Radio Design and Performance Analysis of Multi Carrier-Ultrawideband (MC-UWB) Positioning System

This paper continues discussing the design and development of an advanced integrated wireless system discussed in papers [1, 2, 3] that can be used by emergency responders and health care providers to communicate useful and critical information whenever and wherever they need. The design of a Multi Carrier signal structure and signal processing algorithm that applies a matrix-decomposition-based Multi Carrier range recovery algorithm to obtain a super resolution location solution is discussed in [1], system performance aspects of the Multi Carrier  Ultrawideband (MC-UWB) approach to precise positioning are presented in [2]. The design and performance evaluation of the proposed RF front end receiver structure being developed for precision location system using this Multi Carrier technique is discussed in [3]. This paper presents the recent developments and current progress of the precise position location system, focuses on improvements in the previously presented RF front end structure [3] and describes the design of the required digital back end of the receiver structure. The design and performance of the entire receiver structure and a high level overview of the transmitter structure are presented in this paper. The designed prototype system is very well suited for real time position location and tracking of first responders and emergency rescuers, within one meter accuracy. INTRODUCTION: PRECISE POSITIONING SYSTEM The advanced integrated wireless devices of the future should be capable of precisely locating and tracking the user and can assist the user with communications and incident management operations in the field in real-time. Such an advanced personnel location and navigation system can be used in various applications and this paper will focus on the development of a precise positioning system for first responders in emergency situations. Extensions to the system discussed in this paper will allow sending instructions about future moves to the first responder and sending feedback about the physiological status of the first responder to a command center. Such an advanced system should be small in size and rugged enough to survive in extreme environment, should have good accuracy under zero visibility conditions. The advanced integrated system to be designed should be such that it is capable of location tracking and at the same time be capable of monitoring and transmitting physiological information like temperature, heart rate, blood oxygen level and other statistics, such as ambient temperature and breathing air level, related to the first responder. Finally the system should be reliable and simple to use. Figure 1 shows the high level application overview of the envisioned precise positioning system. The emergency vehicles and personnel carry an ad hoc MC-UWB based device. The signals received at the vehicles are used to calculate the relative position of the firefighters in and around the building. The location of the firefighter is displayed at a command and control display from where the firefighter is provided emergency exit guidance and information for locating firefighters in trouble. The two important design issues while developing such a system are precise location estimate and high data rate requirements in presence of a high multipath environment. Ultrawideband signal structures have been widely studied as an option for precise position location [4, 5]. Even though short pulse widths of UWB signal offer the advantage that multipath components can be resolved directly, it is not a suitable due to interference to existing systems. Figure 1: Precise Positioning System Application Overview The most important piece of such a system is clearly a ability to track and locate the emergency personnel carrying wireless devices with high precision in a highmultipath environment and real-time field operations. Many solutions have been proposed for precise positioning systems using GPS [6, 7]. However indoor accuracy limitations, multipath effects and low signal power levels make GPS not a suitable solution for our applications, where the target indoor location accuracy is one meter or less. The signal processing algorithms used to extract position from Multi Carrier signal were proposed earlier [1, 2]. The Multi Carrier signal structure used is an Orthogonal Frequency Domain Multiplexed (OFDM) signal consisting of many sinusoidal subcarriers. Such a signal structure has a major advantage over the ultrawideband signals that are often proposed for performing precision location in high multipath environments as it is easily adapted to conform to existing spectral allocations. This technique is also well suited for use on ad hoc wireless networks, allowing the precision location of wireless nodes with respect to one another. MC-UWB SIGNAL FOR PRECISE POSITIONING AND RECEIVER STRUCTURE Multi Carrier (MC) techniques can efficiently combat frequency selective fading. Such robustness in presence of frequency selective fading is very useful, especially for applications involving high data rate. One of the problems with a single carrier signal structure is that as the symbol rate increases the symbol interval becomes shorter than the delay spread. A Multi Carrier signal structure solves this problem by decreasing the symbol rate and increasing the number of carriers. The basic idea behind the OFDM signal is to take a signal and send it over multiple low rate carriers instead of a single high rate carrier. An OFDM signal consists of many sinusoidal subcarriers. These subcarriers are orthogonal and therefore do not overlap with each other. The advantages of using a Multi Carrier signal structure are listed below: Improved spectral efficiency Robust in fading environment Simplified equalization needed High data rate can be achieved Signal generation is simple The structure of the OFDM signal proposed is of the form: