JP2009074974A - Mobile station and location derivation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly estimate the location of a mobile station with high precision regardless of electric field strength. <P>SOLUTION: The mobile station which can wirelessly communicate with a plurality of base stations 120 comprises: a wireless communication section 222 for wirelessly communicating with the plurality of base stations; a location information acquisition section 250 for acquiring the absolute location information of the plurality of base stations; a delay calculation section 252 for measuring a propagation delay time when transmitting/receiving radio waves to/from the plurality of base stations; a distance calculation section 254 for calculating the distance to each of the plurality of base stations on the basis of the propagation delay time; and a location determination section 258 for determining, on the basis of the absolute location information and distance concerning each of the plurality of base stations, the absolute position of the mobile station. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a mobile station capable of wireless communication with a plurality of base stations. More specifically, the present invention relates to a mobile station for deriving the absolute position of a mobile station using propagation delay of radio waves transmitted and received with the base station, and position derivation. Regarding the method.

  In recent years, mobile stations such as mobile phones and PHS (Personal Handy phone System) have become widespread, making it possible to make calls and obtain information regardless of location or time. Such a mobile station connects to a communication network by performing wireless communication with base stations arranged at a predetermined interval. Then, the base station communicates with a base station within the communicable range of the communication partner to establish voice communication between the mobile stations.

  On the other hand, the mobile station described above is provided with a service for displaying the current location on the map and searching for nearby restaurants through the absolute position of the mobile station. In order to receive such services, it is necessary to specify the absolute position of the local station, but unlike the base stations that are fixedly arranged as described above, the mobile station independently grasps the absolute position of the local station. I don't have the technique to do.

  For example, a method using GPS (Global Positioning System) can be considered as means for specifying the position of the mobile station. In such GPS, radio waves from at least three satellites can be captured, and the distance to each satellite can be calculated to determine its absolute position. At this time, if three satellites can be acquired, the position on the plane of the own station can be acquired, and if four satellites can be acquired, further altitude can be acquired. However, GPS is a relatively expensive system and requires time for calculation. Another problem is that it cannot be used in situations where it is difficult to receive satellite radio waves.

In addition, a technique is known in which the absolute position is calculated using the three-point intersection method (three-point positioning method) by combining the electric field intensity of the radio wave received from each base station and the position of the base station (for example, Patent Documents). 1). Furthermore, a technique for transmitting the electric field strength of the radio wave received from each base station and the identification code of the base station to the position management station and causing the position management station to calculate the current position of the own station is disclosed (for example, patents). Reference 2).
Japanese Patent Laid-Open No. 2-044929 Japanese Patent Laid-Open No. 9-247737

  The above-mentioned absolute position estimation technology of a mobile station uses the characteristic that the electric field strength of a received radio wave changes (attenuates) according to the distance to the base station. Refer to the relational expression between the electric field strength and the distance. Thus, the distance between the base station and the mobile station is derived.

  However, in an environment where buildings are densely packed, the electric field strength may be amplified or attenuated due to multipath fading or shadow wing, and may greatly deviate from the original electric field strength. Therefore, the distance from the base station that is uniquely derived from the electric field strength also varies from the actual distance to the long or short, and the position specifying accuracy of the mobile station is extremely reduced.

  Also, in areas where base station installation density is low or where buildings are densely populated, the intensity of received radio waves is relatively low, and the amount of change in distance due to fluctuations in electric field strength increases, increasing distance estimation accuracy. There was also a problem that they could not.

  The present invention has been made in view of the problems of the conventional position identification technology, and an object of the present invention is to estimate the position of a mobile station quickly and with high accuracy regardless of the strength of electric field strength. It is to provide a mobile station and a position derivation method that can be used.

  In order to solve the above problems, according to an aspect of the present invention, a mobile station capable of wireless communication with a plurality of base stations, a wireless communication unit that performs wireless communication with the plurality of base stations, and a plurality of bases The position information acquisition unit that acquires the absolute position information of the station, the delay calculation unit that measures the propagation delay time when radio waves are transmitted to and received from a plurality of base stations, and the distance between each of the plurality of base stations based on the propagation delay time There is provided a mobile station, comprising: a distance calculation unit that calculates a base station; and a position specifying unit that specifies an absolute position of the mobile station based on absolute position information and distance regarding each of a plurality of base stations. The

  In the present invention, the absolute position of the mobile station is grasped by the three-point intersection method (three-point positioning method) using the absolute position of at least three base stations and the distance from the base station. The distance from the base station is calculated using the propagation delay of the radio wave. When deriving such a distance, the conventional electric field strength is easily affected by multipath fading and disturbance, whereas the propagation delay is hardly affected because the time taken for the radio wave to travel through the round-trip path is measured.

  Further, even if the propagation delay is further increased by the wraparound of the radio wave, it does not become faster, so the original propagation delay time can be easily estimated. Therefore, the position of the mobile station can be estimated quickly and with high accuracy regardless of the strength of the electric field strength.

  A reliability determination unit that determines the reliability of the distance to a plurality of base stations is further provided, and the position specifying unit weights the absolute position information and the distance reference for each base station according to the determination result of the reliability determination unit. May be performed.

  The reliability determination unit determines a priority order based on the reliability for the calculated distances to the plurality of base stations, and makes a reference to a highly reliable distance preferentially. Therefore, since the position specifying unit refers to the distance to each base station through weighting based on the reliability, the absolute position of the mobile station is less affected by the distance with low reliability and the influence of the distance with high reliability. growing. With this configuration, a three-point intersection method using a highly reliable distance can be implemented, and the absolute position of the mobile station can be specified with higher accuracy.

  The reliability determination unit may determine the reliability according to the distance from the base station, and the reliability may be higher as the distance calculated by the distance calculation unit is longer.

  In the present invention, a propagation delay is used instead of the electric field strength. However, even with the propagation delay, fluctuation due to the wraparound of the radio wave occurs. However, the ratio of the fluctuation amount of the propagation delay to the distance from the base station has a characteristic that the longer the distance, the smaller the ratio. Therefore, the absolute position of the mobile station can be specified with higher accuracy by preferentially using the one having a long estimated distance.

  The reliability determination unit may determine the reliability according to the dispersion of the distances calculated by the distance calculation unit a plurality of times, and the reliability may be higher as the dispersion is smaller.

  In an area where buildings are densely packed, multipath fading occurs through a plurality of buildings, and dispersion of propagation paths increases. Therefore, if the variance is large, it is assumed that there are many propagation paths between the mobile station and the base station, and the priority order is lowered. If the variance is small, there are many radio waves that are directly propagating, that is, the original propagation delay is measured. Raise priority. Thus, the absolute position of the mobile station can be specified with higher accuracy.

  In order to solve the above problems, according to another aspect of the present invention, there is provided a position derivation method for deriving an absolute position of a mobile station capable of wireless communication with a plurality of base stations, the absolute position of the plurality of base stations. A location information acquisition step for acquiring information, a delay calculation step for measuring a propagation delay time when radio waves are transmitted to and received from a plurality of base stations, and a distance for calculating a distance from each of the plurality of base stations based on the propagation delay time There is provided a position deriving method including a calculation step and a position specifying step of specifying an absolute position of the mobile station based on absolute position information and distance regarding each of a plurality of base stations.

  The component corresponding to the technical idea in the mobile station mentioned above and its description are applicable also to the said position derivation method.

  As described above, the mobile station of the present invention can quickly and accurately estimate the position of the mobile station regardless of the strength of the electric field strength.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  In the mobile station, in order to select the most suitable base station for performing wireless communication among a plurality of base stations near the own station, the electric field strength of the control signal emitted by the base station is measured and the electric field strength is The largest base station is selected as the communication destination. If such a field strength measurement mechanism is used, the distance to the base station can be estimated. However, in the distance estimation using the electric field strength, the measurement accuracy is greatly lowered depending on the environment. If such low-accuracy location information is used, the service provided by the service provider cannot be sufficiently received.

  In this embodiment, the absolute position of the mobile station is estimated using a propagation delay instead of the electric field strength. In the following embodiment, in order to facilitate understanding, the configuration of the entire wireless communication system will be described first, and then the configuration of the mobile station will be described in detail. In addition to the mobile phone and PHS described above, various electronic devices such as a notebook personal computer and a PDA (Personal Digital Assistant) can be applied as the mobile station of this embodiment. Will be described.

(Wireless communication system 100)
FIG. 1 is a system block diagram for explaining the radio communication system 100. The wireless communication system 100 includes a PHS terminal 110 owned by a user, a base station 120, an IP communication network 130 such as the Internet, and a connection selection server 140.

  In the wireless communication system 100, when a user attempts to connect a telephone line from his / her PHS terminal 110 to another PHS terminal 150, a base station in a wireless communicable area according to the operation of the user's PHS terminal 110. As shown in (1) of FIG. 1, the base station 120 requests the connection selection server 140 to establish a communication connection with another PHS terminal 150 via the IP communication network 130.

  Then, the connection selection server 140 selects the base station 120 in the wireless communicable area of the other PHS terminal 150 as shown in (2) in FIG. 1, and communicates with the other PHS terminal 150 possessed by the communication partner. Set up a voice call.

  When the setting of the base station 120 necessary for the voice call is completed, the connection selection server 140 passes the voice call processing between the base stations, and as shown in (3) in FIG. The base stations 120 perform transmission / reception of audio signals directly. At this time, the connection selection server 140 shifts to a standby state for assigning an appropriate base station 120 according to a change in the communication environment of each PHS terminal 110, 150, for example, movement of the PHS terminal 110.

(PHS terminal 110)
Hereinafter, the configuration of the PHS terminal 110 in the wireless communication system 100 will be described.

  FIG. 2 is a functional block diagram showing a hardware configuration of the PHS terminal 110, and FIG. 3 is a perspective view showing an appearance of the PHS terminal 110. As shown in FIG. The PHS terminal 110 includes a terminal control unit 210, a terminal memory 212, a display unit 214, an operation unit 216, a voice input unit 218, a voice output unit 220, and a wireless communication unit 222.

  The terminal control unit 210 manages and controls the entire PHS terminal 110 using a semiconductor integrated circuit including a central processing unit (CPU). The terminal control unit 210 naturally performs a call function and a mail distribution function using the PHS terminal 110 using the program in the terminal memory 212. Further, it also functions as a position information acquisition unit 250, a delay calculation unit 252, a distance calculation unit 254, a reliability determination unit 256, and a position specifying unit 258, which will be described later.

  The terminal memory 212 includes a ROM, a RAM, an EEPROM, a non-volatile RAM, a flash memory, an HDD (Hard Disk Drive), and the like, and stores a program processed by the terminal control unit 210, audio data, and the like.

  The display unit 214 includes a liquid crystal display, EL (Electro Luminescence), PDP (Plasma Display Panel), etc., and is stored in the terminal memory 212 or via an IP communication network 130 (not shown). The GUI (Graphical User Interface) of the Web browser or application provided by the user can be displayed.

  The operation unit 216 includes switches such as a keyboard, a cross key, and a joystick, and receives a user operation input.

  The voice input unit 218 includes a voice recognition device such as a microphone, and converts the user's voice input during a call into an electrical signal that can be processed in the PHS terminal 110.

  The voice output unit 220 includes a speaker, and converts the voice signal of the call partner received by the PHS terminal 110 into voice and outputs the voice. In addition, a ring tone, an operation sound of the operation unit 216, an alarm sound, and the like can be output.

  The wireless communication unit 222 performs wireless communication with the base station 120 in the mobile phone network. As such wireless communication, there is a time division multiplexing method in which a plurality of time slots obtained by time division of frames in the base station 120 are respectively assigned to channels of the PHS terminal 110 to perform communication.

  Next, functions and operations performed using the hardware described in FIGS. 2 and 3 will be described in detail.

  The position information acquisition unit 250 requests acquisition of absolute positions to a plurality of base stations 120 via the wireless communication unit 222, acquires absolute position information stored in advance in each base station 120, and stores the absolute position information in the terminal memory 212. To do.

  The delay calculation unit 252 transmits a signal for measuring propagation delay to each of the plurality of base stations 120 via the wireless communication unit 222, receives a response from the plurality of base stations 120 to the signal, The propagation delay time (about 0 to 20 μsec) by the round trip is measured. The propagation delay measurement may be performed simultaneously using the absolute position information acquisition signal by the position information acquisition unit 250 described above, or may be performed using an independent signal.

  The distance calculation unit 254 calculates a distance from each of the plurality of base stations 120 based on the propagation delay time measured by the delay calculation unit 252. Basically, the propagation delay time and the distance are in a proportional relationship, and the distance from each base station 120 can be obtained by multiplying the propagation delay time by a predetermined count (for example, 300 m / μsec). However, in an area where buildings are densely packed, the propagation delay time may not be uniquely determined due to multipath fading or the like. In such a case, measurement of the propagation delay time by the delay calculation unit 252 is performed a plurality of times, and the distance calculation unit 254 statistically processes the plurality of propagation delay times and extracts a highly reliable propagation delay time. The distance may be obtained.

  When deriving such distances, the conventional electric field strength detects analog quantities and is therefore easily affected by multipath fading and disturbance, whereas propagation delay is less affected by measuring the time of radio waves. . Therefore, the distance can be derived with higher accuracy than the electric field strength.

  Further, even if the propagation delay is further increased by the wraparound of the radio wave, it does not become faster, so the original propagation delay time can be easily estimated. Therefore, the position of the PHS terminal 110 can be estimated quickly and with high accuracy regardless of the strength of the electric field strength.

  The reliability determination unit 256 determines the reliability of the distance to the plurality of base stations 120. In this embodiment, the greater the number of base stations 120 that are distance measurement targets, the higher the position identification accuracy. However, regarding the base station 120 in which the fluctuation amount of the propagation delay time has increased due to multipath fading or the like, the distance is also unreliable. Therefore, the reliability determination unit 256 determines a priority order based on the reliability for the plurality of distances calculated by the distance calculation unit 254, and causes the position specifying unit 258 described later to refer to a highly reliable distance with priority.

  The position specifying unit 258 specifies the absolute position of the PHS terminal 110 itself based on the absolute position information and distance regarding each of the plurality of base stations 120.

  FIG. 4 is an explanatory diagram for describing the position specification of the PHS terminal 110 by the position specifying unit 258. In the present embodiment, the absolute positions of the PHS terminals are grasped by the three-point intersection method using the absolute positions of at least three base stations 120 and the distances from the base stations 120. For example, in FIG. 4, when the distances to the base stations 120A, 120B, and 120C calculated by the distance calculation unit 254 are estimated as a, b, and c, respectively, the base stations 120A, 120B acquired by the position information acquisition unit 250 , 120C, the intersection of the circles having the radius from the absolute position is the current absolute position of the PHS terminal 110.

  In addition, the position specifying unit 258 weights the absolute position information and the distance reference regarding each base station 120 according to the determination result of the reliability determining unit 256.

  As described above, the reliability determination unit 256 determines the priority order based on the reliability for the calculated distances from the plurality of base stations 120. Here, the position specifying unit 258 refers to the distance to each base station 120 through weighting based on the reliability. Specifically, the highly reliable distance is reflected in the three-point intersection method with 100% weighting. If the distance with low reliability is reflected with a weight of 50% or less or not reflected at all, the absolute position of the PHS terminal 110 is less affected by the distance with lower reliability, and the influence of the distance with higher reliability is large. Become. With this configuration, a three-point intersection method using a highly reliable distance can be implemented, and the absolute position of the PHS terminal 110 can be specified with higher accuracy.

  Here, the reliability determination unit 256 can determine the reliability according to the distance from the base station. In this case, the longer the distance calculated by the distance calculation unit 254, the higher the reliability.

  FIG. 5 is an explanatory diagram for explaining a difference in reliability due to a difference in distance. FIG. 5A shows a case where the distance between the PHS terminal 110 and the base station 120 is short, and FIG. 5B shows a case where the distance is long.

In this embodiment, a propagation delay is used instead of the electric field strength. However, even with the propagation delay, fluctuation due to the wraparound of radio waves occurs. However, as shown in FIG. 5A, when the distance to the base station 120 is short, the ratio of the variation (t ₂ −t ₁ ) to the distance (true propagation delay time t ₁ ) is large. When the distance to the base station 120 is long, as shown in FIG. 5B, the ratio of the fluctuation amount (t ₄ −t ₃ ) of the propagation delay time to the distance (true propagation delay time t ₃ ) is small. Become. Therefore, the longer the distance from the base station 120, the smaller the variation ratio with respect to the distance. Therefore, the absolute position of the PHS terminal 110 can be specified with higher accuracy by preferentially using the one with a long estimated distance.

  The reliability determination unit 256 determines the reliability according to the variance of the distances calculated by the distance calculation unit 254 a plurality of times, and assumes that the reliability is higher as the variance is smaller. Here, the variance represents a dispersion of distances, and may be quantified by an arithmetic average obtained by squaring the difference between the average value and each value.

  FIG. 6 is an explanatory diagram for explaining a difference in reliability due to a difference in distribution. 6A shows a case where the dispersion of the distance between the PHS terminal 110 and the base station 120 is large, and FIG. 6B shows a case where the dispersion of the distance is small.

  In an area where buildings are densely packed, multipath fading occurs through a plurality of buildings, and dispersion of propagation paths increases. Therefore, as shown in FIG. 6A, when the variance is large, it is assumed that there are many propagation paths between the PHS terminal 110 and the base station 120, and the priority is lowered. As shown in FIG. Is small, it is assumed that there are many radio waves propagating directly, that is, the original propagation delay is measured, and the priority is raised. In this way, the absolute position of the PHS terminal 110 can be specified with higher accuracy.

(Location derivation method)
Next, a position deriving method for deriving the current absolute position of the PHS terminal 110 itself using the PHS terminal 110 as the mobile station described above will be described.

  FIG. 7 is a flowchart showing a process flow of the position derivation method. First, the PHS terminal 110 searches for nearby base stations 120, and creates each base station 120 identification code and field strength list (S300). Then, a dedicated message for distance measurement is transmitted on the control channel to the base station 120 having the strongest field strength in the field strength list (S302).

  Upon receiving the dedicated message from the PHS terminal 110, the base station 120 adds its own absolute position information (for example, longitude and latitude) and sends it back to the PHS terminal 110 (S304). The PHS terminal 110 acquires the absolute position information from the base station 120 (S306: position information acquisition step) and stores it in the terminal memory 212 (S308).

  In parallel with the acquisition of the absolute position information, the PHS terminal 110 measures the propagation delay time of the returned radio wave (S310: delay calculation step), and based on the radio wave propagation speed and the propagation delay time, The distance is calculated (S312: distance calculation step). Then, regarding the combination of the absolute position of the base station 120 and the distance to the base station 120, the PHS terminal 110 determines whether a sufficient number (predetermined number) for estimating the absolute position of the own station has been acquired (S314). If it is insufficient, the target is moved to the base station 120 having the next highest electric field strength (S316), and the process is repeated from the transmission of the dedicated message.

  When a sufficient number of absolute position information and distances are acquired, the PHS terminal 110 determines the reliability of the absolute position information and distance acquired from each base station 120 based on the distance or variance, and performs weighting (S318). ). Then, based on the absolute position information and distance acquired from each base station 120, the absolute position of the own station is specified according to the three-point intersection method (S320: position specifying step).

  Here, after deriving the distance of each base station 120, the reliability is determined based on the distance and dispersion. However, the present invention is not limited to this, and the reliability is determined using the electric field strength at the start of the position deriving method. It is also possible to narrow down the base station 120 at a long distance, which is likely to be high, and use only the absolute position information and distance of the narrowed base station 120 for the three-point intersection method.

  In such a position deriving method, the position of the PHS terminal 110 can be estimated quickly and with high accuracy regardless of the strength of the electric field strength.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  In the above-described embodiment, the position specifying calculation by the three-point intersection method is executed in the PHS terminal 110 of the own station. However, the present invention is not limited to this, and the absolute position information and distances of the plurality of base stations 120 are temporarily selected. It may be transmitted to the server 140 or the like, and the position specifying calculation may be performed in the connection selection server 140 or the like.

  Further, in this embodiment, the propagation delay time by the round trip path between the PHS terminal 110 and the base station 120 is measured, but when the PHS terminal 110 or the base station 120 knows the absolute time, the forward path or the return path It is also possible to acquire the propagation delay time only by this.

  Note that the steps in the position derivation method of the present specification do not necessarily have to be processed in time series in the order described in the flowchart, but are performed in parallel or individually (for example, parallel processing or object-based processing). Processing).

  The present invention relates to a mobile station capable of wireless communication with a plurality of base stations. More specifically, the present invention relates to a mobile station for deriving the absolute position of a mobile station using propagation delay of radio waves transmitted and received with the base station, and position derivation. Can be used in the way.

It is a system block diagram for demonstrating a radio | wireless communications system. It is the functional block diagram which showed the hardware constitutions of the PHS terminal. It is the perspective view which showed the external appearance of the PHS terminal. It is explanatory drawing for demonstrating the position specification of the PHS terminal by a position specific part. It is explanatory drawing for demonstrating the difference in reliability by the difference in distance. It is explanatory drawing for demonstrating the difference in reliability by the difference in dispersion | distribution. It is the flowchart which showed the flow of the process of the position derivation method.

Explanation of symbols

110 ... PHS terminal 120 ... base station 250 ... position information acquisition unit 252 ... delay calculation unit 254 ... distance calculation unit 256 ... reliability judgment unit 258 ... position specifying unit

Claims (5)

A mobile station capable of wireless communication with a plurality of base stations,
A wireless communication unit that performs wireless communication with the plurality of base stations;
A position information acquisition unit that acquires absolute position information of the plurality of base stations;
A delay calculation unit for measuring a propagation delay time when radio waves are transmitted to and received from the plurality of base stations;
A distance calculation unit for calculating a distance to each of the plurality of base stations based on the propagation delay time;
A position specifying unit that specifies the absolute position of the mobile station based on the absolute position information and distance regarding each of the plurality of base stations;
A mobile station comprising: A reliability determination unit that determines the reliability of the distance to the plurality of base stations;
The mobile station according to claim 1, wherein the position specifying unit weights reference of absolute position information and distance regarding each of the base stations according to a determination result of the reliability determination unit.   The movement according to claim 2, wherein the reliability determination unit determines reliability according to a distance from the base station, and the reliability is higher as the distance calculated by the distance calculation unit is longer. Bureau.   3. The movement according to claim 2, wherein the reliability determination unit determines the reliability according to a variance of the distance calculated by the distance calculation unit a plurality of times, and the reliability is higher as the variance is smaller. Bureau. A position derivation method for deriving an absolute position of a mobile station capable of wireless communication with a plurality of base stations,
A position information acquisition step of acquiring absolute position information of the plurality of base stations;
A delay calculation step for measuring a propagation delay time when radio waves are transmitted to and received from the plurality of base stations;
A distance calculating step of calculating a distance to each of the plurality of base stations based on the propagation delay time;
A position specifying step for specifying the absolute position of the mobile station based on the absolute position information and distance regarding each of the plurality of base stations;
A position derivation method characterized by comprising:

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