WO2016138663A1

WO2016138663A1 - Interference mitigation in flexible duplex

Info

Publication number: WO2016138663A1
Application number: PCT/CN2015/073693
Authority: WO
Inventors: Peng Cheng; Yin Huang; Neng Wang; Peter Gaal
Original assignee: Qualcomm Incorporated
Priority date: 2015-03-05
Filing date: 2015-03-05
Publication date: 2016-09-09

Abstract

The disclosure provides for mitigating inter-cell interference in flexible duplexing. A first cell may reconfigure a frequency division duplexing (FDD) uplink band to use time division duplexing (TDD) on the FDD uplink band based on downlink and uplink traffic loads of the first cell. The first cell may determine that a second cell is potentially affected by inter-cell interference caused by TDD downlink transmissions by the first cell on the FDD uplink band. The first cell may estimate a potential interference level caused at the second cell on the FDD uplink band by the TDD downlink transmissions for a first user equipment (UE) connected to the first cell. The first cell may then schedule a TDD downlink transmission for the first UE on the FDD uplink band when the potential interference level is less than a threshold. The second cell may use interference cancellation to further mitigate the inter-cell interference.

Description

INTERFERENCE MITIGATION IN FLEXIBLE DUPLEX

BACKGROUND

The present disclosure relates generally to communication systems, and more particularly, to mitigating inter-cell interference in flexible duplexing of wireless communication systems.

Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power) . Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunication standard is Long Term Evolution (LTE) . LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP) . LTE is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using OFDMA on the downlink (DL) , SC-FDMA on the uplink (UL) , and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

For example, there may be instances in which multiple evolved node Bs (eNBs) in a wireless communication network operate in a coordinated manner. In such instances, however, certain resources from a cell associated with one of the eNBs in the network may coincide and interfere with resources from a different cell associated with another of the eNBs in the network. Therefore, it may be desirable to implement mechanisms that address the issues that may arise from such occurrences.

SUMMARY

The disclosure provides for mitigating inter-cell interference in flexible duplexing. Flexible duplexing may be used to increase cell throughput by reconfiguring a frequency division duplexing (FDD) band to use time division duplexing (TDD) to allow additional transmissions in one direction. For example, a first FDD cell may reconfigure its FDD uplink band to use TDD based on downlink and uplink traffic loads of the first cell. This first cell may determine that a second cell is potentially affected by inter-cell interference caused by TDD downlink transmissions by the first cell on the FDD uplink band. The first cell may estimate a potential interference level caused at the second cell on the FDD uplink band by the TDD downlink transmissions for a first user equipment (UE) connected to the first cell. The first cell may then schedule a TDD downlink transmission for the first UE on the FDD uplink band when the potential interference level is less than a threshold. The second cell may use interference cancellation to further mitigate the inter-cell interference.

In an aspect, the disclosure provides a method of mitigating inter-cell interference in flexible duplexing. The method may include reconfiguring, by a first cell, a FDD uplink band to use TDD on the FDD uplink band based on downlink and uplink traffic loads of the first cell. The method may further include determining that a second cell is potentially affected by inter-cell interference caused by TDD downlink transmissions by the first cell on the FDD uplink band. The method may additionally include estimating a potential interference level caused at the second cell on the FDD uplink band by the TDD downlink transmissions for a first UE connected to the first cell. The method may also include scheduling a TDD downlink transmission for the first UE on the FDD uplink band when the potential interference level is less than a threshold.

In another aspect, the disclosure provides a method of mitigating inter-cell interference in flexible duplexing. The method may include receiving, by a second cell, an indication that a first cell operating in a FDD uplink band has reconfigured to use TDD on the FDD uplink band for a TDD downlink transmission to a first UE. The method may also include receiving a configuration of a demodulation reference signal of the first cell, a rank of the downlink transmission, and a precoding vector of the downlink transmission. The method may also include receiving a combined signal including the downlink transmission from the first cell and an uplink transmission from a second UE connected to the second cell. The method may additionally include cancelling the downlink transmission from the combined signal using the demodulation reference signal of the first cell, the rank of the downlink transmission, and the precoding vector of the downlink transmission to improve the uplink transmission from the second UE.

In an aspect, the disclosure also provides an apparatus for mitigating inter-cell interference in flexible duplexing of wireless communications. The apparatus may include a load determination component configured to reconfigure, at a first cell, a FDD uplink band to use TDD on the FDD uplink band based on downlink and uplink traffic loads of the first cell. The apparatus may further include a victim cell component configured to determine that a second cell is potentially affected by inter-cell interference caused by TDD downlink transmissions by the first cell on the FDD uplink band. The apparatus may also include an interference estimator configured to estimate a potential interference level caused at the second cell on the FDD uplink band by the TDD downlink transmissions for a first UE connected to the first cell. The apparatus may additionally include a scheduler configured to schedule a TDD downlink transmission for the first UE on the FDD uplink band when the potential interference level is less than a threshold.

In another aspect, the disclosure provides another apparatus for mitigating inter-cell interference in flexible duplexing of wireless communications. The apparatus may include means for reconfiguring, by a first cell, a FDD uplink band to use TDD on the FDD uplink band based on downlink and uplink traffic loads of the first cell. The apparatus may further include means for determining that a second cell is potentially affected by inter-cell interference caused by TDD downlink transmissions by the first cell on the FDD uplink band. The apparatus may also include means for estimating a potential interference level caused at the second cell on the FDD uplink band by the TDD downlink transmissions for a first UE connected to the first cell. The apparatus may additionally include means for scheduling a TDD downlink transmission for the first UE on the FDD uplink band when the potential interference level is less than a threshold.

In an aspect, the apparatus may futher include means for determining a cell cluster for the first cell based on an interference criterion wherein the reconfiguring is further based on the cell cluster and all cells in the cell cluster reconfigure the uplink band concurrently. In another aspect, the means for determining that the second cell is potentially affected by inter-cell interference caused by TDD downlink transmissions by the first cell on the FDD uplink band may include: means for determining that the second cell has not reconfigured the uplink band to use TDD； means for determining that the second cell has uplink traffic load； and means for determining that a coupling loss between the first cell and the second cell is less than a threshold coupling loss. In another aspect, the means for determining the potential interference level for the first UE may include means for calculating an angle between a line formed by the first cell and the second cell and a line formed by the first cell and the first UE and means for determining the potential interference level based on the angle. In another aspect, the the means for determining the potential interference level for the first UE may include means for calculating a channel correlation between a channel from the first cell to the second cell and a channel from the first cell to the first UE； and means for determining the potential interference level based on the channel correlation. In another aspect, the apparatus may further include means for applying a precoding vector to the scheduled TDD downlink transmission using beamforming to decrease a level of interference at the second cell causedby the scheduled TDD downlink transmission. In another aspect, the apparatus may further include means for determining a potential interference level caused at the second cell on the FDD uplink band by TDD downlink transmissions for additional UEs connected to the first cell and means for scheduling, in order of priority of the additional UEs, a TDD downlink transmission for each additional UE on the FDD uplink band when the respective potential interference level is less than the threshold. The apparatus may also include means for transmitting a cell loading status to the second cell； means for receiving a cell loading status of the second cell and an offloading status of the second cell； means for transmitting a configuration of demodulation reference signal of the first cell, to the second cell； and/or means for performing interference cancellation of a downlink transmission from the second cell for a second UE connected to the second cell.

In another aspect, the disclosure provides a computer-readable medium storing computer executable code for mitigating inter-cell interference in flexible duplexing of wireless communications. The computer-readable medium may include code for reconfiguring, by a first cell, a FDD uplink band to use TDD on the FDD uplink band based on downlink and uplink traffic loads of the first cell. The computer-readable medium may further include code for determining that a second cell is potentially affected by inter-cell interference caused by TDD downlink transmissions by the first cell on the FDD uplink band. The computer-readable medium may also include code for estimating a potential interference level caused at the second cell on the FDD uplink band by the TDD downlink transmissions for a first UE connected to the first cell. The computer-readable medium may additionally include code for scheduling a TDD downlink transmission for the first UE on the FDD uplink band when the potential interference level is less than a threshold. In an aspect, the computer-readable medium may be a non-transitory computer-readable medium.

In another aspect, the disclosure provides an apparatus for mitigating inter-cell interference in flexible duplexing. The apparatus may include at least one interface configured to receive, at a second cell, an indication that a first cell operating in a frequency division duplexing (FDD) uplink band has reconfigured to use time division duplexing (TDD) on the FDD uplink band for a TDD downlink transmission to a first user equipment (UE) , a configuration of a demodulation reference signal of the first cell, a rank of the downlink transmission, and a precoding vector of the downlink transmission. The apparatus may also include a receiver configured to receive a combined signal including the downlink transmission from the first cell and an uplink transmission from a second UE connected to the second cell. The apparatus may also include interference cancellation circuitry configured to cancel the downlink transmission from the combined signal using the demodulation reference signal of the first cell, the rank of the downlink transmission, and the precoding vector of the downlink transmission to improve the uplink transmission from the second UE. In an aspect, the interference cancelling circuitry may a multiple-user detector configured to jointly decode the downlink transmission and the uplink transmission or an iterative decoder configured to iteratively decode the downlink transmission and cancel the decoded downlink transmission from the combined signal.

In another aspect, the disclosure provides an apparatus for mitigating inter-cell interference in flexible duplexing. The apparatus may include means for receiving, at a second cell, an indication that a first cell operating in a frequency division duplexing (FDD) uplink band has reconfigured to use time division duplexing (TDD) on the FDD uplink band for a TDD downlink transmission to a first user equipment (UE) . The apparatus may also include means for receiving a configuration of a demodulation reference signal of the first cell, a rank of the downlink transmission, and a precoding vector of the downlink transmission. The apparatus may also include means for receiving a combined signal including the downlink transmission from the first cell and an uplink transmission from a second UE connected to the second cell. The apparatus may further include means for cancelling the downlink transmission from the combined signal using the demodulation reference signal of the first cell, the rank of the downlink transmission, and the precoding vector of the downlink transmission to improve the uplink transmission from the second UE. The means for cancelling the downlink transmission may include means for performing joint multiple-user detection to decode the downlink transmission and the uplink transmission or means for iteratively decoding the downlink transmission and cancelling the decoded downlink transmission from the combined signal.

In another aspect, the disclosure provides a computer-readable medium storing computer executable code for mitigating inter-cell interference in flexible duplexing of wireless communications. The computer-readable medium may include code for receiving, by a second cell, an indication that a first cell operating in a frequency division duplexing (FDD) uplink band has reconfigured to use time division duplexing (TDD) on the FDD uplink band for a TDD downlink transmission to a first user equipment (UE) . The computer-readable medium may also include code for receiving a configuration of a demodulation reference signal of the first cell, a rank of the downlink transmission, and a precoding vector of the downlink transmission. The computer-readable medium may also include code for receiving a combined signal including the downlink transmission from the first cell and an uplink transmission from a second UE connected to the second cell. The computer-readable medium may also include code for cancelling the downlink transmission from the combined signal using the demodulation reference signal of the first cell, the rank of the downlink transmission, and the precoding vector of the downlink transmission to improve the uplink transmission from the second UE. The code for cancelling the downlink transmission may include code for performing joint multiple-user detection to decode the downlink transmission and the uplink transmission or code for iteratively decoding the downlink transmission and cancelling the decoded downlink transmission from the combined signal. In an aspect, the computer-readable medium may be a non-transitory computer-readable medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams illustrating an example of a communications system including an evolved node B having an inter-cell interference mitigation component in communication with a user equipment.

FIG. 2 is a flowchart illustrating an example of a method of mitigating inter-cell interference.

FIG. 3 is a flowchart illustrating an example of a method of mitigating inter-cell interference.

FIG. 4 is a diagram illustrating an example of flexible duplexing.

FIG. 5 is a diagram illustrating an example of estimating potential interference between a first cell and a second cell based on a UE.

FIG. 6 is a diagram illustrating an example of interference cancellation using multiple-user detection.

FIG. 7 is a diagram illustrating an example of interference cancellation using iterative decoding.

FIG. 8 is a diagram illustrating an example of interference cancellation using multiple-user detection and iterative decoding.

FIG. 9 is a diagram illustrating an example of a network architecture.

FIG. 10 is a diagram illustrating an example of an access network.

FIG. 11 is a diagram illustrating an example of a DL frame structure in LTE.

FIG. 12 is a diagram illustrating an example of an UL frame structure in LTE.

FIG. 13 is a diagram illustrating an example of a radio protocol architecture for the user and control planes.

FIG. 14 is a diagram illustrating an example of an evolved Node B and user equipment in an access network.

FIG. 15 is a conceptual data flow diagram illustrating the data flow between different modules/means/components in an exemplary apparatus.

FIG. 16 is a diagram illustrating an example of a hardware implementation for an apparatus employing a processing system.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

In an aspect, the present disclosure provides for mitigating inter-cell interference in a flexible duplexing scenario. In a flexible duplexing scenario, an evolved Node B (eNB) providing a cell using frequency division duplexing (FDD) may reconfigure the cell to use time division duplexing (TDD) on an uplink band. Accordingly, the downlink FDD band may be used for downlink traffic and some time slots of the uplink band may also be used for downlink traffic. Accordingly, flexible duplexing may increase downlinkthroughput by repurposing an uplink resource.

In an aspect, however, downlink transmissions on the uplink FDD band may cause inter-cell interference to cells using the uplink FDD band for uplink traffic. The cell that has reconfigured the FDD uplink band to use TDD may be referred to as an aggressor cell. The cell using the FDD uplink band that experiences interference may be referred to as a victim cell. That is, the downlink traffic transmitted by the aggressor cell may interfere with uplink traffic transmitted by one or more user equipment (UEs) connected to a victim cell that has not been reconfigured to use TDD. In another aspect, inter-cell interference may also occur if two cells are reconfigured to use different TDD frame configurations. Inter-cell interference may prevent the victim cell from correctly receiving some uplink transmissions. Accordingly, inter-cell interference may cause latency and/or reduce throughput for uplink transmissions at the victim cell.

In an aspect, an aggressor cell may mitigate interference caused by transmissions in the FDD uplink band by scheduling transmissions to UEs where beamforming can be used to reduce interference to a victim cell. In another aspect, cells may be grouped into clusters such that cells in a cluster are reconfigured concurrently to reduce the number of potential victim cells.

In an aspect, avictim cell may mitigate interference caused by transmissions in the FDD uplink band by applying interference cancellation techniques based on characteristics of the interfering downlink transmissions

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as “elements” ) . These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or any combination of elements may be implemented with a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, digital signal processors (DSPs) , field programmable gate arrays (FPGAs) , programmable logic devices (PLDs) , state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

Accordingly, in one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise a random-access memory (RAM) , a read-only memory (ROM) , an electrically erasable programmable ROM (EEPROM) , compact disk ROM (CD-ROM) or other optical disk storage, magnetic disk storage or other magnetic storage devices, combinations of the aforementioned types of computer-readable media, or any other medium that can be used to store computer executable code in the form of instructions or data structures that can be accessed by a computer.

Referring to FIG. 1A, in an aspect, a wireless communication system 10 includes an evolved nodeB (eNB) 14 in communication with user equipment (UE) 12 and 22. The eNB 14 may provide a cell 14. The terms “eNB” and “cell” may be used interchangeably herein and may refer either an eNB or the cell provided by the eNB depending on the context. A second eNB 20 may be in communication with another UE 30. The wireless communication system 10 may be a coordinated multi-point (CoMP) system in which the eNB 14 and eNB 20 coordinate transmissions. For example, the eNB 14 and the eNB 20 may communicate with each other via a communication link 28 carrying X2 interface signaling. The eNB 14 and the eNB 20 may also communicate with an evolved packet core (EPC) 16. In an aspect, the eNB 14 may use flexible duplexing to offload downlink traffic from an FDD downlink band to an FDD uplink band that is reconfigured for TDD transmissions. With the additional resources used for DL in the FDD uplink band, additional DL capacity may be achieved compared to that available by only using FDD downlink band alone. In an aspect, an FDD uplink band may refer to a frequency range that may be used by at least one cell for uplink transmissions. Accordingly, an FDD uplink band that has been temporarily reconfigured as a TDD band may still be referred to as an FDD uplinkband.

When the first eNB 14 reconfigures the FDD uplink band for TDD transmissions, downlink transmissions on the FDD uplink band may interfere with the second cell 20. For example,

downlink transmissions

24 or 26 may interfere with uplink transmissions 32 because all of the transmissions may use the FDD uplink band. This interference may be referred to as inter-cell interference (ICI) because the

transmissions

24, 26 from the first cell 14 may cause interference at the second cell 20. In an aspect, a downlink TDD transmission 26 to a UE 22 that is closer or in the same direction as the second cell 20 may result in greater ICI than the downlink transmission 24 to the UE 12, which may be located in a direction away from the second cell 20.

The eNB 14 and/or the eNB 20 may include an inter-cell interference mitigation component 40 for reducing interference at the second cell 20 caused by TDD transmissions in the FDD UL band by the first cell 14. For example, the ICI mitigation component 40 at the first cell 14 may reduce ICI by coordinated scheduling and coordinated beamforming to schedule downlink TDD transmissions on the FDD uplink band when beamforming can be used to reduce interference to the second cell 20. The ICI mitigation component 40 may also use clustering to reduce the number of potential victim cells by coordinating reconfiguration to TDD duplexing. The ICI mitigation component 40 at the second cell 20 may reduce interference using an interference cancellation receiver to cancel a downlink TDD transmission 26 from a combined signal including downlink TDD transmission 26 and uplink transmission 32 based on known properties of the downlink TDD transmission 26.

A UE 12 may also be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology. A UE 12 may be a cellular phone, a personal digital assistant (PDA) , a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a global positioning system (GPS) device, a multimedia device, a video device, a digital audio player (e.g., MP3 player) , a camera, a game console, a wearable computing device (e.g., a smart-watch, smart-glasses, a health or fitness tracker, etc) , an appliance, a sensor, a vehicle communication system, a medical device, a vending machine, a device for the Internet-of-Things, or any other similar functioning device. A UE 12 may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, and the like.

An eNB 14 may provide a cell serving the UE 12. In some aspects, multiple UEs such as UE 12 may be in communication coverage with one or more eNBs, including eNB 14 and eNB 20. An eNB 14 may be a station that communicates with the UE 12 and may also be referred to as a base station, an access point, a NodeB, etc. Each eNB, such as eNB 14 may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to a coverage area of an eNB 14 and/or an eNB subsystem serving the coverage area, depending on the context in which the term is used. For example, the eNB 14 may be the cell where the UE 12 initially performs a connection establishment procedure. Such a cell may be referred to as a primary cell or Pcell. Another eNB (not shown) may be operating on another frequency and may be referred to as a secondary cell. It should be apparent that an eNB may operate as either a primary cell or a secondary cell depending on the connection state of the UE 12. A cell ID such as a primary cell identifier (PCI) may be mapped to an eNB. A UE may be within the coverage areas of multiple eNBs. One of these eNBs may be selected to serve the UE. The serving eNB may be selected based on various criteria including radio resource monitoring measurements and radio link monitoring measurements such as receivedpower, path loss, signal-to-noise ratio (SNR) , etc.

An eNB 14 may provide communication coverage for a macro cell, asmall cell, a pico cell, a femto cell, and/or other types of cell. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs 12 with service subscription. The term “small cell, ” as used herein, refers to a relatively low transmit power and/or a relatively small coverage area cell as compared to a transmit power and/or a coverage area of a macro cell. Further, the term “small cell” may include, but is not limited to, cells such as a femto cell, a pico cell, access point base stations, Home NodeBs, femto access points, or femto cells. For instance, a macro cell may cover a relatively large geographic area, such as, but not limited to, several kilometers in radius. In contrast, a pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs 12 with service subscription. A femto cell may cover a relatively small geographic area (e.g., a home) and may allow restricted access by a UE 12 having association with the femto cell (e.g., UE 12 may be subscribed to a Closed Subscriber Group (CSG) , for users in the home, etc.) . An eNB 14 for a macro cell may be referred to as a macro eNB. An eNB 14 for a pico cell may be referred to as a pico eNB. An eNB 14 for a femto cell may be referred to as a femto eNB or a home eNB.

The ICI mitigation component 40 may include hardware and/or software code executable by a processor for mitigating ICI in a flexible duplex scenario. In an aspect, the term “component” as used herein may be one of the parts that make up a system, may be hardware, firmware, and/or software, and may be divided into other components. As illustrated in FIG. 1B, the ICI mitigation component 40 may include a load determination component 42 that determines a traffic load of a cell, a clustering component 48 that determines a cluster of the cell, a victim cell component 50 that determines characteristics of one or more potential victim cells, an interference cancellation (IC) receiver 70 that reduces interference from one or more sources； an X2 interface 76 for communication with another cell； a scheduler 68 for scheduling downlink transmissions to UEs, and a transmitter 78 for transmitting scheduled downlink transmissions.

The load determination component 42 may include hardware and/or software code executable by a processor for determining cell loading properties of the cell 14. For example, the load determination component 42 may determine a downlink traffic load and an uplink traffic load. The downlink traffic load may indicate an amount of downlink traffic scheduled for the UE 12 and/or other UEs connected to the eNB 14. In an aspect, the load determination component 42 may include a downlink queue 44 or otherwise have access to the downlink queue 44. The downlink queue 44 may store downlink traffic for each connected UE before transmission. For example, the downlink queue 44 may be a memory. The load determination component 42 may determine the downlink transmission status by measuring the amount of data in the downlink queue 44. The uplink traffic load may indicate an amount of uplink traffic that the UE 12 and/or other UEs connected to the eNB 14 have to transmit. In an aspect, the connected UEs may request grants for transmitting uplink traffic. The load determination component 42 may determine the grants for each UE based on the uplink traffic load.

The clustering component 48 may include hardware and/or software code executable by a processor for determining a cluster of the cell. In an aspect, one or more cells may be grouped into clusters for flexible duplexing. The cells within a cluster may make the same determination regarding configuration of the uplink FDD band. For example, the cells in the cluster may select a TDD configuration for all of the cells to use concurrently for a particular frame. Accordingly, inter-cell interference between the cells may be minimized because traffic will be moving in the same direction on the FDD uplink band. In an aspect, the cells in the cluster may share loading information via the X2 interface 76 and make reconfiguration decisions based on the loading information of all of the cells in the cluster. For example, the cells in the cluster may select a TDD configuration for the uplink FDD band that maximizes throughput of the cells in the cluster.

In an aspect, the clustering component 48 may determine which cluster the cell 14 belongs to based on one or more criteria such as coupling loss, distance, or interference level. For example, the clustering component 48 may determine that the cell 14 belongs to a cluster where each cell in the cluster has a coupling loss of less than 90 decibels (dB) with the cell 14. In an aspect, the clustering component 48 may limit the size of the cluster to provide more flexible duplexing and simpler reconfiguration decisions.

The victim cell component 50 may include hardware and/or software code executable by a processor for determining characteristics of one or more potential victim cells. Apotential victim cell may be any cell that may be affected by inter-cell interference from the cell 14. In an aspect, the potential victim cells may include nearby small cells. The victim cell component 50 may identify potential victim cells based on listening for transmissions from neighbor cells and/or information received from a core network 16 or a macro cell. The victim cell component 50 may include a coupling loss component 52, victim configuration component 54, victim load component 56, and interference estimator 58. In an aspect, the victim cell component 50 may determine that a potential victim cell is likely to be affected by ICI when each of the coupling loss component 52, victim configuration component 54, and victim load component 56 determine that ICI is likely.

The coupling loss component 52 may be configured to determine a coupling loss with the potential victim cell. The coupling loss component 52 may, for example, track long-term interference with the potential victim cell to determine the coupling loss. The coupling loss component 52 may determine that ICI is likely when the coupling loss is less than a threshold, e.g., 90 dB.

The victim configuration component 54 may be configured to determine the duplexing configuration of the potential victim cell. For example, the victim configuration component 54 may receive duplexing configuration information from the potential victim cell via the X2 interface 76. The victim configuration component 54 may determine that ICI is likely when the duplexing configuration is different than the duplexing configuration of the cell 14.

The victim load component 56 may be configured to determine the traffic load of the potential victim cell. The victim load component 56 may receive cell loading information of the potential victim cell via the X2 interface 76. In an aspect, ICI may affect uplink traffic at the potential victim cell. Accordingly, the victim load component 56 may determine that ICI is likely when the potential victim cell has an uplink traffic load.

The scheduler 60 may include hardware and/or software code executable by a processor for scheduling downlink transmissions to one or more connected UEs. In an aspect, when scheduling downlink transmissions on a FDD uplink band configured with TDD flexible duplexing, the scheduler 60 may schedule the downlink transmissions based on an estimated interference level that would be caused by each downlink transmission. The scheduler 60 may schedule downlink transmissions for each connected UE in order of priority of the UE transmissions. For example, the scheduler 60 may schedule a downlink transmission for a UE when the estimated level of interference is less than a threshold and refrain from scheduling the downlink transmission on the FDD uplink band when the estimated level of interference is greater than a threshold. If the scheduler 60 is unable to schedule the downlink transmission on the FDD uplink band, the scheduler 60 may wait until the downlink transmission can be scheduled on the FDD downlink band. In an aspect, the scheduler 60 may include an interference estimator 62 that may estimate an interference level.

The interference estimator 62 may include hardware and/or software code executable by a processor for estimating interference for a downlink transmission based on the UE and the potential victim cell. In an aspect, the interference estimator 62 may estimate interference by calculating an angle between a line formed by the first cell 14 and the second cell 20 and a line formed by the first cell 14 and the first UE 12. In an aspect, the lines may be based on geographic locations that may be determined by GPS signals, signaled over the air, or signaled via the X2 interface 66. Interference may be inversely proportional to the angle. Accordingly, the interference estimator 62 may estimate a high level of interference when the angle is less than a threshold angle. In another aspect, the interference estimator 62 may estimate interference by calculating a channel correlation between a channel from the first cell 14 to the second cell 20 and a channel from the first cell 14 to the first UE 12. The cell 14 may estimate the channels based on received transmissions. The potential interference may be directly proportional to the correlation between the channels. Accordingly, the interference estimator 62 may estimate a high level of interference when the channel correlation exceeds a threshold value.

The interference cancellation (IC) receiver 70 may be a radio-frequency (RF) receiver configured to reduce interference from one or more sources. The IC receiver 70 may include one or more components for reducing interference. For example, the IC receiver 70 may include a multiple-user detector 72. The multiple-user detector 72 may include hardware and/or software code executable by a processor for modeling a system of multiple signals. The multiple-user detector 72 may jointly determine physical dedicated shared channel (PDSCH) channel estimates and interference estimates to detect multiple signals within a combined signal. As another example, the IC receiver 70 may include an iterative decoder 74 that performs demodulation and interference cancellation on signals within a combined signal. The multiple-user detector 72 and the iterative decoder 74 may be used separately or in series to improve signal quality of a desired signal, e.g. an uplink signal from a UE. In an aspect, the IC receiver 70 may use known information about an interfering signal to cancel the interfering signal. For example, the IC receiver 70 may receive a configuration of a demodulation reference signal (DMRS) of an aggressor cell (e.g. a DMRS port) . The IC receiver 70 may also receive transmission characteristics such as a rank and precoding vector of a downlink transmission. The IC receiver may receive such transmission characteristics via the X2 interface or by detecting the transmission characteristics from a received signal.

The X2 interface 76 may include hardware and/or software code executable by a processor for communication with another cell. For example, the X2 interface may include a network interface. The network interface may be for a fiber optic, cable, microwave, satellite, or other communication medium. The X2 interface may be configured to establish a connection with another eNB and provide signaling information to the other eNB over the connection. In an aspect, the ICI mitigation component 40 may use the X2 interface to transmit or receive: cell uplink and downlink loading information, offloading status or duplexing configurations, and/or a DMRS port of an aggressor cell. In an aspect, the X2 interface 76 may transmit or receive additional information that may also be measured or detectedby the eNB 14. For example, an eNB to eNB coupling loss, eNB positions, UE positions, channels to eNBs, channels to UEs, and transmission properties may be measured or detected by the eNB 14, but may also be signaled via the X2 interface.

The transmitter 78 may include an RF transmitter for transmitting a scheduled downlink transmission. In an aspect, the transmitter 78 may include one or more transmit chain components and/or antennas. In an aspect, the transmitter 78 may apply a precoding vector when transmitting the downlink transmission to decrease the level of interference at the second cell using beamforming.

Referring to FIG. 2, in an operational aspect, abase station such as eNB 14 (FIG. 1A) may perform one aspect of a method 200 for mitigating ICI. The eNB 14 may be considered a first eNB and provide a first cell and may be interchangeably referred to as a first cell. While, for purposes of simplicity of explanation, the method is shown and described as a series of acts, it is to be understood and appreciated that the method (and further methods related thereto) is/are not limited by the order of acts, as some acts may, in accordance with one or more aspects, occur in different orders and/or concurrently with other acts from that shown and described herein. For example, it is to be appreciated that a method could alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all illustrated acts may be required to implement a method in accordance with one or more features described herein.

In block 202, the method 200 may optionally include determining a cell cluster for the first cell based on an interference criterion. In an aspect, for example, the clustering component 48 may determine a cluster for the first cell based on the interference criterion. The interference criterion may be, for example, coupling loss, distance, or channel correlation.

In block 204, the method 200 may include reconfiguring, by a first cell, a FDD uplink band to use TDD on the FDD uplink band based on downlink and uplink traffic loads of the first cell. In an aspect, for example, the load determination component 42 may reconfigure, for the first cell 14, the FDD uplink band to use TDD on the FDD uplink band based on downlink and uplink traffic loads of the first cell. The load determination component 42 may determine a TDD configuration for the FDD uplink band. For example, the load determination component 42 may select a TDD configuration having a number of uplink sub-frames and downlink sub-frames that may maximize throughput of the first cell. In an aspect, the load determination component 42 may determine to reconfigure the FDD uplink band based on the cluster of the first cell and the uplink and downlink traffic loads of any other cells in the cluster. Alternatively, the clustering component 48 may indicate an FDD uplinkband reconfiguration based on a decision for the cluster.

In block 206, the method 200 may include determining that a second cell is potentially affected by inter-cell interference caused by TDD downlink transmissions by the first cell on the FDD uplink band. In an aspect, for example, the victim cell component 50 may determine that a second cell 20 is potentially affected by inter-cell interference caused by TDD downlink transmissions by the first cell 14 on the FDD uplink band. In an aspect, the victim cell component 50 may determine that the second cell is potentially affected by inter-cell interference when the second cell has not reconfigured the uplink band to use TDD, the second cell has uplink traffic load, and a coupling loss between the first cell and the second cell is less than a threshold coupling loss.

In block 208, the method 200 may include estimating a potential interference level caused at the second cell on the FDD uplink band by the TDD downlink transmissions for a first user equipment (UE) connected to the first cell. In an aspect, for example, the interference estimator 62 may estimate the potential interference level caused at the second cell on the FDD uplink band by the TDD downlink transmissions for the first UE 12 connected to the first cell 14. In an aspect, the interference estimator 62 may calculate an angle between a line formed by the first cell 14 and the second cell 20 and a line formed by the first cell 14 and the first UE 12. The interference estimator 62 may determine the potential interference level based on the angle. In another aspect, the interference estimator 62 may calculate a channel correlation between a channel from the first cell 14 to the second cell 20 and a channel from the first cell 14 to the first UE 12. The interference estimator 62 may determine the potential interference level based on the channel correlation.

In block 210, the method 200 may include scheduling a TDD downlink transmission for the first UE on the FDD uplink band when the potential interference level is less than a threshold. In an aspect, for example, the scheduler 60 may schedule a TDD downlink transmission for the first UE 12 on the FDD uplink band when the potential interference level is less than a threshold. In an aspect, blocks 208 and 210 may be repeated for each connected UE in order of priority of the downlink transmissions to the connected UEs.

In block 212, the method 200 may optionally include transmitting information to cancel interference at the victim cell. In an aspect, for example, the X2 interface 76 may transmit information to cancel interference at the victim cell. For example, the information may include a configuration of a demodulation reference signal of the first cell 14. The transmitter 78 may transmit other information such as a rank and precoding vector of the downlink transmission, which may be detected by the second cell 20. The rank and precoding vector may also be transmitted over the X2 interface 76.

FIG. 3 is a flowchart illustrating a method 300 for mitigating ICI at a victim cell. In an aspect, the method 300 may be performed by an eNB 20 that receives interference on an FDD uplink band from a first cell 14 using the FDD uplink band for TDD downlink transmissions. As such, method 300 may be performed concurrently with the method 200 described above. For example, in an operational aspect, an eNB such as eNB 20 (FIG. 1A) may perform one aspect of a method 300 while an eNB 14 may perform one aspect of the method 200 describe above with respect to FIG. 2. It should also be appreciated that eNB 14 and eNB 20 may switch roles as the first cell and second cell depending on configuration of the FDD uplink band. While, for purposes of simplicity of explanation, the method is shown and described as a series of acts, it is to be understood and appreciated that the method (and further methods related thereto) is/are not limited by the order of acts, as some acts may, in accordance with one or more aspects, occur in different orders and/or concurrently with other acts from that shown and described herein. For example, it is to be appreciated that a method could alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all illustrated acts may be required to implement a method in accordance with one or more features described herein.

In block 302, the method 300 may include receiving, by a second cell, an indication that a first cell operating in a FDD uplink band has reconfigured to use TDD on the FDD uplink band for a downlink transmission to a first UE. In an aspect, for example, an X2 interface 76 of the eNB 20, providing a second cell, may receive an indication that a first cell 14 operating in a FDD uplink band has reconfigured to use TDD on the FDD uplinkband for a TDD downlink transmission to a first UE 12.

In block 304, the method 300 may include receiving a configuration of a demodulation reference signal of the first cell, a rank of the downlink transmission, and a precoding vector of the downlink transmission. In an aspect, for example, the X2 interface 76 and/or the IC receiver 70 may receiving a configuration of a demodulation reference signal of the first cell, a rank of the downlink transmission, and a precoding vector of the downlink transmission. For example, the X2 interface component 76 may receive the configuration of the demodulation reference signal of the first cell. The IC receiver 70 may detect the rank of the downlink transmission and the precoding vector of the downlink transmission based on, for example, signaling for the UE 12. In an aspect, the configuration of a demodulation reference signal of the first cell, the rank of the downlink transmission, and the precoding vector of the downlink transmission may be received by one or both of the X2 interface component 76 and the IC receiver 70.

In block 306, the method 300 may include receiving a combined signal including the downlink transmission from the first cell and an uplink transmission from a second UE connected to the second cell. In an aspect, for example, the IC receiver 70 may receive the combined signal including the downlink transmission from the first cell and the uplink transmission from the second UE 30 connected to the second cell. The combined signal may also include noise such as additive Gaussian white noise (AGWN) and/or interference from other sources. The different transmissions, noise, and interference may combine in the channel over the air.

In block 308, the method 300 may include cancelling the downlink transmission from the combined signal using the demodulation reference signal of the first cell, the rank of the downlink transmission, and the precoding vector of the downlink transmission to improve the uplink transmission from the second UE. In an aspect, for example, the multiple-user detector 72 and/or the iterative decoder 74 may cancel the downlink transmission from the combined signal using the demodulation reference signal of the first cell, the rank of the downlink transmission, and the precoding vector of the downlink transmission to improve the uplink transmission from the second UE.

FIG. 4 shows a block diagram 400 conceptually illustrating an example of a UL/DL configuration for managing interference between a first cell 14 and a second cell 20. The first cell 14 and the second cell 20 may initially be configured to use FDD. The diagram 400 includes an FDD DL band 405 and an FDD UL band 410 used by the first cell 14 and second cell 20 in communication with one or more UEs 12 in their respective coverage area. The FDD DL band 405 and the FDD UL band 410 may each occupy 1.4–20 megahertz (MHz) and be separated by a guard band to prevent interference between the DL and UL transmissions.

In accordance with the present disclosure, at time T1, the first cell 14 may reconfigure the FDD UL band to use TDD for both UL and DL traffic. In TDD, a single band of 1.4-20 MHz may be used to carry both uplink and downlink transmissions. For example, the single FDD UL band 410 may be reconfiguredas a TDD band carrying both UL and DL transmissions. In TDD, the UL transmissions and DL transmissions may be separated in the time domain by a guard period to prevent interference. The FDD UL band 410, when operating in TDD, may follow a TDD frame configuration. The TDD frame configuration may include, for example, a first downlink subframe 416 followed by a special subframe 412, then a number of uplink subframes 414. The special subframe 412 may include a guard period. After a switching point, which may include another guard period, the remainder of the TDD frame configuration may include downlink subframes 416. In the example shown in FIG. 4, the first cell 14 may configure the FDD UL band with a TDD configuration having 7

downlink subframes

416, 1

special subframe

412, and 2 uplink subframes 414. Accordingly, the first cell 14 may offload downlink transmissions from the FDD DL band 405 to the FDD UL band 410. It should be appreciated that the TDD frame configuration may include other combinations of downlink, special, and uplink sub-frames, which may be selected based on the desired amount of offloading. At time T2, the first cell 14 may switch back to FDD or continue to use TDD for offloading.

The reconfiguration of FDD UL band 410 to use TDD may cause inter-cell interference to the uplink transmissions in the FDD UL band at the cell 20. In particular, the downlink transmissions from the cell 14 may have a relatively strong power compared to uplink transmissions from a UE. Accordingly, the uplink transmissions in subframes 420 may experience strong interference from the cell 14. In order to mitigate the ICI, the ICI mitigation component 40 at cell 14 may schedule only those UEs in subframes 416 where interference can be mitigated by beamforming. The ICI mitigation component at cell 20 may use interference cancellation techniques to cancel the downlink transmissions in subframes 416 from the received signals in subframes 420.

FIG. 5 illustrates a diagram 500 conceptually illustrating estimation of ICI based on a UE 12 and potential victim cell 20. The angle (α) 502 may be formed by a line from the cell 14 to the cell 20 and a second line from the cell 14 and the UE 12. The interference estimator 62 at the first cell 14 may determine the angle 502 based on, for example, GPS coordinates of the first cell 14, second cell 20, and UE 12. The first cell 14 may use a GPS receiver to determine its own location. The first cell 14 may receive GPS coordinates from the UE 12 and the second cell 20. When the angle 502 is large, the first cell 14 may use beamforming to direct a downlink transmission in the direction of the UE 12 and away from the second cell 20. However, when the angle 502 is small, any transmission to the UE 12 may interfere with the second cell 20.

The diagram 500 further illustrates a first channel 504 between the first cell 14 and the second cell 20 and a second channel 506 between the first cell 14 and the UE 12. The interference estimator 62 at the first cell 14 may determine the first channel 504 and the first channel 506 based on channel estimates of received signals from the second cell 20 and the UE 12, respectively. The channel correlation of the channel 504 and the channel 506 may also indicate whether beamforming will be effective for reducing interference to the cell 20.

FIG. 6 is a diagram 600 illustrating interference and interference cancellation. In the diagram 600, signals may be transmitted by a network, the first cell 14, and the second UE 30. For example, i (t) may be an interference signal from the first cell 14 tranmitted over interferer channel hi (t) , x (t) may be a desired signal transmitted over signal channel hs (t) . The signals may be combined and received at the second cell 20. The second cell 20 may use the multiple-user detector 72 to perform multiple-user detection (MUD) 602 on the received signal. In an aspect, MUD 602 may use joint detection of signals. Equation (1) may be used to model a system including multiple signals:

y [k] ＝ H_s [k] x_s [k] + H_l [k] P_l [k] x_l [k] + n [k] (1)

In equation (1) , k may be a subcarrier index, M_r may be a number of receive antennas, M_t may be a number of transmit antennas, L_s may be a number of layers from the serving cell or the desired UE, L_t may be a number of layers from the interfering cell, y [k] may be a received M_r×1 signal vector； H_s [k] may be an effective M_r×L_s serving channel matrix, x_s [k] may be a serving L_s×1 vector of modulation symbols, H_l [k] may be an interferor M_r×M_t channel matrix, x_l [k] may be an interferer L_l×1 vector of modulation symbols, P_l [k] may be an interferor M_t ×L_l precoding matrix and n [k] may be a background noise M_r×1 vector.

In atwo layerbased signaling scheme, a hypothesis space U ＝ {U₁, U₂, U₃, U₄} may be defined for different precoding matrices. A minimum mean squared estimator (MMSE) may be applied to each hypothesis. The best hypothesis may be used for decodingthe individual signals withinthe system.

FIG. 7 is a diagram 700 illustrating interference and interference cancellation. In the diagram 700, signals may be transmitted by a network, the first cell 14, and the second UE 30. For example, i (t) may be an interference signal from the first cell 14 tranmittedover interferer channel hi (t) , x (t) may be a desired signal transmitted over signal channel hs (t) . The signals may be combined and received at the second cell 20. The second cell 20 may use the iterative decoder 74 to improve the signal x (t) . The iterative decoder 74 may use interference cancellation 702 to estimate the interference i ⁽¹⁾ (t) , which may be subtracted from the received signal at 704. The iterative decoder 74 may use demodulation 706 to determine x ⁽¹⁾ (t) , which may then be subtracted from the combined signal at 707, which may be combined with the first estimate of the interference at 708. In a second iteration, the iterative decoder 74 may user interference cancellation 710 to estimate the interference i ⁽²⁾ (t) , which may be subtracted from the combined signal at 712. The x ⁽¹⁾ (t) may then be added back into the combined signal at 714. A second demodulation 716 may determine x ⁽²⁾ (t) , which may be used as the desired signal. The iterative decoder 74 may perform further iterations of interference cancellation and demodulation.

FIG. 8 is a diagram 800 illustrating interference andinterference cancellation. In the diagram 800, signals may be transmitted by a network, the first cell 14, and the second UE 30. For example, i (t) may be an interference signal from the first cell 14 tranmitted over interferer channel hi (t) , x (t) may be a desired signal transmitted over signal channel hs (t) . The signals may be combined and received at the second cell 20. The second cell may use multiple-user detector 72 as described above with respect to FIG. 6 followed by iterative decoder 74 as described above with respect to FIG. 7. In an aspect, the first iteration of interference cancellation 702 may be skipped and the first demodulation 706 performed on the results of MUD 602 instead.

FIG. 9 is a diagram illustrating an LTE network architecture 900 including one or more eNBs having an ICI mitigation component 40 for reducing inter-cell interference. The LTE network architecture 900 may be referred to as an Evolved Packet System (EPS) 900. The EPS 900 may include one or more user equipment (UE) 902, an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) 904, an Evolved Packet Core (EPC) 910, and an Operator’s Internet Protocol (IP) Services 922. The EPS can interconnect with other access networks, but for simplicity those entities/interfaces are not shown. As shown, the EPS provides packet-switched services, however, as those skilled in the art will readily appreciate, the various concepts presented throughout this disclosure may be extended to networks providing circuit-switched services.

The E-UTRAN includes the evolved Node B (eNB) 906 and other eNBs 908, each of which may be an example of the eNB 14 or eNB 20 (FIG. 1A) and include an ICI mitigation component 40. The E-UTRAN may further include a coordination entity 38 for coordinating scheduling among the eNBs based on CoMP techniques. The eNB 906 provides user and control planes protocol terminations toward the UE 902. The eNB 906 may be connected to the other eNBs 908 via a backhaul (e.g., an X2 interface) . The eNB 906 may also be referred to as a base station, a Node B, an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS) , an extended service set (ESS) , or some other suitable terminology. The eNB 906 provides an access point to the EPC 910 for a UE 902. Examples of UEs 902 include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA) , a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player) , a camera, a game console, a tablet, or any other similar functioning device. The UE 902 may also be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

The eNB 906 is connected to the EPC 910. The EPC 910 may include a Mobility Management Entity (MME) 912, a Home Subscriber Server (HSS) 920, other MMEs 914, a Serving Gateway 916, a Multimedia Broadcast Multicast Service (MBMS) Gateway 924, a Broadcast Multicast Service Center (BM-SC) 926, and a Packet Data Network (PDN) Gateway 918. The MME 912 is the control node that processes the signaling between the UE 902 and the EPC 910. Generally, the MME 912 provides bearer and connection management. All user IP packets are transferred through the Serving Gateway 916, which itself is connected to the PDN Gateway 918. The PDN Gateway 918 provides UE IP address allocation as well as other functions. The PDN Gateway 918 and the BM-SC 926 are connected to the IP Services 922. The IP Services 922 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS) , a PS Streaming Service (PSS) , and/or other IP services. The BM-SC 926 may provide functions for MBMS user service provisioning and delivery. The BM-SC 926 may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS Bearer Services within a PLMN, and may be used to schedule and deliver MBMS transmissions. The MBMS Gateway 924 may be used to distribute MBMS traffic to the eNBs (e.g., 906, 908) belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting eMBMS related charging information.

FIG. 10 is a diagram illustrating an example of an access network 1000 in an LTE network architecture. In this example, the access network 1000 is divided into a number of cellular regions (cells) 1002. One or more lower power class eNBs 1008 may have cellular regions 1010 that overlap with one or more of the cells 1002. The lower power class eNB 1008 may be a femto cell (e.g., home eNB (HeNB) ) , pico cell, micro cell, or remote radio head (RRH) . The macro eNBs 1004 are each assigned to a respective cell 1002 and are configured to provide an access point to the EPC 910 for all the UEs 1006 in the cells 1002. Each of the macro eNBs 1004 and the lower power class eNBs 1008 may be an example of the eNB 14 and include an ICI mitigation component 40 for mitigating interference between cells. There is no centralized controller in this example of an access network 1000, but a centralized controller may be used in alternative configurations. The eNBs 1004 are responsible for all radio related functions including radio bearer control, admission control, mobility control, scheduling, security, and connectivity to the serving gateway 916. An eNB may support one or multiple (e.g., three) cells (also referred to as sectors) . The term “cell” can refer to the smallest coverage area of an eNB and/or an eNB subsystem serving a particular coverage area. Further, the terms “eNB, ” “base station, ” and “cell” maybe used interchangeably herein.

The modulation and multiple access scheme employed by the access network 1000 may vary depending on the particular telecommunications standard being deployed. In LTE applications, OFDM is used on the DL and SC-FDMA is used on the UL to support both frequency division duplex (FDD) and time division duplex (TDD) . As those skilled in the art will readily appreciate from the detailed description to follow, the various concepts presented herein are well suited for LTE applications. However, these concepts may be readily extended to other telecommunication standards employing other modulation and multiple access techniques. By way of example, these concepts may be extended to Evolution-Data Optimized (EV-DO) or Ultra Mobile Broadband (UMB) . EV-DO and UMB are air interface standards promulgated by the 3rd Generation Partnership Project 2 (3GPP2) as part of the CDMA2000 family of standards and employs CDMA to provide broadband Internet access to mobile stations. These concepts may also be extended to Universal Terrestrial Radio Access (UTRA) employing Wideband-CDMA (W-CDMA) and other variants of CDMA, such as TD-SCDMA； Global System for Mobile Communications (GSM) employing TDMA； and Evolved UTRA (E-UTRA) , IEEE 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, and Flash-OFDM employing OFDMA. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from the 3GPP organization. CDMA2000 and UMB are described in documents from the 3GPP2 organization. The actual wireless communication standard and the multiple access technology employed will depend on the specific application and the overall design constraints imposed on the system.

The eNBs 1004 may have multiple antennas supporting MIMO technology. The use of MIMO technology enables the eNBs 1004 to exploit the spatial domain to support spatial multiplexing, beamforming, and transmit diversity. Spatial multiplexing may be used to transmit different streams of data simultaneously on the same frequency. The data streams may be transmitted to a single UE 1006 to increase the data rate or to multiple UEs 1006 to increase the overall system capacity. This is achieved by spatially precoding each data stream (i.e., applying a scaling of an amplitude and a phase) and then transmitting each spatially precoded stream through multiple transmit antennas on the DL. The spatially precoded data streams arrive at the UE (s) 1006 with different spatial signatures, which enables each of the UE (s) 1006 to recover the one or more data streams destined for that UE 1006. On the UL, each UE 1006 transmits a spatially precoded data stream, which enables the eNB 1004 to identify the source of each spatially precoded data stream. An eNB 1004 may also identify the source of ICI and cancel the interference from a combined signal received at the eNB 1004.

Spatial multiplexing is generally used when channel conditions are good. When channel conditions are less favorable, beamforming may be used to focus the transmission energy in one or more directions. This may be achieved by spatially precoding the data for transmission through multiple antennas. To achieve good coverage at the edges of the cell, a single stream beamforming transmission may be used in combination with transmit diversity.

In the detailed description that follows, various aspects of an access network will be described with reference to a MIMO system supporting OFDM on the DL. OFDM is a spread-spectrum technique that modulates data over a number of subcarriers within an OFDM symbol. The subcarriers are spaced apart at precise frequencies. The spacing provides “orthogonality” that enables a receiver to recover the data from the subcarriers. In the time domain, a guard interval (e.g., cyclic prefix) may be added to each OFDM symbol to combat inter-OFDM-symbol interference. The UL may use SC-FDMA in the form of a DFT-spread OFDM signal to compensate for high peak-to-average power ratio (PAPR) .

FIG. 11 is a diagram 1100 illustrating an example of a DL frame structure in LTE. A frame (10 ms) may be divided into 10 equally sized subframes. Each subframe may include two consecutive time slots. A resource grid may be used to represent two time slots, each time slot including a resource block. The resource grid is divided into multiple resource elements. In LTE, for a normal cyclic prefix, a resource block contains 12 consecutive subcarriers in the frequency domain and 7 consecutive OFDM symbols in the time domain, for a total of 84 resource elements. For an extended cyclic prefix, a resource block contains 12 consecutive subcarriers in the frequency domain and 6 consecutive OFDM symbols in the time domain, for a total of 72 resource elements. Some of the resource elements, indicated as

R

1102, 1104, include DL reference signals (DL-RS) . The DL-RS include Cell-specific RS (CRS) (also sometimes called common RS) 1102 and UE-specific RS (UE-RS) 1104. UE-RS 1104 are transmitted on the resource blocks upon which the corresponding physical DL shared channel (PDSCH) is mapped. The number of bits carried by each resource element depends on the modulation scheme. Thus, the more resource blocks that a UE receives and the higher the modulation scheme, the higher the data rate for the UE.

FIG. 12 is a diagram 1200 illustrating an example of an UL frame structure in LTE. The available resource blocks for the UL may be partitioned into a data section and a control section. The control section may be formed at the two edges of the system bandwidth and may have a configurable size. The resource blocks in the control section may be assigned to UEs for transmission of control information. The data section may include all resource blocks not included in the control section. The UL frame structure results in the data section including contiguous subcarriers, which may allow a single UE to be assigned all of the contiguous subcarriers in the data section.

A UE may be assigned

resource blocks

1210a, 1210b in the control section to transmit control information to an eNB. The UE may also be assigned

resource blocks

1220a, 1220b in the data section to transmit data to the eNB. The UE may transmit control information in a physical UL control channel (PUCCH) on the assigned resource blocks in the control section. The UE may transmit data or both data and control information in a physical UL shared channel (PUSCH) on the assigned resource blocks in the data section. A UL transmission may span both slots of a subframe and may hop across frequency.

A set of resource blocks may be used to perform initial system access and achieve UL synchronization in a physical random access channel (PRACH) 1230. The PRACH 1230 carries a random sequence and cannot carry any UL data/signaling. Each random access preamble occupies a bandwidth corresponding to six consecutive resource blocks. The starting frequency is specified by the network. That is, the transmission of the random access preamble is restricted to certain time and frequency resources. There is no frequency hopping for the PRACH. The PRACH attempt is carried in a single subframe (1 ms) or in a sequence of few contiguous subframes and a UE can make a single PRACH attempt per frame (10 ms) .

FIG. 13 is a diagram 1300 illustrating an example of a radio protocol architecture for the user and control planes in LTE. The radio protocol architecture for the UE and the eNB is shown with three layers: Layer 1, Layer 2, and Layer 3. Layer 1 (L1 layer) is the lowest layer and implements various physical layer signal processing functions. The L1 layer will be referred to herein as the physical layer 1306. Layer 2 (L2 layer) 1308 is above the physical layer 1306 and is responsible for the link between the UE and eNB over the physical layer 1306.

In the user plane, the L2 layer 1308 includes a media access control (MAC) sublayer 1310, a radio link control (RLC) sublayer 1312, and a packet data convergence protocol (PDCP) 1314 sublayer, which are terminated at the eNB on the network side. Although not shown, the UE may have several upper layers above the L2 layer 1308 including a network layer (e.g., IP layer) that is terminated at the PDN gateway 1318 on the network side, and an application layer that is terminated at the other end of the connection (e.g., far end UE, server, etc.) .

The PDCP sublayer 1314 provides multiplexing between different radio bearers and logical channels. The PDCP sublayer 1314 also provides header compression for upper layer data packets to reduce radio transmission overhead, security by ciphering the data packets, and handover support for UEs between eNBs. The RLC sublayer 1312 provides segmentation and reassembly of upper layer data packets, retransmission of lost data packets, and reordering of data packets to compensate for out-of-order reception due to hybrid automatic repeat request (HARQ) . The MAC sublayer 1310 provides multiplexing between logical and transport channels. The MAC sublayer 1310 is also responsible for allocating the various radio resources (e.g., resource blocks) in one cell among the UEs. The MAC sublayer 1310 is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE and eNB is substantially the same for the physical layer 1306 and the L2 layer 1308 with the exception that there is no header compression function for the control plane. The control plane also includes a radio resource control (RRC) sublayer 1316 in Layer 3 (L3 layer) . The RRC sublayer 1316 is responsible for obtaining radio resources (e.g., radio bearers) and for configuring the lower layers using RRC signaling between the eNB and the UE.

FIG. 14 is a block diagram of an eNB 1410 in communication with a UE 1450 in an access network. In the DL, upper layer packets from the core network are provided to a controller/processor 1475. The controller/processor 1475 implements the functionality of the L2 layer. In the DL, the controller/processor 1475 provides header compression, ciphering, packet segmentation and reordering, multiplexing between logical and transport channels, and radio resource allocations to the UE 1450 based on various priority metrics. The controller/processor 1475 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the UE 1450.

The transmit (TX) processor 1416 implements various signal processing functions for the L1 layer (i.e., physical layer) . The signal processing functions include coding and interleaving to facilitate forward error correction (FEC) at the UE 1450 and mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK) , quadrature phase-shift keying (QPSK) , M-phase-shift keying (M-PSK) , M-quadrature amplitude modulation (M-QAM) ) . The coded and modulated symbols are then split into parallel streams. Each stream is then mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator 1474 may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE 1450. Each spatial stream may then be provided to a different antenna 1420 via a separate transmitter 1418TX. Each transmitter 1418TX may modulate an RF carrier with a respective spatial stream for transmission.

At the UE 1450, each receiver 1454RX receives a signal through its respective antenna 1452. Each receiver 1454RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor 1456. The RX processor 1456 implements various signal processing functions of the L1 layer. The RX processor 1456 may perform spatial processing on the information to recover any spatial streams destined for the UE 1450. If multiple spatial streams are destined for the UE 1450, they may be combined by the RX processor 1456 into a single OFDM symbol stream. The RX processor 1456 then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT) . The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the eNB 1410. These soft decisions may be based on channel estimates computed by the channel estimator 1458. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the eNB 1410 on the physical channel. The data and control signals are then provided to the controller/processor 1459.

The controller/processor 1459 implements the L2 layer. The controller/processor can be associated with a memory 1460 that stores program codes and data. The memory 1460 may be referred to as a computer-readable medium. In the UL, the controller/processor 1459 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the core network. The upper layer packets are then provided to a data sink 1462, which represents all the protocol layers above the L2 layer. Various control signals may also be provided to the data sink 1462 for L3 processing. The controller/processor 1459 is also responsible for error detection using an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support HARQ operations.

In the UL, a data source 1467 is used to provide upper layer packets to the controller/processor 1459. The data source 1467 represents all protocol layers above the L2 layer. Similar to the functionality described in connection with the DL transmission by the eNB 1410, the controller/processor 1459 implements the L2 layer for the user plane and the control plane by providing header compression, ciphering, packet segmentation and reordering, and multiplexing between logical and transport channels based on radio resource allocations by the eNB 1410. The controller/processor 1459 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the eNB 1410.

Channel estimates derived by a channel estimator 1458 from a reference signal or feedback transmitted by the eNB 1410 may be used by the TX processor 1468 to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor 1468 may be provided to different antenna 1452 via separate transmitters 1454TX. Each transmitter 1454TX may modulate an RF carrier with a respective spatial stream for transmission.

The UL transmission is processed at the eNB 1410 in a manner similar to that described in connection with the receiver function at the UE 1450. Each receiver 1418RX receives a signal through its respective antenna 1420. Each receiver 1418RX recovers information modulated onto an RF carrier and provides the information to a RX processor 1470. The RX processor 1470 may implement the L1 layer.

The controller/processor 1475 implements the L2 layer. The controller/processor 1475 can be associated with a memory 1476 that stores program codes and data. The memory 1476 may be referred to as a computer-readable medium. In the UL, the controller/processor 1475 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the UE 1450. Upper layer packets from the controller/processor 1475 may be provided to the core network. The controller/processor 1475 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

FIG. 11 is a conceptual data flow diagram 1500 illustrating the data flow between different modules/means/components in an exemplary apparatus 1502. The apparatus 1502 may be an eNB.

The apparatus 1502 may include a reception module 1504 that receives uplink communications from a UE 1550. The reception module 1504 may include the interference cancellation receiver 70. For example, the reception module 1504 may receive grant requests and/or data from the UE 1550. The reception module 1504 may also receive interference from another eNB 1560. The reception module 1504 may pass the grant requests to the load determination module 1510. The reception module 1504 maypass a combined signal including transmissions from the UE 1550 and the other eNB 1560 to the CI module 1506. The CI module 1506 may apply interference cancellation techniques to decode separate streams from the combined signal and return the decoded data to the reception module 1504.

The X2 interface module 1508 may receive information about the other eNB 1560 such as loading information and interference properties. The X2 module 1508 may also transmit the loading information of the apparatus 1502 to the other eNB 1560. The X2 interface module 1502 may forward or receive loading information from the load determination module 1510. The X2 interface module 1502 may forward interference properties to the reception module 1504 or the CI module 1506.

The load determination module 1510 may include the load determination component 42 (FIG. 1B) . The load determination module 1510 may receive the grant requests forwarded by the reception module 1104. The load determination module 1510 may determine uplink traffic load based on the grant requests. The load determination module 1510 may also receive downlink data from a node in the EPC 1210 such as the serving gateway 1216 or PDN gateway 1218. The load determination module 1510 may determine a downlink traffic load based on the downlink data. The load determination module may also receive a cell cluster from the clustering module 1514. The load determination module may determine a duplexing configuration based on the uplink traffic load, downlink traffic load, and/or clustering information. The load determination module 1506 may send the duplexing configuration to the victim cell module. The load determination module 1506 may forward downlink data for UEs to the scheduling module 1518.

The victim cell module 1512 may include the victim cell component 50 (FIG. 1B) . The victim cell module 1512 may determine potential victim cells based on, e.g., properties of the other eNB 1560 received from the X2 interface module 1508 and/or the reception module 1504. The victim cell module 1512 may share the properties of the other eNB 1560 with the clustering module 1514. The victim cell module 1512 may send one or more victim cell identifiers to the interference estimator module 1516.

The interference estimator module 1516 may include the interference estimator 62 (FIG. 1B) . The interference estimator module may receive the list of victim cells from the victim cell module 1512 and a list of UEs from the scheduling module 1518. The interference estimator module 1516 may estimate an interference level for each UE for each potential victim cell and provide the estimated interference levels to the scheduling module 1518.

The scheduling module 1518 may include the scheduler 60 (FIG. 1B) . The scheduling module 1518 may receive downlink data for UEs from the load determination module 1510 and interference estimates for each UE from the interference estimator module 1516. The scheduling module may schedule TDD transmissions for the downlink data to the UEs when the estimated interference level is less than a threshold. The scheduling module 1518 may provide the TDD transmissions to the transmission module 1520, which may transmit the TDD transmissions as downlink transmissions to the UE 1550.

The apparatus may include additional modules that perform each of the blocks of the algorithm in the aforementioned flow charts of FIGs. 2 and 3. As such, each block in the aforementioned flow charts of FIGs. 2 and 3 may be performed by a module and the apparatus may include one or more of those modules. The modules may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof.

FIG. 16 is a diagram 1600 illustrating an example of a hardware implementation for an apparatus 1502' employing a processing system 1614. The processing system 1614 may be implemented with a bus architecture, represented generally by the bus 1624. The bus 1624 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 1614 and the overall design constraints. The bus 1624 links together various circuits including one or more processors and/or hardware modules, represented by the processor 1604, the

modules

1504, 1506, 1508, 1510, 1512, 1514, 1516, 1518 and the computer-readable medium/memory 1606. The bus 16524 may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

The processing system 1614 may be coupled to a transceiver 1610. The transceiver 1610 is coupled to one or more antennas 1620. The transceiver 1610 provides a means for communicating with various other apparatus over a transmission medium. The transceiver 1610 receives a signal from the one or more antennas 1620, extracts information from the received signal, and provides the extracted information to the processing system 1614, specifically the reception module 1504. In addition, the transceiver 1610 receives information from the processing system 1614, specifically the transmission module 1520, and based on the received information, generates a signal to be applied to the one or more antennas 1620. The processing system 1614 includes a processor 1604 coupled to a computer-readable medium/memory 1206. The processor 1604 is responsible for general processing, including the execution of software stored on the computer-readable medium/memory 1606. The software, when executed by the processor 1604, causes the processing system 1614 to perform the various functions described supra for any particular apparatus. The computer-readable medium/memory 1606 may also be used for storing data that is manipulated by the processor 1604 when executing software. The processing system further includes at least one of the

modules

1504, 1506, 1508, 1510, 1512, 1514, 1516, 1518. The modules may be software modules running in the processor 1604, resident/stored in the computer readable medium/memory 1606, one or more hardware modules coupled to the processor 1204, or some combination thereof. The processing system 1614 may be a component of the eNB 14 and may include the memory 976 and/or at least one of the TX processor 1416, the RX processor 1470, and the controller/processor 1475.

In one configuration, the apparatus 1502 or apparatus 1502’ for wireless communication includes means for reconfiguring, by a first cell, a FDD uplink band to use TDD on the FDD uplink band based on downlink and uplink traffic loads of the first cell. The apparatus 1502/1502’ may further include means for determining that a second cell is potentially affected by inter-cell interference caused by TDD downlink transmissions by the first cell on the FDD uplink band. The apparatus 1502/1502’ may further include means for estimating a potential interference level caused at the second cell on the FDD uplink band by the TDD downlink transmissions for a first user equipment (UE) connected to the first cell. The apparatus 1502/1502’ may further include means for scheduling a TDD downlink transmission for the first UE on the FDD uplink band when the potential interference level is less than a threshold. As described supra, the processing system 1214 may include the TX Processor 1416, the RX Processor 1470, and the controller/processor 1475. As such, in one configuration, the aforementioned means may be the TX Processor 1416, the RX Processor 1470, and the controller/processor 1475 configured to perform the functions recitedby the aforementioned means.

It is understood that the specific order or hierarchy of blocks in the processes/flow charts disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes/flow charts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C, ” “at least one of A, B, and C, ” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C, ” “at least one of A, B, and C, ” and “A, B, C, or any combination thereof” may be A only, B only, C only, Aand B, Aand C, B and C,or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for.”

WHAT IS CLAIMED IS:

Claims

A method ofmitigating inter-cell interference in flexible duplexing, comprising:

reconfiguring, by a first cell, afrequency division duplexing (FDD) uplink band to use time division duplexing (TDD) on the FDD uplink band based on downlink and uplink traffic loads ofthe first cell；

determining that a second cell is potentially affected by inter-cell interference causedby TDD downlink transmissions by the first cell on the FDD uplink band；

estimating a potential interference level caused at the second cell on the FDD uplink band by the TDD downlink transmissions for a first user equipment (UE) connected to the first cell； and

scheduling a TDD downlink transmission for the first UE on the FDD uplink band when the potential interference level is less than a threshold.
The method ofclaim 1, further comprising:

determining a cell cluster for the first cell based on an interference criterion；

wherein the reconfiguring is further based on the cell cluster and all cells in the cell cluster reconfigure the uplinkband concurrently.
The method of claim 1, wherein determining that the second cell is potentially affected by inter-cell interference caused by TDD downlink transmissions by the first cell on the FDD uplinkband comprises:

determining that the second cell has not reconfigured the uplink band to use TDD；

determining that the second cell has uplink traffic load； and

determining that a coupling loss between the first cell and the second cell is less than a threshold coupling loss.
The method of claim 1, wherein determining the potential interference level for the first UE comprises:

calculating an angle between a line formed by the first cell and the second cell and a line formedby the first cell and the first UE； and

determining the potential interference level based on the angle.
The method of claim 1, wherein determining the potential interference level for the first UE comprises:

calculating a channel correlation between a channel from the first cell to the second cell and a channel from the first cell to the first UE； and

determining the potential interference level based on the channel correlation.
The method of claim 1, further comprising applying a precoding vector to the scheduled TDD downlink transmission using beamforming to decrease a level of interference at the second cell causedby the scheduled TDD downlink transmission.
The method of claim 1, further comprising determining a potential interference level caused at the second cell on the FDD uplink band by TDD downlink transmissions for additional UEs connected to the first cell； and

scheduling, in order of priority of the additional UEs, aTDD downlink transmission for each additional UE on the FDD uplink band when the respective potential interference level is less than the threshold.
The method of claim 1, further comprising transmitting cell loading status to the second cell via an X2 interface.
The method of claim 1, further comprising receiving a cell loading status of the second cell and an offloading status ofthe second cell via an X2 interface.
The method ofclaim 1, further comprising:

transmitting a configuration of demodulation reference signal ofthe first cell, to the second cell via an X2 interface.
The method ofclaim 1, further comprising:

transmitting a configuration of demodulation reference signal of the first cell, rank of the TDD downlink transmission, and precoding vector of the TDD downlink transmission to the second cell via an X2 interface.
The method ofclaim 1, further comprising:

performing interference cancellation, by the second cell, of the downlink transmission for the first UE.
The method of claim 12, wherein performing interference cancellation comprises:

receiving a configuration of a demodulation reference signal of the first cell via an X2 interface；

receiving a combined signal including the downlink transmission from the first cell and an uplink transmission from a second UE connected to the second cell； and

detecting a rank of the downlink transmission, and a precoding vector of the downlink transmission；

using joint multiple-user detection or iterative decoding and cancellation based on the demodulation reference signal of the first cell, the rank of the downlink transmission, and the precoding vector of the downlink transmission to improve the received uplink transmission from the second UE.
A method ofmitigating inter-cell interference in flexible duplexing, comprising:

receiving, by a second cell, an indication that a first cell operating in a frequency division duplexing (FDD) uplink band has reconfigured to use time division duplexing (TDD) on the FDD uplink band for a TDD downlink transmission to a first user equipment (UE) ；

receiving a configuration of a demodulation reference signal of the first cell, a rank of the downlink transmission, and a precoding vector of the downlink transmission；

receiving a combined signal including the downlink transmission from the first cell and an uplink transmission from a second UE connected to the second cell； and

cancelling the downlink transmission from the combined signal using the demodulation reference signal of the first cell, the rank of the downlink transmission, and the precoding vector of the downlink transmission to improve the uplink transmission from the second UE.
The method of claim 14, wherein cancelling the downlink transmission comprises:

performing joint multiple-user detection to decode the downlink transmission and the uplink transmission.
The method of claim 14, wherein cancelling the downlink transmission comprises:

iteratively decoding the downlink transmission and cancelling the decoded downlink transmission from the combined signal.
The method of claim 14, wherein the configuration of the demodulation reference signal of the first cell is received via an X2 interface, and the rank of the downlink transmission and the precoding vector of the downlink transmission are detectedby the second cell.
An apparatus for mitigating inter-cell interference in flexible duplexing of wireless communications, comprising:

a load determination component configured to reconfigure, at a first cell, a frequency division duplexing (FDD) uplink band to use time division duplexing (TDD) on the FDD uplinkbandbased on downlink and uplink traffic loads ofthe first cell；

a victim cell component configured to determine that a second cell is potentially affected by inter-cell interference caused by TDD downlink transmissions by the first cell on the FDD uplinkband；

an interference estimator configured to estimate a potential interference level caused at the second cell on the FDD uplink band by the TDD downlink transmissions for a first user equipment (UE) connected to the first cell； and

a scheduler configured to schedule a TDD downlink transmission for the first UE on the FDD uplink band when the potential interference level is less than a threshold.
The apparatus ofclaim 18, further comprising:

a cell clustering component configured to determine a cell cluster for the first cell based on an interference criterion；

wherein the load determination component is further configured to reconfigure the FDD uplink band based on the cell cluster, and all cells in the cell cluster reconfigure the uplinkband concurrently.
The apparatus ofclaim 18, wherein the victim cell component comprises:

a victim configuration component configured to determine that the second cell has not reconfigured the uplinkband to use TDD；

a victim load component configured to determine that the second cell has uplink traffic load； and

a coupling loss component configured to determine that a coupling loss between the first cell and the second cell is less than a threshold coupling loss.
The apparatus ofclaim 18, wherein the interference estimator is configured to:

calculate an angle between a line formed by the first cell and the second cell and a line formed by the first cell and the first UE； and

determine the potential interference level based on the angle.
The apparatus ofclaim 18, wherein the interference estimator is configured to:

calculate a channel correlation between a channel from the first cell to the second cell and a channel from the first cell to the first UE； and

determine the potential interference level based on the channel correlation.
The apparatus ofclaim 18, further comprising a transmitter configured to apply a precoding vector to the scheduled TDD downlink transmission using beamforming to decrease a level of interference at the second cell caused by the scheduled TDD downlink transmission.
The apparatus of claim 18, wherein the interference estimator is further configured to determine a potential interference level caused at the second cell on the FDD uplink band by TDD downlink transmissions for additional UEs connected to the first cell； and

the scheduler is configured to schedule, in order of priority of the additional UEs, aTDD downlink transmission for each additional UE on the FDD uplink band when the respective potential interference level is less than the threshold.
The apparatus of claim 18, further comprising an X2 interface configured to transmit cell loading status to the second cell, receive a cell loading status ofthe second cell and an offloading status of the second cell, or transmit a configuration of a demodulation reference signal ofthe first cell, to the second cell.
The apparatus of claim 18, further comprising an X2 interface configured to transmit a configuration of a demodulation reference signal of the first cell, rank of the TDD downlink transmission, and precoding vector of the TDD downlink transmission to the second cell via an X2 interface.
The apparatus ofclaim 18, further comprising:

an interference cancellation receiver configured to perform interference cancellation of a second downlink transmission for a second UE connected to the second cell.
The apparatus ofclaim 27, wherein the interference cancellation receiver further comprises:

a multiple-user detector configured to decode and cancel the second downlink transmission based on a demodulation reference signal ofthe second cell, the rank ofthe second downlink transmission, and a precoding vector of the second downlink transmission to improve a received uplinktransmission from the first UE.
A computer-readable medium storing computer executable code for mitigating inter-cell interference in flexible duplexing ofwireless communications, comprising:

code for reconfiguring, by a first cell, afrequency division duplexing (FDD) uplinkband to use time division duplexing (TDD) on the FDD uplink bandbased on downlink and uplink traffic loads ofthe first cell；

code for determining that a second cell is potentially affected by inter-cell interference caused by TDD downlink transmissions by the first cell on the FDD uplink band；

code for estimating a potential interference level caused at the second cell on the FDD uplink band by the TDD downlink transmissions for a first user equipment (UE) connected to the first cell； and

code for scheduling a TDD downlink transmission for the first UE on the FDD uplink band when the potential interference level is less than a threshold.