Mobile station position estimation for cellular mobile communication system

Abstract: A mobile station position estimation scheme for a cellular mobile communication system which is capable of estimating a position of a mobile station in a simple manner even in the general cellular mobile communication systems in which base stations are not synchronized. According to this mobile station position estimation scheme, a first signal sequence and a second signal sequence which are uniquely predetermined for the mobile station are exchanged between the mobile station and the base station, and then a position of the mobile station is estimated at one station among the base station and the mobile station, by obtaining a phase difference between the first signal sequence and the second signal sequence and calculating an estimated distance between the base station and the mobile station according to the phase difference.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a mobile station position estimation scheme for estimating a position of a mobile station in a cellular mobile communication system for carrying out communications between a mobile station and base stations, and a base station device and a mobile station device for realizing this mobile station position estimation scheme. DESCRIPTION OF THE BACKGROUND ART In the conventional cellular mobile communication system, it has been impossible to estimate a position of a mobile station in communication state, and for this reason it has been pointed out that there is a problem that a position of a source of an emergency call (such as dial "110" and "119" in Japan, dial "911" in U.S.A.) cannot be identified. There are well known radio based techniques for estimating a position such as the radio navigation schemes for airplanes and ships (beacon, loran, microwave landing system, etc.). However, these techniques are not suitable for the cellular mobile communications. Namely, the beacon requires a radar on a mobile station device so that it is not suitable for compact implementation of a mobile station device. The hyperbolic line of position scheme such as loran requires synchronization among base stations. In general, base stations of the cellular mobile communications are not synchronized with each other so that this scheme is not applicable to the cellular mobile communications, except for the IS-95 scheme of the American ELA/TIA standard which has synchronization among base stations. The microwave landing system can measure a position of an airplane within a particular area at high precision by using a special directional antenna, but it is difficult to measure an arbitrary position of a mobile station by using a simple radio equipment. Recently, the position measurement scheme called GPS (Global Positioning System) that utilizes satellite has become popular, but this is also a system that requires high precision synchronization among satellite stations, and therefore it is applicable only to the IS-95 scheme mentioned above, and not applicable to the general cellular mobile communication systems which are synchronous systems (US 5 508 708 and EP 0 713 344). Thus there has been a problem that the conventionally known radio based position estimation techniques are not suitable for the general cellular mobile communications because the compact implementation of a mobile station device or a radio device of a base station becomes difficult and the synchronization among base stations is required. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a mobile station position estimation scheme for a cellular mobile communication system which is capable of estimating a position of a mobile station in a simple manner even in the general cellular mobile communication systems in which base stations are not synchronized according to the method of claim 1 and the station devices of claims 9 and 11. Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a mobile station device and a base station device for realizing a mobile station position estimation scheme according to an example which is not in accordance with the present invention. Fig. 2 is a timing chart for explaining a manner of calculating a distance between a mobile station and a base station in a mobile station position estimation scheme according to the example. Fig. 3 is a diagram showing an exemplary estimated position of the mobile station obtained by a mobile station position estimation scheme according to the example for a case of using one base station. Fig. 4 is a diagram showing an exemplary estimated position of the mobile station obtained by a mobile station position estimation scheme according to the example, for a case of using two base stations. Fig. 5 is a diagram showing an exemplary estimated position of the mobile station obtained by a mobile station position estimation scheme according to the example, for a case of using one sector of one base station. Fig. 6 is a diagram showing an exemplary estimated position of the mobile station obtained by a mobile station position estimation scheme according to the example, for a case of using two sectors of two base stations. Fig. 7 is a block diagram of a mobile station device and a base station device for realizing a mobile station position estimation scheme according to an embodiment of the present invention, and Fig. 8 is a timing chart for explaining a manner of calculating a distance between a mobile station and a base station in a mobile station position estimation scheme according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to Fig. 1 to Fig. 6, an example of a mobile station position estimation scheme for a cellular mobile communication system which is not according to the present invention but is useful in the understanding of the present invention will be described in detail. Fig. 1 show configurations of a mobile station device 100 and a base station device 200 for realizing the mobile station position estimation scheme of an exemplary case in which the mobile station device 100 measures a distance from the base station device 200 and estimates its own position. The mobile station device 100 comprises a PN1 generation unit 101 for generating a first unique signal sequence PN1, a PN2 generation unit 102 for generating a second unique signal sequence PN2, a transmission signal generation unit 103 for generating transmission signals, a transmission signal processing unit 104 for obtaining mobile station transmission signals of a prescribed format using the transmission signals from the transmission signal generation unit 103 and the first unique signal sequence PN1 from the PN1 generation unit 101, a transmission unit 105 for transmitting the mobile station transmission signals from the transmission signal processing unit 104 through an antenna 111, a reception unit 106 for receiving base station transmission signals from a base station through the antenna 111, a phase detection unit 107 for detecting a phase of received signals received by the reception unit 106, a phase comparison unit 108 for comparing phases of the received signals and the mobile station transmission signals to obtain a phase difference, a distance calculation unit 109 for calculating a distance between the mobile station device 100 and the base station device 200 according to the phase difference obtained by the phase comparison unit 108, and a position estimation unit 110 for estimating a position of the mobile station device 100 according to the distance calculated by the distance calculation unit 109. On the other hand, the base station device 200 comprises a reception unit 206 for receiving the mobile station transmission signals from a mobile station through an antenna 211, a phase detection unit 207 for detecting a phase of received signals received by the reception unit 206, a PN1 generation unit 201 for generating the first unique signal sequence PN1, a PN2 generation unit 202 for generating the second unique signal sequence PN2, a transmission signal generation unit 203 for generating transmission signals, a base station position information generation unit 208 for generating a base station position information, a transmission signal processing unit 204 for obtaining base station transmission signals of a prescribed format using the transmission signals from the transmission signal generation unit 203, the second unique signal, sequence PN2 from the PN2 generation unit 202 and the base station position information from the base station position information generation unit 208, and a synchronized transmission unit 205 for transmitting the base station transmission signals from the transmission signal processing unit 204 in synchronization with the received signals received from the mobile station. Note here that the first unique signal sequence PN1 and the second unique signal sequence PN2 are signal sequences that are uniquely predetermined for each mobile station. In the mobile station device 100 and the base station device 200 with these configuration, the mobile station position estimation is carried out, for example, when this mobile station originates an emergency call, when a user of this mobile station wishes to check his/her own position, when a user of a fixed network or another mobile station wishes to check a position of this mobile station, etc. When this mobile station originates an emergency call, the position estimation can be realized by carrying out the following operation in a course of a call origination procedure. When a user of this mobile station wishes to check his/her own position, the user issues a position check request signal to the mobile station device 100 such that the mobile station device 100 carries out the following operation upon receiving this position check request signal. When a user of a fixed network or another mobile station wishes to check a position of this mobile station, a position check request signal is transmitted to the mobile station device 100 from a base station which is currently in communication with this mobile station such that the mobile station device 100 carries out the following operation upon receiving this position check request signal. Namely, upon receiving the position check request signal, the mobile station device 100 generates the first unique signal sequence PN1 to be used for the position estimation at the PN1 generation unit 101. Then, the transmission signal processing unit 104 converts this first unique signal sequence PN1 along with any other necessary transmission signals from the transmission signal generation unit 103 into a prescribed format, so as to obtain a position estimation reference signal, and the transmission unit 105 transmits this position estimation reference signal to the base station device 200 through the antenna 111. When this position estimation reference signal from the mobile station is received through the antenna 211 at the reception unit 206 of the base station device 200, the first unique signal sequence PN1 is generated at the PN1 generation unit 201, and a phase of PN1 in the received position estimation reference signal is detected by using the generated PN1 at the phase detection unit 207. Then, the second unique signal sequence PN2 is generated at the PN2 generation unit 202, and the transmission signal processing unit 204 converts this second unique signal sequence PN2 along with the base station position information from the base station position information generation unit 208 and any other necessary transmission signals from the transmission signal generation unit 203 into a prescribed format, so as to obtain a position estimation response signal. The synchronized transmission unit 205 then transmits this position estimation response signal to the mobile station device 100 through the antenna 211 in synchronization with the phase of the received PN1. Here, the base station position information is an information indicating latitude, longitude and altitude of the base station, for example. When this position estimation response signal from the base station is received through the antenna 111 at the reception unit 106 of the mobile station device 100, the second unique signal sequence PN2 is generated at the PN2 generation unit 102, and a phase of PN2 in the received position estimation response signal is detected by using the generated PN2 at the phase detection unit 107. Then, the phase comparison unit 108 compares the phase of PN1 in the position estimation reference signal transmitted by the transmission unit 105 and the phase of PN2 in the position estimation response signal received by the reception unit 106, and detects their phase difference. Then, the distance calculation unit 109 calculates a distance between the mobile station device 100 and the base station device 200 from this phase difference, and the position estimation unit 110 estimates the position of this mobile station from the distance calculated by the distance calculation unit 109 and the base station position information of the base station device 200 contained in the position estimation response signal received by the reception unit 106. Fig. 2 is a timing chart for explaining the principle for calculating the distance between the base station and the mobile station in this example. Fig. 2 shows an exemplary case where the first and second unique signal sequences PN1 and PN2 have the equal period. Here, PN1 and PN2 are used as marker signals for measuring a transmission time, and there is no need to continuously transmit them throughout the position estimation period. For example, signals to be transmitted periodically such as frame synchronization signal can be used as PN1 and PN2. The position estimation reference signal transmitted from the mobile station device 100 is received at the base station device 200 after as much delay as a transmission time of an uplink transmission path. The base station device 200 transmits the position estimation response signal in synchronization with the received position estimation reference signal. The mobile station device 100 receives this position estimation response signal after as much delay as a transmission time of a downlink transmission path, and compares the phase of the transmitted position estimation reference signal with the phase of the received position estimation response signal. Here, the measured phase; difference can be converted into a time value A [sec.], where A represents a transmission delay time for going and returning. Consequently, the distance D between the mobile station device 100 and the base station device 200 can be given by: D = Ac/2 [m] where c is the speed of light (which is approximately equal to 3 × 10 8 m/s). Fig. 3 illustrates a manner of estimating the mobile station position in this example. Namely, it is possible to estimate the mobile station device 100 as existing on a circle distanced from the base station device 200 by the distance D. In practice, the measured phase difference contains some error. Taking this error into account, the phase difference as converted into a time value can be given by A ± α [sec.], for example, and then the distance D can be expressed as: (A ± α) c = D ± α = D ± δ where δ = αc. In this case, the estimated position is given by a shaded region shown in Fig. 3. It is possible to improve the precision of the estimated position if the mobile station measures distances with respect to a plurality of base stations. Fig. 4 shows an exemplary case where distances with respect to two base stations are measured. In this case, the mobile station device 100 measures the distance with respect to the base station device 200 by the above described procedure first. When the distance between the mobile station device 100 and the base station device 200 is given by D1 ± δ1 [m] by accounting for error, the first estimated area (a single hatching circular area centered around the base station device 200) shown in Fig. 4 can be obtained. Next, the mobile station device 100 similarly measures the distance with respect to another base station device 300 by the above described procedure. When the distance between the mobile station device 100 and the base station device 300 is given by D2 ± δ2 [m] by accounting for error, the second estimated area (a single hatching circular area centered around the base station device 300) shown in Fig. 4 can be obtained. Then, the estimated position of the mobile station device 100 is given by an overlapping portion (a double hatching area) of the first estimated area and the second estimated area. In addition, when each base station device 200 or 300 covers its cell by a plurality of sectors, it is possible to further improve the precision of the estimated position by carrying out the position estimation for the mobile station device 100 within a sector of the base station device 200 or 300 which is currently in communication with the mobile station device 100, as shown in Fig. 5 for a case of using one base station and Fig. 6 for a case of using two base stations. Referring now to Fig, 7 and Fig. 8, an embodiment of a mobile station position estimation scheme for a cellular mobile communication system according to the present invention will be described in detail. Fig. 7 show configurations of a mobile station device 100 and a base station device 200 for realizing the mobile station position estimation scheme of the embodiment, where the mobile station device 100 has the same configuration as in Fig. 1 described above, whereas the base station device 200 has a configuration different from that of Fig. 1 in that a phase comparison unit 209 is additionally provided and the transmission unit 205 is not a synchronized transmission unit. The other elements identical to those of Fig. 1 are given the same reference numerals in Fig. 7. In the embodiment, the initial operation of the mobile station device 100 is the same as in the first embodiment. Namely, upon receiving the position check request signal, the mobile station device 100 generates the first unique signal sequence PN1 to be used for the position estimation at the PN1 generation unit 101. Then, the transmission signal processing unit 104 converts this first unique signal sequence PN1 along with any other necessary transmission signals from the transmission signal generation unit 103 into a prescribed format, so as to obtain a position estimation reference signal, and the transmission unit 105 transmits this position estimation reference signal to the base station device 200 through the antenna 111. When this position estimation reference signal from the mobile station is received through the antenna 211 at the reception unit 206 of the base station device 200, the first unique signal sequence PN1 is generated at the PN1 generation unit 201, and a phase of PN1 in the received position estimation reference signal is detected by using the generated PN1 at the phase detection unit 207. Then, the second unique signal sequence PN2 is generated at the PN2 generation unit 202, and the phase comparison unit 209 compares the detected phase of PN1 in the received position estimation reference signal and the phase of PN2 to be included in the base station transmission signals so as to obtain a first phase difference. Then, the transmission signal processing unit 204 converts this second unique signal sequence PN2 and information on the first phase difference along with the base station position information from the base station position information generation unit 208 and any other necessary transmission signals from the transmission signal generation unit 203 into a prescribed format, so as to obtain a position estimation response signal. The transmission unit 205 then transmits this position estimation response signal to the mobile station device 100 through the antenna 211 in synchronization with the phase of the received PN1. When this position estimation response signal from the base station is received through the antenna 111 at the reception unit 106 of the mobile station device 100, the second unique signal sequence PN2 is generated at the PN2 generation unit 102, and a phase of PN2 in the received position estimation response signal is detected by using the generated PN2 at the phase detection unit 107. Then, the phase comparison unit 108 compares the phase of PN1 in the position estimation reference signal transmitted by the transmission unit 105 and the phase of PN2 in the position estimation response signal received by the reception unit 106, so as to obtain a second phase difference. Then, the distance calculation unit 109 calculates a distance between the mobile station device 100 and the base station device 200 from the first phase difference indicated in the position estimation response signal received by the reception unit 106 and the second phase difference obtained by the phase comparison unit 108, and the position estimation unit 110 estimates the position of this mobile station from the distance calculated by the distance calculation unit 109 and the base station position information of the base station device 200 contained in the position estimation response signal received by the reception unit 106. Fig. 8 is a timing chart for explaining the principle for calculating the distance between the base station and the mobile station in the embodiment. Here, similarly to the example described with reference to Figs 1 to 6, the position estimation reference signal transmitted from the mobile station device 100 is received at the base station device 200 after as much delay as a transmission time of an uplink transmission path. However, in the embodiment, the base station transmits the position estimation response signal at independent timing without establishing synchronization with the received position estimation reference signal. On the other hand, the base station measures the phase difference (first phase difference) between the received position estimation reference signal and the position estimation response signal to be transmitted, and includes information on this first phase difference in the position estimation response signal. The mobile station device 100 receives this position estimation response signal after as much delay as a transmission time of a downlink transmission path, and measures the phase difference (second phase difference) between the phase of the transmitted position estimation reference signal and the phase of the received position estimation response signal. Here, the measured first and second phase differences can be converted into time values A [sec.] and B [sec.], respectively. In addition, suppose that the first and second unique signal sequences PN1 and PN2 have the same period g [sec.]. In this case, a transmission delay time for going and returning can be given by d = (A + B) - g). Consequently, the distance D between the mobile station device 100 and the base station device 200 can be given by: D = cd/2 [m] where c is the speed of light (which is approximately equal to 3 × 10 8 m/s). When the distance between the mobile station and the base station is obtained, the position of the mobile station can be estimated in a similar manner to that described in the Figs. 1 to 6 example. Note that the position estimation scheme of the present invention becomes more effective when the transmission rate of a radio transmission path is higher because the precision in the phase difference measurement can be improved. In this regard, the spread codes of CDMA (Code Division Multiple Access) provide a fast chip rate even when a data transmission rate is low, so that it is possible to use the spread codes of CDMA as the unique signal sequences used by the present invention. In such a case, the transmission signal processing unit of the mobile station device and the base station device shown in Fig. 7 carries out a processing for spreading the other transmission signals (or dummy signals when there is no other transmission signals) and the base station position information (in a case of the base station device) by using the unique signal sequence given by the spread code of CDMA, and transmits the resulting signal as the position estimation reference signal or the position estimation response signal from the transmission unit. Else, the transmission signal processing unit of the mobile station device and the base station device shown in Fig. 7 includes the unique signal sequence given by the spread code of CDMA in the position estimation reference signal or the position estimation response signal of the prescribed format, and transmits the resulting signal from the transmission unit. Note also that, the embodiment described above has been directed to a case where the mobile station device measures the distance and estimates the mobile station position, but the similar scheme in which the base station measures the distance and estimates the mobile station position can also be realized by exchanging the roles of the base station device and the mobile station device in the above description. Here however, in a case of the position estimation using a plurality of base stations, it is necessary exchange information among the base stations so as to obtain the estimated position by combining the measured distances and the position information for a plurality of base stations. The scheme in which the base station device measures the distance requires a larger processing load on the base station, but can reduce amount of signals in the radio section. Namely, in the cellular mobile communication in general, the base station normally transmits a regulation information, a channel structure information, etc., through a broadcast channel, and the unique signal sequence required by the present invention can be included in this broadcast channel so as to improve the efficiency because then the only new radio signal required for the position estimation will be a single signal to be transmitted by the mobile station. In particular, in a case of using the spread codes as the unique signal sequences in the CDMA mobile communication, the spread codes are already contained in information transmitted by the broadcast channel so that it is not even necessary to add a new information element to the broadcast channel. Note that, in a case of realizing the position estimation using a plurality of base stations, it is necessary for the mobile station to exchange the position estimation reference signal and the position estimation response signal with each base station, so that amount of signals in the radio section increases. In addition, there are cases where the position estimation precision can be lowered because of differences in the distance measurement time with respect to different base stations. For this reason, it is effective to adopt a scheme in which the mobile station carries out the simultaneous multi-code transmission in a plurality of code division multiplexed channels for signals to be transmitted to a plurality of base stations. Alternatively, it is also effective to adopt a scheme for dividing the transmission channel into slots and time division multiplexing signals to be transmitted to a plurality of base stations into the transmission channel of a frame structure. In practice, the received signal contains signals coming through a plurality of transmission paths (multipath) in overlap. The scheme of the present invention is capable of realizing:the accurate position estimation when it is possible to measure the phase of direct wave, and under the multipath environment, it is possible to keep error small by extracting a signal having the shortest delay time and using it for the phase measurement. Consequently, the phase detection unit of the mobile station device and the base station device shown in Fig. 7 detects the phase by receiving the receiving timing information for a signal having the shortest delay time from the reception unit. In the case of using a RAKE receiver in the CDMA mobile communication, a timing of a finger having the shortest delay time will be used. Note however that it is also possible to carry out the check of the phase, the judgement of the signal, etc.. by using signal after the RAKE combining. As described, according to the present invention, one of the base station and the mobile station transmits the first unique signal sequence, and the other one of the base station and the mobile station calculates a first phase difference between the first unique signal sequence and the second unique signal sequence to be transmitted, and transmits information on the first phase difference and the second unique signal sequence to that one of the base station and the mobile station without establishing synchronization with respect to the first unique signal sequence. Then, that one of the base station and the mobile station calculates a second phase difference between the first unique signal sequence and the received second unique signal sequence, and estimates the position of the mobile station by calculating the estimated distance between the base station and the mobile station according to information on the first phase difference and the second phase difference, so that it is possible to estimate the position of the mobile station in a simple manner even in the general cellular mobile communication systems in which base stations are not synchronized. It is to be noted that, besides those already mentioned above, many modifications and variations of the above embodiment may be made without departing from the novel and advantageous features of the present invention. Accordingly, all such modifications and variations are intended to be included within the scope of the appended claims.

Claims: A mobile station position estimation method in a cellular mobile communication system for carrying out communications between mobile stations and base stations, comprising the steps of: (a) exchanging between a base station and a mobile station a first signal sequence and a second signal sequence which are uniquely predetermined for the mobile station; and (b) estimating a position of the mobile station at either one of the base station and the mobile station, by obtaining a phase difference between the first signal sequence and the second signal sequence and calculating an estimated distance between the base station and the mobile station according to the phase difference; wherein at the step (a), said either one of the base station and the mobile station transmits the first signal sequence to another one of the base station and the mobile station, and said another one of the base station and the mobile station obtains a first phase difference by comparing phases of the first signal sequence as received by said another one of the base station and the mobile station and the second signal sequence to be transmitted by said another one of the base station and the mobile station, and transmits information on the first phase difference and the second signal sequence to said either one of the base station and the mobile station; at the step (b), said either one of the base station and the mobile station obtains a second phase difference by comparing phases of the first signal sequence as transmitted by said either one the base station and the mobile station and the second signal sequence as received by said either one of the base station and the mobile station, and calculates the estimated distance by using the first phase difference and the second phase difference, and wherein the mobile station exchanges the first signal sequence and the second signal sequence with respect to each one of at least two base stations which are not synchronized at the step (a), and the step (b) calculates estimated distances of the mobile station with respect to each of said base stations separately and estimates the position of the mobile station by combining the estimated distances of the mobile station with respect to said at least two base stations, there being a respective first signal sequence and a respective second signal sequence associated with the mobile station for each said base station, and a respective first phase difference for each said base station is obtained and transmitted at step (a), and a respective second phase difference for each said base station is obtained at step (b). The method of claim 1, wherein when a multipath signal is received at the step (a), said another one of the base station and the mobile station obtains the respective first phase difference by using the respective first signal sequence received from a path having a shortest delay time. The method of claim 1, wherein when a multipath signal is received at the step (a), said either one of the base station and mobile station obtains the respective second phase difference by using the respective second signal sequence received from a path having a shortest delay time at the step (b). The method of claim 1, wherein the cellular mobile communication system is a mobile communication CDMA scheme, and the first signal sequence and the second signal sequences are spread codes of the CDMA scheme. The method of claim 1, wherein at the step (a), the mobile station carries out simultaneous multi-code transmission by code division multiplexing signals to be transmitted with respect to said at least two base stations. The method of claim 1, wherein at the step (a), the mobile station carries out transmission by time division multiplexing signals to be transmitted to said at least two base stations into a channel of a frame structure. The method of claim 1, wherein the step (b) estimates the position of the mobile station to be within an estimated position area obtained by accounting for a prescribed error in positions distanced by the estimated distance from a said base station in a service area of the said base station; and when the mobile station exchanges the respective first signal sequence and the respective second signal sequence with respect to each one of the base stations at the step (a), the step (b) calculates estimated distances of the mobile station with respect to said at least two base stations separately, and estimates the position of the mobile station to be within an area in which a plurality of estimated position areas obtained from the estimated distances of the mobile station with respect to said at least two base stations are overlapping. The method of claim 1, wherein the step (b) estimates the position of the mobile station to be within an estimated position area obtained by accounting for a prescribed error in positions distanced by the estimated distance from a said base station in a sector of the said base station which is currently in communication with the mobile station; and when the mobile station exchanges the respective first signal sequence and the respective second signal sequence with respect to each one of the base stations at the step (a), the step (b) calculates estimated distances of the mobile station with respect to said at least two base stations separately, and estimates the position of the mobile station to be within an area in which a plurality of estimated position areas obtained from the estimated distances of the mobile station with respect to said at least two base stations are overlapping. A station device to be used as either one of a base station and a mobile station in a cellular mobile communication system for carrying out communications between mobile stations and at least two base stations, which base stations are not synchronized, by a method as claimed in claim 1, comprising: a transmission unit for transmitting to another one of the base station and the mobile station the respective first signal sequence which is uniquely predetermined for the mobile station: a reception unit for receiving the respective second signal sequence which is uniquely predetermined for the mobile station and information on the respective first phase difference indicating a phase difference between the respective first signal sequence and the respective second signal sequence as obtained by said another one of the base station and the mobile station, which are transmitted by said another one of the base station and the mobile station; and a position estimation unit for estimating a distance of the mobile station by obtaining the respective second phase difference by comparing phases of the respective first signal sequence transmitted by the transmission unit and the respective second signal sequence received by the reception unit, and calculating an estimated distance between each base station and the mobile station according to the respective first phase difference received by the reception unit and the respective second phase difference, and estimating a position from the estimated distances. The station device of claim 9, wherein when the reception unit receives a multipath signal, the position estimation unit obtains the respective second phase difference by using the respective second signal sequence received from a path having a shortest delay time. A station device to be used as either one of a base station and a mobile station in a cellular mobile communication system for carrying out communications between mobile stations and at least two base stations, which base stations are not synchronized, by a method as claimed in claim 1, comprising: a reception unit for receiving the respective first signal sequence transmitted by another one of the base station and the mobile station, which is uniquely predetermined for the mobile station; and a transmission unit for obtaining the respective first phase difference by comparing phases of the respective first signal sequence received by the reception unit and the respective second signal sequence which is uniquely predetermined for the mobile station, and transmitting the respective second signal sequence and information on the respective first phase difference to said another one of the base stations and the mobile station, so as to enable said another one of the base stations and the mobile station to obtain the respective second phase difference by comparing phases of the respective first signal sequence and the respective second signal sequence and estimate a position of the mobile station by calculating an estimated distance between each base station and the mobile station according to the respective first phase difference and the respective second phase difference. The station device of claim 11, wherein when the reception unit receives a multipath signal, the transmission unit obtains the respective first phase difference by using the respective first signal sequence received from a path having a shortest delay time.

Inventors: OHNO KOUJI, ONOE SEIZO, UEBAYASHI SHINJI, OHNO, KOUJI, ONOE, SEIZO, UEBAYASHI, SHINJI
Applicants: NIPPON TELEGRAPH & TELEPHONE, NTT MOBILE COMMUNICATIONS NETWORK INC.
Application year: 1998
Main classification: H04Q7
IPC codes: G01S5, H04W64