Radio link and handover failure handling

Wireless link and handover failure handling

This creation is about wireless communication systems.

In the second stage of the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), the wireless transmission and reception unit (WTRU) will select cells belonging to the same evolved node-B (eNodeB) after the radio link (RL) fails. The meta situation is listed for further research (FFS). It has been proposed that if the WTRU selects different cells from the same eNodeB, there is no interaction between the WTRU and the eNodeB, and the activity cannot be resumed. Currently, Radio Access Network 2 (RAN2) stipulates that if a WTRU selects a cell from a different eNodeB, it needs to become idle via Radio Resource Control (RRC). Currently, the RAN2 decision on RL failure is based on two stages. These two stages manage the behavior associated with RL failure and are shown in Figure 1.

When a radio problem is detected, the first phase begins, which results in a failed RL detection. Therefore, there is no standard (T₁) Based on WTRU mobility.

When the radio link failure is detected, the second phase begins, which causes the RRC to be idle. WTRU-based mobility is still valid, which is timer-based (T₂)。

Table 1 below describes how mobility is currently handled when RL fails.

<tables><img file="TWM340666U_D0001.tif" /></tables>

Recently, it has been proposed to divide the handover into two (2) stages similar to RL failure, and a similar handover failure handling procedure is proposed.

In the first phase, the WTRU tries to synchronize and access the target cell, as in the timer T₁period. In the second phase, after the handover fails, the WTRU interrupts the handover and tries to reestablish the lost connection with the network, for example, in the timer T₂period. After the second phase, the UE enters RRC_IDLE.

Figure 2 shows the two stages of managing activities associated with handover failure during the mobility period controlled by the network according to the current proposal.

The first stage starts when the synchronization to the target cell is attempted for the first time; and leads to handover failure detection. During this time, there is no WTRU-based mobility, which is based on timers or other (e.g. counting) standards (T₁)。

The second phase starts with handover failure detection, which results in RRC_IDLE. Based on timer (T₂), WTRU-based mobility is still effective.

Table 2 describes how mobility is handled regarding handover failures.

<tables><img file="TWM340666U_D0002.tif" /></tables>

Moreover, non-controversial random access during handover is currently allowed. Similarly, the current non-dispute-based random access procedure shown in Figure 3 includes the allocation of random access preambles via dedicated signaling in the downlink (DL), where the eNodeB allocates six preambles to the WTRU. (6) An undisputed random access preamble of bits (that is, a random access preamble that is not in the set broadcast on the BCH). When DL data arrives, the preamble is sent using Media Access Control (MAC) (for example, layer 1 (L1)/layer 2 (L2) control channel or MAC control packet data unit (PDU)), And it is sent via a handover (HO) command generated by the target eNodeB and sent from the source eNodeB for handover.

Then, the WTRU transmits the allocated undisputed random access preamble on the RACH in the uplink link. The random access response from the eNB is sent on the DL-SCH. The response (in a variable window of one or more transmission time intervals (TTI)) is semi-synchronized with message 1 and sent to C-RNTI or RA-RNTI (FFS) on the L1/L2 control channel.

The random access response at least includes timing correction information for handover and initial UL permission, and timing correction information for DL data arrival. In addition, the RA preamble identification is transmitted to the routing area radio network temporary identification (RA-RNTI) on the L1/L2 control channel.

If the response is sent to the cellular RNTI (C-RNTI) on the L1/L2 control channel, the response can only be used by one WTRU in a downlink shared channel (DL-SCH) message, or if the response is in When the L1/L2 control channel is sent to the RA-RNTI, the response is used by one or more WTRUs in a DL-SCH message.

What is needed is an improved device for handling radio link and handover failures.

The disclosed device is used to handle RL and handover failures based on context transmission details and RACH procedures, which enhance the failure handling procedures. After the RL fails, the wireless transmission and reception unit (WTRU) includes the WTRU identification and the evolved node-B (eNB) and the evolving node-B (eNB) as an information element (IE) in the RRC connection request and/or cell update message or any other RRC message / Or the identity of the cell.

The term "wireless transmission/reception unit (WTRU)" referred to below includes but is not limited to user equipment (UE), mobile station, fixed or mobile subscriber unit, pager, mobile phone, personal digital assistant (PDA), computer or Any other type of user equipment that can work in a wireless environment. The term "its site" referred to below includes but is not limited to Node-B, site controller, access point (AP) or any other peripheral devices that can work in a wireless environment.

Referring to Figure 4, an LTE wireless communication network (NW) 10, for example, includes one or more WTRUs 20, one or more Node Bs 30, and one or more cells 40. Each WTRU includes a processor 21, and each node The B 30 includes a processor 31, and each cell 40 includes one or more Node Bs (NB or eNB) 30. Both the processors 21 and 31 are configured to execute the disclosed methods for handling radio link (RL) and handover failure.

Throughout the disclosed method, context information refers to any radio resource control (RRC) context, security context, packet data convergence protocol (PDCP) context, or any layer context that may be continued in mobility. However, for the sake of brevity, the term context or RRC context may be used as each type of context disclosed above.

When the RL failure is detected by the WTRU 20, the WTRU 20 starts the mobility procedure (ie, cell reselection). In the usual cell reselection procedure, the WTRU 20 reselects any available cell after the RL fails, and via a cell update or a radio resource control (RRC) connection request, the WTRU 20 sends its WTRU identification to the eNodeB ( eNB) 30. The eNB 30 uses the received WTRU identity to detect whether the WTRU 20 is under the control of the eNB 30 before the radio link failure occurs.

A method and device are disclosed, wherein after a radio link (RL) or handover (HO) failure, the WTRU 20 includes its WTRU identity (such as TMSI/IMSI/IMEI or any other UE identity) and eNB identity and/or cell The identifier is used as an information element (IE) in the RRC connection request, cell update message, or any other RRC message.

Once the WTRU 20 camps on the eNB (ie, target eNB) after cell reselection, the information contained in the IE is transmitted to the target eNB. If the target eNB where the WTRU 20 resides is different from the eNB where the WTRU 20 resides before the RL failure (ie, the source eNB), the target eNB uses the eNB identification and/or cell ID contained in the IE to contact the source The eNB informs the source eNB of the identity of the WTRU 20. Next, the target eNB requests the source eNB to transmit the context parameters of the WTRU 20. Alternatively, the target eNB may also inform the source eNB of the cell identity.

If the source eNB finds context information that matches the identity of the WTRU 20, the source eNB transmits the context information to the target eNB. Then, the target eNB may send a response to the cell update of the WTRU 20, an RRC connection request, or any other RRC procedure initiated by the WTRU, indicating that the WTRU 20 may reuse the previous context.

If the context is not discovered by the source eNB, the target eNB performs cell update/RRC connection establishment procedures or any other RRC procedures. When the target eNB receives a request to re-establish the RRC connection from the WTRU 20, the target eNB signals all layer 1 and layer 2/3 parameters as if it should have signaled a new RRC connection. Then, the WTRU 20 can delete any stored context information that is applicable to the old cell. Alternatively, if no context is found, the WTRU 20 may enter the RRC idle without waiting for the expiration of the timer T2, and restart the process or wait for the expiration of the timer T2 to enter the RRC idle.

The disclosed IE may be included by the WTRU 20, and the IE includes information about the eNB on which the WTRU 20 last camped. According to this alternative embodiment, the processor 21 includes the eNB identification and/or cell identification in the IE only when a handover failure is detected.

If the target eNB where the WTRU 20 resides is the same as the source eNB before the failure and if the eNB finds a context for the WTRU 20, (the eNB discovers the context by checking whether the eNB has a context that matches the identity of the WTRU 20), Then upon receiving the RRC CONNECTION REQUEST (RRC connection request) from the WTRU 20 (or upon receiving any other RRC procedure initiated by the WTRU), the eNB may instruct the WTRU 20 to use the same context information that the eNB had before the failure occurred. . Otherwise, the eNB may signal all layer 1 and layer 2/3 parameters to the WTRU 20, as if the eNB should signal a new RRC connection. Then, the WTRU 20 may delete any stored context information.

The following describes a flowchart of the disclosed method used by the processor 21 of the WTRU 20 for handling RL failure. When RL failure is detected (step 500), the WTRU 20 performs an initial access procedure to gain access to the selected target eNB (step 501). Next, the WTRU 20 transmits an IE to the target eNB. The IE at least contains the eNB ID of the source eNB where the WTRU 20 has camped before (step 502). Then, after the RRC context is obtained by the target eNB, the WTRU 20 receives the context from the target eNB, for example, from the source eNB.

According to the disclosed method, the duration of the period during which the target eNB retains the radio access control (RAC) context is preferably determined based on the specific implementation. The same is true for determining whether the transmission of context information between the target eNB and the source eNB only occurs when the radio link fails.

If the target eNB where the WTRU 20 resides is the same as the source eNB where the WTRU 20 resides before the handover, it can instruct the WTRU 20 to use the The same contextual information that it had before the failure occurred.

As those skilled in the art understand, the WTRU 20 that resides in the same cell or resides on the same eNB before the RL fails helps save network resources. Likewise, the disclosed method may alternatively include that during the cell selection procedure after the RL failure, the WTRU 20 considers the source eNB identity, so the cell from the source eNB is better than the cell from a different eNB. According to this alternative embodiment, preferably, the WTRU 20 determines the priority of the detected eNBs in the following order: the last cell where the WTRU 20 resides before; the cell from the same eNodeB where the WTRU 20 resides before; And cells from any other eNodeB.

Because fast camping and call initiation are the main criteria after failure, other parameters for cell reselection may or may not be considered by the WTRU 20 in the case of radio link failure; only the eNB identity (or cell Element ID), and the cell signal strength are sufficient to guide cell selection when the radio link fails. According to this method, the identification (eNB and cell) can be broadcast in the system information message together with the cell ID.

For handover failure, a method is disclosed, in which when the WTRU 20 moves to a different cell and the different cell belongs to the same eNB, based on the WTRU 20 identification, the WTRU 20 has moved to identify whether the eNB has a WTRU 20 context . If the eNB has the context, the eNB signals the WTRU 20 to use the same context as before. Because the context is stored about the eNB and not about the cell, the WTRU 20 can use the same context. As an alternative, according to this method, as disclosed above, the same priority order for cell selection for RL failure described above applies to eNB handover failure.

When the WTRU 20 moves to a cell from a completely different eNB, the similar procedure for radio link failure disclosed above can also be used. It should be noted that in such a handover procedure, the last eNB identity that the WTRU 20 can store may be the source eNB or the target eNB, depending on the stage at which the handover procedure failed. According to the disclosed method, preferably, the WTRU 20 stores the source eNB as the last eNB where the WTRU 20 resides until the handover is successfully completed. Regardless of whether the WTRU sends the source eNB or target eNB identification to the last eNB where the WTRU resides, the procedure itself will not be affected.

An important aspect of being able to regain the context is because the WTRU resides in the cell in the RACH procedure as soon as possible and sends Message 1 (i.e. random access preamble). If there is a delay in this procedure, the eNB can delete the context, thus invalidating the context reacquisition procedure. Therefore, a method for enhancing random access channel (RACH) procedures for RL and handover failure is disclosed. According to this method, a dedicated signature is assigned to the WTRU 20 during the handover procedure. Then, the assigned special signature immediately following the RL or switching failure is used as the access source cell. For example, the HO command (or any sending message) assigns two dedicated signatures to the WTRU 20. In the event of a failure (for example, if the WTRU 20 cannot try to access the target cell), a dedicated signature will be used by the WTRU 20. Used to access the target cell, and another dedicated signature will be used by the WTRU 20 to access the source cell (or any other cell).

If the handover is successfully completed, the WTRU 20 may (implicitly or explicitly) release the signature back to the network in the handover confirmation message. In the event of a failure during the handover procedure, the WTRU 20 can use this second dedicated signature and try to access the network as soon as possible. Because WTRU 20 uses a dedicated signature, it can recover from failures more quickly.

Alternatively, a set of dedicated signatures is exclusively broadcast in the broadcast channel (BCH) group for RL failure, and the set of dedicated signatures is used by the WTRU 20 in the event of RL or handover failure. In another alternative embodiment, a set of universal dedicated signatures that are valid in all cells can be used for RL failure. The set of general and dedicated signatures can be sent in the switching message or broadcast in the system information message. Then, the WTRU can use the universal dedicated signature to access any cell after the failure.

An alternative RACH procedure is published, instead of assigning a dedicated signature for use in the case of failure to the WTRU 20, at least one signature (such as a random access preamble) in the current group broadcast on the BCH can be Determined/reserved for access to cells following failure. According to this alternative embodiment, the WTRU 20 obtains the reserved signature from the BCH (or a handover (HO) command may inform the WTRU 20 of the reserved signature to be used in the event of failure). Once the WTRU 20 obtains the reserved signature, if the WTRU 20 experiences RL or the handover fails, the WTRU 20 uses the reserved signature.

Another alternative embodiment is disclosed in which a higher access level for RL failure handling is used. According to this alternative embodiment, the WTRU 20 associates RL failure handling with higher access level services, and therefore may end the network reselection with lower compensation or higher priority. In this case, when the WTRU 20 attempts to access the cell after the RL fails, because the WTRU 20 may have a higher access level service, and therefore may try to compensate at a lower level or there is no difference between RACH attempts. Compensation interval access network 10. Similarly, after RL failure, the WTRU 20 may have a higher probability of accessing the network with a lower access level service than other WTRUs, and it may have a longer compensation interval.

In another alternative method for RACH access, the WTRU 20 increases its power faster, so the network has a higher chance of detecting it, and therefore prioritizes a given WTRU 20. Table 3 describes the behavior of the WTRU 20 during RL failure according to the disclosed method.

<tables><img file="TWM340666U_D0003.tif" /></tables>

<tables><img file="TWM340666U_D0004.tif" /></tables>

For the second phase, in order to resume activity when the WTRU 20 returns to the same cell, or when the WTRU 20 selects a different cell from the same eNodeB or a different eNB, a method is disclosed in which the WTRU 20 accesses via a random access procedure Cell. The non-access stratum (NAS) identifier used in the random access procedure is also used by the eNB to determine whether the eNB has the RRC context stored for the WTRU 20. If the eNB finds an RRC context that matches the identity of the WTRU 20, the eNB sends a message in response to the RRC CONNECTION REQUEST (for example, RRC CONNECTION RESPONSE (RRC connection response)) or any other RRC procedure initiated by the WTRU, instructing the WTRU 20 to reuse it. The stored RRC context.

If the eNB does not find the RRC context matching the WTRU 20 identity, the new eNB uses the eNB identity transmitted by the WTRU 20 to directly contact the previously camped eNB. As disclosed above, alternatively, the eNB may obtain the WTRU identity or WTRU context from a mobility management entity (MME).

If the context is found and transmitted in the old eNB, the eNB sends a message in response to RRC CONNECTION REQUEST (eg, RRC CONNECTION RESPONSE), or any other RRC procedure initiated by the WTRU, instructing WTRU 20 to reuse its stored RRC context . If no context is found in both the new and old eNBs, an RRC connection establishment procedure occurs, and the WTRU 20 discards its stored RRC context. In the case that the network sends a response to the RRC procedure initiated by the WTRU 20, the network 10 indicates whether the WTRU 20 can use the old context information it had before the failure to build a stack, or the network 10 sends a new one in the response message The parameters are used by the WTRU 20 to build its stack. Once the WTRU 20 receives the response message from the network 10 and processes it, the WTRU 20 sends a completion message to the network 10 to indicate that the network 10 has completed the configuration on its side.

Table 4 below describes the mobility of the WTRU 20 during handover failure according to the disclosed method.

<tables><img file="TWM340666U_D0005.tif" /></tables>

<tables><img file="TWM340666U_D0006.tif" /></tables>

For the second phase, in order to resume activity when the WTRU 20 returns to the same cell, or when the WTRU 20 selects a different cell from the same eNB or a different eNB, a method is disclosed in which the WTRU 20 accesses via a random access procedure Cell. The non-access stratum (NAS) identifier used in the random access procedure is also used by the eNB to determine whether the eNB has a stored RRC context for the WTRU 20. If the eNB finds an RRC context that matches the identity of the WTRU 20, the eNB sends a message (for example, RRC CONNECTION RESPONSE) or any other RRC procedure initiated by the WTRU in response to the RRC CONNECTION REQUEST, instructing the WTRU 20 to reuse its stored RRC context .

If the eNB does not find an RRC context that matches the identity of the WTRU 20, the new eNB uses the eNB identity transmitted by the WTRU 20 to directly contact the previously camped eNB. As disclosed above, alternatively, the eNB may obtain the WTRU identity or WTRU context from the MME.

If the context is found and transmitted in the old eNB, it sends a message (for example, RRC CONNECTION RESPONSE) or any other RRC procedure initiated by the WTRU in response to the RRC CONNECTION REQUEST to instruct the WTRU 20 to reuse its stored RRC context. If no context is found in the new or old eNB, the usual RRC connection establishment procedure takes place and the WTRU 20 preferably discards its stored RRC context. It should be noted that the use of the priority order column for cell selection in Tables 3 and 4 is an alternative method, and regardless of the priority order, if other priority orders for cell selection/reselection are used, the disclosed program is still Available.

Although the features and elements of this creation are described in specific combinations in the above embodiments, each feature or element can be used alone without other features and elements, or in various combinations with or without other features and elements. Under the circumstances. The method or flowchart provided in this creation can be implemented in a computer program, software, or firmware executed by a general-purpose computer or processor, where the computer program, software, or firmware is included in a computer-readable storage medium in a tangible manner middle. Examples of computer-readable storage media include magnetic media such as read-only memory (ROM), random access memory (RAM), registers, buffer memory, semiconductor storage devices, internal hard drives, and removable disks, Magneto-optical media and optical media such as CD-ROM discs and digital versatile discs (DVD).

For example, suitable processors include: general-purpose processors, special-purpose processors, conventional processors, digital signal processors (DSP), multiple microprocessors, one or more microprocessors associated with the DSP core, Controller, microcontroller, dedicated integrated circuit (ASIC), field programmable gate array (FPGA) circuit, any kind of integrated circuit (IC) and/or state machine.

The processor associated with the software can be used to implement a radio frequency transceiver for use in a wireless transmission and reception unit (WTRU), user equipment (UE), terminal, base station, radio network controller (RNC) or any host Use it in a computer. WTRU can be used in combination with modules implemented in hardware and/or software, such as cameras, camera modules, video phones, speaker phones, vibration devices, speakers, microphones, TV transceivers, hands-free headsets, keyboards, Bluetooth<img file="TWM340666U_D0007.tif" />Module, frequency modulation (FM) wireless unit, liquid crystal display (LCD) display unit, organic light-emitting diode (OLED) display unit, digital music player, media player, video game console module, Internet browser And/or any wireless local area network (WLAN) or ultra-wideband (UWB) module.

<p>RRC. . . Radio source control</p><p>T1. . . Based on other standards</p><p>T2. . . Based on timer</p><p>UE. . . User equipment</p><p>eNB. . . Evolved Node-B</p><p>10. . . LTE wireless communication network</p><p>20. . . WTRU</p><p>30. . . Node B</p><p>40. . . Cell</p><p>21, 31. . . processor</p><p>RL. . . Radio link</p><p>IE. . . Information element</p>

A more detailed understanding can be obtained from the detailed description given below as an embodiment in conjunction with the accompanying drawings. in:

Figure 1 shows the failure of the traditional radio link;

Figure 2 shows the traditional handover failure;

Figure 3 shows the traditional non-controversial random access procedure;

Figure 4 is a block diagram of the wireless communication system; and

Figure 5 shows a flowchart of the disclosed method for handling radio link failure.