Requirements of an OFDMA Pseudolite Indoor Geolocation System

Transcription

1 Requirements of an OFDMA Pseudolite Indoor Geolocation System Ilir F. Progri, Member ION, Giftet Inc., Pomona, CA; Matthew C. Bromberg, Elected Engineering, MA; William R. Michalson, Member ION, Worcester Polytechnic Institute, Worcester, MA; Jinling Wang, University of New South Wales, Australia; R. James Duckworth, Worcester Polytechnic Institute, Worcester, MA; and John Lavrakas, President of ION, Advanced Research Corp., Newport, OR BIOGRAPHY Dr. Ilir F. Progri is the President and CEO of Giftet Inc. a privately held company for developing Global Navigation Software, and Web Solutions (Giftet). Dr. Progri s eleven year career in GPS consists of all aspects of signals and system specifications, simulation, software development and implementation of significant new capabilities in GPS and indoor geolocation systems. Dr. Progri has led research and development engineering projects for over eight years. He has over fifty published papers and one patent in all aspects of geolocation systems. Ilir has received over thirty citations from experts, researchers, and scientists of US, Canada, Australia, Finland, France, Germany, UK, and China etc. Dr. Progri is a member of ION, AIG, Associate Fellow member of RIN, and a senior member of the IEEE, Com Soc, and AESS. Ilir received his Doctor of Philosophy (Ph.D.) degree and Master s of Science (MS) degree in Electrical Engineering from Worcester Polytechnic Institute (WPI), Worcester, Massachusetts in May 23 and in May 1997 respectively. He received his Diploma of Engineer Degree in Electrical Engineering from the Polytechnic University of Tirana (PUT), Albania in July Dr. Matthew C. Bromberg is the President of Elected Engineering. For the last 1 years Dr. Bromberg has been involved in the research and development of array processing algorithms for reuse enhancement for wireless communication systems and for interference mitigation for both commercial and military applications. Dr. Bromberg has several patents and papers in the wireless communications and signal processing area. Dr. William R. Michalson is a Professor in the ECE Department at the Worcester Polytechnic Institute where he performs research and teaches in the areas of navigation, communications and computer system design. He supervises the WPI Center for Advanced Integrated Radio Navigation (CAIRN) and has been involved with navigation projects for both civilian and military applications with a special emphasis on navigation and communication techniques in indoor, underground or otherwise GPS-deprived situations. Dr. Jinling Wang is a senior lecturer in the School of Surveying & Spatial Information System at the University of New South Wales. He is a member of the editorial board for the international journal GPS SOLUTIONS, and Chairman of the international study group on pseudolite applications in positioning and navigation within the International Association of Geodesy's Commission 4. He was 24 President of the International Association of Chinese Professionals in Global Positioning Systems (CPGPS), He holds a PhD in GPS/Geodesy from Curtin University of Technology, Australia. Dr. R. James Duckworth is an Associate Professor in the Electrical and Computer Engineering department at WPI. He obtained his PhD in parallel processing from the University of Nottingham in England. He joined WPI in Duckworth teaches undergraduate and graduate course in computer engineering focusing on microprocessor and digital system design, including using VHDL and Verilog for synthesis and modeling. His main research area is embedded system design. He is a member of the ION, IEE, IEEE, and BCS and is a Chartered Engineer of the Engineering Council of the UK. Mr. John Lavrakas is a leading authority in the field Global Positioning System technology. In addition to professional consulting services to clients, Mr. Lavrakas has spoken on GPS and its applications at national conferences, published articles on GPS, and served as an expert consultant to magazines and newspapers on GPS matters over the past 15 years. Mr. Lavrakas has twentyseven years experience in GPS, including providing engineering support in the development and maintenance of the GPS Control Segment headquartered at Schriever Air Force Base in Colorado, development of an Air Force GPS receiver for range applications, activation and operation of the GPS Operations Center, and numerous projects involving defining and assessing civilian needs for satellite navigation. Mr. Lavrakas is also the current President of the Institute of Navigation. ABSTRACT In this paper, the requirements of an Orthogonal Frequency Division Multiple Access (OFDMA) pseudolite indoor geolocation system are proposed. Previously we have proposed an OFDMA pseudolite indoor geolocation system using a direct signal processing approach that operates at 3dB signal to noise ratio (SNR) with no multipath. 1821

2 The requirements of an OFDMA pseudolite indoor geolocation system consists primarily of: 1. OFDMA general system requirements 2. OFDMA pseudolite (or transmitter) requirements 3. OFDMA receiver requirements 4. OFDMA financial, business plan requirements. First, as far as general system requirements are concerned, the geolocation information for each pseudolite consists of the pseudolite s position and time and the ability of the system to perform distance measurement under severe multipath conditions which is typical indoors. Second, OFDMA pseudolite requirements concern the signal design (or structure), signal modulation, power levels etc. For each pseudolite this information is binary encoded data at a symbol rate of 1 KHz. The encoded geolocation signal is modulated on the corresponding [ ] MHz carrier signal via a Frequency Division Multiple Access (FDMA) modulator to mitigate cross-channel interference encountered in an indoor geolocation environment. The Orthogonal Frequency Division Multiplexed (OFDM) signal is then used to provide distance information. Four (4) transmitters are simulated to enable a geolocation estimate on the receiver. Third, the receiver consists of four channels, each one of which is designated to a single transmitter. On each receiving channel the received signal is down-converted, demodulated and decoded. Four distance estimates are used in a Least Squares filter to provide an estimate of the receiver location and time. We have added the ability to perform distance measurement; we have analyzed the effect of the transmitter stability on the position accuracy; we have assessed the effects of the transmitter and receiver oscillator drift (short term stability) on positioning accuracy; we are investigating techniques for detecting an extremely weak LOS signal in the presence of severe multipath; and finally, we are studying techniques for maintaining lock on the LOS signal in the presence of severe multipath; i.e., to enable a high sensitivity receiver. Fourth, we have provided a summary of the financial or business plan requirements which include financial requirements for phase I, II, and III of the analysis, development, and mass production of the system. INTRODUCTION In this paper we describe the requirements for designing and developing an OFDMA pseudolite indoor geolocation system based on the work that we performed thus far in the signal design, unified channel model, and receiver acquisition and tracking algorithms [1-8]. Previously we proposed a 3-D OFDMA pseudolite indoor geolocation system a possible candidate for indoor geolocation [1, 5]. Our direct approach is good for SNR 3 db or higher. Ranging accuracy is better than 2 cm in a noisy environment [1, 5]. Moreover, initially we have proposed a global maximum likelihood GPS parameter estimation technique as a means of joint time and frequency estimation [6]. This technique appeared to provide an order of magnitude performance improvement against a sliding correlator GPS receiver [6]. We have also performed a study in the field a unified indoor geolocation channel model taking into consideration the actual channel models and measurements currently reported in the literature [1, 7]. The main objective of this paper is to apply the knowledge learned thus far and propose the requirements of an OFDMA indoor geolocation system. It is hoped that this approach will provide superior ranging performance under severe multipath Rayleigh fading channel and produce a high sensitivity anti-jam geolocation receiver. The paper is organized as follows: First we propose the general requirements of an OFMDA pseudolite indoor geolocation system which consists of at least four OFDMA transmitters, channel and at least one high sensitivity anti-jam OFDMA receiver. In this paper we have enhanced the OFDMA transmitter by considering in phase (I) and quadrature (Q) OFDMA signals. We have enhanced the receiver design by considering a maximum likelihood estimation technique or a global Bayesian using Mote Carlo Markov Chain (MCMC) integration for a high sensitivity signal acquisition and tracking for our complex OFDMA signal. We also consider a more realistic Rayleigh channel model. Further details of the Rayleigh channel parameters are disclosed in our previous paper included herein [7]. We consider a few simulation scenarios of an OFDMA pseudolite geolocation system. Second we discuss the financial and business plan requirements which include the financial and business plan requirements for phase I (analysis and simulation), II (initial development and testing), and III (mass production or product development). Fifth and last we provide some conclusions in respect to the general requirements for building an OFDMA indoor geolocation system. GENERAL REQUIREMENTS The general requirements of an OFDMA pseudolite indoor geolocation system include: (a) OFDMA pseudolite indoor geolocation system requirements, (b) OFDMA pseudolite (or transmitter) requirements, (c) OFDMA receiver requirements. First, let us discuss the general system requirements of an OFDMA pseudolite indoor geolocation system. 1822

3 6. OFDMA general system requirements The general system requirements of an OFDMA pseudolite indoor geolocation system consists of the following: 1. An OFDMA pseudolite indoor geolocation system must consist of at least 4 or more OFDMA pseudolites and one or more OFDMA receivers. 2. The coverage area of an OFDMA indoor geolocation system is that of a semi-sphere with radius R which is a system parameter. Typically R would be in the range of 1 m or several hundred meters. Because R is a system s parameter that it s going to define the requirements of transmitter s signal power and channel bandwidth. An example of an OFDMA pseudolite indoor geolocation system is illustrated in Figure 1. The purpose of this example is to illustrate a typical OFDMA pseudolite indoor geolocation system. These systems are becoming more and more prevalent given the need for precise geolocation inside buildings to protect civilians in cases such as parents guarding and monitoring their children, or doctors monitoring their patients in hospitals, or police or security forces monitoring their inmates etc. 3-D scenario of an OFDMA pseudolite indoor geolocation system TR2 11th floor 6 5 True receiver location Estimated receiver location TR1 TR3 4 OFDMA pseudolites should be located at the outside perimeter and at a reasonable height or the highest possible position of the building or complex buildings. 3 z (m) 3. Portability and flexibility are the desired in that the system should have the ability to reconfigure itself. TR4 Direction of movement An OFDMA system should have the ability to perform distance measurement via time of arrival measurement (TOA) as illustrated in [1, 4, and 5]. 1st floor Starting point Under these conditions an OFDMA pseudolite indoor geolocation system should provide cm level 3-D position accuracy and cm/sec level velocity accuracy 99.9 % of the time y (m) Good signal area x (m) Figure 1: The 3-D scenario of an OFDMA pseudolite indoor geolocation system. 1.5 receiver position error on x receiver position error on y receiver position error on z 1 error (m) time (s) Figure 2: A scenario of 4 transmitter 3-D OFDMA pseudolite indoor geolocation system can achieve 22.9 cm on x and y coordinates and 78.2 cm on z level positioning accuracy 99.9 % of the time (or 3.1 sigma value). ION GNSS 2th International Technical Meeting of the Satellite Division, 25-28, September 27, Fort Worth, TX 1823

4 This 3-D scenario of an OFDMA pseudolite indoor geolocation system contains 4 pseudolites placed on top of an 11 story building. The true OFDMA receiver location is shown in blue. The estimated OFDMA receiver location is shown in red. As indicated in Figure 2 the estimated OFDMA receiver location is within cm levels of the true receiver location 99.9 % of the time because a 4-transmitter 3-D OFDMA pseudolite indoor geolocation system can achieve 22.9 cm on x and y coordinates and 78.2 cm on z level positioning accuracy 99.9 % of the time (or 3.1 sigma value). OFDMA Pseudolite (or Transmitter) The requirements for designing an OFDMA pseudolite (or transmitter) include the following: 1. QPSK modulation for combining the I and Q channels and maintaining the time orthogonality between the I and Q channels. 2. Size of the pseudolite should be as small as possible using COTs. 3. Pseudolite should be powered up from a 12V/6~ Hz outlet via a power supply via an AC/DC converter. 4. The pseudolite signal power should range from 5 to 1 dbm at distances from 1 m to 1 m from the pseudolite in free space. In an actual indoor environment signal degradation will be higher, which could lead to actual pseudolite signal levels at 1 m to be 15 dbm. 5. Data rate of at least 1 khz or higher. 6. One of the pseudolites should be designated as the master pseudolite and all the others are designated as slave pseudolites. All the clock parameters of the other pseudolites should be referenced to the master pseudolite. 7. The user must be able to enter the pseudolite location via a GPS receiver having surveying the location of the pseudolite first. Some of the characteristics of an OFDMA pseudolite signal design are presented below. OFDMA signal design OFDMA is known as the combination of OFDM with FDMA. It takes advantage of the multidimensional orthogonality of the waveforms to enable a ranging signal separation and detection. The transmitted signal is a superposition of sinusoids (or tones) equally spaced in the frequency domain. A tone is defined as a narrowband signal whose bandwidth does not exceed 4 khz. This kind of signal structure is often referred to as OFDM owing to the exact orthogonality of its components over a fundamental period [4]. In this section we revisit the mathematics of the signal structure to take advantage of the new notation. Let s i (t) be the complex OFDM transmitted signal from the i-th transmitter before up-conversion, which is defined as K (1) s ( t) = exp[ j( ω t + φ )] i k= 1 k i where ω is the signal radian frequency, φ i is the initial phase, and the subscript k denotes the frequency component of the OFDM signal. Without loss of generality let assume that the initial phase of the signal is zero; i.e., φ i =. The signal spectrum of a typical OFDMA pseudolite indoor geolocation system is illustrated in Figure 3. As shown in Figure 3 there are 4 pseudolites signals equally spread in the frequency range of 81 to 419 MHz with center frequencies of 1, 2, 3 and 4 MHz. We have previously illustrated some of the benefits of this signal structure in [1, 4, and 5]. OFDMA receiver design requirements The requirements for an OFDMA receiver include but are not limited to: 1. A single or multiple antennae. Multiple antennae maybe desired if interference and jamming protection is required. 2. At least 8 db of receiver dynamic range is required to enable signal acquisition and tracking from all the pseudolites [7]. OFDMA Signal Spectrum FDMA Modulation 1 st TX 2 nd TX 3 rd TX 4 th TX OFDM Modulation f (MHz) f 1 f 2 f 3 f N f (MHz) Figure 3: The signal spectrum of an OFDMA pseudolite indoor geolocation system. 1824

5 3. If possible the receiver should perform the signal processing at the RF frequency via software defined radio. 4. The receiver should employ either a maximum likelihood parameter estimation or Bayesian Monte Carlo Markov Chain (MCMC) integration for joint signal acquisition and tracking [6, 8]. 5. The receiver should have the ability to de-spread, demodulate, decode and perform distance measurement between the receiver and all pseudolites taking into account the effect of transmitter clock stability on position accuracy; such effects will include the transmitter and receiver oscillator drift (short term stability) on positioning accuracy. 6. The signal processing on the receiver design should include techniques for detecting an extremely week LOS signal and for maintaining lock on the LOS signal in the presence of severe multipath, interference, and jamming. 7. Each receiver channel should have a status indicating the quality of the signal from the following list: Excellent (EX): ideal signal reception. No signal reflection or obstruction or db signal degradation which means that power loss is only due to transmitter receiver geometry; i.e., free space signal propagation. Very good (VG): very good signal reception, minor reflection or signal obstruction or 1dB signal degradation. Good (G): good signal reception, some reflection and signal obstruction or 2dB signal degradation. Average (AV): average signal reception due to reflections and signal obstructions or 3dB signal degradation. Poor (PO): poor signal reception due to significant reflections and signal obstructions or 4dB signal degradation. Very poor (VP): very poor signal reception due to extreme (or severe) signal reflections and signal obstructions or 5dB to 8 db signal degradation. Noise (NO): no signal is present or no useful signal information is available. OFDMA simulation requirements Simulation requirements of an OFDMA pseudolite indoor geolocation system are the following: 1. An OFDMA pseudolite indoor geolocation system must be fully and accurately simulated in MATLAB and Simulink. 2. Simulink and MATLAB simulation must include signal characteristics, OFDMA pseudolite design, OFDMA receiver design, and channel characteristics. 3. Simulation must allow portability and flexibility in that signal characteristics and channel parameters can be changed and altered to allow simulation of desired scenarios and be able to test all the desired signal levels on the software. 4. Examples of simulation requirements are provided in [1, 4, and 5] which may be reused and improved to include the added requirements of an OFDMA pseudolite indoor geolocation system. The methodology that we will follow will be illustrated further in Giftet Inc. software products which will be presented in the future ION meetings. An example of the Simulink implementation of an OFDMA pseudolite indoor geolocation system is illustrated in Figure 4. Figure 4 depicts the block diagram of an OFDMA pseudolite indoor geolocaiton system. As shown in Figure 4 a typical OFDMA system contains four OFDMA pseudolites (or transmitters). The output of each transmitter is the real and the imaginary component of the OFDMA signal. The real and imaginary components are combined together to form the complex OFDMA signal. Each OFDMA signal is applied to a Multipath Rayleigh Fading Channel the output of which is entered into a summing node. The output of the summing node is applied to an Additive White Gaussian Noise (AWGN) component whose output is applied to four receiver channels. The outputs of each receiver channel are applied to a delay detection and distance estimation whose outputs are entered into a multiplexer and then to a display. There are a couple of reasons why we have enhanced the OFDMA signal to contain a real and imaginary component in contrast to our previous OFDMA signal model which contained only a real component [9] as illustrated also in Figure 3. First, the enhanced OFDMA signal design is more robust than the previous OFDMA signal design [9] due to the added benefit of the orthogonality of both the I and Q signals. Second, a complex signal waveform enables simulation of a Rayleigh, Rician, and lognormal. 1825

6 Figure 5 depicts the multipath Rayleigh fading parameters for channel 1 (left) and channel 2 (right). Figure 6 depicts the multipath Rayleigh fading parameters for channel 3 (left) and channel 4 (right). For the purposes of the simulation we have selected a multipath Rayleigh fading channel with four paths; therefore, there the path delay vector will contain four values and the path gain vector will contain four gain value because we have assumed that there is one direct LOS path, the 1 st reflection path, 2 nd reflection path, and the 3 rd reflection path. Typically the LOS path and the 1 st reflection path have the dominant effects. As a worst case scenario we have assumed that the 1 st reflection path gain is 3dB higher than the LOS gain for three out of the four OFDMA pseudolites. As we have analyzed in our previous publication the probability that the NLOS path gain is 3dB higher than the LOS path gain is 1 out of 6.3 days, which is a very rare event and therefore we have selected that as a worst case scenario! Even under these conditions an OFDMA pseudolite indoor geolocation system achieves ranging accuracy on the order of ten cm or less and overall cm level position error 99.9 % of the time. Figure 4: Simulink block diagram of an OFDMA pseudolite indoor geolocation system. 1826

7 Figure 5: Multipath Rayleigh fading channel 1 (left) and channel 2 (right). Figure 6: Multipath Rayleigh fading channel 3 (left) and channel 4 (right). An example of the received OFDMA signal waveform is given in Figure 7. We see four OFDM signals centered at.1,.2,.3, and.4 GHz distorted due to severe Rayleigh multipath fading. We note that each OFDM transmitter s signal requires roughly 4 MHz bandwidth or 34 MHz RF frontend receiver bandwidth. We may change this requirement depending on cost of the available spectrum at the time of system implementation. FINANCIAL AND BUSINESS REQUIRMENT PLAN In order to enable the complete analysis, design and development, testing and marketing, mass production (or manufacturing) and distribution of an OFDMA pseudolite indoor geolocation system the following 3-phase financial requirements process must be in place: Phase I: complete analysis and simulation Phase I will require a span of 6 months to 9 months during which the complete analysis and software simulation of an OFDMA pseudolite indoor geolocation system is performed. The total cost of Phase I is approximately $1, for 9 months. Approximately $1, will go towards purchasing MATLAB, Simulink, Communications blockset and toolbox, Signal Processing and Tookbox, RF blockset and toolbox, Control blockset and toolbox and other necessary components. 1827

8 Figure 7: Distorted, received OFDMA signal due to Rayleigh fading channel. The output of Phase I is a complete simulation of the endto-end OFDMA pseudolite indoor geolocation system in MATLAB and Simulink. Phase II: design, development, and test The phase II will require a span of 1.5 years to 2 years during which the complete design and development of an OFDMA pseudolite indoor geolocation system is performed. The total cost of the system will be in the range of $5, - $75,. This cost will go towards: 1. Renting a space such as an executive offices 2. Hiring an RF engineering 3. Hiring a digital design engineer 4. Hiring an accountant and office manager 5. Hiring a technician 6. Computers, development tools, and other office supplies 7. Commercial off the self hardware components etc. 8. Companies overhead The output of phase II will be 4 OFDMA pseudolite indoor geolocation systems prototypes. Phase III: marketing, mass production (or manufacturing) and distribution (or sales) Phase III will require a span of 2-3 years during which the marketing, mass production, and distribution of an OFDMA indoor geolocation system will occur. The total cost of the system will be in the range of $ 2 million to $ 3 million. Initial targeted geographic areas are as follows: US, Australia, Europe, and Asia. In US, the initial states will be California, Texas, Massachusetts, etc. In Australia, the initial targeted area is Sydney. In Europe, the initial targeted areas are Great Britain, Germany, France and other EU members. In Asia the initial targeted areas are Japan, China, Hong Kong. It is hoped that the production cost of an OFDMA pseudolite indoor geolocation system which contains 4 pseudolite and up to 4 receivers will be ~$

9 Let assume that we will produce during the 1 st year we produce 5 units and sell these units at $25 then the company will make $25, profit which totals 6.67 % of the total capital. Let us assume that during the 2 nd year we reduce the cost to $15/unit and we produce 1 units which total $1.5 million and sell these units at $2 then the company will profit $5,. Let s assume that during the 3 rd year we reduce the cost to $1/unit and we produce 2 units which total $2 million and sell these units at $15 then the company will profit $1 million at which point we can start paying off the venture capital or if there is no venture capital then we can start making real money. The money can be obtained via at least two ways: (1) government funding projects or (2) venture capital. Interested investors or project managers should contact: Ilir F. Progri, Ph.D., President and CEO Giftet Inc. 218 Spencer Ave Pomona, CA Tel./Fax. (99) ifprogri@verizon.net WWW. CONCLUSION In conclusion we have provided the requirements of an ODMA pseudolite indoor geolocation system which are (1) OFDMA system requirements, (2) OFDMA pseudolite signal requirements, (3) OFDMA receiver requirements, and (4) OFDMA financial and business requirements plan. We are at the state that we have accumulated an extensible body of knowledge for designing an OFDMA pseudolite indoor geolocation system. We have provided the requirements and as such we are looking for investors and avenues for funding for continuing this research and ultimately for building an OFDMA pseudolite indoor geolocation system. We have also proposed a preliminary financial and business requirement plan. 3. Cyganski, D., J.A. Orr, W.R. Michalson, Performance of a precision indoor positioning system using a multi-carrier approach, Proceedings of ION NTM 24, San Diego, CA, January 26-28, Progri, I.F., W.R. Michalson, and D. Cyganski, An OFDM/FDMA indoor geolocation system, NAVIGATION J. Inst. Nav., vol. 51, nr. 2, pp , summer Progri, I.F., W. Ortiz, W.R. Michalson, and J. Wang The Performance and Simulation of an OFDMA Pseudolite Indoor Geolocation System, in Proc. ION GNSS-26, Fort Worth, TX, pp , Spt Progri, I.F., M.C. Bromberg, and W.R. Michalson, Maximum likelihood GPS parameter estimation, NAVIGATION J. Inst. Nav., vol. 52, nr. 4, pp , winter Progri, IF, W.R. Michalson, J. Wang, M.C. Brmberg, Field measurement data on support of a unified indoor geolocation channel model, in Proc. ION- NTM 27, pp., San Diego, CA, Jan Bromberg, M.C., and I.F. Progri, An anti-jam GPS receiver, using Markov Chain, Monte Carlo integration, in Proc IEEE/ION PLANS 26, Coronado, CA, pp , Apr. 26. REFERENCES 1. Progri, I.F. An assessment of indoor geolocation systems, Ph.D. dissertation, Worcester Polytechnic Institute, Worcester, MA, May Cyganski, D., J.A. Orr, W.R. Michalson, A multicarrier technique of precise geolocation for indoor/multipath environments, Proceedings of ION GPS/GNSS, 23, Portland, OR, Sept. 9-12,