Method and apparatus for location finding in a CDMA system

A CDMA wireless communication system having plural base stations capable of locating a communication unit, comprising:

• (a) a first base station comprising:
• (i) first base station transmitter sending a first spread spectrum signal including a location request to the communication unit, the spread spectrum signal being spread by a known first sequence of spreading symbols;
• (ii) a first base station receiver receiving a second spread spectrum signal including a response message from the communication unit, the second spread spectrum signal being spread by a known second sequence of spreading symbols, and the response message including a receive time of a first symbol of the first sequence and a transmit time of a first symbol of the second sequence, the first base station receiver further comprising a first base station detector receiving a predetermined symbol of the second sequence from the communication unit and determining a receive time of the predetermined symbol;
• (b) a second and a third base station comprising a second and a third receiver, respectively, for receiving the predetermined symbol of the second sequence and determining a second and third receive times, respectively, of the predetermined symbol;
• and
• (c) a controller coupled to the first, second and third base stations, comprising means for determining a location of the communication unit from the receive time of the first symbol of the first sequence by the communication unit, the transmit time of the first symbol of the second sequence by the communication unit, the first, second and third receive times of the predetermined symbol, and predetermined information about the first, second and third base stations.

A method for determining a subscriber location in a CDMA communication system having plural base stations, comprising:

• (a) receiving a signal from the subscriber at each of a first base station, a second base station and a third base station, the signal being formed via modulation by a known sequence of spreading symbols;
• (b) determining a first receive time of a symbol of the known sequence of spreading symbols at the first base station, a second receive time of the symbol at the second base station, and a third receive time of the symbol at the third base station;
• and
• (c) determining the location of the subscriber unit from the first, second and third receive times and further predetermined information about the first, second and third base stations.

A method for determining the location of a subscriber unit communicating in a CDMA wireless communication system having plural base stations, comprising, in the subscriber unit:

• (a) receiving a first signal from a first base station of the plural base stations and a second signal from a second base station of the plural base stations, the first and second signals being formed via modulation by a known first sequence of spreading symbols and a known second sequence of spreading symbols, respectively;
• (b) determining a first receive time of a first symbol of the first sequence, and a second receive time of a further symbol of the second sequence;
• and
• (c) determining the location of the subscriber unit from the first and second receive times and further information about the first and second base stations.

A subscriber unit operable for determining its own location while communicating in a CDMA (code division multiple access) wireless communication system having plural base stations, the subscriber unit comprising:

• (a) a receiver receiving a first signal from a first base station of the plural base stations and a second signal from a second base station of the plural base stations, the first and second signals being formed via modulation by a known first sequence of spreading symbols and a known second sequence of spreading symbols, respectively;
• (b) a detector determining a first receive time of a first symbol of the first sequence, and a second receive time of a further symbol of the second sequence;
• and
• (c) a location processor determining the location of the subscriber unit from the first and second receive times and further information about the first and second base stations.

A method for providing information for use in determining the location of a subscriber unit communicating in a CDMA wireless communication system having plural base stations, comprising, in the subscriber unit:

• (a) receiving a first signal from a first base station of the plural base stations, the first signal being formed via modulation by a known first sequence of spreading symbols having a predetermined number of symbols;
• (b) determining a receive time of a first symbol of the first sequence;
• (c) determining a transmit time of a first symbol of a second sequence of spreading symbols modulating a data signal to form a second signal;
• (d) forming a response message as part of the data signal including the receive time of the first symbol of the first sequence and transmit time of the first symbol of the second sequence;
• and
• (e) transmitting the second signal including transmitting the first symbol of the second sequence at the transmit time determined, and transmitting the response message.

A method for determining a location of a subscriber in a CDMA communication system having plural base units including active base stations and inactive units, comprising:

• (a) receiving a signal indicative of an emergency;
• (b) determining if at least three of the active base stations can receive a signal from the subscriber, and if not, activating at least one of the inactive units as an auxiliary base station;
• (c) controlling a group consisting of at least three of the active base stations which can receive a signal from the subscriber, and any auxiliary base stations activated in step (b), to each transmit a spread spectrum signal having a common symbol sequence;
• (d) determining each receive time at the subscriber of a same symbol of the symbol sequence for each spread spectrum signal transmitted in step (c), respectively, and sending a response from the subscriber including said each receive time;
• and
• (d) determining the location of the subscriber based on said receive times.