HK1168234B - Method and apparatus for monitoring for a radio link failure - Google Patents

Description

Method and apparatus for monitoring radio link failure

Cross Reference to Related Applications

This application claims the benefit of united states provisional application 61/159,649 filed 3/12/2009, united states provisional application 61/218,171 filed 6/18/2009, united states provisional application 61/248,264 filed 10/2/2009, united states provisional application 61/250,773 filed 10/12/2009, and united states provisional application 61/256,687 filed 10/30/2009, which are all hereby incorporated by reference in their entireties.

Technical Field

The present application relates to wireless communications.

Background

Wireless communication systems are constantly evolving to meet the need for continuous and faster access to data networks. To meet these needs, wireless communication systems may use multiple carriers for data transmission. A wireless communication system using multiple carriers for data transmission may be referred to as a multi-carrier system. The use of multiple carriers may be extended to cellular and non-cellular wireless systems.

Multi-carrier systems may increase the available bandwidth in a wireless communication system based on the number of available carriers. For example, a dual carrier system may double the bandwidth compared to a single carrier system, and a triple carrier system may triple the bandwidth compared to a single carrier system. In addition to gains in throughput, it may be desirable to achieve diversity and joint scheduling gains. This will greatly improve the quality of service (QoS) for the end user. Also, multiple carriers may be used in conjunction with Multiple Input Multiple Output (MIMO).

In the third generation partnership project (3GPP) release 8(R8) and release 9(R9) specifications currently used for single carrier Long Term Evolution (LTE), a wireless transmit/receive unit (WTRU) ensures that once its radio connection (i.e., Radio Resource Control (RRC) connection) to the system is established, it is maintained. The WTRU performs radio link monitoring and, once a physical layer problem is detected, increases its monitoring activity until it recovers from the physical layer problem. If the problem persists and the conditions for recovery from the physical layer problem cannot be met, the WTRU assumes a Radio Link Failure (RLF). Once RLF occurs, the WTRU performs a recovery procedure (e.g., RRC connection reestablishment).

More specifically, several 3GPP documents describe radio link monitoring in current specific LTE systems (with one carrier). The WTRU monitors whether a Downlink (DL) radio quality exceeds a threshold (Q) every frame or every Discontinuous Reception (DRX) cycle depending on whether DRX is activated_outAnd Q_in). When radio link quality ratio Q_inGood or specific Q_outPoor, the physical layer may indicate synchronization or non-synchronization to higher layers (e.g., RRC layer). The time period of this evaluation depends on whether DRX is used. The radio link quality is measured in terms of block error rate (bler) of hypothetical Physical Downlink Control Channel (PDCCH) transmission transmissions, taking into account Physical Control Format Indicator Channel (PCFICH) errors with a particular hypothetical transmission configuration.

Upon receiving a predefined number (e.g., N310) of consecutive out-of-sync indications, the RRC detects that a physical layer problem has occurred and starts a recovery timer (e.g., T310). If the recovery timer expires before a predefined number (e.g., N311) of consecutive synchronization indications is received, (i.e., "recovery of physical layer problem"), the RRC determines that RLF has occurred and initiates a connection re-establishment procedure or release of the RRC connection depending on whether Access Stratum (AS) security is activated. The evaluation period of the radio link quality evaluation at the time of resuming timer operation has no relation to whether it is configured or not, as if DRX was not used. This means that the WTRU will turn on its receiver to evaluate the radio link quality even if no data is received according to the DRX rules.

In addition, the RRC may also determine that RLF has occurred if there is an indication of a random access problem from the Medium Access Control (MAC) or an indication from the Radio Link Control (RLC) that the maximum number of retransmissions has been reached.

To further improve the achievable throughput and coverage of LTE-based radio access systems and meet the requirements of international mobile telecommunications advanced (IMT-advanced) requirements of reaching 1Gbps and 500Mbps in the DL and Uplink (UL) directions, respectively, the 3GPP standards body is currently working on LTE-advanced (LTE-a). One improvement proposed for LTE-a is carrier aggregation and support for flexible bandwidth scheduling features. One motivation for this is to allow DL and UL transmission bandwidths to exceed the 20MHz in release 8(R8) LTE, (e.g., 40MHz to 100 MHz).

When a WTRU operates on multiple carriers, the criteria for radio link monitoring and the actions that should be taken when a radio link problem is detected need to be redefined, as compared to the single carrier case. This is because different radio conditions may exist on different component carriers and modifications to the control channel structure and related procedures may be required compared to the single carrier case.

Disclosure of Invention

Methods and apparatus for monitoring for radio link failure in LTE-a systems implementing carrier aggregation are described. The method includes criteria for determining a radio link failure, a recovery event, and actions that the WTRU may take when the event occurs.

Drawings

A more detailed understanding can be derived from the following description of examples, taken in conjunction with the accompanying drawings, in which:

fig. 1 illustrates an LTE wireless communication system/access network;

fig. 2 is a block diagram of an LTE wireless communication system;

figure 3 shows additional details of a processor within a WTRU in the system of figure 2;

fig. 4, 5A, 5B, 6, 7A, 7B and 8 are flow diagrams of a process for monitoring a carrier; and

fig. 9 and 10 show how DL and UL carriers are configured to perform RRC primary carrier re-establishment procedures.

Detailed Description

When referred to hereafter, the term "wireless transmit/receive unit (WTRU)" 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 counter, or any other type of user equipment capable of operating in a wireless environment.

When referred to hereafter, the term "base station" includes, but is not limited to, a node B, a site controller, an Access Point (AP), or any other type of interfacing device capable of operating in a wireless environment.

When referred to below, the term "Primary Component Carrier (PCC)" includes, without loss of generality, a carrier of a WTRU configured to operate using multiple component carriers for which certain functionalities (e.g., acquisition of security parameters and non-access stratum (NAS) information) apply only. The WTRU may be configured with at least one downlink pcc (dl pcc) and one uplink pcc (ul pcc). Thus, a carrier that is not a PCC for a WTRU is hereinafter referred to as a Secondary Component Carrier (SCC).

For WTRUs configured to operate with multiple component carriers, PDCCH monitoring and/or Physical Downlink Shared Channel (PDSCH) reception for PCC (if configured) will typically be activated and may be managed by DRX (if configured). PDCCH monitoring (if configured) and/or PDSCH reception for the configured SCC may be activated or deactivated and may be managed by DRX (if configured) when activated.

When a WTRU operates using multiple component carriers, cross-carrier (cross-carrier) scheduling may be supported (i.e., scheduling between multiple carriers using the PDCCH). If cross-carrier scheduling is possible, there is no need to monitor PDCCH in all configured and/or active carriers.

When referred to hereinafter, the term "PDCCH carrier" includes carriers for which the WTRU is configured to monitor the PDCCH. When a WTRU operates using multiple component carriers, the WTRU may be configured with one or more PDCCH carriers.

When referred to hereinafter, the term "anchor carrier" includes a PDCCH carrier for which the WTRU additionally monitors for downlink assignments and/or uplink grants applicable to different carriers in the WTRU's configuration. When a WTRU operates using multiple component carriers, the WTRU may be configured with one or more anchor carriers.

When referred to in the following, the term "scheduled set" comprises at least one anchor carrier and at least one non-anchor carrier (possibly a PDCCH carrier itself), wherein the anchor carrier can also provide control signaling for the non-anchor carriers in the set. When a WTRU operates using multiple component carriers, the WTRU may be configured with one or more scheduling sets. For example, when a WTRU is configured to operate using two or more component carriers (i.e., frequencies or cells), each of these carriers may have different characteristics and logical associations with the network and the WTRU, and the operating frequencies may be grouped to form more than one scheduling set, where each set includes at least a primary or anchor carrier, and a secondary carrier. Alternatively, a WTRU may be configured with a single scheduling set (i.e., there is a single primary or anchor carrier, and one or more secondary carriers).

Fig. 1 illustrates an LTE wireless communication system/access network 10 that includes an evolved universal terrestrial radio access network (E-UTRAN) 20. The E-UTRAN 20 includes a WTRU100 and several evolved node Bs (eNBs) 150. The WTRU100 communicates with the eNB 150. The enbs 150 may use the X2 interface to interface with each other. Each eNB 150 is connected with a Mobility Management Entity (MME)/serving gateway (S-GW)180 through an S1 interface. Although a single WTRU100 and three enbs 150 are shown in fig. 1, it should be apparent that any combination of wireless and wired devices may be included in the LTE wireless communication system/access network 10.

Fig. 2 is a block diagram of an LTE wireless communication system 200, the wireless communication system 200 including a WTRU100, an eNB 150, and an MME/S-GW 180. As shown in fig. 2, the WTRU100, eNB 150 and MME/S-GW 180 are configured to perform a method of monitoring radio links using aggregated carriers.

In addition to the components that may be found in a typical WTRU, the WTRU100 includes a processor 255 with an optional link memory 260, at least one transceiver 265, an optional battery 270, and an antenna 275. The processor 255 is configured to perform a method of maintaining validity of system information using the aggregated carriers. The transceiver 265 is in communication with the processor 255 and the antenna 275 to facilitate the transmission and reception of wireless communications. The transceiver 265 includes a transmitter and a receiver (not separately shown). If the battery 270 is used in the WTRU 210, the battery 270 powers the transceiver 265 and the processor 255.

In addition to the components that may be found in a typical eNB, the eNB 150 includes a processor 280 with an optional link memory 282, a transceiver 284, and an antenna 286. The processor 280 is configured to perform a method of monitoring radio links using aggregated carriers. The transceiver 284 is in communication with the processor 280 and the antenna 286 to facilitate the transmission and reception of wireless communications. The eNB 150 is connected to an MME/S-GW 180, which MME/S-GW 180 includes a processor 288 with an optional linking memory 290.

As shown in fig. 2, a WTRU100 communicates with a node B150, both configured to perform a method in which UL transmissions from the WTRU100 are sent to the node B150 using multiple UL carriers 65, while downlink transmissions are processed using multiple carriers 70.

Figure 3 shows additional details of the processor 255 in the WTRU 100. As shown in FIG. 3, processor 255 may include a plurality of recovery timers 325₁，325₂，...，325_NAnd a plurality of counters 330₁，330₂，330₃，330₄，...，330_N。

Although terminology specific to LTE or LTE-a systems is used herein to describe various schemes in radio link monitoring, it should be understood that evolved High Speed Packet Access (HSPA) systems using multiple carriers or cells are also applicable to these schemes.

Several possible approaches are defined for carrier aggregation according to the arrangement of UL/DL control channels on the component carriers. The scheme for radio link monitoring may depend on which of these control channel methods is used.

Radio link monitoring

As shown in fig. 3, to determine whether a radio link failure has occurred, a set of timers 325 and counters 330 in a processor 255 within the WTRU100 may be used to perform radio link monitoring. In this approach, the WTRU100 detects and recovers physical layer problems using a set of counters (e.g., N310, N311) and a single recovery timer (e.g., T310) to detect radio link failure. Upon detecting a radio link failure, the WTRU100 performs an RRC connection re-establishment procedure or an RRC connection release procedure (depending on whether AS security is activated).

Radio link monitoring for radio link failure detection purposes may be based on in-sync and out-of-sync indications from the primary DL carrier. In the method, radio link monitoring is performed using one specific DL carrier of a set of different component carriers activated for the WTRU. Thus, the physical layer reports to the RRC layer an indication of synchronization and an indication of non-synchronization, at least from the DL carrier being monitored for radio link failure (i.e., the primary DL carrier); the indication may also be reported for other DL carriers for other purposes than radio link failure detection, e.g., to manage a set of configured component carriers (e.g., secondary carriers).

As shown in fig. 4, a process (400) for monitoring a radio link includes determining (i.e., identifying) a primary DL carrier among a set of component carriers configured for the WTRU100 (405). The at least one primary DL carrier may be identified according to one or a combination of the following methods:

1) the primary DL carrier is acquired from the network through RRC signaling (either dedicated or from system information). The signaling may be provided while the WTRU is configured (or reconfigured) with multiple carriers. The indication of which carrier is the primary DL carrier may be explicit or implicit. For example, the primary DL carrier may be implicitly the first carrier provided in the RRC configuration message. Alternatively, the primary DL carrier may be implicit to the DL carrier on which the WTRU is operating when the WTRU receives an RRC message configuring itself with an additional carrier. If the WTRU is configured or reconfigured with a single DL carrier, that carrier may be implicitly the primary DL carrier.

2) The DL anchor carrier providing PDCCH signaling is determined to be the primary carrier. In particular, if the WTRU is configured with a single DL anchor carrier (i.e., the WTRU is configured with a single scheduling set), the WTRU determines that carrier as its primary carrier.

3) The WTRU determines a primary DL carrier from a plurality of configured and active PDCCH carriers (e.g., active DL carriers at "active times" according to DRX rules) for which the WTRU monitors the PDCCH (i.e., the primary DL carrier dynamically changes based on PDDCH activity on the primary DL carrier and other DL carriers). If more than one DL carrier is active and a single DL carrier is selected, there is a predefined or signaled priority between DL carriers to determine which carrier to select. If no DL carrier is actively monitoring PDCCH (e.g., at DRX active time), the primary carrier may be determined from the set of DL carriers configured or activated for the WTRU. In this case, there may also be predefined or signaled priorities between DL carriers.

Referring again to FIG. 4, the process 400 further includes using the first counter 330₁(e.g., N310) to count the number of out-of-sync indications from the primary DL carrier (410) and to start recovery timer 325 if a predefined number of out-of-sync indications from the primary carrier is counted₁(e.g., T310) (415), wherein the counting is by first counter 330₁And (4) determining. The process (400) further includes using a second counter 330₂The number of synchronization indications from the primary DL carrier is counted (420) and determined at the recovery timer 325₁Before expiry, the second counter 330₂Whether a predefined number of synchronization indications from the primary DL carrier are counted (425). Resume timer 325 if the number of synchronization indications from the primary DL carrier reaches the predefined number of synchronization indications₁And first and second counters 330₁And 330₂All are stopped and reset (430). If the number of synchronization indications from the primary DL carrier does not reach the predefined number of synchronization indications, declaring a radio link failure occurred (435) and performing a connection re-establishment procedure or an RRC connection release procedure (440).

The radio link monitoring may also be based on the functionality of obtaining an indication of synchronization and an indication of non-synchronization on multiple DL carriers within a given time period, typically equal to the synchronous/non-synchronous measurement frequency, e.g. one subframe. In this method, the physical layer measures indications of synchronization and out-of-synchronization from multiple DL carriers (hereinafter referred to as "set of monitored DL carriers") and applies a function to combine these indications into a single indication of synchronization or a single indication of out-of-synchronization to be reported to the RRC layer. Such merging may be performed, for example, using one or more of the following methods:

1) reporting the combined synchronization indication to the RRC if at least one synchronization indication is measured for a DL carrier from the set of monitored DL carriers;

2) if the number of synchronization indications for carriers in the set of monitored DL carriers is greater than (greater than or equal to) the number of out-of-synchronization indications, the combined synchronization indications are reported to the RRC.

3) Otherwise, if the synchronization indication cannot be reported according to, for example, one of the methods described above, the combined out-of-sync indication is reported to the RRC.

As shown in fig. 5A and 5B, a process 500 for monitoring a radio link includes determining a set of monitored DL carriers (505). The set of monitored DL carriers may be determined according to one or a combination of the following methods:

1) the set of monitored DL carriers is provided by the network through RRC signaling (dedicated or from system information). The set may be defined as the same set as the set of DL carriers configured and/or activated for the WTRU.

2) The set of monitored DL carriers is a set of one or more anchor carriers monitored by the WTRU.

3) The WTRU may determine (i.e., identify) those PDCCH carriers (or those primary or anchor DL carriers) that it is monitoring for PDCCHs in a given subframe, e.g., PDCCH carriers that are configured and activated and/or are "active time" in DRX operation (i.e., the set of monitored DL carriers dynamically changes based on PDCCH activity). If the WTRU does not monitor the PDCCH (or for any primary or anchor DL carrier) for any DL carrier, e.g., no DL carrier is in DRX active time, the set of monitored DL carriers may include a predefined or signaled primary DL carrier or set of DL carriers.

Referring again to fig. 5A and 5B, the process 500 further includes combining the out-of-sync indication from each carrier in the set of monitored DL carriers into a combined out-of-sync indication (510), and combining the in-sync indication from each carrier in the set of monitored DL carriers into a combined in-sync indication (515). The process 500 further includes using the first counter 330₁(e.g., N310) to count the number of merged out-of-synch indications (520), and start recovery timer 325 on condition that a predefined number of merged out-of-synch indications are counted₁(e.g., T310) (525), the count being by the first counter 330₁And (4) determining. The process (500) further includes using a second counter 330₂To count 530 the number of merged synchronization indications and determine 325 at the recovery timer₁Before expiration, whether a predefined number of merged synchronization indications is counted (535). If the number of merged synchronization indications reaches the predefined number of synchronization indications, the timer 325 is resumed₁And first and second counters 330₁And 330₂All are stopped and reset (540). If the number of merged synchronization indications does not reach the predefined number of synchronization indications, a radio link failure is declared (545) and a connection re-establishment procedure or an RRC connection release procedure is performed (550).

Radio link monitoring may be performed within a "scheduled set" of component carriers as described above. The anchor carrier may correspond to a "primary carrier. This may be achieved by having all carriers of the scheduling set controlled by the same PDCCH or a separate PDCCH. Similarly, it is possible to send Acknowledgement (ACK)/Negative Acknowledgement (NACK) feedback and Channel Quality Indicator (CQI)/Precoding Matrix Indicator (PMI)/Routing Indicator (RI) reports belonging to DL transmissions from the scheduling set of carriers from a separate "primary" UL carrier.

In one approach, the recovery timer is not running and only the primary carrier is monitored. When a radio link problem is detected on the primary carrier (N310 out-of-sync indication), a recovery timer 325 in the WTRU100 is started (i.e., started)₁(e.g., T310) and immediately initiate radio link quality monitoring on all DL carriers of the scheduling set (i.e., on the SCC), possibly only for the SCC which is also a PDCCH carrier. Thus, the physical layer now provides an indication of synchronization and an indication of non-synchronization for each DL carrier (i.e., for the PCC and all SCCs). The non-DRX evaluation period may be used for all DL carriers regardless of whether DRX is used on the DL carrier. Thus, the WTRU100 may continue to receive on the DL carrier.

Recovery timer 325₁(e.g., T310) stops (resume timer 325) upon receiving a predefined number (e.g., N311) of consecutive synchronization indications from the same carrier₁The value of (d) may be carrier-dependent). If the carrier is different from the primary carrier, the WTRU100 may initiate transmission of the report, the network may initiate a procedure to reestablish the PCC based on the transmission, or may perform a "primary reestablishment," as further described below.

The WTRU100 may first initiate an evaluation period on a subset of DL carriers (within the scheduling set) that have been configured for aggressive reception (i.e., PDCCH and/or PDSCH reception) and then, in a second phase, take turns detecting other DL carriers within the cell if no continuous synchronization indication is detected from any of the carriers in the subset. The need to start with a subset of carriers and take turns detecting other carriers is based on WTRU capabilities.

If timer 325 is recovered₁(e.g., T310) expires, the WTRU may initiate a recovery procedure, such as performing a connection re-establishment procedure or an RRC connection release procedure in a single carrier scenario, for example (depending on whether security is activated). Alternatively, the occurrence of partial radio link failures for the primary carrier (or "scheduling set" for the carrier) may be considered and appropriate action may be taken as described below.

As shown in fig. 6, a process 600 for monitoring a radio link includes starting a recovery timer (605), counting a number of synchronization indications for each of a plurality of DL carriers in a scheduling set of component carriers (610), and determining whether a predefined number of synchronization indications have been received from a particular one of the carriers before the recovery timer expires (615). If a predefined number of synchronization indications are not received from a particular one of the carriers before the recovery timer expires, a radio link failure is declared (620) and a connection re-establishment procedure or an RRC connection release procedure is performed (625). If a predefined number of synchronization indications are received from a particular one of the carriers before the recovery timer expires, the recovery timer is stopped and reset (630) and a determination is made as to whether the particular one of the carriers is a primary carrier (635). If it is determined that a particular one of the carriers is not a primary carrier, a primary re-establishment procedure is performed (640).

In another approach, the first recovery timer 325 upon receiving an indication of continuous out-of-sync of a predefined number (e.g., N310) of one or more carriers in a first subset of DL carriers (e.g., at least one of a PCC, an anchor carrier, or a PDCCH carrier of a "scheduling set"), (e.g., a PCC, an anchor carrier, or a PDCCH carrier of a "scheduling set"), is used to determine a first recovery timer₁(e.g., T310) is started (i.e., started), and upon receiving a first predefined number (e.g., N311) of consecutive synchronization indications for the first timer applicable carrier, the first recovery timer 325₁And (5) stopping. If the first recovery timer 325₁Upon expiration (due to the absence of receipt of a first predefined number (e.g., N311) of consecutive synchronization indications), a second recovery timer 325 is started₂(e.g., T310 repetitions) and radio link quality monitoring is initiated on a different subset of DL carriers (e.g., all SCCs or all PDCCH carriers or all DL carriers of the "scheduling set"). Thus, the physical layer now provides an indication of synchronization and non-synchronization for each carrier of the scheduling set. Second recovery timer 325₂May be repeated with the first recovery timer 325 (e.g., T310 repetition)₁Are the same or different (e.g., T310). The non-DRX evaluation period may be used for all carriers regardless of whether DRX is used on these carriers. Thus, the number of the first and second electrodes,the WTRU100 may receive continuously on these carriers.

Upon receiving a second predefined number (e.g., N311 repetitions) of consecutive synchronization indications from the same carrier (the second predefined number being carrier dependent), a second recovery timer 325₂And (5) stopping. If the carrier is different from the primary carrier, the WTRU100 may perform a "primary re-establishment" procedure as follows.

The WTRU100 may first initiate an evaluation period on a subset of DL carriers (within the scheduling set) that have been configured for aggressive reception and then, in a second phase, take turns detecting other DL carriers in the cell if no continuous synchronization indication is detected from any of the carriers in the subset. The need to start with a subset of carriers and take turns detecting other carriers is based on WTRU capabilities.

If the second recovery timer 325₂Expired, then the connection re-establishment procedure or RRC connection release procedure is performed (depending on whether security is activated) as in the single carrier case. Alternatively, partial radio link failures may occur in view of the primary carrier (or the scheduled set of carriers) and appropriate action may be taken as described below.

As shown in fig. 7A and 7B, a process 700 for monitoring a radio link includes starting a first recovery timer (705), counting a number of synchronization indications for each of a plurality of DL carriers in a scheduled set of component carriers (710), and determining whether a first predefined number of synchronization indications have been received from a particular one of the carriers before the first recovery timer expires (715). If a first predefined number of synchronization indications are not received from a particular one of the carriers before the first recovery timer expires, a radio link failure is declared (720) and a connection re-establishment procedure or an RRC connection release procedure is performed (725). If a first predefined number of synchronization indications is received from a particular one of the carriers before the first recovery timer expires, the first recovery timer is stopped and reset (730), a second recovery timer is started (735), the number of synchronization indications for each of a plurality of DL carriers in a scheduling set of component carriers is counted (740), and before the second recovery timer expires, it is determined whether a second predefined number of synchronization indications is received from the same particular one of the carriers (745). If a second predefined number of synchronization indications is not received from a particular one of the carriers before the second recovery timer expires, a radio link failure is declared (720) and a connection re-establishment procedure or an RRC connection release procedure is performed (725). If a second predefined number of synchronization indications is received from a particular one of the carriers before the second recovery timer expires, the second recovery timer is stopped and reset (750), and a determination is made as to whether the particular one of the carriers is a primary carrier (755). If it is determined that a particular one of the carriers is not a primary carrier, a primary re-establishment procedure is performed (760).

In another approach, the first recovery timer 325₁(e.g., T310) is started (i.e., started), and a second recovery timer 325 is started₂(e.g., T310 repeats) are also initiated. Radio link quality monitoring is started immediately on all DL carriers of the scheduling set. Thus, the physical layer now provides an indication of synchronization and non-synchronization for each carrier of the scheduling set. The non-DRX evaluation period may be used for all carriers regardless of whether DRX is used on these carriers. Thus, the WTRU100 may continue to receive on these carriers.

The WTRU100 may first initiate an evaluation period on a subset of DL carriers (within the scheduling set) that have been configured for aggressive reception. If no consecutive synchronization indications are detected from any of the carriers in the subset, alternate detection of other DL carriers in the cell is performed, based on WTRU capabilities.

Upon receiving a predefined number (e.g., N311) of consecutive synchronization indications from the primary carrier, a first recovery timer 325₁And (5) stopping.

Upon receiving a predefined number (e.g., N311) of consecutive co-carriers from the same primary or secondary carrierStep indicates that the second recovery timer 325 is₂Stop (the predefined number of values may depend on the carrier).

If the first recovery timer 325₁Expires and the second recovery timer 325₂Previously stopped due to the reception of a predefined number (e.g., N311) of consecutive synchronization indications, the WTRU100 may perform a "master re-establishment" procedure as described below.

If the first recovery timer 325₁Expires and the second recovery timer 325₂Having previously expired (i.e., not having been stopped by receipt of N311 consecutive synchronization indications), a connection re-establishment procedure or an RRC connection release procedure is performed as in the case of single carrier (depending on whether security is activated or not). Alternatively, partial radio link failures may occur in consideration of the primary carrier (or the scheduled set of carriers) and appropriate action may be taken as described below.

If the second recovery timer 325₂Expires and the first recovery timer 325₁Having expired before, a connection re-establishment procedure or RRC connection release procedure is performed as in the case of single carrier (depending on whether security is activated or not). Alternatively, partial radio link failures may occur in consideration of the primary carrier (or the scheduled set of carriers) and appropriate action may be taken as described below.

As shown in fig. 8, a process 800 for monitoring a radio link includes starting a first recovery timer and a second recovery timer (805), counting a number of synchronization indications for each of a plurality of DL carriers in a scheduled set of component carriers (810), and determining whether a predefined number of synchronization indications have been received from a primary carrier before expiration of both recovery timers (815). If a predefined number of synchronization indications are not received from the primary carrier before the expiration of both recovery timers, a radio link failure is declared (820) and a connection re-establishment procedure or an RRC connection release procedure is performed (825). If a predefined number of synchronization indications are received from the primary carrier before both recovery timers expire, any non-expired recovery timers are stopped and reset (830) and a primary re-establishment procedure is performed (835).

In another approach, all carriers in the scheduling set are monitored. The radio link monitoring procedure is performed independently and in parallel on each carrier of the scheduling set. Thus, for each carrier, the physical layer indicates synchronization and non-synchronization to higher layers. The number of consecutive in-sync and out-of-sync indications is tracked separately for each carrier. When a predefined number (N310) of consecutive out-of-sync indications are received for a particular carrier, the WTRU100 detects a "radio link problem" for the particular carrier. The WTRU100 starts a recovery timer 325 specific to that carrier₁(e.g., T310). The recovery timer 325 if a predefined number (N311) of consecutive synchronization indications is received for the carrier₁And (5) stopping. The value of the timer 325 and the predefined number of synchronization indications may be carrier dependent. Upon recovery of timer 325₁For carrier expiration, the following behavior is performed according to the type of the carrier (e.g., whether the DL CC is a PCC or SCC).

If the carrier is an SCC, the WTRU may perform actions when a "partial radio link failure" is detected for that carrier without affecting operation on other carriers (PCC or non-PCC).

If the carrier is a PCC, the WTRU100 may perform one or a combination of the following:

1) the primary reestablishment procedure, as described below, wherein the new PCC is not running the recovery timer 325₁If any-otherwise the option is not available;

2) an action taken when a "partial radio link failure" is detected for all carriers in the scheduling set to which the carrier (e.g., possibly a PCC, where the PCC is also an anchor carrier). If timer 325 is recovered₁Running on all carriers of the scheduling set, the process may be performed.

If DRX is per carrier based, the evaluation period of the in-sync and out-of-sync indications on a given carrier depends on the DRX activity of that carrier. Optionally, the evaluation period of the in/out-of-sync indication is specific for each carrier (DRX dependent) as long as no recovery timer 325 is running for any carrier. The evaluation period of the in/out-of-sync indication (for all carriers or for a particular subset of carriers signaled by higher layers) corresponds to the evaluation period of the continuous reception (non-DRX) or the reception with higher loading rate (duty rate) while the recovery timer 325 is running for any carrier. Such monitoring increases the chances of quickly detecting radio link problems on other carriers and thus can potentially minimize the loss of data or connections, given that radio link problems can be correlated among carriers. Alternatively, when the recovery timer 325 is run for any carrier (or any carrier in a particular set of carriers signaled by higher layers), the value of the recovery timer 325 and the predefined number of synchronization indications for a given carrier may be modified.

Another possible scheme is UL/DL scheduling for carriers that are advertised on the same carrier. This may be achieved, for example, by having the WTRU100 monitor the PDCCH for each carrier to which it is allocated. There may also be a more general scheme where there are multiple anchor carriers and their corresponding scheduling sets of carriers. The former scheme may be seen as a specific case of the latter, where the scheduled set of anchor carriers includes the anchor carrier. Thus, the scheme described in this paragraph will be described in terms of a more general scheme with multiple PDCCH carriers. One of the PDCCH carriers may correspond to the "primary" carrier, which, as previously described, is monitored for the purpose of radio link failure detection.

In this scheme, all active PDCCH carriers in a cell that the WTRU100 is configured to receive are monitored, even when the recovery timer is not running. DRX reception on active carriers may be applied on a per carrier basis. Thus, if the WTRU100 monitors (for) PDCCH on a given carrier in a given subframe, this does not mean monitoring PDCCH on other carriers. Alternatively, DRX reception may be applied jointly on all active carriers.

In one approach, the radio link monitoring procedure is performed independently and in parallel on each PDCCH carrier. Thus, for each PDCCH carrier, the physical layer indicates synchronization and non-synchronization to the higher layer. The number of consecutive synchronization and out-of-synchronization indications is tracked separately for each PDCCH carrier. When a predefined number (N310) of consecutive out-of-sync indications are received for that carrier, the WTRU100 detects a "radio link problem" for that particular carrier. The WTRU100 starts a recovery timer 325 (e.g., T310) specific to that PDCCH carrier. The recovery timer 325 is stopped if a second predefined number (N311) of consecutive synchronization indications is received for the carrier. The value of the timer 325 and the predefined number of consecutive synchronization indications may be carrier-dependent. If the recovery timer 325 expires, a radio link failure is declared for the PDCCH carrier of interest. This event may be referred to as a "partial radio link failure". Once a partial radio link failure occurs, the WTRU100 may take actions as described below to inform the network and potentially remove or recover the carrier. If a radio link failure condition is detected for all PDCCH carriers in the cell for which the WTRU100 is configured to receive (possibly only for PDCCHs that are also PCC and/or anchor carrier), the WTRU100 may act like the currently defined radio link failure procedure for a single carrier, i.e., initiate a re-establishment procedure or release the RRC connection.

If DRX is per carrier based, the evaluation period of the in-sync and out-of-sync indications on a given PDCCH carrier depends on the DRX activity of that carrier. Optionally, the evaluation period for the in/out-of-sync indication is specific to each PDCCH carrier (DRX dependent) as long as no recovery timer 325 is running for any PDCCH carrier (possibly only for PDCCH that is also PCC and/or anchor carrier). While the recovery timer 325 (e.g., T310) is running for any PDCCH carrier (possibly only for PDCCHs that are also PCC and/or anchor carrier), the evaluation period for the in/out of sync indication (for all PDCCH carriers or for a particular subset of the primary carrier signaled by a higher layer) corresponds to the evaluation period for continuous reception (non-DRX) or reception with higher loading rate. Such monitoring increases the chances of quickly detecting radio link problems on other primary carriers and may also potentially minimize loss of data or connections given that radio link problems may be correlated among carriers. Alternatively, when the recovery timer 325 (e.g., T310) is running for any carrier (or any carrier in a particular set of carriers signaled by higher layers), the value of the recovery timer 325 and the predefined number of consecutive synchronization indications (e.g., N310, T310, and N311) for a given carrier may be modified.

In another approach, the radio link monitoring procedure is implemented independently and in parallel on each scheduling set of component carriers, according to one of the methods described above. Detection of radio link problems on any PDCCH carrier (possibly only for PDCCH that is also PCC and/or anchor carrier) may result in a primary re-establishment or partial radio link failure. The value of the resume timer 325 and the predefined number of consecutive synchronization indications (e.g., N310, N311, T310, and (if applicable) T310 repetitions) may depend on the scheduling set.

Upon a partial radio link failure on one PDCCH carrier (possibly only for PDCCH that is also PCC and/or anchor carrier), WTRU100 may take action to inform the network and potentially remove or recover the PDCCH carrier and/or the entire scheduling set for the anchor PDCCH carrier (if applicable). If a radio link failure condition is detected for all PDCCH carriers in the cell for which the WTRU100 is configured to receive (possibly only for PDCCHs that are also PCC and/or anchor carrier), the WTRU100 may act as if it were the currently defined radio link failure procedure for the single carrier, (i.e., initiate a re-establishment procedure or release the RRC connection).

If DRX is per carrier based, the evaluation period of the in-sync and out-of-sync indications on a given PDCCH carrier depends on the DRX activity of that carrier. Optionally, the evaluation period for the in/out-of-sync indication is specific to each PDCCH carrier (DRX dependent) as long as no recovery timer 325 is running for any PDCCH carrier (possibly only for PDCCH that is also PCC and/or anchor carrier). When the recovery timer is running for any PDCCH carrier (possibly only for PDCCH that is also PCC and/or anchor carrier), the evaluation period for the in/out of sync indication (for all PDCCH carriers or for a particular subset of PDCCH carriers signaled by higher layers) corresponds to the evaluation period for continuous reception (non-DRX) or reception with higher loading rate. Such monitoring increases the chances of quickly detecting radio link problems on other PDCCH carriers and may also potentially reduce the loss of data or connections given that radio link problems may be correlated among carriers. Alternatively, when the recovery timer 325 (e.g., T310) is running for any PDCCH carrier (or any carrier in a particular set of carriers that is signaled by a higher layer), the value of the recovery timer 325 and the predefined number of consecutive synchronization indications for a given carrier (e.g., N310, T310, N311, and, if applicable, T310 repetitions) may be modified.

Actions upon detection of partial or complete radio link failure

The procedure described below is applicable to "partial radio link failure" detection for downlink carriers configured with PDCCH. It is also applicable to the detection of failure of a downlink carrier configured with PDSCH instead of PDCCH.

Alternatively, if one of the carriers on which the WTRU is configured to operate has a particular role (e.g., PPC, anchor carrier or DL carrier corresponding to "special cell" or "serving cell"), the following procedure may be applied when that carrier fails.

Upon detecting a partial radio link failure (radio link failure detected by a subset of DL active carriers), an explicit notification may be sent to the eNB of the partial radio link failure or may be left to the eNB to implicitly detect the partial radio link failure.

The explicit indication may be signaled by a Physical Uplink Control Channel (PUCCH), a MAC Control Element (CE), or an RRC measurement report. The PUCCH may indicate a very low CQI report or a unique CQI code point. MAC CE and RRC measurement reporting require DL carrier identifiers to be indicated. When a partial radio link failure of a carrier occurs, a new measurement event may be defined to trigger the transmission of an RRC measurement report.

The WTRU100 may stop UL transmission and refrain from pairing UL carriers with the failed DL carrier. The pairing with the DL carrier is a pairing for hybrid automatic repeat request (HARQ) feedback or a pairing for PDCCH scheduling. Scheduling for the UL carrier is prohibited if all DL carriers that can provide scheduling for the UL carrier fail.

The WTRU100 may stop UL transmission and release resources on any UL carrier whose timing advance is adjusted with respect to DL carriers that have experienced partial radio link failure. Alternatively, this may occur when there are no other DL carriers for which the same timing advance can be applied without radio link problems. If there is at least one such DL carrier, the WTRU100 continues with UL transmission and adjusts the timing advance with respect to that DL carrier.

Further, the WTRU100 may take the same action as if the timing advance timer had expired for any UL carrier whose timing advance was adjusted with reference to the DL carrier that experienced a partial radio link failure.

Implicit eNB detection may be based on UL Discontinuous Transmission (DTX) detection for PUCCH or HARQ feedback corresponding to DL carriers.

When a partial radio link failure is detected, a partial MAC reset may be applied to the DL carrier of interest and the HARQ processes associated with that DL carrier are flushed. Furthermore, the same method applies to any UL carrier where transmission is stopped and resources are released, according to one of the above schemes.

When the WTRU100 detects a partial radio link failure, it indicates to the network a cell Identification (ID) or carrier ID (corresponding to the carrier on which the radio link failure occurred), and also a list of other cells that the WTRU is camped on (if different carriers are from different cells in the network). Alternatively, if a partial radio link failure occurs, the WTRU100 may indicate the cell ID or carrier ID of the last PCC, as well as the cell ID or carrier ID of the new PCC.

It is possible that one of the carriers (or one of the PDCCH carriers) has a specific role (e.g., PPC, anchor carrier or DL carrier corresponding to "special cell" or "serving cell") with respect to the allocation of specific security parameters. If a partial radio link failure occurs in the "serving cell", the WTRU100 automatically selects a new "serving cell" in one of the remaining carriers and informs the network of the selection. Alternatively, the WTRU may report that a partial radio link failure occurred in the serving cell and may perform a reallocation based on an indication from the network. After reassigning the serving cell, the WTRU100 may act as if a security parameter has changed, involving a re-establishment of a Packet Data Convergence Protocol (PDCP) entity.

Primary reconstruction procedure

When the WTRU detects that a radio link failure occurs on the DL primary carrier and monitoring of other non-primary carriers indicates that one or more carriers are acceptable, a primary re-establishment procedure may be triggered, where a synchronization indication for one or more carriers is sent to higher layers. As previously defined, the process may be applied to PCC only. Alternatively, the procedure may be applied to any "PDCCH carrier". The primary re-establishment procedure is limited to a subset of DL carriers within the cell that the WTRU100 is configured to actively receive.

As shown in fig. 9, an RRC primary carrier reestablishment procedure is implemented to request the network 900 to change the DL primary carrier, the network 900 including a WTRU 905 and an eNB 910. In the initial state, DL primary carrier 955 is in a condition of radio link failure, DL non-primary carriers 960 and 965 have a synchronization indication, UL carrier 970 is paired with DL primary carrier 955 and UL carrier 975 is paired with DL non-primary carrier 960.

Once the WTRU 905 switches to a new carrier, the WTRU 905 implicitly designates one of the carriers as the new primary carrier, (e.g., based on signal strength or signal quality). Since the network 900 may maintain the context of the WTRU for a limited duration after the radio link failure procedure has occurred, the same set of system parameters (e.g., Random Access Channel (RACH), access class barring, or any other suitable parameters) as previously applied on the primary carrier may be applied to the new primary carrier used by the WTRU 905. Once the WTRU 905 switches to the new primary carrier, the WTRU 905 may implicitly use the information obtained from the old primary carrier. Alternatively, the WTRU 905 may read the selected System Information Blocks (SIBs) and then continue to read the RACH when accessing a new primary carrier. Alternatively, upon switching its primary carrier through the 1-bit field, the network 900 may inform whether the network 900 should continue to use the parameters from the current primary carrier.

The WTRU 905 transmits a Scheduling Request (SR) on the PUCCH of the UL carrier 975 paired with the DL non-primary carrier 960, the DL non-primary carrier 960 having a synchronization indication. Alternatively, the RACH procedure may be applied to generate the SR, if necessary. If there is another primary carrier in the cell that does not have radio link problems and that applies the same timing advance, then no RACH procedure is needed.

The WTRU 905 then starts searching for WTRU-specific search spaces for DL non-primary carriers 960 based on rules similar to LTE release 8(R8) to find PDCCH candidates. Since Downlink Control Information (DCI) format 0 contains UL grant of the UL Shared Channel (SCH) in UL carrier 975, the PDCCH candidates match the cell radio network temporary identifier (C-RNTI) of WTRU 905.

The WTRU 905 sends an RRC message on the UL-SCH in UL carrier 975 requesting the network to transition the DL primary carrier 955 to the DL carrier 960.

The hybrid automatic repeat request (HARQ) buffer remains intact throughout the process.

Once the WTRU 905 switches to a new carrier, the WTRU 905 continuously monitors the previous primary carrier for which a radio link failure occurred and reports to the network if a predefined number of synchronization indications occurred or the signal strength on the previous primary carrier was above a certain threshold. This is useful if the network has allocated the primary carrier on which the WTRU is camped to the WTRU as the "preferred" component carrier.

In case no PDCCH is received after a predefined number of subframes, another SR is sent on UL carrier 975.

If a predefined number of SRs are transmitted on UL carrier 975 without receiving a PDCCH with DCI format 0, the SR is transmitted on another UL carrier paired with a DL non-primary carrier with a synchronization indicator (in which case the SR may be transmitted on UL carrier 970). If no PDCCH with DCI format 0 is received from any DL non-primary carrier, the procedure fails and the WTRU 905 may perform the existing RRC reestablishment procedure.

Once the change of DL primary carrier is completed, the network 1000 changes the UL primary carrier, or this may be performed implicitly based on which UL carrier is paired with the new DL primary carrier.

Asymmetric situation

To handle asymmetric cases, such as one UL carrier and N DL carriers, specific PUCCH resources (different cyclic shifts) may be indicated by higher layers to indicate an allocation where a specific scheduling request should be received on multiple different DL carriers. For example, UL allocations for scheduling requests transmitted using PUCCHx and PUCCHy are received on the DL primary carrier, but allocations in response to the SR transmitted from PUCCHz and PUCCHz +1 are received on DL carrier n and DL carrier n +1, respectively.

Alternatively, another new type of scheduling request may be used in LTE-a, with an explicit indication that no allocation should be received on the primary carrier. As shown in fig. 10, an RRC primary carrier reestablishment procedure may be implemented to request the network 1000, which network 1000 includes a WTRU1005 and an eNB1010, to change the DL primary carrier. In the initial state, the DL primary carrier 1055 is in a radio link failure condition, DL non-primary carriers 1060 and 1065 have a synchronization indication, and UL carrier 1070 is established.

Once the WTRU1005 switches to a new carrier, the WTRU1005 implicitly designates one of the carriers as the new primary carrier, (e.g., based on signal strength). Since the network 1000 may preserve the context of the WTRU for a limited duration after the radio link failure procedure occurs, the same set of system parameters as used on the previous primary carrier (e.g., RACH, access class barring, or any other suitable parameters) are applied to the new primary carrier used by the WTRU 1005. Once the WTRU1005 switches to the new primary carrier, the WTRU1005 may implicitly use the information obtained from the old primary carrier. Alternatively, when accessing a new primary carrier, the WTRU1005 may read the selected System Information Block (SIB) and then continue to read the RACH. Alternatively, when switching its primary carrier through a 1-bit field, the network 1000 may inform whether the network 1000 should continue to use the parameters from the current primary carrier.

The WTRU1005 sends a new type of SR on the PUCCH of UL carrier 1070 with another bit to indicate that the allocation should not be received on the DL primary carrier 1055. Alternatively, a Physical Random Access Channel (PRACH) procedure may be applied to generate the SR, if needed.

The WTRU1005 starts searching for WTRU-specific search spaces for all DL non-primary carriers 1060 and 1065 with synchronization indications based on rules similar to LTE R8 to find PDCCH candidates. Since DCI format 0 contains an UL grant for the UL-SCH in UL carrier 1070, the PDCCH candidates match the C-RNTI of WTRU 1005.

The WTRU1005 sends an RRC message on the UL-SCH in UL carrier 1070 requesting the network to switch the DL primary carrier 1055 to DL carrier 1060.

In the whole process, the HARQ buffer is intact.

Another approach is based on a new MAC CE command indicating a DL primary carrier change. The MAC CE order may explicitly specify the new DL primary carrier. Referring again to fig. 10, the WTRU1005 selects either the DL non-primary carrier 1060 or the DL non-primary carrier 1065 based on the best signal strength, or the DL carrier indicating that a continuous synchronization indication was detected first. In any event, MAC CE commands may also be sent instead of RCC messages. In this case, the acknowledgement may be sent by the MAC CE instead of an implicit acknowledgement based on PDCCH reception.

The RRC primary re-establishment procedure may be part of a larger intra-cell handover procedure. The configuration (e.g., DRX cycle, semi-persistent scheduling (SPS), PUCCH/PDCCH and HARQ entity/process) applied on the source DL and possibly UL primary carriers may be transferred to the new target primary carrier (once the new carrier is established). In contrast to inter-cell handover, it is in practice possible to avoid RLC and PDCP re-establishment, although MAC reset flushing of HARQ buffers seems to be a necessary consequence.

Once the WTRU1005 switches to a new carrier, the WTRU1005 continuously monitors the previous primary carrier for which a radio link failure occurred and reports to the network if a predefined number of synchronization indications occurred or the signal strength on the previous primary carrier was above a certain threshold. This is useful if the network 1000 has allocated the primary carrier occupied by the WTRU1005 as the "preferred" component carrier to the WTRU 1005.

Recovery procedure

The WTRU1005 may autonomously consider the carriers for which partial radio link failure has occurred to be "deactivated" and remove them from the connection configuration state in RRC. Alternatively, the WTRU1005 performs these actions upon receiving an explicit notification from the network 1000. In the latter case, the WTRU1005 considers the carrier to be in a "dormant" state and performs special monitoring and recovery actions as described below.

In case radio link failure is detected on all carriers in the network, the WTRU sends to the network cell IDs or carrier IDs corresponding to all component carriers, or cell IDs or carrier IDs corresponding to the primary component carrier.

For each detected downlink radio link failure carrier, a carrier identifier (numbered intracell) or radio frequency channel number (e.g., E-UTRA absolute radio frequency channel number (EARFCN)) broadcast in system information of the LTE-a cell or indicated in a dedicated carrier allocation message is sent in an RRC message (e.g., an RRC connection reestablishment message or other RRC level message) to the LTE-a eNB or network to facilitate the LTE-a eNB to begin a recovery action (e.g., reassigning a data path or control path to one or more other downlink carriers, carriers that are new or existing for the WTRU of interest within the LTE-a cell).

It is also necessary to indicate the radio link failure cause to the eNB or network for distinguishing whether the root cause of the problem is a detected out-of-sync, RLC unrecoverable error, PDCP integrity problem or other related problem.

In the same case, the WTRU may also indicate the signal strength and/or signal quality of the DL carrier that has been actively received (and optionally some other DL carriers monitored for the event) to facilitate eNB carrier re-establishment decisions or handover decisions. If the carrier that detects the radio link failure comprises a PDCCH carrier, and if the LTE-a cell is configured with PDCCH carriers of more than one of the cells, the WTRU needs to include measurements of another PDCCH carrier.

When a detected carrier of a radio link failure is signaled in an RRC message, the affected data plane Protocol Data Unit (PDU) sequence numbers in the PDCP and/or RLC levels, the transmit and receive (which may also be included in their respective HARQ process identifications) transport block sizes and their transport channel or logical channel numbers, and other related channel configuration parameters. However, status PDUs in the affected data plane, PDCP or RLC level, may also be generated and sent to the eNB, if still possible to prepare for data recovery behavior. If the detected carrier of the radio link failure carries a control plane bearer, the related RRC, PDCP or RLC sequence number needs to be sent.

The WTRU may continue to transmit and receive, UL and DL, on other unaffected carriers, while deferring transmission or reception of carriers UL and DL or DL with affected radio link failures until a new allocation of affected data path channels is received from the eNB.

Once the WTRU has sent an RRC message for a full or partial radio link failure detection/re-establishment request, the WTRU starts a timer 325. If the WTRU does not receive an eNB or network message in reply to the radio link failure detection/re-establishment request message at the expiration of the timer 325, the WTRU may retransmit the same message again. The retransmission may be repeated a predefined number of times and thereafter the WTRU will release all of its radio resources and enter idle mode.

Upon detecting a partial radio link failure, the WTRU performs one or a combination of the following to ensure that it can receive subsequent signaling from the network from other non-failed carriers. The WTRU may activate or reactivate one or more carriers that are configured but deactivated or in a dormant state (if such a state is defined). The WTRU continuously monitors the PDCCH for other carriers configured with PDCCH reception. Each subframe is a fraction of the active time of these carriers until a stop condition occurs. Alternatively, the WTRU defers its normal DRX behavior on these carriers. Optionally, this applies to the specific carriers configured by the network for this behavior, or to carriers with a periodic on-duration (on-duration) of a period above a threshold, provided DRX is configured on a per carrier basis, or without any periodic on-duration.

The stop condition corresponds to one or a subset of the following events: receiving a reconfiguration message from the network, receiving a MAC PDU from the network from any Control Channel (CC), recovering carriers on which a partial radio link failure occurred, and detecting a full radio link failure.

With knowledge that the WTRU applies the following behavior, once a partial radio link failure is detected, the network knows that it can send subsequent signaling on these carriers regardless of whether these carriers are in the active state or DRX state.

Optionally, the above activation and/or DRX suspension may be applied when no PDCCH has been configured for other carriers that has not failed and one or a combination of the following rules is not satisfied: the carrier is activated or in an active state (if there is an "active/inactive" state); or the carrier is configured with a periodic on-state duration, with a possible additional condition being that the period is below a threshold.

The network may provide UL grant on one of the DL active carriers without radio problems or partial radio link failure conditions and the WTRU starts the RACH procedure using RACH configuration broadcast from one of the DL carriers without radio problems. This may allow the network to identify that the DL carrier (or one of the DL carriers) that has advertised the RACH resources that the WTRU uses for its random access procedure and therefore should send any UL grant from that (or one of) DL carrier(s) is still in good radio conditions.

Alternatively, the RACH procedure is initiated when a particular DL carrier (e.g., "special cell") fails. The WTRU may request to initiate a RACH procedure using a RACH configuration broadcast from that particular carrier (or "special cell") unless a radio problem is detected on that carrier. Thus, the network understands that a radio problem has occurred on a "special cell" based on the WTRU initiating the RACH procedure using resources (UL carrier and preamble) that are not broadcast from the special cell. Based on this information, the network can take action in place of the special cell, e.g., initiate RRC reconfiguration with or without mobility.

If one of the WTRU's configured carriers is used to perform a specific role (e.g., PCC, anchor carrier, or DL carrier corresponding to "special cell" or "serving cell"), a specific action may need to be taken in case of failure of that carrier. The following procedure applies when one of the following conditions is satisfied: (a) performing radio link monitoring on a per carrier basis (as described above) and the failed carrier or one of the carriers corresponds to a special cell (when at least one carrier still has not failed), or (b) performing radio link monitoring for the special cell or PCC and declaring a radio link failure, but the signal quality from the other carriers with which the WTRU is configured is still acceptable.

In one approach, the WTRU initiates an RRC connection reestablishment procedure (assuming security is activated) when the special cell or PCC fails. However, the process is modified. For example, the following modifications may occur:

1) instead of performing a normal cell selection procedure, the WTRU selects a cell corresponding to one of the carriers for which there is no radio problem configured. The WTRU may choose the carrier based on a predetermined or pre-signaled priority, or based on signal quality, or by assigning a priority to the DL carrier paired with the UL carrier where the PUCCH resource exists, or randomly. The selected cell may be considered as a new special cell (or PCC) that is "recommended" by the WTRU. If all the carriers configured by the WTRU fail, the WTRU returns to cell selection.

2) The WTRU sends the RRC connection reestablishment message through a RACH procedure initiated using resources broadcast by the selected cell (as described above). Optionally, this step is performed if there is no PUCCH resource on the paired UL carrier.

3) The WTRU sends an RRC connection reestablishment message by first sending a scheduling request directly on any available PUCCH (i.e., without performing a random access procedure), or on a PUCCH allocated on an UL carrier paired with a DL carrier without radio problems.

4) The PDCP, RLC and/or MAC sublayers may not be re-established or reset.

5) The secret key may not be modified.

6) The WTRU may include information about the signal quality or signal strength of one or a subset of the DL carriers. Optionally, the information may be reported for a DL carrier corresponding to the cell selected by the WTRU. This cell is normally reconfigured by the network as a new "special cell".

In another approach, the WTRU does not initiate the RRC connection reestablishment procedure when a failure of a "special cell" is detected. Instead, the WTRU performs one or a combination of the following actions:

1) the random access procedure is initiated using RACH resources broadcast by the DL carrier (as described herein) that has not failed. The DL carrier from which the WTRU chooses RACH resources (UL carrier, preamble) may be considered to correspond to the new special cell that the WTRU "recommends". Following this procedure, the network may proceed with RRC reconfiguration modified for the particular cell (with or without mobility), typically corresponding to WTRU recommendations. Optionally, this step is performed if PUCCH resources are not allocated to the UE or allocated to the WTRU on the UL carrier paired with the DL carrier that has not failed.

2) Any combination of the above. With these actions, the network continues to perform modified RRC reconfiguration (with or without mobility) for the particular cell.

After a partial radio link failure of a carrier, the WTRU may use one or a combination of the following methods to facilitate the final recovery of the carrier if radio conditions improve.

In one approach, after the radio link recovery timer 325 (e.g., T310) expires, the WTRU targets Q_inAnd Q_outThe threshold value continuously evaluates the quality and the physical layer correspondingly continuously sends synchronization and out-of-sync indications to higher layers, but the periodicity (and measurement duration) of these indications can be increased compared to the periodicity before partial radio link failure to avoid unnecessary waste of battery energy. For example, the parameters for in-sync and out-of-sync indication measurements and reporting may be restored to correspond to the DRX configuration of the carrier. Alternatively, the periodicity of synchronization or non-synchronization may be restored to a predefined value or a value (possibly carrier-specific) previously signaled by higher layers (broadcast or dedicated).

The WTRU determines that a failed carrier attempt can be recovered if a small fraction of the most recent synchronization indications is above a threshold, or alternatively if a certain minimum number of consecutive synchronization indications is obtained. These thresholds may also be predefined values or values previously transmitted by higher layers. When this occurs, the WTRU may perform one or a combination of the following actions to request the network to resend the transmission on the failed carrier.

The WTRU ensures that it has valid system information belonging to the failed carrier. This may be achieved by comparing the current value tag of the system information with the previously stored value tag of the system information for that carrier. Optionally, the WTRU may retrieve all system information from the broadcast of the carrier.

The WTRU may send an RRC message to indicate recovery of the carrier. Such RRC messages may be sent on any carrier or any carrier that has not failed. It consists of a measurement report (in which case a new event can be defined to trigger the report). In this case, the WTRU waits to receive an acknowledgement message from the network before considering the success of the recovery. The acknowledgement may be an explicit RRC message or an implicit detection by a PDCCH order on the DL carrier with WTRU identity. The confirmation message may include a value tag of the system information (belonging to the failed carrier) to facilitate verification that the WTRU still has valid system information, or the WTRU may retrieve the current value tag to ensure it has valid system information.

The WTRU may initiate a RACH procedure based on RACH parameters specific to the failed carrier. A successful RACH procedure (where the RACH response is from the failed carrier) can then be effectively translated in a successful recovery.

When a successful recovery occurs, the WTRU may recover activity on the previously failed carrier and evaluate in particular the synchronization/de-synchronization according to the parameters used before the failure. If the UL carrier is paired with the recovered DL carrier for HARQ feedback or scheduling on PDCCH, the associated UL carrier is also recovered.

Optionally, the WTRU evaluates the in-and out-of-sync indications for a limited duration, after which the in-and out-of-sync indications are not measured. This may be accomplished by starting a new timer when T310 expires and stopping the in/out-of-sync evaluation when the timer expires. The value of the timer may be predefined or sent by higher layers.

Alternatively, the WTRU may evaluate the in-synchronization and out-of-synchronization indications if or as long as the Reference Signal Received Power (RSRP) or Reference Signal Received Quality (RSRQ) measurements of the carriers are above a threshold, which may be predefined or sent by higher layers.

As described above, the WTRU may notify the network when it stops evaluating synchronization and dyssynchrony due to a timer expiring or RSRP/RSRQ falling below a threshold. Alternatively or additionally, the WTRU may operate as if the carrier is "deactivated" and delete the carrier from its connection configuration state in the RRC.

The WTRU may permanently stop measuring in-and-out-of-sync in case the network explicitly deactivates the failed carrier.

Alternatively, if no new timer is applied, the WTRU continues to resume until the network explicitly informs the WTRU to disable the resume process. In this case, whenever the WTRU detects the recovery of the DL carrier, it indicates reactivation through MAC or RRC signaling.

The network attempts to recover the failed carrier by sending DL assignments to the WTRU from time to time. Such DL allocation may, for example, consist of a request to initiate a RACH procedure providing dedicated RACH parameters and possibly system information related signaling (e.g., value flags or Information Elements (IEs) of system information belonging to failed carriers).

The WTRU may monitor the DL allocation from the network and have certain constraints to prevent excessive battery consumption. For example, the following limitations may be used alone or in combination.

The WTRU may monitor the DL allocation in a particular subframe according to a known pattern that is predefined or pre-sent by higher layers. The pattern may be periodic and may or may not correspond to a DRX configuration of WTRUs belonging to a failed carrier before a partial radio link failure occurred.

The WTRU may monitor the DL allocation if the signal strength and/or signal quality on the carrier is above a threshold, which is predefined or pre-sent by higher layers.

The WTRU may monitor the DL allocation for a certain period of time after a partial radio link failure occurs. The WTRU may consider the carrier as "deactivated" and update its RRC connection configuration context accordingly after the time period.

The WTRU may monitor the DL allocation for a certain period of time after requesting recovery of the failed carrier by sending a message to the network (if the scheme is used in conjunction with the previous scheme).

When the WTRU decodes an allocation from the network on the failed carrier, the WTRU may immediately consider the recovery to be successful. Alternatively, the WTRU may consider the recovery to be successful after completing the RACH procedure after receiving the DL assignment.

When successful recovery occurs, the WTRU deletes the monitored restriction conditions and recovers monitoring the PDCCH according to the configuration used before the failure.

In another approach, the WTRU starts performing RSRP and/or RSRQ measurements on failed carrier frequencies according to certain predetermined measurement configurations. The WTRU may also discontinue measurements performed according to the measurement configuration defined for that frequency (if such a configuration exists) before a partial radio link failure occurs. The predetermined measurement configuration (applicable to the partial radio link failure status of a carrier) may be provided after configuring and/or activating the carrier. Alternatively, it may be a common measurement configuration applicable to any carrier for which a partial radio link failure has occurred, either predefined or provided by dedicated or broadcast signaling. Alternatively, the measurement configuration is provided by the network (or notified by the WTRU) when a partial radio link failure is detected.

A measurement report from the measurement configuration may be sent to one of the other carriers for which a failure has not occurred. Based on the measurement report, the network initiates recovery of the failed carrier using RRC signaling and/or as per the previous embodiments.

In a system using carrier aggregation, a WTRU may initiate a RACH procedure in connected mode from an UL carrier to regain synchronization with transmissions from the UL carrier. This may occur when the WTRU is still synchronized into the network for its transmission from the UL carrier.

When a random access problem occurs with a RACH procedure initiated from one of the configured UL carriers, the radio link failure condition for carrier aggregation may be modified based on one of the following methods.

In one approach, when no recovery timer 325 (e.g., T300, T301, T304, or T311) is running, and if the WTRU is not synchronizing for transmissions from any UL carrier, the WTRU considers that a radio link failure is to be detected when a random access problem occurs. Thus, the timing advance timer is not running for any UL carrier.

In another approach, the WTRU considers a radio link failure to be detected in a random access problem when no recovery timer 325 (e.g., T300, T301, T304, or T311) is running and if the random access problem occurs after the last expiration of a time advance timer applicable to the carrier (i.e., since the WTRU last lost synchronization with the transmission of the UL carrier) for all or a subset of the other UL carriers (or configured by the network) that may initiate a RACH procedure.

Referring again to fig. 3, the WTRU100 monitors for radio link failure. The WTRU100 includes a processor 255 configured to determine a primary DL carrier from a set of component carriers configured or activated for the WTRU 100.

First counter 330 in WTRU100₁May be configured to count out-of-sync indications from the primary DL carrier. Recovery timer 325 in WTRU100₁Configurable to indicate out-of-sync from primary DL carrierStarting with a predefined number of counts, by the first counter 330₁And (4) determining. Second counter 330 in WTRU100₂Is configured to count synchronization indications from the primary DL carrier.

In the event that the second counter does not count a predefined number of synchronization indications from the primary DL carrier before the recovery timer expires, a radio link failure is declared.

An RRC connection reestablishment procedure may be initiated in which the WTRU100 selects a cell corresponding to one of the component carriers for which there is no radio problem.

The RRC connection reestablishment message may be sent by initiating a Random Access Channel (RACH) procedure using resources broadcast by the cell selected by the WTRU100, which corresponds to one of the component carriers for which there is no radio problem.

The SR may be transmitted on the PUCCH, and an RRC connection reestablishment message may be transmitted. The PUCCH may be allocated on an UL carrier paired with a DL carrier without radio problems.

A primary DL carrier may be selected from a plurality of DL carriers, wherein the selected primary DL carrier has a largest coverage among the plurality of DL carriers.

A primary DL carrier may be selected from a plurality of DL carriers, wherein the selected primary DL carrier provides PDCCH signaling.

The primary DL carrier may be selected from a plurality of DL carriers that are at DRX active time based on a predefined or transmitted priority.

The primary DL carrier may be obtained from the network through RRC signaling.

In the event that the second counter counts a predefined number of synchronization indications from the primary DL carrier before the recovery timer expires, a radio link failure is declared, and a connection reestablishment procedure or an RRC connection release procedure may be performed if the radio link failure is declared.

While the timer 325 is recovering₁Recovery timer 325 in WTRU100 on a condition that a predefined number of synchronization indications are received from the primary carrier before expiration₁May be stopped.

The primary reestablishment procedure is performed in the event that a predefined number of synchronization indications are not received from the primary carrier before the recovery timer expires.

Referring again to fig. 3, the WTRU100 includes a plurality of out-of-sync indication counters (e.g., 330)₁，330₂，330₃) Configured to count an out-of-sync indication from each of a plurality of PDCCH carriers activated for the WTRU. Recovery timer 325 in WTRU100₁May be configured to start upon counting a predefined number of out-of-sync indications from a particular one of the PDCCH carriers. Synchronization indication counters (e.g., 330)₄) May be configured to count synchronization indications from a particular PDCCH carrier.

At recovery timer 325_{1 is at}In the event that the predefined number of synchronization indications expires before counting, a partial radio link failure associated with a particular PDCCH may be declared.

Examples

1. A method implemented by a wireless transmit/receive unit (WTRU) for monitoring for radio link failure, the method comprising:

a primary Downlink (DL) carrier is determined among a set of component carriers configured or activated for the WTRU.

2. The method of embodiment 1, further comprising:

counting an out-of-sync indication from a primary DL carrier using a first counter in the WTRU;

starting a recovery timer in a WTRU on a condition that a predefined number of out-of-sync indications from a primary DL carrier are counted, wherein the counting is determined by a first counter; and

a synchronization indication from the primary DL carrier is counted using a second counter in the WTRU.

3. The method of embodiment 2, further comprising:

declaring a radio link failure if the second counter does not count a predefined number of synchronization indications from the primary DL carrier before the recovery timer expires; and

a Radio Resource Control (RRC) connection re-establishment procedure is initiated in which the WTRU selects a cell corresponding to one of the component carriers in which no radio problems have occurred, wherein no radio problems exist in the one of the component carriers.

4. The method of embodiment 2, further comprising:

declaring a radio link failure if the second counter does not count a predefined number of synchronization indications from the primary DL carrier before the recovery timer expires; and

transmitting a Radio Resource Control (RRC) connection reestablishment message by initiating a Random Access Channel (RACH) procedure using resources broadcast by a cell selected by the WTRU, wherein the cell selected by the WTRU corresponds to one of the component carriers in which there is no radio problem.

5. The method of embodiment 2, further comprising:

declaring a radio link failure if the second counter does not count a predefined number of synchronization indications from the primary DL carrier before the recovery timer expires; and

transmitting a Scheduling Request (SR) on a Physical Uplink Control Channel (PUCCH); and

a Radio Resource Control (RRC) connection reestablishment message is transmitted.

6. The method of embodiment 5 wherein the PUCCH is allocated on an Uplink (UL) carrier that is paired with a DL carrier that has no radio problems.

7. The method as in any one of embodiments 1-6, wherein the primary DL carrier is selected from a plurality of DL carriers, wherein the selected primary DL carrier has a largest coverage among the plurality of DL carriers.

8. The method as in any one of embodiments 1-6, wherein a primary DL carrier is selected from a plurality of DL carriers, wherein the selected primary DL carrier provides Physical Downlink Control Channel (PDCCH) signaling.

9. The method as in any one of embodiments 1-6, wherein the primary DL carrier is selected from a plurality of DL carriers that are in Discontinuous Reception (DRX) active time based on a predefined priority or a signaled priority.

10. The method as in any one of embodiments 1-6, wherein the primary DL carrier is obtained from the network through Radio Resource Control (RRC) signaling.

11. The method according to any of embodiments 2-10, further comprising:

declaring a radio link failure if the second counter does not count a predefined number of synchronization indications from the primary DL carrier before the recovery timer expires; and

in case a radio link failure is declared, a connection re-establishment procedure or a Radio Resource Control (RRC) connection release procedure is performed.

12. The method according to any of embodiments 2-10, further comprising:

the recovery timer is stopped in the event that a predefined number of synchronization indications are received from the primary carrier before the recovery timer expires.

13. The method according to any of embodiments 2-10, further comprising:

the primary reestablishment procedure is performed in the event that a predefined number of synchronization indications are not received from the primary carrier before the recovery timer expires.

14. A method implemented by a wireless transmit/receive unit (WTRU) for monitoring for radio link failure, the method comprising:

counting an out-of-sync indication from each of a plurality of Physical Downlink Control Channel (PDCCH) carriers activated for the WTRU;

starting a recovery timer in a WTRU on a condition that a predefined number of out-of-sync indications from a particular one of the PDCCH carriers is counted; and

the synchronization indications from a particular PDCCH carrier are counted.

15. The method of embodiment 14, further comprising:

declaring a partial radio link failure associated with a particular PDCCH if a recovery timer expires before counting a predefined number of synchronization indications.

16. A wireless transmit/receive unit (WTRU) for monitoring for radio link failure, the WTRU comprising:

a processor configured to determine a primary Downlink (DL) carrier in a set of component carriers configured or activated for a WTRU;

a first counter configured to count out-of-sync indications from a primary DL carrier;

a recovery timer configured to start if a predefined number of out-of-sync indications from a primary DL carrier is counted, the count being determined by a first counter; and

a second counter configured to count synchronization indications from the primary DL carrier.

17. The WTRU of embodiment 16 wherein on a condition that the second counter does not count a predefined number of in-sync indications from the primary DL carrier before the recovery timer expires, a radio link failure is declared and a Radio Resource Control (RRC) connection re-establishment procedure is initiated, wherein the WTRU selects a cell corresponding to one of the component carriers in which there is no radio problem.

18. The WTRU of embodiment 16 wherein on a condition that the second counter does not count a predefined number of in-sync indications from the primary DL carrier before the recovery timer expires, a radio link failure is declared and a Radio Resource Control (RRC) connection re-establishment message is transmitted by initiating a Random Access Channel (RACH) procedure using resources broadcast by a WTRU-selected cell with a cell of one of the component carriers in which there is no radio problem.

19. The WTRU of embodiment 16 wherein on a condition that the second counter does not count a predefined number of synchronization indications from the primary DL carrier before the recovery timer expires, a radio link failure is declared and a Scheduling Request (SR) is transmitted on a Physical Uplink Control Channel (PUCCH) and a Radio Resource Control (RRC) connection reestablishment message is transmitted.

20. The WTRU of embodiment 19 wherein the PUCCH is allocated on an Uplink (UL) carrier paired with a DL carrier without radio problems.

21. A WTRU as in any one of embodiments 16-20 wherein a primary DL carrier is selected from a plurality of DL carriers, wherein the selected primary DL carrier has a maximum coverage among the plurality of DL carriers.

22. A WTRU as in any one of embodiments 16-20 wherein a primary DL carrier is selected from a plurality of DL carriers, wherein the selected primary DL carrier provides Physical Downlink Control Channel (PDCCH) signaling.

23. The WTRU as in any one of embodiments 16-20 wherein the primary DL carrier is selected from a plurality of DL carriers in Discontinuous Reception (DRX) active time based on a predefined priority or a signaled priority.

24. A WTRU as in any one of embodiments 16-20 wherein a primary DL carrier is acquired from a network through Radio Resource Control (RRC) signaling.

25. The WTRU as in any one of embodiments 16-24 wherein a radio link failure is declared on a condition that the second counter does not count a predefined number of in-sync indications from the primary DL carrier before the recovery timer expires, and a connection re-establishment procedure or a Radio Resource Control (RRC) connection release procedure is performed on a condition that the radio link failure is declared.

26. The WTRU as in any one of embodiments 16-25 wherein the recovery timer is stopped on a condition that a predefined number of synchronization indications are received from the primary carrier before the recovery timer expires.

27. The WTRU as in any one of embodiments 16-26 wherein the primary re-establishment procedure is performed on a condition that a predefined number of synchronization indications are not received from the primary carrier before the recovery timer expires.

28. A wireless transmit/receive unit (WTRU) for monitoring for radio link failure, the WTRU comprising:

a plurality of out-of-synchronization indication counters configured to count out-of-synchronization indications from each of a plurality of Physical Downlink Control Channel (PDCCH) carriers activated for the WTRU;

a recovery timer configured to start if a predefined number of out-of-sync indications from a particular one of the PDCCH carriers is counted; and

a synchronization indication counter configured to count synchronization indications from a specific PDCCH carrier.

29. The WTRU of embodiment 28 wherein a partial radio link failure associated with a particular PDCCH is declared on a condition that a recovery timer expires before a predefined number of in-sync indications are counted.

Even though the features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements. The methods or flow charts provided herein may be implemented in a counter program, software, or firmware that may be incorporated into a counter-readable storage medium for execution by a general purpose counter or processor. Examples of the counter machine-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).

Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a Data Signal Processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit, and/or a state machine.

A processor in association with software is used to implement a radio frequency transceiver for a Wireless Transmit Receive Unit (WTRU), User Equipment (UE), terminal, base station, Radio Network Controller (RNC), or any master counter. 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 phone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a speakerphone, a keyboard, and BluetoothA 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 (12)

1. A method implemented by a wireless transmit/receive unit (WTRU) for monitoring for radio link failure, the method comprising:

counting out-of-synch indications from each of a plurality of secondary component carriers activated for the WTRU and a primary component carrier, wherein the primary component carrier and the plurality of secondary component carriers are associated with different base stations;

starting a recovery timer in the WTRU on a condition that a predefined number of out-of-sync indications from at least one of the secondary component carriers is counted;

counting synchronization indications from the at least one of the secondary component carriers; and

sending a radio link failure associated with the at least one of the secondary component carriers to the primary component carrier on a condition that the recovery timer expires before a predefined number of synchronization indications is counted.

2. The method of claim 1, wherein the primary component carrier is obtained from a network through Radio Resource Control (RRC) signaling.

3. The method of claim 1, further comprising:

performing one of a connection re-establishment procedure or a Radio Resource Control (RRC) connection release procedure on a condition that a radio link failure is declared.

4. The method of claim 1, further comprising:

stopping the recovery timer on a condition that a predefined number of synchronization indications are received from the at least one of the secondary component carriers before the recovery timer expires.

5. The method of claim 1, further comprising:

performing a primary re-establishment procedure on a condition that a predefined number of synchronization indications are not received from the at least one of the secondary component carriers before the recovery timer expires.

6. A method implemented by a wireless transmit/receive unit (WTRU) for monitoring for radio link failure, the method comprising:

counting an out-of-sync indication from each of a plurality of Physical Downlink Control Channel (PDCCH) carriers activated for the WTRU, wherein the plurality of PDCCH carriers configured with a PDCCH include a primary carrier configured with a PDCCH associated with a base station and at least a secondary carrier configured with a PDCCH associated with another base station;

starting a recovery timer in the WTRU on a condition that a predefined number of out-of-sync indications from a particular PDCCH carrier of the plurality of PDCCH carriers is counted;

counting synchronization indications from the at least one secondary carrier configured with PDCCH; and

on a condition that the recovery timer expires before a predefined number of synchronization indications is counted, sending a radio link failure notification associated with the at least one secondary carrier configured with PDCCH to the primary carrier configured with PDCCH.

7. The method of claim 6, wherein the PDCCH configured primary carrier is selected from the plurality of carriers configured with PDCCHs, wherein the selected PDCCH configured primary carrier has a highest coverage in the plurality of carriers configured with PDCCHs.

8. The method of claim 6, wherein the primary carrier configured with PDCCH is selected from the plurality of carriers configured with PDCCH that are in Discontinuous Reception (DRX) active time based on a predefined or signaled priority.

9. The method of claim 6, wherein the primary carrier configured with the PDCCH is obtained from a network through Radio Resource Control (RRC) signaling.

10. The method of claim 6, further comprising:

performing one of a connection re-establishment procedure or a Radio Resource Control (RRC) connection release procedure on a condition that a radio link failure is declared.

11. The method of claim 6, further comprising:

stopping the recovery timer on a condition that a predefined number of synchronization indications are received from the at least one secondary carrier before the recovery timer expires.

12. The method of claim 6, further comprising:

performing a primary re-establishment procedure on a condition that a predefined number of synchronization indications are not received from the at least one secondary carrier configured with PDCCH before the recovery timer expires.