WO2008096240A1 - Method and apparatus for providing interference coordination in handover signaling - Google Patents

Method and apparatus for providing interference coordination in handover signaling Download PDF

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Publication number
WO2008096240A1
WO2008096240A1 PCT/IB2008/000264 IB2008000264W WO2008096240A1 WO 2008096240 A1 WO2008096240 A1 WO 2008096240A1 IB 2008000264 W IB2008000264 W IB 2008000264W WO 2008096240 A1 WO2008096240 A1 WO 2008096240A1
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Prior art keywords
base station
frequency
transmission
user equipment
suspension
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PCT/IB2008/000264
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French (fr)
Inventor
Leping Huang
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Nokia Corporation
Nokia Inc.
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Priority to US88851607P priority Critical
Priority to US60/888,516 priority
Application filed by Nokia Corporation, Nokia Inc. filed Critical Nokia Corporation
Publication of WO2008096240A1 publication Critical patent/WO2008096240A1/en

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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W36/00Hand-off or reselection arrangements
    • H04W36/16Performing reselection for specific purposes
    • H04W36/20Performing reselection for specific purposes for optimising the interference level
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W36/00Hand-off or reselection arrangements
    • H04W36/08Reselecting an access point

Abstract

An approach is provided for providing interference coordination in handover signaling. An interference condition is determined based on a measurement report from a terminal. A transferring base station instructs a targeted base station to suspend transmission to mitigate the interference condition. The transferring base station generates a signal to instruct the terminal to handover to the targeted base station.

Description

METHOD AND APPARATUS FOR

PROVIDING INTERFERENCE COORDINATION

IN HANDOVER SIGNALING

RELATED APPLICATIONS

Ji)OO i J This application claims the benefit of the earlier filing date under 35 U. S. C. §1 19(e) of U.S. Provisional Application Serial No. 60/888,516 filed February 06, 2007, entitled "Method and System For Providing Interference Coordination In Handover Signaling," the entirety of which is incorporated by reference.

BACKGROUND

|I)(M)2| Radio communication systems, such as a wireless data networks (e.g., Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, spread spectrum systems (such as Code Division Multiple Access (CDMA) networks), Time Division Multiple Access (TDMA) networks, etc.), provide users with the convenience of mobility along with a rich set of services and features. This convenience has spawned significant adoption by an ever growing number of consumers as an accepted mode of communication for business and personal uses. To promote greater adoption, the telecommunication industry, from manufacturers to service providers, has agreed at great expense and effort to develop standards for communication protocols that underlie the various services and features. One area of effort involves handover procedures, particularly intra-frequency handover, within a communication system. j 00031 Therefore, there is a need for an approach for providing efficient and reliable handover signaling. SOME EXEMPLARY EMBODIMENTS

|()004] These and other needs are addressed by various exemplary embodiments of the invention, in which an approach is presented for providing interference coordination in handover signaling.

[00051 According to one embodiment of the invention, a method comprises receiving a measurement report from a user equipment. The method also comprises determining an interference condition with a target base station based on the measurement report. The method also comprises instructing the target base station to suspend transmission to mitigate the interference condition, and generating a signal instructing the user equipment to handover to the target base station j 00061 According to another embodiment of the invention, an apparatus comprises a processor configured to receive a measurement report from a user equipment. The processor is further configured to determine an interference condition with a target base station based on the measurement report, and to instruct the target base station to suspend transmission to mitigate the interference condition. The processor generates a signal instructing the user equipment to handover to the target base station.

100071 According to another embodiment of the invention, a method comprises receiving a command from a base station to suspend transmission to avoid interference with a user equipment that is served by the base station. The suspension of the transmission is performed during handover of the user equipment from the base station. The command is generated based on a measurement report from the user equipment. The method also comprises generating a confirmation message for transmission to the base station in response to the command. The confirmation message specifies duration of the suspension of the transmission and a confirmed frequency

100081 According to yet an exemplary embodiment, an apparatus comprises a transceiver configured to receive a command from a base station to suspend transmission to avoid interference with a user equipment that is served by the base station. The suspension of the transmission is performed during handover of the user equipment from the base station. The command is generated based on a measurement report from the user equipment. The apparatus also includes a processor configured to generate a confirmation message for transmission to the base station in response to the command. The confirmation message specifies duration of the suspension of the transmission and a confirmed frequency.

!0009I Still other aspects, features, and advantages of the invention are readily apparent from the following detailed description, simply by illustrating a number of particular embodiments and implementations, including the best mode contemplated for carrying out the invention. The invention is also capable of other and different embodiments, and its several details can be modified in various obvious respects, all without departing from the spirit and scope of the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

|00 I 0| The invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements and in which:

|001 l | FIG. 1 is a diagram of a communication system capable of providing reliable handover signaling, according to an exemplary embodiment of the invention;

|00 ! 2| FIG. 2 is a flowchart of a handover process involving suspending transmission of a target base station to avoid interference, in accordance with an embodiment of the invention;

|00π| FIG. 3 is a flowchart of a handover process wherein a target base station confirms frequency selection and timing information, in accordance with an embodiment of the invention;

|00 l4| FIG. 4 is a ladder diagram of a process for providing intra-MME/UPE (Mobile Management Entity/ User Plane Entity) handover procedure;

|0015| FIG. 5 is a ladder diagram of a process for providing source-destination interference coordination based on a handover procedure, in accordance with an embodiment of the invention; i 001 () I FIG. 6A and 6B are diagrams showing distribution of a dominant cumulative interference plus noise ratio (DCINR) under various scenarios, in accordance with an embodiment of the invention;

I ()0 l 7| FIG. 7 is a diagram of hardware that can be used to implement an embodiment of the invention;

10018 j FIGs. 8A-8D are diagrams of communication systems having exemplary long-term evolution (LTE) architectures, in which the system of FIG. 1 can operate, according to various exemplary embodiments of the invention; and

|00 il>) FIG. 9 is a diagram of exemplary components of an LTE terminal configured to operate in the systems of FIGs. 8A-8D, according to an embodiment of the invention

DESCRIPTION OF PREFERRED EMBODIMENT

|0020| An apparatus, method, and software for providing a reliable handover signaling are disclosed. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. It is apparent, however, to one skilled in the art that the embodiments of the invention may be practiced without these specific details or with an equivalent arrangement. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention.

|0021 j Although the embodiments of the invention are discussed with respect to a communication network having a Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) architecture, it is recognized by one of ordinary skill in the art that the embodiments of the inventions have applicability to any type of communication system and equivalent functional capabilities.

|OO22 | FIG. 1 is a diagram of a communication system capable of providing reliable handover signaling, according to an exemplary embodiment of the invention. By way of example, the communication of FIG. 1 utilizes an architecture compliant with the long term evolution (LTE) of UMTS (Universal Mobile Telecommunications System) terrestrial radio access network (UTRAN) in 3GPP; this more fully described below with respect to FIGs. 8A-8D. As shown, a user equipment (UE) 101 communicates with one or more base stations 103, which under the 3GPP LTE architecture are denoted as an enhanced Node B's (eNBs) 103. At any one moment, the UE 101 is served by a single base station 103. The UE 101 can be any type of mobile stations, such as handsets, terminals, stations, units, devices, or any type of interface to the user (such as "wearable" circuitry, etc.). In this architecture, a Mobile Management Entity (MME) 105 is connected to each base station 103. Additionally, a User Plane Entity (UPE) 107 provides, for example, Internet Protocol IP header compression and encryption of user data streams, termination of U-plane packets for paging reasons, and switching of U-plane for support of UE mobility. Although shown as two separate entities, the MME 105 and UPE 107 can constitute a single component. j 00231 Handover (HO) signaling plays an important role for ensuring reliable transfer of an ongoing call or data session, as described in FIGs. 2-5. In one embodiment, a 3GPP, LTE/3.9G system is a frequency reuse- 1 system without soft handover. During this process, the UE 101, which is currently served by the source base station 103a, selects another base station 103d (denoted as the target base station). Ln an exemplary embodiment, the handover procedure is deployed in an E-UTRAN - or 3.9G/LTE - which is a packet-data-based transmission system. Also, the approach supports intra-frequency, inter-frequency and intra-RAT (Radio Access Technology) handover.

10024 j Typically, intra-frequency handover is triggered when UE 101 is in the cell edge of current serving cell. In a frequency reuse- 1 system such as LTE, UE 101 may experience strong interference and low SNIR (Signal to Noise plus interference) (e.g., less than -5db) on the downlink (DL) when the UE 101 is near the cell edge. Given such low SNIR, BLER (Block Error Ratio) of message after ARQ and HARQ (Hybrid Automatic Repeat Request) can be still very low in some scenarios. Consequently, there is a concern whether HO execution signaling (mainly HO command in DL) can be reliably transmitted between the eNB 103 and the UE 101. In other words, there may be a coverage problem of HO execution signaling in LTE. j 00251 In an LTE intra-frequency handover procedure, the following observations are noted. First, at the time of handover, target eNB 103b is typically the strongest interferer to UE 101. Receiver power from target eNB 103b is generally stronger than that of any other cells, including its current source eNB 103a. Second, measurement reports can be generated to include information about a strongest interferer (e.g., target eNB) 103b. Third, before generating a HO (Handover) command, the source eNB 103a exchanges messages (e.g., context data/context confirm) with the target eNB 103b via, for example, X2 interface 109. The X2 interface 109, which provides an interface between the eNBs 103. To minimize packet loss during HO, packet forwarding from the source eNB 103a to the target eNB 103b is supported using the X2 interface 109. For instance, when HO occurs involving changes of the serving eNB, packets that are buffered in the source eNB 103a are forwarded to the target eNB 103b via the X2 interface 109. The X2 interface 109 includes two parts: 1) C-plane: X2-C interface is C-plane interface between eNBs 103; and 2) U-plane: X2-U interface is U-plane interface between eNBs 103. The X2-C interface can provide mobility functions (for UE 101 mobility between eNBs 103), including, for example, HO signaling and control of U-plane tunnels. This interface also provides multi-cell radio resource management (RRM) functions, including measurement reporting and general X2 management and error handling functions. The X2-U interface supports the tunneling of end user packets between the eNBs 103.

|002(>| FIG. 2 is a flowchart of a handover process involving suspending transmission of a target base station to avoid interference, in accordance with an embodiment of the invention. To improve the reliability of HO signaling, the processes of FIGs. 2-3 involves a source base station coordinating with a target base station to suspend, for example, the DL (Downlink) transmission at target base station at the time and frequency when source base station transmits HO command to the handover UE. Such coordination can be implemented with small modification on current HO signaling (context data/context confirm). By canceling the strongest interference to HO command when HO, both the reliability and coverage of HO command can be improved.

100271 In contrast with a general ICIC (Inter-cell Interference Coordination) scheme, the processes of FIGs. 2-3, according to various embodiments, exhibit the following features. First, there need not be a centralized/distributed server to manage the interferer map, because the target base station as the strongest interferer is canceled. Secondly, the process need not require any extra signaling to coordinate the interference. In one embodiment, existing HO signaling on a U- plane interface (e.g., X2 interface) can be utilized, along with a measurement report on the radio link. 1002 Hj As shown, in step 201, the UE 101 transmits a measurement report (e.g., channel quality indicator report) that specifies the strongest interferer to the UE 101 to the source base station 103a. Upon receiving the transmitted measurement report, the source base station 103a, per step 203 determines whether an interference condition exists based on the measurement report. Next, the source base station 103a instructs, as in step 205, the target base station 103b to suspend transmission as to mitigate (or avoid all together) the interference condition; the command or message that conveys the instruction can include timing information (e.g., duration of the suspension of the transmission, start time of the HO command, etc.) and a candidate frequency, for example. In step 207, the target base station 103b confirms the instructions; namely, the timing information and candidate frequency are confirmed. Thereafter, the source base station 103a signals to the user equipment 101 to handover to the target base station 103b, according to the confirmed timing information and the frequency (step 209).

|002')| The process of confirming the timing information and the frequency is more detailed in FIG. 3, as next described.

|0030| FIG. 3 is a flowchart of a handover process wherein a target base station confirms frequency selection and timing information, in accordance with an embodiment of the invention. In step 301, the target base station 103b receives a command from the source base station 103a based on interference between the target base station 103b with the UE 101 , which is served by source base station 103a. The command specifies a candidate frequency and timing information. The target base station 103b, per step 303, confirms the candidate frequency specified by the source base station 103a or selects from other candidate frequencies. That is, the target base station 103b can elect to utilize a frequency of its choosing; such frequency or frequencies can be determined using measurement reports from user equipment that the target base station 103b presently serves. In step 305, the target base station 103b generates a confirmation message specifying the confirmed frequency and confirmed timing information to the source base station 103a. The target base station 103b, per step 307, transmits the confirmation message to the source base station 103a in response to command.

10031 1 To better appreciate the above processes, it is instructive to examine a baseline HO procedure, as shown in FIG. 4. 10032| FIG. 4 is a ladder diagram of a process for providing intra-MME/UPE (Mobile Management Entity/ User Plane Entity) handover procedure. Under this scenario, the MME 105/UPE 107 transmits packet data to the source base station 103a (e.g., eNB), per step 401. In step 403, data is received by the UE 101 from the source eNB 103a. The source eNB 103a, per step 405, periodically allocates UL resources for the UE 101 to transmit UL feedback. In step 407, the UE 101 transmits a measurement report, using the UL allocations, to the source eNB 103a. The source eNB 103a, per step 409, utilizes the measurement report (e.g., indicative of the radio channel conditions) to determine whether to handover the UE 101 to the target base station 103b. The source eNB 103a then generates a context data message, specifying the UE radio access network (RAN) context, and transmits the message to the target eNB 103b (step 41 1 ). In step 413, the context message is stored and Cell-Radio Network Temporary Identity (C-RNTI) is reserved. A confirm message, which provides a new C-RNTI, is forwarded to the source eNB 103a, per step 415.

|0033| Upon receiving the context confirm message (e.g., new C-RNTI) from the target eNB 103b, the source eNB 103a allocates UL resources for the UE 101 (step 417). In step 419, the source eNB 103a transmits a handover command to UE 101.

J0034] The UE 101 receives HO command with necessary parameters -- e.g., new C-RNTI, possible starting time, target eNB SIBs, etc. In step 421 , the UE 101 starts to detach from the old cell and subsequently synchronizes to a new cell.

100351 Additionally, the source eNB 103a delivers, per steps 423 and 425, buffered data packets to the target eNB 103b. These user data packets are then received by the target base station 103b (step 427).

100361 Tn step 429, the UE 101 performs synchronization to the target eNB 103b and then starts acquiring UL timing advance (TA), after expiry of a starting time in the HO command. The target eNB 103b, in turn, responds with UL allocation and timing advance (step 43 1 ) for the UE 101 , which sends a HO confirm message (per step 433) back to the target eNB 103b. This completes the handover procedure for the UE 101 .

(0037) At this point, the source eNB 103a receives packet data (per step 435) from the MME 105/UPE 107, and the target eNB 103b completes the handover procedure with a 110 complete message to the source eNB 103a and provides an update message to the MME 105/UPE 107 regarding the HO completion (per steps 437 and 439). The source eNB can then clear already forwarded data from its buffers, as in step 441. As shown, the MME 105/UPE 107 can perform path switching, per step 443.

|0038| In step 445, the source eNB 103a continues forwarding UE data if there are remaining packets stored in the buffers. Further, data packets are received from the MME 105/UPE 107 at the target eNB 103b, which relays these packets to the UE 101 (now in its new cell), per steps 447 and 449.

|0039j In the above procedure, when UE 101 is poor radio condition, for example, UE 101 is in the cell edge of current serving cell using frequency reuse system (e.g., LTE), the UE 101 may experience strong interference when UE 101 has to receive HO execution signaling (HO command in DL). Moreover, at the time of HO, target eNB 103b is typically the strongest interferer to UE 101. Therefore, there is a need for providing efficient and reliable handover signaling during an intra-LTE handover is performed.

J(HMOi FIG. 5 is a ladder diagram of a process for providing source-destination interference coordination based on a handover procedure, in accordance with an embodiment of the invention. One aspect of this exemplary embodiment is that the baseline HO procedure explained in FIG. 4 can largely remain in tact. That is, steps 501-507 resembles that of steps 401-407 of the baseline HO procedure. In step 507, the UE 101 generates a measurement report, e.g., a channel quality indicator report, upon triggering a measurement event. In other words, when certain conditions (e.g., rules set by system information or specification, etc.) have been satisfied. For instance, the event can involve exceeding a particular interference level. It is recognized that this also implicitly reports to the source eNB 103a the strongest interferer to the downlink radio link from the source eNB 103a to the UE 101. The source eNB 103a, per step 409, utilizes the measurement report (e.g., indicative of the radio channel conditions) to determine whether to handover the UE 101 to the target base station 103b. In other words, when the source eNB 103a determines that the UE 101 should handover to target eNB 103b because of poor radio condition, it also knows that target eNB 103b is the strongest interferer to the radio link from source eNB 103a to UE 101. 10041 1 Based on the determined radio condition, the source eNB 103a includes information regarding candidate frequency (e.g., sub-band, resource block identifier (RB ID), etc.) and timing information (e.g., duration of time the base station wants to transmit the HO command) in a context data message as part of the HO decision, per steps 509-513. In other words, the source eNB 103a passes relevant information (e.g., context data (UE RAN context), frequency, duration, etc.) in a HO request. In step 515, the context message is stored, and the C-RNTI is reserved.

|0042| If the target eNB 103b decides to accept the UE 101 to serve, the target eNB 103b selects a frequency (e.g., which can be the candidate frequency from the source base station 103a) and the timing information (e.g., time period or duration which the target base station 103b prefers to not transmit, start time of the HO command, etc.). This information is included in the context confirm message (e.g., new C-RNTI, frequency, and duration of start time of HO command). After obtaining resources, the target eNB 103b, per step 517, delivers to the source eNB 103a, the context confirm message - which includes configuration information together with a temporary identifier (new C-RNTI) with respect to the corresponding UE 101.

[0043] The steps from DL allocation to deliver of user data (steps 519-527) are similar to those corresponding ones in the process of FIG. 4. By contrast, the target eNB do not transmit at the specified (or confirmed) frequency during one of two time periods: (1 ) from the transmission of the context confirm message (step 515) to the delivery of the user data (step 527); or (2) from the start time plus to the duration. Otherwise, the remaining steps 529-551 can be executed as in the baseline HO procedure of FIG. 4.

[00441 According to certain embodiments, various techniques can be utilized to derive the time the target eNB should not transmit. For example, if the delay on the X2 interface 109 is not long, the period of muting time (target eNB 103b stop transmission) starts from the transmission of context confirm, and ends when the delivered user data (i) message (in step 527) is received. After receiving a context confirm message, the source eNB 103a can immediately start the transmission of HO command at the frequency specified by target eNB 103b. If X2 interface delay is long, the starting time and duration by which target eNB 103b should not transmit can be specified by the target eNB 103b; this information can be included in the context confirm message. After receiving the context confirm message, the source eNB 103a starts the transmission of HO command at the starting time and frequency specified by target eNB 103b. The HO command is transmitted to UE 101. The duration/starting time can be derived by eNB 103 from channel condition, HARQ (Hybrid Automatic Repeat Request) retransmission delay, X2 interface delay as well as other factors. It is noted that this message will not be interfered by the target eNB 103b. Consequently, the BLER (Block Error Ratio) of the HO command at UE 101 can be improved over the conventional systems.

S 0045 j Furthermore, various techniques, according to the certain embodiments, can be utilized to determine the frequency by which target eNB 103b should suspend its transmission. One approach is that the source eNB 103a determines one frequency for the target eNB 103b based on a Channel Quality Indicator (CQI) report feedback, and/or power mask of soft frequency reuse (SFR) is used from UEs it is serving. Another approach provides that the source eNB 103a proposes several frequency candidates to the target eNB 103b; the target eNB 103b can determine one from the candidates based on CQI report feedback from UEs it is serving and/or power mask of SFR.

I ()04<ι I It is noted that in an asynchronous network, reference signal of the target eNB 103b may still interfere with the transmission of HO Command from source eNB 103 a. In other words, the interference to HO Command cannot be fully cancelled in an asynchronous network. In traditional systems, it is assumed that the density of pilot is very low (e.g., one every 6 sub- carrier in frequency domain, 1-2 every 14 symbols in time domain). The collision/overlapping probability between pilot from the target eNB 103b, and the HO command from the source eNB 103a is still very low.

[00471 It is instructive to examine certain observations regarding the dominant interferer (see R 1-070390, 3GPP TSG RAN WGl #47bis meeting, entitled "open loop DL transmit diversity for common control channels," which is incorporated herein by reference in its entirety. A dominant interference is defined by using a measure called Dominant Cumulative Interference plus Noise Ratio (DCINR) as below.

DCINR(L) = .

Figure imgf000012_0001
j 00481 As seen in FIG. 5, the source eNB 103a signals a DL allocation followed by a handover command to the UE 101 (steps 519 and 521). At this point, the UE 101 can detach from the old cell and synchronize to the new cell. Handover confirmation is performed between the UE 101 and the target eNB 103b, which then signals a completion with the source eNB 103a. Subsequently, the target eNB 103b provides the UE 101 update to the MME 105/UPE 107. Ultimately, data transmission resumes.

|(>04^| The source eNB 103a can decide whether to turn on (i.e., enable) this feature based on current channel quality, CQI report feedback from UE 101, load etc. If the DL channel quality from source eNB 103a to UE 101 is reliable, source eNB 103a can turn off this feature, and not propose any time- frequency to mute to target eNB 103b . This can increase throughput in target eNB 103b.

10050 i FIG. 6A and 6B are diagrams showing distribution of a dominant cumulative interference plus noise ratio (DCINR) under various scenarios, in accordance with an embodiment of the invention. Graph 601, as shown in FIG. 6A, relates to a study of the entire population of users (i.e., user equipment), wherein the left most curve is the strongest interferer and the right most, the weakest.

10051 1 FIG. 6B shows the dominant interference of UE at cell edge, where HO typically occurs. Graph 603 shows the interference from strongest interferer (target cell when intra- frequency happens) counts for roughly 30% of the total interference. In other words, if the target eNB does not transmit in DL at the time and frequency when transmitting HO command, the total interference to HO command can be reduced by 30% on average. Depending on the exact channel code, at least l~2db gain to SNIR of HO command message can be realized, and the BLER of HO message can be minimized.

100521 From the HO perspective, reliability of HO signaling may become a bottleneck to LTE system. The described process of FIG. 5 requires minimum (to no) modification on traditional system architecture, but yet achieves similar level of gain regarding coverage and reliability of HO signaling.

100531 From the ICIC perspective, comparing with normal ICIC scheme, first, this approach, according to certain embodiments, avoids complicated functionality to manage interferer map (which eNB is the strongest interferer to which UE). Secondly, this approach avoids extra signaling to update/maintain interferer, and signaling of interference coordination; the existing HO signaling can be used on the X2 interface and the measurement report on the radio link. It is further noted that if the transmission of HO command failed, the UE will move to the idle state, and start cell reselection. The whole procedure due to the failure of HO command will cause an intolerable delay (e.g., at least 500ms interruption time).

I Ot*5-41 One of ordinary skill in the art would recognize that the processes for handover signaling may be implemented via software, hardware (e.g., general processor, Digital Signal Processing (DSP) chip, an Application Specific Integrated Circuit (ASIC), Field Programmable Gate Arrays (FPGAs), etc.), firmware, or a combination thereof. Such exemplary hardware for performing the described functions is detailed below with respect to FIG. 7.

100551 FIG. 7 illustrates exemplary hardware upon which various embodiments of the invention can be implemented. A computing system 700 includes a bus 701 or other communication mechanism for communicating information and a processor 703 coupled to the bus 701 for processing information. The computing system 700 also includes main memory 705, such as a random access memory (RAM) or other dynamic storage device, coupled to the bus 701 for storing information and instructions to be executed by the processor 703. Main memory 705 can also be used for storing temporary variables or other intermediate information during execution of instructions by the processor 703. The computing system 700 may further include a read only memory (ROM) 707 or other static storage device coupled to the bus 701 for storing static information and instructions for the processor 703. A storage device 709, such as a magnetic disk or optical disk, is coupled to the bus 701 for persistently storing information and instructions.

! 00561 The computing system 700 may be coupled via the bus 701 to a display 71 1 , such as a liquid crystal display, or active matrix display, for displaying information to a user. An input device 713, such as a keyboard including alphanumeric and other keys, may be coupled to the bus 701 for communicating information and command selections to the processor 703. The input device 713 can include a cursor control, such as a mouse, a trackball, or cursor direction keys, for communicating direction information and command selections to the processor 703 and for controlling cursor movement on the display 71 1. |0057| According to various embodiments of the invention, the processes described herein can be provided by the computing system 700 in response to the processor 703 executing an arrangement of instructions contained in main memory 705. Such instructions can be read into main memory 705 from another computer-readable medium, such as the storage device 709. Execution of the arrangement of instructions contained in main memory 705 causes the processor 703 to perform the process steps described herein. One or more processors in a multiprocessing arrangement may also be employed to execute the instructions contained in main memory 705. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the embodiment of the invention. In another example, reconfigurable hardware such as Field Programmable Gate Arrays (FPGAs) can be used, in which the functionality and connection topology of its logic gates are customizable at run-time, typically by programming memory look up tables. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and software.

10058! The computing system 700 also includes at least one communication interface 715 coupled to bus 701. The communication interface 715 provides a two-way data communication coupling to a network link (not shown). The communication interface 715 sends and receives electrical, electromagnetic, or optical signals that carry digital data streams representing various types of information. Further, the communication interface 715 can include peripheral interface devices, such as a Universal Serial Bus (USB) interface, a PCMCIA (Personal Computer Memory Card International Association) interface, etc.

100591 The processor 703 may execute the transmitted code while being received and/or store the code in the storage device 709, or other non-volatile storage for later execution. In this manner, the computing system 700 may obtain application code in the form of a carrier wave.

100001 The term "computer-readable medium" as used herein refers to any medium that participates in providing instructions to the processor 703 for execution. Such a medium may take many forms, including but not limited to non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as the storage device 709. Volatile media include dynamic memory, such as main memory 705. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise the bus 701. Transmission media can also take the form of acoustic, optical, or electromagnetic waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, CDRW, DVD, any other optical medium, punch cards, paper tape, optical mark sheets, any other physical medium with patterns of holes or other optically recognizable indicia, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave, or any other medium from which a computer can read.

10061 1 Various forms of computer-readable media may be involved in providing instructions to a processor for execution. For example, the instructions for carrying out at least part of the invention may initially be borne on a magnetic disk of a remote computer. In such a scenario, the remote computer loads the instructions into main memory and sends the instructions over a telephone line using a modem. A modem of a local system receives the data on the telephone line and uses an infrared transmitter to convert the data to an infrared signal and transmit the infrared signal to a portable computing device, such as a personal digital assistant (PDA) or a laptop. An infrared detector on the portable computing device receives the information and instructions borne by the infrared signal and places the data on a bus. The bus conveys the data to main memory, from which a processor retrieves and executes the instructions. The instructions received by main memory can optionally be stored on storage device either before or after execution by processor.

(0062| By way of example, the communication system of FIG. 1 utilizes an architecture compliant with the UMTS terrestrial radio access network (UTRAN) or Evolved UTRAN (E- UTRAN) in 3GPP, as next described.

100631 FIGs. 8A-8D are diagrams of communication systems having exemplary LTE architectures, in which the system of FIG. 1 can operate, according to various exemplary embodiments of the invention. By way of example (shown in FIG. 1), the base station and the UE can communicate in system 800 using any access scheme, such as Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Wideband Code Division Multiple Access (WCDMA), Orthogonal Frequency Division Multiple Access (OFDMA) or Single Carrier Frequency Division Multiple Access (SC-FDMA) or a combination thereof. In an exemplary embodiment, both uplink and downlink can utilize WCDMA. In another exemplary embodiment, uplink utilizes SC-FDMA, while downlink utilizes OFDMA. i 00641 The MME (Mobile Management Entity)/Serving Gateways 801 are connected to the eNBs in a full or partial mesh configuration using tunneling over a packet transport network (e.g., Internet Protocol (IP) network) 803. Exemplary functions of the MME/Serving GW 801 include distribution of paging messages to the eNBs, IP header compression, termination of U-plane packets for paging reasons, and switching of U-plane for support of UE mobility. Since the GWs 801 serve as a gateway to external networks, e.g., the Internet or private networks 803, the GWs 801 include an Access, Authorization and Accounting system (AAA) 805 to securely determine the identity and privileges of a user and to track each user's activities. Namely, the MME Serving Gateway 801 is the key control-node for the LTE access-network and is responsible for idle mode UE tracking and paging procedure including retransmissions. Also, the MME 801 is involved in the bearer activation/deactivation process and is responsible for selecting the SGW (Serving Gateway) for a UE at the initial attach and at time of intra-LTE handover involving Core Network (CN) node relocation.

(00651 A more detailed description of the LTE interface is provided in 3GPP TR 25.813, entitled "E-UTRA and E-UTRAN: Radio Interface Protocol Aspects," which is incorporated herein by reference in its entirety.

100661 In FIG. 8B, a communication system 802 supports GERAN (GSM/EDGE radio access) 804, and UTRAN 806 based access networks, E-UTRAN 812 and non-3GPP (not shown) based access networks, and is more fully described in TR 23.882, which is incorporated herein by reference in its entirety. A key feature of this system is the separation of the network entity that performs control-plane functionality (MME 808) from the network entity that performs bearer-plane functionality (Serving Gateway 810) with a well defined open interface between them SI l . Since E-UTRAN 812 provides higher bandwidths to enable new services as well as to improve existing ones, separation of MME 808 from Serving Gateway 810 implies that Serving Gateway 810 can be based on a platform optimized for signaling transactions. This scheme enables selection of more cost-effective platforms for, as well as independent scaling of, each of these two elements. Service providers can also select optimized topological locations of Serving Gateways 810 within the network independent of the locations of MMEs 808 in order to reduce optimized bandwidth latencies and avoid concentrated points of failure.

|0067| The basic architecture of the system 802 contains following network elements. As seen in FIG. 8B, the E-UTRAN (e.g., eNB) 812 interfaces with UE via LTE-Uu. The E-UTRAN 812 supports LTE air interface and includes functions for radio resource control (RRC) functionality corresponding to the control plane MME 808. The E-UTRAN 812 also performs a variety of functions including radio resource management, admission control, scheduling, enforcement of negotiated uplink (UL) QoS (Quality of Service), cell information broadcast, ciphering/deciphering of user, compression/decompression of downlink and uplink user plane packet headers and Packet Data Convergence Protocol (PDCP).

[00681 The MME 808, as a key control node, is responsible for managing mobility UE 101 identifies and security parameters and paging procedure including retransmissions. The MME 808 is involved in the bearer activation/deactivation process and is also responsible for choosing Serving Gateway 810 for the UE. MME 808 functions include Non Access Stratum (NAS) signaling and related security. MME 808 checks the authorization of the UE to camp on the service provider's Public Land Mobile Network (PLMN) and enforces UE roaming restrictions. The MME 808 also provides the control plane function for mobility between LTE and 2G/3G access networks with the S3 interface terminating at the MME 808 from the SGSN (Serving GPRS Support Node) 814. The principles of PLMN selection in E-UTRA are based on the 3GPP PLMN selection principles. Cell selection can be required on transition from MME DETACHED to EMM-IDLE or EMM-CONNECTED. The cell selection can be achieved when the UE NAS identifies a selected PLMN and equivalent PLMNs. The UE 101 searches the E-UTRA frequency bands and for each carrier frequency identifies the strongest cell. The UE 101 also reads cell system information broadcast to identify its PLMNs. Further, the UE 101 seeks to identify a suitable cell; if it is not able to identify a suitable cell, it seeks to identify an acceptable cell. When a suitable cell is found or if only an acceptable cell is found, the UE 101 camps on that cell and commences the cell reselection procedure. Cell selection identifies the cell that the UE 101 should camp on.

|006()| The SGSN 814 is responsible for the delivery of data packets from and to the mobile stations within its geographical service area. Its tasks include packet routing and transfer, mobility management, logical link management, and authentication and charging functions. The S6a interface enables transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system (AAA interface) between MME 808 and HSS (Home Subscriber Server) 816. The SlO interface between MMEs 808 provides MME relocation and MME 808 to MME 808 information transfer. The Serving Gateway 810 is the node that terminates the interface towards the E-UTRAN 812 via Sl-U.

100701 The S 1 -U interface provides a per bearer user plane tunneling between the E-UTRAN 812 and Serving Gateway 810. It contains support for path switching during handover between eNBs 812. The S4 interface provides the user plane with related control and mobility support between SGSN 814 and the 3GPP Anchor function of Serving Gateway 810.

10071 1 The Sl 2 is an interface between UTRAN 806 and Serving Gateway 810. Packet Data Network (PDN) Gateway 818 provides connectivity to the UE 101 to external packet data networks by being the point of exit and entry of traffic for the UE 101. The PDN Gateway 818 performs policy enforcement, packet filtering for each user, charging support, lawful interception and packet screening. Another role of the PDN Gateway 818 is to act as the anchor for mobility between 3GPP and non-3GPP technologies such as WiMax and 3GPP2 (CDMA IX and EvDO (Evolution Data Only)).

100721 The S7 interface provides transfer of QoS policy and charging rules from PCRF (Policy and Charging Role Function) 820 to Policy and Charging Enforcement Function (PCEF) in the PDN Gateway 818. The SGi interface is the interface between the PDN Gateway and the operator's IP services including packet data network 822. Packet data network 822 may be an operator external public or private packet data network or an intra operator packet data network, e.g., for provision of IMS (IP Multimedia Subsystem) services. Rx+ is the interface between the PCRF and the packet data network 822.

100731 As seen in FIG. 8C, the eNB utilizes an E-UTRA (Evolved Universal Terrestrial Radio Access) (user plane, e.g., RLC (Radio Link Control) 815, MAC (Media Access Control) 817, and PHY (Physical) 819, as well as a control plane (e.g., RRC 821)). The eNB also includes the following functions: Inter Cell RRM (Radio Resource Management) 823, Connection Mobility Control 825, RB (Radio Bearer) Control 827, Radio Admission Control 829, eNB Measurement Configuration and Provision 831, and Dynamic Resource Allocation (Scheduler) 833.

10074 j The eNB communicates with the aGW 801 (Access Gateway) via an Sl interface. The aGW 801 includes a User Plane 801a and a Control plane 801b. The control plane 801b provides the following components: SAE (System Architecture Evolution) Bearer Control 835 and MM (Mobile Management) Entity 837. The user plane 801b includes a PDCP (Packet Data Convergence Protocol) 839 and a user plane functions 841. It is noted that the functionality of the aGW 801 can also be provided by a combination of a serving gateway (SGW) and a packet data network (PDN) GW. The aGW 801 can also interface with a packet network, such as the Internet 843.

[00751 In an alternative embodiment, as shown in FIG. 8D, the PDCP (Packet Data Convergence Protocol) functionality can reside in the eNB rather than the GW 801. Other than this PDCP capability, the eNB functions of FIG. 8C are also provided in this architecture.

[0076| In the system of FIG. 8D, a functional split between E-UTRAN and EPC (Evolved Packet Core) is provided. In this example, radio protocol architecture of E-UTRAN is provided for the user plane and the control plane. A more detailed description of the architecture is provided in 3GPP TS 36.300.

100771 The eNB interfaces via the Sl to the Serving Gateway 845, which includes a Mobility Anchoring function 847, and to a Packet Gateway (P-GW) 849, which provides an UE IP address allocation function 857 and Packet Filtering function 859. According to this architecture, the MME (Mobility Management Entity) 861 provides SAE (System Architecture Evolution) Bearer Control 851, Idle State Mobility Handling 853, NAS (Non- Access Stratum) Security 855.

100781 FIG. 9 is a diagram of exemplary components of an LTE terminal capable of operating in the systems of FIGs. 8A-8D, according to an embodiment of the invention. An LTE terminal 900 is configured to operate in a Multiple Input Multiple Output (MIMO) system. Consequently, an antenna system 901 provides for multiple antennas to receive and transmit signals. The antenna system 901 is coupled to radio circuitry 903, which includes multiple transmitters 905 and receivers 907. The radio circuitry encompasses all of the Radio Frequency (RF) circuitry as well as base-band processing circuitry. As shown, layer-1 (Ll) and layer-2 (L2) processing are provided by units 909 and 91 1, respectively. Optionally, layer-3 functions can be provided (not shown). Module 913 executes all MAC layer functions. A timing and calibration module 915 maintains proper timing by interfacing, for example, an external timing reference (not shown). Additionally, a processor 917 is included. Under this scenario, the LTE terminal 900 communicates with a computing device 919, which can be a personal computer, work station, a PDA, web appliance, cellular phone, etc.

100791 While the invention has been described in connection with a number of embodiments and implementations, the invention is not so limited but covers various obvious modifications and equivalent arrangements, which fall within the purview of the appended claims. Although features of the invention are expressed in certain combinations among the claims, it is contemplated that these features can be arranged in any combination and order.

Claims

CLAIMSWHAT IS CLAIMED IS:
1. A method comprising: receiving a measurement report from a user equipment; determining an interference condition with a target base station based on the measurement report; instructing the target base station to suspend transmission to mitigate the interference condition; and generating a signal instructing the user equipment to handover to the target base station.
2. A method according to claim 1, wherein the step of instructing includes generating a message indicating timing information related to the suspension of the transmission, the method further comprising: transmitting the signal to the user equipment according to the timing information indicated in the message.
3. A method according to claim 2, further comprising: receiving a confirmation message from the target base station, wherein the confirmation message specifies duration of the suspension of the transmission and a confirmed frequency.
4. A method according to claim 3, wherein the message further includes a candidate frequency for the suspension of the transmission, and the confirmed frequency is the candidate frequency or another frequency selected by the target base station.
5. A method according to claim 2, further comprising: transmitting user data corresponding to the user equipment to the target base station, wherein the duration is determined from time of receipt of the confirmation message and start of the transmission of the user data.
6. A method according to claim 1, wherein the timing information includes a starting time and a duration of the suspension of the transmission.
7. A method according to claim 1, further comprising: determining the starting time and the duration based on either channel condition, retransmission delay, interface delay, or a combination thereof.
8. A method according to claim 1, wherein the measurement report includes a channel quality indicator report, the method further comprising: determining the candidate frequency based on the channel quality indicator report or power mask of soft frequency reuse.
9. A method according to claim 1 , wherein a plurality of frequency candidates including the frequency candidate is provided to the target base station for selection by the target base station.
10. A method according to claim 9, wherein the selection of one of the frequency candidates is based on a power mask of soft frequency reuse or a channel quality indicator report provided by a user equipment served by the target base station.
1 1. An apparatus comprising: a processor configured to receive a measurement report from a user equipment, wherein the processor is further configured to determine an interference condition with a target base station based on the measurement report, and to instruct the target base station to suspend transmission to mitigate the interference condition, the processor generating a signal instructing the user equipment to handover to the target base station.
12. An apparatus according to claim 1 1 , wherein the instruction to the target base station includes a message indicating timing information related to the suspension of the transmission, the apparatus further comprising: a transceiver configured to transmit the signal to the user equipment according to the timing information indicated in the message.
13. An apparatus according to claim 12, wherein the transceiver is configured to receive a confirmation message from the target base station, the confirmation message specifying duration of the suspension of the transmission and a confirmed frequency.
14. An apparatus according to claim 13, wherein the message further includes a candidate frequency for the suspension of the transmission, and the confirmed frequency is the candidate frequency or another frequency selected by the target base station.
15. An apparatus according to claim 12, wherein the transceiver is further configured to transmit user data corresponding to the user equipment to the target base station, the duration being determined from time of receipt of the confirmation message and start of the transmission of the user data.
16. An apparatus according to claim 11, wherein the timing information includes a starting time and a duration of the suspension of the transmission.
17. An apparatus according to claim 11, wherein the processor is further configured to determine the starting time and the duration based on either channel condition, retransmission delay, interface delay, or a combination thereof.
18. An apparatus according to claim 1 1, wherein the measurement report includes a channel quality indicator report, the processor being further configured to determine the candidate frequency based on the channel quality indicator report or power mask of soft frequency reuse.
19. An apparatus according to claim 1 1, wherein a plurality of frequency candidates including the frequency candidate is provided to the target base station for selection by the target base station.
20. An apparatus according to claim 19, wherein the selection of one of the frequency candidates is based on a power mask of soft frequency reuse or a channel quality indicator report provided by a user equipment served by the target base station.
21. A method comprising: receiving a command from a base station to suspend transmission to avoid interference with a user equipment that is served by the base station, wherein the suspension of the transmission is performed during handover of the user equipment from the base station, the command being generated based on a measurement report from the user equipment; and generating a confirmation message for transmission to the base station in response to the command, the confirmation message specifying duration of the suspension of the transmission and a confirmed frequency.
22. A method according to claim 21, wherein the command includes timing information related to the suspension of the transmission, wherein the base station is further configured to transmitting the command to the user equipment according to the timing information indicated in the message.
23. A method according to claim 22, further comprising: transmitting the confirmation message to the base station, wherein the confirmation message specifies duration of the suspension of the transmission and a confirmed frequency.
24. A method according to claim 23, wherein the message further includes a candidate frequency for the suspension of the transmission, and the confirmed frequency is the candidate frequency or another frequency.
25. A method according to claim 22, further comprising: receiving user data corresponding to the user equipment from the base station, wherein the duration is determined from time of receipt of the confirmation message and start of transmission of the user data.
26. A method according to claim 21, wherein the timing information includes a starting time and a duration of the suspension of the transmission.
27. A method according to claim 21, wherein the base station is further configured to determine the starting time and the duration based on either channel condition, retransmission delay, interface delay, or a combination thereof.
28. A method according to claim 21, wherein the measurement report includes a channel quality indicator report, the base station being further configured to determine the candidate frequency based on the channel quality indicator report or power mask of soft frequency reuse.
29. A method according to claim 21 , further comprising: receiving a plurality of frequency candidates including the frequency candidate from the base station; and selecting one of the frequency candidates, wherein the selection of one of the frequency candidates is based on a power mask of soft frequency reuse or a channel quality indicator report provided by another user equipment.
30. An apparatus comprising: a transceiver configured to receive a command from a base station to suspend transmission to avoid interference with a user equipment that is served by the base station, wherein the suspension of the transmission is performed during handover of the user equipment from the base station, the command being generated based on a measurement report from the user equipment; and a processor configured to generate a confirmation message for transmission to the base station in response to the command, the confirmation message specifying duration of the suspension of the transmission and a confirmed frequency.
31. An apparatus according to claim 30, wherein the command includes timing information related to the suspension of the transmission, wherein the base station is further configured to transmit the command to the user equipment according to the timing information indicated in the message.
32. An apparatus according to claim 31, wherein the transceiver is further configured to transmit the confirmation message to the base station, and the confirmation message specifies duration of the suspension of the transmission and a confirmed frequency.
33. An apparatus according to claim 32, wherein the message further includes a candidate frequency for the suspension of the transmission, and the confirmed frequency is the candidate frequency or another frequency.
34. An apparatus according to claim 31 , wherein the transceiver is further configured to receive user data corresponding to the user equipment from the base station, wherein the duration is determined from time of receipt of the confirmation message and start of transmission of the user data.
35. An apparatus according to claim 30, wherein the timing information includes a starting time and a duration of the suspension of the transmission.
36. An apparatus according to claim 30, wherein the base station is further configured to determine the starting time and the duration based on either channel condition, retransmission delay, interface delay, or a combination thereof.
37. An apparatus according to claim 30, wherein the measurement report includes a channel quality indicator report, the base station being further configured to determine the candidate frequency based on the channel quality indicator report or power mask of soft frequency reuse.
38. An apparatus according to claim 30, wherein the processor is further configured to receive a plurality of frequency candidates including the frequency candidate from the base station, and to select one of the frequency candidates, wherein the selection of one of the frequency candidates is based on a power mask of soft frequency reuse or a channel quality indicator report provided by another user equipment.
PCT/IB2008/000264 2007-02-06 2008-02-06 Method and apparatus for providing interference coordination in handover signaling WO2008096240A1 (en)

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