Apparatus, method and system for mobile wireless communication hand-off utilizing ISDN multiway capabilities

An apparatus, method and system are provided for hand-off of a communication session utilizing ISDN multiway capabilities, in which the communication session of a mobile unit on a first call path is transferred from a serving base station to a target base station. The preferred system includes a switch coupled to a serving base station and a target base station, wherein the serving base station includes instructions to request a second call path to the target base station and to request a multiway feature. The switch then establishes the second call path from the serving base station to the target base station via the switch, and combines the communication session of the first call path with the second call path to form a multiway communication session. The mobile unit then communicates with the target base station for continuation of the communication session through a first leg of the multiway communication session, and the serving base station is released from a second leg of the multiway communication session, completing the hand-off.

FIELD OF THE INVENTION

The present invention relates, in general, to wireless communication systems, and more particularly, to an apparatus, method and system for mobile wireless communication hand-off utilizing ISDN multiway capabilities.

BACKGROUND OF THE INVENTION

Mobile wireless communication systems typically employ many base stations (such as cell sites) to provide wireless communication throughout a given geographic region. As a mobile unit (or mobile station) may traverse the geographic region, the communication to and from the mobile unit may occur through one or more of these base stations. To maintain an ongoing communication session during such transitions between base stations, various hand-off methods have evolved to transfer the wireless communication with the mobile unit from one base station to another base station, while maintaining such an ongoing call or session.

In the prior art, for some of the various methods utilized during such hand-offs, the communication session may suffer from some degree of interruption, which may be noticeable to the consumer of wireless communication services. As a consequence, a need remains to provide for comparatively seamless hand-offs, which do not interrupt ongoing communication sessions and which are imperceptible to the consumer.

In addition, while other prior art systems may provide comparatively seamless hand-offs, such hand-offs typically utilize considerable network resources. In an Autoplex® system, for example, in addition to switches and base stations, another network entity referred to as an Executive Call Processor (“ECP”) selects a server at the new cell site, while another network entity referred to as a Call Processing Database Node (“CDN”) transmits various data link messages to the current and new cell sites, adding an additional path to the existing call, directing the new cell site to activate a wireless voice link, and directing the current (serving) cell site to direct the mobile to retune to the new wireless voice link at the new cell site.

As a consequence, a need remains for a wireless communication system to provide comparatively seamless and imperceptible hand-offs. In addition, such a wireless communication system should be reasonably efficient and capable of cost-effective implementation, eliminating or minimizing the use of additional network resources.

SUMMARY OF THE INVENTION

The wireless communication system of the present invention provides virtually seamless and imperceptible hand-offs of communication sessions of mobile units. The various embodiments of the present invention are reasonably efficient and capable of cost-effective implementation in existing communication equipment such as switches and base stations. Moreover, the various embodiments of the present invention eliminate or minimize the use of additional network resources such as ECPs and CDNs, while being compatible with other intelligent network devices and systems.

In accordance with the present invention, an apparatus, method and system are provided for hand-off of a communication session utilizing a multiway connection, in which the communication session of a mobile unit is transferred from a serving base station to a target base station. The preferred system includes a switch coupled to a serving base station and a target base station, preferably over digital lines having multiple, independent channels, such as Integrated Services (“ISDN”) lines having two 64 Kbps “B” channels and one 16 Kbps “D” channel for a Basic Rate Interface (“BRI”). Typically, each of the various base stations include a plurality of terminals which handle and process the communication sessions with mobile units and, in general, one or more terminals are assigned directory numbers (“DNs”). Each terminal within a base station in the preferred system is assigned two B channels for voice service, with multiway capabilities, and a “D” channel for signaling in an ISDN BRI implementation. In general, the communication session (to be handed off) is occurring on one of the channels, such as on a first B channel. When a hand-off of the communication session is indicated, the serving base station generates on the second, heretofore unused B channel, a separate, second call path to the target base station via the switch. The serving base station then initiates a conference (or other multiway) request to the switch to merge or conference the existing communication session in the first channel with the call path on the second channel. The mobile unit is then directed to tune to, or otherwise communicate with the target base station for connection to the communication session on the second call path. The serving base station then disconnects its call path legs from the communication session, leaving the communication session up between the mobile user, the target base station and the switch.

As a consequence, the communication session of the mobile unit has been handed off, seamlessly and without interruption, from the serving base station to the target base station. Such a hand-off has also occurred utilizing minimal network resources, the switch and the base stations, without involvement of other intelligent or supervisory network elements.

The multiway (or conference) call path from the serving base station to the switch is established through the transmission of various messages between the serving base station and the switch. The switch is correspondingly configured to acknowledge and connect the first and second call paths to create a multiway call path with the target base station, upon receipt of these various messages. As discussed in greater detail below, these various messages may be combined in a variety of ways.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned above, a need remains for a wireless communication system to provide comparatively seamless and imperceptible hand-offs, which is reasonably efficient and capable of cost-effective implementation, and which eliminates or minimizes the use of additional network resources such as ECPs and CDNs. In accordance with the present invention, a system, apparatus and method are illustrated which provide such advantages, namely, providing relatively seamless and imperceptible wireless hand-offs while utilizing minimal network resources (namely, utilizing existing switches and base stations configured in accordance with the invention), while simultaneously eliminating the prior art utilization of other network elements such as ECPs and CDNs.

FIG. 1is a block diagram illustrating such a system embodiment100in accordance with the present invention. As illustrated inFIG. 1, the system100includes a switch110and one or more base stations (equivalently, cell sites)120, such as first base station120Aand second base station120B. The switch110is preferably a telecommunication switch such as a 5 ESS® switch manufactured by Lucent Technologies, Inc. which has been configured to operate in accordance with the present invention, as discussed in greater detail below. The switch is coupled to a network130, for additional call routing. The switch110may also be included within a mobile switching center, and may also be coupled to other intelligent network devices (not illustrated). The base stations120include wireless transceivers, for wireless communication with various mobile units (equivalently, mobile stations)140, such as cellular or other wireless telephones, wireless modems, or other wireless communication devices. The switch110and base stations120are coupled to each other utilizing signaling and/or trunking lines150,151and152as known in the art. In the preferred embodiment, the switch110is connected to the various base stations120(via signaling and/or trunking lines150and152) using Basic Rate Interface “BRI” lines of an Integrated Services Digital Network (“ISDN”), with each of the base stations120having a plurality of (preferably independent) “B” channels for voice services and multiway capabilities and a “D” channel for signaling and other messaging. The base stations120include a plurality of terminals (not separately illustrated) having one or more assigned directory numbers.

As any mobile unit140traverses a geographic region and becomes farther away from any given base station120with which it has been in communication, the signal or power levels of such wireless communication to and from the mobile unit140typically drop below a preferred threshold or range. Under these circumstances, it is preferable for the given base station120to hand-off the communication to another base station120having higher signal strength to and from the given mobile unit140. Continuing to refer toFIG. 1, for example, the mobile unit140Ahaving a communication session (at a time t<t1) is currently served by first base station120A, illustrated as communication or call path legs160(wireless) and161(wireline) using a first B channel (B1). The portion of the communication session between the switch110and the network130is separately illustrated as call path155. In these circumstances, the first base station120Ais generally referred to as a serving base station or serving cell site. As the mobile unit140Atravels toward the vicinity of mobile unit140C, it may become necessary or preferable for the first, serving base station120Ato hand-off the communication session of mobile unit140Ato the second base station120B. In these circumstances, the second base station120Bis generally referred to as a target base station or target cell site. Such a hand-off, in accordance with the present invention, is illustrated below with respect toFIGS. 2 and 3.

FIG. 2is a block diagram illustrating a system embodiment, with the first call (or communication path) illustrated from the switch110and first base station120Ato the mobile unit140A(call path161on channel B1and call path160, respectively) and a second call (or communication) path illustrated from the first base station120A, via switch110, to the second base station120B(call paths162and170). In accordance with the present invention, and as explained in greater detail below, the serving base station120Acreates the second call path using an available second B channel (B2), to the target base station120Bvia switch110, illustrated as call paths or legs162and170. Serving base station120Athen transmits a multiway (or other conference) request to switch110, to conference or merge the first call path and the second call path on the two independent channels (B1and B2), establishing a multiway connection among the mobile unit140A, the serving base station120Aand the target base station120B. As discussed in greater detail below, in the preferred embodiment, this is accomplished through various call set up messages and the multiway capabilities of ISDN. The completion of the hand-off then proceeds as illustrated below with reference toFIG. 3.

FIG. 3is a block diagram illustrating a system embodiment, with the second communication path illustrated during completion of a hand-off and the commencement of a tear down of the first communication path, in accordance with the present invention. When the multiway (conference) call path (combined call legs161,162and170) has been established, (i.e., when the first and second call paths have been merged at the switch110), in accordance with the present invention, the mobile unit140Athen tunes to a specified channel of or otherwise sets up a communication path to the base station120B, illustrated as call path (or leg)175, for continuing the same communication session via a portion of the multiway call path, namely, call path (or leg)170. The hand-off of the communication session from the serving base station to the target base station is then complete, and the communication path legs160,161and162may then be torn down, with the communication session continuing uninterrupted through call paths (legs)175,170, and155, as illustrated inFIG. 3.

As may be apparent from the above discussion, the hand-off of the communication session, from the first, serving base station120Ato the second, target base station120B, utilizing multiway capabilities (e.g., of ISDN), occurs seamlessly and without interruption. In addition, such a hand-off is accomplished without the need for additional network resources.

FIG. 4is a block diagram illustrating an apparatus embodiment200in accordance with the present invention. As discussed in greater detail below, such an apparatus200may be included within, or distributed between, a switch110and/or a base station120of a system100. (Numerous other variations and equivalent embodiments will be readily apparent and are also within the scope of the present invention). The apparatus200includes a processor210, a network interface215, and a memory220. The network interface215is utilized to receive and to transmit the various communication links (legs or paths), and also to receive and transmit messages or other signaling, such as to transmit multiway (conference) requests, when the apparatus200is embodied within a base station120; or to receive multiway (conference) requests, when the apparatus200is embodied within a switch110. The network interface215is also utilized for transmission and reception of various requests and responses discussed below, such as call set up messages and information messages. The memory220may be a magnetic hard drive, an optical storage device, RAM, FLASH, or any other type of memory, data storage apparatus or circuit. The memory220is used to store information pertaining to call placement, call set up, routing information, and configuration or program instructions, as discussed in greater detail below.

Continuing to refer toFIG. 4, the processor210may include a single integrated circuit (“IC”), or may include a plurality of integrated circuits or other components connected, arranged or grouped together, such as microprocessors, digital signal processors (“DSPs”), custom ICs, application specific integrated circuits (“ASICs”), field programmable gate arrays (“FPGAs”), associated memory (such as RAM and ROM), and other ICs and components. As a consequence, as used herein, the term processor should be understood to equivalently mean and include a single IC, or arrangement of custom ICs, ASICs, processors, microprocessors, controllers, FPGAs, or some other grouping of integrated circuits which perform the functions discussed above with reference toFIGS. 1–3, and also discussed below with reference toFIG. 5, with associated memory, such as microprocessor memory or additional RAM, DRAM, SRAM, MRAM, ROM, EPROM or E2PROM. The processor210with its associated memory may be configured (via programming, FPGA interconnection, or hard-wiring) to perform the methodology of the invention, as discussed above with reference toFIGS. 1–3and as discussed below with reference toFIG. 5. For example, the methodology may be programmed and stored, in the processor210with its associated memory (and/or memory220) and other equivalent components, as a set of program instructions (or equivalent configuration or other program) for subsequent execution when the processor210is operative (i.e., powered on and functioning). Equivalently, when the processor210with its associated memory and other equivalent components are implemented in whole or part as FPGAs, custom ICs and/or ASICs, the FPGAs, custom ICs or ASICs also may be designed, configured and/or hard-wired to implement the methodology of the invention. In the preferred embodiment, the processor210is implemented in its entirety as a microprocessor, which is programmed to implement the methodology of the invention.

FIG. 5is a flow diagram illustrating a method embodiment in accordance with the present invention. Beginning with start step300, the method determines that a hand-off is necessary or preferable, step305. This may be accomplished through various methods known in the art, from various requests transmitted by the serving base stations, such as base station120A, with responses from the potential target base stations, such as base station120B, or by determinations made by the particular mobile unit140. Next, a target base station is selected for a hand-off, also as known in the art, step310, such as second base station120B. Following or as part of this selection process in step310, in the preferred embodiment of the invention, there is an exchange of information (via signaling path151inFIG. 1) between the serving base station and the target base station, including a designation of a directory number (“DN”) of a terminal of the selected target base station for use in establishing the second call path for the upcoming hand-off. The serving base station then initiates a second call path (on a second ISDN B channel) to the selected target base station (using the selected DN of the target base station), via a switch, step315. In step320, the serving base station directs the switch to establish a multiway (conference) connection between the first call path having the communication session (on the first channel B1) and the second call path (on the second channel B2), thereby creating a multiway communication session.

In the preferred embodiment, steps315and320may be accomplished in a variety of ways. In the preferred embodiment, the switch has been configured (populated) with an indicator that particular directory numbers (DNs) associated with the terminals of the various base stations have call features allowing multiway or other conferencing features. To commence the hand-off by creating the second call path, the serving base station120transmits a SETUP message to the switch110for a new call, and receives a corresponding acknowledgement from the switch110. The call is preferably established on a second channel (B2) available to the serving base station, with the second channel B2preferably designated in a channel identification field of the SETUP message. The serving base station then transmits one or more information (“INFORMATION”) messages to the switch110, preferably information messages on a separate (signaling) channel, which are compatible with ISDN Q.931 standards. In the preferred embodiment, a first information message (or equivalently, a first sequence of information messages) from the serving base station to the switch are utilized, in which the first information message (or sequence of information messages) designates the selected DN (previously communicated) of a terminal at the target base station for the hand-off, with the DN preferably encoded in a keypad field of the information message. The switch (utilizing appropriate ISDN Q.931 compatible messages such as SETUP, ALERTING, and CONNECT) then establishes the second call path in the second channel (B2) between the serving base station and the target base station.

In the preferred embodiment, following establishment of the second call path (in step315), for step320, the serving base station then requests that the switch110place the second call path “on hold” (using a HOLD message for B2and receiving a corresponding HOLD ACK from the switch). The serving base station then transmits a second information message to the switch directing the switch to invoke a multiway (conference) feature on the communication session of the first call path (on the first channel B1) (i.e., creating a multiway session between the communication session of the first call path (on the first channel B1) with the second call path (on the second channel B2)). In the preferred embodiment, the second information message (INFO) includes a conference or multiway request in a feature activation field, and further designates channel B1, and in response, receives an information message (INFO) from the switch which includes a conference or multiway request in a feature indication field, and further also designates channel B1. Using a “RETRIEVE” message to the switch designating channel B2, with a corresponding acknowledgement from the switch, the serving base station requests the switch to take the second call path on the second channel B2off “hold”, effectively merging the communication session of the first call path on the first channel B1with the second call path on the second channel B2, establish the multiway links (or multiway session). It should be noted that throughout this procedure, the communication session of the first call path has not been interrupted or interfered with in any way.

Alternatively, the multiway or conference feature could be activated by transmitting a feature activation element, denoting a multiway or conference connection as part of the initial SETUP message, eliminating the second information message. As another alternative, the conference or multiway feature activation element may be included within a field of the first sequence of information messages which also contain the target base station terminal's directory number as a keypad element.

Following the creation of the multiway communication session in steps315and320, in accordance with the present invention, in step325the mobile unit140Atunes to a specified channel of or otherwise sets up a communication path to the target base station120Bfor continuation of the communication session through the conferenced leg (call path170) of the multiway session, i.e., through a first portion or first leg of the multiway session. This communication path from the mobile unit to the target base station is illustrated inFIG. 3as call path175.

In the preferred embodiment, a variety of methods may be utilized to provide for the establishment of call path175; for example, the mobile unit140Amay be directed by the serving base station to communicate with (or tune to a channel of) the target base station, or the mobile unit140Amay initiate such a communication with or tuning to the target base station. As the various target and serving base stations have independent signaling paths (illustrated generally as a signaling and/or trunking line151inFIG. 1), the target base station then generally notifies the serving base station that the serving base station may now drop (tear down) its (second) portion or second leg of the multiway session (the portion of call paths161and162, between the switch110and the first base station120A). As a consequence, in step330, the previously serving base station (120A) disconnects from the multiway session, and the switch110releases the call to this previously serving base station, thereby tearing down the communication paths or legs161,162and160(from the switch110to the first base station120Aand mobile unit140A), with the communication session continuing uninterrupted through links or call paths155,170and175as illustrated inFIG. 3. Step330is preferably accomplished by the transmission of a “DISCONNECT” message from the previously serving base station120Ato the switch110, followed by a release message transmitted from the switch110to the base station120A, followed by a release complete message transmitted from the previously serving base station120Ato the switch110. Following the release of step330, the method may end, return step335.

Numerous advantages of the present invention may be apparent from the above discussion. First, as illustrated above, the wireless communication system of the present invention provides virtually seamless and imperceptible hand-offs of communication sessions of mobile units. Second, the various embodiments of the present invention are reasonably efficient and capable of cost-effective implementation in existing communication equipment such as switches and base stations. Moreover, the various embodiments of the present invention eliminate or minimize the use of additional network resources such as ECPs and CDNs, while being compatible with other intelligent network devices and systems.