Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/0005—Control or signalling for completing the hand-off
  • H04W36/0055—Transmission or use of information for re-establishing the radio link
  • H04W36/0058—Transmission of hand-off measurement information, e.g. measurement reports
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/0005—Control or signalling for completing the hand-off
  • H04W36/0009—Control or signalling for completing the hand-off for a plurality of users or terminals, e.g. group communication or moving wireless networks
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/02—Buffering or recovering information during reselection ; Modification of the traffic flow during hand-off
  • H04W36/023—Buffering or recovering information during reselection
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/24—Reselection being triggered by specific parameters
  • H04W36/32—Reselection being triggered by specific parameters by location or mobility data, e.g. speed data
  • H04W36/322—Reselection being triggered by specific parameters by location or mobility data, e.g. speed data by location data
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W84/00—Network topologies
  • H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
  • H04W84/04—Large scale networks; Deep hierarchical networks
  • H04W84/042—Public Land Mobile systems, e.g. cellular systems
  • H04W84/047—Public Land Mobile systems, e.g. cellular systems using dedicated repeater stations

Definitions

• Embodiments of the present invention generally relates to a handover procedure in a communication system, and more particularly to a method, a system, an apparatus, an eNodeB, a mobile node, and a computer program for fast handover in high speed mobile environment.
• Mobile relaying in a cellular network can help provisioning of high data rate coverage in high-speed railway environments, reducing the influence of penetration loss, reducing the handover overhead, prolonging the battery lifetime for user equipment and generally enhancing cell capacity and effective throughput.
• a method for handover at a source eNB may comprise: receiving a measurement report sent periodically from a mobile node, wherein the sending of the measurement report is triggered no later than the mobile node arriving at a Reference Triggering Point (RTP), and the measurement report comprises location, velocity and signal strength information etc. of the mobile node; performing handover preparation; and executing handover to a target eNB no later than the mobile node arriving at a Reference Handover Point (RHP).
• RTP Reference Triggering Point
• performing the handover preparation comprises: in response to the time the mobile node runs to the RHP is equal to or shorter than a Handover Time Threshold (HTT), sending a resource configuration request message to the target eNB, such that the target eNB executes the resource configuration and requests data bi-casting; and receiving a resource configuration request ACK message from the target eNB; wherein the HTT is equal to P+T, wherein P is reporting period of the measurement report, and T is the time for the resource configuration and signaling for establishing the data bi-casting.
• HTT Handover Time Threshold
• a method for handover at a mobile node may comprise sending periodically a measurement report to a source eNB, wherein the sending is triggered no later than the mobile node arriving at a Reference Triggering Point (RTP), and the measurement report comprises location, velocity and signal strength information etc. of the mobile node.
• RTP Reference Triggering Point
• an apparatus for handover at a source eNB may comprise a report receiving unit, configured to receive a measurement report sent periodically from a mobile node, wherein the sending of the measurement report is triggered no later than the mobile node arriving at a Reference Triggering Point (RTP), and the measurement report comprises location, velocity and signal strength information etc. of the mobile node; a handover preparation unit, configured to perform handover preparation; and handover executing unit, configured to execute handover to a target eNB no later than the mobile node arriving at a Reference Handover Point (RHP).
• RTP Reference Triggering Point
• an apparatus for handover at a mobile node may comprise report sending unit, configured to send periodically a measurement report to a source eNB, wherein the sending is triggered no later than the mobile node arriving at a Reference Triggering Point (RTP), and the measurement report comprises location, velocity and signal strength information etc. of the mobile node.
• RTP Reference Triggering Point
• an apparatus which comprises at least one processor and at least one memory including computer program code.
• the memory and the computer program code are configured to cause the apparatus to perform embodiments of the method of the first aspect of the invention or embodiments of the method of the second aspect of the invention.
• a computer program product which, comprises at least one computer readable storage medium having a computer readable program code portion stored thereon.
• the computer readable program code portion comprises program code instructions for perform embodiments of the method of the first aspect of the invention or embodiments of the method of the second aspect of the invention.
• the measurement results may be reported in time by defining a RTP and the handover may be executed timely by defining a RHP.
• the handover preparation including data bi-casting may be started not too early, such that the consumption of network resources may be minimized.
• the handover time may be reduced and the handover success probability may be improved.
• FIG. 1 illustrates an exemplary scenario where the fast handover scheme in high-speed mobile environment may be implemented according to embodiments of the present invention
• FIG. 2 illustrates an exemplary signal flow of the fast handover scheme according to embodiments of the present invention
• FIG. 3 is a schematic block diagram of an apparatus 300 that may be configured to practice the exemplary embodiments of the present invention.
• FIG. 4 is a schematic block diagram of an apparatus 400 that may be configured to practice the exemplary embodiments of the present invention.
• FIG. 5 illustrates a simplified block diagram of a network element 500 that is suitable for use in practicing the exemplary embodiments of the present invention
• Fig. 6 illustrates the simulation results of Handover Failure Probability with different RN velocity
• Fig. 7 illustrates the simulation results of Handover Overall Procedure Delay with different RN velocity
• Fig. 8 illustrates the simulation results of Handover Interruption Time.
• the handover procedure can be divided into four parts: measurement, handover preparation, handover execution and handover completion.
• a Reference Trigger Point is set to trigger periodic sending of the measurement report; a Reference Handover Point (RHP) is set to trigger the execution of the handover.
• RTP Reference Trigger Point
• RHP Reference Handover Point
• HTT Handover Time Threshold
• ST Speed Threshold
• ST is set to determine whether the embodiments of the present invention should be applied.
• the ST may be set as 40m/s or 60m/s. Other values may also be used.
• Fig. 1 illustrates an exemplary scenario where the fast handover scheme in high-speed mobile environment may be implemented according to embodiments of the present invention.
• eNBs 101, 102, and 103 are disposed along the railway through which a high-speed train 104 goes.
• a Relay Node (RN) 105 is attached to the high-speed train 104, which may be referred as a mobile relay node.
• the eNBs 101, 102, and 103 may communicate with each other via X2 interface 108, and communicate with a Mobile Management Entity/Serving- Gateway (MME/S-GW) 106 via S 1 interface 107.
• MME/S-GW Mobile Management Entity/Serving- Gateway
• the eNBs 101 , 102, and 103 may also communicate with the RN 105 via Un interface 109.
• the UEs may communicate with the eNBs 101, 102, or 103 via the RN 105.
• the mobile Relay Node 105 may be other mobile nodes, such as a UE, a mobile femtocell, a mobile AP, etc.
• the mobile Relay Node 105 is taken as an example to explain the embodiments of the present invention.
• the communication network is deployed with linear coverage pattern, i.e., each cell only has two neighbor cells, a forward cell and a backward cell.
• Such arrangement can reduce the number of eNBs under measurement to 1/6 of original number so as to expedite the measurement of the handover,
• embodiments of the present invention may also be applied in the conventional cellular network arrangement.
• Fig. 1 illustrates the scenario where the train 104 is driving from a cell served by the eNB 102 (i.e., the source eNB) towards a cell served by the eNB 103 (i.e., the target eNB), the train direction being indicated by the arrow 110.
• Fig. 1 also shows the reference points as introduced in embodiments of the present invention, i.e., Reference Trigger Point (RTP) 111 and Reference Handover Point (RHP) 113.
• RTP Reference Trigger Point
• RHP Reference Handover Point
• the relay node 105 attached to the train 104 would begin to report the measurement result periodically.
• the measurement report should include position coordinate (X, Y) (m) and the velocity V of the relay node 105 besides the conventional measurement information.
• the source eNB 102 receives the measurement report periodically and extracts the position and velocity information from the measurement report. If the time the train 104 or the relay node 105 runs to the RHP 113 is equal to or shorter than the Handover Time Threshold (HTT), and optionally if V > Speed Threshold (ST), then the source eNB 102 would perform handover preparation.
• HTT Handover Time Threshold
• ST Speed Threshold
• the handover preparation can include resource configuration procedure at the target eNB 103 and the establishment of data bi-casting.
• the source eNB 102 When the train 104 arrives at the RHP 113 or satisfies other handover conditions before the train 104 arrives at the RHP 113, i.e., no later than the train 104 arriving at the RHP 113, the source eNB 102 would begin to execute handover.
• the RTP 111 is a statistical average value of the position where the measurement process should start, which means the latest position where the measurement report must be triggered.
• the RHP 113 is a statistical average value of the position where the handover execution process should start, which means the latest position where the handover execution must start.
• the HTT is the earliest time for starting handover preparation and data bi-casting. Assuming measurement reporting period is P, handover preparation time and signaling overhead for establishing data bi-casting is T, then HTT is P+T.
• the measurement results may be reported in time by defining RTP 111 and the handover may be executed timely by defining RHP 113. Moreover, by defining HTT, the handover preparation including data bi-casting may be started not too early, such that the consumption of network resources may be minimized.
• Fig. 2 illustrates an exemplary signal flow of the fast handover scheme according to embodiments of the present invention.
• Fig. 2 has shown the signal flow between UE 120, Relay Node (RN) 105, Source eNB 102, Target eNB 103, MME 106a and S-GW 106b in order to effect a fast handover.
• RN Relay Node
• the MME/S-GW 106 provides area restriction information to the source eNB 102.
• the source eNB 102 configures the measurement procedure of the relay node (RN) 105 according to the area restriction information.
• the configuration may be implemented by Measurement Configuration IE (Information Element) in RRCConnectionReconfiguration message.
• the Measurement Configuration may include measurement objects, reporting configurations (including measurement trigger by Event or Period, measurement report contents, etc.), measurement identities, measurement gaps, etc.
• the event-triggered period measurement report criteria may be, for example A3 as defined in LTE. Event A3 is that neighbor cell becomes better than an offset relative to the serving cell.
• the RN 105 will send measurement report to the source eNB 102 periodically.
• the measurement report may include measurement result such as a reference signal received quality (RSRQ), a reference signal received power (RSRP), etc.
• RSRQ reference signal received quality
• RSRP reference signal received power
• the measurement report should further include position coordinate (X, Y) (m) and the velocity V of the relay node 105.
• both the conventional event- triggered reporting criteria and the RTP can trigger the measurement report. Namely, if the RN 105 has not arrived at the RTP but certain event-triggered reporting criteria (such as A3) is satisfied, the measurement result report will start in advance and the location will be recorded.
• certain event-triggered reporting criteria such as A3
• the source eNB 102 will receive the measurement report from the RN 105 periodically.
• the source eNB 102 extracts position and velocity information from the measurement report.
• the source eNB 102 will send "Resource Configuration Request Message" to the target eNB 103, such that the target eNB 103 can execute the resource configuration and requests data bi-casting. Otherwise, the source eNB 102 will wait for the next measurement report.
• the HTT is satisfied means that, the time the RN 105 runs to the RHP is equal to or shorter than the HTT, wherein the HTT equals to P+T, P is the reporting period of the measurement report, and T is the handover preparation time and signaling time for establishing the data bi-casting.
• the time the RN 105 runs to the RHP may be calculated based on the position and velocity information extracted from the measurement report and other known information (e.g., the position of RHP). The calculation is very simple, and thus the detailed description is omitted herein.
• the Resource Configuration Request Message sent to the target eNB 103 may contain the resource that the RN 105 needs, position and velocity information, UE context information etc.
• the target eNB 103 will prepare for the incoming handover and configure needed resource in advance.
• the target eNB After completing the resource configuration procedure, at step 5, the target eNB will send "Bi-cast Start Request Message" to the S-GW 106b through the MME 106a. Then the S-GW 106b will bi-cast the data packet to both the source eNB 102 and the target eNB 103 through S 1 interface at the same time.
• the S-GW 106b sends a "Bi-cast Start Request ACK Message" containing the first bi-cast packet ID to the target eNB 103 through the MME 106a to inform that the packets bi-cast has started.
• the measurement report (i.e., the position and velocity infon-nation of the RN 105) helps to decide the starting time of the resource configuration in the target eNB 103, and the data bi-casting is requested immediately after the resource configuration of the target eNB 103 is completed. Because the S-GW 106b starts bi-casting downlink data to both the source eNB 102 and the target eNB 103 right after the channel of the target eNB 103 is activated and before the handover execution process starts, it can reduce handover interruption time with the minimal consumption of network resources compared to the conventional bi-casting scheme in LTE system.
• the target eNB 103 will respond a "Resource Configuration Request ACK Message" to the source eNB 102.
• This message is a RRC message which contains the "MobilityControlInfo" that the RN 105 needs to handover and other access parameters, for example, C-RNTI, target eNB security algorithm identifiers, dedicated RACH preamble and etc.
• the first bi-cast packet ID is also contained.
• the source eNB 102 will deal with other measurement items at the same time.
• the source eNB 102 sends a "Handover (HO) Command Message" to the RN 105 directly.
• This message contains the same information as the "Resource Configuration Request ACK Message”.
• both the conventional handover criteria and the RHP can start the handover execution. Namely, if the RN 105 has not arrived at the RHP but certain handover criteria are satisfied, then the handover will start in advance and the location of handover is recorded. Otherwise, the handover procedure will be executed when the RN 105 arrives at the RHP.
• the source eNB 102 sends the buffered packets which have not sent to the target eNB by bi-cast through the X2 interface.
• the S-GW 106b would send the packet ID that has bi-casted to the source eNB so that the source eNB 102 can forward fewer packets.
• the source eNB 102 sends a "SN Status Transfer Message" to the target eNB 103 to convey uplink PDCP SN receiver status and downlink PDCP SN transmitter status.
• the source eNB 102 sends the packet IDs to the target eNB 103 through X2 interface when it receives the ACK from the RN 105 and the target eNB 103 will delete the relevant packets, i.e, the packets whose IDs are received from the source eNB 102.
• the target eNB 103 will send remaining packets to the RN 105 once the RN 105 accesses to the target eNB 103.
• the RN 105 Upon the reception of the HO message, the RN 105 will detach from the source eNB 102 and synchronize to the target eNB 103,
• the RN 105 performs synchronization to the target eNB and accesses to the target eNB via RACH.
• the target eNB responds with UL allocation and timing advance (TA) for the RN 105 (step 11).
• TA timing advance
• the RN 105 After the RN 105 has successfully accessed to the target eNB 103, at step 12, the RN 105 will send a "Handover (HO) Confirm Message" to the target eNB 103. From now on, the RN 105 has established normal communication link with the target eNB 103 and then the data packets stored in the target eNB 103 starts to transmit.
• HO Heandover
• the target eNB 103 sends a "Source Path Release Request Message" to the MME 106a to inform that the RN 105 has changed cell.
• the MME 106a sends a "Source User Plane Release Request Message" to the S-GW 106b.
• the S-GW 106b releases the downlink data path of the source eNB 102, and at step 16, the S-GW 106b sends a "Source User Plane Release Request ACK Message" to the MME 106a.
• the MME 106a confirms the "Source Path Release Request Message" with a "Source Path Release Request ACK Message" to the target eNB 103.
• the target eNB 103 After receiving the "Source Path Release Request ACK Message" from the MME 106a, at step 18, the target eNB 103 sends a "UE Context Release Message" to the source eNB 102 to inform success of handover and trigger the release of resources of the source eNB 102.
• the source eNB 102 Upon the reception of the "UE Context Release Message", at step 19, the source eNB 102 releases radio and C-plane related resources associated to the UE context. Thus, the handover is completed.
• this time is calculated based on the position and velocity of the RN 105. That is, each time the source eNB 102 receives the report from the RN 105, it will calculate the time t that the RN arrives at the RHP and compare this time t with the HTT, If HTT, then the handover preparation and data bi-casting may start.
• the target eNB 103 when resource configuration of the target eNB 103 has completed, the target eNB 103 will request data packets bi-casting from the S-GW 106b. Once the RN 105 access to the target eNB 103, it can receive packets from the target eNB immediately.
• the bi-casting start time is right after the time the resource configuration of the target eNB 103 is completed, so it is much closer to the handover execution time and it will decrease the handover interruption time and ensure seamless handover. Besides, the bi-casting time is minimized so that the consumption of network resources is decreased.
• the reference points RTP and RHP are both obtained based on vast statistic data of the fast handover.
• the RTP and RHP may be updated based on the measurement report so as to ensure the accuracy of those reference points.
• the RN 105 runs across the cell, the point where the RN 105 satisfies the event-triggered reporting criteria and the point where the handover condition based on radio signal measurement is satisfied are recoded, no matter the point is front or behind the reference points. These two points may be referred as the measured trigger point and measured handover point.
• the acquisition of this point needs the help of the target eNB 103. That is, the measurement will not stop after handover to the target eNB 103. Then the RN 105 will send the report to the target eNB 103, and the target eNB 103 evaluates the ideal handover point based on the report information.
• the RTP and RHP may be updated according to at least one of the following schemes.
• RP ⁇ l - l / 2) ⁇ - ⁇ , + (1 / 2)' RP, (measure, n)
• RP represents either one of the RTP and RHP
• the value of RP is the distance to the source eNB
• RP ⁇ measwe n) is the latest measurement reference point based on the measurement of the mobile RN
• RP n is the updated reference point
• RP n _ is the old reference point
• X 0 is equal to 0
• ⁇ and K are coefficient factors.
• the initial RP may be set according to various criteria.
• the initial RHP may be based on the actual measurement when the network is established.
• the initial RHP may be set as the center point of two neighbor eNBs or based on certain engineering test.
• the initial RHP is set to R P ⁇ measure and certain handover criteria are satisfied, e.g., the following formula (1) is satisfied.
• the RSRP represents Reference Signal Received Power as measured at the RN.
• the initial RTP may be set as (P+ T) - far from the RHP ahead, where V max represents the maximum velocity of high-speed trains.
• the initial RTP may be set as RTP (measure ) when the first train runs across and certain event-triggered reporting criteria are satisfied.
• Fig. 3 is a schematic block diagram of an apparatus 300 that may be configured to practice the exemplary embodiments of the present invention.
• the apparatus 300 may be incorporated into the source eNB 102 and be configured to perform methods of the exemplary embodiments of the present invention.
• the apparatus 300 may comprise a report receiving unit 301 , a handover preparation unit 302, and a handover executing unit 303.
• the report receiving unit 301 may be configured to receive a measurement report sent periodically from a mobile relay node, wherein the sending of the measurement report is triggered no later than the mobile relay node arriving at a Reference Triggering Point (RTP), and the measurement report comprises location, velocity and signal strength information etc. of the mobile relay node.
• the handover preparation unit 302 may be configured to perform handover preparation.
• the handover executing unit 303 is configured to execute handover to a target eNB no later than the mobile relay node arriving at a Reference Handover Point (RHP).
• RHP Reference Handover Point
• the handover preparation unit 302 may be configured to: in response to the time the mobile relay node runs to the RHP is equal to or shorter than a handover Time Threshold (HTT), send a resource configuration request message to the target eNB, such that the target eNB executes the resource configuration and requests data bi-casting; and receive a resource configuration request ACK message from the target eNB, wherein the HTT is equal to P+T, wherein P is reporting period of the measurement report, and T is the time for the resource configuration and signaling for establishing the data bi-casting.
• the resource configuration request ACK message may includes the first bi-casted packet ID.
• the sending of the resource configuration request message is further in response to the speed of the mobile relay node being higher than a Speed Threshold (ST).
• ST Speed Threshold
• the data bi-casting is requested almost immediately after the resource configuration of the target eNB is completed.
• the RTP and RHP may be updated bases on the measurement report.
• the RTP and RHP may be updated according to the schemes 1 -3 as described previously.
• Fig. 4 is a schematic block diagram of an apparatus 400 that may be configured to practice the exemplary embodiments of the present invention.
• the apparatus 400 may be incorporated into the relay node RN 105 and be configured to perform methods of the exemplary embodiments of the present invention.
• the apparatus 400 may comprise a report sending unit 401 , a receiving unit 402, and an accessing unit 403.
• the report sending unit 401 may be configured to send periodically a measurement report to a source eNB, wherein the sending is triggered no later than the mobile relay node arriving at a Reference Triggering Point (RTP), and the measurement report comprises location and velocity information of the mobile relay node.
• RTP Reference Triggering Point
• the receiving unit 402 may be configured to receive a handover command from the source eNB.
• the handover command may include an ID of the first packet being bi-casted.
• the accessing unit 403 is configured to access to a target eNB.
• the RTP may be updated bases on the measurement report.
• the RTP may be updated according to the schemes 1-3 as described previously.
• Fig. 5 illustrates a simplified block diagram of a network element 500 that is suitable for use in practicing the exemplary embodiments of the present invention.
• the network element 500 includes a data processor (DP) 503, a memory (MEM) 504 coupled to the DP 503, and a communication interface 505 coupled to the DP 503.
• the MEM 504 stores a program (PROG) 506.
• the communication interface 505 may represent any interface that is necessary for communication with other network elements, such as X2 interface for bidirectional communications between eNBs, SI interface for communication between the MME/S-GW and the eNB, or Un interface for communication between the eNB and the RN.
• the program (PROG) 506 may be configured, together with the DP 503, to cause the network element 500 to act as the source eNB 102 and operate in accordance with the exemplary embodiments of the invention. In other embodiments, the program (PROG) 506 may be configured, together with the DP 503, to cause the network element 500 to act as the mobile relay node RN 105 and operate in accordance with the exemplary embodiments of the invention.
• the embodiments of the present invention may be implemented by computer software executable by the DP 503 of the network element 500, or by hardware, or by a combination of software and hardware.
• Fig. 6 illustrates the simulation results of Handover Failure Probability with different RN velocity.
• Hysteresis is 3 dB in left part and 2dB in right part. Because the ST is set as 60m/s, when velocity is higher than 60m/s, then the Handover Failure Probability reduces significantly about 20-30 percentages when hysteresis is 3 dB and 5-10 percentages when hysteresis is 2 dB.
• Fig. 7 illustrates the simulation results of Handover Overall Procedure Delay with different RN velocity.
• the handover delay hysteresis is determined by propagation and velocity of RN. When velocity is higher than 60m/s, then the Tho deiay reduces significantly about 150 ms.
• the proposed handover procedure delay can well satisfy the handover delay hysteresis. From the simulation result in Fig. 8, it is known that the Handover Interruption Time reduced about 5ms caused by packet fluctuation delay.
• the foregoing computer program instructions can be, for example, sub-routines and/or functions.
• a computer program product in one embodiment of the invention comprises at least one computer readable storage medium, on which the foregoing computer program instructions are stored.
• the computer readable storage medium can be, for example, an optical compact disk or an electronic memory device like a RAM (random access memory) or a ROM (read only memory).

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• 2012
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