WO1999022530A1

WO1999022530A1 - Method and apparatus for completing a handover between wireless communication systems

Info

Publication number: WO1999022530A1
Application number: PCT/US1998/015970
Authority: WO
Inventors: Timothy Leo Moran
Original assignee: Motorola Inc.
Priority date: 1997-10-29
Filing date: 1998-07-31
Publication date: 1999-05-06
Also published as: KR100336590B1; DE19882749T1; GB0008705D0; FI20001011A; CN1276950A; KR20010031565A; GB2346514B; GB2346514A; CN1276673C; DE19882749B4; FR2770363B1; FR2770363A1; JP2001522178A

Abstract

The handover method of a communication signal (270) associated with a mobile communication unit (209) operates between a first wireless communication system (202) and a second wireless communication system (204). The first wireless communication system includes a landline switching element (211), a computing platform (212) and a first base station system element (206). The second wireless communication system includes a mobile switching element (216) and a second base station system element (208). The method includes establishing multiple circuit links between the first base station system element and the mobile switching element, and then detecting, by the first wireless communication system, that a handover of the communication signal is desired. The method further includes forwarding, by the computer platform, a message (260) from the computer platform to the mobile switching element, and selecting, by the first wireless communication system, a selected circuit link (250) from the multiple circuit links. Based on the message, allocating, by the second wireless communication system, a mobile communication resource and finally transferring the communication signal to the mobile communication resource via the selected circuit link (250).

Description

METHOD AND APPARATUS FOR COMPLETING A HANDOVER BETWEEN WIRELESS COMMUNICATION SYSTEMS

FIELD OF THE INVENTION

The present invention relates generally to communication systems and, more particularly, to a method and apparatus for completing a handover between wireless communication systems.

BACKGROUND OF THE INVENTION

Communication systems consisting of land mobile radio, cellular radiotelephone, personal communication system (PCS), and various other types are well known. A typical multiple access wireless communication system such as a digital radio frequency (RF) radiotelephone system includes a base station system, (BSS), having one or more base station transmitters and receivers (BTSs), and at least one base station controller (BSC). The BSS communicates via an RF channel with a mobile communication unit, commonly referred to as a mobile station (MS), operating within a coverage area served by a BTS. The BSCs are linked to mobile switching centers (MSC) which provide a connection between the multiple access wireless communication system and the public switched telephone network (PSTN) as well as interconnection of various cellular radiotelephone communication systems. The MSC provides the switching function as well as call routing, call billing, and subscriber features, among other things. The BSC provides mobility management functions such as mobile station registration, location updating, and handover. One such multiple access wireless communication system, which may be referred to as a MSC-based architecture, is a direct sequence code division multiple access (DS-CDMA) cellular communication systems, such as set forth in the TLA Interim Standard (IS)-95A, Mobile Station-Base Station Compatibility Standards for Dual- Mode Wideband Spread Spectrum Cellular Systems, Telecommunications Industry Association, Washington, D. C. July 1993 [IS-95A]. According to these standards, coded communication signals are transmitted in common 1.25 megahertz (MHz) carriers between the BSS and mobile stations that are communicating in the service coverage areas of the BSS.

Multiple access wireless communication system functionality may be also accomplished through an alternate architecture. Such an architecture, commonly referred to as Generic C architecture, utilizes an landline switch, for example, a class 5 service switching point (SSP), to provide the switching function for the wireless communication system, thereby mitigating the need for an MSC. The SSP may also serve to provide the connection between the Generic C wireless communication system and the PSTN. In a Generic C wireless communication system, at least one base station system (BSS) is linked to the SSP. In addition, the SSP is in communication with a service control point (SCP). The SCP is a database is a database, remotely located from the SSP, which communicates with the SSP to provide customer-specific information. The SCP, when queried by the SSP, provides information to the SSP via a radio access system controller /visitor location register (RASC/VLR). The RASC/VLR which provides wireless communication system access to a landline switch may be collocated with the SCP. Communication system service providers as well as communication system users desire handover capability between wireless communication systems configured with different architectures. For example, a mobile station, having received a landline originated call while initially traveling in a wireless communication system served by a Generic C architecture, may require a handover of its communication signal to a wireless communication system served by a MSC-based architecture.

Implementing mobile station handover capability between two Generic C architecture wireless communication systems has been specified in standards. Currently, implementing mobile station handover capability between a wireless communication served by a Generic C architecture and a wireless communication system served by a MSC-based architecture has not been specified or designed. Therefore, a need exists for a method and apparatus for completing a handover of a mobile communication signal between architecturally different wireless communication systems.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, the foregoing need is addressed by a method for handover of a communication signal associated with a mobile communication unit operating between a first wireless communication system and a second wireless communication system. The first wireless communication system includes a landline switching element, a computing platform and a first base station system element. The second wireless communication system includes a mobile switching element and a second base station system element. The method includes establishing multiple circuit links between the first base station system element and the mobile switching element, and then detecting, by the first wireless communication system, that a handover of the communication signal is desired. The method further includes forwarding, by the computer platform, a message from the computer platform to the mobile switching element, and selecting, by the first wireless communication system, a selected circuit link from the multiple circuit links. Based on the message, allocating, by the second wireless communication system, a mobile communication resource and finally transferring the communication signal to the mobile communication resource via the selected circuit link..

According to another aspect of the present invention, an apparatus for completing a handover of a communication signal associated with a mobile communication unit from a first wireless communication system to a second wireless communication system. The first wireless communication system includes a landline switching element and a first base station system element, and the second wireless communication system includes a mobile switching element and a second base station system element. The apparatus includes a circuit link established between the first base station system element and the mobile switching element, and a computing platform in communication with the first base station system element and the mobile switching center. Upon detecting that a handover of the communication signal is desired, the computing platform forwards a message from the computing platform to the mobile switching element, and the second wireless communication system allocates a mobile communication resource, the circuit link and mobile communication resource providing a path for transferring, by the first wireless communication system, the communication signal from the first wireless communication system to the second wireless communication system..

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a typical wireless communication system.

FIG. 2 depicts two wireless communication systems, one having a Generic C architecture and the other having an MSC-based architecture.

FIG. 3 depicts wireless communication systems as shown in FIG.

2, further illustrating aspects of the preferred embodiment of the present invention.

FIG. 4 is a flow chart of a method for completing a handover of a communication signal between two wireless communication systems, according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to the drawings, wherein like numerals designate like components, FIG. 1, a wireless communication system 100, such as a direct sequence code division multiple access (DS-CDMA) digital radiotelephone system is shown. Base stations 110, 112, and 114 may communicate with mobile station 116, via radio frequency (RF) channels which provide physical paths over which communication signals such as voice, data, and video are transmitted, operating within coverage area 120. Base station locations are chosen to provide overlapping coverage areas. Base stations 110, 112, and 114, are coupled to a base station controller (BSC) 150, which includes, among other things, a processor 162 and a memory 164 and which is in turn is coupled to a mobile switching center /visitor location register (MSC/VLR) 160, also including, among other things, a processor 162 and a memory 164. A BSC 150 and its associated base stations, such as base stations 110, 112, and 114, may be referred to as a base station system (BSS). MSC 160 is coupled to PSTN 170. Calls originating with or terminating at mobile station 116 are processed through MSC 160 to either a wireline customer linked to the public switched telephone network (PSTN) 170 or other radiotelephone communication system users serviced by MSC 160 or other MSCs (not shown). The BSC and MSC operate according to well known methods and are commercially available from Motorola, Inc.

FIG. 2 illustrates a first and second wireless communication system. The first wireless communication system, a Generic C architecture wireless communication system 202, herein referred to as

Generic C system 202 and an MSC-based architecture wireless communication system 204.

Typical Generic C architectures were developed to integrate wireless communication services using 800 MHz and 1800 MHz bandwidth capabilities from wireless base station systems, and landline communication elements. Accordingly, Generic C system 202 utilizes an existing landline end office 211, which includes a landline end office switch 216 such as a class 5 switch, coupled to a base station system element 206 in order to provide wireless communication services. Landline end office 211 also provides the interface to a public switching telephone network (PSTN) 210.

Base station system element 206 includes a BSC 213 coupled to a BTS 214 and a BTS 215, although additional BSCs and BTSs may be included. BSC 213 is in communication with BTS 214 via a signaling link 235 and at least one trunking line 236, and BTS 215 via a signaling link 238 and at least one trunking line 237. Signaling links 235 and 238 may be implemented using one of a number of appropriate protocols. A suitable base station system element 206 may be purchased from Motorola, Inc.

Landline end office 211 is coupled to a computing platform 212 via signaling link 230. Computing platform 212 includes a service control point (SCP) capable of providing service specific information to landline end office switch 216, a mobility manager function, commonly referred to as an radio access system controller (RASC), capable of coupling base station system element 206 to landline end office 211, and a location register (VLR) capable of providing a local wireless subscriber database. Such a computing platform may be referred to as a SCP/RASC/VLR. Unlike a MSC-based architecture, switching functions associated with wireless communication calls are performed in landline end office switch 216 per routing instructions from the SCP. Computing platform 212 communicates with landline end office 211 using a signaling protocol such as Advanced Intelligent Network (AIN) 0.1 , Bellcore, August 1992, (AIN 0.1) over an out-of-band signaling link 230, for example SS7. Computing platform 212 may also be in communication with a home location register 240 which provides a permanent subscriber database.

Landline end office 211 communicates with base station system element 206 via a signaling link 234 and a plurality of trunk lines such as El or Tl, although only a trunking line 231 is shown. In addition, base station system element 206 provides a signaling link 232 to computing platform 212. Signaling links 234 and 232 are provided via out-of-band, bi-directional signaling such as SS7 able to support IS-634 protocol for digital and analog mobility management signaling. The second wireless communication system, an MSC-based wireless communication system 204 includes a mobile switching center /visitor location register (MSC/VLR) 216 in communication with a base station system element 208 and a home location register (HLR) 217. MSC/VLR 216 may also be in communication with, and responsive to PSTN 210. MSC/VLR 216 provides the switching and routing capabilities for base station system element 208.

MSC/VLR 216 communicates with base station system element 208 via a signaling link 242. Signaling link 242, responsible for conveying mobility management signaling from base station system element 206, may be implemented using a TIA Interim Standard 634 (IS-634) protocol as defined in TIA/EIA/IS-634, MSC-BS Interface for Public 800 MHz, December, 18, 1995. MSC/VLR 216 provides switching capabilities for base transceiver stations 224 and 225. Audio traffic between MSC/VLR 216 and base station system element 208 is transported via a plurality of trunking lines, although only trunking line 241 is shown.

Location registers such as HLR 217 and visitor location registers are databases which, among other things, store the location and service profile information of a mobile station such as MS 206. The visitor location register provides a local database to MSC 216 for registering a visiting mobile communication unit. The visitor location register, having obtained the information from HLR 217, a permanent database, retains this information as long as a mobile communication unit resides in the geographical area of MSC/VLR 216. Base station system element 208 includes a BSC 223 coupled to a

BTS 224 and a BTS 225, although additional BSCs and BTSs may be included. BSC 223 is in communication with BTS 224 via a signaling link 245 and at least one trunking line 246, and BTS 225 via a signaling link 248 and at least one trunking line 247. Signaling links 245 and 248 may be implemented using one of a number of appropriate protocols.

A mobile station 209 is depicted as traveling in the coverage area of base station system 206 and communicating, via well known radio frequency air interface specifications, such as IS-95 or IS-91, to base station system 206. Mobile station 209 may be in communication with another mobile station or a landline station via landline end office 211. As mobile station 209 approaches the outer boundaries of coverage provided by Generic C system 202, a mobile communication signal 270 associated with mobile station 209 must be handed-over to another wireless communication system in order to continue the call in progress. Lack of mobile communication signal handover capability between the two wireless communication system results in communication signal 270 being terminated.

Handover capability between the two wireless communication systems depicted in FIG. 2 is illustrated in FIG 3, according to a preferred embodiment of the present invention. Elements additional to those shown in FIG. 2 which are required to provide mobile communication signal handover capability are shown in FIG. 3. The establishment of an IS-41 signaling link 261 between computing platform 212 and MSC/VLR 216, the addition of an IS-41 handover message 260 in computing platform 212, and the addition of dedicated terrestrial circuit(s) 250 between base station system 206 and MSC/VLR 216 provide the additional elements needed to support handover capability.

In FIG. 4 a flow chart representing a method, generally designated 400 of completing a handover of mobile communication signal 270 between the two wireless communication systems depicted in FIG. 3, is illustrated.

Method 400 starts at step 41, where dedicated terrestrial circuit(s) are established between a source base station controller 213 of a Generic C architecture wireless communication system 202, and a MSC/VLR 216 of an MSC-based architecture wireless communication system 204.

At step 42, an IS-41 messaging capability is established between a computing platform 212 and MSC/VLR 216. The IS-41 messaging capability is established via an IS-41 signaling link 261. Next, at step 44, a mobile station 209 establishes an RF link between mobile station 209 and source base station controller 213 via a source base transceiver station 215, the RF link carrying a mobile communication signal 270.

At step 46, source base station controller 213, upon noting a decrease in signal strength of mobile communication signal 270, notifies computing platform 212 of the need for a mobile communication signal handoff. Source base station controller 213 notes the need for a handover from source base transceiver station 215 to a target base transceiver, based on information contained in a handover message, for example a Handover Required message. In addition to containing the identity of the mobile station, the Handoff Required message contains the CELL ID, or coverage area in which the mobile station is traversing. Next, at step 48, based on the handover message, computing platform 212 determines that mobile station 209 is traveling in an coverage area served by target base transceiver station 224.

At step 50, computing platform 212 selects one of the dedicated terrestrial circuits, the selection resulting in a selected terrestrial circuit 250 able to carry the mobile station audio traffic.

Next at step 52, computing platform 212 invokes the IS-41 messaging capability between itself and MSC/VLR 216, in order to request a handover of the communication signal from source base transceiver station 215 to a target base transceiver station 224. For example, an IS-41 Facilities Directive Invoke message which contains relevant information including the identity of selected circuit link 250, is sent from the computing platform 212 to MSC/VLR 216 via signal link 261. Next, MSC/VLR 216 sends a request message to target base station controller 223 requesting the handover of communication signal 270 between source base station transceiver 215 and target base station transceiver 224, at step 54. For example, MSC/VLR 216 sends an IS-634 Handover request message to target base station controller 223 which contains the identity of target base transceiver station 224.

At step 56, target base station controller 223 responds to MS /VLR 216 with an acknowledgment message containing information describing resource allocation of target base transceiver station 224. For example, an IS-634 Handoff Acknowledgment message which contains the allocated target RF channel associated with target base station transceiver 224, may be used.

Next, at step 58, MSC/VLR 216 forwards the information describing resource allocation of target base transceiver 224 to computing platform 212 via the IS-41 messaging capability in order to acknowledge the request described at step 54. For example, in response to the IS-41 Facilities Directive Invoke message from computing platform 212, MSC/VLR 216 returns an IS-41 Facilities Directive Return Result message to computing platform 212.

The required information describing resource allocation associated with target base transceiver 224 is sent to source base station transceiver 215 via a handover command message at step 60 for example, via a T1.659 Handover Command message. In addition to the allocated target RF channel, the resource allocation includes the terrestrial circuit. Next at step 62, source base station controller 213 instructs mobile station 209 to acquire the allocated target RF channel via an appropriate air-interface message, for example, a J-STD-008 Extended Handoff Direction message.

At step 64, source base station controller 213 routes mobile station audio traffic between landline end office and MSC/VLR 216 via circuit 251 and selected circuit link 250.

Next, target base station controller 223 detects that a reliable communication signal 280 associated with mobile station 209 exists on the allocated target RF channel and subsequently informs MSC/VLR 216 via a Handoff Complete message at step 66.

Finally, at step 68, the MSC/VLR 216 informs the computing platform 212 of the completed connection via an IS-41 Mobile On Channel Invoke message.

Although a handover of a mobile communication signal from a Generic C architecture wireless communication system to a MSC-based wireless communication system is described above, it is contemplated in an alternate embodiment that a handover may be accomplished from a MSC-based wireless communication system to a Generic C architecture wireless communication system. It will be apparent that other forms of the invention, and embodiments other than the specific embodiments described above, may be devised without departing from the spirit and scope of the appended claims and their equivalents.

Claims

CLAIMSI claim:

1. A method for completing a handover of a communication signal associated with a mobile communication unit from a first wireless communication system to a second wireless communication system, the first wireless communication system comprising a landline switching element, a computing platform and a first base station system element, and the second wireless communication system comprising a mobile switching element and a second base station system element, the method comprising:

establishing a plurality of circuit links between the first base station system element and the mobile switching element, the first base station element and the mobile switching element responsive to the computing platform; detecting, by the first wireless communication system, that a handover of the communication signal is desired; forwarding, by the computer platform, a message from the computer platform to the mobile switching element; selecting, by the first wireless communication system, a selected circuit link from the plurality of circuit links; based on the message, allocating, by the second wireless communication system, a mobile communication resource; and transferring the communication signal to the mobile communication resource via the selected circuit link.

2. The method according to claim 1, wherein prior to the step of detecting, establishing a first signaling link between the mobile communication unit and the landline switching element, a portion of the first signaling link traversing the first base station system element.

3. The method according to claim 1 wherein the step of forwarding the message further comprises:

invoking, by the computer platform, a messaging capability between the computing platform and the mobile switching element; requesting, via the messaging capability, a handover of the communication signal from the first base station element to the second base station element.

4. The method according to claim 1, wherein the mobile communication resource comprises a radio frequency channel between the second base station system element and the mobile communication unit.

5. The method according to claim 4 wherein the mobile communication resource further comprises a signaling link and a traffic link between the second base station system element and the mobile switching element.

6. The method according to claim 4 wherein prior to the step of transferring, establishing a second signaling link between the mobile communication unit and the landline switching element, a portion of the second signaling link including the mobile communication resource.

7. The method according to claim 1, wherein the first wireless communication system comprises a Generic C architecture based wireless communication system.

8. The method according to claim 1, wherein the landline switching element comprises a class 5 switch.

9. The method according to claim 1, wherein the second wireless communication system comprises one of a code division multiple access (CDMA) system, a time division multiple access (TDMA) system and an analog communication system.

10. The method according to claim 1, wherein the communication signal is associated with a wireless communication unit.