Patent Publication Number: US-9894570-B2

Title: Methods of performing cell change without receiving description of resources in a target cell

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/690,750 filed Jan. 20, 2010, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     Some cells are uncontrolled in the sense that a PLMN (public land mobile network) operator does not control the location and/or operation of the cell. Other cells are controlled in the sense that the operator does control the both the location and operation of the cells. Examples of uncontrolled cells include, for example, CSG (closed subscriber group) cells, cells controlled by home enode b&#39;s and home node b&#39;s. These cells are also sometimes referred to as being “uncoordinated” in the sense that they are not subject to normal radio/cell planning. 
     It is generally understood that there are many methods of performing a handover for controlled cells. Inbound handover in this context refers to a cell change from a target cell&#39;s perspective where resources (for example timeslots, frequency channels, scrambling codes, etc.) for transmission and/or reception in the cell are allocated to a mobile station in advance of the mobile station performing a cell change to that cell, particularly in response to a request from the controller of the device&#39;s serving cell. 
     While the uncontrolled cells may be configured to use spectrum that is owned by the operator, the network operator does not have the same control over uncontrolled cells as for controlled cells. Typically, the network operator does not own the support structure (towers etc.), does not own or control the backhaul connection (e.g. Digital Subscriber Line (DSL) connections), does not know or control when a given uncontrolled cell is going to be switched on, and may not know or control the locations of uncontrolled cells. The operator will typically still have control of various parameters such as operating frequency, transmit power, etc. if the operator owns the spectrum license. 
     In order to perform a handover to a target cell, controlled or uncontrolled, a MS (mobile station) typically needs to provide identifying information relating to the target cell to the current serving cell so that it can initiate a handover process. In particular, the current serving cell needs to be able to communicate with (possibly via a core network) the cell controller for the target cell. However, the current serving cell may not be aware of how to reach the cell controller for the target cell, particularly if the target cell is an uncontrolled cell, unless provided with explicit identification information for the cell (such as a cell global identity). This makes handover to such cells difficult. In contrast, for a controlled target cell, it may be sufficient for the mobile station to provide the current serving cell with information about the target cell. This does not require or cause the acquisition of any broadcast information from the target controlled cell for the serving cell to be able to reach the cell controller for the target controlled cell, since the serving cell or some part of the network may be able to map other identifying features of the cell (such as operating frequency, scrambling code etc.) to the identity of the target cell or its controller. 
     A cell controller may not necessarily map physical layer identities (such as frequency, spreading code, etc.) of an uncontrolled cell (more generally, another cell) to the identity of its respective controller (or to an identifier which can be used elsewhere in the core network to route messages to the target controller). 
     An example handover procedure, including a handover preparation phase, for controlled cells is shown in  FIG. 3 . The PS (packet switched) Handover Command (also “PS Handover CMD” in  FIG. 1 ) is constructed at the target cell controller based on the resources allocated during the preparation phase, and is transferred transparently via the core network and serving cell controller to the mobile station. 
     As part of a handover preparation, messages need to be routed from the serving cell controller to the target cell controller. In some implementations, handover is triggered in response to a measurement report, PCCN (packet cell change notification) or similar message received from the MS (mobile station). These messages identify target cells only by their physical layer identities and even this may be indirect, e.g. by means of an index into a list of such identities. These physical layer identities are not globally unique, but may be unique for a given serving cell, i.e. the tuple &lt;target cell physical layer identity, serving cell&gt; is typically unique for target cells that are controlled cells. 
     For handover to controlled cells, typically serving cell controllers are configured with sufficient information to allow messages to be routed to the appropriate target cell controller. For example, this may be by means of a mapping table of &lt;target cell physical layer identity&gt;→&lt;target cell global ID&gt;, where the target cell global ID can be used to route messages within the core network to the appropriate cell controller. Alternatively, the mapping may be stored at some node other than the serving cell controller, e.g. a core network node such as an MSC (mobile switching centre) or SGSN (serving GPRS support node). 
     Alternatively, the serving cell controller may be configured to know that it is also the controller of the target cell. Traditionally, this situation might be quite common, as cell controllers are organized (broadly) in geographical arrangement (i.e. many cells in a geographic locality will be controlled by the same controller). However, considering that there are now multiple different radio access technologies (with corresponding different controllers) with overlapping coverage and that new cell controllers (particularly for uncontrolled cells) are less likely to control multiple cells, this scenario becomes less common. If the cell controller is the same for both old cell and target cells, then the cell controller knows if it is able to complete the handover. The possibility of two distinct controllers adds more complexity. 
     If a target cell controller does not support handover (more generally if handover is not supported in respect of the target cell), the preparation phase will fail. The target cell controller may in this case indicate an appropriate cause, for example “PS Handover not Supported in Target BSS or Target system” (see 3GPP TS 48.018 sub-clause 11.3.8, covering handovers towards a GSM/GPRS/EDGE cell). To avoid repeated failed handover attempts to controlled cells, cell controllers may store information about the possibility to complete a handover towards particular controlled target cells. 
     Currently, cell change while in “dedicated mode” of the GERAN RAT (radio access technology), or more generally in a corresponding mode in another RAT (for example a mode during which a circuit-switched connection, such as a voice call, is ongoing) requires a preparation phase to ensure resources are available in the target cell. The preparation phase may for example include one or more of:
         a request for handover sent from a serving cell controller (see for example, 3.1.5.1.1 in 3GPP TS 48.008) which is forwarded to a target cell controller (see 3GPP TS 23.009, section 6.1);   allocation of resources by the target cell controller in the target cell (for example as described in 3.1.5.2 of 3GPP TS 48.008); and   generation of a message identifying the reserved resources in the target cell (as described in, for example, 3.1.5.2.1 in 3GPP TS 48.008).       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the application will now be described with reference to the attached drawings in which: 
         FIG. 1  is a schematic diagram of a mobile station, serving cell and target cell; 
         FIG. 2  is a block diagram of a mobile station; 
         FIG. 3  shows a messaging sequence for a conventional handover; 
         FIG. 4  shows a messaging sequence for a cell change for a circuit-switched call that does not involve providing a description of resources in the target cell in advance of the cell change; 
         FIGS. 5 and 6  are flowcharts of methods for execution by a mobile station or cell controller; and 
         FIGS. 7A-7B  show short handover options details. 
     
    
    
     DETAILED DESCRIPTION 
     It should be understood at the outset that although illustrative implementations of one or more embodiments of the present disclosure are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether or not currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents. 
     In the description that follows, cell controller is a generic term which could, for example, refer to base station controllers (BSC), radio network controllers (RNC) or eNodeB (eNB) or Home eNodeB; generally for the purpose of this description, it is used to mean an entity which controls the cell in some sense. For example, a cell controller might be an entity which initiates a handover preparation procedure for a mobile station (“serving cell controller”) or which allocates resources in a target cell as part of a handover procedure (“target cell controller”). The serving cell controller may, for example, be responsible for processing measurement reports, cell change notifications and similar messages received from a mobile station and based on these (and other implementation-specific considerations) generating mobility commands (such as packet cell change order messages) to be transmitted to the mobile station and/or initiating handover preparation. A GERAN BSS is an example. The same entity or entities may function as a serving cell controller in respect of the cell when performing a serving cell role and a target cell controller when the same cell is performing a target cell role. A cell controller may perform the control function for one or multiple cells. In some cases, a cell controller performs the control function for one cell and is co-located with other cell components, such as a component containing a wireless transceiver, such as a base station. A cell controller may be a part of a BSS (base station subsystem) which includes the transceiver. References to a cell sending or receiving something refer to a wireless transceiver sending or receiving something, possibly under control of the cell controller of the cell. 
     Referring to  FIG. 1 , shown is a schematic diagram in which a mobile station  10  has a wireless connection to a serving cell transceiver  12  within serving cell  13 . Also shown is a serving cell controller  14 , target cell transceiver  15  within target cell  17 , and target cell controller  16 . Of course, other network elements may be present, such as core network elements  18  and other cell controllers  20 . The core network elements may, for example, include one or more of an SGSN (serving GPRS support node), MSC (mobile switching centre), MME (mobility management entity). The signalling over the air interface (between a transceiver and a mobile station) is typically performed at the RLC (radio link control)/MAC (medium access control) layer. Signalling between a BSS and core network is separate from RLC/MAC. 
     The serving cell controller  14  is configured with a mobility control unit  30  that enables the serving cell controller to perform one or a combination of two or more of the serving cell controller methods described herein. The mobility control unit  30  may be implemented in hardware, or software running on a processing platform such as a processor or combination of processors, or a combination of hardware and software. The mobility control unit  30  may be implemented as part of/a change to another component forming part of a serving cell controller. The serving cell controller  14  includes other components (not shown) to allow it to perform the serving cell controller functionality. 
     The target cell controller  16  is configured with an inbound mobility controller  32  that enables the target cell controller to perform one or a combination of two or more of the target cell controller methods described herein. The inbound mobility controller  32  may be implemented in hardware, or software running on a processing platform such as a processor or combination of processors, or a combination of hardware and software. The inbound mobility controller  32  may be implemented as part of/a change to another component forming part of a target cell controller. The target cell controller  16  includes other components (not shown) to allow it to perform the target cell controller functionality. 
     A cell controller may be implemented that includes both the mobility control unit  30  and the inbound mobility controller  32 . 
     The mobile station  10  has at least one antenna  20 , and at least one wireless access radio  22 . In addition, them mobile station is configured with a cell change controller  24  that enables the mobile station to perform one or a combination of two or more of the mobile station methods described herein. The cell change controller  24  may be implemented in hardware, or software running on a processing platform such as a processor or combination of processors, or a combination of hardware and software. The cell change controller  24  may be implemented as part of/a change to another component forming part of a mobile station. The mobile station  10  includes other components (not shown) to allow it to perform mobile station functionality. 
     Various embodiments that comprise methods implemented by a mobile station or cell controller will now be described with reference to  FIGS. 5 and 6 . For each method, unless clearly necessary for the method to function, it is not necessary that the steps be executed in the sequence depicted or described. 
       FIG. 5  is a flowchart of a method for execution in a network. The method involves assigning dedicated resources to a mobile station for a circuit switched call ( 5 - 1 ). This may occur in the serving cell at call origination if the call originated in the serving cell, or may occur in respect of a pre-existing circuit-switched call when the mobile station moved into the current cell. The method continues with sending to a mobile station a command that instructs the mobile station to, or indicates that the mobile station should, perform a cell change during the circuit switched call to a target cell, and re-establish the circuit-switched call within the target cell, the command containing no description of resources in the target cell ( 5 - 2 ). 
     In some embodiments, the command is generated by a serving cell controller while in other embodiments, the command is a cell change response command generated by a target cell controller. 
       FIG. 6  is a flowchart of a method for execution by a mobile station. The method involves establishing a circuit-switched call ( 6 - 1 ); receiving a command during the circuit-switched call that instructs the mobile station to perform a cell change to a target cell and re-establish a circuit-switched call within the target cell, the command containing no description of resources in the target cell ( 6 - 2 ); performing a cell change to the target cell ( 6 - 3 ). 
     Further embodiments provide computer readable media having computer executable instructions stored thereon, that when executed by an appropriate processing device, such as a mobile device or a cell controller, execute any one or more of the methods described herein. 
     Command for Simplified Handover with Call Re-Establishment 
     A method is provided that allows a network to control cell change by a mobile station currently in dedicated mode in somewhat of a “handover-like” manner, without requiring a preparation phase. The methods are handover-like in the sense that they are network controlled, specifically, under control of the serving cell controller. They do differ from full handover in that resources in the target cell are not described to the mobile station in advance of the mobile station connecting to the target cell. 
     The embodiments described herein assume a mobile station is in dedicated mode, but more generally, these methods are applicable for a mobile station that has an ongoing circuit-switched call such as, but not necessarily, voice or is in a mode where cell change requires resources to be reserved in the target cell and a description of these resources to be provided to the mobile station in advance of the cell change. In some embodiments, the method is applied specifically to uncontrolled cells. More generally, the method is applicable to any cell type, not just uncontrolled cells. 
     An example of such a procedure is illustrated in  FIG. 4 . Various exchanges are depicted between a mobile station  70 , a serving cell controller  72 , a target cell controller  74 , and an MSC (mobile switching centre)  76 . At  4 - 1 , the MS is in dedicated mode, and has an ongoing voice call. MSC  76  is the MSC for the mobile station  10  during this time. At  4 - 2 , the MS detects a target cell and performs signal strength measurements. At substantially the same time, the MS also detects part or all of the physical layer identity of the target call. At  4 - 3 , the measurement report is sent to the serving cell controller  72 . This contains an indication of a physical layer identity of the target cell. At  4 - 4 , the serving cell controller  72  sends a command for cell change without description of resources in target call, “cell change WDR” in  FIG. 4 , that contains a target cell identifier to the mobile station  70 . At  4 - 5 , the MS acquires system information in the target cell. At  4 - 6 , the MS requests re-establishment of the voice call to the target cell controller  74 . At  4 - 7 , the request is forwarded by the target cell controller  74  to the MSC  76 . At  4 - 8 , RR (radio resource) connection establishment occurs. At  4 - 9 , the MS  70  is in dedicated mode. MSC  76  is the MSC for the mobile station  10  at this time. The MSC  76  is typically the same after the cell change, as depicted; in some cases, it may be a different MSC. Respecting block  4 - 2 , in some implementations, the mobile station may know some of the physical layer identity, e.g. the carrier frequency in advance. The signal strength measurement and determination of the complete physical layer identity are performed substantially simultaneously in some systems. For example, for CDMA systems, the mobile station may perform a search to find a cell&#39;s spreading code; or, for GSM (frequency multiplexed), the mobile station may tune to the cell (which requires the mobile station to know at least some of its physical layer identity) and then measures signal strength. 
     In some circumstances, block  4 - 2  may be achieved without any interruption to service. This can be achieved, for example, by scheduling measurements to be performed within measurement gaps or “idle” frames, when no data is transferred within the source cell; this is substantially unnoticeable to the user. Note that in contrast, in the conventional full handover approach, SI (system information) reading may be required in advance of sending a handover command, particularly in respect of target cells which are uncontrolled cells. If SI reading is required, it is not always possible to schedule measurement and detection of target cells during gaps/idle frames. Rather, this may require a significant duration during which the mobile station cannot transmit or receive in the serving cell. These gaps may be coordinated by the network (so that, for example, the network does not send data during these gaps) or not (the MS simply autonomously is not tuned to the serving cell for a significant period of time e.g. 80 ms or more, during which data may continue to be transmitted to the MS in the serving cell); the “or not” case is particularly relevant for voice, because voice data would not normally be retransmitted later. 
     In some embodiments, the command for cell change without description of resources in target call is based on a modification to an existing handover command that is otherwise used for handover with a description of resources allocated in the target cell. A detailed example of such a command is given below. Alternatively, it may be a completely new message. In GSM voice, the command for cell change without description of resources in target call may be sent on the “main DCCH” (dedicated control channel), which is usually the “FACCH” fast associated control channel, associated with the voice resource (timeslot). 
     Steps  4 - 4 , 4 - 6 ,- 7  do not form part of existing handover procedures defined for controlled cells. The remaining steps may be omitted/performed out of order; additional steps that may or may not be based on existing procedures (e.g. transport layer connection establishment between target cell controller and MSC) may be included. In some embodiments, step  4 - 4  may be triggered by one or a combination of a measurement report, proximity indication or anything else (or nothing). 
     In some embodiments, if the target cell is a uncontrolled cell, the serving cell controller sends the command for cell change without description of resources in target call only if it is informed (e.g. as part of the measurement report) that the mobile station has determined that it is permitted to access the target cell. For example, the mobile station may maintain a whitelist of CSGs to which the mobile station is permitted access, and the mobile station can determine whether it is permitted access to a given CSG cell on the basis of the whitelist. 
     Call re-establishment refers to steps taken to continue an existing circuit-switched call, as opposed to establishing a completely new call. There are existing call re-establishment procedures that have been defined for execution in certain circumstances when radio link failure has occurred. An example of call re-establishment for GSM and UTRAN is defined in 3GPP TS 24.008. These procedures provide for various messaging capabilities to allow call re-establishment after call failure to occur. The embodiment described above may employ the existing signalling applicable to deal with call failure for call re-establishment in the context of cell reselection when call failure has not in fact occurred. This has the potential benefit that call re-establishment may be more likely to be supported in the target cell than handover. More generally, any signalling approach may be employed to order the mobile station to perform a cell change while in a dedicated or similar mode without performing the preparation phase and re-establish a circuit-switched call in the target cell. The signalling approach used may be based on existing signalling such as the call re-establishment signalling defined to deal with call failure, or may be completely new. 
     In some embodiments, existing solutions can be used to ensure that at step  4 - 7 , the request is forwarded to the correct MSC: specifically, the NRI (network resource identifier, which identifies an MSC/SGSN) may be included within the mobile station&#39;s (temporary) identity (see 3GPP TS 23.236) which is provided to the cell controller. 
     Advantageously, with the approach described, the network maintains control over mobility, signalling may be reduced as there is no need to send any SI data to the serving cell; cell changes may occur sooner as there is no need to wait for SI acquisition, reporting SI to serving cell controller, or handover preparation phase. 
     The described approach may be beneficial in various circumstances. A first example of where this may be beneficial is where the target cell is known not to support inbound handover. A second example of where this may be beneficial is where it is not known whether the target cell supports inbound handover and the preparation may therefore fail. A third example of where this may be beneficial is where the radio conditions applicable to the mobile station are deteriorating rapidly and the serving cell wishes to trigger cell change without incurring the delay of a full handover preparation procedure. Also, this approach may avoid the serving cell controller having to use or support additional signaling associated with handover to controlled cells. 
     Mechanisms Using Handover Command with No Resources Indicated 
     In another embodiment, a cell change response command is constructed by the target cell controller and is forwarded to the mobile station transparently via the serving cell, and the cell change response command does not contain any allocation of resources in the target cell. The cell change response command is a response in the sense that it is generated in response to a cell change indication (e.g. HANDOVER REQUIRED message see 3GPP TS 48.008) sent by a serving cell controller. An example of a sequence leading to this response is a serving cell controller sending a message indicating that a handover is required to a MSC, the MSC sending a handover request to the target cell controller, and the target cell controller sending a cell change response, to the mobile station transparently via the MSC and serving cell controller. In some embodiments, the cell change response command is based on an existing handover command in the sense that in the situation where inbound handover in respect of the target cell is supported, through settings of at least part of the contents of the command to be a first set of contents, the command is a command for handover in the normal sense with resources being allocated in the target cell and described to the mobile station in advance of the cell change. However, by setting at least part of the contents to be a second set of contents, the command functions to indicate to the mobile station that no resources have been allocated in the target cell. Alternatively, the cell change response command may be completely new. This approach may be applied to target cells that are uncontrolled cells, but more generally can be applied to any target cell type. This solution may, for example, be employed in a case where the serving cell controller initiates a handover preparation phase but the target cell controller does not support full handover functionality. This scenario may arise for example, if the serving cell controller does not know whether the target cell supports inbound handover. 
     In some embodiments, the cell change response command may include an indication to perform cell reselection and that no resources are allocated. Such a command is an instruction to the mobile station to perform the cell change by moving to idle mode in the new cell, and to perform cell access from idle mode. For example, the cell change response command may contain a field having a first state that instructs the mobile station to perform reselection to the new cell even though no resources are described in the handover command (for example, because no resources have been reserved in the target cell, or because resources have been reserved but are not described), the field having a second state distinct from the first state. The RESEL field described in the detailed example below is a specific example. References to idle mode refer, for example, to a mode in which a mobile station has not received (and is not using) an assignment of resources to be used for data (inc. voice) transmission or reception in the cell. 
     In some embodiments, the cell change response command may include an indication that inbound handover in respect of the target cell is not supported. The indication may indicate PS-handover, CS-handover, PS+CS (DTM) handover, or all types. This indication is included depending on the support of the corresponding features by the target cell controller. The HO support field described in the detailed example below is a specific example. 
     In some embodiments, the cell change response command may include a reference number to allow the MS to identify itself in the target cell quickly. The reference number may, for example, be a random number allocated by the target cell controller. 
     In some embodiments, the target cell controller may construct a cell change response command containing from zero to any one or more of the indications described above. Handover capability may, for example, be based on the feature support for the corresponding cell and/or the capability of the target cell controller. A detailed example is given below for the case where the target cell is a GSM cell. Corresponding functionality can be implemented for UMTS/E-UTRAN target cells. 
     Mobile Station Response to the Cell Change Response Command 
     The cell change response command with zero or more of the indications is sent by the target cell controller to the mobile station through the serving cell. 
     The mobile station behaves differently depending upon what indication(s) are received in the cell change response command. 
     Cell Change Response Command Indicates “Perform Reselection; No Resources Allocated” 
     In the event the cell change response command indicates to the mobile station to perform reselection and no resources allocated, the mobile station performs the cell change, moves to idle mode in the new cell, and performs cell access from idle mode, for example using the call re-establishment procedure based approach described above. 
     If the reference number is provided, the mobile station provides this to the target cell controller at (or soon after) initial access in the target cell; in this case, the mobile station may omit sending capability information (since the target controller will have received this as part of the handover preparation phase). 
     Cell Change Response Command does not Indicate “Perform Reselection, No Resources Allocated” 
     In a first option, when the cell change response command does not contain an indication to perform reselection, no resources allocated, a cell change is performed, for example together with the call re-establishment based procedure described above. In a second option, when the cell change response command does not contain an indication to perform reselection, no resources allocated, the MS stays in the serving cell and sends a Handover Failure message indicating “no resources are available” in the target cell. 
     In some embodiments, one or both of the two above-discussed options are available. Which of these two options to apply may be standardized, signalled as a policy by the network (e.g. in system information), or additionally signalled in the cell change response command constructed by the target cell controller, or be determined by the mobile station (for example, in an implementation-specific manner). 
     Subsequent Network Behaviour 
     In some embodiments, if the MS does subsequently access the target cell, the target cell controller sends a Handover Complete to the MSC (or more generally send a similar message to the appropriate core network node) to indicate that the MS has completed the cell change. 
     In some embodiments, if the MS remains in the serving cell (including where it unsuccessfully attempted to access the target cell and returned to the serving cell), the network (on response of the appropriate failure message from the mobile) behaves as per existing procedures for this scenario. Note that one of the benefits of this solution is that serving cell behaviour is not necessarily changed hence there is not necessarily any impact on serving cell controllers. 
     The provided approaches may provide much of the functionality of handover, with reduced implementation on target cell controllers in the sense that they do not require handover access detection, resource pre-allocation, or the capability to describe pre-allocated resources in a handover command. The approaches may allow a MS to become aware that handover is not fully supported in the target cell. The approaches do not necessarily impact the serving cell controller. The handover command may be shorter than if resources are allocated. This may make for faster/more reliable transmission in the serving cell. Finally, the approaches allow for core network coordination of cell change (e.g. in case serving MSC/SGSN changes). 
     Detailed Example 
     The following is an example of a handover procedure, shown in terms of changes to 3GPP TS 44.018 v.9.3.0. In this example, the above-referenced cell change response command is implemented as a modified version of an existing handover command. 
     3.4.4 Handover Procedure 
     3.4.4.1 Handover Initiation 
     The network initiates the handover procedure by sending a HANDOVER COMMAND message to the mobile station on the main DCCH. It then starts timer T3103. 
     If the HANDOVER COMMAND message refers to a cell to which the mobile station is not synchronized to, this shall not be considered as an error (see 3GPP TS 45.008).
         NOTE: The network should take into account limitations of certain mobile stations to understand formats used in the Frequency List IE, Frequency Short List IE, and Cell Channel Description IE used in the HANDOVER COMMAND message, see sub-clause 10.5.2.13, sub-clause 10.5.2.14, and sub-clause 10.5.2.1b.       

     When sending this message on the network side, and when receiving it on the mobile station side, all transmission of signalling layer messages except for those RR messages needed for this procedure and for abnormal cases, is suspended until resuming is indicated. These RR messages can be deduced from sub-clauses 3.4.3 and 8.5.1 “Radio Resource management”. 
     Upon receipt of a HANDOVER COMMAND message which describes reserved resources in the target cell, the mobile station initiates, as described in sub-clause 3.1.4, the release of link layer connections, disconnects the physical channels (including the packet resources, if in class A mode of operation), commands the switching to the assigned channels and initiates the establishment of lower layer connections (this includes the activation of the channels, their connection and the establishment of the data links). 
     Upon receipt of a HANDOVER COMMAND message which does not describe reserved resources in the target cell, and where the RESEL bit is set to ‘1’ (see sub-clause 10.5.2.76), the mobile station performs as specified above, except that access to the new cell is from idle mode using the procedure for call re-establishment. 
     Upon receipt of a HANDOVER COMMAND message which does not describe reserved resources in the target cell, where the RESEL bit is set to ‘0’ (see sub-clause 10.5.2.76), and which indicates that CS Handover (or, in the case of DTM Handover, DTM Handover) is not supported, the mobile station remains in the current cell and transmits a HANDOVER FAILURE message on the main DCCH with cause “Handover not supported by target cell”. 
     Upon receipt of a HANDOVER COMMAND message which does not describe reserved resources in the target cell, where the RESEL bit is set to ‘0’ (see sub-clause 10.5.2.76), and which indicates that CS Handover (or, in the case of DTM Handover, DTM Handover) is supported, the mobile station remains in the current cell and transmits a HANDOVER FAILURE message on the main DCCH with cause “No resources in the target cell”. 
     The HANDOVER COMMAND message contains:
         The characteristics of the new channels, including for the multislot configuration and the TCH/H+TCH/H+ACCHs configuration the exact ACCHs to be used. The message may also contain definitions of the channel mode to be applied for one or several channel sets. If a previously undefined channel set is defined by the HANDOVER COMMAND message, a definition of the channel mode for the new channel set shall be included in the message. This may be omitted if the Short Handover Options IE is present and indicates that the mobile station shall perform cell change and no reserved resources are described in the HANDOVER COMMAND.   The characteristics of the new cell that are necessary to successfully communicate (e.g. frequency list in the case of slow frequency hopping), including the data that allows the mobile station to use the pre-knowledge about synchronization it acquires by the measurement process (i.e. BSIC+BCCH frequency).   Optionally, a_power command (cf. 3GPP TS 45.008). The power level defined in this power command shall be used by the mobile station for the initial power on the new channel(s). It shall not affect the power used on the old channel(s).   Optionally, an indication of the physical channel establishment procedure to be used.   A handover reference, used as specified in the following sub-clause. The choice of the handover reference by the network is out of the scope of this specification and left to the manufacturers.
 
3.4.4.2 Physical Channel Establishment
       

     Four procedures are defined. The support of three of them is mandatory in the mobile station. The pseudo-synchronization case is optional in the mobile station. A pseudo-synchronized handover can be commanded only to a mobile station that can support it, as indicated in the classmark. 
     As an alternative to these procedures, the mobile station shall perform channel establishment by means of the call re-establishment procedure if indicated in the previous sub-clause. 
     The following is an example of a handover command implemented as changes to 3GPP TS 44.018 v.9.3.0. 
     9.1.15 Handover Command 
     This message is sent on the main DCCH by the network to the mobile station to change the dedicated channel configuration, timing adjustment needed. See table 9.1.15.1. 
     Message type: HANDOVER COMMAND 
     Significance: dual 
     Direction: network to mobile station 
                     TABLE 9.1.15.1                  HANDOVER COMMAND message content                                     IEI   Information element   Type/Reference   Presence   Format   length                   RR management Protocol   Protocol Discriminator   M   V   ½           Discriminator   10.2           Skip Indicator   Skip Indicator   M   V   ½               10.3.1           Handover Command   Message Type   M   V   1           Message Type   10.4           Cell Description   Cell description   M   V   2               10.5.2.2           Description of the   Channel Description 2   M   V   3           first channel, after   10.5.2.5a           time           Handover Reference   Handover Reference   M   V   1               10.5.2.15           Power Command and   Power Command and   M   V   1           Access type   Access type               10.5.2.28a       D-   Synchronization   Synchronization   O   TV   1           Indication   Indication               10.5.2.39       02   Frequency Short List,   Frequency Short List   C   TV   10            after time   10.5.2.14       05   Frequency List, after   Frequency List   C   TLV   4-131           time   10.5.2.13       62   Cell Channel   Cell Channel   C   TV   17            Description   Description               10.5.2.1b       10   Description of the   Multislot Allocation   C   TLV   3-12            multislot configuration   10.5.2.21b       63   Mode of the First   Channel Mode   O   TV   2           Channel (Channel Set 1))   10.5.2.6       22   Short Handover Options   Short Handover Options   O   TLV   3               10.5.2.76                    
9.1.15.17 Short Handover Options
 
     If this IE is present and indicates “Perform reselection—no resources allocated”, then mobile station shall ignore the “Description of the first channel, after time” and any other optional or conditional IEs included in the message. 
     10.5.2.76 Short Handover Options 
     The Short Handover Options information element is coded as shown in  FIGS. 7A-7B . 
     The described embodiments contain references to messages that contain no description of resources in the target cell, be they allocated or assigned for example. In other embodiments, the message contains substantially no description of resources in the target cell. 
     Some of the embodiments described can be implemented in the context of one or more of the following standards, all of which are incorporated by reference in their entirety:
         3GPP TS 44.060 (latest version is v.9.2.0) “General Packet Radio Service (GPRS); Mobile Station (MS)—Base Station System (BSS) interface; Radio Link Control/Medium Access Control (RLC/MAC) protocol”.   3GPP TS 45.008: “Radio subsystem link control”. (latest version is v.9.1.0)   3GPP TS 44.018 “Mobile radio interface layer 3 specification; Radio Resource Control Protocol”. (latest version is 9.3.0)   3GPP TS 48.008 “Mobile Switching Centre—Base Station System (MSC-BSS) interface; Layer 3 specification” (latest version is 9.1.0)   3GPP TS 43.129 Packed-switched handover for GERAN A/Gb mode; Stage 2 (defines Handover Preparation; latest version is 9.0.0)   3GPP TS 48.018 “General Packet Radio Service (GPRS); Base Station System (BSS)—Serving GPRS Support Node (SGSN); BSS GPRS protocol (BSSGP)” (more PS Handover stuff; latest version is 9.0.0)       

     Numerous modifications and variations of the present application are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the application may be practised otherwise than as specifically described herein.