Intersystem handover method and apparatus

• US 6,115,608 A
• Filed: 09/10/1997
• Issued: 09/05/2000
• Est. Priority Date: 09/10/1997
• Status: Expired due to Term

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Northern Telecom Limited (Nortel Networks Corporation)
• Inventors: Duran, Jose M., Wang, Xiaomei
• Primary Examiner(s): Bost, Dwayne D.
• Assistant Examiner(s): Gary, Erika A.
• Application Number:
  US08/926,610
• Time in Patent Office: 1,091 Days
• Field of Search: 455/436, 455/552, 455/553, 455/422, 455/437, 455/438, 455/439, 455/442, 455/448, 455/432, 455/426
• US Class Current: 455/436
• CPC Class Codes: H04W 36/14 Reselecting a network or an air interface
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 84/042 Public Land Mobile systems, e.g. cellular systems

Abstract

A method and apparatus for providing seamless transfer of a active call between cellular communication systems operating in different signal formats and different modes of handoff request initiation. An example being a mobile initiated CDMA/FDMA/TDMA system like IS-661 and a TDMA/FDMA network initiated system like PCS 1900. The system which initiates handoff requests internally is aware of all the IDs of all the BTSs of the other communication system with which it is to interact and the MSs monitors signals of both formats for maintaining a table of received signals from nearby cells, the cell IDs and signal quality, while maintaining an active call and the further ability to transmit a handover request on a command channel while in the active call mode.

Claims

1. A cellular communication system comprising, in combination:

a MSC (mobile services switching center);

a type A BTS (base transceiver station) in communication with said MSC and forming a cellular area within which the BTS may communicate with MSs (mobile station)s in a first signal format, said type A BTS responding to system type A initiated handoff requests relating to active calls in the type A format and responding to handover requests initiated by and generated from an MS relating to active calls in the type B format; and

a type B BTS in communication with said MSC and forming a cellular area, distinct from and within a portion of the cellular area formed by said type A BTS, within which the type B BTS may communicate with MSs (mobile station)s in a second signal format.

2. A cellular communication system comprising, in combination:

a MSC (mobile services switching center);

a type A BTS (base transceiver station) in communication with said MSC and forming a cellular area within which the BTS may communicate with MSs (mobile station)s in a first signal format; and

a type B BTS in communication with said MSC and forming a cellular area, distinct from and within a portion of the cellular area formed by said type A BTS, within which the BTS may communicate with MSs (mobile station)s in a second signal format, said type B BTS responding to system initiated type A handover requests relating to active calls in the type A format and responding to MS initiated handoff requests relating to active calls in the type B format.

3. A method of transferring a MS (mobile station) active call from BTS-A (a base station transceiver operating in a first communication signal format) to BTS-B (a base station transceiver operating in a second communication signal format) where BTS-A comprises part of a cellular communication system that allows mobile initiated handoffs and BTS-B comprises part of a cellular communication system where a BSC (base station controller) initiates handoffs and where the two systems communicate through a common MSC (mobile services switching center) comprising, the steps of:

receiving a request for handover initiated by a MS having an active call with a BTS-A specifying BTS-B as a target;

transmitting the request for handover from BTS-A through MSC to BTS-B;

allocating radio resources at BTS-B;

returning an acknowledgement signal from BTS-B through said BSC and said MSC to BTS-A;

transmitting a handover command from said MSC to BTS-A for forwarding to the MS making the handover request;

receiving a signal, from the MS making the handoff request, over the allocated resources of BTS-B;

transmitting a communication from BTS-B to said MSC that the handover has been completed; and

clearing the radio resources at BTS-A that were being used for the active call.

4. Apparatus for transferring a MS (mobile station) active call from BTS-A (a base station transceiver operating in a first communication signal format) to BTS-B (a base station transceiver operating in a second communication signal format) where BTS-A comprises part of a cellular communication system that allows mobile initiated handoffs and BTS-B comprises part of a cellular communication system where a BSC (base station controller) initiates handoffs and where the two systems communicate through a common MSC (mobile services switching center) comprising, in combination:

means for receiving a request for handover from a MS at a BTS-A specifying a BTS-B as a target;

means for transmitting the request for handover from BTS-A through a MSC to BTS-B;

means for allocating radio resources at said BTS-B;

means for returning an acknowledgement signal from said BTS-B through said BSC and said MSC to said BTS-A;

means for transmitting a handover command from said MSC to said BTS-A for forwarding to the MS making the handover request;

means for receiving a signal from the MS making the handoff request over the allocated resources of said BTS-B;

means for transmitting a communication from said BTS-B to said MSC that the handover has been completed; and

means for clearing the radio resources at said BTS-A that were being used for the active call.

5. A method of transferring a MS (mobile station) active call from BTS-B (a base station transceiver operating in a first communication signal format) to BTS-A (a base station transceiver operating in a second communication signal format) where BTS-A comprises part of a cellular communication system that allows mobile initiated handoffs and BTS-B comprises part of a cellular communication system where a BSC (base station controller) initiates handoffs and where the two systems communicate through a common MSC (mobile services switching center) comprising, the steps of:

determining that a handover should be made from BTS-B to BTS-A through information collected by said BSC;

informing the MSC that BTS-A should receive a handover;

transmitting the request for handover from MSC to BTS-A;

allocating radio resources at BTS-A;

returning an acknowledgement signal from BTS-A to said MSC;

transmitting a handover command from said MSC to BTS-B for forwarding to the MS having the active call in question with BTS-B;

receiving a signal from the MS over the allocated resources of BTS-A; and

clearing the radio resources at BTS-B that were being used for the active call.

6. Apparatus for transferring a MS (mobile station) active call from BTS-B (a base station transceiver operating in a first communication signal format) to BTS-A (a base station transceiver operating in a second communication signal format) where BTS-A comprises part of a cellular communication system that allows mobile initiated handoffs and BTS-B comprises part of a cellular communication system where a BSC (base station controller) initiates handoffs and where the two systems communicate through a common MSC (mobile services switching center) comprising, in combination:

means for determining that a handover should be made from a BTS-B to a BTS-A through information collected by a BSC;

means for informing a MSC that said BTS-A should receive a handover request;

means for transmitting the request for handover from said MSC to said BTS-A;

means for allocating radio resources at said BTS-A;

means for returning an acknowledgement signal from said BTS-A to said MSC;

means for transmitting a handover command from said MSC to said BTS-B for forwarding to the MS having the active call in question with said BTS-B;

means for receiving a signal from the MS over the allocated resources of said BTS-A; and

means for clearing the radio resources at said BTS-B that were being used for the active call.

7. A cellular communication system having top level, intermediate level and bottom level administrative functions in appropriate top level, intermediate level and bottom level means, each of any bottom level means forming a distinct defined cell for communicating with MSs (mobile stations) within its distinct defined cell comprising, in combination:

a first plurality of bottom level means communicating with MSs within their cells in a first signal format, said bottom level means, of said first plurality, expecting to receive handoff requests via and initiated by a higher level portion of the system;

a second plurality of bottom level means communicating with MSs within their cells in a second signal format, said bottom level means, of said second plurality, expecting to receive handoff requests from and initiated by a MS; and

a dual mode MS, ready to transfer to a bottom level means of said first plurality and having an active call linked through a bottom level means of said second plurality, having means for sending a handover request, on a command channel, to a particular bottom level means of said first plurality.

8. Dual format cellular communication system comprising, in combination:

a MSC (Mobile services Switching Center);

first format apparatus connected to and controlled by said MSC, including at least one BSS-A (type A base station subsystem), said at least one BSS-A making handoff determinations directly relating to active calls in said first format and receiving handover requests indirectly from at least one MS having an active call in a format different from said first format wherein the handover request specifies a particular BTS; and

second format apparatus connected to and controlled by said MSC, including at least one BSS-B (type B base station subsystem), said at least one BSS-B receiving handoff requests directly from at least one MS having an active call in said second format and receiving handover requests from said MSC relating to a MS having an active call in a format different from said second format wherein the handover request specifies a particular BTS.

9. The method of accommodating handoffs and intersystem handovers when a system A is network initiated and a system B is mobile initiate and both systems A and B are controlled by a single MSC comprising the steps of:

receiving handover requests at a BSS-B (system B base station subsystem) relating to system A active calls indirectly from a BSS-A (system A base station subsystem) via a MSC (Mobile services Switching Center); and

receiving handoff requests at said BSS-B relating to system B active calls directly from a MS (mobile station) engaged in the active call.

10. The method of accommodating handoffs and intersystem handovers when a system A is network initiated and a system B is mobile initiated and both systems A and B are controlled by a single MSC comprising the steps of:

internally initiating handoffs at a BSS-A (system A base station subsystem) relating to system A active calls; and

receiving handover requests at said BSS-A relating to system B active calls indirectly from a MS (mobile station) via a BSS-B (system B base station subsystem) in system B and the MSC.

11. The method of handing-off and handing-over active calls between network initiated and mobile initiated systems both systems being controlled in part by a single MSC comprising the steps of:

receiving BSC generated handoff requests for network initiated system active calls at a network initiated system BTS;

receiving MS generated handover requests for mobile initiated system active calls at a network initiated system BTS;

receiving MS generated handoff requests for mobile initiated system active calls at a mobile initiated system BTS; and

receiving BSC generated handover requests for network initiated system active calls at a mobile initiated system BTS.

12. A cellular communication system comprising, in combination:

a network initiated cellular system including BTSs (base station transceiver subsystem)s and associated BSCs (base station controller)s;

a mobile initiated cellular system including BTSs and associated BSCs; and

a MSC (mobile services switching center) connected to both said network initiated and said mobile initiated cellular systems, the BTSs of said mobile initiated system receiving handoff requests from MSs (mobile station)s relative mobile initiated cellular system active calls and receiving intersystem handover requests relative network initiated cellular system active calls.

13. A dual mode cellular communication system wherein both cellular modes are controlled by a common MSC comprising, in combination:

a network initiated cellular system including BTSs (base station transceiver subsystem)s and associated BSCs (base station controller)s, said BTSs receiving handoff requests initiated by a BSC and handover requests initiated by a MS (mobile station); and

a mobile initiated cellular system including BTSs (base station transceiver subsystem)s, said BTSs receiving handoff requests directly from a MS and handover requests from initiated by a BSC.

14. Cellular phone apparatus for communicating with communication systems operating in first and second signal formats and being controlled by a common MSC comprising, in combination:

first means for monitoring radio signals of a first format and storing information as to received signal quality and cell IDs of base station transceivers supplying the received signals;

second means for monitoring radio signals of a second format and storing information as to received signal quality and cell IDs of base station transceivers supplying the received signals;

third means for determining that, while communicating with another phone in the first signal format, the cellular phone apparatus needs to be handed over to a transmitter broadcasting in the second signal format;

fourth means for sending a handover request in said first signal format for forwarding to a specific base station transceiver operating in said second signal format;

fifth means for receiving a switch command in said first signal format authorizing said phone to use said second signal format for communicating with said another phone; and

sixth means for switching communications with said another phone to said second signal format in accordance with the instructions of said switch command.

15. The method of maintaining an active call presently interacting with a transceiver in a cell using a first signal format while switching to a transceiver cell operating in a second signal format where one of said first and second signal formats is associated with a network-initiated handoff and the other is associated with a transceiver-associated handoff and wherein both cells are controlled by a single MSC (Mobile services Switching Center) comprising the steps of:

continuously monitoring the strength of received radio signals of both first and second formats;

determining that a handover request to a base station, from which signals of said second signal format are being received, is appropriate;

transmitting a handover request in said first signal format in response to the determination of said last named means; and

switching the active call to said second signal format in response to a switch command signal received in said first signal format.

16. The method of maintaining a first communication signal format active call from a MS (mobile station) while the MS is moving between communication systems and wherein one system is network initiated and the other is mobile initiated and further wherein one system uses a first communication signal format and the other uses a second communication signal format and even further wherein a single MSC (master switching center) controls both systems comprising, the steps of:

continuously monitoring any received radio signals from BTSs (base station transceiver)s of both the network initiated and the mobile initiated systems through the use of separate radio subsystems in the MS while maintaining an active call in said first signal format;

transmitting a handover request in said first signal format in response to a determination within said MS that said active call could be more reliably maintained with a BTS using said second communication signal format; and

switching the active call to said second signal format in response to a switch command signal received from the system BTS supplying the active call in said first communication signal format.