HK1159407B - Method and apparatus for performing a serving hs-dsch cell change - Google Patents

Description

Method and apparatus for performing serving HS-DSCH cell change

Technical Field

The present application relates to wireless communications.

Technical Field

High Speed Downlink Packet Access (HSDPA) is a feature proposed in release 5 of the third generation partnership project (3GPP) specifications. HSDPA uses three important concepts to achieve maximum spectral efficiency, these three concepts being: adaptive Modulation and Coding (AMC), fast physical layer retransmissions (i.e., hybrid automatic repeat request (HARQ)), and fast node B scheduling.

Handover is a process in which a wireless transmit/receive unit (WTRU) transitions from one cell to another without interrupting service. Fig. 1 shows a conventional handover from one cell to another. In HSDPA, the WTRU 102 monitors channels in a single cell, referred to as a "serving high speed downlink shared channel (HS-DSCH) cell". When a handover occurs, the WTRU 102 needs to transition to the new serving HS-DSCH cell (the target cell 106) and stop communicating with the old serving HS-DSCH cell (the source cell 104). This procedure is also referred to as serving HS-DSCH cell change.

The WTRU continuously measures the signal strength of the neighboring cells. Once the signal strength measured on the monitored common pilot channel (CPICH) of the neighboring cell exceeds the signal strength of the serving cell (i.e., event 1D), the WTRU indicates the change of the best cell to the Radio Network Controller (RNC). Preferably, the change of cell is reported from the WTRU to the RNC via a Radio Resource Control (RRC) measurement report. The measurement report contains the measurement value and a cell Identification (ID). The RNC then makes a decision as to whether a serving HS-DSCH cell change should occur.

To initiate a serving HS-DSCH cell change, a Serving Radio Network Controller (SRNC) requests a Controlling Radio Network Controller (CRNC) to allocate HS-DSCH resources (e.g., HS-DSCH radio network temporary identity (H-RNTI), high speed shared control channel (HS-SCCH) codes, HARQ resources, etc.) for WTRUs in a target cell via Radio Network Subsystem Application Part (RNSAP) and Node B Application Part (NBAP) messages. Once the HS-DSCH resources are reserved, the CRNC provides all messages to the SRNC, which sends back an RRC handover message to the WTRU. The RRC messages used to indicate the serving HS-DSCH cell change to the WTRU include, but are not limited to, physical channel reconfiguration messages, transport channel reconfiguration messages, radio bearer reconfiguration messages, and active set update messages.

The RRC handover message provides the WTRU with the radio access parameters needed for the WTRU to start monitoring the target cell. In addition, the RRC message may provide an activation time when handover should occur.

There are two types of handovers: synchronous handover and asynchronous handover. In asynchronous handover, the network and the WTRU do not activate and switch resources simultaneously. The activation time for the WTRU in the handover command is set to "now". This reduces the latency associated with the handover procedure. However, this increases the likelihood of data loss.

In synchronous handover, the network and the WTRU activate and switch resources simultaneously. The network must set the activation time to a Conservative (Conservative) value to account for various delays, such as scheduling delays, retransmissions, configuration times, etc. Although synchronous switching minimizes data loss, it may result in longer delays.

Typically, the RRC handover message is sent to the WTRU via the source node-B. The delay associated with the procedure for serving HS-DSCH cell change may cause handover message failure resulting in an unacceptable dropped call rate. Several proposals have been proposed to optimize the serving HS-DSCH cell change procedure.

According to these proposals, the WTRU and the node B may be pre-loaded (pre-configured) with HS-DSCH related configurations. The WTRU and node B are pre-configured with a radio link reconfiguration prepare/prepare state when a cell is added to the active set and if the RNC decides that the cell can be added to the "HSDPA active set". When a change in best cell occurs (i.e., event 1D), the target node B may be instructed to start scheduling the WTRU for a radio link reconfiguration execution/start state. This enables the WTRU and the node B to start communication faster.

The WTRU may monitor the resource and target cell HS-SCCH in parallel. Upon a best cell change, the WTRU sends a measurement report 1D message. After waiting a configurable amount of time, the WTRU begins monitoring the HS-SCCH of the preloaded target cell in addition to the HS-SCCH of the source cell. With this scheme, service interruption can be reduced.

The target node B may be implicitly redirected when the first scheduling occurs. When the RNC authorizes the handover and the node B is configured and ready, the target node B may schedule the WTRU on one of a plurality of HS-SCCHs that are monitored by the WTRU. The first scheduled occurrence from the target node implicitly confirms a successful handover. To avoid packet loss, the source node B may provide the RNC with a status of how much data still needs to be transmitted.

The handover (or redirection) indication may be sent by the target node B via an HS-SCCH order (order), via a new physical layer channel, or via a Serving Cell Change Channel (SCCCH) using the same channel coding as the E-RGCH and the E-DCHHARQ identifier channel associated with the enhanced dedicated channel (E-DCH), but using different signature sequences. The WTRU acknowledges the handover indication by changing the uplink scrambling code or by using a specific value (e.g., 31) of the Channel Quality Identifier (CQI).

Following the above proposal, according to another proposal, the WTRU requirements may be limited to only one HS-SCCH of the preconfigured/non-serving cell that monitors for the triggering event 1D. Events 1A and 1B can be reused with different parameter values to create one "HS-DSCH service candidate set", which is a subset of cells that are almost as good as the best cells. Event 1A is triggered if a cell in the active set becomes almost as good as the active set. The target node B configuration is pre-configured and the HS-SCCH codes are allocated. The first HS-SCCH code in the list is called the primary HS-SCCH code. A pre-configuration is sent to the WTRU. When event 1D occurs, the WTRU only starts monitoring the primary HS-SCCH of the target node-B, except for the HS-SCCH of the source node-B. Upon receiving the first schedule of the target node-B, the WTRU stops receiving the HS-DSCH from the source cell. The target node-B treats the received Acknowledgement (ACK) from the WTRU as an indication of a successful handover.

According to yet another proposal, the handover instruction (i.e. handover message) may be sent over the target cell using a common channel with a known configuration. The WTRU may monitor the HS-SCCH on the target cell using a common HS-DSCH radio network temporary identity (H-RNTI). The common information may be broadcast through a System Information Block (SIB) or configured through a dedicated RRC message. To increase the reliability of the handover message, the network may send the message through both the source and target cells.

To allow a WTRU in CELL _ DCH state to receive a serving HS-DSCH CELL change message through a target CELL using common resources, the WTRU must be able to read SIBs to acquire HS-DSCH system information. According to conventional 3GPP specifications, the WTRU is not allowed to read the required SIBs while in CELL _ DCH. In addition, because the messages broadcast on the SIB can only be repeated according to the repetition factor, the WTRU may not be given enough time to acquire the information. This may result in failure to receive the handover instruction. In addition, when dedicated pre-loaded resources are used to enhance the serving HS-DSCH cell change, such enhancements cannot be used to perform the change of the best cell outside the active set.

Disclosure of Invention

A method and apparatus for performing a serving HS-DSCH cell change from a source cell to a target cell is disclosed. The RNC may preload the WTRU with the HS-DSCH for the target cell. The WTRU receives and stores the preloaded HS-DSCH configuration. The WTRU may start monitoring the HS-SCCH on the target cell using the preloaded HS-DSCH configuration for the target cell on the condition that the measurement report is triggered by event 1D. The WTRU may start a timer when the WTRU starts monitoring the HS-SCCH on the target cell and stop monitoring the HS-SCCH on the target cell once the timer expires.

Drawings

The invention will be understood in more detail from the following description, given by way of example and understood in conjunction with the accompanying drawings, in which:

fig. 1 illustrates a conventional handover from one cell to another cell; and

fig. 2 is a flow diagram of a target cell monitoring process according to one embodiment.

Figure 3 is a block diagram of an example WTRU.

Detailed Description

The term "wireless transmit/receive unit (WTRU)" as referred to below 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 equipment capable of operating in a wireless environment. The term "node-B" as referred to hereinafter includes, but is not limited to, a base station, a site controller, an Access Point (AP), or any other type of interfacing device capable of operating in a wireless environment.

The "serving HS-CSCH cell change message" referred to below may include, but is not limited to, an RRC reconfiguration message or an active set update message that may reconfigure the WTRU to change the serving HS-DSCH cell or the target HS-SCCH order. Reference hereinafter to "HS-DSCH common resources" refers to a set of HS-DSCH resources (i.e., H-RNTI, HS-SCCH coding, HARQ memory allocation, etc.) that may be used by one or a group of WTRUs to receive downlink messages. The HS-DSCH common resources may be broadcast or provided via dedicated RRC messages. The "HS-DSCH dedicated resources" or "dedicated resources" referred to below refer to a set of pre-loaded target cell information that is provided to the WTRU as part of the active set update procedure.

An embodiment of acquiring the HS-DSCH common resources will be described below.

According to one embodiment, the WTRU acquires the HS-DSCH common resources through an SIB or via RRC signaling from the network in the Cell _ DCH. Typically, the WTRU is not allowed or configured to read SIBs sent over the Broadcast Control Channel (BCCH) while in CELL _ DCH. The HS-DSCH common resources for enhanced CELL _ FACH are broadcast via SIB5/5bis and only WTRUs in idle mode, CELL _ FACH, CELL _ PCH and URA PCH can read this SIB5/5 bis. In this embodiment, while in the CELL _ DCH state, the WTRU is allowed to read the SIB5/5bis (or any other SIB in which the HS-DSCH common resource message is provided).

The HS-DSCH common resources used for receiving the serving HS-DSCH CELL change message may be the same as the resources used for enhanced CELL _ FACH in SIB5/5bis or may be a new set of messages reserved for serving HS-DSCH CELL change. Alternatively, only the HS-SCCH encoding and HARQ storage allocation may be the same as for enhanced CELL _ FACH, but a common H-RNTI pool may be reserved only for serving HS-DSCH CELL change messages. Signaling Radio Bearer (SRB) mapping information for sending SRBs for serving HS-DSCH cell change (i.e., mapping it to logical channel IDs and/or queue IDs) may be broadcast or the WTRU may use the retrieved SRB mapping information while in the source cell.

The repetition of the system information broadcast in the SIB can vary from every 4 frames to every 4096 frames. This parameter is configured and provided in the main information block and, depending on the repetition factor, this may result in a delay of the SIB acquisition time. The WTRU does not have to read the HS-DSCH common resource information on the SIB at all times. The WTRU may be configured to read the HS-DSCH common resource information so that the WTRU is ready to start receiving downlink traffic before or while the network is sending information over the target cell. Thus, the WTRU may take into account the repetition factor, the time it takes to read it, the time it takes to configure resources, and so on.

The WTRU may read the system information block to acquire HS-DSCH common resources based on one or a combination of the following triggers:

(1) once event 1D is triggered, the WTRU may read the SIB of the neighbor cell that triggered event 1D (i.e., the best cell in the monitored set) and store the HS-DSCH common resource information;

(2) once the quality of the neighbor cell is better than the quality of the serving cell (i.e., before the trigger initiation time (Ttrigger)), the WTRU may read and store HS-DSCH common resource information;

(3) the WTRU may read and store HS-DSCH common resource information once the quality of the neighboring cell becomes better (by) than the serving cell by a pre-configured hysteresis value;

(4) the WTRU may read and store HS-DSCH common resource information for each cell added to the active set once the cell is added to the active set via an active set UPDATE (ACTIVE SET UPDATE) procedure, or once event 1A is triggered by the WTRU. The WTRU may have to store the cell ID and HS information associated with each cell. When the change of the best district occurs, the WTRU extracts the HS-DSCH common resource information corresponding to the district and configures HS-DSCH resources correspondingly;

(5) after a time interval Tn from the best cell change and this continues, the WTRU may read and store the HS-DSCH common resource information for the best cell in the monitored set;

(6) once event 1A is triggered, the WTRU may read and store HS-DSCH common resource information for the new cell added to the active set;

(7) if event 1A is triggered and the new cell becomes the best cell in the active set, the WTRU may read and store the HS-DSCH common resource information for the new cell added to the active set.

(8) The WTRU may read and store HS-DSCH common resource information for any new cells whose measured quality (e.g., received power on any downlink reference channel such as the common pilot channel (CPICH)) exceeds a pre-configured threshold; or

(9) The WTRU may read and store HS-DSCH common resource information for any new cells whose measured quality (e.g., received power at any downlink reference channel such as the common pilot channel (CPICH)) is close to a threshold pre-configured for the quality of the serving cell.

Alternatively, the HS-DSCH common resource information may be sent to the WTRU through dedicated RRC signaling. For example, the HS-DSCH common resource information may be included in an active set UPDATE (ACTIVE SET UPDATE) message sent to the WTRU when a new cell is added to the active set.

To limit the total amount of memory required to store HS-DSCH common resource information from multiple cells, the WTRU may be configured to store HS-DSCH common resource information for only the N strongest cells or the M newest cells that have caused any of the triggering criteria mentioned above. The WTRU may be configured to periodically delete HS-DSCH common resource information stored in memory, delete HS-DSCH common resource information from memory for any cell whose monitored quality is below a certain threshold, or delete HS-DSCH common resource information for any cell removed from the WTRU's active set.

Embodiments for monitoring a target cell are disclosed below.

The WTRU may start monitoring the target cell using common or dedicated resources when one or a combination of the following criteria are met:

(1) whenever a measurement report is sent to the network indicating event 1D;

(2) whenever a measurement report is sent to the network indicating event 1A and a change in the best cell is detected;

(3) whenever event 1A or 1D is triggered (i.e. before sending the measurement report);

(4) since a measurement report of event 1D or event 1A indicating a change on the best cell is transmitted to the network time interval (Tm);

(5) after a time interval (Tn) from when the WTRU was received, an RLC layer acknowledgement indicating that the measurement report was successfully received by the network;

(6) at the time of explicit signaling from the source node B. The explicit signaling may be an HS-SCCH order sent by the source cell to instruct the WTRU to start monitoring the target cell. Alternatively, the explicit signaling may be a reserved value sent to the WTRU on the E-DCH absolute grant channel (E-AGCH) (e.g., a reserved value where all HARQ processes are deactivated or used for this purpose only, with grant 0);

(7) as long as the channel quality of the source node B is below the system configured threshold; or

(8) As long as a radio link failure is detected at the source node B.

The WTRU may stop monitoring the target cell in one or a combination of the following criteria:

(1) after a predetermined time interval (Tp) has elapsed since the time the WTRU started monitoring the target cell, and no handover message has been received. If a handover message (i.e., RRC message or HS-SCCH) is received, the WTRU may stop monitoring the target cell HS-SCCH for the order;

(2) after a periodic timer for retransmitting the measurement report has expired and/or the WTRU sends another measurement report to the network. If the target cell is still the best cell and if the criteria for starting to monitor the target cell have been met, the WTRU starts monitoring the same target cell again. If the best cell in the monitored set has changed, the WTRU must stop monitoring the current cell and start monitoring the new cell according to one of the criteria disclosed above;

(3) whenever a radio link failure is detected in the source cell and there has not been a handover message or indication from the target cell for a configured amount of time;

(4) whenever a received handover message results in an invalid configuration and a handover failure occurs; or

(5) When an RLC layer status report is received at the WTRU indicating that the RRC measurement report has not been successfully received by the network.

If a radio link failure occurs while the WTRU desires a handover message, the WTRU may report measurements made at the neighboring cells prior to reporting the radio link failure, optionally while reporting the latest measurements performed. This information may be sent in a cell update message or as a measurement report message after the cell update is sent. This may allow the network to move the WTRU to CELL _ DCH without any additional delay in soft handover.

Fig. 2 is a flow diagram of a target cell monitoring process 200 according to one embodiment. The WTRU monitors the serving HS-DSCH cell and one or more neighboring cells (step 202). The WTRU checks if event 1D is triggered (step 204). If event 1D is not triggered, the WTRU continues to monitor the serving HS-DSCH cell. If event 1D is triggered, the WTRU sets a timer time Tp (step 206) and starts monitoring the target cell HS-DSCH (if preconfigured) (step 208). The WTRU checks if a handover message (i.e., RRC message or HS-SCCH order) is received (step 210). If a handover message for the target cell is received, the WTRU performs a serving HS-DSCH cell change (step 212). If no handover message is received, the WTRU checks whether the timer Tp expires (step 214). If the timer Tp has expired, the WTRU stops monitoring the target cell HS-SCCH (step 216). If the timer time Tp has not expired, the WTRU continues to monitor the target cell HS-SCCH.

Disclosed below are embodiments of HARQ process sharing when received from a source cell and a target cell.

Special attention must be paid to the way HARQ processes are handled when the WTRU is required to start monitoring the target cell using common or dedicated HS-DSCH resources. Because the WTRU may still receive data in the downlink through the source cell, the WTRU may not be able to refresh the HARQ process used by the source cell. However, in case of common HS-DSCH reception or reception of dedicated messages over the target cell, at least one HARQ process is required to be able to receive data from the target cell.

According to one embodiment, additional HARQ processes may be reserved to receive handover messages on the target cell. The target node-B knows that the WTRU uses only one HARQ process.

Alternatively, the WTRU may have two sets of HARQ processes, one set for reception through the source cell and another set configured for reception through the target cell. HARQ system information for the additional set of HARQ resources may be provided as part of the HS-DSCH common system information. This would require the WTRU to establish a new set of HARQ processes each time a handover message on the target cell is expected.

Alternatively, the WTRU may use the same HARQ process as the source cell when the WTRU decodes its H-RNTI (common, specific, or dedicated to the serving cell) on the HS-SCCH. In this case, the WTRU may have to flush the HARQ buffer before receiving data over the target HS-PDSCH. The WTRU must ensure that no data from the source cell is received while receiving data from the target cell. The network may ensure that data is not transmitted on the source cell when the target cell transmits a handover command. This may be achieved by an Iub indication from the RNC to the source node B. Alternatively, the WTRU may use the fact that data is always sent on the source cell as an indication that the data received on the target cell is not specific to the WTRU. Alternatively, the source cell may continue to send data, and the WTRU may not monitor the HS-DSCH of the source cell when receiving the message on the target cell.

Alternatively, the HARQ process is split between the source cell and the target cell. For example, when the WTRU expects a message on the target cell (i.e., monitors the target cell), half of the HARQ processes are dedicated to the source cell and the other half are used for the target cell. The ratio of HARQ processes for the source cell and the target cell may be a predefined value, a system configuration value, as part of the HS-DSCH common system information. The network may send an indication to the source cell using Iub signaling to configure the source cell to begin using only a portion of the available HARQ processes.

Alternatively, the WTRU may establish a new secondary MAC-ehs or MAC-hs sub-entity for the target cell that the WTRU is monitoring.

The WTRU may flush the soft buffer of HARQ processes configured for the target cell. This refresh procedure occurs when the WTRU starts monitoring the target cell or when the desired RNTI is decoded in the HS-SCCH of the target cell.

The WTRU may monitor the source cell and the target cell and if the HARQ process indicated in the HS-SCCH of the source cell interferes with the HARQ process used by the target cell, the WTRU may take this as an indication that the message is not intended for the WTRU. This is valid when the HARQ process is shared between the source cell and the target cell, and the network does not allow the source cell to transmit on the same HARQ process as the target cell.

The WTRU must ensure that at least the queue in which the SRB (i.e., RRC handover message) is received can be reset. The WTRU may simply reset the reordering variables to their initial values and may discard any reserved fields from the re-formed entity if appropriate. Alternatively, the WTRU may flush the HARQ processes associated with the target cell or all HARQ processes previously used at the source cell.

Embodiments for performing the HS-DSCH serving cell change procedure will be disclosed below.

Once the WTRU considers the handover to be successful, the WTRU releases the resources that the WTRU has allocated from the source cell. The WTRU may release the resources of the source cell on one or a combination of the following:

(1) if a handover message is received and the confirmation of the message configuration in the RRC has been successfully completed;

(2) if a handover message is received and an activation time different from the current one is specified (resources are released at a given activation time);

(3) as long as the WTRU knows that the message received on the source cell is specific to the WTRU;

(4) upon decoding the HS-SCCH on the target cell with the desired H-RNTI; or

(5) At the time of explicit signaling from the source node B. The signaling is provided via HS-SCCH orders in the source cell to instruct the WTRU to start decoding the target node-B and to release resources of the stolen source node-B. Alternatively, the signaling may be provided using a reserved value in the E-AGCH (e.g., grant-0 or deactivation of all HARQ processes).

When the serving HS-DSCH cell change procedure is completed, it is required that the WTRU may reset only the HARQ process and the HARQ memory associated with the HARQ process used for the source cell.

Embodiments for a serving cell change to a cell not in the active set are disclosed below.

According to one embodiment, the WTRU may use the preloaded HS-DSCH configuration on the target cell if the change of the best cell corresponds to a cell already included in the active set and the HS-DSCH configuration has been provided to the WTRU (i.e., preloaded), and the WTRU may use the HS-DSCH common resources to receive a handover command over the target cell if a new best cell is not included in the active set or a change of the best cell in the active set is detected but no preloaded HS-DSCH configuration is available. The WTRU uses either dedicated resources or common resources to trigger measurement reporting and start monitoring the target cell in accordance with one of the embodiments disclosed above. Depending on whether the WTRU is using common or dedicated resources, the WTRU may receive an RRC reconfiguration message or an active set update message (in the case of using common resources) through the target cell or only receive a handover indication from the target cell (in the case of using dedicated resources).

According to another embodiment, the WTRU may assume that one or more of the H-RNTI and HS-SCCH codes for the source cell will also be available for the target cell. The WTRU monitors a target cell that uses the same H-RNTI and one or more HS-SCCH codes that the WTRU is using for the source cell. When the network configures the WTRU, the network detects whether the same H-RNTI and/or HS-SCCH code is available for the target cell. If so, the network may send a handover message to the WTRU via the target cell that is using the same H-RNTI and/or one or more HS-SCCH codes.

Alternatively, the HS-SCCH coding may be provided by a SIB or preconfigured for all WTRUs. The handover message may be sent over the target cell using the same dedicated H-RNTI used in the source cell if they are available in the target cell. Otherwise, the handover message is sent through the source cell. The network may use an HS-SCCH order in the target cell with the same H-RNTI as used in the source cell to confirm that this same H-RNTI has been configured for the target cell. The WTRU then monitors the target cell with the same H-RNTI to receive the handover message. Alternatively, if the HS-SCCH order has not been received, the WTRU may start monitoring the common H-RNTI in the target cell or only the source cell. The WTRU may optionally monitor the HS-SCCH in the target cell for both common and dedicated H-RNTIs in the source cell.

According to another embodiment, a Serving Cell Change Channel (SCCCH) is used on the target cell and/or the source cell, which may be masked with a UTRAN radio network temporary identity (U-RNTI), a cell radio network temporary identity (C-RNTI), an H-RNTI, or an E-DCH radio network temporary identity (E-RNTI) of the source cell to instruct the WTRU to listen to the common H-RNTI or to confirm that a previous source H-RNTI has also been allocated in the target cell.

According to another embodiment, the HS-SCCH order or HS-SCCH may be sent by the source cell using the source cell specific H-RNTI to indicate to the WTRU that the same H-RNTI has been confirmed in the target cell. The WTRU may then move to the target cell and monitor the HS-SCCH with the H-RNTI used by the source cell. Alternatively, a special reserved value in the E-AGCH of the source cell may be used to make the same indication.

According to another embodiment, the handover instruction may be sent by using a target cell of the HS-SCCH of a special format, where the U-RNTI of the WTRU is used instead of the H-RNTI to address the WTRU in the HS-SCCH (i.e., masked using the U-RNTI instead of the H-RNTI). This embodiment can also be used for the change of the best cell in the active set.

According to another embodiment, the WTRU uses the given default configuration in case the best cell change occurs outside the active set. The default configuration is used only by the WTRU to receive handover commands through the target cell. If a group of WTRUs have the same default configuration, the network allows only one WTRU to use it at a time.

The above-described embodiments may also be used to confirm that the same E-DCH resources (e.g., E-RNTI, E-AGCH coding, etc.) are also allocated in the target cell in case of an E-DCH serving cell change. The acknowledgement may be sent in the target cell using a special reserved value on the E-AGCH of the previous source cell E-RNTI mask.

For the embodiments described above, the WTRU may not attempt to receive the message on the condition that it decodes the previous source H-RNTI in the HS-SCCH of the target cell, and it does not correspond to the configured HS-SCCH order. The same applies to E-AGCH masked with the previous source E-RNTI. The WTRU may not use the absolute grant indicated in the target cell if the special reserved value is not decoded.

Optionally, the WTRU may be provided with at least one of fractional dedicated physical channel (F-DPCH) information, Dedicated Physical Control Channel (DPCCH) information, high speed dedicated physical control channel (HS-DPCCH) information, and E-DCH resources of neighboring cells, along with a default configuration or a common configuration. If the WTRU is confirmed to use the default configuration or to access resources separately, the WTRU may be triggered to start a power control cycle and attempt to synchronize with the target node-B when confirmed.

Embodiments for simultaneous reception from a source cell and a target cell are disclosed below. The WTRU receives handover commands from both the target cell and the source cell. This may be achieved by performing a type of soft handover from the source cell and the target cell. This may be applied to intra-node B handovers or inter-node B handovers.

To allow for soft handover, the source cell and the target cell need to be synchronized so that all cells with different MAC-ehs PDUs of the same size and the same Transmission Sequence Number (TSN) are provided from both queues. Alternatively, the MAC-ehs PDU size may not be the same, and the size of the reordering PDUs (which are the priority sequence containing the corresponding SRB) and the TSN number of the reordered PDUs may be the same.

Soft combining of PDUs may be performed in a reordering queue of a WTRU. The reordering queue may be reserved for SRBs used to send handover messages. The TSN number must be synchronized (i.e., starting from 0) or the source node B must explicitly indicate to the target node B the TSN number to use. This would require the source cell and WTRU to reset to the reordering variables of the reordering queue to which the SRB is mapped. The scheduling of MAC-ehs PDUs from both cells must be such that the maximum delay between the source cell and the target cell exceeds the T1 timer configured for the respective reordering queue. This may be accomplished by giving the data and/or WTRU a higher priority than any other data and/or WTRU.

The creation of reordering PDUs of the same size can be achieved by using one or a combination of the following options. If there is a serving cell change within the node B, the source cell may indicate to the target cell the size it receives from the WTRU at each Transmission Time Interval (TTI), and optionally the CQI. By ensuring first priority scheduling, the source cell and the target cell may optionally be lightly synchronized. The TSN number may optionally be provided to the target node B or source cell, target cell, and the WTRU resets both of their reordering variables to their initial default values.

Alternatively, the target cell may monitor the HS-DPCCH sent by the WTRU to the source cell and create a MAC-ehs PDU based on the received CQI. Alternatively, the target cell and the source cell may always create reordering PDUs of the same size. A predefined reordering PDU size may always be used for handover messages. Alternatively, the WTRU may be allowed to multiplex more than one reordering PDU from the same reordering queue in one TTI. More particularly, if the reordering PDU size is preconfigured to x bits and the selected transport block size is y bits, where y > x, the WTRU may include an INT (y/x) reordering PDU in a given transport block. Each reordering PDU has a Transmission Sequence Number (TSN), even though they may correspond to the same reordering queue.

Alternatively, the MAC-ehs PDUs may be created independently in the source node-B and the target node-B (i.e., different sizes, different TSNs, and different reordering queues). Soft combining of the messages is performed in the RLC level. Alternatively, the source cell and the target cell may be transmitted in alternating TTIs.

For simultaneous transmission in the source and target cells, the HS-SCCH may be sent in a single cell (either through the source cell or through the target cell), while the HS-PDSCH (including the RRC handover command) may be sent through both cells. In this case, a new HS-SCCH format is defined to indicate HS-PDSCH information in both cells, or a regular HS-SCCH format may be used and the WTRU implicitly knows that the HS-SCCH format is applicable to both cells. Alternatively, the HS-SCCH may be transmitted in two cells, while the HS-PDSCH may be transmitted in only one cell, either the source cell or the target cell. Alternatively, the HS-SCCH and HS-PDSCH may be transmitted in two cells.

Embodiments for HS-SCCH-less (less) operation received in the target cell are disclosed below.

The reception of the handover message in the target cell may be achieved without the need for HS-SCCH. This may be achieved by masking the private or public H-RNTI with a Cyclic Redundancy Check (CRC), which is used for transmission over the HS-DSCH. The message may be sent using a limited HS-DSCH configuration (e.g., one or two HS-PDSCH codes), using a limited set of transport block sizes, and a limited modulation coding scheme to simplify the blind detection of transport blocks performed by the WTRU. The "HS-DSCH information" includes the HS-PDSCH configuration and the H-RNTI may be decided as described in the previous embodiments.

Alternatively, the HS-SCCH-reduction operation for receiving the handover instruction may be applied in the source cell in addition to or instead of the target cell. The above described embodiments may also be applied to HS-SCCH-less operation. The decoding of the H-RNTI in HS-SCCH is identical to the H-RNTI in CRC.

Figure 3 is a block diagram of an exemplary WTRU 300. The WTRU 300 includes a receiving unit 302, a monitoring unit 304, a memory 306, and a controller 308. The receiving unit 302 is configured to receive a channel including the HS-SCH. The monitoring unit 304 is configured to monitor signals on the source cell and the at least one neighboring cell. The memory 306 is configured to store pre-loaded HS-DSCH resource information for the target cell. The controller 308 is configured to perform control functions with respect to serving HS-DSCH cell change from the source cell to the target cell in accordance with the embodiments disclosed above. For example, the controller 308 is configured to detect event 1D for the target cell, start a timer if the measurement report is triggered by event 1D, and control the receiving unit to start monitoring HS-SCCH on the target cell using the pre-loaded HS-DSCH resources for the target cell.

The controller 308 may be configured to perform handover to the target cell if a handover message is received before the timer expires. The controller 308 can be configured to stop monitoring the HS-SCCH at the target cell if the timer expires before receiving the handover message for the target cell. The receiving unit 302 may be configured to receive messages from the source cell and the target cell simultaneously, at least one HARQ process being reserved for receiving messages from the target cell. The receiving unit 302 may be configured to receive messages from the source cell and the target cell simultaneously, the same HARQ process for the source cell being used to receive messages from the target cell. The controller 308 can be configured to release HS-DSCH resources in the source cell in case a handover message is received from the target cell before the timer expires. The controller 308 can be configured to release HS-DSCH resources in the source cell upon decoding the HS-SCCH on the target cell with the desired H-RNTI. The receiving unit 302 may be configured to receive HS-SCCH only in the target cell and to receive HS-PDSCH on the source cell and the target cell based on the received HS-SCCH.

Examples

1. A method for performing a serving HS-DSCH cell change from a source cell to a target cell.

2. The method of embodiment 1 comprising the WTRU receiving, and storing, preloading, an HS-DSCH configuration for the target cell.

3. The method of embodiment 2 further comprising the WTRU detecting an event 1D with respect to the target cell.

4. The method of embodiment 3 further comprising the WTRU starting a timer.

5. The method as in any of embodiments 3-4 further comprising the WTRU starting monitoring HS-SCCH on the target cell using a pre-loaded HS-DSCH configuration for the target cell on a condition that a measurement report is triggered by the event 1D.

6. The method as in any one of embodiments 2-5 further comprising the WTRU determining whether a handover message for the target cell is received.

7. The method of embodiment 6 further comprising the WTRU ceasing to monitor the HS-SCCH on the target cell on a condition that a handover message for the target cell is received.

8. The method as in any one of embodiments 6-7 wherein the handover message is one of a target cell HS-SCCH order and an RRC message.

9. The method as in any one of embodiments 5-8 further comprising the WTRU ceasing to monitor the HS-SCCH on the target cell on a condition that the timer expires before receiving a handover message for the target cell.

10. The method as in any one of embodiments 5-9 further comprising the WTRU releasing HS-DSCH resources in the source cell on a condition that a handover message is received from the target cell before the timer expires.

11. The method as in any one of embodiments 5-10 further comprising the WTRU releasing HS-DSCH resources in the source cell when decoding an HS-SCCH on the target cell with a desired H-RNTI.

12. A WTRU configured to perform a serving high speed downlink shared channel (HS-DSCH) cell change from a source cell to a target cell.

13. The WTRU of embodiment 12 comprising a receiving unit configured to receive a high speed shared control channel (HS-SCCH).

14. The WTRU as in any one of embodiments 12-13 comprising a channel monitoring unit configured to monitor signals on the source cell and at least one neighboring cell.

15. The WTRU as in any one of embodiments 12-14 comprising a memory configured to store pre-loaded HS-DSCH resource information for the target cell.

16. The WTRU of embodiment 15 comprising a controller configured to detect an event 1D with respect to the target cell, start a timer if a measurement report is triggered by the event 1D, and control the receiving unit to start monitoring the HS-DSCH on the target cell using pre-loaded HS-DSCH resources for the target cell.

17. The WTRU of embodiment 16 wherein the controller is configured to stop monitoring the HS-SCCH on the target cell on a condition that a handover message for the target cell is received.

18. The WTRU of embodiment 17 wherein the handover message is one of a target cell HS-SCCH order and an RRC message.

19. The WTRU as in any one of embodiments 17-18 wherein the controller is configured to stop monitoring the HS-SCCH on the target cell on a condition that the timer expires before a handover message for the target cell is received.

20. The WTRU as in any one of embodiments 17-19 wherein the controller is configured to release HS-DSCH resources in the source cell on a condition that a handover message is received from the target cell before the timer expires.

21. The WTRU as in any one of embodiments 17-20 wherein the controller is configured to release HS-DSCH resources in the source cell when decoding an HS-SCCH on the target cell with a desired H-RNTI.

Although the features and elements of the present invention are described in the 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 tangibly embodied in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of the computer-readable storage medium include Read Only Memory (ROM), Random Access Memory (RAM), registers, buffer 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).

For example, suitable processors include: 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, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) circuit, any Integrated Circuit (IC), and/or a state machine.

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 video telephone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, a microphone, a,A module, a Frequency Modulation (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 Wideband (UWB) module.

Claims (14)

1. A method for performing a serving high speed downlink shared channel (HS-DSCH) cell change from a source cell to a target cell by a wireless transmit/receive unit (WTRU), the method comprising:

the WTRU receiving and storing HS-DSCH target cell pre-configuration information;

the WTRU determining an event 1D with respect to the target cell;

the WTRU triggering a measurement report in response to the event 1D;

the WTRU starting a timer;

monitoring, by the WTRU, a high speed shared control channel (HS-SCCH) on the target cell with the HS-DSCH target cell pre-configuration information for cell change information until the timer expires; and

wherein the WTRU uses the HS-DSCH target cell pre-configuration information during the HS-DSCH cell change.

2. The method of claim 1, wherein a network component provides the HS-DSCH target cell pre-configuration information during an active set update.

3. The method of claim 1, further comprising:

the WTRU determining whether a handover message for the target cell is received; and

the WTRU stops monitoring the HS-SCCH on the target cell in response to the handover message for the target cell.

4. The method of claim 3, wherein the handover message is one of a target cell HS-SCCH order or a Radio Resource Control (RRC) message.

5. The method of claim 1, further comprising:

the WTRU stops monitoring the HS-SCCH on the target cell in response to the timer expiring before receiving a handover message for the target cell.

6. The method of claim 1, further comprising:

the WTRU releases HS-DSCH resources in the source cell in response to receiving a handover message from the target cell prior to expiration of the timer.

7. The method of claim 1, further comprising:

the WTRU releases HS-DSCH resources in the source cell upon decoding the HS-SCCH on the target cell with a desired HS-DSCH radio network temporary identity (H-RNTI).

8. A wireless transmit/receive unit (WTRU) for performing a serving high speed downlink shared channel (HS-DSCH) cell change from a source cell to a target cell, the WTRU comprising:

means configured to receive and store HS-SCCH target cell pre-configuration information;

means configured to determine event 1D with respect to the target cell;

means configured to trigger a measurement report in response to the event 1D;

means configured to start a timer;

means configured to monitor a high speed shared control channel (HS-SCCH) on the target cell with the HS-DSCH target cell pre-configuration information for cell change information until the timer expires; and

wherein the HS-DSCH target cell pre-configuration information is used during the HS-DSCH cell change.

9. The WTRU of claim 8, wherein a network component provides the HS-DSCH target cell pre-configuration information during an active set update.

10. The WTRU of claim 8, further comprising:

means configured to determine whether a handover message for the target cell is received; and

means configured to stop monitoring the HS-SCCH on the target cell in response to the handover message for the target cell.

11. The WTRU of claim 10 wherein the handover message is one of a target cell HS-SCCH order or a Radio Resource Control (RRC) message.

12. The WTRU of claim 8, further comprising:

means configured to stop monitoring HS-SCCH on the target cell in response to the timer expiring before receiving a handover message for the target cell.

13. The WTRU of claim 8, further comprising:

means configured to release HS-DSCH resources in the source cell in response to receiving a handover message from the target cell before the timer expires.

14. The WTRU of claim 8, further comprising:

means configured to release HS-DSCH resources in the source cell upon decoding HS-SCCH on the target cell with a desired HS-DSCH radio network temporary identity (H-RNTI).