SWITCHING BETWEEN CIRCUIT-SWITCHED AND PACKET SWITCHED NETWORKS

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

This invention relates generally to communication systems, and, more particularly, to wireless communication systems.

2. DESCRIPTION OF THE RELATED ART

Wireless communication systems typically include one or more base stations (or nodes-B) for providing wireless connectivity to mobile units in a geographic area (or cell) associated with each base station (or node -B). Mobile units and base stations communicate by transmitting modulated radiofrequency signals over a wireless communication link, or air interface. The air interface includes downlink (or forward link) channels for transmitting information from the base station to the mobile unit and uplink (or reverse link) channels for transmitting information from the mobile unit to the base station. The uplink and downlink channels are typically divided into data channels, random access channels, broadcast channels, paging channels, control channels, signaling channels, and the like. The uplink and downlink channels may be shared or dedicated. The air interface may form part of a circuit or channel between the mobile unit and another entity. For example, two mobile units may be connected by a circuit or channel that includes a first air interface between a first mobile unit and a first base station that is coupled to a network, a circuit or channel within the network, and a second air interface between a second base station and a second mobile unit.

Networks are typically divided into two types: circuit-switched networks and packet switched networks. A circuit switched network supports dedicated circuits (or channels) that are used for communication between nodes and terminals. A circuit that is dedicated to a communication session in a circuit switched network cannot be used by other callers until the circuit is released and a new connection is set up. Even if no actual communication is taking place in a dedicated circuit, dedicated channels remain unavailable to other users for the duration of the communication session. Channels that are available for new calls are referred to as idle channels. Ordinary voice phone service is typically circuit-switched. For example, the telephone company may reserve a specific physical path from a calling party to the number of a called party for the duration of the call. During that time, no one else can use the physical lines involved. In contrast, packet switched networks split traffic data (e.g., digital representations of sound and/or computer data) into packets that are routed over a shared network. Each packet is individually addressed so packet switched networks do not require a dedicated path to help the packet find its way to its destination. Many pairs of nodes may therefore communicate concurrently over the same channel. Some packet-switched networks, such as the X.25 network, support virtual circuit-switching. A virtual circuit- switched connection is a dedicated logical connection that allows sharing of the physical path among multiple virtual circuit connections.

Mobile units that have an existing wireless communication session in a network may handoff between different base stations in the network. For example, when a mobile unit roams from a cell served by a first base station in a circuit-switched network to a cell served by a second base station in the circuit-switched network, a handoff between the first and second base station may be triggered based on measurements of a pilot signal strength. Similarly, when a mobile unit roams from a cell served by a first node-B in a packet-switched

network to a cell served by a second node -B in the packet-switched network, the communication session associated with the mobile unit may be handed off between the first and second node-B. However, no voice call continuity triggers have been defined for internetwork handoffs between circuit- switched and packet switched networks. Conventional circuit-switched and packet switched networks therefore perform radio resource management independently of the other type of network, e.g., circuit-switched networks perform radio resource management for the cells in the circuit-switched network independently of considerations of cells in proximate packet switched networks. The absence of joint consideration of radio resources in circuit-switched and packet switched networks may limit the spectral efficiency of multiple cells that belong to different switching domains to a sub- optimal level.

SUMMARY OF THE INVENTION

The present invention is directed to addressing the effects of one or more of the problems set forth above. The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

In one embodiment of the present invention, a method is provided for switching between circuit- switched and packet switched network domains. One embodiment of the method includes generating, at a mobile unit, a trigger for handing off the mobile unit between a circuit switched network and a packet switched network based on at least one

characteristic of at least one radio resource of the circuit-switched network and at least one characteristic of at least one radio resource of the packet-switched network. Alternatively, the trigger may be generated within at least one of the circuit switched network or the packet switched network. The generated trigger may then be received at entities in the network, such as base stations and/or nodes-B.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

Figure 1 conceptually illustrates one exemplary embodiment of a wireless communication system, in accordance with the present invention;

Figure 2 conceptually illustrates a first exemplary embodiment of a method of handing off a mobile unit between a circuit-switched and a packet-switched portion of a wireless communication system, in accordance with the present invention; and

Figure 3 conceptually illustrates a second exemplary embodiment of a method of handing off a mobile unit between a circuit-switched and a packet-switched portion of a wireless communication system, in accordance with the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of

specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions should be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

Portions of the present invention and corresponding detailed description are presented in terms of software, or algorithms and symbolic representations of operations on data bits within a computer memory. These descriptions and representations are the ones by which those of ordinary skill in the art effectively convey the substance of their work to others of ordinary skill in the art. An algorithm, as the term is used here, and as it is used generally, is conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of optical, electrical, or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise, or as is apparent from the discussion, terms such as "processing" or "computing" or "calculating" or "determining" or "displaying" or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical, electronic quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

Note also that the software implemented aspects of the invention are typically encoded on some form of program storage medium or implemented over some type of transmission medium. The program storage medium may be magnetic (e.g., a floppy disk or a hard drive) or optical (e.g., a compact disk read only memory, or "CD ROM"), and may be read only or random access. Similarly, the transmission medium may be twisted wire pairs, coaxial cable, optical fiber, or some other suitable transmission medium known to the art. The invention is not limited by these aspects of any given implementation.

The present invention will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present invention with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present invention. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the

understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.

Figure 1 conceptually illustrates one exemplary embodiment of a wireless communication system 100. In the illustrated embodiment, the wireless communication system 100 includes portions of both circuit-switched networks and packet-switched networks. The portion of the circuit-switched network that is shown in Figure 1 includes one or more base stations 105 for providing wireless connectivity to one or more associated geographic areas that are conventionally referred to as cells 110. However, persons of ordinary skill in the art having benefit of the present disclosure should appreciate that the base stations 105 may also be configured to provide wireless connectivity to one or more sectors within the cells 110. The base station 105 may provide wireless connectivity according to the core Code Division Multiple Access (CDMA2000) wireless air interface standard known as IxRTT (1 times Radio Transmission Technology), which is used to identify the version of the CDMA2000 radio technology that operates in a pair of 1.25 MHz radio channels (one times 1.25 MHz, as opposed to three times 1.25 MHz in 3xRTT). However, persons of ordinary skill in the art having benefit of the present disclosure should appreciate that the illustrated embodiment is not intended to limit the present invention and the circuit-switched portion of the wireless communication system 100 may alternatively operate according to different standards and/or protocols.

Base station controllers (BSC) 115 may be used to coordinate the operation of the one or more base stations 105. In the illustrated embodiment, the base station controller 115 includes a circuit- switched radio resource management function (CS-RRM) 120 that is responsible for managing call admission, handoff, maintaining quality of service, as well as other tasks known to persons of ordinary skill in the art. The circuit-switched radio resource management function 120 may perform its designated functions based upon information associated with air interfaces supported by the base stations 105, radio resource management rules, information indicating current and/or maximum network capacities, and the like. For example, the circuit-switched radio resource management function 120 may determine whether to admit or handoff a new call to the base station 105 based on reverse link quality measurements, radio resource management rules that may be applied to the call, current network capacity, an anticipated quality of service for the admitted or handed off call, and the like. For another example, the circuit-switched radio resource management function 120 may determine whether to admit or handoff a new call to the base station 105 based on a measured power of a pilot signal provided by the circuit-switched network.

The portion of the packet-switched network that is shown in Figure 1 includes one or more nodes-B 125 for providing wireless connectivity to one or more associated cells 130. However, persons of ordinary skill in the art having benefit of the present disclosure should appreciate that the nodes-B 125 may also be configured to provide wireless connectivity to one or more sectors within the cells 130. The nodes-B 125 may provide wireless connectivity according to the Evolution-Data Optimized or Evolution-Data Only (EV-DO) standards and/or protocols, which have been standardized by 3rd Generation Partnership Project 2 (3GPP2) as part of the CDMA2000 family of standards. The EV-DO standards are typically classified as a broadband technology because it utilizes a broad band of radio frequencies and

EV-DO employs multiplexing techniques such as CDMA as well as Frequency division duplex (FDD) to maximize the amount of data transmitted. However, persons of ordinary skill in the art having benefit of the present disclosure should appreciate that the illustrated embodiment is not intended to limit the present invention and alternative embodiments of the packet-switched portion of the wireless communication system 100 may operate according to different standards and/or protocols.

Radio network controllers (RNC) 135 may be used to coordinate the operation of the one or more nodes-B 125. In the illustrated embodiment, the radio network controller 135 includes a packet-switched radio resource management function (PS-RRM) 140 that is responsible for managing call admission, handoff, maintaining quality of service, as well as other tasks known to persons of ordinary skill in the art. The packet-switched radio resource management function 140 may perform its designated functions based upon information associated with air interfaces supported by the nodes-B 125, radio resource management rules, information indicating current and/or maximum network capacities, and the like. For example, the packet- switched radio resource management function 140 may determine whether to admit or handoff a new call to the nodes-B 125 based on reverse link quality measurements, radio resource management rules that may be applied to the call, current network capacity, an anticipated quality of service for the admitted or handed off call, and the like. For another example, the packet-switched radio resource management function 140 may determine whether to admit or handoff a new call to the nodes-B 125 based on a measured power of a pilot signal provided by the packet-switched network.

The radio network controller 135 and the base station controller 115 may be able to communicate with each other, e.g. via wired and/or wireless connections (not shown) in the

wireless communication system 100. The messages exchanged between the radio network controller 135 and the base station controller 115 may be used to coordinate operation of the radio network controller 135 and the base station controller 115. The messages may be formed and/or exchanged based on any communication standards, protocols, or combination thereof.

In the illustrated embodiment, a mobile unit 145 is present in the wireless communication system 100. In the interest of clarity a single mobile unit 145 is shown in Figure 1. However, persons of ordinary skill in the art having benefit of the present disclosure should appreciate that the present invention is not limited to a single mobile unit 145 and in alternative embodiments numerous mobile units 145 may be present in the wireless communication system 100. The mobile unit 145 is capable of forming wireless communication links with either the packet-switched portion of the wireless communication system 100 or the circuit-switched portion of the wireless communication system 100. In the illustrated embodiment, the mobile unit 145 is located in (or has roamed into) a region where the cell 110 overlaps with the cell 130. Consequently, the mobile unit 145 may establish concurrent wireless communication links with the packet-switched and the circuit-switched portions of the wireless communication system 100. The packet- switched and circuit- switched radio resource management functions 120, 140 may jointly and/or dynamically determine which portion of the wireless communication system 100 should be used to provide wireless connectivity to the mobile unit 145, e.g., to provide the best spectral efficiency across multiple modulation types, coding, bands, multi-carrier systems, and the like.

Triggers for handing off the mobile unit 145 between the circuit- switched and the packet-switched portions of the wireless communication system 100 can be based on characteristics of radio resources of the circuit-switched portion and/or characteristics of radio resources of the packet- switched portion of the wireless communication system 100. In one embodiment, the mobile unit 145 can perform measurements on the signals received over common pilot channels associated with the circuit-switched and the packet-switched portions of the wireless communication system 100. These measurements can be reported to the radio network controller 135 and/or the base station controller 115, which may use the measurements to evaluate different potential configurations. Alternatively, the radio network controller 135 and/or the base station controller 115 may perform measurements of signals received on the associated reverse links and use these measurements to evaluate the different potential configurations. The radio network controller 135 and/or the base station controller 115 may also use radio resource management rules, quality of service considerations, and the like to invite what the different potential configurations. The radio network controller 135 and the base station controller 115 may then jointly determine whether to handoff the mobile unit 145 to the circuit- switched portion or the packet- switched portion of the wireless communication system 100.

Figure 2 conceptually illustrates a first exemplary embodiment of a method 200 of handing off a mobile unit (UE) between a circuit-switched and a packet-switched portion of a wireless communication system. The mobile unit communicates with a base station controller (BSC) of a circuit-switched network and a radio network controller (RNC) of a packet-switched network. The method 200 illustrates a mobile-unit-initiated handoff from a circuit-switched portion of a wireless communication system to a packet-switched portion of the wireless communication system. However, persons of ordinary skill in the art having

benefit of the present disclosure should appreciate that the techniques illustrated in Figure 2 apply equally well to a mobile-unit-initiated handoff from the packet-switched portion to the circuit-switched portion of the wireless communication system.

In the illustrated embodiment, the mobile unit receives (as indicated by the arrow 205) measurement control information from the base station controller over a broadcast channel. The measurement control information may be communicated as an information element in a control message and may include information indicative of one or more reporting events, such as the thresholds that may be used to trigger a message that reports results of one or more measurements to the base station controller. The mobile unit may then measure (at 210) pilot power strengths of pilot signals transmitted over forward links between the mobile unit and the circuit-switched portion of the network and the packet-switched portion of the network. Based on the reporting events trigger, the mobile unit reports (at 215) the measurement results to the radio resource management function implemented in the base station controller and/or the radio network controller. For example, the mobile unit may report (at 215) the measurement results if the pilot signal strength associated with the packet- switched domain exceeds the pilot signal strength associated with the circuit-switched domain. In one embodiment, the report includes information indicating a selected candidate cell, sector, carrier, and/or band in the packet-switched domain.

In one embodiment, the radio resource management function in the base station controller may communicate (at 220) with the corresponding radio resource management function in the radio network controller. For example, the two radio resource management functions may communicate (at 220) to determine the radio resource status in the packet- switched domain. If the base station controller receives positive feedback from the radio

network controller, indicating that sufficient radio resources are available to support handoff of the mobile unit to the packet-switched domain, the circuit-switched radio resource management sends (at 225) the radio resource management signaling message to the mobile unit that indicates that the requested handoff has been approved. The mobile unit may then accept or reject the decision. Once the mobile unit has received (at 225) the acknowledgment for the voice call continuity handoff and accepted the proposed handoff, the mobile unit sends (at 230) a request for the handoff to a control entity in the core network (not shown), e.g., via a non-access stratum procedure.

A packet-switched radio access bearer may then be formed (at 235) in response to the handoff request. In various embodiments, the radio access bearer may be formed (at 235) using the requested candidate packet-switched cell, sector, carrier, and/or band. Once the radio access bearer for the packet-switched domain has been formed, the mobile unit may initiate or form the packet-switched radio access bearer (at 240) and then remove or tear down (at 245) the circuit-switched radio access bearer to the base station controller. Accordingly, the method 200 is a make-then-break (or soft handover) technique in which the mobile unit may maintain concurrent radio access bearers with the circuit-switched domain and the packet-switched domain during the handover procedure. However, persons of ordinary skill in the art having benefit of the present disclosure should appreciate that the method 200 is not limited to make-then-break techniques.

Figure 3 conceptually illustrates a second exemplary embodiment of a method 300 of handing off a mobile unit between a circuit-switched and a packet-switched portion of a wireless communication system. The mobile unit communicates with a base station controller (BSC) of a circuit-switched network and a radio network controller (RNC) of a

packet- switched network. The method 300 illustrates a network-initiated handoff from a circuit-switched portion of a wireless communication system to a packet-switched portion of the wireless communication system. However, persons of ordinary skill in the art having benefit of the present disclosure should appreciate that the techniques illustrated in Figure 3 apply equally well to a network-initiated handoff from the packet-switched portion to the circuit-switched portion of the wireless communication system.

In the illustrated embodiment, the base station controller measures (at 305) reverse link quality measurements for the reverse link between the mobile unit and the circuit- switched portion of the network. Although not depicted in Figure 3, the radio network controller may also measure reverse link quality for the reverse link between the mobile unit and the packet-switched portion of the network. The base station controller then determines whether or not the reverse link quality measurements could trigger a potential handoff of the mobile unit to the packet-switched domain. For example, a handoff may be triggered when the reverse link quality measurements fall below a selected threshold. In some embodiments, the base station controller may also consider other characteristics when determining whether a potential handoff may be triggered. For example, the base station controller may consider radio resource management rules that may be applied to the call, current network capacity, an anticipated quality of service for the admitted or handed off call, and the like. Based on the reporting events trigger, the base station controller may transmit (at 310) a message indicating the potential handoff to the mobile unit.

In one embodiment, the radio resource management function in the base station controller may also communicate (at 315) with the corresponding radio resource management function in the radio network controller. For example, the two radio resource management

functions may communicate (at 315) to determine the radio resource status in the packet- switched domain. If the base station controller receives positive feedback from the radio network controller, indicating that sufficient radio resources are available to support handoff of the mobile unit to the packet-switched domain, the circuit-switched radio resource management sends (at 320) the radio resource management signaling message to the mobile unit that indicates that the handoff has been approved. The mobile unit may then accept or reject the decision. Once the mobile unit has received (at 320) the acknowledgment for the voice call continuity handoff and accepted the proposed handoff, the mobile unit sends (at 325) a request for the handoff to a control entity in the core network (not shown), e.g., via a non-access stratum procedure.

A packet- switched radio access bearer may then be formed (at 330) in response to the handoff request. In various embodiments, the radio access bearer may be formed (at 330) using the requested candidate packet-switched cell, sector, carrier, and/or band. Once the radio access bearer for the packet-switched domain has been formed, the mobile unit may initiate or form the packet-switched radio access bearer (at 335) and then remove or tear down (at 340) the circuit-switched radio access bearer to the base station controller. Accordingly, the method 300 is a make-then-break (or soft handover) technique in which the mobile unit may maintain concurrent radio access bearers with the circuit-switched domain and the packet-switched domain during the handover procedure. However, persons of ordinary skill in the art having benefit of the present disclosure should appreciate that the method 300 is not limited to make-then-break techniques.

Embodiments of the techniques described herein may have a number of advantages over conventional practice. The voice call continuity switching triggers defined herein may

be dependent on radio conditions such as signal-to-interference-plus-noise ratios (SINR) and/or the received energy (Ec/Nt) and therefore using these triggers for handoffs may improve the overall air link quality. Embodiments of the techniques described herein may also be used to dynamically configure the handover triggers. In one embodiment, different system configurations may be transmitted over the broadcast control channel for measurement purposes or via a dedicated radio resource management message. In the mobile-initiated case, the mobile unit measures pilot channels for both systems and then reports these to the radio resource management functions on the circuit-switched and packet- switched networks, which may permit the two domains to coordinate handoff decisions. In the network-initiated case, the node-B and base stations in the circuit-switched and packet- switched domains may measure reverse link qualities and report these to one or more of the radio resource management entities so that handoff decisions may be coordinated between the circuit-switched and packet-switched domains.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope of the invention. Accordingly, the protection sought herein is as set forth in the claims below.