Non-data-aided ML symbol timing estimation in MIMO correlated fading channels

In this paper, the non-data-aided (NDA) maximum likelihood (ML) symbol timing estimator in MIMO correlated channel is derived. It is found that the extended square nonlinearity estimator in [9] is just a special case of the proposed algorithm. Furthermore, the conditional Cramer-Rao bound (CCRB) and the modified Cramer-Rao bound (MCRB) are also established. Simulation results under different operating conditions (e.g., number of antennas and correlation between antennas) are given to assess the performances of the NDA ML estimator and it is found that the mean square errors (MSE)s of the NDA ML estimator i) are close to the CCRBs, but not the MCRBs; ii) are approximately independent of the number of transmit antennas; iii) are inversely proportional to the number of receive antennas and iv) correlation between antennas has little effect on the SE performance.published_or_final_versio

Multiple timing offsets compensation in cooperative communication systems

Cooperative communication systems have attracted much attention recently due to their desirable performance gain while using single antenna terminals. However, most of the existin works on cooperative communications require perfect timing synchronization among users, which is usually not true in practical systems. In this paper, a general framework of the re-synchronization filter design is developed in order to com pensate the multiple timing offsets at the destination. The proposed method is applied to different scenarios with varying degrees of timing misalignment and is numerically shown to provide excellent performances that approach the perfectly synchronized case. © 2009 IEEE.published_or_final_versionThe 16th International Conference on Digital Signal Processing (DSP 2009), Santorini-Hellas, Greece, 5-7 July 2009. In Proceedings of 16th DSP, 2009, p. 1-

Improved estimation of clock offset in sensor networks

Clock synchronization is an important issue for the design of a network composed of small sensor nodes. Based on the two-way timing message exchange mechanism and assuming an exponential network delay distribution, many analytical results have been presented in the literature by applying the techniques from statistical signal processing. This paper derives the minimum variance unbiased estimator for the clock offset for both symmetric and asymmetric exponential delay cases. For the asymmetric delays, it is shown to be a function of both the minimum and the mean link delays. This result is a very significant contribution since only the minimum link delay observations have been used to estimate the clock offset in the past. For the symmetric case, it is shown to coincide with the maximum likelihood estimator. In addition, the result is also applicable to clock synchronization problem in general computer networks. ©2009 IEEE.published_or_final_versionThe IEEE International Conference on Communications (ICC 2009), Dresden, Germany, 14-18 June 2009. In Proceedings of IEEE ICC, 2009, p. 1-

On performance bounds for timing estimation under fading channels

In timing synchronization, the Cramér Rao Bound has been used as performance bounds for timing estimation in AWGN channel. However, the instantaneous CRB for timing estimation in fading channels depends on the channel realizations and may fail to bound the mean square error (MSE) of the estimator because the equivalent signal-to-noise ratio (SNR) is too low. In this paper, we demonstrate that the conventional CRB for timing estimation is no longer valid in fading channels. Furthermore, a new performance bound called Weighted Bayesian CRB (WBCRB) is proposed for the estimation of both single and multiple timing offsets under fading channels. The relationship between the conventional CRB and WBCRB are discussed in details, where numerical results show that the WBCRB is a valid bound for all SNR even under fading channels. ©2009 IEEE.published_or_final_versionThe IEEE Conference on Wireless Communications and Networking (WCNC 2009), Budapest, Hungary, 5-8 April 2009. In Proceedings of IEEE WCNC, 2009, p. 1-

Timing synchronization in decode-and-forward cooperative communication systems

Cooperative communication systems have attracted much attention recently due to their desirable performance gain while using single antenna terminals. This paper addresses the joint timing and channel estimation problem, and furthermore the resynchronization of multiple timing offsets in a cooperative relay system. The estimations of timing and channel are conducted in two phases and the associated Cramér-Rao bounds (CRB) are derived for both phases. It is demonstrated that the conventional CRB is not valid for timing parameters under fading conditions, and a new bound called Weighted Bayesian CRB is proposed. With the timing and channel estimates, a general framework of the resynchronization filter design is developed in order to compensate the multiple timing offsets at the destination. The proposed methods are applied to different scenarios with varying degrees of timing misalignment and are numerically shown to provide excellent performances that approach the perfectly synchronized case. © 2009 IEEE.published_or_final_versio

Symbol-timing estimation in space-time coding systems based on orthogonal training sequences

Space-time coding has received considerable interest recently as a simple transmit diversity technique for improving the capacity and data rate of a channel without bandwidth expansion. Most research in space-time coding, however, assumes that the symbol timing at the receiver is perfectly known. In practice, this has to be estimated with high accuracy. In this paper, a new symbol-timing estimator for space-time coding systems is proposed. It improves the conventional algorithm of Naguib et al. such that accurate timing estimates can be obtained even if the over-sampling ratio is small. Analytical mean-square error (MSE) expressions are derived for the proposed estimator. Simulation and analytical results show that for a modest oversampling ratio (such as Q equal to four), the MSE of the proposed estimator is significantly smaller than that of the conventional algorithm. The effects of the number of transmit and receive antennas, the oversampling ratio, and the length of training sequence on the MSE are also examined. © 2005 IEEE.published_or_final_versio

ML symbol synchronization for OFDM-based WLANs in unknown frequency-selective fading channels

Based on the maximum-likelihood principle and the preamble structure of IEEE 802.11a WLAN standard, this paper proposes a new symbol synchronization algorithm for IEEE 802.11a WLANs over frequency-selective fading channels. In addition to the physical channel, the effects of filtering and unknown sampling phase offset are also considered. Loss in system performance due to synchronization error is used as a performance criterion. Computer simulations show that the proposed algorithm has comparable performances to the algorithm based on the generalized Akaike information criterion (GAIC), but the proposed algorithm exhibits reduced complexity. © 2004 IEEE.published_or_final_versio

Quantization errors in overlapped block digital filtering methods

In digital signal processing applications involving filtering long sequences, block filtering methods like overlapsave and overlap-add are widely used. Like all finite-precision applications, overlap-save and overlap-add methods are also affected by quantization errors. The goal of this paper is to calculate and make a quantitative comparison of the overall quantization noise resulting from the two methods in terms of power (variance) of the quantization noise. Multiple quantization noise sources are taken into consideration in the computation of the variances. The calculations reveal that the overlap-add approach is more prone to quantization noise compared to the overlap-save approach due to the addition of overlapping sections between overlap-add output blocks. Copyright © 2013 IARIA

Signal processing techniques for synchronization of wireless sensor networks

Plenary PaperClock synchronization is a critical component in wireless sensor networks, as it provides a common time frame to different nodes. It supports functions such as fusing voice and video data from different sensor nodes, time-based channel sharing, and sleep wake-up scheduling, etc. Early studies on clock synchronization for wireless sensor networks mainly focus on protocol design. However, clock synchronization problem is inherently related to parameter estimation, and recently, studies of clock synchronization from the signal processing viewpoint started to emerge. In this article, a survey of latest advances on clock synchronization is provided by adopting a signal processing viewpoint. We demonstrate that many existing and intuitive clock synchronization protocols can be interpreted by common statistical signal processing methods. Furthermore, the use of advanced signal processing techniques for deriving optimal clock synchronization algorithms under challenging scenarios will be illustrated. © 2010 SPIE.published_or_final_versio