Nima Alam

A DSRC Doppler-Based Cooperative Positioning Enhancement for Vehicular Networks With GPS Availability

Position information, as a fundamental element for many of the modern vehicle-based logistic applications, is comprehensively provided by Global Navigation Satellite Systems (GNSS) such as the Global Positioning System (GPS). A variety of applications, including navigation and intelligent transpiration systems, require position data with certain accuracy. However, the shortcomings of GNSS, such as limited accuracy and availability, have been a motivation for recently emerging Cooperative Positioning (CP) methods based on vehicle-vehicle and vehicle-infrastructure communications. The majority of earlier CP methods assume the availability of distances between the participating nodes as a main parameter, using common techniques of radio ranging such as the Received Signal Strength (RSS), Time of Arrival (TOA), and Time Difference of Arrival (TDOA). However, the feasibility of these radio-ranging methods in the harsh environment of vehicular networks is questionable. Avoiding the radio-ranging challenges, in this paper, a new CP method is presented to improve the GPS estimates using internode range-rates based on the Doppler shift of the carrier of Dedicated Short-Range Communications (DSRC) signals, which is the nominated medium for vehicular communication. Depending on the speed of the participating vehicles and traffic intensity, improvement of up to 48% over the GPS accuracy is achieved. Because the Doppler effect is used, relative mobility of the nodes, which is generally a challenge for radio-ranging techniques, is a requirement for the proposed method, making it a more suitable solution for vehicular applications. Addressing the viability of the proposed technique, Doppler-based range-rating is verified in practice using DSRC transceivers. One section of highway is surveyed and modeled for simulation. In addition, GPS estimates are provided by feeding GPS signals, generated by a GPS signal generator, to a real GPS receiver.

Cooperative Positioning for Vehicular Networks: Facts and Future

Intelligent transportation systems (ITSs) are increasingly being considered to mitigate the impacts of road transportation, including road injuries, energy waste, and environmental pollution. Vehicular positioning is a fundamental part of many ITS applications. Although global navigation satellite systems (GNSSs), e.g., Global Positioning System (GPS), are applicable for navigation and fleet management, the accuracy and availability of GNSSs do not meet the requirements for some applications, including collision avoidance or lane-level positioning. Cooperative positioning (CP) based on vehicular communications is an approach to tackle these shortcomings. The applicability of vehicular CP techniques proposed in the literature is questionable due to viability issues, including internode distance estimation, which is an important part of many CP techniques. Conventional CP systems such as differential GPS (DGPS) and other augmentation systems are also effectively incapable of addressing the given ITS applications. In this paper, modern and conventional CP systems are discussed, and the viability of radio ranging/range rating and constraints of vehicular communications as main pieces of modern CP systems are investigated. The general performance boundaries for modern CP systems are explained, as is the gap existing between the positioning accuracy required for crucial ITS applications and what modern CP can provide. This is followed by introduction of a novel trend for vehicular CP research, which is a potential reliable solution using a modified concept of real-time kinematic (RTK) GPSs for vehicular environments.

Relative Positioning Enhancement in VANETs: A Tight Integration Approach

Position information is a fundamental requirement for many vehicular applications such as navigation, intelligent transportation systems (ITSs), collision avoidance, and location-based services (LBSs). Relative positioning is effective for many applications, including collision avoidance and LBSs. Although Global Navigation Satellite Systems (GNSSs) can be used for absolute or relative positioning, the level of accuracy does not meet the requirements of many applications. Cooperative positioning (CP) techniques, fusing data from different sources, can be used to improve the performance of absolute or relative positioning in a vehicular ad hoc network (VANET). VANET CP systems are mostly based on radio ranging, which is not viable, despite being assumed in much of the literature. Considering this and emerging vehicular communication technologies, a CP method is presented to improve the relative positioning between two vehicles within a VANET, fusing the available low-level Global Positioning System (GPS) data. The proposed method depends on no radio ranging technique. The performance of the proposed method is verified by analytical and experimental results. Although the principles of the proposed method are similar to those of differential solutions such as differential GPS (DGPS), the proposed technique outperforms DGPS with about 37% and 45% enhancement in accuracy and precision of relative positioning, respectively.

Improving Cooperative Positioning for Vehicular Networks

Cooperative positioning (CP) can potentially improve the accuracy of vehicle location information, which is vital for several road safety applications. Although concepts of CP have been introduced, the efficiency of CP under real-world vehicular communication constraints is largely unknown. Our simulations reveal that the frequent exchange of large amounts of range information required by existing CP schemes not only increases the packet collision rate of the vehicular network but reduces the effectiveness of the CP as well. To address this issue, we propose simple easily deployable protocol improvements in terms of utilizing as much range information as possible, reducing range broadcasts by piggybacking, compressing the range information, tuning the broadcast frequency, and combining multiple packets using network coding. Our results demonstrate that, even under dense traffic conditions, these protocol improvements achieve a twofold reduction in packet loss rates and increase the positioning accuracy of CP by 40%.

Dynamic Path Loss Exponent and Distance Estimation in a Vehicular Network Using Doppler Effect and Received Signal Strength

Global Navigation Satellite Systems (GNSS) can be used for navigation purposes in vehicular environments. However, the limited accuracy of GNSS makes it unsuitable for applications such as vehicle collision avoidance. Improving the positioning accuracy in vehicular networks, Cooperative Positioning (CP) algorithms have emerged. CP algorithms are based on data communication among vehicles and estimation of the distance between the nodes of the network. Among the variety of radio ranging techniques, Received Signal Strength (RSS) is very popular due to its simplicity and lower cost compared to other methods like Time of Arrival (TOA), and Time Difference of Arrival (TDOA). The main drawback of RSS- based ranging is its inaccuracy, which mostly originates from the uncertainty of the path loss exponent. Without knowing the environment path loss exponent, which is a time-varying parameter in the mobile networks, RSS is effectively useless for distance estimation. There are many approaches and techniques proposed in the literature for dynamic estimation of the path loss exponent within a certain environment. Most of these methods are not functional for mobile applications or their efficiency decreases dramatically with increasing mobility of the nodes. In this paper, we propose a method for dynamic estimation of the path loss exponent and distance based on the Doppler Effect and RSS. Since this method is fundamentally based on the Doppler Effect, it can be implemented within networks with mobile nodes. The higher the mobility of the nodes, the better performance of the proposed technique. This contribution is important because vehicles will be equipped with Dedicated Short Range Communication (DSRC) in the near future.

An Instantaneous Lane-Level Positioning Using DSRC Carrier Frequency Offset

A novel approach is proposed to enable vehicles to estimate their instantaneous position with lane-level accuracy, which is not achievable using Global Navigation Satellite Systems (GNSSs). This system can be used to enhance position-based applications such as Intelligent Transportation Systems (ITSs), including navigation and lane-level traffic guidance and warning. The system uses the carrier frequency offset (CFO) of the dedicated short-range communication (DSRC) signal, broadcast by two infrastructure beacons. The main advantages of the proposed method over other potential technologies such as radio-frequency identification (RFID) and buried loops are its simpler required infrastructure and functionality using vehicular communication platforms. Analysis of the proposed technique indicates acceptable reliability and performance. Empirical test results confirm the viability of the method.

A modified multidimensional scaling with embedded particle filter algorithm for cooperative positioning of vehicular networks

Vehicular communication technologies are on their way to be recognized as staples of modern societies. One important challenge to safety-related applications of vehicular communication is provision of semi-precise positioning. Cooperative positioning is proposed for that purpose, and of course from research point of view is very attractive. From the practical point of view the attractiveness of cooperative positioning lies in its independence from any major additional infrastructure other than the vehicular communication systems. This paper introduces a new positioning algorithm for localization of mobile networks, in general, that applies directly to vehicular networks. The algorithm is based on the well known multidimensional algorithm and shows impressive performance compared to its counterparts in the vehicular positioning literature.

Cooperative Inertial Navigation for GNSS-Challenged Vehicular Environments

Cooperative positioning (CP) is an approach for positioning and/or positioning enhancement among a number of participants, which communicate and fuse their position-related information. Due to the shortcomings of Global Navigation Satellite Systems (GNSSs), modern CP approaches are considered for improving vehicular positioning where the GNSS cannot address the requirements of the specific applications such as collision avoidance or lane-level positioning. An inertial navigation system (INS) has not been considered for CP in the literature. The hybrid INS/GNSS methods used for positioning enhancement in standalone nodes cannot be classified as CP because the position-related data are not communicated between at least two independent entities. In this paper, we present a novel CP technique to improve INS-based positioning in vehicular networks. This cooperative inertial navigation (CIN) method can be used to enhance INS-based positioning in difficult GNSS environments, such as in very dense urban areas and tunnels. In the CIN method that is proposed, vehicles communicate their inertial measurement unit (IMU) and INS-based position data with oncoming vehicles traveling in the opposite direction. Each vehicle fuses the received data with those locally observed and the carrier frequency offset (CFO) of the received packets to improve the accuracy of its position estimates. The proposed method is analyzed using simulations and is also experimentally verified. The experimental results show up to 72% improvement in positioning over the standalone INS-based method.

An INS-Aided Tight Integration Approach for Relative Positioning Enhancement in VANETs

Relative positioning among vehicles is a fundamental parameter for advanced applications of intelligent transportation systems such as collision avoidance and road safety. However, the level of positioning accuracy achievable using Global Navigation Satellite Systems does not meet the requirements of these applications. Cooperative positioning (CP) techniques can be used for improving the performance of absolute or relative positioning in a vehicular ad hoc network (VANET). The tight integration of Global Positioning System (GPS) data among communicating vehicles has already been introduced by the authors as a tight CP approach with specific advantages over differential GPS (DGPS) for relative positioning. In this paper, we propose an enhanced tight CP technique adding low-cost inertial navigation sensors and GPS Doppler shifts. Based on analytical and experimental results, the new method outperforms its predecessor and DGPS by 10% and 24%, respectively.

A DSRC-Based Traffic Flow Monitoring and Lane Detection System

Intelligent Transportation Systems (ITS) are developing to increase transportation efficiency and mitigate its negative impacts on society. Traffic flow monitoring, traffic guidance and traffic signal control are some of ITS applications relying on vehicle passage rate in the streets. There are already some conventional techniques for vehicle counting. In this work a novel method is proposed for vehicle passage and lane detection based on the relative acceleration between the vehicle and two anchor nodes which broadcast packets periodically using Dedicated Short Range Communication (DSRC), the nominated medium for vehicle-vehicle and vehicle-infrastructure communication. Depending on the speed of the vehicle, the performance of the proposed method is 95% or higher.