Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
  • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
  • H04B7/2643—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using time-division multiple access [TDMA]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W72/00—Local resource management
  • H04W72/50—Allocation or scheduling criteria for wireless resources
  • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
  • H04W72/541—Allocation or scheduling criteria for wireless resources based on quality criteria using the level of interference
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
  • H04J11/0023—Interference mitigation or co-ordination
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L5/00—Arrangements affording multiple use of the transmission path
  • H04L5/14—Two-way operation using the same type of signal, i.e. duplex
  • H04L5/1469—Two-way operation using the same type of signal, i.e. duplex using time-sharing
  • H04L5/1484—Two-way operation using the same type of signal, i.e. duplex using time-sharing operating bytewise
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
  • H04W16/14—Spectrum sharing arrangements between different networks
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
  • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
  • H04B7/2643—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using time-division multiple access [TDMA]
  • H04B7/2656—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using time-division multiple access [TDMA] for structure of frame, burst
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J2211/00—Orthogonal indexing scheme relating to orthogonal multiplex systems
  • H04J2211/003—Orthogonal indexing scheme relating to orthogonal multiplex systems within particular systems or standards
  • H04J2211/005—Long term evolution [LTE]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W72/00—Local resource management
  • H04W72/12—Wireless traffic scheduling

Definitions

• LTE Long Term Evolution
• UMTS Universal Mobile Telecommunications System
• 3 GPP Third Generation Partnership Project
• DL downlink
• UL uplink
• MIMO multiple-input multiple-output
• the method includes scheduling user equipments (UEs) served by a first set of base stations in accordance with a first time division duplex (TDD) configuration.
• the first set of base stations is located between a second set of base stations in a first region that operates in a second TDD configuration and a third set of base stations in a second region that operate in a third TDD configuration.
• the first TDD configuration has no downlink subframe colliding with an uplink subframe of the second TDD configuration.
• the method also includes restricting UEs served by the first set of base stations to avoid user equipment to user equipment interference with UEs and base stations operating with the third TDD configuration.
• the computer program product includes a non-transitory computer- readable medium having non-transitory program code recorded thereon.
• the program code includes program code to schedule user equipments (UEs) served by a first set of base stations in accordance with a first time division duplex (TDD) configuration.
• the first set of base stations is located between a second set of base stations in a first region that operates in a second TDD configuration and a third set of base stations in a second region that operate in a third TDD configuration.
• the first TDD configuration has no downlink subframe colliding with an uplink subframe of the second TDD configuration.
• the program code also includes program code to restrict UEs served by the first set of base stations to avoid user equipment to user equipment interference with UEs and base stations operating with the third TDD configuration.
• the apparatus includes a memory and a processor(s) coupled to the memory.
• the processor is configured to schedule user equipments (UEs) served by a first set of base stations in accordance with a first time division duplex (TDD) configuration.
• the first set of base stations is located between a second set of base stations in a first region that operates in a second TDD configuration and a third set of base stations in a second region that operate in a third TDD configuration.
• the first TDD configuration has no downlink sub frame colliding with an uplink subframe of the second TDD configuration.
• the processor is also configured to restrict UEs served by the first set of base stations to avoid user equipment to user equipment interference with UEs and base stations operating with the third TDD configuration.
• the method includes determining when downlink time division duplex (TDD) communications of a first user equipment (UE) experience interference from uplink TDD communications of a second UE when communication frames of the first UE and second UE are aligned.
• TDD downlink time division duplex
• the method also includes scheduling communications to reduce the interference.
• the apparatus includes means for determining when downlink time division duplex (TDD) communications of a first user equipment (UE) experience interference from uplink TDD communications of a second UE when communication frames of the first UE and second UE are aligned.
• TDD downlink time division duplex
• the apparatus also includes means for scheduling
• the processor(s) is configured to determine when downlink time division duplex (TDD) communications of a first user equipment (UE) experience interference from uplink TDD communications of a second UE when communication frames of the first UE and second UE are aligned.
• the processor(s) is also configured to schedule communications to reduce the interference.
• FIGURE 1 is a diagram illustrating an example of a network architecture
• FIGURE 2 is a diagram illustrating an example of an access network
• FIGURE 3 is a diagram illustrating an example of a downlink frame structure in LTE.
• FIGURE 4 is a diagram illustrating an example of an uplink frame structure in LTE.
• FIGURE 5 is a diagram illustrating an example of a radio protocol architecture for the user and control plane.
• FIGURE 7 is a block diagram conceptually illustrating an example of a telecommunications system.
• FIGURE 8 is a block diagram conceptually illustrating an example of a telecommunications system.
• FIGURE 9 is a block diagram conceptually illustrating an example of a telecommunications system.
• FIGURE 10 is a block diagram illustrating a method for supporting different LTE-TDD configurations in neighboring regions or adjacent carriers according to one aspect of the present disclosure.
• FIGURE 1 1 is a block diagram illustrating a method for supporting different LTE-TDD configurations in neighboring regions or adjacent carriers according to one aspect of the present disclosure.
• FIGURE 12 is a block diagram illustrating the data flow between different modules/means/components in an exemplary apparatus.
• processors include microprocessors,
• DSPs digital signal processors
• FPGAs field programmable gate arrays
• PLDs programmable logic devices
• state machines gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure.
• 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.
• 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.
• 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 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.
• FIGURE 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 IP Services 122.
• the EPS can interconnect with other access networks, but for simplicity, those entities/interfaces are not 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 (eNodeB) 106 and other eNodeBs 108.
• the eNodeB 106 provides user and control plane protocol terminations toward the UE 102.
• the eNodeB 106 may be connected to the other eNodeBs 108 via a backhaul (e.g., an X2 interface).
• the eNodeB 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.
• BSS basic service set
• ESS extended service set
• the eNodeB 106 provides an access point to the EPC 110 for a UE 102.
• 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, 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.
• the eNodeB 106 is connected to the EPC 1 10 via, e.g., an SI interface.
• the EPC 1 10 includes a Mobility Management Entity (MME) 1 12, other MMEs 114, a Serving Gateway 1 16, and a Packet Data Network (PDN) Gateway 1 18.
• MME 112 is the control node that processes the signaling between the UE 102 and the EPC 1 10.
• the MME 1 12 provides bearer and connection management. All user IP packets are transferred through the Serving Gateway 1 16, 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 1 18 is connected to the Operator's IP Services 122.
• the Operator's IP Services 122 may include the Internet, the Intranet, an IP Multimedia Subsystem (IMS), and a PS Streaming Service (PSS).
• IMS IP Multimedia Subsystem
• PSS PS Streaming Service
• FIGURE 2 is a diagram illustrating an example of an access network 200 in an LTE network architecture.
• the access network 200 is divided into a number of cellular regions (cells) 202.
• One or more lower power class eNodeBs 208 may have cellular regions 210 that overlap with one or more of the cells 202.
• the lower power class eNodeB 208 may be a remote radio head (RRH), a femto cell (e.g., home eNodeB (HeNodeB)), pico cell, or micro cell.
• the macro eNodeBs 204 are each assigned to a respective cell 202 and are configured to provide an access point to the EPC 1 10 for all the UEs 206 in the cells 202.
• the eNodeBs 204 are responsible for all radio related functions including radio bearer control, admission control, mobility control, scheduling, security, and connectivity to the serving gateway 1 16.
• the modulation and multiple access scheme employed by the access network 200 may vary depending on the particular telecommunications standard being deployed.
• OFDM is used on the downlink and SC-FDMA is used on the uplink to support both frequency division duplexing (FDD) and time division duplexing (TDD).
• FDD frequency division duplexing
• TDD time division duplexing
• EV-DO Evolution-Data Optimized
• UMB Ultra Mobile Broadband
• 3GPP2 3rd Generation Partnership Project 2
• UTRA Universal Terrestrial Radio Access
• W-CDMA Wideband-CDMA
• GSM Global System for Mobile Communications
• E-UTRA Evolved UTRA
• UMB Ultra Mobile Broadband
• Wi-Fi IEEE 802.11
• WiMAX IEEE 802.16
• Flash-OFDM employing OFDMA.
• 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.
• the eNodeBs 204 may have multiple antennas supporting MIMO technology.
• MIMO technology enables the eNodeBs 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 steams 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 (i.e., applying a scaling of an amplitude and a phase) and then transmitting each spatially precoded stream through multiple transmit antennas on the downlink.
• 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.
• each UE 206 transmits a spatially precoded data stream, which enables the eNodeB 204 to identify the source of each spatially precoded data stream.
• 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.
• 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.
• a guard interval e.g., cyclic prefix
• the uplink may use SC-FDMA in the form of a DFT-spread OFDM signal to compensate for high peak-to-average power ratio (PAPR).
• PAPR peak-to-average power ratio
• FIGURE 3 is a diagram 300 illustrating an example of a downlink frame structure in LTE.
• a frame (10 ms) may be divided into 10 equally sized sub-frames. 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.
• 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.
• 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 downlink shared channel (PDSCH) is mapped.
• PDSCH physical downlink shared channel
• 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.
• FIGURE 4 is a diagram 400 illustrating an example of an uplink frame structure in LTE.
• the available resource blocks for the uplink 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 uplink 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 410a, 410b in the control section to transmit control information to an eNodeB.
• the UE may also be assigned resource blocks 420a, 420b in the data section to transmit data to the eNodeB.
• the UE may transmit control information in a physical uplink 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 uplink shared channel (PUSCH) on the assigned resource blocks in the data section.
• An uplink 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 uplink synchronization in a physical random access channel (PRACH) 430.
• the PRACH 430 carries a random sequence and cannot carry any uplink 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 only a single PRACH attempt per frame (10 ms).
• FIGURE 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 eNodeB 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 eNodeB over the physical layer 506.
• 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 eNodeB on the network side.
• MAC media access control
• RLC radio link control
• PDCP packet data convergence protocol
• 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 1 18 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.).
• IP layer e.g., IP layer
• the PDCP sublayer 514 provides multiplexing between different radio bearers and logical channels.
• the PDCP sublayer 514 also provides header
• 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.
• the radio protocol architecture for the UE and eNodeB 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).
• RRC sublayer 516 is responsible for obtaining radio resources (i.e., radio bearers) and for configuring the lower layers using RRC signaling between the eNodeB and the UE.
• 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)).
• FEC forward error correction
• BPSK binary phase-shift keying
• QPSK quadrature phase-shift keying
• M-PSK M-phase-shift keying
• M-QAM M-quadrature amplitude modulation
• 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.
• 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).
• FFT Fast Fourier Transform
• 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 eNodeB 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 eNodeB 610 on the physical channel.
• the data and control signals are then provided to the
• controller/processor 659
• the controller/processor 659 implements the L2 layer.
• 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.
• 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.
• ACK acknowledgement
• NACK negative acknowledgement
• 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.
• 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 eNodeB 610.
• controller/processor 659 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the eNodeB 610.
• Channel estimates derived by a channel estimator 658 from a reference signal or feedback transmitted by the eNodeB 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.
• the uplink transmission is processed at the eNodeB 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.
• the controller/processor 675 implements the L2 layer.
• 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.
• 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.
• controller/processor 675 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.
• LTE-TDD long term evolution, -time division duplexed
• LTE-TDD the same communication spectrum is used for both uplink transmission from the UEs to the eNodeB and for downlink transmission from an eNodeB to the UEs.
• the uplink and downlink transmissions are orthogonalized in time, however, to coordinate when UEs receive and when they transmit.
• Table 1 The different TDD configurations supported in LTE are shown in Table 1 below.
• D indicates a subframe for downlink (DL) (i.e., eNodeB to UE communications)
• U indicates a subframe for uplink (UL) (i.e., UE to eNodeB communications)
• S indicates a special subframe.
• a special subframe may include downlink Orthogonal Frequency Division Multiplexed (OFDM) symbols, a guard period, and uplink OFDM symbols.
• OFDM Orthogonal Frequency Division Multiplexed
• neighboring eNodeB base stations are typically synchronized with the same subframe boundaries.
• a neighboring base station may operate in the same TDD configuration as its neighbors.
• two neighboring base stations may both operate using TDD configuration 0 with a downlink subframe, a special subframe, and three uplink subframe, repeating every 5 ms. So when one base station is in downlink, its neighbor may be in downlink as well.
• a UE being served by one base station may experience interference in a downlink subframe from a neighboring base station, particularly if the UE is located near the service boundaries between the two base stations.
• FIGURE 7 An example is shown in FIGURE 7.
• the UE 702 is served by the eNodeB 704 at the edge of the service area 707.
• Downlink transmission 712 is the desired signal to be received by the UE 702.
• the UE 702 also receives downlink (DL) transmission 714 from the non-serving eNodeB 708, as the UE 702 is close to the edge of the service area 710 of the non-serving eNodeB 708.
• the downlink transmissions 714 from the eNodeB 708 may interfere with the UE receiving the desired downlink transmission 712. Because a UE is typically connected to the strongest available cell, interfering downlink transmission 714 is likely to be weaker, or in the same range of strength, than the desired downlink transmission 712.
• LTE-TDD is primarily designed for the case when neighboring cells use the same configuration
• neighboring base stations may operate using different TDD configurations. This may lead to uplink communications for one base station occurring at the same time as downlink communications for another base station.
• a UE may experience downlink interference from a UE engaging in uplink communications with a neighboring eNodeB operating in a different TDD configuration. An example of this scenario is shown in FIGURE 8.
• the eNode B-A 808 is engaged in uplink communications 818 during its uplink subframe with the UE-A 820 at the same time the eNodeB-B 804 is engaged in downlink communications 812 during its downlink subframe with the UE- B 802. That is, the UE-A 820 is in an uplink subframe at the same time as the UE-B 802 is in a downlink subframe.
• the uplink transmissions 814 of the UE-A 820 may interfere with the downlink reception of the UE-B 802. Even though the UE-A 820 may be transmitting at a much lower power than the eNodeB 804, if the UE-A 820 is close enough to the UE-B 802, the uplink interference 814 from the UE-A 820 may be a stronger received signal from the perspective of the UE-B 802 than the intended downlink communication 812 from the eNodeB 804. This situation may lead to pronounced interference to the UE-B 802.
• UEs may not be designed to handle such interference.
• UEs may be designed assuming similar interference levels on all downlink subframes. Even one subframe seeing such interference may lead to poor performance on several subframes and possibly result in link failure and a dropped call.
• Two examples of situations that may lead to radio link failure are illustrated.
• a UE may be filtering its channel estimates obtained from a common reference signal (CRS) over multiple subframes without weighing according to the interference level.
• the channel estimation may be corrupted by the UE to UE interference (such as that illustrated in FIGURE 8) on one subframe leading to poor performance on one or more following subframes.
• automatic gain control AGC may be controlled based on received signal power. Having one subframe with a large received power may cause the AGC to assume a large average received power resulting in poor quantization on downlink subframes not observing UE to UE interference and possible radio link failure.
• Similar interference issues may also occur if two adjacent carriers use different TDD configurations, resulting in subframes that are downlink for one carrier and uplink for another. For example, if one carrier communicates in bandwidth spectrum 2305 to 2325 MHz while another carrier communicates in bandwidth spectrum 2327.5 to 2357.5 MHz, the guard band between them is only 2.5 MHz.
• the interference issues in this case may cause two problems. First, UE transmission leakage from its own carrier spectrum to a neighboring carrier's spectrum may cause higher interference in the neighboring UEs bandwidth. The interference caused would decrease as frequency spacing increases. Data allocated on the edge closer to the interfering carrier would see more of this interference than data allocated on the center resource blocks. Second, for a UE of the first carrier, the transmit power in its bandwidth may cause AGC saturation at a neighboring UE operating on the second carrier (similar to the AGC issues described above with regard to the example of FIGURE 8).
• An aggressor UE (the UE causing the UE to UE interference) is said to be connected to an aggressor eNodeB.
• a victim UE (the UE experiencing the UE to UE interference) is said to be connected to a victim eNodeB.
• the victim eNodeB and aggressor eNodeB may communicate over a backhaul or similar communication channel to share TDD configurations as well as information regarding potential UE to UE interference experienced by each of the eNodeBs' UEs.
• One potential solution to the interference scenarios described above is to schedule the aggressor UE (by the aggressor eNodeB) for uplink communications (i.e., transmissions) only during uplink subframes of the victim eNodeB.
• Another potential solution may be to avoid edge resource blocks (i.e., communication resources on the border of the communication spectrum that may lead to interference) for downlink subframes of the victim eNodeB used by aggressor UEs for uplink communications.
• edge resource blocks i.e., communication resources on the border of the communication spectrum that may lead to interference
• all UEs served by the aggressor eNodeB may be scheduled so that they only engage in uplink communications during uplink subframes of the victim eNodeB. This may be easier to implement in the case of UE to UE interference when the neighboring eNodeBs operate with different TDD
• the above solution may be easier to implement in the case where the victim and aggressor eNodeB are operated by the same operator. If the victim and aggressor eNodeBs are operated by different commercial operators, it may be difficult to place restrictions on an eNodeB of one commercial operator to improve communication performance of a competing commercial operator.
• eNodeBs at the edge of a commercial operator's geographic region may be configured so that the victim operator's eNodeBs use a configuration that has no downlink subframes overlapping with uplink subframes of the other operator. This configuration will avoid any UE to UE interference issues for the victim eNodeB UEs.
• Victim operator's eNodeBs that are farther away from the region edge may use any desired TDD configuration.
• FIGURE 9 shows eNodeBs of neighboring commercial operators (operator A and operator B). The eNodeB 902 is with operator A while eNodeBs 904, 906, and 908 are with operator B.
• the eNodeB 904 may operate using configuration C, which avoids UE to UE interference with configuration A used by the eNodeB 902.
• operator B may avoid interference issues with operator A along the edge between the operator regions.
• any interference issues between potential victim or aggressor UEs may be contained entirely within the network of operator B, allowing for implementation of other solutions.
• operator B may choose to configure eNodeBs 906 and 908 to operate using configuration B to avoid UE to UE interference between the eNodeB 904 and eNodeBs 906 and 908, all within operator B's control. And even if potential issues arise between configuration B and configuration C, they may be resolved within the same operator (for example, by rescheduling an interfering UE as described above).
• Downlink subframes of TDD configuration 0 do not collide with uplink subframes of any other TDD configurations, as subframe 0 and subframe 5 (the only downlink subframes of TDD configuration 0) are downlink subframes for all TDD configurations.
• edge eNodeBs of one operator are radio frame aligned with edge eNodeBs of another operator, an operator may choose to operate its edge eNodeBs in TDD configuration 0.
• potential UE to UE interference is avoided on downlink subframes for UEs being served by those edge eNodeBs, regardless of the TDD configuration used by the other operator.
• Operating in TDD configuration 0 in this manner may avoid a victim operator having to change its TDD configuration if the aggressor operator changes its TDD configuration.
• Other approaches/TDD configurations may also be used.
• the UE 912 which is close to the UE 914, may experience interference from the UE 914 during subframes 3 and 4 when the UE 914 is engaged in uplink communications and the UE 912 is attempting to engage in downlink communications.
• the eNodeB 904 may instruct the UE 912 to switch to TDD configuration 0, thereby avoiding interference to the UE 912 from the UE 914 in subframes 3 and 4.
• TDD configurations are typically communicated to a UE within system information block (SIB) 1, which is common to all UEs.
• SIB system information block
• additional signaling of the TDD configuration may be introduced.
• the eNodeB may employ mechanisms to identify which UEs are observing the illustrated UE to UE interference.
• Multiplexing UEs with different TDD configurations may present other challenges for an eNodeB such as coordinating HARQ timelines, acknowledgement/negative acknowledgment (ACK/NACK) or channel quality index (CQI) transmissions.
• ACK/NACK acknowledgement/negative acknowledgment
• CQI channel quality index
• Such signals may be transmitted on orthogonal pilot sequences by different UEs, but rearranging these signals may be performed when serving UEs operating in different TDD configurations. Sample techniques for controlling adjusted communications for the above solutions are discussed below.
• the physical uplink control channel contains CQI and ACK signals.
• UEs operating in different TDD configurations may attempt to use the same PUCCH resource.
• CQI periodicity may be configured by an eNodeB so that UEs do not try to communicate CQI using the same resources.
• a PUCCH resource used by a UE to send ACK signals depends on when the UE received the downlink information (e.g., PDCCH/PDSCH) and on the UE TDD configuration. PDCCH locations and PDSCH assignments for different UEs may be planned to avoid PUCCH collisions during uplink communications.
• Uplink control resources may also be increased so that different resources are allocated for UEs using different TDD configurations.
• PUCCH offsets (which are UE specific parameters) may be used to assign the resources to UEs to avoid collision.
• Sounding reference signals SRS are transmitted on the uplink for uplink channel measurement.
• An eNodeB can configure SRS periodicity and subframe offset to avoid collisions between UEs.
• Physical HARQ Indicator Channel (PHICH) is a downlink channel where UEs receive acknowledgments for transmitted uplink data.
• PHICH collisions (where different UEs are looking for acknowledgments in the same location/resource) may be avoided by using a larger number of PHICH groups.
• UE specific parameters may orthogonalize the PHICH so that UEs are not looking for acknowledgements in similar resources.
• Detecting victim UEs also presents challenges.
• One solution identifies when a UE is repeatedly having difficulty communicating on the same subframes. This may be information about which downlink subframes of a victim eNodeB correspond to uplink subframes of a neighboring eNodeB.
• the eNodeB may focus on such conflicting subframes or the eNodeB may compare those conflicting subframes with other non- conflicting subframes proving difficult for a victim UE to decode. Based on the results of the eNodeB inquiry, the eNodeB may determine whether to implement one of the solutions discussed above.
• a further technique may be applied when a UE is experiencing interference from a neighboring bandwidth. Based on sub-band CQI reports (i.e., CQI reports corresponding to different regions in the communication frequency), the victim UE may indicate a decreasing interference as the UE moves away from the bandwidth of the interfering UE. If this behavior is identified, then the victim UE may be identified as experiencing UE to UE interference.
• sub-band CQI reports i.e., CQI reports corresponding to different regions in the communication frequency
• Detecting an aggressor UEs namely UEs causing or likely to cause UE to UE interference also presents challenges.
• a UE is on the edge of a cell and can detect a strong signal from a non-serving base station (for example with a high RSRP) that is using a different
• Uplink subframes transmit uplink data, ACK/NACK messages (acknowledging receipt of downlink data), channel quality index (CQI) reports, and sounding reference signals (SRSs).
• a base station may limit UE uplink activity by only sending a UE uplink grants for desired subframes. If a UE uplink transmission attempt fails (as indicated by an ACK/NACK message from a base station to a UE), a UE may attempt uplink retransmission at an uplink subframe not scheduled by the base station.
• a base station may send an acknowledgment message to the UE, even if the original transmission of a data packet was not decoded successfully. The base station may then schedule a new grant to the UE requesting the unsuccessfully decoded data packet be retransmitted.
• CQI and SRS periodicity and subframe offsets may be configured by a base station such that those messages are only sent on desired uplink subframes.
• Uplink ACK/NACK messages are sent on specific uplink subframes corresponding to specific downlink subframes.
• a base station may schedule downlink messages to the UE on downlink subframes with an ACK/NACK configuration matching desired uplink subframes.
• scheduling of uplink resources of potential aggressor UEs may be prioritized to avoid edge resource blocks of subframes that would cause the interference.
• UEs can be identified as potential aggressors based on resource allocations and transmission power.
• UEs transmitting at a high power and/or UEs allocated a large number of resource blocks could be identified as potential aggressors.
• uplink communications of an identified interfering UE are scheduled to avoid edge resource blocks of subframes that would cause the interference.
• the aggressor UEs are allocated fewer resources.
• aggressor UEs control the interference on their own, or report to a base station that they are aggressors.
• FIGURE 10 illustrates a method 1000.
• a device schedules user equipments (UEs) served by a first set of base stations in accordance with a first time division duplex (TDD) configuration.
• the first set of base stations is located between a second set of base stations in a first region that operates in a second TDD configuration and a third set of base stations in a second region that operate in a third TDD configuration.
• the first set of base stations being between the second set and third set does not necessarily mean the base stations are collinear. Further, each set may include one or more base stations.
• FIGURE 1 1 illustrates a method 1 100.
• a device determines when downlink time division duplex (TDD) communications of a first user equipment (UE) experience interference from uplink TDD communications of a second UE when communication frames of the first UE and second UE are aligned.
• a device schedules communications to reduce the interference.
• the eNodeB 610 is configured for wireless communication including means for determining, means for restricting, and means for scheduling.
• the means may be the transmit processor 616, receive processor 670, antenna 620, controller processor 675 and/or memory 646 configured to perform the functions recited by the means.
• the aforementioned means may be any module or any apparatus configured to perform the functions recited by the aforementioned means.
• FIGURE 12 is a diagram illustrating an example of a hardware
• the processing system 1214 may be implemented with a bus architecture, represented generally by the bus 1224.
• the bus 1224 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 1214 and the overall design constraints.
• the bus 1224 links together various circuits including one or more processors and/or hardware modules, represented by the processor 1222 the modules 1202, 1204, and the computer-readable medium 1226.
• the bus 1224 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 includes a determining module 1202, a scheduling module 1204, and a restricting module 1206.
• the determining module 1202 can determine when downlink TDD communications of a first UE experience interference from uplink TDD communications of a second UE when communication frames of the first UE and second UE are aligned.
• the scheduling module 1204 can schedule communications to reduce interference.
• the scheduling module 1204 can also schedule UEs served by a first set of base stations in accordance with a first TDD configuration.
• the first set of base stations is located between a second set of base stations in a first region that operates in a second TDD configuration and a third set of base stations in a second region that operate in a third TDD configuration.
• the first TDD configuration has no downlink subframe colliding with an uplink subframe of the second TDD configuration.
• the restricting module 1206 can restrict UEs served by a first set of base stations to avoid user equipment to user equipment interference with UEs and base stations operating with a third TDD configuration.
• modulators/demodulators 654a-r the antenna 652a-r, and/or the controller/processor 659.
• DSP digital signal processor
• ASIC application specific integrated circuit
• FPGA field programmable gate array
• a general- purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine.
• a processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more
• a software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.
• An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium.
• the storage medium may be integral to the processor.
• the processor and the storage medium may reside in an ASIC.
• the ASIC may reside in a user terminal.
• the processor and the storage medium may reside as discrete components in a user terminal.
• 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 transmitted over as one or more instructions or code on a computer-readable medium.
• Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another.
• a storage media may be any available media that can be accessed by a general purpose or special purpose computer.
• 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 means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium.
• Disk and disc 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.

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• 2012
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