Patent EA-002006-B1 (EA)
Title: Positioning system for digital telephone networks
Inventor: DUFFETT PETER
IPC: H04W64/00
Filed: 1998-10-21
Abstract: 1. A positioning system comprising at least two receivers of a digital telephone network having a plurality of transmission sources, the first of which receivers is at a known location and the second of which is a mobile receiver whose position is to be determined, said system utilising transmission signals having a format at least a portion of which has predetermined values or a portion which is repeated, each receiver including a reference clock; means for generating in each receiver a reference signal locked to the reference clock, the reference signal having a similar format to the transmission signals and thus a portion identical to the portion of the received signal which has predetermined values or which is repeated; and means, in each receiver, for comparing the received transmission signal and the reference signal to determine their relative time offset to enable thereby the position of the second receiver to be determined by determining the time delay between the respective signals received at both receivers. 2. A positioning system according to claim 1, wherein said reference signal is generated from the known characteristics of said transmission signals. 3. A positioning system according to claim 2, wherein said reference signal is generated from a first received transmission. 4. A positioning system comprising at least two receivers of a digital telephone network having a plurality of transmission sources, the first of which receivers is at a known location and the second of which is a mobile receiver whose position is to be determined, said system utilising transmission signals having a format at least a portion of which has predetermined values, and the relative time offsets of the transmission signals received at each receiver from said transmission sources being measured relative to each other in said receivers by means for comparing the received transmission signals from the different transmission sources with one another to determine their relative time offsets and thereby determine the position of the second receiver by determining the time delay between the respective signals received at both receivers. 5. A positioning system comprising at least two receivers of a digital telephone network having a plurality of transmission sources, the first of which receivers is at a known location and the second of which is a mobile receiver whose position is to be determined, said system utilising transmission signals having a format at least a portion of which is sequentially repeated, in which the relative time offsets of the transmission signals received at each receiver from said transmission sources are measured relative to each other in said receivers by means for comparing the sequentially received transmission signals from the different transmission sources with one another to determine their relative time offset and thereby determine the position of the second receiver by determining the time delay between the respective signals received at both receivers. 6. A positioning system according to any of claims 1 to 5, further including a central processor, said central processor receiving from the receivers data representing the relative time offset of the transmission signals received at each receiver from the transmission sources, and for determining the position of the second receiver by determining the time delay between the respective signals received at both receivers from said relative time offset. 7. A positioning system according to claim 6, wherein said central processor receives said data from the receivers via one or more packets of a data service in a GSM network. 8. A positioning system according to claim 6 or claim 7, wherein data representing the position of said mobile receiver is transmitted from said central processor. 9. A positioning system according to claim 8, wherein data representing the position of said mobile receiver is transmitted from said central processor to said mobile receiver. 10. A positioning system according to any of claims 1 to 9, wherein the transmission signals are control channel signals. 11. A positioning system according to claim 10, wherein the transmission signals comprise BCCH signals of a GSM network. 12. A positioning system according to any of claims 1 to 9, wherein the transmission signals comprise numbered TDMA frames repeated at predetermined intervals and wherein said receivers are arrange to make recordings of the transmission signals from said transmission sources relative to the time of arrival of a given numbered frame, thereby to synchronise the start of said recordings. 13. A positioning system according to any of claims 1 to 12, adapted to determine the time delay between the respective signals received at both receivers at such time when said mobile receiver is not otherwise engage. 14. A positioning system according to any of claims 1 to 13, wherein the receivers are multi-channel receivers. 15. A positioning system according to any of claims 1 to 14, wherein measurements of both the phase difference and the time delay between the arrival of the signals at each of the said receivers are determined, which phase measurements are used in addition to the time measurements in order to make improved estimates of the time delays, in order to determine the position of the second receiver. 16. A positioning system according to any of claims 1 to 15, including means for minimising the effects of multipath propagation by identifying and measuring the time of arrival of a signal received from a transmission source, relative to a reference signal locked to an internal reference clock, in time or equivalent transformed space, said means auto-correlating a measured part of said received signal; constructing a template comprising a portion of the auto-correlation of an expected part of said received signal and a portion of the auto-correlation of a part of the measured part of said received signal; cross-correlating the expected part of said received signal with the measured part of said received signal; and  measuring the offset at which the template best fits the cross-correlation as the time of arrival of the signal broadcast by a transmission source relative to said reference signal. 17. A positioning system according to claim 16, wherein the means for constructing the template comprises means for combining a portion of the auto-correlation of an expected part of said received signal corresponding to offset times before that of the central peak of said received signal with a portion of the auto-correlation of a part of the measured part of said received signal corresponding to offset times after that of the central peak. 18. A digital telephone network incorporating a positioning system according to any of the preceding claims. 19. A digital telephone network according to claim 18, further including plural fixed receivers at known locations; and means for synchronising said network by establishing the time offsets measured by said plural fixed receivers. 20. A digital telephone network according to claim 18, further including plural fixed receivers at known locations, each of said receivers having an interna clock; and means for synchronising said fixed receivers by establishing the time offsets of their respective interna clocks. 21. A digital telephone network according to claim 20, further including means for synchronising said network by establishing transmission time offsets of said transmission sources from said fixed receivers. 22. A digital telephone network according to claim 20, further including means for establishing the position of a transmission source from said fixed receivers. 23. A handset for a digital telephone network incorporating a positioning systemaccording to claim 4 or claim 5 or any of claims 6 to 17 when dependent thereon, said handset including means for measuring the relative time offsets of the transmission signals received at the handset from a number of transmission sources by comparing the received transmission signals from the different transmission sources with one another; and means for transmitting data representing said relative time offset, for determination of the position of the handset. 24. A handset for a digital telephone network incorporating a positioning system according to any of claims 1 to 3 or any of claims 6 to 17 when dependent thereon, said handset including a reference clock; means for generating a reference signal locked to the reference clock the reference signal having a similar format to the transmission signals and thus a portion identical to the portion of the received signal which has predetermined values or which is repeated; means for comparing the received transmission signal and the reference signal to determine their relative time offset; means for transmitting data representing said relative time offset to enable thereby the position of the handset to be determined. 25. A method of determining the position of a mobile receiver in a digital telephone network positioning system having at least two receivers, the first of which is at a known location and the second of which is mobile, the method comprising transmitting signals from a plurality of sources, the transmission signals having a format at least a portion of which has predetermined values or a portion of which is repeated; determining the time offset, of the transmission signals received at each receiver from a transmission source relative to a reference clock of each receiver, by generating a reference signal locked to the reference clock, the reference signal having a similar format to the transmission signals and including a portion identical to the predetermined values or determining the time delay between the respective signals received at both receivers by determining their relative time offset, to thereby determine the position of the second receiver. 26. A method according to claim 25, wherein said reference sign