Ferit Ozan Akgul

Indoor geolocation in the absence of direct path

Severe multipath in indoor areas causes undetected direct path (UDP) conditions, which pose a serious challenge to the design of robust precision indoor geolocation systems. Based on a scenario on the third floor of the Atwater Kent Laboratory at the Worcester Polytechnic Institute, we explain the reason for frequent absence of direct path, and introduce and analyze the effectiveness of two novel approaches to mitigating the large ranging errors caused by UDP conditions. The first technique exploits nondirect paths for ranging, while the second approach relies on cooperative localization for wireless sensor and ad hoc networks

On RSS and TOA based indoor geolocation - a comparative performance evaluation

Recently wireless positioning using existing network infrastructure has become an attractive value added application in campus and local area networks. However, many complexities, intrinsic to indoor radio propagation create technical challenges for the localization algorithms to meet indoor positioning requirements. Variety of algorithms using received signal strength (RSS) or time of arrival (TOA) has been used for this purpose. There is a literature gap in performance and system bandwidth requirement comparison between RSS and TOA based techniques used for indoor geolocation. In this paper we present experimental results that demonstrate a systematic comparison between these two techniques. Using a 2D ray tracing (RT) software to create a common repeatable framework for performance evaluation, we present a comparison among two RSS based and two TOA based indoor positioning algorithms in a typical office environment

Identification of the Absence of Direct Path in Indoor Localization Systems

Ultra-wideband (UWB) indoor positioning systems based on time of arrival (TOA) techniques are considered to be the high precision alternatives to those employing received signal strength (RSS) or angle of arrival (AOA) due to their superior time-domain resolution. However, the performance of such systems may easily be degraded by the blockage of the direct path (DP) and occurrence undetected direct path (UDP) condition. By erroneous detection of the other multipath components (MPCs) as DP, which is the indicator of the true distance between the transmitter and the receiver, substantial errors will be introduced into the system. The real challenge is to be able to identify the class of the receiver location, therefore, to remedy the ranging measurement in UDP condition. In this paper we propose a methodology to identify and mitigate the UDP conditions, which can substantially improve the overall indoor positioning accuracy.

Bounds on performance of hybrid WiFi-UWB cooperative RF localization for robotic applications

Precise localization has attracted considerable traction in the area of cooperative assignments for robots in indoor applications. When dealing with indoor applications we are limited to the type of signals that can be used for precise localization which is our prime goal. There are limitations to the well known GPS and also vision-based modality where the non-line-of-sight (NLOS) conditions can significantly degrade the results. Hence there is a need for alternative approaches for more precise indoor localization. Precise localization information is an enabler for better coordinated tasks where multiple robots are at play. In this paper, the hybrid cooperative localization accuracy for a multi-robot operation is examined. We use a mix of empirical and theoretical models for ranging estimates in a typical indoor environment on the third floor of the Atwater Kent Laboratory (AKL) at Worcester Polytechnic Institute. The two widely used ranging techniques are Time Of Arrival (TOA) using Ultra-wideband (UWB) and Received Signal Strength (RSS) using WiFi signals. The Cramér-Rao-Lower-Bound (CRLB) on the performance of hybrid localization techniques are determined in our multi-robot operation scenarios based on empirical data for UWB TOA-based and the theoretical WiFi RSS-based ranging. The performance of the hybrid localization of robots are examined when the robots are equipped with UWB radios and operate in cooperative mode using known WiFi Anchors.

AOA Assisted NLOS Error Mitigation for TOA-Based Indoor Positioning Systems

One of the major challenges for TOA-based accurate indoor positioning systems is the blockage of the LOS path, or equivalently direct path (DP), due to obstructions. Since accurate ranging of these systems depend on the detection of the DP between the transmitter and receiver, significant errors will be introduced into the ranging measurements once the DP cannot be detected. This condition is hence called the undetected direct path (UDP) condition. Owing to the fact that indoor wireless channels exhibit rich multipath propagation, the multipath components other than the DP may be utilized in mitigating errors occurring in UDP areas. In this paper, we introduce a method based on both TOA and AOA information from other multipath components to substantially mitigate the ranging error. We present our results as a comparison with commonly used methods for TOA-based ranging and we show that our proposed technique outperforms these traditional methods.

Neural Network Assisted Identification of the Absence of Direct Path in Indoor Localization

Time of Arrival (TOA) based indoor positioning systems are considered to be the high precision alternatives to other positioning systems employing received signal strength (RSS) or Angle of Arrival (AOA). However, such systems suffer from the blockage of the direct path (DP) and occurrence of undetected direct path (UDP) condition and their performance degrades drastically in such conditions. Erroneous detection of the other multipath components (MPCs) as DP, which is the indicator of the true distance between the transmitter and the receiver, will introduce substantial ranging and localization errors into the system. Therefore, identification of the occurrence of large ranging errors and absence of DP from the received radio signal is our subsequent concern. After identification, the second step is to remedy the ranging errors in such UDP conditions. In this paper we present a methodology, based on an application of artificial neural network (ANN) design, to identify the UDP conditions and mitigate the ranging error using statistics extracted from wideband frequency domain indoor measurements conducted in a typical office building. The system bandwidth used for the frequency domain measurement was 500 MHz centered around 1 GHz.

Location awareness for everyday smart computing

Rapid advances in the area of digital systems is an enabler for ubiquitous computing making devices smaller and smarter and paving the way for an interconnected digital world. The most influential digital technology that has changed the lives of so many people and made the interconnected world a possibility is undoubtedly the development of wireless cellular communications. In the early stages of cellular wireless telephony development there was only one idea in mind: communication between people without the need for wires. The hexagonal cellular principles laid out by Ring and Young at AT&T Bell Labs in 1947 were the initial steps towards realizing the goal of ubiquitous communication. Global cellular networks, now serving more than 4 billion people around the world is a true testimony to the visions of many computer pioneers such as Mark Weiser, past CTO of Xerox PARC, who first coined the term, ubiquitous. Thus internetworking of “things” gains particular importance with the wide availability of smart devices capable of performing tasks well beyond voice communication. One key component of ubiquitous computing is “location awareness” and is a field of intensive research for various applications requiring varying levels of accuracy. This paper briefly discusses the basics of common location technologies and focuses on cellular based positioning and its practicality for location awareness for everyday smart gadgets.

A Study of the Effects of Reference Point Density on Toa-Based UWB Indoor Positioning Systems

The performance of ultra-wideband (UWB) indoor positioning systems based on time of arrival (TOA) techniques is generally affected by the density of reference points (RPs), as well as undetected direct path (UDP) conditions. For a fixed number of reference points (RPs), the performance of some indoor positioning algorithms tends to degrade as the size of the area is increased, i.e. the RP density is decreased. In this paper, we evaluate the effects of RP density on the performance of different positioning algorithms in the presence of empirical distance measurement error (DME) models derived from UWB measurements in typical indoor environments. We then present functional relationships between RP density and positioning mean-square error (MSE) for these algorithms. These relationships can be used for more effective indoor positioning system design and deployment. Finally, we investigate the effects of bandwidth with respect to improving the performance of these algorithms

A New Ray Optical Statistical Model for Multipath Characteristics Pertinent to Indoor Geolocation

A ray optics based statistical multipath channel model has been developed to describe the indoor multipath propagation including the important parameters such as path gain, time-of-arrival, angle-of-arrival and number of multipath components. Development of such a model is crucial for performance evaluation of indoor positioning systems. Based on a comprehensive ray-tracing database obtained on the 3rd floor of Atwater Kent Laboratories at Worcester Polytechnic Institute, multipath time-of-arrival relative to first arrival has been modeled using a lognormal distribution, angle-of-arrival has been modeled as a 3 peak doppler-like probability density function relative to the transmitter-receiver interconnection line. Path gains have been modeled using the information obtained from path arrival along with statistical object interactions such as reflection and transmission, and the number of multipath components has been modeled by a distance dependent exponential function.

Path Persistency for High Precision Ranging in Different Building Architectures

Indoor positioning systems employing high bandwidth (up to ultra-wideband) time-of-arrival methods have attracted a lot of attention recently owing to their potential for precise localization and tracking of personnel or assets inside buildings where the GPS systems fail to operate. However, these systems suffer heavily due to severe multipath in indoor areas, leading to large positioning errors since direct path cannot be detected due to obstructions. This in turn leads to a condition that we call undetected-direct-path condition. An effective solution would be to exploit other multipath components to aid in the localization by analyzing their persistency in indoor areas. Tracking the mobile station in the absence of direct path is dependent on the internal structure of the building. We present how this method can be applied in different buildings to aid in the time- of-arrival based ultra-wideband localization and we propose a methodology to analyze the effect of different parameters of a building on the statistical behavior of persistency.