GB2357397A

GB2357397A - Method of locating a mobile unit in a low coverage area of a cellular telephone system

Info

Publication number: GB2357397A
Application number: GB9929626A
Authority: GB
Inventors: Brendan Patrick Ludden; Luis Lopes
Original assignee: Motorola Ltd
Current assignee: Motorola Solutions UK Ltd
Priority date: 1999-12-16
Filing date: 1999-12-16
Publication date: 2001-06-20
Anticipated expiration: 2019-12-16
Also published as: GB9929626D0; GB2357397B

Abstract

A method for providing increased communications coverage to a mobile station (MS) (14) for measurement of transmissions therefrom, e.g. for location, uses a sufficient number of remote stations (RS) (16,18) typically other mobile stations within communications range of the MS (14) so that the number of BTSs (10) and RSs (16,18) within communications range of the MS (14) collectively number at least three. A paging message is sent from the BTS (10) to each of the RSs (16,18) via a stand-alone dedicated control channel (SDCCH), each paging message including at least one temporary mobile subscriber identity number (TMSI) identifying a destination RS (16,18) for the paging message and at least one pseudo-TMSI comprising instructions to the destination RS (16,18) to measure a transmission from the MS (14). A measurement is taken at each of the RSs (16,18) and sent to the BTS (10) via the SDCCH during the setup of the call. The measurement may relate to time of arrival of transmissions from the MS (14). The invention is useful as a technique for locating the position of a MS without the need for it to be within communication range of at least three base transceiver stations.

Description

2357397 METHOD AND APPARATUS FOR ENHANCEMENT OF LOW-COVERAGE AREAS IN

SUPPORT OF MOBILE STATION MEASUREMENT TECHNIQUES IN A CELLULAR TELEPHONE SYSTEM

FIELD OF THE INVENTION

The present invention relates to wireless communication systems in general, and more particularly to methods and apparatus for enhancement of low- coverage areas in support of mobile station measurement techniques in a cellular telephone system.

BACKGROUND OF THE INVENTION

Methods and apparatus for providing measurements of mobile stations (MS) in a cellular telephone network, such as determining the location of a mobile station (MS), are well known in the art. In one method, known as hyperbolic trilateration, at least three base transmission stations (BTS) at known locations send transmissions to an MS whose location is to be determined. The time of arrival (TOA) of each of the transmissions at the MS is noted according to the MS internal clock, and the time difference of arrival (TDOA) of transmissions from at least two different pairs of BTSs is calculated. Where the BTSs transmit in synchronicity, a hyperbola may be demarcated between each BTS pair by presenting multiple solutions for each transmission's time of flight (TOF). The intersection between two hyperbolae indicates the estimated location of the MS.

Where the BTSs transmit asynchronously, such as in a cellular telephone system based on the Global System for Mobile Communications (GSM), the hyperbolae may be demarcated once the BTS transmission time offsets are calculated by making TDOA measurements at a known position, such as via a Location Measurement Unit (LMU) as is known for Enhanced Observed Time Differential (EOTD) systems.

Prior art MS location techniques fall short, however, in low-coverage areas, such as rural areas, where an MS is unable to "see" the three BTSs needed in order to perform the I TDOA measurements. This might be due to the MS not being within range of three BTSs simply by virtue of BTSs being placed relatively far apart, or due to obstructions or interference. While this may be solved by providing additional BTSs, the cost of doing so for the purpose of MS location usually cannot be justified, especially in rural areas where the installation of land lines in support of BTSs generally incurs a far greater cost than such installation in urban areas.

SUMMARY OF THE INVENTION

The present invention seeks to provide methods and apparatus for enhancement of low-coverage areas in support of mobile station measurement techniques in a cellular telephone system that overcome the disadvantages of the prior art.

According to one aspect of the present invention, a method for providing increased communications coverage to a mobule station (MS) for measurement of transmissions therefrom, including the steps of providing at least one base transceiver station BTS for communicating with the MS and a sufficient number of remote stations (RS) within communications range of the MS and the BTS such that there is at least one RS provided and such that the number of BTSs and RSs within cornmunications range of the MS collectively number at least three, sending a paging message from the BTS to each of the RSs via a stand alone dedicated control channel (SDCCH), each paging message including at least one temporary mobile subscriber identity number (TMSI) identifying a destination RS for the paging message and at least one pseudo-TMSI including instructions to the destination RS to measure a transmission from the MS, sending a paging response from each of the RSs to the BTS whereupon the BTS discontinues communications with the RS prior to the assignment of a traffic channel (TCH) therebetween, receiving a transmission from the MS at each of the RSs, taking a measurement at each of the RSs of the transmission in accordance with the 2 instructions, initiating a call from each of the RSs to the BTS and sending the measurement from each of the RSs to the BTS via the SDCCH during the setup of the call whereupon the BTS discontinues communications with the RS prior to the assignment of a traffic channel (TCH) therebetween.

Further in accordance with a preferred embodiment of the present invention the method is further characterized by the RSs communicating wirelessly only.

Still further in accordance with a preferred embodiment of the prOsent invention the method is further characterized by the measurement being a time-of- arrival measurement of the transmission.

According to a second aspect of the present invention a c-ellular telephone system comprises at least one mobile station (MS) and at least one base transmission station (BTS) for communication therewith, and a sufficient number of remote stations (RS) within communications range of the MS and the BTS such that there is at least one RS provided and such that the number of BTSs and RSs within communications range of the MS collectively number at least three, wherein the BTS is operative to send a paging message to each of the RSs via a stand-alone dedicated control channel (SDCCH), each paging message including at least one temporary mobile subscriber identity number (TMSI) identifying a destination RS for the paging message and at least one pseudo-TMSI including instructions to the destination RS to measure a transmission from the MS, and wherein each of the RSs is operative to send a paging response to the BTS whereupon the BTS discontinues communications with the RS prior to the assignment of a traffic channel (TCH) therebetween, and wherein each of the RSs is operative to receive a transmission from the MS and take a measurement of the transmission in accordance with the instructions, and wherein each of the RSs is operative to initiate a call to the BTS and wherein each of the RSs is operative to send the measurement to 3 the BTS via the SDCCH during the setup of the call whereupon the BTS discontinues communications with the RS prior to the assigninent of a traffic channel (TCH) therebetween.

Further in accordance with a preferred embodiment of the present invention the system is further characterized in that the RSs communicate wirelessly only.

Still further in accordance with a preferred embodiment of the present invention the system is further characterized in that the measurement is a time-of- arrival measurement of the transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the appended drawings in which:

Fig. 1 is a simplified illustration of a system for enhancement of lowcoverage areas in support of mobile station measurement techniques in a cellular telephone system, constructed and operative in accordance with a preferred embodiment of the present invention; and Fig. 2 is a simplified flowchart illustration of a method of operation of the system of Fig. 1, operative in accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF A PREFFERED EMBODIMENT

Reference is now made to Fig. 1 which is a simplified illustration of a system for enhancement of low-coverage areas in support of mobile station measurement techniques in a cellular telephone system, constructed and operative in accordance with a preferred embodiment of the present invention. In Fig. 1 a base transmission stations (BTS) 10 of a cellular telephone system is shown having a communication range represented by a circle 12.

A mobile station (MS) 14 is shown within communication range 12 of BTS 10. In accordance 4 with the present invention two remote stations (RS) 16 and 18 are provided. Portions of the communications ranges of RS 16 and 18 are represented by arc projections 20 and 22 respectively and are shown to include BTS 10 and MS 14. For the purpose of,the present invention it is appreciated that were there a BTS present in the system of Fig. I in addition to BTS 10 and in whose communications range MS 14 could be found, that only one RS would need to be provided within communications range of BTS 10 and MS 14, as long as the number of BTSs and RSs within communications range of MS 14 collectively rAimber at least three.

RSs 16 and 18 typically support wireless communications only, thereby obviating the need for land-based communications lines connecting RSs 16 anL-d 18 to central network components of the cellular telephone system. RSs 16 and 18 are preferably capable of receiving wireless communications from MS 14 and supporting bidirectional communications with BTS 10 in accordance with known techniques, preferably those known for use with GSM.

Reference is now made to Fig. 2 which is a simplified flowchart illustration of a preferred method of operation of the system of Fig. 1. In the method of Fig. 2 BTS 10 sends a paging message, such as a type 3 GSM paging message, to each of RSs 16 and 18, typically via a stand-alone dedicated control channel (SDCCH) (step 100). The paging message typically includes at least one temporary mobile subscriber identity number (TMSI) identifying the either RS 16 or RS 18 as the destination RS for the paging message. The paging message also typically includes at least one "pseudo-TMSI," being not a TMSI but rather having the same data structure of a TMSI, including instructions to the destination RS and readable by the RS to make a measurement associated with MS 14, such as. a time-of arrival (TOA) of a transmission from MS 14. The instructions may be encoded in the pseudo TMSIs using any suitable encoding technique known in the art and decoded using any suitable known decoding technique. As an acknowledgement of having received the paging message each RS sends a paging response to BTS 10 (step I 10). Once the paging response is received from the RS BTS 10 preferably discontinues communications with the RS prior to the assignment of a traffic channel (TCH) between BTS 10 and the RS (step 120). Thus, no call need be made between BTS 10 and RSs 16 and 18. Rather, RSs 16 and 18 are able to receive their instructions encoded in the paging message itself After receiving the paging message from BTS 10, RSs 16 and 18 decode the pseudo-TMSI payload into measurement instructions using known means (step 130). RSs 16 and 18 then take the indicated measurement of MS 14 in accordance with said instructions (step 140). Once the measurement is taken, RSs 16 and 18 preferably initiate a call to BTS 10 (step 150). In initiating the call RSs 16 and 18 typically send their TMSIs to BTS 10, thereby identifying themselves (step 160). RSs 16 and 18 then send the measurement information to BTS 10 via the SDCCH during the setup of the call (step 170). Once RSs 16 and 18 finish transferring the data, cornmunications between BTS 10 and RSs 16 and 18 are again preferably discontinued prior to the assignment of a traffic channel (TCH) between BTS 10 and RSs 16 and 18 (step 180).

It is appreciated that SDCCHs may be dynamically assigned on TCHs between BTS 10 and RSs 16 and 18 for the purpose of transfer of the measurement data, such as when the existing SDCCH capacity proves insufficient.

The use of the TMS1 paging scheme described hereinabove is believed to provide a faster method for activation of RSs than may be achieved using existing protocols known for cellular telephone systems such as the simple messaging system (SMS).

While the methods and apparatus disclosed herein may or may not have been described with reference to specific hardware or software, the methods and apparatus have been described in a manner sufficient to enable persons of ordinary skill in the art to readily 6 adapt commercially available hardware and software as may be needed to reduce any of the embodiments of the present invention to practice without undue experimentation and using conventional techniques.

VVhile the present invention has been described with reference to a few specific embodiments, the description is intended to be illustrative of the invention as a whole and is not to be construed as limiting the invention to the embodiments shown. It is appreciated that various modifications may occur to those skilled in the art that, while not spe&fically shown

Claims

herein, are nevertheless within the scope of the appended Claims.

7 CLAIMS 1. A method for providing increased communications coverage to a MS (14) for measurement of transmissions therefrom, including the steps of; providing at least one base transceiver station (BTS) for communicating with the MS and a sufficient number of remote stations (RS) (16,18) within communications range of said MS (14) and the BTS (10) such that there is at least one RS (16,18) provided and such that the number of BTSs (10) and RSs (16,18) within communications range of said MS (14) collectively number at least three; sending a paging message (100) from the BTS (10) to each of the RSs (16, 18) via a: stand-alone dedicated control channel (SDCCH), each paging message comprising at least one temporary mobile subscriber identity number (TMSI) identifying a destination RS (16,18) for the paging message and at least one pseudo-TMSI comprising instructions to said destination RS (16,18) to measure a transmission from said MS (14); sending a paging response (110) from each of the RSs (16,18) to the BTS (10) whereupon the BTS (10) discontinues communications (120) with the RS (16, 18) prior to the assignment of a traffic channel (TCH) therebetween; receiving a transmission from said MS (14) at each of the RS s (16,18); taking a measurement (140) at each of the RSs (16,18) of the transmission in accordance with the instructions; initiating a call (150) from each of the RSs (14) to the BTS (10); and sending said measurement (170) from each of the RSs (16,18) to the (10) via said SDCCH during the setup of said call whereupon said BTS (10) discontinues communications (180) with the RS (16,18) prior to the assignment of a traffic channel (TCH) therebetween.

8 2. A method according to claim I further characterized by the RSs (16,18) communicating wirelessly only.

3. A method according to claim 1 or claim 2 in which further characterized by said measurement being a time-of-arrival measurement of the transmission.

4. A cellular telephone system comprising at least one mobile statj bn (MS) (14) and at least one base transmission station (BTS) (10), for communicapon therewith, and a sufficient number of remote stations (RS) (16,18) withii! communications range of the MS (14) and the BTS (10) such that there is at least one RS (16, 18) provided and such that the number of BTSs (10) and RSs (16,18) within communications range of said MS (14) collectively number at least three; wherein the BTS (10) is operative to send a paging message (100) to each of said RSs (16,18) via a stand-alone dedicated control channel (SDCCH), each paging message incuding at least one temporary mobile subscriber identity number (TMSI) identifying a destination RS (16,18) for the paging message and at least one pseudoTMSI including instructions to said destination RS (16,18) to measure a transmission from said MS (14); and wherein each of said RSs (16,18) is operative to send a paging response (110) to the BTS (10) whereupon the BTS (10) discontinues communications (120) with the RS (16,18) prior to the assignment of a traffic channel (TCH) therebetween; and wherein each of the RSs (16,18) is operative to receive a transmission from said MS (14) and take a measurement (140) of the transmission in accordance with the instructions; 9 and wherein each of thed RSs (14) is operative to initiate a call (150) to the BTS (10); and wherein each of the RSs (16,18) is operative to send said measurement (170) to the BTS (10) via the SDCCH during the setup of the call whereupon said BTS (10) discontinues communications (180) with the RS (16,18) prior to the assignment of a traffic channel (TCH) therebetween.

5. A system according to claim 4 further characterized in that the RSs (16,18) communicate wirelessly only.

6. A system according to claim 4 or claim 5 further characterized in that the measurement is a time-of-arrival measurement of said transmission.

7. A method for providing increased communications coverage to a mobile station for measurement of transmission therefrom substantially as hereinbefore described with reference to the drawings.

8. A cellular telephone system substantially as hereinbefore described with reference to the drawings.