Inertial Measurement Unit based Virtual Antenna Arrays - DoA Estimation and Positioning in Wireless Networks

Today we have different location based services available in a mobile phone or mobile station (MS). These services include: direction finding to nearby ATMs, locating favorite food restaurants, or finding any target destination. Similarly, we see different applications of the positioning and navigation systems in firefighting or other rescue operations. The common factor in almost all of the location based services is the system's ability to determine the user's current position, with reference to a floor plan or a navigation map. Current technologies are using sensor data measurements from one or more sensors, available to the positioning device, for positioning and navigation. Typical examples are radio based positioning such as global positioning system, inertial sensors based inertial navigation system, or camera based positioning systems. Different accuracy and availability conditions of the positioning and navigation solution can be obtained depending on the positioning algorithms and the available sensor information.Nowadays, the focus of research in positioning and navigation has been mostly on the use of existing hardware infrastructure and low-cost solutions, such that the proposed technique can be deployed with ease and without extra infrastructure requirements as well as without any expensive sensor equipment. In this work, we investigate a novel idea for positioning using existing wireless networks and low-cost inertial sensor measurements available at the MS. We propose to use received baseband radio signal along with inertial sensor data, such as accelerometer and rate gyroscope measurements, for direction of arrival (DoA) estimation and positioning. The DoA information from different base stations or access points can be used to estimate the MS position using triangulation technique. Furthermore, due to size and cost restrictions it is difficult to have real antenna arrays at the MS, the idea of DoA estimation and positioning is proposed to be used with single antenna devices by using the so-called virtual antenna arrays.We have presented our research results in three different papers. We provide measurement based results to perform a quantitative evaluation of DoA estimation using arbitrary virtual antenna arrays in 3-D; where a state-of-the-art high-resolution algorithm has been used for radio signal parameter estimation. Furthermore, we provide an extended Kalman filter framework to investigate the performance of unaided inertial navigation systems with 3-axis accelerometer and 3-axis rate gyroscope measurements, from a six-degrees-of-freedom inertial measurement unit. Using the extended Kalman filter framework, we provide results for position estimation error standard deviation with respect to integration time for an unaided inertial navigation system; where the effect of different stochastic errors noise sources in the inertial sensors measurements such as white Gaussian noise and bias instability noise is investigated. Also, we derive a closed form expression for Cramér-Rao lower bound to investigate DoA estimation accuracy for a far-field source using random antenna arrays in 3-D. The Cramér-Rao lower bound is obtained using known antenna coordinates as well as using estimated antenna coordinates, where the antenna coordinates are estimated with an uncertainty whose standard deviation is known. Furthermore, using Monte-Carlo simulations for random antenna arrays, we provide Cramér-Rao lower bound based performance evaluation of random 3-D antenna arrays for DoA estimation

Source Localization Using Virtual Antenna Arrays

Using antenna arrays for direction of arrival (DoA) estimation and source localization is a well-researched topic. In this paper, we analyze virtual antenna arrays for DoA estimation where the antenna array geometry is acquired using data from a low-cost inertial measurement unit (IMU). Performance evaluation of an unaided inertial navigation system with respect to individual IMU sensor noise parameters is provided using a state space based extended Kalman filter. Secondly, using Monte Carlo simulations, DoA estimation performance of random 3-D antenna arrays is evaluated by computing Cramér-Rao lower bound values for a single plane wave source located in the far field of the array. Results in the paper suggest that larger antenna arrays can provide significant gain in DoA estimation accuracy, but, noise in the rate gyroscope measurements proves to be a limiting factor when making virtual antenna arrays for DoA estimation and source localization using single antenna devices

An Unbiased Lipid Phenotyping Approach To Study the Genetic Determinants of Lipids and Their Association with Coronary Heart Disease Risk Factors.

Direct infusion high-resolution mass spectrometry (DIHRMS) is a novel, high-throughput approach to rapidly and accurately profile hundreds of lipids in human serum without prior chromatography, facilitating in-depth lipid phenotyping for large epidemiological studies to reveal the detailed associations of individual lipids with coronary heart disease (CHD) risk factors. Intact lipid profiling by DIHRMS was performed on 5662 serum samples from healthy participants in the Pakistan Risk of Myocardial Infarction Study (PROMIS). We developed a novel semi-targeted peak-picking algorithm to detect mass-to-charge ratios in positive and negative ionization modes. We analyzed lipid partial correlations, assessed the association of lipid principal components with established CHD risk factors and genetic variants, and examined differences between lipids for a common genetic polymorphism. The DIHRMS method provided information on 360 lipids (including fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, and sterol lipids), with a median coefficient of variation of 11.6% (range: 5.4-51.9). The lipids were highly correlated and exhibited a range of associations with clinical chemistry biomarkers and lifestyle factors. This platform can provide many novel insights into the effects of physiology and lifestyle on lipid metabolism, genetic determinants of lipids, and the relationship between individual lipids and CHD risk factors

Comparison of Frequency Domain Equalizers to Time Domain Equalizers in WCDMA

Future mobile platforms will contain an increased amount of wireless technologies. As technologies mature it will be necessary to find synergies between them. This could be in the form of reusing hardware blocks and algorithms. By using Fast Fourier Transforms (FFT/IFFT) and performing channel cancellation/equalization in frequency domain for wideband code division multiple access (WCDMA) will provide us a platform which can support LTE and WiFi together with WCDMA. In this thesis, an equalizer based on Fast Fourier Transforming (FFT) the input signal, cancelling the propagation channel in frequency domain, and finally reverting to time domain using an IFFT would be devised for WCDMA. The performance of frequency domain equalizer is then compared with traditional time domain equalizer based on G-RAKE method for different performance metrics. To evaluate and compare the performance of frequency domain equalizer (FFT) with time domain equalizer (G-RAKE), a simulator is made in IT++. Several simulations are performed and the obtained results are analyzed in Matlab. Firstly, for channel estimation at the receiver, common pilot channel (CPICH) is used and multiple channel estimates are obtained to get a filtered channel estimate. Along-with CPICH pilot symbols, data symbols of a desired user and four other user‟s data symbols are transmitted from the base-station (Node B). Using QPSK signaling, un-coded bit-error-rate (BER) results of the desired data user are compared for the two equalization methods. Simulation results are obtained for single path and multi-path propagation channels with different delay spread values. Included in the modeling are one receive and transmit antenna, other cell interference, i.e., non-white noise, frequency errors at mobile station (UE), and analog-to-digital (A/D) quantization

Tightly Coupled Positioning and Multipath Radio Channel Tracking

Radio based localization is an active research topic with a wide range of applications. In this paper, we focus on localization of a radio receiver equipped with an inertial measurement unit. The localization is performed while simultaneously constructing a map of the small scale fading pattern in the local radio environment. The map in our case is a ray-trace-based multipath channel model. This solution is enabled by sensor fusion of information from the channel estimation data and the inertial sensors, and it does not assume any knowledge of, e.g., transmitter locations. The sensor data is fused in a recursive state space model that combines the kinematic motion model with the ray-based radio channel model, and the state vector is estimated using a particle filter. The choice of the particle filter is justified by the multimodal characteristics of the posterior likelihood distributions that follows from the nonlinearities of the problem. The work is assuming a single receiver antenna but the approach can also be transferred to multiple antenna systems. We study the performance of the approach under realistic assumptions, based on the performance of today’s low-cost inertial sensors and radio systems, including accelerometer and gyroscope noise, and also radio receiver frequency error and noise. Simulations show a significant improvement in long-term positioning performance, evaluated against dead reckoning. The work is concluded with experiments which serve as a proof of concept for the proposed technique, using no extra equipment compared to what can be found in a modern cellular phone

Direction of Arrival Estimation with Arbitrary Virtual Antenna Arrays using Low Cost Inertial Measurement Units

In this paper, we have investigated the use of virtual antenna arrays at the receiver to do single antenna direction-of-arrival estimation. The array coordinates are obtained by doing simple dead reckoning using acceleration and angular speed measurements from a low cost micro-electro-mechanical system inertial measurement unit (IMU). The proposed solution requires no extra hardware in terms of receiver chains and antenna elements. Direction-of-arrival estimation results are obtained using a high resolution SAGE algorithm. Measurement results show that the direction-of-arrival can be estimated with a reasonable accuracy in an indoor environment

Radio and IMU based indoor positioning and tracking

Navigation using inertial measurement units (IMUs) is an interesting area of research. Due to the low cost hardware and simple implementation, the approach looks very attractive. But the performance of the IMUs to provide sub-meter accuracy over a longer period of time is still not sufficient, so different approaches have been adopted to increase the performance at the cost of extra hardware and/or infrastructure. Our solution is based on the use of already existing radio infrastructure, where amplitude and phase variations in a received radio signal at the user terminal is used together with the IMU to do a tightly coupled estimation of navigation and radio signalmultipath components. The results show that the approach has the potential to enhance the performance of IMU based navigation significantly

Optimal virtual array length under position imperfections

This article contains a study of how spatial errors and receiver imperfections affect the angle of arrival estimation accuracy for virtual antenna arrays. A virtual antenna array consists of one receiver element whose location is tracked as the element is moved and in this work, linear arrays are studied. If the location of the receiver is tracked using an inertial measurement unit, an interesting trade-off emerges. The array should extend as far as possible but since the position estimates from the unaided inertial measurement unit become increasingly uncertain over time, the angle of arrival estimation will deteriorate. Several algorithms are available for estimating the angle of arrival in such a scenario but the one used for evaluation here is a sparse enforcing least squares method

On the Performance of Random Antenna Arrays for Direction of Arrival Estimation

A single antenna based virtual antenna array at the receiver can be used to find direction of different incoming radio signals impinging at the receiver. In this paper, we investigate the performance of random 3D virtual antenna arrays for DoA estimation. We have computed a Cramer-Rao Lower Bound (CRLB) for DoA estimation if the true antenna positions are not known, but these are estimated with an uncertainty. Position displacement is estimated with an extended Kalman filter (EKF) by using simulated data samples of acceleration and rotation rate which are corrupted by stochastic errors, such as, white Gaussian noise and bias drift. Furthermore, the effect of position estimation error on the DoA estimation performance is evaluated using the CRLB. The results show that the number of useful elements in the antenna array is limited, because the standard deviation of the position estimation error grows over time

Non-line-of-sight based radio localization with dual-polarization antenna arrays

This work presents an approach for radio-based localization in non-line-of-sight (NLOS) environments by leveraging a dual-polarization antenna array. By estimating the polarization of the received signal, it is possible to estimate the angle of reflection of a NLOS signal. An estimate of the position of the transmitter concerning the receiver can be obtained based on a joint estimation of the reflection angle of several NLOS signals together with their respective directions of arrival (DOAs) and time differences of arrival (TDOAs). A set of numerical simulations is used to assess the performance of the proposed method