Abstract:
A method and apparatus for supporting inter-frequency and inter-radio access technology (inter-RAT) handover are disclosed. A network provides measurement gap parameters for configuring a measurement gap to a wireless transmit/receive unit (WTRU). The WTRU then performs a measurement based on the measurement gap parameters. Such measurement includes inter-frequency frequency division duplex (FDD) measurements, inter-RAT global standard for mobile communication (GSM) measurements, and inter-RAT universal mobile telecommunication system (UMTS) measurements.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 60/945,973 filed on Jun. 25, 2007, which is incorporated by reference as if fully set forth. 
     
    
     FIELD OF INVENTION 
       [0002]    The application is related to wireless communication systems. 
       BACKGROUND 
       [0003]    The Third generation partnership project (3GPP) has recently initiated a long term evolution (LTE) program to bring new technology, new network architecture and configuration and new applications and services to the wireless cellular network in order to provide improved spectral efficiency, reduced latency, faster user experiences and richer applications and services with less cost. While LTE aims at realizing an evolved universal terrestrial radio access network (E-UTRAN), LTE concepts also apply to high speed packet access (HSPA) enhancements. 
         [0004]    In previous universal mobile telecommunication system (UMTS) releases, there are three (3) kinds of handover scenarios: intra-frequency, inter-frequency and inter-RAT. 
         [0005]    Intra-frequency handovers may be performed without a wireless transmit/receive unit (WTRU) tuning away from its current frequency. Inter-frequency and inter-RAT handovers require that the WTRU sequentially tune its radio to more than one frequency or RAT, e.g. global system for mobile communication (GSM), and UMTS, in order to perform measurements. In order to achieve this objective, a network signals compressed mode gap parameters to the WTRU which may be utilized by the WTRU to measure, detect and confirm an identity of the inter-frequency or inter-RAT cells. The signaled parameters may include measurement gap purpose, the measurement gap length, measurement gap duration, and other similar parameters. 
         [0006]    A LTE network may have inter-frequency and inter-RAT handovers. In the case of inter-RAT handovers in LTE, there are two (2) RATs, GSM and UMTS. It is desirable to define new gap parameters, more specifically new measurement gap parameters, to facilitate handovers. 
       SUMMARY 
       [0007]    A method and apparatus for supporting inter-frequency and inter-RAT handover is defined. A network provides measurement gap parameters for configuring a measurement gap to a WTRU. The WTRU then performs measurements based on the measurement gap parameters. These measurements include, but are not limited to, inter-frequency frequency division duplex (FDD) measurements, inter-RAT GSM measurements, and inter-RAT UMTS measurements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein: 
           [0009]      FIGS. 1-2  illustrate one example of a possible handover scenario; and 
           [0010]      FIG. 3  shows an exemplary WTRU and eNB. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    When referred to hereafter, the terminology “WTRU” (wireless transmit/receive unit) includes but is not limited to a User Equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, or any other type of user device capable of operating in a wireless environment. When referred to hereafter, the terminology “evolved Node-B (eNB)” includes but is not limited to a Node-B (NB), base station, a site controller, an access point (AP), or any other type of interfacing device capable of operating in a wireless environment. A “measurement gap configuration” comprises at least one of a measurement gap parameter, neighboring cell list and other measurement information. 
         [0012]    Measurement gap parameters are provided, that are signaled for inter-frequency and inter-RAT measurement and procedures, where the behavior of a WTRU under certain measurement gap patterns is unspecified. These measurement gap parameters are applicable to any wireless communication systems including, but not limited to, 3GPP UMTS, LTE, and HSPA enhancements (HSPA+). The measurement gap parameters facilitate handover procedures. 
         [0013]      FIGS. 1-2  show an example of a possible handover (inter-RAT or inter-frequency) scenario.  FIG. 1  represents the network state prior to a possible handover, where WTRU  40  is in cell  10  and is receiving signaling from eNB  30  and WTRU  50  is in cell  20  receiving signaling from eNB  60 . In  FIG. 1 , WTRU  40  has moved into an area covered by cell  10  and cell  20  requiring a possible handover (HO). Prior to the HO, the WTRU  40  is configured to take one or more measurements, relative to cell  20 , based upon measurement gap parameters specified by the eNB  30 , examples of which are described below, according to measurement purposes, examples of which are also described below. Based upon the results of these measurements, eNB  30  will decide if the handover of WTRU  40  will take place. 
         [0014]    The embodiments described below use LTE as a context for clarity. However, one skilled in the art will recognize that the new measurement gap parameters are applicable to many types of network environments. 
         [0015]    In LTE, there are three different measurement scenarios: intra-frequency, inter-frequency, and inter-RAT. In LTE, since there are two RATs to measure, the measurement gaps may be used for at least three different purposes: inter-frequency FDD measurements, inter-RAT GSM measurements, and inter-RAT UMTS measurement. Other RATs are feasible and anticipated by this application. New parameters are defined that may be used to configure and activate the measurement gaps in the WTRU. 
         [0016]      FIG. 3  shows representative examples of a WTRU  300  and an eNB  350 . The eNB  350  processor  390  retrieves the measurement gap parameters from memory  395  and transmits the parameters to a WTRU  300  via transmitter  380 . The WTRU  300  receives the measurement gap parameters via receiver  320 . Processor  310  processes the parameters and stores them in memory  315 . The processor  310  performs measurements based upon the stored parameters according to the behaviors and purposes described below. 
         [0017]    Examples of these new parameters are defined in Table 1. The parameters in Table 1 may be referred to by a variety of names and yet still retain the same meaning. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Information 
                   
                   
                   
                   
               
               
                 Element/Group 
                   
                   
                 Type and 
               
               
                 name 
                 Need 
                 Multi 
                 reference 
                 Semantics description 
               
               
                   
               
             
             
               
                 Measurement gap 
                 MP 
                 1 to 
                   
                   
               
               
                 pattern sequence 
                   
                 &lt;maxMGPS&gt; 
               
               
                 (MGPS) 
               
               
                 &gt; Measurement Gap 
                 MP 
                   
                 MGPSI 
                 Measurement Gap Pattern Sequence 
               
               
                 Pattern Sequence 
                   
                   
                   
                 Identifier establishes a reference to the 
               
               
                 Identifier (MGPSI) 
                   
                   
                   
                 measurement gap pattern sequence. 
               
               
                   
                   
                   
                   
                 Up to &lt;MaxMGPS&gt; simultaneous 
               
               
                   
                   
                   
                   
                 measurement gap pattern sequences 
               
               
                   
                   
                   
                   
                 can be used 
               
               
                 &gt;MGPS Status Flag 
                 MP 
                   
                 Enumerated 
                 This flag indicates whether the 
               
               
                   
                   
                   
                 (activate, 
                 Measurement Gap Pattern Sequence 
               
               
                   
                   
                   
                 deactivate) 
                 shall be activated or deactivated. 
               
               
                 &gt;Measurement gap 
                 CV- 
                   
                 Integer (0 . . . X) 
                 Frame Number of the first frame of the 
               
               
                 (MG) frame 
                 Active 
                   
                   
                 first measurement gap pattern within 
               
               
                 Activation number 
                   
                   
                   
                 the Measurement Gap Pattern 
               
               
                   
                   
                   
                   
                 Sequence. 
               
               
                 &gt; Measurement gap 
                 OP 
               
               
                 pattern sequence 
               
               
                 configuration 
               
               
                 parameters 
               
               
                 &gt;&gt;MGMP 
                 MP 
                   
                 Enumerated 
                 Measurement Gap pattern sequence 
               
               
                   
                   
                   
                 (As 
                 Measurement Purpose (MGMP). 
               
               
                   
                   
                   
                 mentioned in 
               
               
                   
                   
                   
                 4.1) 
               
               
                 &gt;&gt;MGPRC 
                 MP 
                   
                 Integer (0 to 
                 The number of Measurement gap 
               
               
                   
                   
                   
                 X) 
                 patterns within the Measurement Gap 
               
               
                   
                   
                   
                   
                 Pattern Sequence. 
               
               
                 &gt;&gt;MGSN 
                 MP 
                   
                 Integer (0 
                 Measurement Gap Starting Sub-frame/ 
               
               
                   
                   
                   
                 to X) 
                 TTI Number (MGSN) 
               
               
                   
                   
                   
                   
                 The sub-frame/symbol number of the 
               
               
                   
                   
                   
                   
                 first Measurement gap sub- 
               
               
                   
                   
                   
                   
                 frame/symbol within the “MG frame 
               
               
                   
                   
                   
                   
                 Activation number” above. 
               
               
                 &gt;&gt;Measurement gap 
                 MP 
                   
                 Integer (0 to 
                 The length of the first Measurement 
               
               
                 length (MGL)1 
                   
                   
                 X) 
                 Gap within the Measurement gap 
               
               
                   
                   
                   
                   
                 pattern 
               
               
                 &gt;&gt;MGLn (n: 2 to X) 
                 OP 
                   
                 Integer (0 to 
                 The length of the nth (any subsequent) 
               
               
                   
                   
                   
                 X) 
                 Measurement Gap within the 
               
               
                   
                   
                   
                   
                 Measurement gap pattern 
               
               
                 &gt;&gt;Measurement gap 
                 MP 
                   
                 Integer (0 to 
                 Measurement gap distance indicates 
               
               
                 distance (MGD) 
                   
                   
                 X, 
                 the number of sub frames/symbols 
               
               
                   
                   
                   
                 undefined) 
                 between starting sub frames of two 
               
               
                   
                   
                   
                   
                 consecutive measurement gaps within 
               
               
                   
                   
                   
                   
                 a measurement gap pattern. If there is 
               
               
                   
                   
                   
                   
                 only one measurement gap in the 
               
               
                   
                   
                   
                   
                 measurement gap pattern, this 
               
               
                   
                   
                   
                   
                 parameter shall be set to undefined. 
               
               
                 &gt;&gt;Measurrement gap 
                 MP 
                   
                 Integer 
                 The duration of Measurement gap 
               
               
                 pattern length 
                   
                   
                   
                 pattern 1. 
               
               
                 (MGPL)1 
               
               
                 &gt;&gt;Initial transmit 
                 MP 
                   
                 Enumerated 
                 Initial Transmit Power can refer to the 
               
               
                 power (ITP) 
                   
                   
                   
                 need for any power adjustment after a 
               
               
                   
                   
                   
                   
                 measurement gap period for uplink. 
               
               
                 &gt;&gt;N Identify abort 
                 CV- 
                   
                 Integer(1 to 
                 Indicates the maximum number of 
               
               
                   
                 Initial 
                   
                 X) 
                 times the WTRU will use a 
               
               
                   
                 BSIC 
                   
                   
                 measurement gap pattern to attempt to 
               
               
                   
                   
                   
                   
                 decode the unknown BSIC of the GSM 
               
               
                   
                   
                   
                   
                 cell in the initial BSIC identification 
               
               
                   
                   
                   
                   
                 procedure 
               
               
                 &gt;&gt;T Reconfirm abort 
                 CV-Re- 
                   
                 Real(0.x by 
                 Indicates the maximum time allowed 
               
               
                   
                 confirm 
                   
                 step of 0.y) 
                 for the re-confirmation of the BSIC of 
               
               
                   
                 BSIC 
                   
                   
                 one GSM cell 
               
               
                   
                   
                   
                   
                 in the BSIC re-confirmation procedure. 
               
               
                   
                   
                   
                   
                 The time is given in steps of 0.5 
               
               
                   
                   
                   
                   
                 seconds. 
               
               
                 &gt;&gt;N Abort UMTS 
                 CV- 
                   
                   
                 Indicates the maximum number of 
               
               
                   
                 PSC 
                   
                   
                 times the WTRU will use a 
               
               
                   
                 decode 
                   
                   
                 measurement gap pattern to attempt to 
               
               
                   
                   
                   
                   
                 decode the UMTS cell in the PSC 
               
               
                   
                   
                   
                   
                 detection procedure 
               
               
                 &gt;&gt;&gt; N Abort UMTS 
                 OP 
                   
                   
                 Indicates the maximum number of 
               
               
                 P-SCH 
                   
                   
                   
                 times the WTRU will use a 
               
               
                   
                   
                   
                   
                 measurement gap pattern to attempt to 
               
               
                   
                   
                   
                   
                 decode the Primary synchronization 
               
               
                   
                   
                   
                   
                 channel 
               
               
                 &gt;&gt;&gt; N Abort UMTS 
                 OP 
                   
                   
                 Indicates the maximum number of 
               
               
                 S-SCH 
                   
                   
                   
                 times the WTRU will use a 
               
               
                   
                   
                   
                   
                 measurement gap pattern to attempt to 
               
               
                   
                   
                   
                   
                 decode the Secondary Synchronization 
               
               
                   
                   
                   
                   
                 channel 
               
               
                 &gt;&gt;&gt; N Abort UMTS 
                 OP 
                   
                   
                 Indicates the maximum number of 
               
               
                 PSC 
                   
                   
                   
                 times the WTRU will use a 
               
               
                   
                   
                   
                   
                 measurement gap pattern to attempt to 
               
               
                   
                   
                   
                   
                 latch on to the scrambling code 
               
               
                 &gt;&gt; T reconfirm Abort 
                 CV- 
                   
                   
                 Indicates the maximum time allowed 
               
               
                 UMTS 
                 Reconfirm- 
                   
                   
                 for reconfirmation of the UMTS cells by 
               
               
                   
                 PSC 
                   
                   
                 just performing measurements on that 
               
               
                   
                   
                   
                   
                 PSC 
               
               
                 Number of 
                 MP 
                   
                 Integer 
                 This is for Proposal 2 or 3 when one GP 
               
               
                 Measurement 
                   
                   
                 {0 . . . N} 
                 will support more than one 
               
               
                 Purposes In One Gap 
                   
                   
                   
                 measurement purpose 
               
               
                 of a gap pattern(GP) 
               
               
                 Sequence of 
                 MP 
                   
                 Enumerated 
                 The sequence will be according to the 
               
               
                 Measurement 
                   
                   
                   
                 assignment, but the elements are from 
               
               
                 Purposes In One Gap 
                   
                   
                   
                 the measurement purposes listed 
               
               
                   
                   
                   
                   
                 below. 
               
               
                   
               
             
          
         
       
     
         [0018]    When the measurement gap patterns are to be activated in a WTRU for an already configured measurement gap, the parameters in Table 2 may be used. The parameters in Table 2 may be referred to by a variety of names and yet still retain the same meaning. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Information 
                   
                   
                 Type and 
                   
               
               
                 Element/Group name 
                 Need 
                 Multi 
                 reference 
                 Semantics description 
               
               
                   
               
             
             
               
                 MG reconfiguration 
                 MP 
                   
                 Integer 
                 Reconfigured frame number of the 
               
               
                 frame activation number 
                   
                   
                 (0 . . . X) 
                 Measurement Gap Pattern 
               
               
                   
                   
                   
                   
                 Sequence. 
               
               
                 Measurement gap 
                 MP 
                 1 to 
               
               
                 pattern sequence 
                   
                 &lt;maxMGPS&gt; 
               
               
                 &gt;MGPSI 
                 MP 
                   
                 MGPSI 
                 Measurement Gap Pattern Sequence 
               
               
                   
                   
                   
                   
                 Identifier 
               
               
                   
                   
                   
                   
                 establishes a reference to the 
               
               
                   
                   
                   
                   
                 measurement gap pattern sequence. 
               
               
                   
                   
                   
                   
                 Up to &lt;MaxMGPS&gt; simultaneous 
               
               
                   
                   
                   
                   
                 measurement gap pattern sequences 
               
               
                   
                   
                   
                   
                 can be used 
               
               
                 &gt;MGPS Status Flag 
                 MP 
                   
                 Enumerated 
                 This flag indicates whether the 
               
               
                   
                   
                   
                 (activate, 
                 Measurement Gap Pattern Sequence 
               
               
                   
                   
                   
                 deactivate) 
                 it shall be activated or deactivated. 
               
               
                 &gt;MG frame Activation 
                 CV- 
                   
                 Integer 
                 Frame Number of the first frame of 
               
               
                 number 
                 Active 
                   
                 (0 . . . X) 
                 the first measurement gap pattern 
               
               
                   
                   
                   
                   
                 within the Measurement Gap 
               
               
                   
                   
                   
                   
                 Pattern Sequence. 
               
               
                   
               
             
          
         
       
     
         [0019]    Measurement Gap Information and Uses 
         [0020]    For inter-frequency measurements, the WTRU may need to perform conventional FDD measurements. For inter-RAT measurements for GSM, the WTRU may use the measurement gaps for any one or more of the following purposes as in UMTS:
       Received signal strength indicator (RSSI) measurements;   Base station identity code (BSIC) Identification; and   BSIC reconfirmation.       
 
         [0024]    In LTE, in some specific cases, the WTRU may perform a full frequency scan to lock onto a GSM cell. 
         [0025]    For inter-RAT measurements for wideband code division multiple access (WCDMA), if the WTRU receives, in its neighboring cell list, UMTS absolute radio frequency channel numbers (UARFCNs) with a corresponding primary synchronization code (PSC), the WTRU may simply perform PSC reconfirmation. 
         [0026]    For inter-RAT measurements for wideband code division multiple access (WCDMA), if the WTRU receives in its neighboring cell list, UMTS absolute radio frequency channel numbers (UARFCNs) without a corresponding primary synchronization code (PSC), the WTRU may use the measurement gaps for the following three step procedure:
       Synchronization with a primary synchronization channel (P-SCH);   Synchronization with a secondary synchronization channel (S-SCH); and   Locking onto a scrambling code.       
 
         [0030]    After the cell has been identified and measured, the network may provide a gap for reconfirming the existence of the PSC by performing measurements on it. This may be indicated to the WTRU by using an appropriate measurement purpose such as PSC reconfirmation. 
         [0031]    Also in LTE, for some specific cases, the WTRU may perform a full frequency scan for locking onto the UMTS cell. In such cases, the measurement gap purpose may be any one or more of the following:
       FDD measurements;   RSSI measurements;   BSIC identification;   BSIC reconfirmation;   P-SCH synchronization;   S-SCH synchronization;   PSC identification;   PSC reconfirmation;   GSM full frequency scan;   UMTS full frequency scan;   Time division duplex (TDD)—3.84 Mcps; and   TDD—1.28 Mcps.
 
The last two of the above options may not be required if the network signals the absolute radio frequency channel numbers (ARFCNs) and the UARFCNs.
       
 
         [0044]    Alternatively, if the PSC is signaled in the neighboring cell list, or if the network configures the WTRU with a single measurement purpose for detecting and measuring the UMTS cell in one gap and configures the WTRU to use another gap for reconfirming the existence of the PSC, then the measurement gap purposes may be as follows:
       FDD measurements;   RSSI measurements;   BSIC identification;   BSIC reconfirmation;   PSC detection;   PSC reconfirmation;   GSM full frequency scan;   UMTS full frequency scan;   TDD—3.84 Mcps; and   TDD—1.28 Mcps.
 
The last two options of full frequency scan may not be needed if the network signals the ARFCNS and the UARFCNs.
       
 
         [0055]    Alternatively, the network may use a bitmap to signal the specific measurement purpose. 
         [0056]    Behavior of a WTRU in Specific Measurement Gap Scenarios. 
         [0057]    WTRU behaviors in a few example measurement scenarios are given hereinafter. 
         [0058]    If there are multiple measurement gaps, if Gap 2 is signaled to start before Gap 1 ends, a WTRU behavior is undefined, or if Gap 2 exceeds a measurement gap pattern length, a WTRU behavior is undefined (or the WTRU rejects such a measurement configuration). 
         [0059]    If an attempt to activate a measurement gap pattern for the same measurement purpose (MGMP) as an already active measurement gap pattern occurs, then a WTRU behavior is undefined (or the WTRU rejects such a measurement configuration). 
         [0060]    If measurement gaps are sent more than once to the WTRU in the same cell, (e.g., once in a setup message and later in a handover message), and if both measurement gaps have the same sequence identifier, (i.e., measurement gap pattern sequence identifier (MGPSI)), then the most recent set of measurement gap parameters may be used by the WTRU to override the earlier set of measurement gap parameters. 
         [0061]    If timing information is maintained during a handover and if no information on the measurement gap parameters is sent during the handover command, the WTRU may temporarily deactivate the measurement gap and reactivate it at the appropriately calculated or indicated sub-frame number in the new cell. In an inter-frequency handover, the neighboring cell list, if present, may need to be transmitted to the WTRU upon its entry into the new cell. If the WTRU does not receive the neighboring cell list upon its entry into the new cell, the WTRU will use its stored measurement configuration. 
         [0062]    If timing information is not maintained during a handover, and if no information on the measurement gap parameters is sent during the handover command, the WTRU may temporarily deactivate the measurement gap and reactivate it at the appropriately calculated sub-frame number in the new cell or wait for an explicit activation message from the network with the sub-frame number to start the measurement gap in the new cell. In such case, in an inter-frequency handover, the neighboring cell list, if present, may need to be transmitted to the WTRU upon its entry into the new cell. If the WTRU does not receive the neighboring cell list upon its entry into the new cell, the WTRU will use its stored measurement configuration. 
         [0063]    During a handover, if any new configuration or activation parameters are sent during an existing measurement gap in the handover command, the WTRU may continue to use the old measurement gap parameters in the new cell unless they are explicitly deactivated in the old cell. Alternatively, the WTRU may temporarily deactivate the measurement gap and reactivate it at the appropriately indicated or calculated sub-frame number in the new cell. In an inter-frequency handover, the neighbor cell list, if present, may need to be transmitted to the WTRU upon its entry into the new cell. If the WTRU does not receive the neighboring cell list upon its entry into the new cell, the WTRU will use its stored measurement configuration. 
         [0064]    Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements. The methods or flow charts provided herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). 
         [0065]    Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine. 
         [0066]    A processor in association with software may be used to implement a radio frequency transceiver for use in a wireless transmit receive unit (WTRU), user equipment (UE), terminal, base station, radio network controller (RNC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software, such as a camera, a video camera module, a videophone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, a Bluetooth® module, a frequency modulated (FM) radio unit, a liquid crystal display (LCD) display unit, an organic light-emitting diode (OLED) display unit, a digital music player, a media player, a video game player module, an Internet browser, and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB) module.