Juan Chóliz

A Framework for UWB-Based Communication and Location Tracking Systems for Wireless Sensor Networks

Ultra wideband (UWB) radio technology is nowadays one of the most promising technologies for medium-short range communications. It has a wide range of applications including Wireless Sensor Networks (WSN) with simultaneous data transmission and location tracking. The combination of location and data transmission is important in order to increase flexibility and reduce the cost and complexity of the system deployment. In this scenario, accuracy is not the only evaluation criteria, but also the amount of resources associated to the location service, as it has an impact not only on the location capacity of the system but also on the sensor data transmission capacity. Although several studies can be found in the literature addressing UWB-based localization, these studies mainly focus on distance estimation and position calculation algorithms. Practical aspects such as the design of the functional architecture, the procedure for the transmission of the associated information between the different elements of the system, and the need of tracking multiple terminals simultaneously in various application scenarios, are generally omitted. This paper provides a complete system level evaluation of a UWB-based communication and location system for Wireless Sensor Networks, including aspects such as UWB-based ranging, tracking algorithms, latency, target mobility and MAC layer design. With this purpose, a custom simulator has been developed, and results with real UWB equipment are presented too.

Accurate indoor wireless location with IR UWB systems a performance evaluation of joint receiver structures and TOA based mechanism

Impulse radio (IR) ultra wide-band (UWB) is one of the most promising wireless technologies to develop both indoor and outdoor location and tracking applications. Due to its high bandwidth and short duration pulses, UWB potentially allows a great accuracy in distance measurements based on time of arrival (TOA) estimations. The main objective of this paper is to compare and to provide a qualitative and quantitative evaluation of different TOA-based distance estimation mechanisms joint to receiver architectures proposed for UWB systems. This comparison has been done in terms of accuracy and the effect of characteristic parameters of the transmitted signal, propagation conditions and signal-to-noise ratio has been analyzed. With this purpose a simulation tool has been developed, where the different receiver architectures, estimation mechanisms and channel models proposed on 802.15.4a have been implemented.

Comparison of Algorithms for UWB Indoor Location and Tracking Systems

With the popularity of navigation applications and the integration of GPS in user devices, location-awareness is becoming an essential feature demanded by users. Nevertheless, location-awareness in indoor environments is still limited by the inability of GPS to operate indoors. With a centimeter-level ranging resolution, Ultra-Wideband (UWB) is one of the most promising technologies to provide indoor location. Several location & tracking algorithms have been proposed in the literature to compute users position according to the estimated distances to some reference nodes, each one providing the best performance in certain conditions. Nevertheless, most of these proposals are evaluated under too specific or simplistic conditions that do not account realistically for the specific implications of the UWB-based distance estimation and the indoor environment. This paper aims to evaluate the performance of different location and tracking algorithms on a realistic indoor scenario and with a specific UWB indoor ranging model, analyzing their advantages and drawbacks in relation to different conditions and system design parameters.

Evaluation of TOA estimation algorithms in UWB receivers

UWB technology is especially suitable for location and tracking applications due to its high bandwidth, which allows a great accuracy on Time Of Arrival (TOA) estimation. Nevertheless, the achievement of this goal on multipath environments requires the design of efficient detection algorithms. The main objective of this paper is to compare and to provide a qualitative and quantitative evaluation of different TOA-based distance estimation mechanisms joint to receiver architectures proposed for UWB systems. This comparison has been done in terms of accuracy and the effect of characteristic parameters of the transmitted signal, propagation conditions and signal-to-noise ratio has been analyzed. With this purpose a simulation tool has been developed and the different receiver architectures and estimation mechanisms have been implemented, as well as the different channel models proposed on 802.15.4a.

Evaluation of algorithms for UWB indoor tracking

Ultra-Wideband (UWB) stands out as one of the most promising technologies for the development of indoor location & tracking systems, providing very precise time of arrival measurement and consequently centimeter-level resolution in distance estimation. Once the distances to multiple reference nodes are estimated, several location & tracking algorithms can be used to compute users position. Position calculation is a widely studied topic, and many different methods have been proposed in the literature and evaluated under different conditions. Nevertheless, evaluation scenarios are usually generic and too simplistic. The rigorous evaluation of location & tracking algorithms should take into account the specific error distribution of UWB-based distance estimation and the implications of indoor tracking scenarios, such as users mobility, the number of reference nodes and the distance between them. The objective of this paper is to provide a realistic evaluation of the performance of different location & tracking algorithms (trilateration, least square — multidimensional scaling, extended Kalman filter and particle filter) in indoor environments using a specific UWB-based ranging model to characterize the distribution of distance estimation error.

Coexistence of MB-OFDM UWB with Impulse Radio UWB and other radio systems

The level of interference caused by Ultra-Wideband (UWB) systems in current radio services has been widely studied, both theoretically and with measurement campaigns, although most of them focus on pulse-based UWB systems. This paper presents experimental results on the coexistence of Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) UWB systems when they are working in close proximity to other radio technologies such as UMTS, WiMAX, LTE, WiFi, Bluetooth and ZigBee. As restrictive spectrum masks have been imposed to UWB, no degradation is detected on those systems except for WiMAX as it operates in the same frequency band. On the other hand, MB-OFDM may be disturbed even by systems operating in a different frequency band due to spurious out-of-band emissions. The coexistence between MB-OFDM and Impulse Radio (IR) UWB systems is also addressed and experimental results are presented showing that IR UWB may interfere with MB-OFDM UWB systems causing a degradation on Packet Error Rate, which is limited due to the low activity factor of IR UWB.

Evaluation of cooperative techniques in an interworking UWB-UMTS platform

Low power spectral density of UWB (ultra wideband) systems allows spectrum reutilization, but harmless coexistence with other radio systems must be guaranteed. Regulation establishes limits to emitted power spectral density necessary to assure that UWB devices do not interfere with any other radio devices nearby. But coexistence between UWB and other radio service collocated in the same device must be assured by the manufacturer, which is usually a design challenge. This paper presents cooperative techniques as an alternative to improve protection over possible victim services when UWB and other radio service are collocated in the same device. Different detection and protection methods are proposed and implemented on a UWB/UMTS interworking platform. Possible degradation on UWB link due to protection methods is evaluated and the whole platform performance is tested through a measurement campaign.

Coexistence and interworking between UMTS and UWB: a performance evaluation of a UMTS/UWB interoperability platform

Ultra wideband (UWB) radio technology is nowadays one of the most promising technologies for medium-short range communications. It has a wide range of applications including high data rate systems and low data rate systems with location and tracking. The interoperation of UWB with Wide Area Networks (WAN) technologies is very interesting in order to extend the scope of UWB applications, but harmless coexistence between them must be assured. Extensive research is being focused to the development of efficient mitigation techniques and the collaboration between both radio services is an interesting solution when UWB is collocated in the same device with other radio technology. In this paper a UMTS/UWB interworking platform is presented, which allows remote monitoring of a UWB body area network for medical applications. The coexistence between UMTS and UWB is evaluated and cooperative mitigation techniques are proposed and implemented in the platform.

UWB in Heterogeneous Access Networks: location-aware services

Mobile position-aware systems combined with modern wireless technologies are getting more and more important and everyone seems to realize that the market is a high potential industry. For mobile network it is a way to differentiate many mobile applications and services from PC (Personal Computer) applications and wired Internet services. Using mobile devices, LBSs (Location-Based Service) leverage a user-s physical location to provide enhanced services and experiences. LBSs enable a range of applications and services, such as navigation and mobile map services, workforce tracking, finding points of interest, and obtaining weather information. Nowadays most of the applications are based on the GPS (Global Positioning System). However, the availability of indoor location, which is not covered by satellite-based systems, and fast time to position fix is more and more needed for LBSs. This fact opens the door to UWB (Ultra Wide band) as a key technology to be taken into account in the development of novel and promising locationaware services, due to its intrinsic features for providing accurate indoor localization. Indoor location provided by UWB combined with cellular networks such as HSPA (High Speed Packet Access) or WiMAX (Worldwide Interoperability for Microwave Access) will open the door to a large set of new location-aware services.

Architectures for location data acquisition and distribution in UWB indoor tracking systems

Ultra-wideband radio technology is one of the most promising technologies for indoor Location & Tracking applications, allowing the development of combined data transmission and location networks. But UWB faces important challenges due to its short range, which entails the need of a high number of fixed reference nodes, and limited data rate, which limits the amount of mobile nodes that can be tracked and the frequency of position updates. Therefore, suitable network architectures must be used and the amount of resources used for localization must be carefully evaluated. In this paper, different tracking system architectures are proposed and evaluated, as well as different strategies for the acquisition and distribution of location information. Other design parameters as the number of anchor nodes used for location, the anchor selection method and the position update rate are also discussed.