Method and apparatus for locating a remote unit within a communication system
Timing Advance information is obtained from base stations ( 103–105 ), and is utilized by a remote unit ( 113 ) to approximate the Time of Arrival (TOA) of the signals from each base station. The remote unit ( 113 ) accesses a single base station to determine its timing advance. In order to increase accuracy, the remote unit ( 113 ) then repeats the process, but during the next iteration, the transmission timing is advanced or delayed by a fraction of a bit (e.g. ¼ bit). The base station responds with a new timing advance value. This process is repeated until it is determined how many fractions of bit increments the remote unit ( 113 ) is away from a known timing advance boundary of the base station. Once known, this information is utilized to determine the location of the remote unit ( 113 ).
1. A method for locating a remote unit within a communication system, the method comprising the steps of:
transmitting a first message to a base station;
determining a timing advance based on the first message;
advancing or retarding transmission circuitry;
transmitting a second message to the base station;
determining a second timing advance based on the second message;
determining a location based on advancing or retarding transmission circuitry by a fraction of a timing-advance bit;
wherein the step of determining a distance from the base station comprises the steps of determining a value for C, wherein C is approximately equal to:
D TA −(N−½)D ADV where,
D TA =a distance to a timing-advance boundary;
D ADV =distance attributed to advancing/retarding the transmission circuitry: and
N=a number of iterations in timing advance that causes a change in the timing advance.
2. The method of claim 1 wherein the step of transmitting the first message comprises the step of transmitting the first message on a Random Access Channel.
3. The method of claim 1 further comprising the steps of:
transmitting a third message to a second base station;
determining a third timing advance based on the third message;
advancing or retarding transmission circuitry;
transmitting a fourth message to the second base station;
determining a fourth timing advance based on the fourth message; and
determining the location based on the first, the second, the third, and the fourth timing advance.
4. The method of claim 3 wherein the step of determining the location comprises the step of determining the location based on a Time of Arrival (TOA) technique.
5. The method of claim 1 wherein the step of determining the location comprises the step of determining a distance from the base station.
6. A method for determining a distance (C) from a base station, the method comprising the steps of:
determining a distance to a timing-advance boundary (D TA );
determining a distance attributed to advancing or retarding transmission circuitry (D ADV );
determining a number of iterations (N) of advancing or retarding transmission that causes a change in a timing advance; and
determining C based on D TA , D ADV , and N.
7. The method of claim 6 wherein the step of determining the distance attributed to advancing or retarding transmission circuitry comprises the step of determining the distance attributed to advancing or retarding transmission circuit by a fraction of a timing-advance bit.
8. An apparatus for determining location, the apparatus comprising:
a transceiver outputting a first message and a second message, wherein the second message is advanced or retarded in time by a fraction of a timing-advance bit; and
logic circuitry determining a first and a second timing advance value based on the first and the second message and determining a distance from a first base station based on the first and the second timing advance values; wherein the distance from the firm base station is calculated based on the formula:
D TA −( N −½) D ADV where,
D TA =a distance to a timing-advance boundary
D ADV =a distance attributed to advancing/retarding the transmission circuitry; and
N=a number of iterations in timing advance that causes a change in the timing advance.
9. The apparatus of claim 8 wherein the first and the second messages comprise messages transmitted on a Random Access Channel (RACH).
10. The apparatus of claim 8 further comprising location finding equipment coupled to the logic unit, the location finding equipment having a first distance from a first base station as an input, having a second distance from a second base station as an input, having a third distance from a third base station as an input, and calculating a location based on the first, the second, and the third distances.