Ultrawideband Radar Processing Using Channel Information from Communication Hardware Literature Review by Bryan WestcottAbstract Channel information provided by impulse-radio ultrawideband communications is used in radar applications requiring information on the surrounding physical environment. Many algorithms used by sonar are applied to this problem due to the similarities of the technology. Echolocation and map-building algorithms are particularly relevant, but the problem is significantly different since directionality information is not available. The use of other communications devices as distributed sources provides opportunities for unique algorithms. I. INTRODUCTION Emerging ultrawideband technology potentially offers hundred-megabit-per-second data rates and sub-centimeter radar resolution [1]. The baseband filtering and receiver designs are the same, and both applications use information on the arrival times of all incoming pulses. Radar applications use the arrival time of each pulse to determine distances to reflecting objects, whereas communications use the arrival times to set up correlators to collect signal energy. Since the majority of work is already being performed by the communication hardware, this literature survey evaluates the applications of radar signal processing algorithms to channel information from that hardware in order to obtain useful information about the surrounding physical environment. Location-based services, such as emergency-911, are already proving popular in the cellular industry [2]. GPS is limited by accuracy and does not work well indoors, and would benefit from complementary location algorithms [3]. Location-based security is a great potential application to prevent wireless networks from being accessed outside of a building [4]. These applications and others could be implemented, and provide useful location-based services to complement ubiquitous data connectivity.II. BACKGROUND A. Implementation Issues While one could easily add extra hardware and antennas to accomplish these tasks, the point of this survey is to only use communication hardware available, which saves the cost, space and power of extra hardware. The only required modification is to make information from channel estimation available for signal processing. Rake receivers are common with CDMA and impulse-radio ultrawideband technology [1], and could be a great source of this timing information. Successive interference cancellation (SIC) is one of the few practical multiuser detection technologies [5]. This technology has potential for future ad-hoc network design, which is itself a natural option for range-limited ultrawideband (UWB) communication hardware, and is also a great source since multipath of all nearest users is decoded as well to increase capacity [6]. The spatial diversity provided by Multi-Input Multi-Output (MIMO) approaches effectively acts as an antenna array for more accurate radar processing. Fortunately, the IEEE 802.15 TG4a Wireless Personal Area Network Task Group is working on many of the practical issues involved with using ultrawideband communication hardware for radar applications, including the synchronization and hardware modifications required [7]. This work is based on the Multi-Band Orthogonal Frequency Division Multiplexing Alliance (MBOA) ultrawideband implementation, but much of the work could be adapted to the impulse-radio implementation. The goal of this working group is to make radar processing possible from the communication hardware, allowing future applications to be entirely software issues [8]. B. Related Technology Due to the similar resolution and baseband processing of ultrawideband radar and sonar, much of the work done in sonar signal processing can be applied to this technology. Thetechnologies are so similar that one ultrasonic positioning system by Kazys [9] proposed the use of orthogonal CDMA signals with cyclic deconvolution to process all reflections by all transmitters, which is essentially identical to SIC for impulse radio ultrawideband communications. Many algorithms rely on specular propagation, which occurs in both electromagnetic and acoustic signals when the wavelength is much less than the dimensions of the major features of the environment. In specular propagation walls have mirror-like reflection, right-angle corners reflect back to all directions and edges will diffract back to all directions. Echolocation is a particularly useful area of research, commonly used in robot navigation, where geometric information about the local environment is obtained by measuring the time of flight of ultrasonic pulses [10] and dates back to the analysis of biological echolocation used by bats [11]. While most applications use sensor arrays to calculate the direction of a range measurement, those based on position information alone are more applicable to the single-antenna ultrawideband radar case, since direction of arrival cannot be measured. The impulse response of a wireless channel determines the arrival time of all multipath (similar to acoustic echoes), which must then be processed to obtain useful information about the environment. III. RELOCATION ALGORITHMS The task of relocation involves fitting the current data to a position on a known map of an environment. The first approach by Lim and Leonard [12] uses range information alone provided by time-of-flight calculations, and is most relevant to the current situation as no information is available on the direction of the range measurements. In this algorithm the pair-wise interpretation algorithm of Grimson and Lozano-Perez [13] is applied to every combination of a pair of objects and a pair of range measurements. Thiswill produce one, two or zero possible positions for each pair. One solution corresponds to the intersection of two lines drawn normal to two planar objects, two solutions corresponds to one or both of the objects being a diffracting edge or corner, and no solution corresponds to objects that cannot match a measurement. Multiple
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