stage acquisition scheme which exploits the TR signal structure to achieve a significant improvement in the mean detection time performance when compared with a conventional single-stage acquisition scheme.

The usage of long spreading sequences and the fine timing resolution result in a large search space during acquisition in ultra-wideband (UWB) systems. This paper presents a two-stage signal acquisition scheme for UWB systems employing a hybrid signaling format involving direct sequence (DS) spreading and time hopping (TH), which significantly reduces the search space. The resulting acquisition system consists of two stages, one each for the acquisition of the TH and DS sequences. The dense multipath channel typical of UWB systems implies that there can exist more than one phase to which the receiver can lock on and achieve satisfactory demodulation performance subsequent to acquisition. We define the set of such phases as the hit set. The hybrid signaling format coupled with the multi-phase hit set help significantly improve the acquisition performance of the UWB system. The performance of the proposed acquisition system, measured in terms of the mean detection time, is evaluated analytically and supported by computer simulation

The asymptotic performance of timing acquisition systems having fixed dwell time in multipath fading channels is investigated. The detrimental effect of the multipath channel fading on the acquisition performance is isolated by considering the asymptotic performance as the average signal-to-noise ratio (SNR) increases. It is found that for any threshold such that the average probability of false alarm is less than a given tolerance, the channel fading results in a lower bound on the asymptotic average probability of miss which is nontrivial for a variety of fading scenarios. A threshold-based direct-sequence spread-spectrum signal acquisition system is considered and it is found that the detrimental effect of channel fading on asymptotic acquisition performance, albeit nontrivial, is not very significant. The asymptotic acquisition performance of two threshold-based acquisition schemes for ultra-wideband (UWB) signals with time-hopping (TH) spreading are also evaluated and compared. For both schemes, the detrimental effect of the channel fading on the asymptotic acquisition performance turns out to be significant.

In this paper, we investigate the asymptotic performance of threshold-based timing acquisition systems having fixed dwell time in multipath fading channels. We show that if the system involves the comparison of a decision statistic to a threshold in order to detect the true symbol timing, then it may not be possible to make the average probability of error in acquisition arbitrarily small, even if the signal-to-noise ratio increases without bound.

Low transmission power and a highly spread bandwidth makes the acquisition of ultra-wideband (UWB) signals a difficult problem. In a packet-based network employing UWB modulation in the physical layer, long preambles need to be prepended to each packet because the low signal power requires the receiver to process the signal for long periods of time in order to estimate the timing of the signal. The long spreading or hopping sequences used in UWB systems result in a large search space for the acquisition system at the receiver. This work presents a signal acquisition system for UWB which employs a hybrid signaling format involving direct sequence (DS) spreading and time hopping (TH), significantly reducing the search space in the UWB acquisition system. The acquisition system employs equal gain combining (EGC) which enables the utilization of the energy of the dense multipath, typical of a UWB channel. The performance of the acquisition system has been analytically evaluated and is corroborated through simulation.