Pakorn Ubolkosold

A Data Fusion Approach for Improved Positioning in GSM Networks

Reliable position estimation of a Mobile Station (MS) in a GSM network is important for many applications. Because of the diverse environments including urban, rural, outdoor and indoor and the communication signals which are usually not designed for positioning, it is difficult to obtain an accurate position estimation by using only one type of measurement. Therefore, data fusion solutions which integrate two or more types of measurement have been proposed to provide position estimation with better accuracy, reliability and coverage. In this paper, a data fusion method of integrating two different types of measurement in GSM networks, namely Timing Advance (TA) and Received Signal Strength (RSS), by using an Extended Kalman Filter (EKF) to estimate the MSs position is addressed. Several simulations based on synthetic data reveal that the estimator can track the real state under different movement situations, and that the estimated position components converge quickly to the reference values where the simulated scenario fits the model. Comparing the estimation results of the proposed method with the methods of using only TA measurements and using only RSS measurements, respectively, the data fusion method yields improved positioning accuracy.

A New Closed-Form Frequency Estimator in the Presence of Fading-Induced Multiplicative Noise

This paper deals with the correlation-based carrier frequency offset estimation (CFO) problem in the presence of fading-induced multiplicative noise. We derive a new closed- form estimator using the nonlinear least-squares principle in conjunction with the summation-by-parts formula. The proposed estimator, as opposed to most of the existing methods, is able to operate at the maximum estimation range of about plusmn0.5 the symbol rate without the additional phase unwrapping and robust to the lack of information on the form of the correlation of the multiplicative noise. The performance of the proposed estimator is shown to be efficient in both non-fading and fading scenarios.

Simple Carrier Frequency Offset Estimators in Frequency Flat-Fading Channels

In this paper, the nonlinear least-squares (NLS) estimator for frequency offset in flat-fading channels is systematically derived. A simple interpolation technique is introduced to improve the estimation accuracy of the resulting NLS estimator, especially when the number of zeros padded in FFT is insufficient. Furthermore, we propose an approximated NLS estimator which significantly simplifies the implementation complexity of the full structure NLS estimator. The degree of simplification is defined by the approximated number of complex multiplications required by each estimator. All the estimators derived in this paper do not require any information about the channel correlation as needed for most of the existing techniques. The simulation results show that the performances of two simplified NLS estimators are as good as that obtained from the full structure NLS estimator.

Data-Aided Timing Acquisition in UWB Differential Transmitted Reference Systems

Timing acquisition constitutes a major challenge in realizing highly efficient ultra-wideband (UWB) systems for applications such as indoor wireless communications. To bypass channel estimation the transmitted reference (TR) signaling is a promising candidate. In this paper, we suggest a novel data-aided timing acquisition technique for frame-level synchronization in differential transmitted reference (DTR) UWB systems. Being based on parallel integrate-and-dump (I&D) operations within different pulse-pair correlator branches, the proposed timing acquisition technique performs particularly well at higher signal-to-noise ratio (SNR). The good performance of it is confirmed by simulation results

Bit Error Performance of Differential Impulse Radio UWB Systems

Differential transmitted reference (DTR) ultra-wideband (UWB) impulse radio (IR) system is one of the most attractive solution for realizing non-coherent low data rate and low complexity UWB systems. In this paper, the bit error rate (BER) performance of DTR-UWB receivers conditioned on a channel realization is analyzed. The modeling of low complexity DTR-UWB systems using equivalent system models is presented. The average BER is verified through simulation for different signal-to-noise ratio (SNR) values. It is also compared to the average BER derived using the equivalent system model.

Constrained-trajectory based GPS/INS integration for reliable position and attitude determination

In this paper, we propose a constrained method to incorporate a priori flight trajectory information into the GPS derived navigation solutions which will ensure the availability and reliability of the GPS solutions even when the number of satellites reduces to less than four. Moreover, we fuse the navigation solutions derived from the proposed constrained method with those obtained from the inertial navigation system (INS) in order to fully gain their complementary features of both systems. The simulation results show that the proposed scheme provides the complete 6 degree-of-freedom (DoF) state at high data rate with only two satellites required.

Clock synchronization protocol for distributed satellite networks

Several future space missions are being planned with large number of spacecrafts at low Earth orbit (LEO) and beyond where clock synchronization using GPS will partly be impossible or insufficient. Onboard local clock synchronization devices will be required to replace or augment the available GPS measurements to keep the clocks of the spacecrafts synchronized at low cost. Clock synchronization is very important for many applications, e.g. bi/multi-static SAR systems require clock synchronization for the accurate interferometric phase evaluation. This paper presents a method to relatively synchronize the clocks in such distributed satellite networks when GPS is not available.

GPS/INS Integration for Footprint Chasing in Bistatic SAR Experiments

The paper starts with a brief consideration of a novel bistatic SAR experiment and the requirements on attitude and position determination in SAR. GPS/INS integration strategies are summarized. To obtain an affordable system for the antenna pointing for footprint chasing, low-cost inertial measurement units are in the focus. By an observability analysis it is proven that additional redundant attitude information as it can be derived from a multi-antenna GPS receiver can remarkably aid the integration.

Communication and TOA Estimation with Differential Impulse Radio UWB systems

Differential Transmitted Reference (DTR) ultra-wideband (UWB) impulse radio (IR) system is one of the most attractive solutions for realizing non-coherent low data rate and low complexity UWB systems. Indeed, Transmitted Reference (TR) signaling, in combination with an Autocorrelation Receiver(AcR), allows a lower design complexity compared to coherent receivers. In this paper, the design of DTR-UWB radio modules for wireless sensor networks (WSN), capable of communication and localization, is addressed. Bit error rate (BER) performance of the DTR-UWB receivers conditioned on a channel realization is analyzed. The modelling of low complexity DTR-UWB systems using equivalent system models is presented. The average BER is verified through simulation for different signal-to-noise ratio (SNR) values, and is also compared to the average BER derived using the equivalent system model. We suggest a data-aided time of arrival (TOA) estimator for DTR-UWB systems, using least squares estimation technique and the equivalent system model.

Nonlinear Least-Squares Frequency Offset Estimator and Its Simplified Versions for Flat-Fading Channels

In this paper, the nonlinear least-squares (NLS) estimator for frequency offset in flat-fading channels is systematically derived. A simple interpolation technique is introduced to improve the estimation accuracy of the resulting NLS estimator, especially when the number of zeros padded in FFT is insufficient. Furthermore, we propose an approximated NLS estimator which significantly simplifies the implementation complexity of the full structure NLS estimator. All the estimators derived in this paper do not require any information about the channel correlation as needed for most of the existing techniques. The simulation results show that the performances of two simplified NLS estimators are as good as that obtained from the full structure NLS estimator