System and method for searching for mobile device

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates generally to telecommunications, and more specifically to systems and devices for locating mobile transceivers.

【0002】

[Conventional technology]

Description of Related Technologies Mobile communications have grown tremendously over the last decade. Mobile communications were once limited to critical phone calls in the absence of wire communications, but many people now use mobile communications as their primary means of communication. .. In addition, many today's mobile communications include processing capabilities such as PDAs (Personal Digital Assistants), handheld computers, notebook computers, and other devices. Some pagers also have bidirectional communication capabilities.

【0003】

Sometimes it is desirable to find a mobile communication device with some accuracy. A clear example of an application in which mobile exploration services are beneficial is the connection with emergency (ie, 911) services. In an emergency, the user of the mobile device may not know his location, or the user may be in a stressed state confused about his current location. This can result in critical emergency services such as police, fire and ambulance services being sent to the wrong location.

【0004】

Other services may also require location information for optimal efficiency. For example, a company can provide a "roadside assistance" service or a "gatekeeper" service to a customer for a fee. These services can provide mobile device users with directions to the nearest gas station, towing services, directions, and more. In order to effectively implement these services, it will be desirable to have fairly accurate information about the user's location.

【0005】

One solution would be to provide a GSP (Global Positioning System) device within each phone, which could send location information as part of a service request. While GSP devices can generate highly accurate location information, they require clear reception of signals from multiple satellites. Normally, satellite signals cannot be received accurately while the mobile communication device is inside a building or while a tall building surrounds the mobile communication device. Therefore, GSP location services will not work in many situations where they are most needed.

【0006】

Several solutions use triangulation to determine location based on transmissions from mobile devices. These solutions include TOA (Time of Arrival) and TDOA (Time of Arrival) techniques. Time synchronization is especially important for receivers (usually base stations) that receive the signal. This is because even small variations (even as short as tens of nanoseconds) can cause considerable inaccuracy in the resulting location calculations.

【0007】

[Problems to be Solved by the Invention]

Therefore, there is a need in the industry for highly accurate methods and devices for determining the location of mobile communication devices.

【0008】

[Means for solving problems]

The present invention provides a system for finding one of a plurality of mobile communication devices. The transmitter transmits a first signal, which has a device identification code and a time indicator to identify a particular mobile communication device to be sought. A circuit inside each of the mobile communication devices receives the first signal and transmits the second signal in response to a match between the identification code of the first signal and the internal identification code. Each of the plurality of receivers has an internal clock. When the first signal is received, these clocks are set based on the time indicator in the first signal. When the second signal is received, the time difference between the first signal and the second signal is determined. The control circuit determines the location of a particular mobile communication device according to the time difference determined by the plurality of receivers.

【0009】

The present invention provides considerable advantages over prior art. First, extremely accurate location information can be derived. Second, it is possible to transmit signals using prior art available within the building. Third, the effect of propagation delay is eliminated within the receiver. Fourth, only three receivers are needed to clearly locate the mobile communication device. However, more receivers can provide higher accuracy.

【0010】

For a more complete understanding of the present invention and its advantages, the following description, which should be received in conjunction with the accompanying drawings, is then referred to.

【0011】

The present invention is best understood in connection with FIGS. 1-6 of the drawings, where the same numbers are used for the same elements of different drawings.

【0012】

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 illustrates a prior art technique for locating the mobile communication device 10. Typically, a plurality of receivers 12, which are base stations, are located in the wide vicinity of the mobile communication device 10. The transmitter 14, which can also be located in the base station, operates in the wide vicinity of the mobile communication device 10. Network control 16 is coupled to receiver 12 and transmitter 14.

【0013】

In operation, the network must synchronize itself or use an external source (ie, the GSP clock) for synchronization. It is important that the receivers are time synchronized, as described in more detail below. When the transmitter 14 receives a command from the network control 16 to search for the mobile communication device 10, it issues a signal (start signal) that identifies the specific mobile communication device 10 under search. This signal is also received by the receiver 12. The mobile communication device 10 identified by this signal will broadcast a signal (timing signal) in response to this start signal. Alternatively, it is possible to initiate a triangulation using information such as call settings, framing information, or other overhead.

【0014】

The mobile communication device 10 has a limited range of outputs. Some of the receivers 12 detect the timing signal (R1 through R4 in the illustration in Figure 1), while the other receivers do not receive it (R5 in the illustration in Figure 1). Each receiver 12 that receives the signal detects the time when the signal was received there. If the time of reception of the timing signal exceeds the time threshold from the reception of the start signal, the timing signal is invalid.

【0015】

Each receiver 12 stores a value indicating the time when the timing signal is received, based on the internal clock of each receiver. Assuming that the timing signal is valid, the time of reception from each receiver 12 is used to calculate the location of the mobile communication device 10. The TDOA method is usually used because the origination time of the location pulse is generally not known to the accuracy required for location determination. Using that technique, the difference in arrival times between receivers 12 is used in triangulation calculations. Therefore, triangulation is T_1-2, T_1-3, And T_1-4Run using, where T_X-YIs the receiver R_XAnd receiver R_YThe difference in reception of timing signals between.

【0016】

The system for locating the mobile communication device 10 described above has some drawbacks. First, the transmitter 14 and receiver 12 in the network must be highly synchronized. Day clock times for all receivers must be synchronized within tens of nanoseconds for accurate search of the mobile communication device 10. Second, the mobile communication device 10 is responsible for generating a timing signal in response to identifying the start signal, and therefore additional functionality is required on each mobile communication device 10. Third, four receivers 12 must receive a valid timing signal to obtain at least three triangulation points. This reduces the effective range of the network. This is because the receivers are not in close proximity outside the metropolitan area. Fourth, delays within each receiver due to antennas, cables, and internal components will vary from receiver to receiver. These delays can affect the time stamps associated with receiving the timing signal and therefore must be normalized and removed taking that into account. Again, erroneous calculation of delays within the range of tens of nanoseconds can significantly affect the accuracy of location calculations.

【0017】

FIG. 2 illustrates an improved location device and method for locating the mobile communication device 20. Again, there are usually multiple receivers 22, which are base stations, roughly in the vicinity of the mobile communication device 20. The transmitter 24, which can also be located within the base station, is also roughly near the mobile communication device 20. Network control 26 is coupled to receiver 22 and transmitter 24.

【0018】

To locate the mobile communication device 20, network control 26 commands transmitter 24 to generate a first signal, S1, which contains a time stamp and an identifier unique to a single mobile communication device 20. .. This signal is broadcast to the mobile communication device 20 and the receiver 22 in the vicinity of the transmitter 24. Each receiver 24 that receives the signal S1 uses the S1 signal to set its internal clock to the time indicated in the time stamp. For the highest accuracy, each receiver 22 is fixed and compensates for the distance between the known transmitter 24 and receiver 22. Therefore, all receivers 22 in the vicinity will be automatically synchronized to a high degree using each S1 signal.

【0019】

The same signal S1 is received by the mobile communication device 20, one of which is identified by the signal S1 (if it is within the broadcast area of transmitter 24). When the identified mobile communication device 20 receives the signal S1, the identified mobile communication device 20 re-broadcasts the signal as the signal S2. The receiver 22 in the broadcast communication area of the mobile communication device 20 receives the re-broadcast communication signal S2. In the illustrated embodiment of FIG. 2, receivers R1 through R4 receive the rebroadcast communication signal, while receiver R5 is outside the range of mobile communication device 20.

【0020】

The rebroadcast communication signal S2 can take several forms. In the first embodiment, the mobile communication device 20 receives the signal S1 at the first frequency and immediately broadcasts the signal as the signal S2 at the second frequency. In the second embodiment, the mobile communication device 20 receives the first signal and transmits the signal S2 at the same frequency. The mobile communication device 20 can also add information such as a value indicating the propagation delay through the electronics of the mobile communication device 20 to the signal, as shown in FIG.

【0021】

The receiver 22 receives the signal S2 and notes the time when the signal S2 is received based on the internal clock time set according to the signal S1. The time it takes for this signal to travel from transmitter 24 to a given receiver is therefore T._S2-T_S1And here, T_S1Is the time when the S1 signal was received and T_S2Is the time when S2 was received.

【0022】

Any propagation delay in the receiver between receiving S1 or S2 and remembering the time of reception will differ by T._S2-T_S1It should be noted that it is removed in determining.

【0023】

As shown in Figure 4a, the time difference T_S2-T_S1Indicates the distance between the transmitter 24 and the mobile communication device 20 plus the distance between the mobile communication device 20 and the receiver 22. Since the locations of transmitter 24 and receiver 22 are fixed and known, the possibility for a given time difference can be defined as an ellipse that focuses on transmitter 24 and receiver 22. The network control 26 can use this information to pinpoint the location of the mobile communication device 20.

【0024】

If the three receivers 22 are close enough to the transmitter 24 and the mobile communication device 20 to receive the S1 and S2 signals, then it is possible to define three ellipses, which are the transmitter 24. , Receiver 22 location and T_S2-T_S1Corresponds to the distance defined by. As shown in Figure 4b, the three ellipses will intersect at the location of mobile communication device 20.

【0025】

Note that the ellipses do not have to intersect exactly for accurate location determination. For example, if an unknown delay through the mobile communication device 20 enlarges the ellipse to create an area 30 between the intersections of three points between the ellipses, as shown in FIG. 4c, the minimum square determination of the center of the area 30. However, the location of the mobile communication device 20 can be approximated well.

【0026】

Furthermore, if no more than two receivers have valid data, the location of the mobile communication device 20 may be located at one of the intersections of the two points. Information from the user, a map, or other information such as the corner of arrival can be used to disambiguate.

【0027】

As mentioned above, the S2 signal can be an iterative version of the S1 signal at different frequencies, or the S2 signal can be received and retransmitted at the same frequency. Shifting the S1 signal to a different frequency can be performed via the simple circuit shown in Figure 5 with almost no time delay. In this embodiment, the mixing circuit 40 is provided within the mobile communication device 20. The mixing circuit 40 receives the S1 signal from the transmitter 22 via the antenna 42. The filter / coupler 43 separates the signal from any signal being output at the same time and allows the signal to pass through the filter / amplifier 44 for further tuning. The output of the filter / amplifier 44 is input to the mixer 46 along with the output of the oscillator 48, which shifts the frequency of the S1 signal to the desired intermediate frequency (IF). The IF signal is passed through the band filter 50. The output of the band filter 50 is received by the mixer 52 along with the output of the oscillator 54, which further shifts the frequency to the desired second frequency.

【0028】

FIG. 6 illustrates a circuit for receiving an S1 signal and transmitting an S2 signal at the same frequency. In this embodiment, the S1 signal is received from the transmitter 24 via the antenna 62. The S1 signal is tuned through the filter / amplifier 64. The output of the filter / amplifier 64 is received by the mixer 66 along with the output of the oscillator 68, which converts the S1 signal to the desired intermediate frequency. The IF signal is demodulated in binary format within the demodulator 70. The demodulated bits are stored in a memory / processing circuit 72, which adds any desired additional data to the signal. The data related to the signal S2 is output from the memory / processing circuit 72 to the modulator 74. The output of the modulator 74 is converted by the mixer and oscillator 68 to the original frequency of the signal S1. The S2 signal is then amplified and transmitted using the antenna 62.

【0029】

Demodulating the signal from the transmitter and remodulating it requires a considerable delay within the mobile communication device 20. Therefore, the signal is sent from transmitter 24 to mobile communication device 20 and then to receiver 22, adding information about the delay through mobile communication device 20, which can vary between different mobile communication devices. It is desirable to provide a more accurate measurement of the time traveled. Time, therefore, T_S2-T_S1-T_dCalculated as, where T_dIs the delay via the mobile communication device 20.

【0030】

The present invention provides considerable advantages over prior art. First, extremely accurate location information can be derived. Second, it is possible to transmit signals using prior art available within the building. Third, the propagation delay in the receiver is eliminated. Fourth, only three receivers are needed to locate the mobile communication device 20. However, more receivers can provide higher accuracy.

【0031】

Although the detailed description of the present invention is directed to embodiments as some examples, various modifications of these embodiments, as well as alternative embodiments, may be suggested to engineers in the art. .. The present invention includes any modified or alternative embodiment within the scope of the claims.

[Simple explanation of drawings]

[Figure 1]

It is a figure which illustrates the prior art for finding a mobile communication device.

[Figure 2]

It is a figure which shows the communication system which has the location service which has an automatic synchronization function.

[Fig. 3]

FIG. 5 represents a signal used to locate a desired mobile communication device.

[Fig. 4a]

FIG. 5 illustrates possible locations of a mobile device for a single receiver using the present invention.

[Fig. 4b]

FIG. 4a illustrates the intersection of three sets of possible locations.

[Fig. 4c]

FIG. 4a illustrates the intersection of three sets of possible locations according to FIG. 4a in the event of an unexpected delay.

[Fig. 5]

It is a figure which illustrates the frequency shift circuit.

[Fig. 6]

It is a figure which illustrates the circuit for re-broadcasting a signal at a common frequency.

[Explanation of symbols]

12, 22, R1, R2, R3, R4, R5 receivers 14, 24 transmitter 16, 26 network control circuit 40, 60 retransmission circuit 42, 58, 62 antennas 44, 56, 64, 78 filters / amplifiers 46, 52, 66, 76 mixer 48, 54, 68 oscillator 50 band filter 70 demodulator 72 Memory / processing circuit 74 modulator S1, S2 signal