Patent Application
20080019320
The foregoing and other aspects of embodiments of this invention are made more evident in the following Detailed Description, when read in conjunction with the attached Drawing Figures, wherein:
The exemplary embodiments of this invention address the problems discussed above, and provide a simple and effective solution subject to optimal response time and radio signaling overhead. However, in the LTE system, as presently proposed, no such information has been introduced for use in HO control-related control messages. This deficiency may be expected to detrimentally impact the performance of the overall HO process in the LTE system when deployed.
An exemplary embodiment of this invention provides for the introduction of L2 status information IEs, which may include RLC and/or PDCP information, in HO control-related messages enabling the sender to obtain a latest ACK/NACK report during the HO execution, which results in a faster lossless handover. In addition, the use of the exemplary embodiments of this invention improves the efficiency of using the radio and transport resources at least for the reason that unnecessary re-transmissions due to a delayed ACK during the HO is avoided.
Reference is made first to
During a HO event that is of interest to the exemplary embodiments of this invention there will at least one second eNode B, referred to as 12′. In the non-limiting example discussed below the eNode B 12 may be considered the Source eNode B, i.e., the eNode B to which the UE 10 is currently connected and communicating in the associated serving cell, and the eNode B 12′ may be considered the Target eNode B, i.e., the eNode B to which the UE 10 is to be connected and communicating with in the target cell after the HO procedure is completed. Note that in practice the serving cell and the target cell may at least partially overlap one another.
In general, the various embodiments of the UE 10 can include, but are not limited to, cellular telephones, personal digital assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, image capture devices such as digital cameras having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback appliances having wireless communication capabilities, Internet appliances permitting wireless Internet access and browsing, as well as portable units or terminals that incorporate combinations of such functions.
The exemplary embodiments of this invention may be implemented by computer software executable by the DP 10A of the UE 10 and the DP 12A of the eNode Bs 12 and 12′ and 12′, or by hardware, or by a combination of software and hardware.
The MEMs 10B, 12B and 14B may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The DPs 10A, 12A and 14A may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples.
The exemplary embodiments of this invention are beneficial for use in an intra-system HO of a type shown in
In accordance with the exemplary embodiments of this invention at least one L2 status IE, e.g., RLC SN and/or PDCP SN, is included in the HO control-related RRC messages. Taking the HO signaling flow shown in
The three messages that are enhanced in accordance with the exemplary embodiments of this invention are depicted with an asterisk (*) in
More specifically, at (2-1) the UE 10 is triggered to send a MEASUREMENT REPORT by rules set by, for example, system information and/or specification. At (2-2) the source eNB 12 makes a decision based on the MEASUREMENT REPORT and RRM information to hand off the UE 10. The source eNB 12 prepares the target eNB 12′ for handover and passes relevant information in the Handover Request. At (2-3) the target eNB 12′ prepares for HO with L1/L2 and responds to the source eNB 12 by providing a new C-RNTI and possibly other parameters, such as access parameters, SIBs, etc. After reception of the accepted preparation of HO, the source eNB 12 starts forwarding data packets to the target eNB 12′. At (2-4*) the UE 10 receives the Handover Command with associated parameters, such as the new C-RNTI, a starting time, target eNB SIBs, etc., from the source eNodeB 12. The UE 10 may acknowledge reception of the Handover Command with a RLC acknowledgment procedure. In accordance with the exemplary embodiments of this invention the UL L2 status information IE may be included in the Handover Command message received from the source eNodeB 12. At (2-5), and after expiry of the starting time in the Handover Command, the UE 10 performs synchronisation to the target eNB 12′ and begins acquiring the UL TA. At (2-6*) the network responds with the UL allocation and TA. These parameters are used by the UE 10 to send the Handover Confirm to the target eNB 12, which completes the handover procedure for the UE 10. The network may acknowledge reception of the Handover Confirm with a RLC acknowledgment procedure. Further in accordance with the exemplary embodiments of this invention the DL L2 status information IE may be included in the Handover Confirm message sent from the UE 10 to the target eNodeB 12′. At (2-7a*) the target eNB 12′ informs success of the HO to the source eNB 12, which may then clear already forwarded data from its buffers. The source eNB 12 may still continue to forward UE 10 data if some remains in its buffers, or if the UPE 14 continues to forward data to it. Further in accordance with the exemplary embodiments of this invention the DL L2 status information IE may be included in the Handover Completed message sent from the target eNodeB 12′ to the source eNodeB 12 to avoid unnecessary data forwarding, as was described above. At (2-7b) the UE 10 location information is updated to the MME/UPE 14 in order to enable the UPE to forward packets directly to the target eNB 12′.
The content of the L2 status information IE, in one simple example, may be just the last in-order received PDCP/RLC SDU SN. As another example, the L2 status information IE may include information descriptive of all missing SDU(s)/segments and the last received SDU/segment, where in general a PDCP PDU is composed of a PDCP SDU and a RLC PDU is composed of RLC SDU(s) and/or segment(s) thereof. The PDCP SN can be different from the RLC SN and the RLC may or may not know of the PDCP SN.
In accordance with the exemplary embodiments of this invention L2 status information IE is introduced and embedded in HO control messages of the RRC that are exchanged between UE 10 and the source/target eNode Bs 12, 12′ as an optional IE.
In accordance with the exemplary embodiments of this invention at least one L2 status IE is included in the HO control-related RRC messages. Taking the HO signaling flow shown in
The three messages that are enhanced in accordance with the exemplary embodiments of this invention are depicted with an asterisk (*) in
At (4-0) the UE 10 context within the source eNB 12 contains information regarding roaming restrictions which where provided either at connection establishment or at the last TA update. At (4-1) the source eNB 12 configures the UE 10 measurement procedures according to the area restriction information. Measurements provided by the source eNB 12 may assist the function controlling the UE's 10 connection mobility. At (4-2) the UE 10 is triggered to send a MEASUREMENT REPORT by the established rules, for example rules set by system information, specification, etc. At (4-3) the source eNB 12 makes a decision to hand off the UE 10 based on the MEASUREMENT REPORT and RRM information. At (4-4) the source eNB 12 issues a HANDOVER REQUEST message to the target eNB 12′ passing necessary information to prepare the HO at the target side (UE X2 signaling context reference at source eNB 12, UE S1 EPC signaling context reference, target cell ID, RRC context, SAE bearer context). UE X2/UE S1 signaling references enable the target eNB 12′ to address the source eNB 12 and the EPC. The SAE bearer context may include any necessary RNL and TNL addressing information. At (4-5) admission control may be performed by the target eNB 12′ dependent on the received SAE bearer QoS information to increase the likelihood of a successful HO, if the resources can be granted by the target eNB 12′. The target eNB 12′ configures the required resources according to the received SAE bearer QoS information and reserves a C-RNTI. At (4-6) the target eNB 12′ prepares HO with L1/L2 and sends the HANDOVER REQUEST ACKNOWLEDGE to the source eNB 12. The HANDOVER REQUEST ACKNOWLEDGE message includes a transparent container to be sent to the UE 10 as part of the handover command. The container may include new C-RNTI, possibly some other parameters, e.g., access parameters, SIBs, etc. The HANDOVER REQUEST ACKNOWLEDGE message may also include RNL/TNL information for the forwarding tunnels, if necessary. At (4-7*) the source eNB 12 generates the Handover command (RRC message) towards the UE 10. The Handover command includes the transparent container, which has been received from the target eNB 12′. The source eNodeB performs the necessary integrity protection and ciphering of the message. The UE 10 receives the Handover command with necessary parameters (e.g., new C-RNTI, possible starting time, target eNB 12′ SIBs etc.) and is commanded by the source eNB 12 to perform the HO. It is probable that UE 10 needs to acknowledge reception of the Handover command with RLC acknowledgment procedure. In accordance with the exemplary embodiments of this invention the UL L2 status information IE may be included in the Handover command message received from the source eNodeB 12. At (4-8) after expiry of the starting time in the Handover command, the UE 10 performs a synchronization to the target eNB 12′ and then starts acquiring the UL timing advance. At (4-9) the network responds with a UL allocation and timing advance. At (4-10*) when the UE 10 has successfully accessed the target cell, the UE 10 sends the Handover confirm message (C-RNTI) to the target eNB 12′ to indicate that the handover procedure is completed for the UE 10. The target eNB 12′ verifies the C-RNTI sent in the Handover confirm message. Further in accordance with the exemplary embodiments of this invention the DL L2 status information IE may be included in the Handover Confirm message sent from the UE 10 to the target eNodeB 12′. At (4-11) the EPC is informed that the UE 10 has changed cells. The UPE switches the downlink data path to the target side and can release any U-plane/TNL resources towards the source eNB 12. At (4-12) the EPC confirms the Handover complete message with the HANDOVER COMPLETE ACK message. At (4-13*) by sending the RELEASE RESOURCE message the target eNB 12′ informs the source eNB 12 of the success of the HO and triggers the release of resources. The timing for the target eNB 12′ to send this message may be anywhere after steps (4-10) or (4-12) and prior to the source eNodeB 12 flushing its DL buffer. Further in accordance with the exemplary embodiments of this invention the DL L2 status information IE may be included in the RELEASE RESOURCE message sent from the target eNodeB 12′ to the source eNodeB 12 to avoid unnecessary data forwarding, as was described above. Upon reception of the RELEASE RESOURCE message at (4-14) the source eNB 12 can release radio and C-plane related resources associated to the UE 10 context.
Setting the content of the L2 status information IE, such as in the aforementioned two examples, may be determined (on a HO-by-HO basis) by the sending side, such as by the L2 receiver. In this manner it is possible to achieve an optimal trade-off between simplicity and efficiency for L2 lossless HO support.
Various criteria may be considered when making a determination as to setting the content of the L2 status information IE. Several non-limiting examples are as follows.
(A) The supported ARQ scheme may be taken into consideration, such as selective ARQ or cumulative go-back-N ARQ (e.g., see D. Bertsekas and R. Gallager, Data Networks, Prentice Hall, 1992). There may also be a hybrid ARQ scheme allowing both selective and cumulative retransmissions on a case-by-case basis. In the go-back-N scheme, the simplest content with the last in-order SDU SN may typically be sufficient. The details of all missing SDU(s)/segments would typically not be needed in the go-back-N approach but selective counterpart. The location and operation of the supported L2 in-order delivery function together with possible reordering of out-of-order received service data units (e.g., which L2 protocol(s) are involved and how) may also be taken into consideration. In E-UTRAN it may be that PDCP is involved in reordering of L2 SDU(s) and L2 in-order delivery at least at HO. In this case, L2 status information should include explicit PDCP status information unless such the PDCP status information were already embedded in RLC status information.
(B) The QoS characteristics or requirements of the user being handed off may be taken into consideration. For example, data losses to some certain extent may be tolerated by some users but not others, which on the other hand may tolerate some certain delay.
(C) The available network resources when the HO occurs may be taken into consideration. For example, the selective re-transmission is generally less resource-consuming, and may be preferred for use under heavy network loading conditions.
(D) The efficiency-simplicity trade-off factors of the network operation and performance may be considered. For simplicity reasons, it may be sufficient to use cumulative re-transmissions for all data users when they are handed off.
The determination of the content of the L2 status information IE may be based on one or more of these considerations, or in combination with yet other considerations.
Also provided is a flexible L2 status information format to limit the HO signaling overhead and thus conserve the use of the bandwidth between the UE 10 and the eNode Bs 12, 12′.
In an exemplary embodiment there is provided a network element, such as the source eNode B 12, that sends UL L2 status information IE in a HO command message to a UE 10.
In another exemplary embodiment there is provided a mobile device, such as a UE 10, that sends a DL L2 status information IE in a HO confirm message to a network element, such as the target eNode B 12′.
In a further exemplary embodiment there is provided a network element, such as the target eNode B 12′, that sends a DL L2 status information IE in a HO completed message to another network element, such as the source eNode B 12.
In another exemplary embodiment there is provided a network element, such as the target eNode B 12′, that sends a DL L2 status information IE in a resource release message to another network element, such as the source eNode B 12.
In the foregoing exemplary embodiments the content of the L2 status information IE may comprise a last in-order received L2 SDU SN and/or information descriptive of, for example, missing SDU(s)/segments and a last received SDU/segment.
In the foregoing exemplary embodiments the content of the L2 status information IE may be fixed, or it may be made variable from one instance of a HO to another instance. Various criteria may be taken into consideration when determining the content of the L2 status information IE. These criteria may include, but are not limited to, one or more of: the supported ARQ scheme, the QoS characteristics or requirements of the user being handed off, the available network resources when the HO occurs, and the efficiency-simplicity trade-off factors of the network operation and performance.
Based on the foregoing it should be apparent that the exemplary embodiments of this invention provide a method, apparatus and computer program product(s) to provide HO-related status information in HO control messages that are exchanged between the UE and the source/target eNode Bs.
In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the exemplary embodiments of this invention may be illustrated and described as block diagrams, message flow diagrams, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.
As such, it should be appreciated that at least some aspects of the exemplary embodiments of the inventions may be practiced in various components such as integrated circuit chips and modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be fabricated on a semiconductor substrate. Such software tools can automatically route conductors and locate components on a semiconductor substrate using well established rules of design, as well as libraries of pre-stored design modules. Once the design for a semiconductor circuit has been completed, the resultant design, in a standardized electronic format (e.g., Opus, GDSII, or the like) may be transmitted to a semiconductor fabrication facility for fabrication as one or more integrated circuit devices.
Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of this invention.
Furthermore, some of the features of the various non-limiting and exemplary embodiments of this invention may be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.
This patent application claims priority under 35 U.S.C. § 119(e) from Provisional Patent Application No. 60/831,858, filed Jul. 18, 2006, the disclosure of which is incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60831858 | Jul 2006 | US |
