UWB positioning accuracy and enhancements

OFDM based systems are extremely sensitive to time and frequency synchronization errors. This paper addresses the issue of time synchronization. In this paper we are presenting a simple and novel technique for time synchronization. The time synchronization error causes Inter Symbol Interference and hence must be corrected at receiver. In many wireless communication systems, the data packets or frame start with the preamble called training symbol followed by data symbols. The training symbol consists of some specific pattern. The similar frame structure is used for this new algorithm which consists of training symbol followed by OFDM data symbols. This novel technique uses new pattern for training symbol which consists of all identical samples. After applying our new algorithm, a peak is obtained at the end of training symbol. This is used to mark beginning of frame and estimation of timing error. Estimation error graph and BER graph are presented for 4QAM and 16 QAM in this paper. The results are shown for AWGN channel. The technique used is simple and results are encouraging and can be used in any of the OFDM based system.

It is very difficult to eliminate the time synchronization error completely. The influence of time synchronization error on direct source position algorithm was researched. The signal model with time synchronization error was given firstly. Then the CRLB of position estimation under the condition that the time synchronization error is exist was derived. In the last, the influence was analyzed by Monte Carlo simulations. The simulation results show that the Cramer-Rao lower bound, under the condition the time synchronization error is exist, is deteriorated obviously compared with the condition the time is synchronized perfectly; when the time synchronization error is shorter than the signal sample period, the CRLBs are same with different time synchronization errors; however the position accuracy of direct source position algorithm drops sharply, if the time synchronization error is not being considered.

In all wireless communication systems and especially in OFDM and MIMO-OFDM system synchronization is crucial. The receivers do not know the beginning and the end of the OFDM symbols, so the placement of the FFT window. Moreover, they have their own sampling frequency asynchronous with that of the transmitter. These two points show two synchronization concepts: time and frequency. An error of time synchronization in the reception may cause loss of the orthogonality of subcarriers. This is why it is important to have a robust synchronization algorithm and know its effect on system performance. Several estimation techniques for time and frequency offset have been proposed in the literature, but varied test conditions make comparison difficult. In this paper, we use Schmidl and Cox algorithm as a symbol timing synchronization algorithm for OFDM system. We also see the preamble structure using the equations provided in the IEEE 802.16d. Simulation results show the effect caused by carrier frequency offset (CFO) and timing frequency offset (STO) on the performance of an OFDM system in a WiMAX context.

Structural damage detection based on wireless sensor networks can be affected significantlyby time synchronization errors among sensors. Precise time synchronization of sensor nodeshas been viewed as crucial for addressing this issue. However, precise time synchronizationover a long period of time is often impractical in large wireless sensor networks due to twoinherent challenges. First, time synchronization needs to be performed periodically,requiring frequent wireless communication among sensors at significant energy cost.Second, significant time synchronization errors may result from node failures which arelikely to occur during long-term deployment over civil infrastructures. In this paper, adamage detection approach is proposed that is robust against time synchronizationerrors in wireless sensor networks. The paper first examines the ways in whichtime synchronization errors distort identified mode shapes, and then proposes astrategy for reducing distortion in the identified mode shapes. Modified values forthese identified mode shapes are then used in conjunction with flexibility-baseddamage detection methods to localize damage. This alternative approach relaxesthe need for frequent sensor synchronization and can tolerate significant timesynchronization errors caused by node failures. The proposed approach is successfullydemonstrated through numerical simulations and experimental tests in a lab.

The soil conditions within the array of the Mad Dog suction anchor locations vary significantly. One anchor Cluster is located in a slump unit where both soft and stiff clay as well as sand layers are encountered. Due to the highly variable soil conditions five different anchor dimensions were used. The paper presents relevant installation considerations and field performance results. Predicted and observed embedment pressures, tilt and twist as the anchor penetrated are presented. Introduction The Mad Dog prospect is located in the Green Canyon Area of the Gulf of Mexico. The water depth at the site varies from about 1370 m (4500ft) on top of the Escarpment to about 1680 m (5500 ft) below. The field architecture consists of a truss Spar platform moored by a taut leg system consisting 11 polyester lines distributed in three Clusters with suction anchors at the end to provide holding capacity. Suctions anchors were selected as the preferred option due tohigh positioning accuracy which is important in a slump deposit where soil conditions may change significantly within short distancesrobustness to varying/uncertain soil conditions can be accommodated by using different anchor diameters and depth to diameter ratios andproven technology with more than 500 suction anchors installed worldwide at more than 50 locations per 2003 (Andersen et al (2005). Soil investigation The soil investigation was planned and performed following an integrated approach. Geophysical and geological analysis were performed prior to the main soil investigation and concluded that there was a high degree of confidence of homogeneous sediments at all anchors locations in Clusters 1 and 3. Therefore only one boring and one (two) CPTs were performed at each of these Clusters. The conclusion from reviewing geophysical data at Cluster 2 was that there was low confidence of homogeneous sediments at each anchor location and therefore the geotechnical field program consisted of one boring and one CPT at each anchor location (in total 4 borings and 4 CPTs were performed at Cluster 2), see Field Architecture shown on Figure 1 below. Figure 1. Mad Dog field architecture with the 3 anchor clusters (available in fullpaper) Penetration analysis The penetration analysis includes calculation ofskirt penetration resistanceunderpressure needed to reach target depthallowable underpressure limited to avoid large soil Heavesoil heave inside the anchor The penetration resistance, Qtot, is calculated as the sum of wall friction, Qside, and skirt tip bearing capacity, Qtip:Mathematical equation (Available in full paper) whereAside = total side areaAtip = total tip area?= remolding factor, assumed equal to 1/St, where St is the sensitivityz = penetration depthsuDSS = characteristic direct simple shear strengthsu,tipAV = characteristic average shear strength at skirt tip level

Global navigation satellite systems (GNSS) are often integrated with inertial measurement units (IMU) for navigation in urban environments. The ability of these integrated systems to achieve precise positioning and navigation is highly dependent on accurate time synchronization. While the current time synchronization algorithms are capable of achieving millisecond-level synchronization in open environments, their performance deteriorates significantly in complex urban environments due to the impact on GNSS measurements of non-line-of-sight (NLOS) signals and multipath effects. Here we propose a loosely coupled GNSS/IMU integration time synchronization error modeling and compensation algorithm to tackle this problem in the context of urban vehicle navigation. In the algorithm, the time synchronization error is augmented as a state variable in the Robust Extended Kalman Filter (REKF), with the robustness factor threshold being dynamically adjusted based on the time synchronization error. Furthermore, we have designed a system time synchronization detection scheme based on two detection factors, with the aim of achieving high-precision GNSS/IMU time synchronization in complex urban environments. Experimental results show that the proposed algorithm synchronizes data time to the millisecond level in urban positioning environments. This represents an improvement of more than 90% in time synchronization precision compared to the traditional EKF-based time synchronization algorithm, and an improvement of more than 60% compared to the REKF-based time synchronization algorithm. Furthermore, compared to the EKF-based GNSS/IMU fusion algorithm, the proposed algorithm enhances the accuracy of the determination of both position and velocity in the horizontal and 3D directions by more than 50% and heading accuracy by 85%.

In this paper, we propose a robust STBC transmission scheme to combat the timing synchronization errors over frequency-selective multiple-access channels. First, the equivalent channel model in the presence of timing synchronization errors is derived and we find that the synchronization errors result in an equivalent channel model with larger number of correlated channel taps. Based on this correlated equivalent channel model, the statistical power profile is analyzed and a robust statistical bit loading algorithm is proposed. At the receiver, by exploiting the algebraic structure of the Alamouti STBC, a closed-form expression of the QR receiver is derived which further simplifies computational complexity. Simulation results show that our proposed scheme is robust to timing synchronization errors.

This paper presents the details of a simulation based study performed to investigate the BER performance degradation (sensitivity) of OFDM systems due to time synchronization error at the demodulator. It is shown that an OFDM system incorporating a cyclic prefix (CP) has an asymmetric effect on the received constellation with synchronization error away from CP introducing intersymbol interference (ISI), while that towards the CP introducing only a phase error. We approximate the time synchronization error by a Gaussian distributed random variable, in order to evaluate the BER sensitivity of OFDM systems to timing error. The BER performance was evaluated for an AWGN channel and a multipath fading channel in terms of the synchronization error variance. The results of this investigation will be useful in developing time synchronization algorithms in OFDM systems to achieve a particular BER performance target for a given channel condition.

Most OFDM analyses assume idealized conditions when it comes to the waveform at the receiver in terms of time and frequency synchronization. In addition, often a cyclic prefix (CP) longer than the channel delay spread is assumed, and thus the impact of the possible inter-symbol interference (ISI) from adjacent OFDM symbols is not a consideration. This work provides a consolidated framework for study and analysis of OFDM systems with imperfections. The imperfections include time and frequency synchronization errors, and channel delay spread beyond the CP duration. Transmit as well as receive filtering operations are explicitly modeled, and different receiver detection criteria are considered. The use of an OFDM waveform for UWB applications is known to be a promising choice to simplify the receiver design and to maximize the bandwidth scalability, as well as the adaptation to various spectrum allocations. We present bit error rate (BER) sensitivity analysis to key system parameters for OFDM-based UWB applications. From these sensitivity analyses, we see graceful performance degradation with decreasing CP length and increasing residual frequency error. The performance degradation can be much more critical for timing synchronization errors.

Acoustic target tracking is one of the application areas of wireless sensor networks (WSNs) in which time synchronization error influences the results of target tracking. Algebraic numerical methods are used to solve simultaneous equations of target tracking. A more efficient approach is to use algebraic geometry for solving simultaneous equations of target tracking, but the analytic study of error propagation in this approach is difficult. Alternatively, a simulative approach can be used for computing the relation between time synchronization error and target tracking error. This relation helps the middleware layer of WSNs to adjust the resynchronization time of the network more accurately in support of end users' and application programs' requirements for quality of service (QoS). This paper presents two different simulations for extracting the relation between time synchronization error and target tracking error.

Wireless sensor networks (WSNs) have been used in many fields due to its wide applicability. In this kind of network, each node is independent of each other and has its own local clock and communicates wirelessly. Time synchronization plays a vital role in WSNs and it can ensure accuracy requirements for coordination and data reliability. However, two key challenges exist in large-scale WSNs that are severe resource constraints overhead and multihop time synchronization errors. To address these issues, this paper proposes a novel unmanned aerial vehicle (UAV)-assisted low-consumption time synchronization algorithm based on cross-technology communication (CTC) for a large-scale WSN. This algorithm uses a UAV to send time synchronization data packets for calibration. Moreover, to ensure coverage and a high success rate for UAV data transmission, we use CTC for time synchronization. Without any relays, a high-power time synchronization packet can be sent by a UAV to achieve the time synchronization of low-power sensors. This algorithm can achieve accurate time synchronization with almost zero energy consumption for the sensor nodes. Finally, we implemented our algorithm with 30 low-power RF-CC2430 ZigBee nodes and a Da Jiang Innovations (DJI) M100 UAV on a 1 km highway and an indoor site. The results show that time synchronization can be achieved accurately with almost zero energy consumption for the sensor nodes, and the time synchronization error is less than 30 s in 99% of cases.

In this paper, we propose a robust STBC transmission scheme to combat timing synchronization errors over frequency-selective multiple-access channels. We start by deriving the equivalent channel model in the presence of timing synchronization errors. Based on this correlated equivalent channel model, the statistical channel power gain profile is analyzed and shown to exhibit unequal channel power gains on different subcarriers. Furthermore, a robust statistical bit loading algorithm is proposed to optimize the BER performance in scenarios where link adaptation based on instantaneous channel information is infeasible or undesirable. Simulation results show that our proposed scheme is robust to timing synchronization errors, providing around 7.5 dB SNR advantage at the BER of 10-4 over the conventional scheme in various channel environments.

In this paper, we study the impact of timing synchronization errors on the performance of Multicarrier Differential Chaos Shift Keying systems over wireless channels. Considering the challenges posed by selective-frequency Rayleigh fading and multipath propagation, we analyze the system’s performance under random timing errors and fading effects. Using analytical modeling, including probability density functions for fading coefficients and truncated density functions for timing synchronization errors, the Bit Error Rate (BER) performance is derived. Numerical simulations validate the theoretical findings and highlight critical system parameters that influence robustness. Our results demonstrate that timing synchronization errors significantly degrade BER performance, particularly under harsh wireless channel conditions. To mitigate this degradation, we analyze and evaluate the effect of timing errors and related parameters on system performance, identifying technical solutions such as increasing the receiver sampling frequency within the chip duration and selecting an optimal spreading factor. These findings provide valuable insight into the design of more resilient noncoherent chaos-based communication systems.

In this paper parametric tracking of channel and synchronization errors for an adaptive multi-dimensional channel estimator for uplink Orthogonal Frequency Division Multiplex Access (OFDMA) communication systems is proposed. The estimator consists of a two-dimensional LMMSE filter. In real world scenarios, channel estimation should work not only in a wide range of terminal velocities and delay spread but it is also confronted with time and frequency synchronization errors affecting the channel estimation and thus limits the performance of both the coherent receiver and overall OFDMA system. We jointly track channel statistics and synchronization errors so that LMMSE filter coefficients closely reflect the current statistics of the channel. Through simulations it is verified that the proposed channel estimator outperforms the robust LMMSE estimator in the presence of synchronization errors and varying channel conditions.

Raw signal simulation is a useful tool for synthetic aperture radar (SAR) system design, mission planning, processing algorithm testing, and inversion algorithm design. Time and frequency synchronization is the key technique of bistatic SAR (BiSAR) system, and raw data simulation is an effective tool for verifying the time and frequency synchronization techniques. According to the two-dimensional (2-D) frequency spectrum of fixed-receiver BiSAR, a rapid raw data simulation approach with time and frequency synchronization errors is proposed in this paper. Through 2-D inverse Stolt transform in 2-D frequency domain and phase compensation in range-Doppler frequency domain, this method can significantly improve the efficiency of scene raw data simulation. Simulation results of point targets and extended scene are presented to validate the feasibility and efficiency of the proposed simulation approach.