Abstract:
Method and system of determining a location of a wireless transmitting device, such as a cellular phone, a wireless PDA or a radio tag, and guiding the searching personnel to physically reach the wireless transmitting device are disclosed that employ a “Movable Detection Station” and a “Guiding and Reference Device”, and optionally a “searching robot”. The movable detection station is carried on board of a moving platform, such as a police car, an ambulance or a fire truck, or carried by searching personnel. The guiding and reference device is a handheld device including a display device that displays position and guiding information to a user, and a reference wireless transmitter that works with a movable detection station. A searching robot is a robot with a reference transmitter installed on it.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority from and is related to the following prior application: “Method and System for Determining a Location of a Wireless Transmitting Device and Guiding the Search for the Same”, United States Provisional Application Number 60/401240, filed Aug. 06, 2002. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable.  
         REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING  
         [0003]    Not Applicable.  
         BACKGROUND OF THE INVENTION  
         [0004]    1. Field of the Invention  
           [0005]    This invention relates generally to wireless systems and, in particular, to determining the location of a wireless transmitting device, and to guiding the search for said wireless transmitting device.  
           [0006]    2. Description of the Related Art  
           [0007]    Wireless devices include cellular, PCS (Personal Communication Systems), cordless and satellite phones, wireless PDAs (Personal Digital Assistants) and laptop computers, two-way pagers, radio tags, etc. Collectively these are referred to herein as “wireless devices”.  
           [0008]    The need for locating, tracking and searching for wireless devices is increasing. Applications include:  
           [0009]    Emergency Response:  
           [0010]    A notable emergency response service is the enhanced 911 (E911) service mandated by the FCC (Federal Communications Commission) for all cellular licensees, broadband Personal Communications Service (PCS) licensees, and certain Specialized Mobile Radio (SMR) licensees in the United States. E911 service is to provide the operators at the PSAP (Public Safety Answering Point) with information such as calling number, location of serving base station, and caller&#39;s Automatic Location Identification (ALI) in longitude and latitude. This automatic information enables the PSAP operators to dispatch emergency response teams for wireless 911 callers in the similar fashion as for the wire line 911 callers. The location accuracy and reliability required by FCC have been revised several times since their first release, compromising what is needed and what is possible. At the time of this invention, the requirements are  
           [0011]    For handset-based solutions: 50 meters for 67 percent of calls, 150 meters for 95 percent of calls;  
           [0012]    For network-based solutions: 100 meters for 67 percent of calls, 300 meters for 95 percent of calls.  
           [0013]    Pursuit of Criminals:  
           [0014]    To allow law enforcement agencies to track and locate wanted criminals who use wireless devices; to allow the public to report information about offensive callers&#39; identification and location.  
           [0015]    Tracking of Fraudulent Calls:  
           [0016]    Cellular telephone fraud causes huge revenue losses to the service providers. Real-time location of fraudulent calls will help stop the spread use of “cloned” phones.  
           [0017]    Recovery of Stolen Vehicles and Valuable Goods:  
           [0018]    Wireless devices attached to the protected objects will enable the tracking and recovery thereof.  
           [0019]    Target Monitoring and Searching:  
           [0020]    Wireless devices attached to the targets can enable the monitoring and searching of such targets, as children, patients, herds, parolees and probationers, controlled materials and equipment, or toxic waste containers.  
           [0021]    Depending on the application, wireless location systems face various technological challenges. Achieving high location accuracy anywhere, anytime, under diversified terrain conditions, and at a low cost is a challenge common to many location applications. Particularly for conventional E911 technologies, the prior art solutions are divided into two major categories: network based and handset based. In network based prior art solutions, location accuracy is sensitive to multipath propagation, number of available detection stations, and geographical geometry of the target in relation to the available detection stations. In handset based prior art solutions using GPS, location accuracy is susceptible to blockage in dense urban areas and inside buildings. The handset based prior art solutions also have problems to provide E911 service to legacy devices already in use. To achieve a required accuracy throughout coverage areas and terrains, the cost is often found far beyond the acceptable limit for operators and many end users. In addition, the prior art E911 solutions do not address the need to guide the search for the target on site.  
         BRIEF SUMMARY OF THE INVENTION  
         [0022]    A method and a system to locate wireless devices that are transmitting wireless signals (referred to herein as “Target Wireless Transmitting Devices”, or “Wireless Transmitting Devices”, or “Target Devices”, or TD for short), and to guide the search personnel(s) or searching robot(s) to physically reach the wireless transmitting devices are described through preferred embodiments.  
           [0023]    In one aspect of this invention, the method utilizes a system that is composed of one or a plurality of detection stations (DS), at least one of the DSs is carried on board of a moving platform (herein referred to as a Movable Detection Station, or MDS, for short), for examples, on board of a police car, an ambulance, a fire truck, a helicopter, a balloon, an airship, a boat, or the like, or carried in hand or on shoulder by the operator of the MDS. Either operating alone or operating in conjunction with other DS and MDS, a MDS measures the location of the TD while moving en route to or around the TD. The method thereby involves making use of the advantages that are made available by the mobility of the MDS, by the movement of the MDS, and by the close distances of the MDS with respect to the TD.  
           [0024]    In another aspect of this invention, the method utilizes a system that is composed of also one or a plurality of handheld devices, referred to as guiding devices. The guiding devices are used to guide their users to reach the exact position of TD on site.  
           [0025]    In yet another aspect of this invention, the method utilizes a system that is composed of also one or a plurality of wireless transmitters that have similar radio properties as the TD, and are referred to as Reference Wireless Transmitting Devices or Reference Transmitter, or RT for short, also carried by the searching personnel(s). The MDS (and DS) measures not only the location of the TD, but also the location of the RT, and provides information about the relative location of the RT with respect to the TD. The method thereby involves making use of the advantages that are made available by the likeness of the radio properties of the TD and RT, by the measurement of the relative (and asymptotically identical) locations of the TD and RT, and by the real time feedback to the search movements. The method also enables a searching robot that is equipped with a RT to work with a MDS accomplishing the searching job.  
           [0026]    In still yet another aspect of the invention, the RT and the guiding device are physically combined, and herein referred to as a Guiding and Reference Device, or GRD for short.  
           [0027]    Other aspects of the invention will become clear thereafter in the detailed description of the preferred embodiments and the claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]    [0028]FIG. 1 illustrates the location determination system and the method associated with thereof, in the on-vehicle operation mode, using a cellular phone as an example of target device;  
         [0029]    [0029]FIG. 2 is an illustration of blockage of line of sight (LOS) and multipath propagation effects in a fictitious urban area that apply to a Movable Detection Station (MDS);  
         [0030]    [0030]FIG. 3 is an illustration of a method of determining whether or not an individually detected earliest arrival propagation path is truly LOS or truly earliest arrival propagation path, in a fictitious multipath scattering environment that applies to a MDS;  
         [0031]    [0031]FIG. 4 illustrates the location determination system and the method associated with thereof, in the off-vehicle operation mode, using a cellular phone as an example of target device;  
         [0032]    [0032]FIG. 5 is an exemplary illustration of preferred display on screen for absolute and relative locations of TD, GRD(s) and MDS(s) in two dimensions, overlaid with local area map and remote sensing photo that are pre-stored on system;  
         [0033]    [0033]FIG. 6 illustrates an alternative embodiment of the location determination system in which the MDS is equipped with an on-MDS BS transmitter, and the method associated with thereof, in the on-vehicle and off-vehicle operation modes, using a cellular phone as an example of target device;  
         [0034]    [0034]FIG. 7 illustrates the location determination system and the method associated with thereof, in a three-dimensional operation mode, using a cellular phone as an example of target device;  
         [0035]    [0035]FIG. 8 is a block diagram of the MDS in accordance with the preferred embodiments of the current invention;  
         [0036]    [0036]FIG. 9 is a block diagram of the GRD in accordance with the preferred embodiments of the current invention. 
     
    
       [0037]    The same reference numerals are used in different FIGS. to denote similar elements.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0038]    In the description hereafter, a cellular phone is used as an example of the Target Device (TD) for convenience of description. It is understood that the method and system described herein do not limit its TD to a cellular phone. Depending on the functionality provided by the TD, the TD may be a cellular phone, a PCS (Personal Communication Systems) phone, a satellite phone, a cordless phone, a two-way pager, a wireless PDA (Personal Digital Assistant), a wireless laptop computer, a data messaging device, a cellular telephone with data messaging capabilities, a wireless Internet appliance, a data communication device (with or without telephony capabilities), or a radio tag, and so on.  
         [0039]    Also in the description hereafter, E911 service is used as an example application for convenience of description. It is understood that the method and system described herein do not limit its application to E911 service.  
         [0040]    [0040]FIG. 1 illustrates the location determination system and the method associated with thereof, in the on-vehicle operation mode, using a cellular phone as an example of TD. Referring to FIG. 1, the TD  10  is a wireless transmitting device whose location is to be determined and searched. The particular TD shown in the figure is a cellular phone that is communicating with a Base Station (BS)  20 A through radio link  40 A, and in some circumstances (e.g., for a CDMA TD in a soft handoff) also communicating with additional BSs simultaneously, such as with BS  20 B via radio link  40 B shown also in the figure. The TD  10  is transmitting wireless signals, for example, in verbal communication with an operator at a Public Safety Answering Point (PSAP, not shown in the figure) after dialing the emergency number “911” adopted in the North America, or staying on the line quietly after dialing “911”, or being called back by an emergency response officer after hanging up his/her “911” call, or being initiated a wireless transmitting session in a Service Option that is specifically designed for location service, e.g., transmitting a pilot signal. Upon receipt of the “911” call, the PSAP operator would obtain the caller&#39;s rough location by means of verbal conversation, and/or by prior art “Phase I” E911 information that is automatically reported to PSAP by the wireless network in terms of serving BS  20 A location, and the round trip delay that may also be available, and/or by prior art “Phase II” E911 information that is reported to PSAP in terms of longitude and latitude of TD  10 , whose corresponding location is denoted in the figure as  60 , that is subject to errors statistically. Emergency response vehicles equipped with Movable Detection Station (MDS)  30 A,  30 B such as police cars, ambulances, and/or fire trucks are dispatched by PSAP to said rough location. Those skilled in the art understand that the parameters or properties of the transmitted signal by the TD  10 , such as the transmitting frequency of the TD, the transmitting slot position of the TD when the TD is operating in TDMA (Time Division Multiple Access) mode, the spreading code information of the TD when the TD is operating in CDMA (Code Division Multiple Access) mode or DSSS (Direct Sequence Spread Spectrum) mode, the frequency hoping information when the TD is operating in frequency hopping mode, phone number, and/or electrical serial number (ESN), can be made available to the MDS  30 A,  30 B from a database installed within or connected to the PSAP, from the wireless network which is connected to the PSAP, and/or from the air interface of the wireless communication system. Using said parameters or properties, the receivers of MDS  30 A,  30 B would attempt to acquire and receive the transmitted signal  50 A,  50 B from the TD  10 , while driving en route to the target location. As shown in the figure, along the route the MDS  30 A would take a plurality of measurements of the incoming signal  50 A′,  50 A while moving from position  30 A′ to position  30 A, and when taking each of the measurements, the position and orientation of MDS  30 A can also be determined using such means as GPS receiver installed on MDS  30 A. The plurality of measurements on parameters of the incoming signal  50 A′,  50 A that are performed at different time instants and different positions  30 A,  30 A′, etc., along the route, together with the corresponding positions and orientations of MDS  30 A that are determined can be transformed into appropriate location estimation methods that are originally proposed for multiple fixed detection stations that take measurements at same time instants. Along the route, the MDS  30 A would continuously take new measurements and continuously refine the estimation of the TD  10  location. Those skilled in the art understand that, in the prior art network based solutions the number of available DSs (usually co-located at the BSs) that “hear” the signal from TD  10  are often found too few, especially in suburban and rural areas; the location geometry of available DSs in prior art that “hear” the signal from TD  10  with respect to the location of TD is often found disadvantageous to the accuracy of the location measurement; the blockage to the line of sight (LOS) propagation path and the multipth propagation effects in urban and suburban areas often cause the DSs at the fixed locations in the prior art network based solutions to produce unacceptable location measurement errors. By using MDS the number of measurements that can be obtained along the route of a MDS movement can be hundreds if not thousands; among them, measurements taken at disadvantageous positions can be excluded or weighted low. The disadvantageous measurements include those having low signal to interference ratios or signal to noise ratios, those of which the LOS or earliest arrival paths are weak or lost; those do not exhibit advantageous geometry with tentatively measured TD location. Said exclusion or weighting process is progressive, i.e., a relatively good measurement will be kept while no better ones are available so far, but once sufficient better measurements become available, those previously preserved relatively “good” ones become not-good-enough and are excluded or weighted lower, and such updating process continues. The detection of the signal to interference ratio or signal to noise ratio can be accomplished by a signal to interference ratio estimator or a signal to noise ratio estimator that is familiar to the skilled in the art; the detection of late arrival multipath propagation paths in an individual measurement for purpose of exclusion in the location calculation can be implemented by a channel impulse response estimator that is familiar to the skilled in the art; disadvantageous geometry with tentatively measured TD location can be measured by geometrical dilution of position (GDOP), which is also well known to the skilled in the art and does not need further explanation. A method that determines whether or not an individually detected earliest arrival propagation path is truly LOS or truly earliest arrival propagation path will be further described subsequently with reference to FIG. 3. The mobility of the MDS can actually correct the measured errors that are caused by blockage of LOS and the multipath propagation through its ray tracing process. This is further explained next by referring to FIG. 2.  
         [0041]    [0041]FIG. 2 is an illustration of blockage of line of sight (LOS) and multipath propagation effects in a fictitious urban area that apply to a MDS. Referring now to FIG. 2, the MDS  30  is moving on a street from position  30 A′ towards  30 A. While at position  30 A′, the LOS  50 A′″ from TD  10  is blocked by building B, but the MDS  30  receives the signal  50 A′ from TD  10  that is reflected by building D. The MDS  30  might think the TD is towards the direction of building D and thereby guides the vehicle of MDS  30  driving towards building D. Upon arriving at position  30 A in front of building D, the MDS  30  would have obtained similar visibility of building D, and MDS  30  thereby begins to see the LOS ray  50 A. Although MDS  30  also sees the reflected path  50 A″, MDS  30  would “realize” that ray  50 A is stronger and arrives earlier, and is a more preferable signal to trace. This guides the MDS  30  driving towards building C where TD  10  is truly located. It can be realized that, without a MDS  30  equipped on board of the emergency response vehicle, a fixed DS co-located at a BS (not shown in the figure) that sees earliest arrival path reflected from building D would have guided the emergency response crew to building D by mistake, and risking the life of the emergency caller.  
         [0042]    [0042]FIG. 3 is an illustration of a method of determining whether or not an individually detected earliest arrival propagation path is truly LOS or truly earliest arrival propagation path, in a fictitious multipath scattering environment that applies to a MDS. Referring now to FIG. 3. A MDS  30  moves along the road and takes measurement on the signals transmitted by TD  10  at positions  30 A,  30 A′ and  30 A″. Buildings A, B, C, and D in the surrounding area form blockage and/or reflection land structures to the signal propagations from TD  10  to MDS  30 . At position  30 A, the MDS  30  detects a propagation path  50 A 1  reflected from building C, but the LOS propagation path  50 A 2  is too weak to be detected due to blockage by building A. Therefore, although arriving later than  50 A 2 ,  50 A 1  is the detected earliest arrival propagation path at position  30 A. When the MDS  30  arrives at position  30 A′, the LOS propagation path  50 A′ 3  is still too weak to be detected due to blockage by building A, however MDS  30  can detect propagation path  50 A′, and  50 A′ 2  reflected from building C and B, respectively. Between  50 A′ 1  and  50 A′ 2 , the MDS  30  can determine that  50 A′ 2  arrives earlier than  50 A′ 1  through its means to distinguish multipaths. Therefore,  50 A′ 1  is determined NOT to be earliest arrival propagation path, while  50 A′ 2  is the individually detected earliest arrival propagation path at position  30 A′. Whether or not the  50 A′ 2  is truly earliest arrival propagation path is still undetermined solely based on measurement taken at position  30 A′. Now, based on the measurements taken at two positions,  30 A and  30 A′, we try to determine jointly whether the individually detected earliest arrival propagation paths,  50 A′ 1  and  50 A′ 2  are truly LOS propagation path or truly earliest arrival path. The method is to measure the difference of the propagation delays of the individually detected earliest arrival propagation paths from TD  10  to MDS  30  at the two positions,  30 A and  30 A′, and also determine the distance between the two positions  30 A and  30 A′; if the delay difference is larger than the distance divided by the speed of light, then, between the two paths, the longer delay path is determined NOT truly LOS propagation path, or NOT truly earliest arrival propagation path; if the delay difference is not larger than the distance divided by the speed of light, then both paths are still UNCERTAIN whether they are truly LOS propagation paths or truly earliest arrival propagation paths. In this example, if the delay from TD  10  to building C and then to  30 A is longer than that from TD  10  to building B and then to  30 A′ by an amount of distance between  30 A and  30 A′ divided by the speed of light, then the individually detected earliest arrival propagation path  50 A′ 1  is NOT truly LOS propagation path or NOT truly earliest arrival propagation path; if the said former delay is shorter than said latter delay by the same said amount, then the individually detected earliest arrival propagation path  50 A′ 2  is NOT truly LOS propagation path or NOT truly earliest arrival propagation path; otherwise, both individually detected earliest arrival propagation paths  50 A 1  and  50 A′ 2  are still UNCERTAIN whether they are truly LOS propagation path or truly earliest arrival propagation path, solely based on measurements taken at positions  30 A and  30 A′. When the MDS  30  arrives at position  30 A″, we see in FIG. 3 that MDS  30  observes the LOS propagation path  50 A″, however MDS  30  itself does not know about this fact and it still needs to use said individual and said joint method to determine it. In the joint determination method, MDS  30  will measure the delay difference of paths  50 A″ and  50 A′ 2 , and determine the distance between  30 A″ and  30 A′, use said rules to find out whether any of the paths  50 A″ and  50 A′ 2  can be determined as NOT truly LOS propagation path or NOT truly earliest arrival propagation path. If the paths  50 A″ and  50 A 1  still remain UNCERTAIN whether they are truly LOS propagation path or truly earliest arrival propagation path, the method can also be further applied to the pair of measurements obtained at positions  30 A″ and  30 A, using the corresponding delay difference and distance between positions  30 A″ and  30 A. While MDS  30  continues to drive further, the method can be further used between any pair of measurements taken along the route where the associated individually detected earliest arrival propagation path remains UNCERTAIN whether it is truly LOS propagation path or truly earliest arrival path.  
         [0043]    Now referring back to FIG. 1, in an alternative embodiment, a plurality of MDSs, hereby represented as  30 A and  30 B, will communicate through direct or indirect radio links (not shown in the figure) with each other, and pass their individually measured parameters regarding signals  50 A, 50 B from TD  10  to each other  30 A, 30 B. The measured parameters obtained by the plurality of MDSs,  30 A, 30 B are combined in solving the location of TD  10 , resulting in higher accuracy and reliability.  
         [0044]    Also referring to FIG. 1, in yet another alternative embodiment, one or a plurality of MDSs  30 A, 30 B will further communicate with fixed DS  70 A, 70 B, which may be co-located at BS  20 A, 20 B, through wireless and/or wired communication channels (not shown in the figure), and share their measured parameters regarding signals  40 A, 40 B, 50 A, 50 B from TD  10  with one anther  30 A, 30 B, 70 A, 70 B. The parameters measured by the MDSs  30 A, 30 B and by the fixed DSs  70 A, 70 B are combined at MDSs  30 A, 30 B and/or at DSs  70 A, 70 B in solving the location of TD  10 , resulting in further improved accuracy and reliability.  
         [0045]    [0045]FIG. 4 illustrates the location determination system and the method associated with thereof, in the off-vehicle operation mode, using a cellular phone as an example of TD. Now referring to FIG. 4. After having determined the site (a localized small area or land structure) where TD  10  is located, either using method and system described above, or using alternative methods and systems, or a combination thereof, the MDS equipped vehicle  30 A parks at a close location on site. The members of the emergency response team equipped with Guiding and Reference Devices (GRD)  100 A, 100 B walk off the vehicle  30 A to approach the exact location of TD  10 . A reference transmitter (RT, to be further explained in the description of FIG. 9 subsequently) within the GRD  100 A, 100 B will set up a call via radio link  110 A, 110 B with the same BS  20 A that TD  10  is communicating with. The call on  100 A, 100 B via radio link  100 A, 110 B is in the same operating mode as that of TD  10 &#39;s call over radio link  40 A, e.g., if TD  10  is calling in CDMA mode, then  100 A, 100 B also calls in CDMA mode, if TD  10  is calling in GSM mode, then  100 A, 100 B also calls in GSM mode, etc. The call of GRD  100 A, 100 B over the radio link  100 A, 110 B is preferred to be at the same frequency as that of TD  10  over  40 A, if possible (e.g., occupying another time slot at the same frequency channel in a TDMA based call, occupying another spreading code at the same frequency channel in a CDMA based call), and when this is impossible (e.g., a call based on FDMA), a channel with as close frequency to the one on radio link  40 A as possible is preferred. The same or close frequency, or more generally, the likeness of the radio properties of the associated signals would make the propagation properties for the radio links of TD  10  and GRD  100 A, 100 B similar and asymptotically identical when the GRD  100 A, 100 B approaches the TD  10 . The radio signals transmitted from GRD  100 A, 100 B are also being received by the MDS  30 A, 30 B via radio links  120 A, 120 B, 120 C, 120 D, and thereby the locations of GRDs  100 A, 100 B are measured by MDS  30 A, 30 B simultaneously while the location of TD  10  is being measured. Although the location measurement accuracy for the TD  10  and that for the GRD  100 A, 100 B each could be individually degraded by blockage of LOS and by multipath propagation, because of the fact that TD  10  and GRD  100 A, 100 B would experience similar and asymptotically identical multipath effects when GRD  100 A, 100 B approaches TD  10 , the relative location between TD  10  and GRD  100 A, 100 B measured by the MDS  30 A, 30 B would have been affected very little and thereby is more reliable than the absolute location measurement. In order for the MDS  30 A, 30 B to have similar detectability on signals transmitted by TD  10  and GRD  100 A, 100 B, other signal properties of TD  10  and GRD  100 A, 100 B, such as transmitted power and durations are also preferably made similar to each other. In some occasions, although the emergency response personnel(s) holding the GRD  100 A, 100 B is very close in distance to the TD  10 , they might be within difference construction structures such as two different stairs separated by a wall and cannot reach each other. Adding a detection means for the likelihood of such occasions will increase the efficiency of the search. Such detection can be achieved by comparing the likeness of the signal characteristics transmitted by TD  10  and GRD  100 A, 100 B, such as comparing the difference in received signal strengths or reported transmitted power levels of the signals from TD  10  and GRD  100 A, 100 B, and/or comparing the likeness of the multipath propagation profiles thereof. The guiding to the search for TD  10  described herein also applies to a method using a searching robot, wherein a robot replaces the search personnel in function, a RT and a compass sensor installed on the robot replaces the GRD  100 A, 100 B functionality in one part (the functionality of the compass sensor will be described subsequently in reference to FIG. 9), and a display device installed on a robot control station replaces the GRD  100 A, 100 B functionality in another part. Other aspects remain the same.  
         [0046]    Also referring to FIG. 4, the MDS  30 A and GRD  100 A, 100 B also include another set of radio transceivers, preferably Wireless Local Area Network (WLAN) transceivers, to communicate with each other via radio link  120 A′, 120 C′. Through radio link  120 A′, 120 C′, information for display on the screen of GRD  100 A, 100 B is conveyed, to display the TD  10  location relative to those of the GRD  100 A, 100 B, optionally also to those of the MDS  30 A, 30 B, and to guide the users of GRD  100 A, 100 B movement by movement in the search for TD  10 . An example of the preferred two dimensional display on screen of GRD  100 A, 100 B and on screen of MDS  30 A, 30 B for absolute and relative locations of the TD  10 , GRI)  100 A, 100 B and MDS  30 A, 30 B is shown in FIG. 5.  
         [0047]    Now referring to FIG. 5. FIG. 5 is an exemplary illustration of preferred display on screen for absolute and relative locations of TD, GRD(s) and MDS(s) in two dimensions. Preferably the display is in color (not being able to shown on FIG. 5 due to document format limitation), the symbols that mark the measured locations of TD  10 , GRD  100 A, 100 B and MDS  30 A, 30 B are overlaid with local area map, and preferably further overlaid with pre-stored remote sensing photo that shows the land structures.  
         [0048]    [0048]FIG. 6 illustrates an alternative embodiment of the location determination system in which the MDS  30 A, 30 B are equipped with an on-MDS BS transmitter, and the method associated with thereof, in the on-vehicle and the off-vehicle operation modes, using a cellular phone as an example of target device. Now referring to FIG. 6, in the same way as in the description of FIG. 1, after TD  10  calls 911, the PSAP (not shown in the figure) dispatches the emergency response vehicles that are equipped with MDS  30 A, 30 B to the rough location according to the information obtained by the said PSAP; the TD  10  is transmitting signals to communicate with its serving BS  20 A via radio link  40 A and in some cases simultaneously with additional BSs, such as BS  20 B via the radio link  40 B; when the MDS  30 A, 30 B are close enough to the location of TD  10 , the MDS  30 A, 30 B can detect the signal being transmitted by TD  10  via radio link  50  and the up link direction of radio link  200  (the direction from TD  10  to MDS  30 A) and can start to measure and refine the location of TD  10 . At a point when the radio link between TD  10  and one of the dispatched emergency response vehicles, say the link  200  between TD  10  and MDS  30 A, becomes of better quality than that of link  40 A (and if available,  40 B), the corresponding MDS  30 A would enable its on-MDS BS transmitter within MDS  30 A, and informs the serving BS  20 A to send handoff/handover command to TD  10 . The said handoff/handover command asks TD  10  to handoff/handover to MDS  30 A. Receiving and executing said handoff/handover command, the TD  10  then establishes two-way communication with MDS  30 A via radio link  200 , and disconnects the radio link(s)  40 A (and  40 B if available). Because of the close-in distance between TD  10  and MDS  30 A and thus the better quality of radio link  200 , the communication between the TD  10  and the emergency response team would be more reliable, and in addition, the power control instructions transmitted by the on-MDS BS transmitter within MDS  30 A that are available in many wireless standards would result in lower average transmitted power at TD  10  due to the close-in distance to MDS  30 A and better quality of radio link  200 , and thereby increase the talk time of battery on TD  10  that may be necessary for the continuation of the location detection in progress. Said power control instructions transmitted by the on-MDS BS transmitter within MDS  30 A can further take the advantage of being able to coordinate with the MDS  30 A measurement activity to further increase the talk time of TD  10 , and optimize the signal to interference ratio for better location measurement accuracy. Additional signal properties can also be controlled in coordination with the MDS  30 A measurement activities for improved accuracy and battery life. In the same way as in the description of FIG. 4, after having determined the site where TD  10  is located, the MDS equipped vehicle  30 A parks at a close location on site; the members of the emergency response team equipped with GRD  100 A, 100 B walk off the vehicle  30 A to approach the exact position of TD  10 . Unlike in FIG. 4, the reference transmitter (to be further explained in the description of FIG. 9) within the GRD  100 A, 100 B will set up a call via radio link  210 A, 210 B with MDS  30 A instead of BS  20 A. The call properties on  100 A, 100 B via radio link  210 A, 210 B are otherwise the same as in FIG. 4, e.g., in the same operating mode as that of TD  10 &#39;s call over radio link  200 , preferred to be at the same frequency as that of TD  10  over  200 , if possible, and when this is impossible (e.g., a call based on FDMA), a channel with as close frequency to the one on radio link  200  as possible is preferred. The way to utilize GRD  100 A, 100 B to search for the exact position of TD  10  is also the same as in the description of FIG. 4. The down link of  210 A, 210 B (from on-MDS BS transmitter within MDS  30 A to the receiver associated with the reference transmitter within GRD  100 A, 100 B) is preferred to perform a new task, to convey the data for display on the screens of GRD  100 A, 100 B, in addition to the possible voice communication between the TD caller and the emergency response officer, eliminating the need for the WLAN transceivers on both MDS  30 A, 30 B and GRD  100 A, 100 B. Further, the power control instructions transmitted by the on-MDS BS transmitter within MDS  30 A to the GRD  100 A, 100 B can take the advantage of being able to coordinate with the MDS  30 A measurement activity to optimize the signal to interference ratio for better location measurement accuracy of GRD  100 A, 100 B, and increase the battery life of GRD  100 A, 100 B as well. The frequency and other signal properties of the on-MDS BS transmitter should be chosen appropriately to minimize the impact to the wireless system operation of BS  20 A, 20 B and their serving users.  
         [0049]    [0049]FIG. 7 illustrates the location determination system and the method associated with thereof, in a three-dimensional operation mode, using a cellular phone as an example of TD. Referring to FIG. 7, in a preferred embodiment, when at least one of MDS  30  is sufficiently close to TD  10 , or after at least one of the MDS  30  is parked on site, the location measurement is conducted in three dimensions, so that the height of TD  10  and height of GRD  100  would not be a degradation factor in determining location in horizontal plane, and further, said height of TD  10  and height of GRD  100  are also measured and reported on screen of GRD  100  and on screen of MDS  30  to provide additional location information. The format of the display for height is preferably a number marked beside each symbol on a two-dimensional graph, or popped-up beside each symbol upon being commanded by user, the value of the height is preferably being displayed in relative to that of the MDS  30 . Alternatively the display for height is in three-dimensional graphical effects.  
         [0050]    In the descriptions thereinbefore, the number of the MDS  30  and the number of GRD  100  are exemplary. In the implementation and application of this invention, the number of MDS  30  can be one or plurality, the number of GRD  100  can also be one or plurality. The number of MDS  30  and the number of GRD  100  are not necessarily equal.  
         [0051]    [0051]FIG. 8 is a block diagram of the MDS in accordance with the preferred embodiments of the current invention. Referring to FIG. 8, the preferred embodiment of MDS  30  is composed of an antenna  305 , a receiver  310 , a GPS antenna  315 , a GPS receiver  320 , a digital signal processing (DSP) subsystem  325 , a calibration antenna  330 , a calibration transmitter and mobile receiver  335 , a display and user interface  345 , a WLAN antenna  350 , a WLAN transceiver  355 , a gravity sensor  360  and a compass sensor  365 . Optionally, the MDS  30  further includes an on-MDS BS transmitter  370  and a transmitting antenna  375 .  
         [0052]    The antenna  305  is used to receive the signals from the TD  10 , and from GRD  100 , 100 A, 100 B for measurement of their locations. The antenna  305  is preferred to be an array antenna so as to enable AOA (angle of arrival) measurement of the signals from TD  10  and GRD  100 , 100 A, 100 B, in addition to such measurements as TOA (time of arrival) and/or TDOA (time difference of arrival) and their variations, as well as other alternative signal parameter measurements. Furthermore, the antenna  305  is preferred to be a three-dimensional array antenna, i.e., the elements of the arrays span in three dimensions, to enable AOA measurement in three dimensions. The antenna  305  is also preferred to be installed on top of the roof of a land vehicle or a water boat, or be installed under lower deck of a helicopter or other types of over-the-air moving platform, to achieve good visibility over a wide range of angles for incoming signals from land structures.  
         [0053]    The receiver  310  converts the RF (radio frequency) signals received by antenna  305  to baseband and digitizes the signals. The functionality of the receiver  310  is familiar to those skilled in the art, such as amplifying, down conversion, filtering, automatic gain control, analog to digital conversion, etc., and thereby does not need to elaborate further. For AOA measurement, preferably the receiver  310  is an array receiver that is composed by a plurality of identical channels whose down-conversion stages utilize a common or synchronized frequency source. Preferably said common frequency source is provided by the GPS receiver  320 . The digitized baseband output of the receiver  310  is provided to the DSP subsystem  325  for further processing as will be further detailed thereafter.  
         [0054]    In an alternative embodiment, the antenna  305  is a narrow beam antenna being installed on a rotating structure with an angle sensor, for measurement of AOA. Said rotating structure is preferably being able to rotate in three dimensions for AOA measurement in three dimensions.  
         [0055]    The GPS antenna  315  receives signals from the GPS (Global Positioning System) satellites or from other satellites that perform the similar functionality, such as GLONASS (Global Navigation Satellite System), BEIDOU, or GALILEO in proposal, although still being referred to herein as GPS antenna. The antenna is preferably being installed on top roof of the moving platform to achieve good visibility of the satellites in sky. The signals received are provided to the GPS receiver  320 .  
         [0056]    The GPS receiver  320  receives signals from GPS satellites provided by the GPS antenna  315 , or receive signals from other types of satellites providing the similar functionality such as GLONASS, BEIDOU or GALILEO, although still being referred to herein as GPS receiver. The GPS receiver  320  by receiving and processing the received signals from said satellites produces following output to the rest of the MDS  30 : the accurate frequency and time reference source; the location of the MDS  30 , 30 A, 30 B in terms of longitude, latitude and height as well as the moving direction of the MDS  30 , 30 A, 30 B, or signals related to thereof.  
         [0057]    The antenna  330  is a radio emitting element that is used for calibrating the array antenna  305  and the array receiver  310 . The antenna  330  is built with fixed and known propagation delays to each element of the array antenna  305 , and preferably is built within the same solid structure of the array antenna  305  to ensure a predetermined delay of the radio link  340  between calibration antenna  330  and each element of the array antenna  305 . The calibration signal fed to the calibration antenna is provided by the calibration transmitter  335  to be described next. The antenna  330  also receives signals from the serving basestation(s)  20 A, 20 B of TD  10 .  
         [0058]    The calibration transmitter part of the calibration transmitter and mobile receiver  335  produces a signal for calibrating the array antenna  305  and the array receiver  310 . Preferably it can be programmed to produce the signal with same frequency and the same modulation formats that the TD  10  and the GRD  100 , 100 A, 100 B would transmit, so that the calibration can be conducted at the exactly same working condition as the MDS  30 &#39;s location measurement operation would be on. Upon receipt of the TD  10  parameters (e.g., frequency and modulation mode), and before starting the location measurement, the MDS  30  will preferably conduct the calibration. The mobile receiver part of the calibration transmitter and mobile receiver  335  receives signals from serving basestation(s)  20 A, 20 B of TD  10  to obtain signaling messages and network timing.  
         [0059]    The display and user interface unit  345  includes a screen to accept data from the DSP subsystems  325  to display the local map with overlaid symbols of TD  10  location, GRD  100 , 100 A, 100 B location and the MDS  30 , 30 A, 30 B location. Preferably the display also shows the stored remote sensing photo of local land structures, being overlaid on the local map. An example has been given in FIG. 5. The unit  345  also accepts user control to the MDS  30 .  
         [0060]    The WLAN transceiver  355  and the antenna  350  transmits the images or image parameters produced by DSP subsystem  325  to the GRD  100 , 100 A, 100 B via radio link, for display on screen of GRD  100 , 100 A, 100 B. Although the unit  355  is referred to herein as a WLAN transceiver and is preferred to utilize a WLAN transceiver, it does not exclude the use of other types of transceivers in implementing the invention.  
         [0061]    The gravity sensor  360  reports information about the vehicle tilt to DSP subsystems  325  for use to correct the AOA measurement computation in DSP subsystems  325 .  
         [0062]    The compass sensor  365  reports the vehicle orientation to DSP subsystems  325  while vehicle is parked, for use to correct the AOA measurement computation in DSP subsystems  325 . For the magnetic compass sensors, the sensor is preferably being calibrated by the direction computed by movement based on GPS while moving, to eliminate the magnetic interference of the vehicle structure.  
         [0063]    Alternatively, the gravity sensor  360  and compass sensor  365  can be combined into a gyroscope based sensor and/or acceleration sensor.  
         [0064]    The DSP subsystem  325  includes signal processing devices such as ASIC (application specific integrated circuits), FPGA (field programmable gate array), DSP processor(s), micro controller(s), and/or general purpose microprocessor(s), memory devices, mass storage devices and peripheral devices. The functionality of DSP subsystem  325  in MDS  30  includes: conducting calibration of the array receiver; computing the AOA, TOA, TDOA and/or other alternative or related parameters of the incoming signals from TD  10  and GRD  100 , 100 A, 100 B; computing the longitude, latitude and height of the TD  10 , GRD  100 , 100 A, 100 B and MDS  30 ; while moving, computing the direction of moving of the MDS  30  based on position changes of the MDS  30  reported by the GPS receiver  320 ; while staying stationary, finding the vehicle orientation based on input from the compass sensor  365 ; finding the vehicle tilt based on input from the gravity sensor  360 ; overlaying the positions of MDS  30  (provided by GPS receiver  320  or computed by DSP subsystem  325 ), the TD  10 , and the GRD  100 , 100 A, 100 B onto a local area map electronically stored in the mass storage device, rotating the overlaid image based on the vehicle moving direction or parking orientation, responding the user&#39;s command from user interface  345  to zoom, move, or attribute change to the image, and producing the final image for display; outputting said image to the display and user interface unit  345 ; outputting the image or image parameters to the WLAN transceiver  355  to transmit to the GRD  100 , 100 A, 100 B for display on the GRD screen(s); controlling and configuring all functional parts within MDS  30 . When the on-MDS BS transmitter  370  and its associated antenna  375  (to be described in the next paragraph) is equipped within MDS  30 , the DSP subsystem  325  (together with receiver  310 ) further performs all additional functionalities that a BS receiver will perform, e.g., decoding of the in coming signals from TD  10  that are passed to DSP subsystem  325  by receiver  310 .  
         [0065]    In an alternative embodiment, the MDS  30  further includes an on-MDS BS transmitter  370 , and its associated antenna  375 . The on-MDS BS transmitter  370  would perform the functionalities of a regular base station transmitter which include performing the communication protocols, converting digital signals to analog, modulating, performing power control for the serving terminals TD  10  and GRD  100 , 100 A, 100 B, up-converting to radio frequency, amplifying the power, and radiating the signal through the antenna  375  to the air. In addition, as has been stated in the description of FIG. 6, the on-MDS BS transmitter  370  and antenna  375 , when in use, can perform the functionalities of the WLAN transceiver  355  and antenna  350  to convey the data for display on screen of the GRD  100 , 100 A, 100 B.  
         [0066]    [0066]FIG. 9 is a block diagram of the GRD in accordance with the preferred embodiments of the current invention. Now referring to FIG. 9, the preferred embodiment of GRD  100  is composed of a reference transmitter  440 , an antenna  450  for the reference transmitter, a WLAN transceiver  430 , an antenna  460  for the WLAN transceiver, a microprocessor  410 , and a display and user interface unit  420 . In alternative embodiments as will be further detailed later, the GRD  100  further includes a GPS receiver  480  and an antenna  490  for the GPS receiver, and a compass sensor  470 .  
         [0067]    The reference transmitter  440  is a device that can transmit the signal at the same or a close frequency and in the same mode of modulation as the TD  10  according to the air interface standard. Depending on the standard in use, usually the transmitter is also required to work with a receiver for such functions as power control, and processing according to protocols defined in the standard. Thereby, in such circumstances the reference transmitter  440  in essence is a mobile station, which includes an associated receiver although not explicitly marked in the figure, and said transmitter (and associated receiver)  440  preferably supports multiple bands and multiple standards. For example, it can also support regular voice communication with any telephone, including calling the TD  10 . As has been described earlier, the main functionality of the reference transmitter is to transmit the signal that is measured by MDS  30 , 30 A, 30 B for determining its location relative to that of the TD  10 .  
         [0068]    The WLAN transceiver  430  communicates with its counterpart WLAN transceiver  355  in MDS  30  (FIG. 8), to receive the data for display on the display and user interface unit  420  of the GRD  100 . Although the unit  430  is referred to herein as a WLAN transceiver and is preferred to utilize a WLAN transceiver, it does not exclude the use of other types of transceivers in implementing the invention.  
         [0069]    The microprocessor  410  controls and configures all the functional units in the GRD  100 . It also accepts user commands from display and user interface unit  420  to control the GRD  100 , including to control the display on the screen, such as zoom, move, change attributes and formats of the image.  
         [0070]    In an alternative embodiment, the compass sensor  470  reports the orientation of the handheld unit of GRD  100  to the microprocessor  410 , and the microprocessor  410  will rotate the image being displayed on screen of display and user interface unit  420  so that the displayed image orientation is always identical to the actual orientation of the GRD  100  body, for convenience of the user to search for the TD  10  in the same direction as shown on screen in relative to the position of GRD  100 .  
         [0071]    In yet another alternative embodiment, while GRD  100  is used in an area where GPS signals are of sufficiently good quality, the GPS receiver  480  and the GPS antenna  490  that are also included in the GRD  100  receive signals from GPS satellites and reports the location of GRD  100  to the microprocessor  410 . The reported position will be transmitted back to MDS  30  via the WLAN transceiver  430  and antenna  460 . Upon receipt of the location from GPS receiver  480  in GRD  100 , the MDS  30  will use said location information to correct the GRD locations measured by MDS  30  itself.  
         [0072]    In still yet another alternative embodiment, as has been stated in the descriptions of FIG. 6 and FIG. 8, when the MDS  30  utilizes an on-MDS BS transmitter  370  and associated antenna  375 , the reference transmitter (and its associated receiver)  440  and antenna  450  can perform the functionalities of the WLAN transceiver  430  and antenna  460  to receive the data for display on screen of display and user interface unit  420 . The WLAN transceiver  430  and antenna  460  can be eliminated from GRD  100  in this embodiment.  
         [0073]    The method and system described thereinbefore, while used in certain location applications other than E911, the wireless transmitting session of the TD  10  can be either TD originated or TD terminated, with or without human involvement. For example, it can be a call made by TD  10  after the TD  10  is triggered by certain means; it can be a call made by a person or by a machine that is terminated at the TD  10 ; it also can be a specially defined transmitting session.  
         [0074]    Throughout this specification, including the claims and drawings, the terminologies of a “reference transmitter (RT)” and a “reference wireless transmitting device” are used interchangeably. Furthermore, as has been stated, when an RT is combined with a “guiding device”, the combined device that has RT and guiding device functionalities is referred to as a guiding and reference device (GRD). According to the context, when referring to a GRD, it may refer to the RT functionality or the guiding device functionality or both of the GRD; when referring to a guiding device, it may mean a standalone guiding device, or the guiding device functionality of a GRD; and when referring to an RT or a reference wireless transmitting device, it may mean a standalone RT or a standalone reference wireless transmitting device, or the RT functionality of a GRD.  
         [0075]    The embodiments described herein are examples of structures, systems or methods having elements corresponding to elements of the invention. This written description may enable those skilled in the art to make and use embodiments having alternative elements that likewise correspond to the elements of the invention. The intended scope of the invention thus includes other structures, systems or methods that do not differ from the invention as described herein, and further includes other structures, systems or methods with insubstantial differences from the invention as described herein.