Abstract:
Embodiments of User Equipment (UE) and methods to support reception of content for use by an application supported by a Port Control Protocol (PCP) client are disclosed herein. The UE may receive, from a PCP server, a first portion of video content for use by the application during a first time period. The UE may send a PCP update message that includes one or more mobility status parameters. The UE may receive a second portion of the video content for use by the application during a second time period. The first and second portions of the video content may be received from a first and a second mobility anchor, which may operate as relays for the PCP server. The second mobility anchor may be determined based on a referred IP prefix included in the PCP date message.

Description:
PRIORITY CLAIMS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 14/279,562, filed May 16, 2014, which claims the benefit of priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application Ser. No. 61/879,014, filed Sep. 17, 2013 and to U.S. Provisional Patent Application Ser. No. 61/898,425, filed Oct. 31, 2013, each of which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments pertain to wireless cellular communications. Some embodiments relate to 3GPP LTE (Long-Term-Evolution) networks. Some embodiments relate to handover (HO) failure in 3GPP LTE networks. Some embodiments relate to radio-link failure (RLF) in 3GPP LTE networks. Some embodiments relate to handover failure recovery and radio-link failure recovery. 
       BACKGROUND 
       [0003]    When a mobile device (e.g., cell phone, UE) with an active or ongoing communication connection (e.g., voice or data call) is moving away from the coverage area of a first cell and entering the coverage area of a second cell, the communication connection is transferred to the second cell (target cell) in order to avoid link termination when the device gets out of coverage of the first cell (source cell). This “transfer of a connection” is termed handover or handoff. There may also be other reasons for performing a handover, such as load balancing. 
         [0004]    In cellular networks, particularly 3GPP LTE heterogeneous networks, handover is becoming increasingly important for device mobility, particularly with the increasing use smaller cells and coverage areas overlaid with smaller cells. Some new use cases that are currently under discussion in 3GPP&#39;s RAN working groups (WGs) are dealing with “small-cell enhancements”. The concept of small-cell enhancements involves deployment of additional low-power nodes under the macro-layer coverage for capacity extension and coverage improvement purposes. In small-cell enhancement situations, devices need to be handed over between these smaller and larger cells. 
         [0005]    One issue with handover is handover failure. Handover failure may occur during certain conditions, such as when a device is undergoing radio-link failure. When handover failure occurs, service interruption may occur. This service interruption may be unsuitable for many applications. 
         [0006]    Thus, there are general needs for techniques to reduce handover failure. There are general needs for techniques to reduce the service interruption time resulting during handover failure. There are also general needs for improved handover techniques that reduce handover failure with small-cell enhancements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  shows a portion of an end-to-end network architecture of an LTE network with various components of the network in accordance with some embodiments; 
           [0008]      FIG. 2  illustrates handover of user equipment (UE) from a serving cell to a target cell in accordance with some embodiments; 
           [0009]      FIG. 3  illustrates a radio-link monitoring (RLM) process in accordance with some embodiments; 
           [0010]      FIG. 4  illustrates a handover process in accordance with some embodiments; 
           [0011]      FIG. 5  illustrates non-contention based random access during handover in accordance with some embodiments; 
           [0012]      FIGS. 6A and 6B  illustrate early transmission of a random-access channel (RACH) 2 message and early termination of a radio-link failure (RLF) timer (T 310 ) in accordance with some embodiments; 
           [0013]      FIGS. 7A and 7B  illustrate early transmission of a RACH 2 message in accordance with some embodiments in comparison with a conventional transmission of a RACH 2 message; 
           [0014]      FIG. 8  illustrates a UE configured for early transmission of a RACH 2 message in accordance with some embodiments; and 
           [0015]      FIG. 9  illustrates a procedure for fast handover recovery in accordance with some embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in, or substituted for, those of other embodiments. Embodiments set forth in the claims encompass all available equivalents of those claims. 
         [0017]      FIG. 1  shows a portion of an end-to-end network architecture of an LTE network with various components of the network in accordance with some embodiments. The network  100  comprises a radio access network (RAN)  100  (e.g., as depicted, the E-UTRAN or evolved universal terrestrial radio access network) and the core network  120  (e.g., shown as an evolved packet core (EPC)) coupled together through an S1 interface  115 . For convenience and brevity sake, only a portion of the core network  120 , as well as the RAN  100 , is shown. The core network  120  includes mobility management entity (MME)  122 , serving gateway (serving GW)  124 , and packet data network gateway (PDN GW)  126 . The RAN  100  includes enhanced node B&#39;s (eNBs)  104  (which may operate as base stations) for communicating with user equipment (UE)  102 . The eNBs  104  may include macro eNBs and low power (LP) eNBs  106 . 
         [0018]    In accordance with some embodiments, UEs  102  may be arranged for fast handover failure recovery. In these embodiments, a UE  102  may be configured to initiate handover (HO) failure recovery by early transmission of a random-access channel (RACH) 2 message. In some embodiments, the early transmission of the RACH 2 message may occur when both a radio-link failure (RLF) timer (T 310 ) and a time-to trigger (TTT) timer are concurrently running. The RACH 2 message is a message transmitted on a random-access channel for radio-resource control (RRC) connection re-establishment. The RLF timer may be activated during radio-link failure as part of a radio-link monitoring (RLM) process and the TTT timer may be activated as part of a handover process. In these embodiments, HO failures that occur when a UE  102  experiences radio-link failure may be significantly reduced. Rather than waiting to transmit a RACH 2 message until after HO failure as part of the RLM process, embodiments disclosed herein provide for an early transmission of the RACH 2 message to initiate handover (i.e., transmission of the RACH 2 message with both the RLF timer and TTT timer are running and prior to the expiration of the RLF timer). In some embodiments, this may be the earliest possible RACH opportunity. These embodiments may help prepare a target cell for handover of the UE  102  and may reduce and/or eliminate service interruption time. These embodiments are discussed in more detail below. 
         [0019]    The MME  122  is similar in function to the control plane of legacy Serving GPRS Support Nodes (SGSN). The MME  122  manages mobility aspects in access such as gateway selection and tracking area list management. The serving GW  124  terminates the interface toward the RAN  100  and routes data packets between the RAN  100  and the core network  120 . In addition, it may be a local mobility anchor point for inter-eNB handovers and also may provide an anchor for inter-3GPP mobility. Other responsibilities may include lawful intercept, charging, and some policy enforcement. The serving GW  124  and the MME  122  may be implemented in one physical node or separate physical nodes. The PDN GW  126  terminates an SGi interface toward the packet data network (PDN). The PDN GW  126  routes data packets between the EPC  120  and the external PDN and may be a key node for policy enforcement and charging data collection. It may also provide an anchor point for mobility with non-LTE accesses. The external PDN can be any kind of IP network, as well as an IP Multimedia Subsystem (IMS) domain. The PDN GW  126  and the serving GW  124  may be implemented in one physical node or separated physical nodes. 
         [0020]    The eNBs  104  (macro and micro) terminate the air interface protocol and may be the first point of contact for a UE  102 . In some embodiments, an eNB  104  may fulfill various logical functions for the RAN  100  including but not limited to RNC (radio network controller functions) such as radio bearer management, uplink and downlink dynamic radio resource management and data packet scheduling, and mobility management. In accordance with embodiments, UEs  102  may be configured to communicate OFDM communication signals with an eNB  104  over a multicarrier communication channel in accordance with an OFDMA communication technique. The OFDM signals may comprise a plurality of orthogonal subcarriers. 
         [0021]    The S1 interface  115  is the interface that separates the RAN  100  and the EPC  120 . It is split into two parts: the S1-U, which carries traffic data between the eNBs  104  and the serving GW  124 , and the S1-MME, which is a signaling interface between the eNBs  104  and the MME  122 . The X2 interface is the interface between eNBs  104 . The X2 interface comprises two parts, the X2-C and X2-U. The X2-C is the control plane interface between the eNBs  104 , while the X2-U is the user plane interface between the eNBs  104 . 
         [0022]    With cellular networks, LP cells are typically used to extend coverage to indoor areas where outdoor signals do not reach well, or to add network capacity in areas with very dense phone usage, such as train stations. As used herein, the term low power (LP) eNB refers to any suitable relatively low power eNB for implementing a narrower cell (narrower than a macro cell) such as a femtocell, a picocell, or a micro cell. Femtocell eNBs are typically provided by a mobile network operator to its residential or enterprise customers. A femtocell is typically the size of a residential gateway or smaller and generally connects to a user&#39;s broadband line. Once plugged in, the femtocell connects to the mobile operator&#39;s mobile network and provides extra coverage in a range of typically 30 to 50 meters for residential femtocells. Thus, a LP eNB (e.g., such as eNBs  106 ) might be a femtocell eNB since it is coupled through the PDN GW  126 . Similarly, a picocell is a wireless communication system typically covering a small area, such as in-building (offices, shopping malls, train stations, etc.), or more recently in-aircraft. A picocell eNB can generally connect through the X2 link to another eNB such as a macro eNB through its base station controller (BSC) functionality. Thus, LP eNB may be implemented with a picocell eNB since it is coupled to a macro eNB via an X2 interface. Picocell eNBs or other LP eNBs may incorporate some or all functionality of a macro eNB. In some cases, this may be referred to as an access point base station or enterprise femtocell. 
         [0023]    In some embodiments, a physical downlink shared channel (PDSCH) may carry user data and higher-layer signaling to a UE  102 . A physical downlink control channel (PDCCH) may carry information about the transport format and resource allocations related to the PDSCH channel, among other things. It also informs a UE  102  about the transport format, resource allocation, and H-ARQ information related to the uplink shared channel. Typically, downlink scheduling (assigning control and shared channel resource blocks to UEs  102  within a cell) is performed at the eNB  104  based on channel quality information fed back from the UEs  102  to the eNB  104 , and then the downlink resource assignment information is sent to a UE on the control channel (PDCCH) used for (assigned to) the UE. 
         [0024]    The PDCCH uses CCEs (control channel elements) to convey the control information. Before being mapped to resource elements, the PDCCH complex-valued symbols are first organized into quadruplets, which are then permuted using a sub-block inter-leaver for rate matching. Each PDCCH is transmitted using one or more of these control channel elements (CCEs), where each CCE corresponds to nine sets of four physical resource elements known as resource element groups (REGs). Four QPSK symbols are mapped to each REG. The PDCCH can be transmitted using one or more CCEs, depending on the size of DCI and the channel condition. There may be four or more different PDCCH formats defined in LTE with different numbers of CCEs (e.g., aggregation level, L=1, 2, 4, or 8). 
         [0025]      FIG. 2  illustrates handover of a UE from a serving cell to a target cell in accordance with some embodiments. As illustrated in  FIG. 2 , an eNB  104  provides wireless communication services to communication devices, such as UE  102 , within cell  201 . The eNB  106  provides wireless communication services to communication devices within cell  203 . The eNB  106  may be a lower power eNB, although the scope of the embodiments is not limited in this respect. A handover may be performed from eNB  104  to eNB  106  to handover communications with the UE  102  from a serving cell, such as cell  201  to a target cell, such as cell  203  as part of a handover process when certain handover criterion are met. These embodiments are described in more detail below. 
         [0026]      FIG. 3  illustrates a radio-link monitoring (RLM) process  300  in accordance with some embodiments. During the RLM process  300 , a UE, such as UE  102 , monitors the radio link during radio-link monitoring phase  302 . In some embodiments, if an average wideband channel quality indicator (CQI) over a 200 ms time period goes below a threshold (e.g., Qout), an out-of-sync condition indication may be reported to the upper layers of the UE  102 . If N310 times consequent out-of-sync condition indications are received by the upper layers, then the RLF timer (T 310 )  310  is started (i.e., activated). If the average wideband CQI over 100ms goes above the threshold (e.g., Qin) and N311 times in-sync indications are reported before the RLF timer  310  expires, the RLF timer  310  is stopped and the radio link may be recovered. If the RLF timer  310  expires, a radio-link failure  305  may be declared and the UE  102  may enter the recovery phase  304  during which the RRC connection reestablishment procedure (resumption of SRB1 and activation of security) and a connection-reestablishment timer (T 311 )  311  are started. The RRC connection reestablishment procedure may succeed, for example, when the context of the UE  102  is available at a target cell  203 . If connection reestablishment is successful, the connection-reestablishment timer T 311  is stopped and the UE  102  may remain in active mode  308 . If connection reestablishment is not successful, timer T 311  may expire and the UE  102  may go into idle mode  309 . Connection reestablishment may include cell selection. As discussed in more detail below, in accordance with embodiments, the UE  102  may be arranged for fast handover failure recovery by early transmission of a RACH 2 message when both the RLF timer (T 310 )  310  and a TTT timer are concurrently running. 
         [0027]      FIG. 4  illustrates a handover process  400  in accordance with some embodiments. The handover process  400  may be initiated when a UE, such as UE  102  ( FIG. 1 ), is moving into a coverage area of another cell (i.e., cell  203  ( FIG. 2 )). In some embodiments, the handover process  400  may be governed by certain events (e.g., Events 1,2,3, and/or 4 as defined in one of the 3GPP LTE standards) which may be based on a reference signal received power (RSRP) or a reference signal received quality (RSRQ). For example, the UE  102  may periodically measure the RSRP of neighboring cells. When the entering condition of an Event is satisfied (i.e., the Event is triggered), the handover process may be started. The RSRP based Event A3 is may be used for the 3GPP LTE handover process. The parameters that govern the HO process (Event A3) are a time-to-trigger (TTT), an A3 offset, a hysteresis, cell specific offsets (Ocn), and a frequency specific offset (Ofn). In the example illustrated in  FIG. 4 , when the RSRP  406  of a target cell goes above the RSRP  404  of serving cell by a threshold  401 , the HO process may be initiated. The UE  102  may wait for a TTT period  402  (by starting the TTT timer) to send a measurement report at time  403  to the serving cell. The serving cell prepares the target cell via the X2 interface  115  (see  FIG. 1 ) and may send a HO command to the UE  102  at time  405 . The UE  102  may perform a contention (target not prepared) or non-contention (target prepared) based random access with the target cell by sending a RACH 2 message. As discussed in more detail below, in accordance with embodiments, the UE  102  may be arranged for fast handover failure recovery by early transmission of the RACH 2 message when both the RLF timer  310  (T 310 ) and a TTT timer are concurrently running. In these embodiments, the RACH 2 message is transmitted when the RLF timer  310  and the TTT timer are both active and before (prior to) the RLF timer  310  or the TTT timer expires. This is unlike conventional techniques in which HO failure recovery is initiated by sending a RACH 2 message after HO failure occurs when the connection reestablishment timer  311  (i.e., timer T 311 ) has already been activated. 
         [0028]      FIG. 5  illustrates non-contention based random access during handover in accordance with some embodiments. In these embodiments, the UE  102  may receive an RRC connection reconfiguration message  502  from the serving cell eNB  104 . The UE  102  may send a RACH 2 message  504  to the target cell eNB  106  ( FIG. 1 ) as part of the handover process  300  ( FIG. 3 ). When a RACH response message  506  is received from the target cell eNB  106 , the UE  102  may send the RRC connection reconfiguration complete message  508  to the target cell since the target cell is prepared to accept the UE  102 . As discussed in more detail below, in accordance with embodiments, the UE  102  may be arranged for fast handover failure recovery by early transmission of a RACH 2 message when both the RLF timer (T 310 )  310  and the TTT timer are concurrently running. 
         [0029]    Conventionally, HO failure occurs when any one of the following happens:
       The UL grant for the measurement report is lost;   The measurement report from the UE is lost;   The HO command from serving cell is lost;   The RACH message to target cell is lost.       
 
         [0034]    These failures may occur due to lower RSRP values from the serving or target cells and may occur during radio link failure. After HO failure, the UE  102  may have to start the network entry process by sending a RACH message to the strongest cell. “The HO command lost” may be the largest contributor towards the overall HO failure rate in an LTE network. Depending on the TTT and RLF (T 310 ) timer expiry there are two failure scenarios: 1) when TTT timer expires while the RLF timer is running; and 2) when the RLF timer expires while the TTT timer is running. These scenarios are illustrated in  FIGS. 7A and 7B  described in more detail below. 
         [0035]    One issue with these conventional techniques is that the recovery from RLF or HO failure starts after HO failure by initiating a network re-entry process at the UE. This results in a longer service interruption and larger latency or delay. Embodiments disclosed herein address these issues by transmitting RACH messages at the earliest possible instant when the RLF timer (T 310 ) and TTT timer are overlapping. The RACH messages may be contention based or non-contention based depending on the intended cell. The target cell or another cell would be prepared early and recovery from handover failure and/or RLF may be faster than with conventional techniques. If HO failure or RLF does not actually occur, the cells and UE  102  may ignore the RACH message and the follow up messages. 
         [0036]      FIGS. 6A and 6B  illustrate early transmission of a random-access channel (RACH) 2 message and early termination of a radio-link failure (RLF) timer (T 310 ) in accordance with some embodiments. As illustrated in  FIGS. 6A and 6B , a UE, such as UE  102 , may initiate HO failure recovery by transmission of RACH 2 message  604  when both the RLF timer (T 310 )  310  ( FIG. 3 ) and the TTT timer are concurrently running. In these embodiments, the RACH 2 message  604  is a message transmitted on a random-access channel for RRC connection re-establishment. 
         [0037]    In accordance with these embodiments, the UE  102  may activate (i.e., set/start) the RLF timer (T 310 ) as part of RLM process  300  ( FIG. 3 ) based on radio-link conditions with a serving cell  201 . The UE  102  may activate the TTT timer as part of a HO process  400  ( FIG. 4 ) based on a measurement reporting event (e.g., Event A3 based on a difference between predetermined reference signals  301  of the serving cell  201  and a target cell  203 ). The UE  102  may determine when both the RLF timer  310  and the TTT timer are active (i.e., concurrently running) to initiate the HO failure recovery by transmission of the RACH 2 message  604 . 
         [0038]    In these embodiments, in response to receipt of a RACH response message  606 , the UE  102  may terminate the RLF timer (T 310 ) at operation  607  (e.g., because channel conditions with an eNB are presumed to be good) and either transmit an RRC connection reconfiguration complete message  608  ( FIG. 6A ) to a target cell eNB  106  for non-contention based random access, or transmit a RRC connection request message  610  ( FIG. 6B ) to a third cell  108  that is neither the target or the serving cell for contention-based random access. 
         [0039]    In some of these embodiments, the RRC connection reconfiguration complete message  608  may be sent to the target cell  106  since the cell would have the UE context since the UE  102  had already initiated the HO process. In these embodiments, a RRC connection request message  610  (i.e., rather than a RRC connection reconfiguration complete message  608 ) may be sent to a third cell  108  since the third cell  108  does not have the context of the UE  102 . The third cell  108  may be arranged to retrieve context from the current serving cell and may send a RACH response. 
         [0040]    In these embodiments, the RACH 2 message  604  may be transmitted when the RLF timer  310  and the TTT timer are both active and before (prior to) expiration of either the RLF timer  310  or the TTT timer. In these embodiments, the UE  102  may concurrently perform the HO process  400  and RLM process  300  as separate and independent processes. Conventional HO failure recovery, on the other hand, is initiated by sending a RACH 2 message after HO failure occurs when the connection reestablishment timer  311  (i.e., timer T 311 ) is activated. 
         [0041]    In these embodiments, the RLF timer  310  (timer T 310 ) may be started when a UE detects physical-layer related problems (e.g., when the UE receives N310 consecutive out-of-sync indications from lower layers). The RLF timer  310  may be stopped, for example, 1) when the UE receives N311 consecutive in-sync indications from lower layers; 2) upon triggering the handover procedure; or 3) upon initiating the connection reestablishment procedure. At expiry of the RLF timer  310 , a radio link failure  305  ( FIG. 3 ) may be declared. The UE  102  may remain in active mode  308  ( FIG. 3 ) initiate a connection reestablishment procedure (recovery phase  304 ) or the UE  102  may be arranged to enter RRC idle mode  309  if a connection was not reestablished, depending on whether security is activated. 
         [0042]    In these embodiments, the connection-reestablishment timer  311  (i.e., timer T 311 ) may be started while initiating a connection reestablishment during the recovery phase  304  and may be stopped upon selection of suitable E-UTRAN cell or a cell using another RAT. At expiry of the timer T 311 , the UE  102  may be arranged to enter RRC idle mode  309  since a connection had not been established with a suitable cell. 
         [0043]    In some embodiments, the RACH 2 message  604  is an unscheduled message that is transmitted on the random-access channel. In these embodiments, the RACH 2 message  604  may initiate an RRC connection re-establishment procedure. In these embodiments, the RACH 2 message  604  may comprise a preamble sequence (e.g., one of 64 possible sequences) that may be decoded by an eNB to identify the UE  102 . In some embodiments, the RACH 2 message may include a Random Access Radio Network Temporary Identifier (RA-RNTI) of the UE  102 . 
         [0044]    In accordance with some LTE embodiments, UE  102  may be arranged to transmit various RACH messages including: a RACH 1 message for initial access from RRC idle mode, the RACH 2 message for RRC connection re-establishment, a RACH 3 message for handover, a RACH 4 message for downlink data arrival during RRC connected mode requiring a random access procedure (e.g., when uplink synchronization status is “non-synchronized”), a RACH 5 message for uplink (UL) data arrival during RRC connected mode requiring random access procedure (e.g., when UL synchronization status is “non-synchronized” or there are no PUCCH resources for SR available), and a RACH 6 message for positioning purposes during RRC connected mode requiring a random access procedure (e.g., when timing advance is needed for UE positioning). 
         [0045]    In some embodiments, when the UE  102  does not receive a RACH response message  606  and the RLF timer  310  has not reset as part of the RLM process  300  (e.g., because channel conditions do not improve), the UE  102  may continue to perform the RLM process  300  and perform a connection reestablishment procedure upon expiration of the RLF timer  310 . In these embodiments, the RLM process  300  may include sending another RACH 2 message to either the same cell or a different cell for link recovery as part of a connection reestablishment procedure upon expiration of the RLF timer  310 . 
         [0046]    In some embodiments, when the RACH 2 message  604  is transmitted to initiate HO failure recovery (i.e., when both the RLF timer  310  and the TTT timer are active), the RACH 2 message  604  may be transmitted to an eNB of a cell having a greatest received signal strength (e.g., a greatest RSRP). When the eNB is associated with either the target cell  203  or the serving cell  201 , the RACH 2 message  604  may be transmitted in accordance with a non-contention random-access based technique (see  FIG. 6A ). When the eNB is associated with neither the target cell  203  nor the serving cell  201 , the RACH 2 message  604  may be transmitted in accordance with a contention-based random-access technique (see  FIG. 6B ). 
         [0047]    In these embodiments, when the RACH 2 message  604  is sent to either the target cell  203  or the serving cell  201 , the target cell  203  and the serving cell  201  may both already have context for the UE  102  allowing either the target cell  203  or the serving cell  201  to respond with the RACH response message  606 . In these embodiments, when the RACH 2 message  604  was sent to a third cell that was neither the target cell  203  nor the serving cell  201 , a non-contention based technique may be used when the third cell has context for the UE  102  (i.e., due to the RLF process) and a contention based technique may be used when the third cell does not have context for the UE  102 . 
         [0048]    In some embodiments, when the TTT timer is running and the RLF timer  310  is not running (i.e., the radio link is not experiencing failure or is in the recovery phase  304 ), the UE  102  may continue to perform the HO process  400  ( FIG. 4 ) and send a RACH 2 message  504  ( FIG. 5 ) to the target cell eNB  106  after receipt of a RRC reconfiguration message  502  ( FIG. 5 ) from the serving cell eNB  104 . In these embodiments, a RACH 2 message would not be sent early. In some embodiments, a RACH 3 message may be sent during normal handover operations (i.e., when the UE  102  is not experiencing radio-link failure). 
         [0049]    In some embodiments, the UE  102  may initially set the RLF timer (T 310 ) based on a CQI (e.g., the wideband CQI) associated with a radio link with the serving cell as part of the RLM process  300 . The UE  102  may set the TTT timer upon satisfaction of a measurement reporting event (i.e., when an event is triggered). In some embodiments, the TTT timer may be set upon the satisfaction of Event A3, which is based a difference between the RSRP of the serving cell and the target cell (e.g., threshold  401  ( FIG. 4 )). In some embodiments, the value if the TTT timer may be set using a Report Configuration information element (IE), although the scope of the embodiments is not limited in this respect. 
         [0050]      FIG. 7A  illustrates the early transmission of a RACH 2 message  604  in comparison with a conventional transmission of a RACH 2 message  704  in the situation when the TTT timer expires while the RLF timer  310  is active.  FIG. 7B  illustrates the early transmission of a RACH 2 message  604  in comparison with a conventional transmission of a RACH 2 message  714  when the RLF timer  310  expires while the TTT timer is active. 
         [0051]    As illustrated in  FIG. 7A , HO failure would conventionally occur at time  712  since either the measurement report had not be received by the serving cell or the HO command may not have been received by the UE  102 . This would result in the transmission of RACH 2 message  704  conventionally as illustrated. As illustrated in  FIG. 7A , RACH 2 message  604  is transmitted earlier than RACH 2 message  704  by time  702  which may allow a target cell to prepare for handover earlier and reduce or eliminate service interruption. In these embodiments, the RACH process is started earlier so the RLF recovery could be achieved earlier. In  FIGS. 7A and 7B , state 1 is the time period before handover measurement event is triggered or the TTT is triggered, state 2 is the time period from when the TTT is triggered and the time when handover failure occurs, and state 3 is the handover recovery period after handover failure. 
         [0052]    As illustrated in  FIG. 7B , HO failure would conventionally occur at time  722  due to radio link failure at time  724  and resulting in the subsequent transmission of the RACH 2 message  714 . As illustrated in  FIG. 7B , RACH 2 message  604  is transmitted earlier than RACH 2 message  714  by time  732  which may allow a target cell to prepare for handover earlier and reduce or eliminate service interruption. In these embodiments, the RACH process is started earlier so the RLF recovery could be achieved earlier. 
         [0053]      FIG. 8  illustrates a UE configured for early transmission of a RACH 2 message in accordance with some embodiments. UE  800  may be suitable for use as UE  102  ( FIG. 1 ). The UE  800  may include physical layer circuitry (PHY)  802  for transmitting and receiving signals to and from eNBs  104  ( FIG. 1 ) using one or more antennas  801 . UE  800  may also include medium access control layer (MAC) circuitry  804  for controlling access to the wireless medium. UE  800  may also include processing circuitry  806  and memory  808  arranged to perform the operations described herein. 
         [0054]    In accordance with some embodiments, the MAC circuitry  804  may be arranged to contend for a wireless medium configure frames or packets for communicating over the wireless medium and the PHY  802  may be arranged to transmit and receive signals. The PHY  802  may include circuitry for modulation/demodulation, upconversion/downconversion, filtering, amplification, etc. In some embodiments, the processing circuitry  806  may include one or more processors. In some embodiments, two or more antennas may be coupled to the physical layer circuitry arranged for sending and receiving signals. The memory  808  may be store information for configuring the processing circuitry  806  to perform the various operations described herein. 
         [0055]    In accordance with embodiments, the UE  800  may also include a RLF timer  310 , a TTT timer  812  and a connection-reestablishment timer  311  (e.g., T 311 ). Processing circuitry  804  may be arranged to perform the RLM process  300  ( FIG. 3 ) and the HO process  400  ( FIG. 4 ). The processing circuitry  804  may also be configured to activate (i.e., set/start) the RLF timer  310  (T 310 ) as part of the RLM process  300  based on radio-link conditions with a serving cell  201 , and activate the TTT timer  812  as part of the HO process  400  based on a reporting event. The processing circuitry  804  may also be configured to determine when both the RLF timer and the TTT timer are active (i.e., concurrently running) to initiate the HO failure recovery by causing transmission of the RACH 2 message by the PHY  802 . 
         [0056]    In some embodiments, the UE  800  may be a mobile device and may be part of a portable wireless communication device, such as a personal digital assistant (PDA), a laptop or portable computer with wireless communication capability, a web tablet, a wireless telephone, a smartphone, a wireless headset, a pager, an instant messaging device, a digital camera, an access point, a television, a medical device (e.g., a heart rate monitor, a blood pressure monitor, etc.), or other device that may receive and/or transmit information wirelessly. In some embodiments, the UE  800  may include one or more of a keyboard, a display, a non-volatile memory port, multiple antennas, a graphics processor, an application processor, speakers, and other mobile device elements. The display may be an LCD screen including a touch screen. 
         [0057]    The antennas  801  may comprise one or more directional or omnidirectional antennas, including, for example, dipole antennas, monopole antennas, patch antennas, loop antennas, microstrip antennas or other types of antennas suitable for transmission of RF signals. In some multiple-input multiple-output (MIMO) embodiments, the antennas may be effectively separated to take advantage of spatial diversity and the different channel characteristics that may result. 
         [0058]    Although the UE  800  is illustrated as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, some elements may comprise one or more microprocessors, DSPs, field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), radio-frequency integrated circuits (RFICs) and combinations of various hardware and logic circuitry for performing at least the functions described herein. In some embodiments, the functional elements may refer to one or more processes operating on one or more processing elements. 
         [0059]    Embodiments may be implemented in one or a combination of hardware, firmware and software. Embodiments may also be implemented as instructions stored on a computer-readable storage device, which may be read and executed by at least one processor to perform the operations described herein. A computer-readable storage device may include any non-transitory mechanism for storing information in a form readable by a machine (e.g., a computer). For example, a computer-readable storage device may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, and other storage devices and media. Some embodiments may include one or more processors and may be configured with instructions stored on a computer-readable storage device. 
         [0060]      FIG. 9  illustrates a procedure for fast handover recovery in accordance with some embodiments. Procedure  900  for fast handover recovery may be performed by a UE, such as UE  102  ( FIG. 1 ) or UE  800  ( FIG. 8 ). 
         [0061]    In operation  902 , the UE  102  may activate the RLF timer (T 310 )  310  ( FIG. 8 ) as part of the RLM process  300  ( FIG. 3 ) based on radio-link conditions with a serving cell  201 . 
         [0062]    In operation  904 , the UE  102  may activate the TTT timer  812  ( FIG. 8 ) as part of a HO process  400  ( FIG. 4 ) based on a measurement reporting event (e.g., Event A3 based on a difference between predetermined reference signals  301  of the serving cell  201  and a target cell  103 ). The HO process  400  and RLM process  300  may be independent processes performed concurrently by the UE  102 . 
         [0063]    In operation  906 , the UE  102  may determine when both the RLF timer  310  and the TTT timer  812  are active (i.e., concurrently running) to initiate the HO failure recovery. 
         [0064]    In operation  907 , the UE  102  may transmit a RACH 2 message to initiate HO failure recovery when it is determined that both the RLF timer  310  and the TTT timer  812  are active and before (prior to) expiration of either the RLF timer  310  or the TTT timer  812 . This is unlike conventional techniques in which HO failure recovery is initiated by sending a RACH 2 message after HO failure occurs when the connection reestablishment timer  311  (i.e., timer T 311 ) ( FIG. 3 ) has already been activated. 
         [0065]    The Abstract is provided to comply with 37 C.F.R. Section 1.72(b) requiring an abstract that will allow the reader to ascertain the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to limit or interpret the scope or meaning of the claims. The following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment.