Method and apparatus for providing mobile unit assisted hard handoff from a CDMA communication system to an alternative access communication system

• US 5,594,718 A
• Filed: 03/30/1995
• Issued: 01/14/1997
• Est. Priority Date: 03/30/1995
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Tiedemann, Edward G. Jr., Gilhousen, Klein S., Weaver, Lindsay A. Jr., Bayley, Gwain
• Primary Examiner(s): MAUNG, NAY AUNG
• Assistant Examiner(s): Carman, Melissa Kay
• Application Number:
  US08/413,306
• Time in Patent Office: 656 Days
• Field of Search: 370/18, 370/94.1, 370/19, 370/21, 370/22, 370/93, 370/60, 370/95.3, 455/33.2, 455/33.1, 455/34.1, 455/34.2, 455/56.1, 379/60, 375/205, 380/34
• US Class Current: 370/331
• 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 48/12 using downlink control channel

Abstract

A method and system for providing a reliable means to perform handoff from a code division multiple access (CDMA) system using a pilot signal to an alternative access communication technique system. Simple pilot box circuitry is added to a set of border base stations. The border base stations are base stations which operate only in the alternative access communication technique and which have coverage areas which are contiguous with coverage areas of CDMA operation base stations. The mobile unit monitors for the pilot signal from the border base stations in the same manner as it monitors for pilot signals from the CDMA operation base stations. When the mobile unit detects the pilot signal corresponding to a border base station, it notifies a system controller in accordance with standard operation. The system controller is aware that the pilot signal corresponds to a border base station and thus triggers a hard handoff process to the alternative access communication technique system in response thereto.

Claims

1. In a system for providing communication with at least one mobile unit, said system comprising a first plurality of base stations providing code division multiple access (CDMA) communication, wherein said first plurality of base stations are clustered physically together, said system further comprising a second plurality of base stations providing communication using an alternative access communication technique wherein said second plurality of base stations surrounds said first plurality of base stations thereby creating a border set of base stations wherein said border set of base stations is a subset of said second plurality of base stations wherein each base station in said border set has a coverage area with a contiguous boundary with a coverage area corresponding to a base station of said first plurality of base stations, a method for providing handoff from said CDMA communication to said alternative access communication technique comprising the steps of:

transmitting from each base station in said first plurality of base stations an identifying pilot signal and CDMA call signals in a first frequency band;

transmitting from each base station in said border set of base stations an identifying pilot signal in said first frequency band and alternative access communication technique call signals in a different frequency band;

measuring at a first mobile unit a pilot signal strength of each of said identifying pilot signals corresponding to a neighboring set of base stations wherein said neighboring set of base stations comprises base stations having coverage areas in proximity to said first mobile unit;

receiving at said first mobile unit a first pilot signal corresponding to a target base station wherein said target base station is a member of said border set of base stations and wherein said target base station is a member of said neighboring set of base stations;

transmitting a message from said first mobile unit to a CDMA system controller via at least one base station in said first plurality of base stations wherein said message indicates receipt of said first pilot signal; and

initiating by said CDMA system controller an intersystem handoff procedure for said first mobile unit with an alternative access communication technique system controller, said CDMA system controller determining availability of resources among said second plurality of base stations through intersystem communication with said alternative access communication technique system controller during said intersystem handoff procedure.

2. The method of claim 1 further comprising the steps of:

communicating from said alternative access communication technique system controller to said CDMA system controller information for operation in said alternative access communication technique for said first mobile unit; and

communicating said information for operation in said alternative access communication technique to said first mobile unit via at least one base station in said first plurality of base stations.

3. The method of claim 1 further comprising the step of transmitting from each base station in said border set of base stations a synchronization channel signal in said first frequency band.

4. The method of claim 3 wherein said synchronization channel signal comprises an indication of a minimum revision level supported by said border set of base stations and wherein said indication denotes a revision level incompatible with said first mobile unit.

5. The method of claim 1 wherein each base station in said first plurality of base stations which comprises multiple sectors transmits a different identifying pilot signal from each of said multiple sectors and wherein each base station in said border set of base stations which comprises multiple sectors transmits an identical identifying pilot signal in each of said multiple sectors having a contiguous boundary with a coverage area corresponding to a base station of said first plurality of base stations.

12. The method of claim 3 further including the step of receiving at said first mobile unit said synchronization channel signal and selecting a mode of operation in response thereto.

13. The method of claim 12 wherein said step of transmitting a message from said first mobile unit to a CDMA system controller includes the step of indicating receipt of said first pilot signal at a signal level in excess of a predefined qualifying signal level.

6. A cellular communication system for providing communication with at least one mobile unit, said system comprising:

a first plurality of base stations clustered physically together for providing code division multiple access (CDMA) communication signals wherein each base station of said first plurality of base stations transmits an identifying pilot signal and wherein said first plurality of base stations are controlled by a CDMA system controller;

a border set of base stations controlled by an alternative system controller in intersystem communication with said CDMA system controller wherein said border set of base stations is a subset of a second plurality of base stations for providing communication using an alternative access communication technique wherein said second plurality of base stations surrounds said cluster of said first plurality of base stations and wherein each base station in said border set has a coverage area with a contiguous boundary with a coverage area corresponding to a base station of said first plurality of base stations and wherein each base station of said border set comprises a self contained pilot generator for providing a transmit pilot signal apparatus comprising;

I channel short code generator means for receiving a universal time input and creating an I channel spreading sequence at a time offset;

a first baseband filter for receiving said I channel spreading sequence and providing a filtered I channel spreading sequence;

a first mixer for modulating said filtered I channel spreading sequence and producing a modulated I output signal;

Q channel short code generator means for receiving a universal time input and creating a Q channel spreading sequence at said time offset;

a second baseband filter for receiving said Q channel spreading sequence and providing a filtered Q channel spreading sequence;

a second mixer for modulating said filtered Q channel spreading sequence and producing a modulated Q output signal;

a summer for summing said modulated I output signal and said modulated Q output signal to produce a summed modulated signal; and

upconversion and amplification means for receiving said summed modulated signal and producing said transmit pilot signal.

7. The cellular communication system of claim 6 wherein at least one base station of said first plurality of base stations comprises multiple sectors and wherein each sector of said at least one base station transmits a unique one of said identifying pilot signal.

8. The cellular communication system of claim 7 wherein at least one base station of said border set comprises multiple sectors and wherein each sector of said at least one base station of said border set transmits an identical one of said transmit pilot signal.

9. The cellular communication system of claim 6 wherein at least one base station of said border set comprises a second self contained pilot generator for providing a second transmit pilot signal having a time offset different from said time offset of said self contained pilot generator.

10. A cellular communication system comprised of a plurality of base stations and a plurality of mobile units wherein said plurality of mobile units may handoff operation from one base station to another base station during an active call, said system comprising:

a first group of said plurality of base stations for communicating active call signals with said plurality of mobile units using a spreading sequence to modulate said active call signals and for transmitting a base station reference signal;

a first mobile unit for monitoring said base station reference signals to assist in handoff from a first base station of said first group of said plurality of base stations to a subsequent base station and for transmitting an indication signal based on said base station reference signal to said first base station;

a first system controller for controlling said first group of said plurality of base stations and for receiving from said first base station said indication signal from said first mobile unit; and

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

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

11. A method of communicating with at least one remote unit using a cellular communication system comprised of a first plurality of base stations for communication using a first modulation technique and a second plurality of base stations for communication using a second modulation technique, said method comprising the steps of:

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

transmitting according to said first modulation technique said identification signal from each base station in said second plurality of base stations which is adjacent to a base station of said first set of base stations; and

determining from said identification signals whether to initiate a change from communication in said first plurality of base stations to communication in said second plurality of base stations.