Cellular radio synchronization

• US 6,667,963 B1
• Filed: 01/14/1999
• Issued: 12/23/2003
• Est. Priority Date: 01/21/1998
• Status: Expired due to Fees

• Current Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Rantalainen, Timo, Ruutu, Ville
• Primary Examiner(s): Ton, Dang
• Assistant Examiner(s): Duong, Frank
• Application Number:
  US09/231,067
• Time in Patent Office: 1,804 Days
• Field of Search: 370/324, 370/331, 370/332, 370/337, 370/347, 370/321, 370/350, 370/442, 370/458, 370/498, 370/503, 370/508, 370/509, 455/456.1, 455/404.2, 455/438, 455/439, 455/502, 375/356, 340/539.11, 340/539.13, 340/573
• US Class Current: 370/337
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04W 56/0045 compensating for timing error by altering transmission time
• CPC Class Codes: H04W 56/0075 based on arrival time vs. expected arrival time

Abstract

A cellular radio network based positioning system for determining the position of a mobile station (16). For each base transceiver station (1 to 5) or cell of the network, a fixed list of base transceiver stations is stored by a Mobile Positioning Centre (13). Each list identifies those base transceiver stations which enable the position of a mobile station served by the corresponding base transceiver station (6) to be optimally determined. The list is transmitted to the mobile station (16) via the serving base transceiver station (6) together with a list of respective real time differences which exist between the serving base transceiver stations and the listed base transceiver stations. The mobile station determines an observed time difference for each of the listed base transceiver stations, relative to the serving base transceiver station (6), from signals broadcast by the listed base transceiver stations. The mobile station listens for synchronization sequences contained in these signals during time windows defined by the various real time differences. The observed time differences are transmitted from the mobile station (6) to the serving base transceiver station (6) and are used by the network to compute the position of the mobile station (16).

Claims

1. A method of determining the position of a mobile communications device in a cellular telephone network and comprising the steps of:

synchronising the mobile communications device to each of a plurality of neighboring base transceiver stations using the method comprising, in a Time Division Multiple Access (TDMA) cellular radio telephone system, synchronising a mobile communications device to a first radio channel transmitted from a first radio transmitter when the mobile communications device is currently synchronised to a second radio channel transmitted from a second radio transmitter, and wherein said first radio channel conveys at least one synchronization feature,

the method further comprising;

determining a real time difference between the operating clocks of said first and second radio transmitters;

transmitting said determined real time difference, or a value or values derived therefrom, from said second transmitter to the mobile communications device, over said second radio channel;

causing the mobile communications device to listen to said first radio channel for said synchronisation feature during a time window or windows derived from said determined real time difference or said value or values derived therefrom; and

wherein said second transmitter belongs to a serving base transceiver station, and determining respective Observed Time Differences (OTDs); and

determining the position of the mobile device using said OTDs and the respective RTDs.

2. A method according to claim 1, wherein said real time difference is determined using time delay relationships obtained for a radio receiver whose position is fixed and known.

3. A method according to claim 2, wherein said step of determining the real time difference between the operating clocks of said first and second radio transmitters comprises:

causing the radio receiver, whose position is known and which is syhchronised to said second radio channel, to listen on said first radio channel for said synchronisation feature and to determine the time of arrival (OTD) of said synchronisation feature, where said time of arrival (OTD) represents the difference between the propagation delays over said first and second radio channels to the mobile device, offset by the real time difference (RTD) between the operating clocks of the two transmitters; and

determining an actual difference (GTD) between the propagation delays over said first and second radio channels to the mobile device using the known positions of said radio receiver and the first and second radio transmitters; and

determining said RTD using said OTD and said GTD.

4. A cellular radio telephone network for use in the method of claim 1, the network comprising:

said first and second radio transmitters associated with respective first and second base station transceiver stations; and

signal processing means for determining said real time differences (RTD);

wherein said second transmitter is arranged to receive said determined real time difference, or said value or values derived therefrom, from said single processing means and to transmit this to a mobile communications device.

5. In a cellular radio telephone system, a method of determining a timing for a neighbouring base transceiver station for the purpose of determining the position of a mobile communications device in a cellular telephone network, the method comprising:

synchronising the mobile device to the neighbouring base transceiver station using the method of claim 4 to enable an Observed Time Difference (OTD) to be obtained, relative to the serving base transceiver station; and

determining said timing using the real time difference (RTD) for the neighbouring base transceiver station relative to the serving base transceiver station, and the observed time difference (OTD) measured for the neighbouring base transceiver station.

6. A mobile communications device for use in the method of claim 1 and comprising:

a radio receiver for receiving said real time difference (RTD) or said value(s); and

signal processing means for defining said time window(s) using said determining real time difference, or said value or values derived therefrom and for causing said radio receiver to listen to said first radio channel for said synchronisation feature during said time window or windows.