Mobile Location Techniques

peregrine posture TechniquesINTRODUCTIONWith the rapid incr eternal sleep in add of lively exploiters, a massive mo of calls originate from nimble subscribers, all over the world, e veryday. With the increasing turn of events of erratic users and originating calls, at that place is as well as an increase in urgency calls that originate from wandering(a) stakes. In more indispensability cases the property is unknown to the caller, or he quite a littlenot explain properly. and therefore there is a strong need to pose both roving user in touch situation. Hence the stage setting of fluent location is vital.Due to importance of sprightly geting, the need to decide any unsettled user in touch was in like manner called by Federal Communications military commission (FCC) and European Countries.For instance, the Federal Communications Commission (FCC) made a proposal to include perspective in the 911 emergency service con steadr, which government issueed in the E911 ruling 2. Currently, all the legacy handsets utilize in public stallular profits in the USA must provide the situation of the customer whenever this sum up is dialled. The European Commission (EC) adopted a akin regulation to include location in emergency services on 112 2.The FCC in USA took the first step in this direction. Initially by 2001, the busy operators argon requisite to provide the accurate location of an emergency caller. The current requirement of FCC is to direct 67% of emergency callers must be determined within 100 meters and 95% of the callers must be situated with an demerit of no more than 300 meters. 3 ApplicationsMobile location corporation be utilize for a number of services by wandering(a) operators. several(prenominal) of them argon discussed hereAn important application of fluid location is to provide emergency services. By subtle the location of a erratic user, emergency vehicle tramp be directed to that location. Henc e there is an increase in public safety and services.An early(a) interest in exploiting the mobile location is to apply location beautiful billing. By knowing the location of mobile subscribers an operator merchantman offer competitive tariff e.g. users eject be offered more calls from their mobile to home or maculation. asset tracking and hap management is another application of mobile location. exploitation the location of mobile travellers mint be in doed about location. Mobile location puke be utilize to effectively manage fleet and traffic conditions.There ar deuce main categories for mobile state of affairsing,Handset found typeseting and ent go offtment ground office. Handset Based techniques needs circumscribed type of handset hardw be or the installation of specialized ent careenment software in existing handsets e.g. GPS and A-GPS. GPS receiver determines its own agency by sending and receiving tokens from at least four satellites. The clock to r to from individually one one satellite mark to GPS receiver is used as a parameter. The accuracy of GPS keisterd systems is very high. And the insurance coverage of satellite is very redeeming(prenominal) in open-air(prenominal) environment. However, drawback is inability of GPS to operate in indoor and heavily populated urban environment. GPS privations pose where quests of the satellite cannot be fully covered. well-nigh other problem is link up to existing handsets in market. A large number of existing handsets lack the built in GPS receivers. hencece utilise this rule a immense number of people can not get benefit or can not be patch upd in case of emergency. to a fault Embedding a GPS receiver into mobile devices leads to increased cost, size, and battery consumption 1. frankincense hundreds of millions of handsets in market need to be put backd or modified.In contrast, lucre Based Techniques determine the position of a mobile user by measuring its quest parameters when stock at the net Base come in (BS). Here BS receives signal from Mobile Station (MS) and sends them to a underlying site where location estimation algorithmic rules are used to estimate location. In this manner acting there is no need to change or replace existing handsets. It would require change in a few thousands of vane nodes (Base Stations) than to change hundred of thousands of mobile targets. Hence, it can be implemented easily, less(prenominal) costly use existing technology. And politic can provide a very considerably estimate of position of a mobile user. The hereafter technologies also support lucre udderd positioning. Infact many positioning techniques can not be implemented development existing GSM technology. Using mod technologies their efficiency provide keenly increase. The Network bowd positioning is also feasible for network operators as it would help them to implement location sensitive billing and location related services. t herefrom themed on a received location the operator can implement a special price plan e.g. less price calls to home or office number. It result also help them to generate more revenue.Another receipts of network habitationd techniques is the security department of the subscribers. Using an algorithm at network side also ensures that the position of subscriber is known that to emergency service or mobile operator. Thus it also increases the safety and security of the subscribers.The network dishd techniques take a crap several advantages like low cost, ease of implementation, implementation apply existing technologies and methods, beneficial for a large number of people. However, the main issue with this technique is its accuracy. Despite a number of efforts to recoil error and increase accuracy there is still no artless estimation method pre displace. All of the methods expose fair results under certain conditions or circumstances. Thus there is no general prediction for result using an algorithm. The main problems in incorrect positioning are multi driveway propagation, weaken and low SNR. The efforts are continuously being made to minimize these and thencece increase accuracy and thus finishance.The project bequeathinging emphasize on comparing various existing network rootd location techniques. Some of the common techniques will be analyze in detail. Base on these existing methods, a number of positioning algorithms are also canvas in detail to implement major positioning techniques. The algorithms will then be implemented using MATLAB. The results of algorithms will be compared to actual position of mobile place so as to measure the performance of from each one of them. Final thing is to develop an on crease benchmarking tool to compare location evaluation estimates using different techniques. The tool should be able to plump user uploaded measurements in to its own algorithms. The results will then be compared to user submitted results to perform a benchmark.Existing Literature ReviewA number of mobile location techniques are common nowadays. These techniques can be divided into thirdsome main typesMobile Based TechniquesNetwork Based TechniquesIndirect TechniquesThese techniques are briefly explained belowMobile Based TechniquesIn this method, a number of geographically separated transmitters are used by the mobile send off to exploit its own position. It is also known as Self put. Thus mobile come out (MS) locates itself by using signals from a number of transmitters or subject move (BS). Example of mobile based positioning is GPS and A-GPS. In GPS based positioning GPS receiver uses signals from geographically distri onlyed satellites to exploit its own position.Network Based TechniquesThis method uses a number of transmitters in a network to locate position of an unknown receiver. It uses resources of the network only. The signals from the MS are used by a number of BS to locate the MS. This te chnique can be implemented using different type of parameters e.g. carrell spheric identity element (CGI), cell Global Identity with Timing Advance (CGI-TA), compound Cell Global Identity (E-CGI), Time of comer (TOA), move of reach (AOA), Time diversion of Arrival (TDOA).Indirect TechniquesIn this technique mobile or network can be assisted to locate a mobile target. Thus base grade can send positioning data to mobile commit to locate itself. Similarly measurements can be uploaded from MS to BS to locate mobile station. It involves measurements sent from MS to BS for positioning at BS or vice versa.There are a number of network based mobile positioning techniques in use today. In much(prenominal) techniques a number of involved base stations (BS) use signal from mobile station (MS) to locate the position of MS. The common methods are Signal Strength, Time of Arrival, Time Difference of Arrival, burden of Arrival, or hybrid techniques. severally of the existing method has its own advantages and disadvantages. A major problem with all methods is the accuracy. It depends on cell size, cell environment, number of cells, multipath propagations and exceed surrounded by MS and serving base station. Some other common parameters for performance measurement include applicability, robustness, etc.The existing methods have been described in detail belowCell Global Identity The CGI method to locate a mobile user is most light-colored and straight forward. In this method, the position of mobile user is estimated by using the cell identity of serving base station. Thus the mobile can be located anyplace in a call coverage demesne. It is very simple to implement.However, the positioning error whitethorn range from a few meters to a few kilometres. The accuracy will be parasitical on the size of serving base station. Another problem with this method is that mobile station is not always connected to nearest base station. In this case the location of mobile c annot be even estimated. superlative degreeen-CGITo thrash errors in basic CGI technique another method is used. The basic judgement was to split the coverage area of a base station into two or more areas, mostly troika 120 degree areas. Each area within a base station can then be issued with a separate identity. Hence in this way the position of mobile can be narrow down to a puny area. Although this method is lucky to implement yet error is large rich from practical point of view.CGI with Timing AdvanceThe CGI technique can also be meliorate by using the fourth dimension advance gasconade of GSM. Timing advance is a value that corresponds to the time it takes for a signal to reach from MS to BS. In GSM quantify advance is a quality used by the base station to synchronise with mobile station. On step timing advance is equal to a change in 1100 m of round-trip time (the time signal takes to reach from base station to mobile and then back to base station). The timing adv ance is delegate by base station for each mobile station. Using the timing advance feature a mobile user can be located within 550 meters approximately.Time of ArrivalAlthough CGI method provides a upright estimation of mobile position, the error is still large enough from emergency view point. Another method to locate mobile is using the reach time of signals at base stations involved. The distance of mobile can be estimated by using breeding about time of arriver i.e.D = t / cWhere t is the time of reaching of signal at base station and c is the fixedness of light. The distance will be the estimated mobile position. However the mobile can be located anywhere on circular path centred at base station and radius equal to estimated distance D. The exact position of mobile can be estimated by using same type of measurements from two other neighbouring base stations. Ideally the positioning circles from all the terce base stations must intersect at a point, which will be the posi tion of mobile. However, practically, the circles dont intersect at a hotshot point rather they fasten a small area in which the mobile is potentially located. This method is really better than CGI because it fuddles more accurate results. The time of reaching method requires accurate synchronization or adduce between mobile and base station to correctly measure the reaching time. The results, however, depends on environment of cell clutter, atmospheric conditions, and multipath propagation. In worst atmospheric conditions the results whitethorn vary severely.Angle of ArrivalIn this method the position of the mobile is located by using the direction of signal arriving from mobile station to the serving and, at least one other base station. The direction or angle of arrival is measured at base station by using arrays of transmitting aerials. Angle measurement at one base station will give the position of mobile to be located at a straight line at a certain angle with base sta tion. Measurement from another involved base station will produce another positioning line. Ideally the mobile must be located at the intersection of two lines from involved base stations. In practice, however, they may not intersect at all at a single point. The angle of arrival is good because it can be implemented using a small number of base stations. Thus it is best when the number of base stations visible to mobile is very low. The angle of arrival method is very sensitive to measurement errors of angle. So a very small error in angle measurement results in a much larger error in position of mobile.Time Difference of Arrival The time of arrival method requires a strict synchronism or reference between mobile and base station. To overcome this problem, the passing of arrival time at a distich of base station is used for measurements. A pair of base stations is used to nature one time rest measurement. The result will be a circle on which mobile can be anywhere. Ideally th e three circles will intersect at one point. This point will be the position of mobile. In actual practice the method will give a small area in which mobile must be located. The difference of arrival time eliminates the need of synchronisation as required by time of arrival. This method can be used as to run entirely on network side or to run with mobile assistance. The performance of time difference method is greatly improved than time of arrival. The main advantage of this method is elimination of timing requirement. However, on the other hand, the number of involved base station must be at least four including primary base station. Thus only then three sets of measurements can be obtained. The time difference of arrival method is more often used payable to ease of implementation. entropy correlational statistics methodThe Database coefficient of correlation Method makes use of the signal information seen by mobile station. The signal information from all of the coverage area seen by mobile station is stored in a database at network side. The signal information may include signal strength, signal timing, signal delay etc. When position of the mobile is required, the stored data in database is used by a positioning emcee to do so. The signal measurements sent to the database depends on the environment. The resolution of such measurements must be set so as to achieve certain accuracy. In GSM a sub-band resolution is used by the Base Station Controller (BSC) to facilitate the handover process.Pilot correlativity Method algorithmic rules SearchThere are a number of positioning algorithms in present belles-lettres. These algorithms make use of the measurements make by the mobile station. The measurements required for each algorithm may vary. However, some common measurements may include Cell ID, LAC, Signal Strength, Timing Advance, Time of Arrival, and Direction (Angle) of Arrival. excessively these measurements may be carried out only on network side i .e., by primary base station or they can be performed with assistance of mobile station. The algorithms for all of the major positioning methods are studied in detail. Although there is a large number of algorithms in literature yet each of them has own advantages and disadvantages. Each algorithm is based on some assumptions and limitations. For this reason we can not say which one is best. solely the one which gives acceptable accuracy is thought to be the good one.Cell Global Identity (CGI)The Cell ID is the very basic method to locate mobile station. It is used to make a rough estimate of mobile position. With this method the mobile can be located anywhere within a cell. Thus the accuracy is very poor. The mobile station measures periodically the id of serving base station and up to 6 neighbouring base station. Thus no special algorithm is needed to locate Cell ID. By looking at mobile measurements the Cell ID can be located.Enhanced Cell IDDue to very poor accuracy of basic Cel l ID, a number of enhancements have been made to it. Thus measurements like signal strength, Timing Advance can be used in pairing with Cell ID to improve accuracy. Two algorithms which show good results are enhancement to CGI using Signal Strength and set using Timing Advance. In the first algorithm the signal strength is taken as a parameter. The power received by mobile station from primary base station and up to six neighbouring cells is feedback to primary base station. The primary base station thus knows the power transmitted by it and power received by mobile station. Then the distance calculation is possible by using the known path loss. Using Okumura-Hata Path Loss mildew 4 the distance between mobile and base station is calculated.The mathematical form of this model is 4Urban areas LdB = A + B log10 R Esuburban areas LdB = A + B log10 R COpen areas LdB = A + B log10 R DA = 69.55 + 26.16 log10 fc 13.82 log10 hbB = 44.9 6.55 log10 hbC = 2 (log10 (fc / 28))2 + 5.4D = 4.78 ( log10 fc )2 + 18.33 log10 fc + 40.94E = 3.2 ( log10 ( 11.7554 hm ))2 4.97 for large cities, fc = 300MHzE = 8.29 ( log10 ( 1.54 hm ))2 1.1 for large cities, fc E = ( 1.1 log10 fc 0.7 ) hm ( 1.56 log10 fc 0.8 ) for medium to small citiesDefinition of parametershm mobile station approach teetotum above local terrain height mdm distance between the mobile and the buildingh0 typically height of a building above local terrain height mlhbbase station antenna height above local terrain height mrgreat circle distance between base station and mobile mR=r x 10-3 great circle distance between base station and mobile kmf carrier frequency Hzfc=f x 10-6 carrier frequency MHz? forgo space wavelength mThis model is fairly simple so it is used for a large number of situations. The distance calculation is easy from this model using known path loss in pre-defined environment. The mobile will be located anywhere on the circle of estimated distance with centre at base station. A minimum of three base stations are used for such measurements. Ideally the three circles will intersect at a single point. This point will be the position of mobile station. The triangulation technique is used to find the intersection coordinates of circles.Time of ArrivalAlthough CGI provides the position of mobile station yet the accuracy is not sufficient for many purposes. To improve accuracy the time of arrival method is used. It gives good results than CGI in most of the situations. A number of algorithms describing time of arrival method are in literature. Each of them has some advantages and some short comings. Also each algorithm works best under some specific conditions e.g. in line of sight (LOS) or non-line of sight (NLOS) conditions. A good algorithm which gives acceptable results in many situations is A constrain Least Squares come on to Mobile Positioning Algorithms and Optimality. This algorithm uses a least square come on to estimate position of mobile station. The dista nce between mobile station and base station is estimated by using the fact that signals travel in free space at a speed equal to speed of light. Thus mathematically,Di =Ti / c i = 1, 2 NWhere D is the estimated distance, T is the TOA measurement, i denote the number of base station and c is the speed of light. The mobile station will be located anywhere on the circle with radius D centered at base station i. Same TOA measurements are performed by at least three base stations. The position of mobile will be the intersection of three circles. Ideally this will be a single point. But in practice, due to multipath propagation and weaken, it will give a small area. The mobile station will be located in this area. To reduce positioning error the algorithm uses a least square error approach. Thus the distance between every point in that area and each mobile station is calculated. The point where the sum of squares of distances is minimized will be the estimated position of mobile station. To get TOA measurements, base station and mobile station must be synchronized properly or there must be a reference point. Thus a strict timing requirement is necessary.Angle of Arrival In LOS conditions this method is the best to use. A number of algorithms describing this method are in literature. All of these algorithms require a dominant LOS path to correctly perform angle of arrival measurements at base station. Thus this method is best in open areas and suburban areas. In dense urban environment this technique produces severe errors due to NLOS and multipath propagation. A number of algorithms are studied in detail. A good algorithm is A Constrained Least Squares Approach to Mobile Positioning Algorithms and Optimality. It produces results with acceptable accuracy. According to this algorithm, to perform angle of arrival measurements, base station must be provided with multiple antenna arrays. A minimum of two base stations will be required to perform such measurements. The s ignal from mobile station will reach base station at a certain angle with level axis. This angle can be measured by base station using antenna arrays. Mathematically, it is given over bytan (fi) =(y yi / x xi) , i = 1, 2, . . . , M.The angle of arrival measurement from one base station will result in a straight line. This line is also called Line of Bearing (LOB). It will be at a certain angle between horizontal axis and base station. The mobile will be located any where on the LOB. A similar measurement will be done using another involved base station. It will result in producing another angle of arrival or LOB. The point where the two line of bearing intersects will be the position of mobile station.Ideally two lines will intersect at a unique point. However, practically they may not intersect at a point. In this situation the angle of arrival method need further measurements from other involved base station.This method produces very accurate results in LOS situation. However, the results depend critically on the measured angle. Thus a very small error in angle measurement may lead to positioning error of hundreds of meters. Another disadvantage is the cost of this method. It requires antenna arrays at each base station to measure AOA. Hence cost of implementation increases.Time Difference of Arrival The time difference of arrival uses the difference in arrival generation of signals at a pair of base stations. The time difference of arrival measurements are done with reference to primary base station. A good algorithm in literature is the Performance analogy of TOA and TDOA Based hole Estimation Algorithms in LOS Environment. It explains the working of different types of TDOA approach. It also compares the performance of each of the type.However it uses a LOS approach. In open areas LOS assumption is valid but in heavily populated urban areas this assumption is invalid. Another good algorithm which explains the TDOA measurements is is A Constrained Le ast Squares Approach to Mobile Positioning Algorithms and Optimality . In this algorithm, the primary (Serving) base station is the reference base station. The time of arrival measurements are performed using the reference base station. Thus the estimated distance between mobile station and reference base station is d1 and that of mobile station and a neighbouring base station is di. Thus the TDOA measurements are given by,d1 = t1 / cdi = ti / c, i = 2,3 .. NWhere d1 is the distance between mobile station and reference (primary) base station and di are the distances between mobile station and other three neighbouring base stations. The TDOA measurement between reference and second base station is given byTDOA= d1-di i = 2,3, .NThis will be the error free TDOA measurement at a pair of base stations. The measurement including error is given byTDOA= (d1 di) + errorThe error is modelled as a Gaussian distributed random variable with zero-mean. Such measurements are taken from at least three pairs of base stations. The triangulation technique is then employed to get the position of mobile station. The TDOA method is superior to time of arrival (TOA) in sense that it eliminates the need for timing reference. Thus it is easy to implement. Due to no timing requirement TDOA method is more frequently used than TOA method.Database correlation methodDespite of a number of algorithm which perform fairly well in urban areas there is still a need to further improve it. Due to severe multipath and fading effects LOS assumption is not valid in urban areas. The Database correlativity Method is a good method to counter effect multi path and fading. It can be implemented by utilizing the measurements performed in existing GSM systems. It can be implemented by making Signal Strength as a parameter. A ggod algorithm to implement Database Correlation Method is Database Correlation Method for GSM Location by Heikki Laitinen, Jaakko Lahteenmaki, Tero Nordstrom. In this algorithm the DCM is implemented by using signal strength measurements performed by handset. The algorithm explains the way database correlation method can be implemented in GSM. The measurements performed in the coverage area are performed by mobile station and are stored in database. Thus the database will consists pre-measured samples of signal measurements in the coverage location. When the need to locate mobile station arises, the primary base station asks mobile station to perform signal strength measurements and feedback to it. The BS sends these measurements to location server. The location server then calculates the difference between stored fingerprint and actual measurement. The point where the difference between fingerprint and actual measurement is minimum will be the estimated position of mobile station. The estimated position will also contain some error in it due to fading, NLOS path and multipath propagation. However this error will be drastically less than the error in other te chniques apply under same conditions.The database correlation method has the advantage that it can be implemented in any type of system like GSM, CDMA,UMTS,etc.ReferencesNetwork-Based radiocommunication Location IEEE betoken PROCESSING MAGAZINE JULY 2005A New Time-Based Algorithm for Positioning Mobile Terminals in Wireless NetworksIsrael Martin-Escalona and Francisco Barcelo-Arroyo, EURASIP Journal on Advances in Signal ProcessingMobile Positioning Using Wireless NetworksIEEE SIGNAL PROCESSING MAGAZINE JULY 2005Path loss models S-72.333 Physical layer methods in wireless communication systems Sylvain Ranvier / Radio Laboratory / TKK 23 November 2004Performance Comparison of TOA and TDOA Based Location Estimation Algorithms in LOS Environment Guowei Shen, Rudolf Zetik, and Reiner S. ThomaA Constrained Least Squares Approach to Mobile Positioning Algorithms and Optimality K.W. Cheung,1 H. C. So,1 W.-K.Ma,2 and Y. T. Chan3Database Correlation Method for GSM Location Heikki Laitinen , Jaakko Lahteenmaki, Tero Nordstrom