Method and system for providing a handoff from a CDMA cellular telephone system

• US 6,240,292 B1
• Filed: 11/23/1999
• Issued: 05/29/2001
• Est. Priority Date: 12/29/1994
• Status: Expired due to Term

• Current Assignee: Cellco Partnership, Inc. (Verizon Communications Inc.)
• Original Assignee: Cellco Partnership, Inc. (Verizon Communications Inc.)
• Inventors: Haberman, Michael, Pierson, Glenn
• Primary Examiner(s): MAUNG, NAY AUNG
• Application Number:
  US09/447,433
• Time in Patent Office: 553 Days
• Field of Search: 455/422, 455/432, 455/434, 455/435, 455/436, 455/437, 455/438, 455/439, 455/442, 455/517, 455/524, 455/525, 370/331, 370/332, 370/335, 370/465, 375/216
• US Class Current: 455/439
• CPC Class Codes: H04W 36/0066 of control information between different types of networks in order to establish a new radio link in the target network
• CPC Class Codes: H04W 36/302 due to low signal strength
• CPC Class Codes: H04W 48/12 using downlink control channel
• CPC Class Codes: H04W 56/00 Synchronisation arrangements

Abstract

A mobile assisted handoff of a mobile station transitioning from a CDMA portion of a cellular telecommunication network to an analog portion of the network is provided as a function of a CDMA pilot signal transmitter located at each analog cell in the analog portion of the network. The mobile station monitors a CDMA pilot signal transmitted from each CDMA cell and each analog cell of the cellular telecommunication network, measures the signal strength of each received CDMA pilot signal and transmits the signal strength to the MTSO. The MTSO determines whether the pilot signal is associated with a CDMA base station or an analog base station. When the mobile station receives a pilot signal from an analog cell whose signal strength is above a first predetermined threshold and the received signal strengths of all pilot signals of the CDMA base stations with which the mobile station is currently in communication are below a second predetermined threshold, the MTSO directs a CDMA to analog handoff message to the mobile station.

Claims

1. A method of conducting a handoff of a mobile station from a first cellular communication system to a second cellular communication system, the first cellular communication system utilizing a code division multiple access (CDMA) communication in accord with a first technique, the second cellular communication system utilizing an alternative communication technique, the method comprising the steps of:

conducting a communication session for the mobile station through one of a plurality of base stations of the first cellular communication system in accord with the first communication technique;

receiving in the mobile station, a CDMA pilot signal compatible with the first communication technique from a CDMA transmitter associated with one of a plurality of base stations of the second cellular communication system; and

directing handoff of the mobile station from the base station of the first cellular communication system to a base station of the second cellular communication system utilizing the alternative communication technique, as a function of the CDMA pilot signal received by the mobile station.

2. A method as in claim 1, further comprising:

breaking the communication for the mobile station through the one base station of the first cellular communication system; and

subsequently making communication for the mobile station through the base station of the second cellular communication system utilizing the alternative communication technique.

3. A method as in claim 2, wherein the alternative communication technique utilizes a different frequency band than the CDMA communication in accord with a first technique.

4. A method as in claim 2, wherein the alternative communication technique utilizes a different modulation than the CDMA communication in accord with a first technique.

5. A method as in claim 2, wherein the alternative communication technique utilizes an analog communication technique.

6. A method as in claim 1, wherein the directing step comprises directing a hard handoff of the mobile station from the first cellular communication system to the second cellular communication system.

7. A method as in claim 1, wherein:

the step of conducting a communication session comprises receiving in the mobile station, a CDMA pilot signal compatible with the first communication technique from the one base station of the first cellular communication system; and

the step of directing handoff comprises recognizing a need for the handoff as a function of levels of the CDMA pilot signal from the one base station of the first cellular communication system and the CDMA pilot signal from the transmitter associated with the one base station of the second cellular communication system.

8. A cellular telecommunications system providing cellular service to a mobile station, comprising:

a first system comprising a plurality of first base stations providing the cellular service in accord with a code division multiple access (CDMA) communication technique;

a first CDMA pilot signal transmitter in the first system and associated with at least one of the first base stations, for transmitting a unique first pilot signal compatible with the CDMA communication technique;

a second system comprising a plurality of second base stations providing the cellular service in accord with an alternate communication technique;

a second CDMA pilot signal transmitter in the second system and associated with at least one of the second base stations, for transmitting a unique second pilot signal compatible with the CDMA communication technique; and

a communication controller, coupled to a plurality of the base stations, for directing a handoff of the mobile station from the first system to the second system as a function of receipt of the unique first pilot signal and the unique second pilot signal.

9. A cellular telecommunications system as in claim 8, wherein the communication controller comprises a mobile telephone switching office (MTSO) in communication with at least the first base stations.

10. A cellular telecommunications system as in claim 8, wherein the second base stations provide the cellular service on a different frequency band than used for the CDMA communication technique of the first system.

11. A cellular telecommunications system as in claim 8, wherein the second base stations provide the cellular service in accord with an analog communication technique.

12. A cellular telecommunications system as in claim 8, wherein the second base stations provide the cellular service in accord with a time division multiple access (TDMA) communication technique.

13. A method of communicating with a remote unit using a cellular communication system comprised of a first plurality of base stations for communication using a first technique and a second plurality of base stations for communication using a second technique different from the first technique, the first technique comprising code division multiple access (CDMA) digital communication on a predetermined frequency band, said method comprising the steps of:

transmitting according to said first technique an identification signal from each base station in said first plurality of base stations;

transmitting according to said first modulation technique an identification signal from at least each base station in said second plurality of base stations which is adjacent one of the first base stations; and

determining from identification signals received in the remote unit whether to initiate a change from communication in the first base stations to communication in the second base stations.

14. A method as in claim 13, wherein the determining step comprises:

receiving identification signals from a plurality of base stations in the remote unit;

sending data regarding received identification signals from the remote unit to a system controller separate from the base stations;

analyzing the received identification signals in the system controller; and

if the received identification signals satisfy predetermined conditions, initiating the change from communication in first base stations to communication in the second base stations.

15. A method as in claim 13, wherein the determining step comprises:

receiving the identification signal from one of the first plurality of base stations in the remote unit and comparing to a first threshold;

receiving the identification signal from one of the second plurality of base stations in the remote unit and comparing to a second threshold; and

determining to initiate the change from communication in the first base stations to communication in the second base stations if the identification signal from one of the first base stations does not exceed the first threshold and the identification signal from one of the second base stations is above the second threshold.

16. A cellular communication system comprised of a plurality of base stations and a plurality of mobile units wherein the mobile units may handoff operation between base stations during an active call, said system comprising:

a first group of said base stations for communicating call signals with active mobile units via a first technique comprising using a code sequence to modulate and transmit active call signals and transmitting a first base station reference signal;

a second group of said plurality of base stations for communicating active calls with the mobile units using an alternative technique and for transmitting an alternative base station reference signal analogous to the base station reference signals transmitted by the first group of base stations;

an identified mobile unit for monitoring the base station reference signals and transmitting indications thereof through a first base station of the first group, to assist in handoff from the first base station of the first group to a subsequent base station; and

a system controller for controlling at least the first group of base stations and for receiving the indications of monitored reference signals from the identified mobile unit and controlling the handoff of the identified mobile unit in response thereto,

wherein the subsequent base station may be a member of the first group of base stations or of the second group of base stations.

17. A cellular communication system as in claim 16, wherein the first group of base stations comprise code division multiple access (CDMA) cellular base stations.

18. A cellular communication system as in claim 17, wherein the second group of base stations comprise analog cellular base stations.

19. A cellular communication system as in claim 17, wherein the second group of base stations comprise time division multiple access (TDMA) base stations.

20. A cellular communication system as in claim 17, wherein the second group of base stations comprise personal communication service (PCS) base stations.

21. A cellular communication system as in claim 17, wherein:

the CDMA cellular base stations of the first group of base stations operate on a first predetermined frequency band; and

the second group of base stations operate on a second predetermined frequency band different from first predetermined frequency band.

22. A method of operation of a mobile unit in a cellular communication system, comprising:

communicating with at least one of a plurality of base stations of a first system using code division multiple access (CDMA) communication;

monitoring one or more reference signals broadcast by the base stations of the first system and sending indications thereof to a system controller;

monitoring one or more reference signals broadcast by a plurality of base stations of a second system and sending indications thereof to the system controller, the reference signals broadcast by the base stations of the second system being analogous to the reference signals broadcast by the base stations of the first system, the base stations of the second system providing communication in a manner different from communication provided by the base stations of the first system;

receiving an instruction from the controller and in response thereto conducting a handoff from the at least one base station of the first system to a base station of the second system; and

communicating via the second system.

23. A method as in claim 22, wherein the step of communicating via the second system comprises communicating with a base station of the second system over a predetermined frequency band used by the second system, which is different from a predetermined frequency band used by the first system.

24. A method as in claim 22, wherein the step of communicating via the second system comprises communicating using a time division multiple access (TDMA) technique.

25. A method as in claim 22, wherein the step of communicating via the second system comprises communicating analog format signals.

26. A method as in claim 22, wherein the conducting of a handoff comprises conducting a hard handoff.

27. A method as in claim 22, wherein the conducting of a handoff comprises:

breaking the CDMA communication with at least one base station of the first system; and

subsequently initiating communication through a base station of the second system.