Mechanism to handle UE assistance information upon handover

The UE, source eNodeB, and/or target eNodeB use one or more existing Radio Resource Control (RRC) messages already available during handover to exchange at least one status report comprising UE assistance information, such as power preference indicators (PPI). The UE and the target eNodeB are thus able to obtain the same up-to-date UE status without any additional signaling. In one embodiment, the UE exchanges a handover preparation status report with the target eNodeB using a first RRC reconfiguration message transmitted from the source eNodeB to the UE, where the handover preparation status report is generated during handover preparation by the target eNodeB. In another embodiment, the UE exchanges a handover execution status report with the target eNodeB during handover execution using a second RRC reconfiguration message transmitted from the UE to the target eNodeB, where the handover execution status report is generated during handover execution. In another embodiment, the UE exchanges multiple status reports with the target eNodeB using multiple RRC reconfiguration messages, where the status reports are generated during handover preparation and handover execution. The handover preparation status report is transmitted from the target eNodeB to the UE and includes the status report as perceived by the target node at the time of handover preparation. The handover execution status report is transmitted from the UE to the target eNodeB and includes the status report as stored in the UE memory at the time of handover execution. The first RRC reconfiguration message is a RRC connection reconfiguration message and the second RRC reconfiguration message is a RRC connection reconfiguration complete message.

TECHNICAL FIELD

The invention disclosed herein generally relates to handover of a mobile device between a source node and a target node in wireless networks, and more particularly relates to the synchronization between a mobile device and a target node of the mobile device's status.

BACKGROUND

The 3rdGeneration Partnership Project (3GPP) has been developing specifications on the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), which includes the Long Term Evolution (LTE) concepts. In RAN2, a Work Item (WI) on enhancements for Diverse Data Applications (eDDA) has been created in Rel-11 to identify and specify mechanisms to enhance the ability of LTE to handle diverse traffic profiles such as social networking applications. The objective of this WI is to identify improvements that increase the network efficiency, extend UE battery lifetime, reduce signaling overhead, and/or enhance user experience and system performance under such traffic loads.

In one scenario within the context of this WI, efficient power consumption is an important characteristic of a mobile device, which is also referred to herein as a User Equipment (UE). One focus area is to change the UE behavior to reduce its power consumption whenever possible. In previous releases of the specification, timers were introduced to enable switching from a connected mode to an idle mode once the timers expire and when there is no data to send. Further, discontinuous reception (DRX) mode was introduced for LTE in 3GPP standards to conserve battery power when the UE remains in the connected mode. There is a wide range of configuration settings available for the DRX parameters that can serve for different types of services, e.g., VoIP, gaming, web browsing, video telephony, etc.

A base station, which is also referred to herein as an eNB, sets various settings for the UE, e.g., the DRX reception mode configuration. There may be scenarios, however, in which the UE has information that is not available at the eNB. Therefore, assistance information provided by the UE to the eNB is considered useful to the eNB. In many scenarios, the UE sends assistance information by sending one or more of a set of predefined values to an eNB. Such assistance information may take the form of a status report, where the predefined values e.g., indicate the priority of a certain service that the UE requests, report certain problems that the UE experiences which the eNB cannot otherwise be aware of, or state the UE's preference for a certain type of connection configuration. The eNB may or may not act upon requests identified by received assistance information. If the eNB decides to act, it will reconfigure the UE connection accordingly. The resulting reconfiguration will be valid until the next connection reconfiguration.

Frequent transmission of such status reports may cause excessive signaling in the network. Avoiding such excessive signaling enables the network to utilize its resources more efficiently, and thus to provide better service. To that end, UE may be restrained from frequent and/or repetitive transmission of the status report. Frequent transmissions may be prevented with a prohibit timer. Repetitive transmissions may be avoided by preventing the UE from sending a status report unless there has been a change to the assistance information.

While such measures effectively reduce the signaling within the network during normal operations, they are not always effective during handover of the UE from a source eNB to a target eNB. Thus, there remains a need for effectively communicating assistance information responsive to a handover decision without increasing the signaling required for such communications.

SUMMARY

Accordingly, a mobile device, a source node, and/or a target node use one or more existing Radio Resource Control (RRC) messages already available during handover to exchange at least one status report. In so doing, the mobile device and the target node are able to obtain the same mobile device status without any additional signaling. In one embodiment, the mobile device exchanges a handover preparation status report with the target node using a first RRC reconfiguration message, where the handover preparation status report is generated during handover preparation. In another embodiment, the mobile device exchanges a handover execution status report with the target node using a second RRC reconfiguration message, where the handover execution status report is generated during handover execution. In another embodiment, the mobile device exchanges multiple status reports with the target node using multiple RRC reconfiguration messages, where the status reports are generated during handover preparation and handover execution. As used herein the “RRC reconfiguration message” comprises RRC_Connection_Reconfiguration and/or RRC_Connection_Reconfiguration messages.

An exemplary method executed by a mobile device comprises a method executed by the mobile device responsive to a handover decision regarding handover of the mobile device from a source node to a target node in a wireless network. The method includes exchanging at least one status report between the mobile device and the target node responsive to the handover decision using at least one Radio Resource Control (RRC) reconfiguration message, where the status report indicates a status of the mobile device. The method also includes synchronizing a first status of the mobile device stored in a memory in the mobile device with a second status of the mobile device stored in a memory in the target node based on the exchanged at least one status report.

An exemplary mobile device in a wireless network comprises a transceiver, a memory, and a processing circuit. The transceiver is configured to exchange at least one status report between the mobile device and a target node in the wireless network responsive to a handover decision using at least one Radio Resource Control (RRC) reconfiguration message. The status report indicates a status of the mobile device. The handover decision represents a decision to handover the mobile device from a service node to the target node. The memory is configured to store a first status of the mobile device. The processing circuit is configured to synchronize the first status of the mobile device with a second status of the mobile device stored in a memory of the target node based on the exchanged at least one status report.

An exemplary method executed by a network node comprises a method executed by the network node responsive to a handover decision regarding handover of a mobile device from a source node to a target node in a wireless network. The method includes exchanging at least one status report between the mobile device and the target node responsive to the handover decision using at least one Radio Resource Control (RRC) reconfiguration message, where the status report indicates a status of the mobile device. The method also includes enabling synchronization between a first status of the mobile device stored in a memory in the mobile device and a second status of the mobile device stored in a memory in the target node based on the exchanged status report(s).

An exemplary network node comprises a processing circuit and at least one of a transceiver and a network interface. The transceiver and/or network interface is/are configured to exchange at least one status report between a mobile device and a target node responsive to a handover decision using at least one Radio Resource Control (RRC) reconfiguration message. The status report indicates a status of the mobile device, and the handover decision represents a decision to handover the mobile device from a source node to the target node. The processing circuit is configured to enable synchronization between a first status of the mobile device stored in a memory in the mobile device and a second status of the mobile device stored in a memory in the target node based on the exchanged status report(s).

DETAILED DESCRIPTION

Frequent transmission of status reports from a transmitting device to a receiving network node in a wireless network may cause excessive signaling in the network. Avoiding such excessive signaling enables the network to utilize its resources more efficiently, and thus to provide better service. Handover of the transmitting device from a source receiving node to a target receiving node, however, presents a special set of circumstances that ultimately require the status report to be synchronized at both the transmitting device and the target receiving node upon handover completion. Conventional techniques directed at addressing the excessive signaling problem, e.g., a prohibit timer and/or repetitive transmission prohibitions, do not always enable this synchronization to occur upon handover completion. To address this problem, the solution disclosed herein uses existing handover messages to exchange the UE status report(s) between the target eNB and the UE. Thus, the solution disclosed herein avoids unwanted excessive signaling while also avoiding a possible mismatch between the status report in the transmitting device and the target receiving node after handover. Throughout this document, UE, source eNB, and target eNB are used as labels for the transmitting device, source receiving node and target receiving node, respectively. It will be appreciated, however, that the solution disclosed herein applies to any transmitting and receiving devices going through handover in a wireless network.

FIG. 1shows an exemplary wireless network100comprising UE110, source eNB120, and target eNB130. The UE110, source eNB120, and target eNB130communicate according to known standards, e.g., LTE. WhileFIG. 1shows only one UE110, one source eNB120, and one target eNB130, it will be appreciated that network100may comprise any number of UEs and eNBs.

UE110comprises a processing circuit112, transceiver114, and memory116. The processing circuit112controls the operation of the UE110according to instructions and programs stored in memory116. Transceiver114comprises a transmitter114aand a receiver114b. Transmitter114a/receiver114bwirelessly transmit/receive signals to/from a remote network node, e.g., an eNB120,130, according to any known wireless standard, e.g., LTE.

Source eNB120comprises a processing circuit122, transceiver124, memory126, and network interface (I/F)128. The processing circuit122controls the operation of the source eNB120according to instructions and programs stored in memory126. Transceiver124comprises a transmitter124aand a receiver124b. Transmitter124a/receiver124bwirelessly transmit/receive signals to/from a remote device, e.g., UE110, and network I/F128communicates with other network nodes, e.g., target eNB130, according to any known standard, e.g., LTE.

Target eNB130comprises a processing circuit132, transceiver134, memory136, and network interface (I/F)138. The processing circuit132controls the operation of the target eNB130according to instructions and programs stored in memory136. Transceiver134comprises a transmitter134aand a receiver134b. Transmitter134a/receiver134bwirelessly transmit/receive signals to/from a remote device, e.g., UE110, and network I/F138communicates with other network nodes, e.g., source eNB120, according to any known standard, e.g., LTE.

The UE110communicates with the source eNB120according to conventional protocols. Per RAN2, UE110may send assistance information to the source eNB120to achieve some desired objective, e.g., requesting a different connection configuration to save power. For example, during an ongoing data session when the UE110is RRC connected and time aligned (presumably when it has mostly background type of traffic, e.g., small, infrequent data packets), the UE110may request a new configuration to reduce its power consumption. This request may take the form of a single bit, referred to as Power Preference Indicator (PPI), transmitted to the source eNB120.

The UE110may provide the assistance information to the source eNB120in the form of a status report. It will be appreciated that the assistance information provided by the UE110to the source eNB120is not limited to the PPI. The status report may include one or more values indicating one or more setting preferences for the UE110, indicating a current status of one or more UE functions or UE hardware elements, and/or indicating a problem being experienced by the UE110. Exemplary setting preferences include but are not limited to a discontinuous reception setting preference for the UE110(e.g., to indicate the UE's willingness for delay sensitive or delay tolerant operation), a power preference for the UE110, a priority preference for a service associated with the UE110, a connection configuration preference for the UE110, and a tolerance preference regarding delay sensitive operations for the UE110. Exemplary statuses include but are not limited to an on/off status of a screen of the UE110, an on/off status of a location function (e.g., a Global Positioning System (GPS) function), an on/off status of the transmitter114a, etc. Exemplary problems that may be reported by the UE110using the status report include an indication of a low or soon to be exhausted battery. Thus, the UE110only provides a status report to the source eNB120at predetermined time intervals, and then only when the assistance information changes.

As previously noted, the special circumstances created by handover do not lend themselves to the solutions applicable to non-handover operations. To overcome these problems without creating more signaling, the solution disclosed herein uses existing handover-related messages to synchronize a UE status with the target eNB120.FIG. 2shows an exemplary signaling diagram for wireless communications before, during, and after handover of UE110from a source eNB129to a target eNB130. To better illustrate the solution disclosed herein, the following first describes the basic signaling associated with an LTE handover, and the corresponding problems associated with synchronizing the UE assistance information.

Before handover, the source eNB120sends measurement control data to the UE110(step1), exchanges packet data with the UE110, and sends uplink allocation information to the UE110. The UE110continues communicating with the source eNB120until the source eNB120makes a handover decision (step3), e.g., based on signal strength measurement reports provided to the source eNB120by the UE110(step2). Responsive to the handover decision (step3), the source eNB120sends a handover request to the target eNB130(step4), at which point handover preparation begins.

During handover preparation, the target eNB130performs admission control, e.g., provides information on available resources in the target cell (step5). If the resources available in the target cell are not able to carry the service after handover, then handover to the target cell is rejected. If the available resources are able to carry the service after handover, the target eNB130sends a handover request acknowledgement to the source eNB120(step6) to complete handover preparation.

Now that handover preparation is complete, handover execution begins. Handover execution includes the UE110receiving, from the source eNB120, downlink allocation information using L1/L2 signaling and a Radio Resource Control (RRC) reconfiguration message, e.g., an RRC_Connection_Reconfiguration message, to the UE110using L3 signaling (step7). Handover execution continues with the UE110detaching from the source eNB120and synchronizing to the target eNB130, and the source eNB delivering buffered and in-transit data packets to the target eNB130(steps8-10). Upon completion of these steps, the UE110sends an RRC reconfiguration message, e.g., an RRC_Connection_Reconfiguration_Complete message, to the target eNB130using L3 signaling (step11). Upon completion of handover execution, the UE110and target eNB130communicate according to conventional protocols, e.g., by exchanging packet data between the UE110and the target eNB130, until the communication session ends (steps12-18).

In an attempt to provide the UE110and the target eNB130with the same UE status information upon handover completion, conventional systems may have the source eNB120forward the latest UE status report to the target eNB130. Thus, the UE110does not have to use conventional protocols to transmit its status to the target eNB130upon handover completion. However, if the UE110sends a status report to the source eNB120before the handover is executed but after the source eNB120forwards the preceding status report to the target eNB130, there may be a mismatch between the UE's current status report and the target eNB's perception of the UE's current status report.

FIG. 3shows one exemplary solution200for addressing the synchronization problems of the conventional solutions. The solution200disclosed herein synchronizes the UE's and target eNB's perception of the UE status report, e.g., the UE's preference on the priority of a certain service that it requests, the UE's reporting on certain problems that it experiences which the receiving node cannot otherwise be aware of, the UE's preference for a certain type of connection configuration after the handover, etc. To avoid excessive signaling issues, the solution disclosed herein uses existing handover messages to exchange the UE status report after the source eNB120makes a handover decision. More particularly, the UE110and the target eNB130exchange at least one status report responsive to the handover decision using at least one RRC reconfiguration message (block210). The status report(s) exchanged using the RRC reconfiguration message(s) enable the UE110and/or the target eNB130to have the same UE status report (block220). It will be appreciated that the disclosed solution is applicable to the previously discussed eDDA WI.

One exemplary embodiment uses a message to exchange the UE status report(s) generated during handover preparation, and thus, to synchronize the UE status with the target eNB's perception of the UE status. In this embodiment, the target eNB130reports its perception of the UE's status to the UE via the source eNB120during handover preparation so that the UE110becomes aware of the target eNB's perception and synchronizes itself with the target eNB130. More particularly, the processing circuit132in the target node130generates a handover preparation status report based on the target eNB's perception of the UE's status stored in the memory136of the target node130during handover preparation. The handover preparation status report indicates the target eNB's perception of the current UE assistance information. A transmitter134ain the target eNB130transmits the handover preparation status report to the source eNB120. The network I/F128in the source eNB120receives the handover preparation status report. To convey the handover preparation status report to the UE110without using any additional signaling, processing circuit122in the source eNB120adds the handover preparation status report to an RRC reconfiguration message, e.g., the RRC_Connection_Reconfiguration message (e.g., step7inFIG. 2), which also includes the mobility control information. Transmitter124atransmits the RRC reconfiguration message from the source eNB120to the UE110. The receiver114bin UE110receives the RRC reconfiguration message, and processing circuit112extracts the handover preparation status report from the received RRC reconfiguration message. In response to the handover preparation status report, the processing circuit112in the UE110sets the UE status according to the target eNB's perceived UE status. Subsequently, the processing circuit112in the UE110maintains this status for the duration of the handover, e.g., until after the UE110sends the RRC_Connection_Reconfiguration_Complete message to the target eNB130, to synchronize the UE's status at the UE110and the target node130.

Another exemplary embodiment uses a message to exchange the UE status report(s) generated during handover execution. Thus, the second embodiment allows the UE110to report its latest power preference status to the target eNB130during handover execution. In this embodiment, the UE110reports its latest status to the target eNB130during handover execution so that the target eNB130becomes aware and synchronizes itself with the UE110. To convey the UE status without using any additional signaling, the processing circuit112in the UE110generates a handover execution status report based on a status of the mobile device110stored in memory116, and adds the generated handover execution status report to an RRC reconfiguration message, e.g., the RRC_Connection_Reconfiguration_Complete message (e.g., step11inFIG. 2) during handover execution. The transmitter114ain the UE110transmits the RRC reconfiguration message to the target eNB130during handover execution to convey the handover execution status report to the target node130. Further, the processing circuit112maintains the status associated with the handover execution status report for the duration of the handover. The receiver134bin the target eNB130receives the RRC reconfiguration message, and processing circuit132extracts the handover execution status report from the received RRC reconfiguration message. Responsive to the handover execution status report, the processing circuit132in the target eNB130sets its UE status equal to that of the handover execution status report to synchronize the UE's status at the UE110and the target node130. Because the handover execution status report included with the RRC reconfiguration message includes the UE assistance information, this embodiment may also enable the elimination of such information from the UE context.

Yet another exemplary embodiment uses messages generated during handover preparation and handover execution to exchange the UE status report(s). In this embodiment, the processing circuit132in the target node130generates a handover preparation status report based on the target eNB's perception of the UE's status stored in the memory136of the target node130during handover preparation. The handover preparation status report indicates the target eNB's perception of the current UE assistance information. A transmitter134ain the target eNB130transmits the handover preparation status report to the source eNB120. The network interface128in the source eNB120receives the handover preparation status report from the target eNB130. To convey the handover preparation status report to the UE110without using any additional signaling, the processing circuit122in the source eNB120adds the received handover preparation status report to an RRC reconfiguration message, e.g., the RRC_Connection_Reconfiguration message (e.g., step7inFIG. 2). Transmitter124atransmits the RRC reconfiguration message from the source eNB120to the UE110. The receiver114breceives the RRC reconfiguration message, and processing circuit112extracts the handover preparation status report from the received RRC reconfiguration message. In response to the handover preparation status report, the processing circuit112in the UE110sets the UE status according to the target eNB's perceived UE status and generates a handover execution status report. To convey the UE status to the target eNB130without using any additional signaling, the processing circuit112in the UE110adds the handover execution status report to another RRC reconfiguration message, e.g., the RRC_Connection_Reconfiguration_Complete message (e.g., step11inFIG. 2) during handover execution. The transmitter114ain the UE110transmits the RRC reconfiguration message to the target eNB130during handover execution to convey the handover execution status report to the target node130. The receiver134bin the target eNB130receives the RRC reconfiguration message, and processing circuit132extracts the handover execution status report from the received RRC reconfiguration message. Responsive to the handover execution status report, the processing circuit132in the target eNB130sets its UE status equal to the handover execution status to synchronize the UE's status at the UE110and the target node130.

The solution disclosed herein ensures the UE110and the target eNB130operate with the same UE assistance information upon completion of the handover. Hence the solution disclosed herein avoids a possible mismatch on the perception of the UE's status between the UE110and the target eNB130. Further, by attaching such status reports to one or more RRC reconfiguration messages, the solution disclosed herein avoids the mismatch problems without using additional signaling.