WO2015027389A1 - Backhaul signaling for interference mitigation and traffic adaptation - Google Patents

Abstract

Certain aspects of the present disclosure relate to methods and apparatus for backhaul signaling in systems performing enhanced interference mitigation and traffic adaptation (eIMTA).

Description

BACKHAUL SIGNALING FOR INTERFERENCE MITIGATION AND

TRAFFIC ADAPTATION

BACKGROUND

Field

[0001] The present disclosure relates generally to communication systems, and more particularly, to methods and apparatus for backhaul signaling in systems performing enhanced interference mitigation and traffic adaptation (elMTA).

Background

[0002] 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 divisional multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

[0003] 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 of an emerging telecommunication standard is Long Term Evolution (LTE). LTE/LTE -Advanced is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3 GPP). It is designed to better support mobile broadband Internet access by improving spectral efficiency, lower costs, improve services, make use of new spectrum, and better integrate 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.

SUMMARY

[0004] Certain aspects of the present disclosure provide a method for wireless communications by a base station (BS). The method generally includes obtaining one or more parameters, each generated as a function of uplink (UL) and downlink (DL) loading of one of the first base station or one or more other base stations, and determining a configuration of DL and UL subframes based on the obtained one or more parameters.

[0005] Certain aspects of the present disclosure provide a method for wireless communications by a base station (BS). The method generally includes obtaining one or more parameters, each generated as a function of interference measured at one of the first base station or one or more other base stations from one of the first base station or one or more other base stations, and mitigating the interference based on the obtained one or more parameters.

[0006] Various processor-based apparatus and computer-program products for performing the above-reference methods are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a diagram illustrating an example of a network architecture.

[0008] FIG. 2 is a diagram illustrating an example of an access network.

[0009] FIG. 3 is a diagram illustrating an example of a DL frame structure in LTE.

[0010] FIG. 4 is a diagram illustrating an example of an UL frame structure in LTE.

[0011] FIG. 5 is a diagram illustrating an example of a radio protocol architecture for the user and control plane.

[0012] FIG. 6 is a diagram illustrating an example of an evolved Node B and user equipment in an access network, in accordance with certain aspects of the disclosure. [0013] FIG. 7 illustrates how different subframe configurations may be used, in accordance with certain aspects of the present disclosure.

[0014] FIG. 8 illustrates different types of interference that may be mitigated, in accordance with certain aspects of the present disclosure.

[0015] FIG. 9 illustrates different types of SSF configurations that may be used to help measure interference, in accordance with certain aspects of the present disclosure.

[0016] FIG. 10 illustrates one example of how a cluster of eNBs may determine different uplink (UL) and downlink (DL) configurations to use, in accordance with certain aspects of the present disclosure.

[0017] FIG. 11 illustrates example operations 1100 performed by a base station (BS), in accordance with certain aspects of the present disclosure.

[0018] FIG. 12 illustrates example operations 1200 performed by a base station (BS), in accordance with certain aspects of the present disclosure.

[0019] The attached APPENDIX provides details for certain aspects of the present disclosure.

DETAILED DESCRIPTION

[0020] Aspects of the present disclosure may help mitigate interference cause by one base station to another base station (eNB-eNB interference) and/or interference caused by one user equipment to another user equipment (UE-UE interference). Such techniques may make use of carefully selected special subframe (SSF) configurations to allow eNB-eNB and/or UE-UE interference measurements.

[0021] 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 only 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.

[0022] 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 hardware, software/firmware, or combinations thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

[0023] 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.

[0024] Accordingly, in one or more exemplary embodiments, the functions described may be implemented in hardware, software/firmware, or combinations 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 RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0025] FIG. 1 is a diagram illustrating an LTE network architecture 100. The LTE network architecture 100 may be referred to as an Evolved Packet System (EPS) 100. The EPS 100 may include one or more user equipment (UE) 102, an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) 104, an Evolved Packet Core (EPC) 1 10, a Home Subscriber Server (HSS) 120, and an Operator's Internet Protocol (IP) Services 122. The EPS can interconnect with other access networks, but for simplicity those entities/interfaces are not shown. Exemplary other access networks may include an IP Multimedia Subsystem (IMS) Packet Data Network (PDN), Internet PDN, Administrative PDN (e.g., Provisioning PDN), carrier-specific PDN, operator-specific PDN, and/or GPS PDN. 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.

[0026] The E-UTRAN includes the evolved Node B (eNB) 106 and other eNBs 108. The eNB 106 provides user and control plane protocol terminations toward the UE 102. The eNB 106 may be connected to the other eNBs 108 via an X2 interface (e.g., backhaul). The eNB 106 may also be referred to as a base station, 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 106 provides an access point to the EPC 1 10 for a UE 102. Examples of UEs 102 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, a netbook, a smart book, or any other similar functioning device. The UE 102 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.

[0027] The eNB 106 is connected by an SI interface to the EPC 110. The EPC 110 includes a Mobility Management Entity (MME) 112, other MMEs 114, a Serving Gateway 116, and a Packet Data Network (PDN) Gateway 118. The MME 112 is the control node that processes the signaling between the UE 102 and the EPC 110. Generally, the MME 112 provides bearer and connection management. All user IP packets are transferred through the Serving Gateway 116, which itself is connected to the PDN Gateway 118. The PDN Gateway 118 provides UE IP address allocation as well as other functions. The PDN Gateway 118 is connected to the Operator's IP Services 122. The Operator's IP Services 122 may include, for example, the Internet, the Intranet, an IP Multimedia Subsystem (IMS), and a PS Streaming Service (PSS). In this manner, the UE102 may be coupled to the PDN through the LTE network.

[0028] FIG. 2 is a diagram illustrating an example of an access network 200 in an LTE network architecture. In this example, the access network 200 is divided into a number of cellular regions (cells) 202. One or more lower power class eNBs 208 may have cellular regions 210 that overlap with one or more of the cells 202. A lower power class eNB 208 may be referred to as a remote radio head (RRH). The lower power class eNB 208 may be a femto cell (e.g., home eNB (HeNB)), pico cell, or micro cell. The macro eNBs 204 are each assigned to a respective cell 202 and are configured to provide an access point to the EPC 110 for all the UEs 206 in the cells 202. There is no centralized controller in this example of an access network 200, but a centralized controller may be used in alternative configurations. The eNBs 204 are responsible for all radio related functions including radio bearer control, admission control, mobility control, scheduling, security, and connectivity to the serving gateway 116.

[0029] The modulation and multiple access scheme employed by the access network 200 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 duplexing (FDD) and time division duplexing (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), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, and Flash-OFDM employing OFDM A. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from the 3 GPP 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.

[0030] The eNBs 204 may have multiple antennas supporting MIMO technology. The use of MIMO technology enables the eNBs 204 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 206 to increase the data rate or to multiple UEs 206 to increase the overall system capacity. This is achieved by spatially precoding each data stream (e.g., 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) 206 with different spatial signatures, which enables each of the UE(s) 206 to recover the one or more data streams destined for that UE 206. On the UL, each UE 206 transmits a spatially precoded data stream, which enables the eNB 204 to identify the source of each spatially precoded data stream.

[0031] 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.

[0032] 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).

[0033] FIG. 3 is a diagram 300 illustrating an example of a DL frame structure in LTE. A frame (10 ms) may be divided into 10 equally sized sub-frames with indices of 0 through 9. Each sub-frame 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, a resource block contains 12 consecutive subcarriers in the frequency domain and, for a normal cyclic prefix in each OFDM symbol, 7 consecutive OFDM symbols in the time domain, or 84 resource elements. For an extended cyclic prefix, a resource block contains 6 consecutive OFDM symbols in the time domain and has 72 resource elements. Some of the resource elements, as indicated as R 302, 304, include DL reference signals (DL- RS). The DL-RS include Cell-specific RS (CRS) (also sometimes called common RS) 302 and UE-specific RS (UE-RS) 304. UE-RS 304 are transmitted only 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.

[0034] In LTE, an eNB may send a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) for each cell in the eNB. The primary and secondary synchronization signals may be sent in symbol periods 6 and 5, respectively, in each of sub frames 0 and 5 of each radio frame with the normal cyclic prefix (CP). The synchronization signals may be used by UEs for cell detection and acquisition. The eNB may send a Physical Broadcast Channel (PBCH) in symbol periods 0 to 3 in slot 1 of subframe 0. The PBCH may carry certain system information.

[0035] The eNB may send a Physical Control Format Indicator Channel (PCFICH) in the first symbol period of each subframe. The PCFICH may convey the number of symbol periods (M) used for control channels, where M may be equal to 1 , 2 or 3 and may change from subframe to subframe. M may also be equal to 4 for a small system bandwidth, e.g., with less than 10 resource blocks. The eNB may send a Physical HARQ Indicator Channel (PHICH) and a Physical Downlink Control Channel (PDCCH) in the first M symbol periods of each subframe. The PHICH may carry information to support hybrid automatic repeat request (HARQ). The PDCCH may carry information on resource allocation for UEs and control information for downlink channels. The eNB may send a Physical Downlink Shared Channel (PDSCH) in the remaining symbol periods of each subframe. The PDSCH may carry data for UEs scheduled for data transmission on the downlink.

[0036] The eNB may send the PSS, SSS, and PBCH in the center 1.08 MHz of the system bandwidth used by the eNB. The eNB may send the PCFICH and PHICH across the entire system bandwidth in each symbol period in which these channels are sent. The eNB may send the PDCCH to groups of UEs in certain portions of the system bandwidth. The eNB may send the PDSCH to specific UEs in specific portions of the system bandwidth. The eNB may send the PSS, SSS, PBCH, PCFICH, and PHICH in a broadcast manner to all UEs, may send the PDCCH in a unicast manner to specific UEs, and may also send the PDSCH in a unicast manner to specific UEs.

[0037] A number of resource elements may be available in each symbol period. Each resource element (RE) may cover one subcarrier in one symbol period and may be used to send one modulation symbol, which may be a real or complex value. Resource elements not used for a reference signal in each symbol period may be arranged into resource element groups (REGs). Each REG may include four resource elements in one symbol period. The PCFICH may occupy four REGs, which may be spaced approximately equally across frequency, in symbol period 0. The PHICH may occupy three REGs, which may be spread across frequency, in one or more configurable symbol periods. For example, the three REGs for the PHICH may all belong in symbol period 0 or may be spread in symbol periods 0, 1, and 2. The PDCCH may occupy 9, 18, 36, or 72 REGs, which may be selected from the available REGs, in the first M symbol periods, for example. Only certain combinations of REGs may be allowed for the PDCCH.

[0038] A UE may know the specific REGs used for the PHICH and the PCFICH. The UE may search different combinations of REGs for the PDCCH. The number of combinations to search is typically less than the number of allowed combinations for the PDCCH. An eNB may send the PDCCH to the UE in any of the combinations that the UE will search.

[0039] FIG. 4 is a diagram 400 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.

[0040] A UE may be assigned resource blocks 410a, 410b in the control section to transmit control information to an eNB. The UE may also be assigned resource blocks 420a, 420b 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 only 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.

[0041] A set of resource blocks may be used to perform initial system access and achieve UL synchronization in a physical random access channel (PRACH) 430. The PRACH 430 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 sub frames and a UE can make only a single PRACH attempt per frame (10 ms).

[0042] FIG. 5 is a diagram 500 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 (LI layer) is the lowest layer and implements various physical layer signal processing functions. The LI layer will be referred to herein as the physical layer 506. Layer 2 (L2 layer) 508 is above the physical layer 506 and is responsible for the link between the UE and eNB over the physical layer 506.

[0043] In the user plane, the L2 layer 508 includes a media access control (MAC) sublayer 510, a radio link control (RLC) sublayer 512, and a packet data convergence protocol (PDCP) 514 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 508 including a network layer (e.g., IP layer) that is terminated at the PDN gateway 118 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.).

[0044] The PDCP sublayer 514 provides multiplexing between different radio bearers and logical channels. The PDCP sublayer 514 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 512 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 510 provides multiplexing between logical and transport channels. The MAC sublayer 510 is also responsible for allocating the various radio resources (e.g., resource blocks) in one cell among the UEs. The MAC sublayer 510 is also responsible for HARQ operations.

[0045] In the control plane, the radio protocol architecture for the UE and eNB is substantially the same for the physical layer 506 and the L2 layer 508 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 516 in Layer 3 (L3 layer). The RRC sublayer 516 is responsible for obtaining radio resources (i.e., radio bearers) and for configuring the lower layers using RRC signaling between the eNB and the UE.

[0046] FIG. 6 is a block diagram of an eNB 610 in communication with a UE 650 in an access network. In the DL, upper layer packets from the core network are provided to a controller/processor 675. The controller/processor 675 implements the functionality of the L2 layer. In the DL, the controller/processor 675 provides header compression, ciphering, packet segmentation and reordering, multiplexing between logical and transport channels, and radio resource allocations to the UE 650 based on various priority metrics. The controller/processor 675 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the UE 650.

[0047] The TX processor 616 implements various signal processing functions for the LI layer (i.e., physical layer). The signal processing functions includes coding and interleaving to facilitate forward error correction (FEC) at the UE 650 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 674 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 650. Each spatial stream is then provided to a different antenna 620 via a separate transmitter 618TX. Each transmitter 618TX modulates an RF carrier with a respective spatial stream for transmission.

[0048] At the UE 650, each receiver 654RX receives a signal through its respective antenna 652. Each receiver 654RX recovers information modulated onto an RF carrier and provides the information to the receiver (RX) processor 656. The RX processor 656 implements various signal processing functions of the LI layer. The RX processor 656 performs spatial processing on the information to recover any spatial streams destined for the UE 650. If multiple spatial streams are destined for the UE 650, they may be combined by the RX processor 656 into a single OFDM symbol stream. The RX processor 656 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, is recovered and demodulated by determining the most likely signal constellation points transmitted by the eNB 610. These soft decisions may be based on channel estimates computed by the channel estimator 658. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the eNB 610 on the physical channel. The data and control signals are then provided to the controller/processor 659.

[0049] The controller/processor 659 implements the L2 layer. The controller/processor can be associated with a memory 660 that stores program codes and data. The memory 660 may be referred to as a computer-readable medium. In the UL, the control/processor 659 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 662, which represents all the protocol layers above the L2 layer. Various control signals may also be provided to the data sink 662 for L3 processing. The controller/processor 659 is also responsible for error detection using an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support HARQ operations.

[0050] In the UL, a data source 667 is used to provide upper layer packets to the controller/processor 659. The data source 667 represents all protocol layers above the L2 layer. Similar to the functionality described in connection with the DL transmission by the eNB 610, the controller/processor 659 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 610. The controller/processor 659 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the eNB 610. [0051] Channel estimates derived by a channel estimator 658 from a reference signal or feedback transmitted by the eNB 610 may be used by the TX processor 668 to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor 668 are provided to different antenna 652 via separate transmitters 654TX. Each transmitter 654TX modulates an RF carrier with a respective spatial stream for transmission.

[0052] The UL transmission is processed at the eNB 610 in a manner similar to that described in connection with the receiver function at the UE 650. Each receiver 618RX receives a signal through its respective antenna 620. Each receiver 618RX recovers information modulated onto an RF carrier and provides the information to a RX processor 670. The RX processor 670 may implement the LI layer.

[0053] The controller/processor 675 implements the L2 layer. The controller/processor 675 can be associated with a memory 676 that stores program codes and data. The memory 676 may be referred to as a computer-readable medium. In the UL, the control/processor 675 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the UE 650. Upper layer packets from the controller/processor 675 may be provided to the core network. The controller/processor 675 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

EXAMPLE INTERFERENCE MITIGATION

[0054] Flexible DL/UL configuration is generally regarded as one efficient way to fully utilize TDD spectrum and is being addressed in 3 GPP enhanced interference mitigation and traffic adaptation (elMTA) SI/WI. FIG. 7 illustrates how different subframe configurations (Configuration 1 and Configuration 2) may be used at different times, depending on DL/UL traffic loading.

[0055] Such techniques may be used to advantage in cases where there may be eNB-eNB or UE-UE interference when adjacent cells having different directions. In order to mitigate the interference between eNB-eNB or UE-UE, many solutions have been discussed, including cell cluster IM (CCIM), scheduling dependent IM (SDIM), interference mitigation based on enhanced inter-cell interference coordination (elCIC) and/or further enhanced inter-cell interference cancellation (FelCIC) schemes and interference suppressing interference mitigation (ISIM).

[0056] Most of such solutions depend on eNB or UE measurement of the interference. However, in the current specifications, eNB-eNB and UE-UE measurement is not supported, so a new design is needed for eNB-eNB and UE-UE measurement if eNB-eNB and/or UE-UE interference is to be mitigated. FIG. 8 illustrates example DL-UL interference when adjacent cells have different directions, including eNB-eNB interference and UE-UE interference.

[0057] Aspects of the present disclosure may help mitigate interference caused by one base station to another base station (eNB-eNB interference) and/or interference caused by one user equipment to another user equipment (UE-UE interference). Such techniques may include forming clusters of cells and causing all of the cells in a cluster to use the same configuration of DL and UL subframes and utilizing subframe-specific power control commands.

[0058] To avoid the negative impact of the DL to UL interference on the UL signal to interference and noise ratio (SINR), the following cell clustering approach has been studied in 3GPP RANI/4: eNBs that have coupling loss less than a threshold are forced to transmit in the same direction. For example, for an outdoor pico cell only scenario, the pico cells are grouped as a cluster if coupling loss between two pico cells is less than a predefined threshold X, and the transmission direction of the pico cells within a cluster shall be the same.

[0059] FIG. 9 illustrates an example of forming cells into clusters and serving UEs.

[0060] The technique of forming clusters of cells may allow more efficient interference mitigation than without clusters, however existing backhaul links may not be sufficient for communicating TDD configurations and loading among cells for elMTA purposes.

[0061] Legacy X2 interface messages have been considered for use in DL-UL interference mitigation. These legacy X2 interface messages include relative narrowband transmit power (RNTP), overload indicator (OI), and high interference indicator (HII). RNTP was introduced to support frequency domain ICIC schemes. OI was introduced to report strong interference caused by high power UL transmissions in neighbor cells. HII was introduced to inform neighboring cell about scheduling cell- edge UEs, so that these cells may react appropriately.

[0062] However, the legacy X2 interface messages do not carry enough information to allow efficient interference mitigation. Therefore, new techniques for backhaul signaling with elMTA are disclosed, according to aspects of the present invention.

EXAMPLE BACKHAUL SIGNALING IN ElMTA

[0063] Use cases or scenarios that need new signaling information exchanged via backhaul in elMTA according to aspects of the present disclosure may include: cell clustering for IM and backhaul signaling for cell clusters, backhaul signaling for BS-BS interference measurement, traffic adaption for interference coordination within a cluster and backhaul signaling for traffic adaptation, and backhaul signaling for power control of BS and UE transmissions.

[0064] According to certain aspects, new techniques for signaling exchanged measurements of eNB - eNB interference are disclosed. The measured eNB - eNB interference (i.e. RSRP) may be sent to one or more surrounding neighbor eNBs via a backhaul link. According to these aspects, the cells may determine to join or leave clusters or mitigate the interference from aggressor eNBs by using this backhaul signaling.

[0065] According to certain aspects, the cells may exchange cell loading information to further improve the efficiency of clustering. According to these aspects, a lowly loaded cell may fall back to a cluster's default configuration, rather than using another configuration and causing interference to other cells.

[0066] According to certain aspects, cells in a cluster may exchange buffer status information in order to more efficiently perform traffic adaptation. However, due to the inevitable backhaul latency and capacity limitation, information to be exchanged over the backhaul needs to be compressed.

[0067] According to certain aspects, cells may exchange their downlink (DL) and uplink (UL) buffer sizes. According to other aspects, cells may exchange a ratio R of their DL-to-UL buffer sizes, i.e. R = B_DLI B_UL, wherein B_DL is the cell's DL buffer size and BUL is the cell's UL buffer size. According to these aspects, the cells may also exchange the sum W of their buffer sizes, i.e. W= B_DL + B_UL.

[0068] The ratio R may be closely related to the UL and DL subframe configuration needed in the cell. According to certain aspects, cells may exchange a quantization of the ratio R, rather than the actual ratio. According to one example, the ratio R may be quantized in three bits according to the chart shown below, although other quantizations using the same or different numbers of bits are included in the scope of this disclosure.

[0069] The sum W of the UL and DL buffer sizes may be used as a measure of the priority or loading of a cell in voting for a cluster configuration. According to certain aspects, cells may exchange a quantization of the sum W, rather than the actual sum. According to one example, cells may exchange a quantization of a single bit, with that bit reflecting whether the size of the UL and DL buffers in the cell exceed a threshold. According to other examples, cells may exchange multiple-bit quantizations, with each value indicating a range including their UL and DL buffer size sum.

[0070] According to certain aspects, a new configuration of UL and DL subframes used in a cluster may be determined based on the ratios Rj and sums W, from each cell i in the cluster. According to one aspect, a new configuration may be determined based on the ratio of total downlink traffic buffer to total uplink traffic inside the cluster, as calculated by this formula: ∑ §R« UL_t ∑(!¾/(¾ + 1»

[0071] According to certain aspects, a new configuration of UL and DL subframes within a cluster may be determined by one eNB within the cluster. That eNB may send the determined configuration to all other eNBs in the cluster. This may be referred to a centralized method of determining UL and DL subframe configurations.

[0072] FIG. 10 illustrates an example of cells in a cluster operating according to the centralized method of determining UL and DL subframe configurations. In this example, each of picocells 1004, 1006, and 1008 send their quantized ratios and quantized sums to the central picocell 1002. The central picocell determines the UL and DL subframe configuration (TDD configuration) and sends the recommended configuration to the other picocells in the cluster.

[0073] According to other aspects, each eNB may receive the all of the ratios Rj and sums Wi from every cell in the cluster and determine a new configuration of UL and DL subframes for use within the cluster. This may be referred to as a distributed method of determining UL and DL subframe configurations.

[0074] FIG. 1 1 illustrates an example of cells in a cluster operating according to the distributed method of determining UL and DL subframe configurations. In this example, each of picocells 1 102, 1 104, 1 106, and 1 108 send their quantized ratios and quantized sums to all of the other picocells. Each picocell determines the UL and DL subframe configuration (TDD configuration) using its own ratio and sum and the ratios and sums supplied by the other picocells.

[0075] According to certain aspects, each eNB switches to the new UL and DL subframe configuration simultaneously. This switch should be simultaneous when using both the centralized and distributed methods of determining UL and DL subframe configurations.

[0076] According to certain aspects, a cluster of cells may use the determined UL and DL configuration for a configurable period of time before determining a new subframe configuration. According to these aspects, the period of time should be larger than the maximum backhaul latency between the cells of the cluster. [0077] FIG. 12 illustrates example operations 1200 of a method for wireless communications by a first base station (BS). The operations 1200 generally include obtaining, at 1202, one or more parameters, each generated as a function of uplink (UL) and downlink (DL) loading of one of the first base station or one or more other base stations. At 1204, the first station may determine a configuration of DL and UL subframes based on the obtained one or more parameters.

[0078] According to certain aspects, the first base station may generate the one or more parameters for the first base station.

[0079] According to certain aspects, the first base station may send the generated parameters to at least one other base station.

[0080] According to certain aspects, the one or more parameters may comprise a size of an uplink (UL) buffer and a size of a downlink (DL) buffer for one of the first base station or one or more other base stations.

[0081] According to certain aspects, the one or more parameters may comprise an indication of a ratio of a size of an uplink (UL) buffer and a size of a downlink (DL) buffer for one of the first base station or one or more other base stations.

[0082] According to certain aspects, the indication of the ratio may comprise a 3 bit quantization of the ratio.

[0083] According to certain aspects, the one or more parameters may comprise an indication of a sum of a size of an uplink (UL) buffer and a size of a downlink (DL) buffer for the one of the first base station or one or more other base stations.

[0084] According to certain aspects, the indication of the sum may comprise a single bit indicating whether the sum exceeds a threshold.

[0085] According to certain aspects, the indication of the sum may comprise two or more bits and may indicate that the sum is within a range of sizes.

[0086] According to certain aspects, the base station may switch to the determined configuration after a configured delay. [0087] According to certain aspects, the base station may determine the configured delay based on a measurement of backhaul latency to one or more other base stations.

[0088] According to certain aspects, the configured delay may be larger than the largest backhaul latency to the one or more other base stations.

[0089] According to certain aspects, the base station may send the determined configuration to at least one other base station.

[0090] According to certain aspects, a cell or cluster of cells may implement an UL dual open loop power control (PC) technique. The cells may mitigate interference by implementing the UL dual open loop PC technique. According to these aspects, UL subframes may be divided into two sets of subframes, and different UL open loop PC parameters may be used for each set of subframes. According to these aspects, the cells in the cluster may determine the UL PC parameters based on exchanged measured eNB - eNB interference (i.e., RSRP) measurements.

[0091] According to certain aspects, a cell or cluster of cells may use a DL PC technique to mitigate interference. According to these aspects, the cells in the cluster may determine the DL PC parameters based on exchanged measured eNB - eNB interference (i.e., RSRP) measurements.

[0092] FIG. 13 illustrates example operations 1300 of a method for wireless communications by a first base station (BS). The operations 1300 generally include obtaining, at 1302, one or more parameters, each generated as a function of interference measured at one of the first base station or one or more other base stations from one of the first base station or one or more other base stations. At 1304, the first base station may mitigate interference caused by the one or more other base stations based on the obtained one or more parameters.

[0093] According to certain aspects, the first base station may generate the one or more parameters for the first base station.

[0094] According to certain aspects, the first base station may send the generated parameters to at least one other base station. [0095] According to certain aspects, the one or more parameters may comprise a reference signal received power (RSRP) for reference signals received from the one of the first base station or one or more other base stations.

[0096] According to certain aspects, mitigating the interference may comprise joining a cluster with at least one of the one or more other base stations, wherein all base stations in the cluster use the same configuration of downlink (DL) and uplink (UL) subframes.

[0097] According to certain aspects, mitigating the interference may comprise leaving a cluster with at least one of the one or more other base stations, wherein all base stations in the cluster use the same configuration of downlink (DL) and uplink (UL) subframes.

[0098] According to certain aspects, mitigating the interference may comprise changing a transmission power level of one or more downlink (DL) transmissions.

[0099] According to certain aspects, mitigating the interference may comprise determining interference may occur in one or more sets of subframes and sending differing power control commands for one or more uplink (UL) transmissions based on which set of subframes the UL transmissions occur in.

[00100] The attached APPENDIX provides details for certain aspects of the present disclosure.

[00101] It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Further, some steps may be combined or omitted. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

[00102] As used herein, a phrase referring to "at least one of a list of items refers to any combination of those items, including single members. As an example, "at least one of: a, b, or c" is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c. [00103] 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." Unless specifically stated otherwise, the term "some" refers to one or more. 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:

Backhaul Signaling in elMTA Appendix

Background - elMTA

• Flexible DL/UL configuration is deemed as one efficient way to fully utilize TDD spectrum and is being addressed in 3GPP elMTA SI/WI.

- Example: Adaptive configuration selection:

Configuration 2

- DL/UL traffic loading:

Time

Background - DL-UL interference in elMTA

• DL-UL interference when adjacent cells having different directions

- eNB-eNB interference

- UE-U interference

PUE

Background - Cell cluster IM

• To avoid the negative impact of the DL to UL interference on the UL SINR, following cell clustering approach has been studied in 3GPP

RAN 1/4.

- eNBs that have coupling loss less than a threshold are forced to transmit in the same direction.

- For example, for outer-door pico only scenario, the pico cells are grouped as a cluster if coupling loss b/w two picos is less than a predefined threshold X; The TX direction of the pico cells within a cluster shall be same.

Backhaul Signaling in elMTA

• Background

- Efficient Interference Mitigation may be achieved with coordination among neighboring cells.

- Existing backhauling for TDD configurations and loading may not be sufficient for elMTA purposes.

Previous Arts: Legacy X2 message for the DL-UL Interference Mitigation

• Relative Narrowband Transmit Power - RNTP

— Relative narrowband transmit power indicator was introduced to support frequency domain ICIC schemes.

• Overload Indicator - 01

— Overload indicator was introduced to report strong

interference caused by high power UL transmissions in neighbor cells.

• High Interference Indicator - HII

— High Interference indicator was introduced to inform

neighboring cell about scheduling cell-edge UEs, so that these cells can react appropriately.

Backhaul Signaling elMTA

• The use cases or scenarios that need new signaling

information exchanged via backhaul in elMTA

- Cell clustering for IM

• Backhaul signaling for cell cluster

- Backhaul signaling for BS-BS interference measurement

- Traffic adaption for coorndnation in intra-cluster

• Backhaul signaling for traffic adaption

- Backhaul signaling for power control

- Backhaul signaling for CSI measurement reporting

Backhaul Signaling for Cell Cluster

• Propose new signaling of exchanging the eNB - eNB

measured interference

- The measured eNB - eNB interference (i.e. RSRP ) should be exchanged to the surrounding neighbor eNB by backhaul.

- By using this backhaul signaling, the cells cluster/de- cluster or mitigate the interference from aggressor eNB.

^• The cell loading information also could be exchanged for further improve the efficiency of clustering.

- i.e. low loading cell can fall back to default CFG.

Backhaul Signaling for eNB - eNB measurement

^• Propose new signaling to exchange

— Neighboring cells should coordinate SSF or UL-DL

configurations to facilitate eNBs take turn to measure each other.

Backhaul Signaling for Traffic Adaption (1/3)

• Problem

- For efficient traffic adaption operation in cell cluster,

backhual exchange of buffer status is necessary,

- Due to inevitable backhual latency and capacity

limitation, infomation exchanged over backhual needs to be compressed

^• Propose:

- Instead of exchange DL and UL buffer size, B_DL and B_UL directly, we consider exchange of

• DL-to-UL buffer size ratio R = ²*, together with

• DL-plus-UL buffer size W = B_DL + B_UL.

Backhaul Signaling for Traffic Adaption (2/3)

• Propose (cont.)

- H is closely related to dynamic UL-DL configuration

• May be used also for !IVI purposes (details to be discussed

later)

• A 3-bit quantization to existing 7 UL-DL configurations can be used (an example refer to the Appendix)

- W reflects priority/loading of a cell in voting for cluster

configuration

• Without W, TA is operated in Round Robin fashion

• 1-bit quantization of W essentially reflects whether a cell has noticeable amount of traffic to be served

• More bits of W reflects priority of a cell better

Backhaul Signaling for Traffic Adaption (3/3)

• Select the new recommended configuration

according to the R_t and W_t from each cell / inside the cluster.

- Defined as the ratio of total downlink traffic buffer to the total uplink traffic inside the cluster .

Coordination the eNB's Transmission in Intra-cluster

• By using new backhaul signaling, R and W for traffic

adaption, the recommended eNB's TDD

configuration can be elected with two methods.

- Centralized method

- Distributed method

Coordination the eNB's Transmission in Intra-cluster

• Optionl: centralized method

- A centralized eNB/unit is identified by the network.

- The quantized traffic ratio R and traffic loading W of each

eNBs in one cluster are all transmitted to the centralized

eNB/unit.

- The centralized eNB/unit decides the new TDD configuration

according to the received quantized information (see above equation).

- The centralized eNB broadcasts new recommended TDD

configuration to the other eNBs inside the cluster.

- All the eNBs should switch to the new recommended TDD

configuration simultaneously with a configurable duration

timer.

- Due to the latency caused by non-ideal backhauling, the

duration timer of new recommended TDD configuration

selection inside the cluster should be larger than two times of assumed MAX. backhaul latency.

Option 1 : Centralized Method

Centralized eNB/unit

identifies by the network

Each eNB transmits traffic

ratio H and loading IV to

the centralized eUB

Centralized eNB decides

the new recommended

TDD configuration

Centralized e B broadcasts the new

recommended TDD configuration to

all other eNBs in cluster.

Exchange traffic ratio and loading

Recommended TDD configuration

All e Bs switch to the new TDD

configuration simultaneously with a

configurable duration timer.

Coordination the eNB's Transmission in Intra-cluster

• Option2: distributed method

- All eNBs exchange the quantized traffic ratio R and traffic

loading 1/1/ to the surrounding eNBs inside one cluster.

- Each eNB decides the new TDD configuration based on

the received quantization information with the same

algorithm (see above equation).

- All the eNBs should switch to the new recommended

TDD configuration simultaneously with a configurable

duration timer.

- Due to the latency caused by non-ideal backhauling, the

duration of new recommended TDD configuration

selection inside the cluster should be larger than the

assumed MAX. backhaul latency.

Option2: Distributed Method

Exchange traffic ratio and loading

Backhaul Signaling for Power Control dual open loop power control

UL sub-frames are divided into two sub-frame sets, different UL open loop PC parameters can be used for different sub-frame set.

The sub-frame set partitioning can be based on TDD

configuration adopted in serving cell and neighbor cells, then selected TDD configuration per cell exchanged via backhaul singling is needed.

DL power control

- When DL PC is used to reduce eNB-eNB interference in elMTA, measured interference or DL TX power information needs to be exchanged b/w neighbor cells via backhaul signaling for cell cluster IM and other IM solutions.

Backhaul Signaling for CSI Measurement Reporting

• For proposed pattern-specific IMR solution, eNB

should exchange the new backhaul information including,

- IMR configuration / IMR pattern of each cells

• eNB needs to know the IMR pattern of surrounding eNBs.

Quantization of DL/UL Traffic Ratio

• 3-bit quantization of DL/UL traffic ratio

- Assumed for intra-cluster coordination of TA

• Note:

- Different quantization schemes may favor either DL or UL transmission

DL/UL traffic ratio quantization

R>9.0 111

Claims

1. A method for wireless communication by a first base station, comprising:

obtaining one or more parameters, each generated as a function of uplink (UL) and downlink (DL) loading of one of the first base station or one or more other base stations; and

determining a configuration of DL and UL sub frames based on the obtained one or more parameters.

2. The method of claim 1, further comprising:

generating the one or more parameters for the first base station.

3. The method of claim 2, further comprising:

sending the generated parameters to at least one other base station.

4. The method of claim 1, wherein the one or more parameters comprise a size of an uplink (UL) buffer and a size of a downlink (DL) buffer for the one of the first base station or one or more other base stations.

5. The method of claim 1, wherein the one or more parameters comprise an indication of a ratio of a size of an uplink (UL) buffer and a size of a downlink (DL) buffer for the one of the first base station or one or more other base stations.

6. The method of claim 5, wherein the indication comprises a 3 bit quantization of the ratio.

7. The method of claim 1, wherein the one or more parameters comprise an indication of a sum of a size of an uplink (UL) buffer and a size of a downlink (DL) buffer for the one of the first base station or one or more other base stations.

8. The method of claim 7, wherein the indication comprises a single bit indicating whether the sum exceeds a threshold.

9. The method of claim 7, wherein the indication comprises two or more bits and indicates that the sum is within a range of sizes.

10. The method of claim 1, further comprising:

switching to the determined configuration after a configured delay.

11. The method of claim 10, further comprising:

determining the configured delay based on a measurement of backhaul latency to the one or more other base stations.

12. The method of claim 10, wherein the configured delay is larger than the largest backhaul latency to the one or more other base stations.

13. The method of claim 1, further comprising:

sending the determined configuration to at least one of the one or more other base stations.

14. A method for wireless communication by a first base station, comprising:

obtaining one or more parameters, each generated as a function of interference measured at one of the first base station or one or more other base stations from one of the first base station or one or more other base stations; and

mitigating the interference based on the obtained one or more parameters.

15. The method of claim 14, further comprising:

generating the one or more parameters for the first base station.

16. The method of claim 15, further comprising:

sending the generated parameters to at least one other base station.

17. The method of claim 14, wherein the one or more parameters comprise a reference signal received power (RSRP) for reference signals received from the one of the first base station or one or more other base stations.

18. The method of claim 14, wherein mitigating the interference comprises joining a cluster with at least one of the one or more other base stations and wherein all base stations in the cluster use the same configuration of downlink (DL) and uplink (UL) subframes.

19. The method of claim 14, wherein mitigating the interference comprises leaving a cluster with at least one of the one or more other base stations and wherein all base stations in the cluster use the same configuration of downlink (DL) and uplink (UL) subframes.

20. The method of claim 14, wherein mitigating the interference comprises changing a transmission power level of one or more downlink (DL) transmissions.

21. The method of claim 14, wherein mitigating the interference comprises determining interference may occur in one or more sets of subframes and sending differing power control commands for one or more uplink (UL) transmissions based on which set of subframes the UL transmissions occur in.