Abstract:
An approach is provided for executing a fast handoff in a radio communication system. An active hard handoff condition associated with a communication session supported by a radio link protocol (RLP) flow and a signaling link protocol (SLP) flow is detected. Transfer of state information and data of the RLP and the SLP is performed over a pre-designated interface from a source entity to a target entity if an active hard handoff condition is detected. The above process is particularly suitable for deployment in radio communication systems, such as a cellular system.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to communications, and more particularly, to providing handoff in a radio communication system.  
       BACKGROUND OF THE INVENTION  
       [0002]     Radio communication systems provide users with the convenience of mobility along with a rich set of services and features. With the vast and rapid adoption of these services, standardization efforts have increased to ensure interoperability as well as provide an evolutionary path to new services and associated infrastructure. One such new service aims to provide increased capacity to support, for instance, a high-rate data service. The International Telecommunications Union (ITU) for International Mobile Telecommunications 2000 (IMT-2000) has made steady progress towards an Internet Protocol (IP)-based radio access network, which utilizes Access Networks (ANs) (or base stations) to serve Access Terminals (ATs) (or mobile stations). An area of interest is the manner active handoff procedures, particularly “hard” handoffs, are conducted as an AT moves from one AN to the next when an active data session is ongoing. In the case of an active hard handoff, the connection is terminated with one AN and reestablished with the next AN. During this procedure, service disruption can easily occur and be detected by the user if the active handoff is slow. Current systems do not possess a pragmatic or efficient approach to this active hard handoff procedure.  
         [0003]     Therefore, there is a need to provide an efficient fast handoff procedure for a radio communication system that supports high-rate data services.  
       SUMMARY OF THE INVENTION  
       [0004]     These and other needs are addressed by the present invention, in which an approach provides a fast handoff in a radio communication system.  
         [0005]     According to one aspect of an embodiment of the present invention, a method for providing a fast handoff in a radio communication system is disclosed. The method includes detecting an active hard handoff condition associated with a communication session supported by a radio link protocol (RLP) flow and a signaling link protocol (SLP) flow. The method also includes initiating transfer of state information of the RLP flow and the SLP flow over a pre-designated interface from a source entity to a target entity if an active hard handoff condition is detected.  
         [0006]     According to another aspect of an embodiment of the present invention, a network apparatus for providing a fast handoff in a radio communication system is disclosed. The apparatus includes a logic configured to detect an active hard handoff condition associated with a communication session supported by a radio link protocol (RLP) flow and a signaling link protocol (SLP) flow. The apparatus also includes a communication interface configured to transfer state information of the RLP flow and the SLP flow over a pre-designated interface from a source entity to a target entity if an active hard handoff condition is detected.  
         [0007]     According to another aspect of an embodiment of the present invention, a method for providing a fast handoff in a radio communication system is disclosed. The method includes means for detecting an active hard handoff condition associated with a communication session supported by a radio link protocol (RLP) flow and a signaling link protocol (SLP) flow. The method also includes means for initiating transfer of state information of the RLP flow and the SLP flow over a pre-designated interface from a source entity to a target entity if an active hard handoff condition is detected.  
         [0008]     According to another aspect of an embodiment of the present invention, a method for providing communication signaling is disclosed. The apparatus includes means for detecting an active hard handoff condition associated with a high rate packet data (HRPD) session supported by one or more radio link protocol (RLP) flows and one or more signaling link protocol (SLP) flows. The method also includes for initiating transfer of state information of the RLP flows and the SLP flows over an A13 interface to a target entity if an active hard handoff condition is detected.  
         [0009]     Still other aspects, features, and advantages of the present invention are readily apparent from the following detailed description, simply by illustrating a number of particular embodiments and implementations, including the best mode contemplated for carrying out the present invention. The present invention is also capable of other and different embodiments, and its several details can be modified in various obvious respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:  
         [0011]      FIG. 1  is a diagram of a radio communication system capable of support fast handoff between Access Networks/Packet Control Functions (ANs/PCFs), in accordance with an embodiment of the present invention;  
         [0012]      FIG. 2  is a diagram of a source entity conveying Radio Link Protocol (RLP) and Signalling Link Protocol (SLP) state information to a target entity, in accordance with various embodiments of the present invention;  
         [0013]      FIG. 3  is a flowchart of a handoff process, in accordance with various embodiments of the present invention;  
         [0014]      FIGS. 4A and 4B  are diagrams of a message specifying RLP state information, in accordance with various embodiments of the present invention; and  
         [0015]      FIG. 5  is a diagram of a message specifying SLP state information, in accordance with various embodiments of the present invention; and  
         [0016]      FIG. 6  is a diagram of hardware that can be used to implement an embodiment of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     An apparatus, method, and software for supporting fast handoff in radio communication system are described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It is apparent, however, to one skilled in the art that the present invention may be practiced without these specific details or with an equivalent arrangement. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention.  
         [0018]     Although the present invention is discussed with respect to a spread spectrum system, it is recognized by one of ordinary skill in the art that the present invention has applicability to any type of radio communication system.  
         [0019]      FIG. 1  is a diagram of a radio communication system capable of support fast handoff between Access Networks/Packet Control Functions (ANs/PCFs), in accordance with an embodiment of the present invention. By way of example, a radio network  100  is a 1× EV-DO (Evolutionary/Data Optimized) system according to the Third Generation Partnership Project 2 (3GPP2) standard that supports High Rate Packet Data (HRPD). The radio network  100  includes one or more access terminals (ATs) of which one AT  101  is shown in communication with an access network (AN)  103  over an air interface. The AT  101  is a device that provides data connectivity to a user. For example, the AT  101  can be connected to a computing system, such as a personal computer, a personal digital assistant, and etc. or a data service enabled cellular handset. The AN  103  is a network equipment that provides data connectivity between a packet switched data network  105 , such as the global Internet and the AT  101 . In cdma2000 systems, the AT  101  is equivalent to a mobile station, and the access network  103  is equivalent to a base station.  
         [0020]     In the radio network  101 , handoffs of communication sessions of the AT  101  can occur between the AN  103  and another AN  107 . In this context, the AN  103  is considered the source AT, while the AN  107  is the target access network. The handoff procedure relating to an active hard handoff, whereby a communication session or connection is “broken” or terminated and reestablished between ANs  103 ,  107 , is described later with respect to  FIGS. 2 and 3 .  
         [0021]     A connection is a particular state of the air-link in which the AT  101  is assigned a Forward Traffic Channel, a Reverse Traffic Channel and associated Medium Access Control (MAC) Channels. During a single HRPD session, the AT  101  and the AN  103  can open and can close a connection multiple times. An HRPD session refers to a shared state between the AT  101  and the AN  103 . This shared state stores the protocols and protocol configurations that were negotiated and are used for communications between the AT  101  and the AN  103 . Other than to open a session, the AT  101  cannot communicate with the AN  101  without having an open session. A more detailed description of the HRPD is provided in 3GPP2 C.S0024 v3.0, entitled “cdma2000 High Rate Packet Data Air Interface Specification,” December 2001, 3GPP2 A.S0007-A v2.0, entitled “Interoperability Specification (IOS) for High Rate Packet Data (HRPD) Access Network Interfaces—Rev. A,” May 2003, and 3GPP2 A.S0008-0 v3.0, entitled “Interoperability Specification (IOS) for High Rate Packet Data (HRPD) Access Network Interfaces,” May 2003; which are incorporated herein by reference in their entireties.  
         [0022]     The AN  103  communicates with a Packet Data Service Node (PDSN)  109  via a Packet Control Function (PCF)  111 . Either the AN  103  or the PCF  111  provides a SC/MM (Session Control and Mobility Management) function, which among other functions includes storing of HRPD session related information, performing the terminal authentication procedure to determine whether an AT  101  should be authenticated when the AT  101  is accessing the radio network  100 , and managing the location of the AT  101 . The PCF  111  is further described in 3GPP2 A.S0001-A v2.0, entitled “3GPP2 Access Network Interfaces Interoperability Specification,” June 2001, which is incorporated herein by reference in its entirety.  
         [0023]     In addition, the AN  103  communicates with an AN-AAA (Authentication, Authorization and Accounting entity)  113 , which provides terminal authentication and authorization functions for the AN  103 .  
         [0024]     As shown, a variety of interfaces are utilized between different network entities. The A8 interface carries user traffic between the AN  103  and the PCF  111 . An A9 interface carries signaling information between the AN  103  and the PCF  111 . Similarly, between the PCF  111  and the PDSN  109  interfaces A10 and A11 are used to carry, respectively, user traffic and signaling information.  
         [0025]     Also, the AN  103  employs the A12 interface to transport signaling information related to terminal authentication between the SC/MM function in the PCF  111  and the AN-AAA  113 .  
         [0026]     An A13 interface supports exchange of signaling information between the source AN  103  and the target AN  107 . According to one embodiment of the present invention, the A13 is used to transfer SLP (signalling link protocol) state variables from a source AN/PCF (depending on 1× EV-DO radio access network architecture). In one example, the A13 interface provides a UDP port number to be used for signaling interconnection to the target AN  107 . In particular, information may be exchanged in either the source to target direction or the target to source direction.  
         [0027]     The procedure for the A13 interface is a message flow to exchange AT and PDSN information between the ANs  103  and  107 . The information is exchanged via the following messages: A13-Session Information Request, A13-Session Information Response, A13-Session Information Confirm, and A13-Session Information Reject. The A13-Session Information Request message is sent by the target AN  107  to request information about an AT  101  from a source AN  103  when the target AN  107  does not have this information. The A13-Session Information Response message is used by the source AN  103  to respond to the target AN&#39;s request to retrieve information about an AT  101 . When the source AN  103  receives an A13-Session Information Request message it checks if the session information for the requested AT  101  exists and if it can authenticate the target AN request. After the source AN  103  has successfully authenticated the message contained in the A13-Session Information Request message and obtained the requested session state information, it sends an A13-Session Information Response message to the target AN  107  with the requested information. The A13-Session Information Confirm message is used by the target AN  107  to inform the source AN  103  that the target AN  107  has successfully received the session information about an AT  101 . The A13-Session Information Reject message is used by the source AN  103  to reject a request from the target AN  107  to retrieve session information from source AN  103 .  
         [0028]     During a handoff, the source AN  103  generates an A13-Handoff Request message to the target AN  107 . The approach, according to one embodiment of the present invention, supplies Radio Link Protocol (RLP) and Signalling Link Protocol (SLP) state information via the A13-Handoff Request message.  
         [0029]      FIG. 2  is a diagram of a source entity conveying Radio Link Protocol (RLP) and Signalling Link Protocol (SLP) state information to a target entity, in accordance with various embodiments of the present invention. It is noted that the PCF  111  can be viewed as being a part of the AN  103 . Thus, for the purposes of explanation, the AN  103  and the PCF  111  considered the same entity in the context of the hard handoff procedure. That is, although not shown, the PCF  111  can also communicate with another PCF, as a target PCF. In this example, the source entity  201  seeks to handoff to a target entity  203 .  
         [0030]     It is recognized that when the inter-AN/PCF active hard handoff occurs, the buffered RLP and SLP packets in the source AN/PCF may cause service disruption if they are not appropriately transferred to the target AN/PCF. One approach would be only to transfer all the packets between AN/PCF; however, such an approach is not complete. By contrast, the system  100  provides an efficient scheme to transfer state information/variables  205  and the information data within in the buffers of RLP (for data) and SLP (for signalling) between the ANs/PCFs.  
         [0031]     According to one embodiment of the present invention, if multiple RLP flows are used for a certain communication session corresponding to an 1× EV-DO access terminal  101  (or mobile station), for example, then all of the multiple RLP state variables and RLP packet data remained in the buffer are transferred using A13.  
         [0032]     As seen in  FIG. 2 , the information  205  carried over the A13 interface can specify RLP variables and/or SLP information. RLP information includes the variables enumerated in Table 1.  
                           TABLE 1                                   NAME   DESCRIPTION                           V(S) NN     Sequence number of the first octet of the               next RLP packet to be sent, of the RLP               flow NN           V(R) NN     Sequence number of the first octet of the               next RLP packet expected to be received,               of the RLP flow NN           V(N) NN     Sequence number of the first octet of the               next RLP packet needed for sequential               delivery, of the RLP flow NN                      
 
         [0033]     As regards the SLP state variables, two parts are defined: Signaling link protocol—Delivery layer (SLP-D) and Signaling link protocol—Fragmentation layer (SLP-F).  
                                                                   TABLE 2                                   NAME   DESCRIPTION                                    Signaling link protocol - Delivery layer (SLP-D)                V(S)   Sequence number of the next SLP-D               packet to be sent           V(N)   Sequence number of the next expected               SLP-D packet;           Rx   Mapping vector of received packets            Signaling link protocol - Fragmentation layer (SLP-F)                Sync   The SLP-F synchronized status flag                      
 
         [0034]     The RLP state information and the SLP state information, in one embodiment of the present invention, can be specified in a handoff request message, as more fully explained with respect to  FIGS. 4A, 4B  and  5 .  
         [0035]      FIG. 3  is a flowchart of a handoff process, in accordance with various embodiments of the present invention. In step  301 , the AN  103  determines whether an active hard handoff has detected. Upon detection of the handoff, the source AN  103  transfers the state information  205  (of  FIG. 2 ) and information data to the target AN  107  via the A13 interface (step  303 ). Thereafter the handoff process concludes and the target AN  107  processes the communication session, per steps  305  and  307 .  
         [0036]      FIGS. 4A and 4B  are diagrams of a packet specifying RLP state information, in accordance with various embodiments of the present invention. By way of example, the RLP state information can be specified in an A13-Handoff Request Message  401  relating to the radio link protocol (RLP) state information.  
                                                     TABLE 3                                   INFORMATION   ELEMENT               ELEMENTS   DIRECTION   TYPE                                        RLP State   Source--&gt;   O   C           Information   Target           SLP State   Source--&gt;   O   C           Information   Target                        
         [0037]     It is noted that the RLP state information is included when the radio link protocol is not sending NAK (Negative Acknowledgements) messages for missing frames.  
         [0038]     Table 4 enumerates the various fields in the A13-Handoff Request Message format of  FIGS. 4A and 4B  for RLP state information.  
                   TABLE 4                       RADIO LINK PROTOCOL           ELEMENTS (FIELD)   DESCRIPTION                   A13 Element Identifier 403   Indicates the type of message on the A13           interface       Length 405   The number of octets in this element           following the Length field 405       Forward ActivatedRLPFlow   The number of forward ActivatedRLPFlow       Count 407   Count RLP flows       Reverse ActivatedRLPFlow   The number of reverse ActivatedRLPFlow       Count 409   Count RLP flows       Forward RLIID Entry;   Delimiter for start of Forward RLPID entry       Forward ActivatedRLPFlow       Count 411       Forward RLPIDLength NN     The length of forward RLPID of flow NN       413       Reverse RLPIDLength NN     The length of reverse RLPID of flow NN       435       Forward SequenceLength NN     The length of forward RLP sequence number       415   of flow NN       Forward RLPID NN  417   RLPID of forward RLP flow NN       Forward RLPID Entry 431   Delimiter for end of Forward RLPID entry       V(S) NN  419, 441   Sequence number of the first octet of the next           RLP packet to be sent, of the RLP flow NN       V(R) NN  421, 443   Sequence number of the first octet of the next           RLP packet expected to be received, of the           RLP flow NN       V(N) NN  423, 445   Sequence number of the first octet of the next RLP packet           needed for sequential delivery, of the RLP flow NN       Forward RLPDataLength NN     Number of Octet of forward RLP packets, of       [H] 425   RLP flow NN, which were not transmitted           before the handoff occurred       Forward RLPDataLength NN     Number of Octet of forward RLP packets, of       [L] 427   RLP flow NN, which were not transmitted           before the handoff occurred       Reverse SequenceLength NN     The length of reverse RLP sequence number       437   of flow NN       Reverse RLPID NN  439   RLPID of reverse RLP flow NN       Reverse RLPDataLength NN     Number of Octet of reverse RLP packets, of       [H] 447   RLP flow NN, which were not transmitted           before the handoff occurred       Reverse RLPDataLength NN     Number of Octet of forward RLP packets, of       [L] 449   RLP flow NN, which were not transmitted           before the handoff occurred       Reverse RLPData NN  451   Reverse RLPID packets, of RLP flow NN,           which were not transmitted before the handoff           occurred       Reverse RLPID Entry 453   Delimiter for end of Reverse RLPID Entry                  
 
         [0039]      FIG. 5  is a diagram of a message specifying SLP state information, in accordance with various embodiments of the present invention. Table 5 describes the fields of the message  501  conveying SLP state information.  
                   TABLE 5                       SIGNALING LINK           PROTOCOL ELEMENTS       (FIELD)   DESCRIPTION                   A13 Element Identifier 501   Indicates the type of message on the A13           interface       Length 503   This field indicates the number of octets in           this element following the Length field       Sync 505   Synchronized status flag for the SLP-F layer       V(S) SLP-D 507   Sequence number of the next SLP-D packet           to be sent       V(N) 509   Sequence number of the next expected SLP-           D packet       V(S) SLP-F 511   Sequence number of the next SLP-F packet           to be sent       Rx 513   8-bit (i.e., 2 S  bit, where S=3) vector;           Rx[i] = ‘1’if the           SLP-D packet with sequence           number i was received       SLPDataLength[i] 515   Number of octet of SLP packet       SLPData[i] 517   SLP packet                    
         [0040]     The processes described advantageously provide fast handoff in a radio communication system. These processes can be executed through a variety of hardware and/or software configurations.  
         [0041]      FIG. 6  illustrates exemplary hardware upon which an embodiment according to the present invention can be implemented. A computing system  600  includes a bus  601  or other communication mechanism for communicating information and a processor  603  coupled to the bus  601  for processing information. The computing system  600  also includes main memory  605 , such as a random access memory (RAM) or other dynamic storage device, coupled to the bus  601  for storing information and instructions to be executed by the processor  603 . Main memory  605  can also be used for storing temporary variables or other intermediate information during execution of instructions by the processor  603 . The computing system  600  may further include a read only memory (ROM)  607  or other static storage device coupled to the bus  601  for storing static information and instructions for the processor  603 . A storage device  609 , such as a magnetic disk or optical disk, is coupled to the bus  601  for persistently storing information and instructions.  
         [0042]     The computing system  600  may be coupled via the bus  601  to a display  611 , such as a liquid crystal display, or active matrix display, for displaying information to a user. An input device  613 , such as a keyboard including alphanumeric and other keys, may be coupled to the bus  601  for communicating information and command selections to the processor  603 . The input device  613  can include a cursor control, such as a mouse, a trackball, or cursor direction keys, for communicating direction information and command selections to the processor  603  and for controlling cursor movement on the display  611 .  
         [0043]     According to one embodiment of the invention, the processes of  FIGS. 2 and 3  can be provided by the computing system  600  in response to the processor  603  executing an arrangement of instructions contained in main memory  605 . Such instructions can be read into main memory  605  from another computer-readable medium, such as the storage device  609 . Execution of the arrangement of instructions contained in main memory  605  causes the processor  603  to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the instructions contained in main memory  605 . In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the embodiment of the present invention. In another example, reconfigurable hardware such as Field Programmable Gate Arrays (FPGAs) can be used, in which the functionality and connection topology of its logic gates are customizable at run-time, typically by programming memory look up tables. Thus, embodiments of the present invention are not limited to any specific combination of hardware circuitry and software.  
         [0044]     The computing system  600  also includes at least one communication interface  615  coupled to bus  601 . The communication interface  615  provides a two-way data communication coupling to a network link (not shown). The communication interface  615  sends and receives electrical, electromagnetic, or optical signals that carry digital data streams representing various types of information. Further, the communication interface  615  can include peripheral interface devices, such as a Universal Serial Bus (USB) interface, a PCMCIA (Personal Computer Memory Card International Association) interface, etc.  
         [0045]     The processor  603  may execute the transmitted code while being received and/or store the code in the storage device  609 , or other non-volatile storage for later execution. In this manner, the computing system  600  may obtain application code in the form of a carrier wave.  
         [0046]     The term “computer-readable medium” as used herein refers to any medium that participates in providing instructions to the processor  603  for execution. Such a medium may take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as the storage device  609 . Volatile media include dynamic memory, such as main memory  605 . Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise the bus  601 . Transmission media can also take the form of acoustic, optical, or electromagnetic waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, CDRW, DVD, any other optical medium, punch cards, paper tape, optical mark sheets, any other physical medium with patterns of holes or other optically recognizable indicia, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave, or any other medium from which a computer can read.  
         [0047]     Various forms of computer-readable media may be involved in providing instructions to a processor for execution. For example, the instructions for carrying out at least part of the present invention may initially be borne on a magnetic disk of a remote computer. In such a scenario, the remote computer loads the instructions into main memory and sends the instructions over a telephone line using a modem. A modem of a local system receives the data on the telephone line and uses an infrared transmitter to convert the data to an infrared signal and transmit the infrared signal to a portable computing device, such as a personal digital assistant (PDA) or a laptop. An infrared detector on the portable computing device receives the information and instructions borne by the infrared signal and places the data on a bus. The bus conveys the data to main memory, from which a processor retrieves and executes the instructions. The instructions received by main memory can optionally be stored on storage device either before or after execution by processor.  
         [0048]     While the present invention has been described in connection with a number of embodiments and implementations, the present invention is not so limited but covers various obvious modifications and equivalent arrangements, which fall within the purview of the appended claims.