Presence Of Timing Offsets Research Articles

Magnetic Sensor-Based Multi-Vehicle Data Association

Sensors have been playing an increasingly important role in smart cities. Using small roadside magnetic sensors provides a cost-efficient method for monitoring vehicle traffic. However, there are significant challenges associated with vehicle data misalignment due to the timing-offsets between sensors and missed or increased data because of vehicle lane-changing. In this paper, we propose a novel traffic information acquisition and vehicle state estimation scheme using multiple road magnetic sensors. To efficiently solve the multi-sensor registration problem in the presence of timing-offset, we develop a linear discrimination analysis method to achieve vehicle separation and classification. To handle the situation of lane-changing, we propose a data smoothing technique based on a multi-hypotheses tracker that exploits vehicle correlation. The road density effect on the probability of correct data association is investigated, with numerical and experimental results provided. The results show that our proposed scheme can effectively detect vehicles with a 95.5% accuracy rate. It also outperforms some other speed sensing methods in terms of the vehicle speed estimation accuracy.

Spectrum Efficient Joint Frequency Offset and Channel Estimation for Time-Asynchronous Amplify-and Forward Two-Way Relay Networks

This paper considers the problem of the joint channel and carrier frequency offset (CFO) estimation for asynchronous amplify-and-forward (AF) two-way relay networks (TWRNs). This problem has not been solved to the best of our knowledge, and the presence of timing offsets between the two terminals, in addition to the frequency offsets, makes it necessary to develop signal sampling and joint estimation schemes that explicitly take into account both offsets. As potential solutions, we investigate two estimation strategies. The first strategy is pilot-based estimation, and in this context, we develop the maximum-likelihood joint CFO and channel estimator. Then, we consider the semi-blind estimation strategy, proposing a novel estimator based on expectation maximization (EM). As an alternative to the EM, we also investigate decision-directed (DD) semi-blind estimation. The semi-blind Cramer-Rao bound (CRB) is also obtained as a benchmark. Extensive experiments are used to compare the different estimation methods, showing that the proposed EM algorithm yields significantly lower mean-squared error than both the pilot-based estimator and the DD estimator and converges to the obtained CRB. It also yields much better symbol error rates. This is achieved at a reasonable computational complexity, and only a limited number of EM iterations are sufficient for convergence. The main contribution of our work is the development of the EM estimator, the corresponding CRB, and the use of simulations to demonstrate the superior performance of the proposed EM algorithm compared to other potential solutions.

Joint MMSE-FDE & Spectrum Combining for a Broadband Single-Carrier Transmission in the Presence of Timing Offset

Frequency-domain equalization (FDE) based on minimum mean square error (MMSE) is considered as a promising equalization technique for a broadband single-carrier (SC) transmission. When a square-root Nyquist filter is used at a transmitter and receiver to limit the signal bandwidth, the presence of timing offset produces the inter-symbol interference (ISI) and degrades the bit error rate (BER) performance using MMSE-FDE. In this paper, we discuss the mechanism of the BER performance degradation in the presence of timing offset. Then, we propose joint MMSE-FDE & spectrum combining which can make use the excess bandwidth introduced by transmit filter to achieve larger frequency diversity gain while suppressing the negative effect of the timing offset.

Noncoherent Ultra-Wideband (De)Modulation

Ultra-wideband (UWB) radios have received increasing attention recently for their potential to overlay legacy systems, their low-power consumption and low-complexity implementation. Because of the pulsed or duty-cycled nature of the ultra-short transmitted waveforms, timing synchronization and channel estimation pose major, and often conflicting, challenges and requirements. In order to address (or in fact bypass) both tasks, we design and test noncoherent UWB (de)modulation schemes, which remain operational even without timing and channel information. Relying on integrate-and-dump operations of what we term "dirty templates," we first derive a maximum likelihood (ML) optimal noncoherent UWB demodulator. We further establish a conditional ML demodulator with lower complexity. Analysis and simulations show that both can also be applied after (possibly imperfect) timing acquisition. Under the assumption of perfect timing, our noncoherent UWB scheme reduces to a differential UWB system. Our approach can also be adapted to a transmitted reference (TR) UWB system. We show that the resultant robust-to-timing TR (RTTR) approach considerably improves performance of the original TR system in the presence of timing offsets or residual timing acquisition errors