Patent Description:
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.

These multiple access technologies are 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 is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP).

LTE technology 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. As the demand for mobile broadband access continues to increase, however, there exists a need for further improvements in LTE technology. Research and development continue to advance LTE technology not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.

<CIT> discloses certain aspects to provide various mechanisms that allow a user equipment to convey information regarding one or more attributes to a base station during a random access (RA) procedure. The attributes may include, for example a capability of the UE (e.g., to support a particular feature or version of a standard) or a condition of the UE (e.g., if it is currently experiencing an interference condition).

The invention is carried out in accordance with the independent claims.

This has outlined, rather broadly, the features and technical advantages of the present disclosure in order that the detailed description that follows may be better understood. Additional features and advantages of the disclosure will be described below. It should be appreciated by those skilled in the art that this disclosure may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. The novel features, which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages, will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.

Aspects of the telecommunication systems are presented with reference to various apparatus and methods. These apparatus and methods are 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").

Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, firmware, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

Accordingly, in one or more exemplary embodiments, the functions described may be implemented in hardware, software, or combinations thereof. 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.

<FIG> is a diagram illustrating an LTE network architecture <NUM>, which may be an LTE/LTE-Advanced (LTE/-A) network, in which base station-to- base station interference mitigation may be performed, according to one aspect of the present disclosure. LTE and LTE-Advanced are collectively referred to as "LTE". The LTE network architecture <NUM> may be referred to as an Evolved Packet System (EPS) <NUM>. The LTE network architecture <NUM> may include one or more user equipment (UE) <NUM>, an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) <NUM>, an Evolved Packet Core (EPC) <NUM>, a Home Subscriber Server (HSS) <NUM>, and an Operator's IP Services <NUM>. The EPS can interconnect with other access networks, but for simplicity those entities/interfaces are not shown. As shown, the EPS provides packet-switched services, however, as those skilled in the art will readily appreciate, the various concepts presented throughout this disclosure may be extended to networks providing circuit-switched services.

The E-UTRAN includes the evolved Node B (eNodeB) <NUM> and other eNodeBs <NUM>. The eNodeB <NUM> provides user and control plane protocol terminations toward the UE <NUM>. The eNodeB <NUM> may be connected to the other eNodeBs <NUM> via a backhaul (e.g., an X2 interface). The eNodeB <NUM> 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 eNodeB <NUM> provides an access point to the EPC <NUM> for a UE <NUM>. Examples of a UE <NUM> include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a netbook, a smartbook, an ultrabook, 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 <NUM> 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 <NUM> is connected to the EPC <NUM> via, e.g., an S1 interface. The EPC <NUM> includes a Mobility Management Entity (MME) <NUM>, other MMEs <NUM>, a Serving Gateway <NUM>, and a Packet Data Network (PDN) Gateway <NUM>. The MME <NUM> is the control node that processes the signaling between the UE <NUM> and the EPC <NUM>. All user IP packets are transferred through the Serving Gateway <NUM>, which itself is connected to the PDN Gateway <NUM>. The PDN Gateway <NUM> is connected to the Operator's IP Services <NUM>. The Operator's IP Services <NUM> may include the Internet, the Intranet, an IP Multimedia Subsystem (IMS), and a packet switched streaming service (PSS).

<FIG> is a diagram illustrating an example of an access network <NUM> in an LTE network architecture. In this example, the access network <NUM> is divided into a number of cellular regions (cells) <NUM>. One or more lower power class eNodeBs <NUM> may have cellular regions <NUM> that overlap with one or more of the cells <NUM>. The lower power class eNodeB <NUM> may be a remote radio head (RRH), a femto cell (e.g., home eNodeB (HeNodeB)), pico cell, or micro cell. The macro eNodeBs <NUM> are each assigned to a respective cell <NUM> and are configured to provide an access point to the EPC <NUM> for all the UEs <NUM> in the cells <NUM>. There is no centralized controller in this example of an access network <NUM>, but a centralized controller may be used in alternative configurations. The eNodeBs <NUM> are responsible for all radio related functions including radio bearer control, admission control, mobility control, scheduling, security, and connectivity to the serving gateway <NUM>.

The modulation and multiple access scheme employed by the access network <NUM> may vary depending on the particular telecommunications standard being deployed. In LTE applications, OFDM is used on the downlink and SC-FDMA is used on the uplink to support both frequency division duplex (FDD) and time division duplex (TDD). As those skilled in the art will readily appreciate from the detailed description to follow, the various concepts presented herein are well suited for LTE applications. However, these concepts may be readily extended to other telecommunication standards employing other modulation and multiple access techniques. By way of example, these concepts may be extended to Evolution-Data Optimized (EV-DO) or Ultra Mobile Broadband (UMB). EV-DO and UMB are air interface standards promulgated by the 3rd Generation Partnership Project <NUM> (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 <NUM> (Wi-Fi), IEEE <NUM> (WiMAX), IEEE <NUM>, and Flash-OFDM employing OFDMA. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from the 3GPP organization. CDMA2000 and UMB are described in documents from the 3GPP2 organization. The actual wireless communication standard and the multiple access technology employed will depend on the specific application and the overall design constraints imposed on the system.

The eNodeBs <NUM> may have multiple antennas supporting MIMO technology. The use of MIMO technology enables the eNodeBs <NUM> 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 <NUM> to increase the data rate or to multiple UEs <NUM> 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) <NUM> with different spatial signatures, which enables each of the UE(s) <NUM> to recover the one or more data streams destined for that UE <NUM>. On the uplink, each UE <NUM> transmits a spatially precoded data stream, which enables the eNodeB <NUM> to identify the source of each spatially precoded data stream.

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

In the detailed description that follows, various aspects of an access network will be described with reference to a MIMO system supporting OFDM on the downlink. 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 uplink may use SC-FDMA in the form of a DFT-spread OFDM signal to compensate for high peak-to-average power ratio (PAPR).

<FIG> is a diagram <NUM> illustrating an example of a downlink frame structure in LTE. A frame (<NUM>) may be divided into <NUM> equally sized subframes. 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 (RB). The resource grid is divided into multiple resource elements. In LTE, a resource block contains <NUM> consecutive subcarriers in the frequency domain and, for a normal cyclic prefix in each OFDM symbol, <NUM> consecutive OFDM symbols in the time domain, or <NUM> resource elements. For an extended cyclic prefix, a resource block contains <NUM> consecutive OFDM symbols in the time domain and has <NUM> resource elements. Some of the resource elements, as indicated as R <NUM>, <NUM>, include downlink reference signals (DL-RS). The DL-RS include Cell-specific RS (CRS) (also sometimes called common RS) <NUM> and UE-specific RS (UE-RS) <NUM>. UE-RS <NUM> is transmitted only on the resource blocks upon which the corresponding physical downlink shared channel (PDSCH) is mapped. The number of bits carried by each resource element depends on the modulation scheme. Thus, the more resource blocks that a UE receives and the higher the modulation scheme, the higher the data rate for the UE.

<FIG> is a diagram <NUM> 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) <NUM>. The PRACH <NUM> 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 (<NUM>) or in a sequence of few contiguous subframes and a UE can make only a single PRACH attempt per frame (<NUM>).

<FIG> is a diagram <NUM> 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 <NUM>, Layer <NUM>, and Layer <NUM>. Layer <NUM> (L1 layer) is the lowest layer and implements various physical layer signal processing functions. The L1 layer will be referred to herein as the physical layer <NUM>. Layer <NUM> (L2 layer) <NUM> is above the physical layer <NUM> and is responsible for the link between the UE and eNodeB over the physical layer <NUM>.

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

The PDCP sublayer <NUM> provides multiplexing between different radio bearers and logical channels. The PDCP sublayer <NUM> 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 eNodeBs. The RLC sublayer <NUM> 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 <NUM> provides multiplexing between logical and transport channels. The MAC sublayer <NUM> is also responsible for allocating the various radio resources (e.g., resource blocks) in one cell among the UEs. The MAC sublayer <NUM> is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE and eNodeB is substantially the same for the physical layer <NUM> and the L2 layer <NUM> 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 <NUM> in Layer <NUM> (L3 layer). The RRC sublayer <NUM> 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.

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

The TX processor <NUM> implements various signal processing functions for the L1 layer (i.e., physical layer). The signal processing functions includes coding and interleaving to facilitate forward error correction (FEC) at the UE <NUM> 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. Each spatial stream is then provided to a different antenna <NUM> via a separate transmitter <NUM> TX. Each transmitter <NUM> TX modulates an RF carrier with a respective spatial stream for transmission.

At the UE <NUM>, each receiver <NUM> RX receives a signal through its respective antenna <NUM>. Each receiver <NUM> RX recovers information modulated onto an RF carrier and provides the information to the receiver (RX) processor <NUM>. The RX processor <NUM> implements various signal processing functions of the L1 layer. The RX processor <NUM> performs spatial processing on the information to recover any spatial streams destined for the UE <NUM>. 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 <NUM>. The soft decisions are then decoded and de-interleaved to recover the data and control signals that were originally transmitted by the eNodeB <NUM> on the physical channel. The data and control signals are then provided to the controller/processor <NUM>.

The controller/processor <NUM> implements the L2 layer. The controller/processor can be associated with a memory <NUM> that stores program codes and data. In the uplink, the controller/processor <NUM> provides de-multiplexing 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 <NUM>, which represents all the protocol layers above the L2 layer. Various control signals may also be provided to the data sink <NUM> for L3 processing. The controller/processor <NUM> is also responsible for error detection using an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support HARQ operations.

In the uplink, a data source <NUM> is used to provide upper layer packets to the controller/processor <NUM>. The data source <NUM> represents all protocol layers above the L2 layer. Similar to the functionality described in connection with the downlink transmission by the eNodeB <NUM>, the controller/processor <NUM> 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 <NUM>. The controller/processor <NUM> is also responsible for HARQ operations, retransmission of lost packets, and signaling to the eNodeB <NUM>.

Channel estimates derived by a channel estimator <NUM> from a reference signal or feedback transmitted by the eNodeB <NUM> may be used by the TX processor <NUM> to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor <NUM> are provided to different antenna <NUM> via separate transmitters <NUM> TX. Each transmitter <NUM> TX modulates an RF carrier with a respective spatial stream for transmission.

The uplink transmission is processed at the eNodeB <NUM> in a manner similar to that described in connection with the receiver function at the UE <NUM>. Each receiver <NUM> RX receives a signal through its respective antenna <NUM>. Each receiver <NUM> RX recovers information modulated onto an RF carrier and provides the information to a RX processor <NUM>. The RX processor <NUM> may implement the L1 layer.

The controller/processor <NUM> implements the L2 layer. In the uplink, the controller/processor <NUM> provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the UE <NUM>. Upper layer packets from the controller/processor <NUM> may be provided to the core network.

The controller/processor <NUM> and the controller/processor <NUM> may direct the operation at the eNodeB <NUM> and the UE <NUM>, respectively. The controller/processor <NUM> and/or other processors and modules at the eNodeB <NUM> may perform or direct the execution of various processes for the techniques described herein. The controller/processor <NUM> and/or other processors and modules at the UE <NUM> may also perform or direct the execution of the functional blocks illustrated in use in the method flow chart of <FIG> and/or other processes for the techniques described involving base station-to-base station interference mitigation. The memories <NUM> and <NUM> may store data and program codes for the eNodeB <NUM> and the UE <NUM>, respectively.

When communications of a single radio access technology or different radio access technologies in neighboring communication spectrums are operating at the same time, potential interference between devices may occur. For example, if one communication device is attempting to receive communications at the same time as when another device is transmitting, and both devices are using the same or proximate portions of a communication spectrum, the receiving device may experience interference. Another example of interference/collision is when UEs get assigned the same resources (e.g., time/frequency/code).

<FIG> illustrates a physical random access channel (PRACH) process <NUM> according to an aspect of the present disclosure that may lead to interference. At time <NUM>, a random access preamble signature is randomly chosen by the UE (User Equipment) <NUM>. The UE transmits the random access preamble on time/frequency resources that are pre-designated as PRACH resources by the eNodeB (evolved Node B) <NUM>. At time <NUM>, a random access response is sent by the eNodeB <NUM> on a PDSCH (Physical Downlink Shared Channel), and addressed with an ID (RA-RNTI (Random Access Radio Network Temporary Identifier)). The random access response identifies the timefrequency slot in which the preamble is detected. Unfortunately, if multiple UEs <NUM> collide (i.e., interfere) by selecting the same signature in the same time/frequency resource, each UE <NUM> receives the RAR (Random Access Response).

As further illustrated in <FIG>, at time <NUM>, the UE <NUM> transmits the first scheduled uplink transmission on a PUSCH (Physical Uplink Shared Channel) in response to the RAR (Random Access Response). The subframe on which the UE <NUM> sends the first scheduled uplink transmission is determined according to the subframe on which the RAR is received by the UE <NUM>. At time <NUM>, if multiple UEs <NUM> collide and the eNodeB <NUM> cannot decode their scheduled transmissions, then the UEs <NUM> restart the PRACH process after reaching the maximum number of HARQ (Hybrid Automatic Repeat reQuest) transmissions. If one of the colliding scheduled transmissions is decoded while the other is not, then the eNodeB <NUM> transmits a contention resolution message addressed to a C-RNTI (Cell Radio Network Temporary Identifier) indicated in the scheduled transmission (or to a temporary C-RNTI). HARQ feedback is transmitted only by the UE <NUM> that detects its own UE identity (or C-RNTI). The other UEs <NUM> remain silent and exit the random access procedure.

In long term evolution (LTE)-time division duplex (LTE-TDD), the same communication spectrum is used for both uplink transmissions from the UEs <NUM> to the eNodeB <NUM> and for downlink transmissions from an eNodeB <NUM> to the UEs <NUM>. The uplink and downlink transmissions are orthogonalized in time; however, to coordinate when the UEs <NUM> receive and when they transmit. The different TDD configurations supported in LTE are shown in Table <NUM> below.

In LTE-TDD, there are seven possible TDD configurations that identify whether a particular subframe is uplink (UL), downlink (DL) or a special (S) subframe for each uplink (UL) downlink (DL) configuration, as shown in Table <NUM>. In RAN1/RAN4 (Radio Access Network Layer <NUM>/Radio Access Network Layer <NUM>), there is an active Release <NUM> study item on "Further Enhancements to LTE TDD for DL-UL Interference Management and Traffic Adaptation" (eIMTA). The TDD eIMTA proposal specifies an adaptive change to the LTE-TDD configuration based on current traffic conditions. The time scale for reconfiguration could be as small as <NUM> milliseconds (ms). It should be noted that while any non-legacy UEs <NUM> and the eNodeB <NUM> may adaptively change their LTE-TDD configuration in accordance with the proposal, any legacy UEs <NUM> remain in the original LTE-TDD configuration. In some cases, this results in a legacy UE <NUM> transmitting on a subframe that is actually a downlink subframe for the eNodeB <NUM>, which may lead to interference.

<FIG> is a block diagram <NUM> illustrating base station-to-base station interference according to an aspect of the present disclosure. The following example demonstrates a potential interference issue when two adjacent cells deploy different LTE-TDD configurations. For example, a first cell (<NUM>) deploys a first configuration, and an adjacent, second cell (<NUM>) deploys a second configuration. In this example, an uplink subframe <NUM> of the first cell <NUM> does not match a downlink subframe <NUM> of the second cell <NUM>. As a result, the possibility of base station-to-base station interference arises when an uplink subframe <NUM> of the first cell <NUM> collides with the downlink subframe <NUM> of the second cell <NUM>.

<FIG> is a block diagram <NUM> illustrating base station-to-base station interference according to an aspect of the present disclosure. In this particular example, the eNodeB operating according to configuration <NUM> sees eNodeB to eNodeB interference due to the collision between the uplink subframe <NUM> and the downlink subframe <NUM>, as shown in <FIG>. As shown in <FIG>, the mismatched uplink and downlink subframes between UEs <NUM>-<NUM> and <NUM>-<NUM> cause eNodeB to eNodeB interference between eNodeB <NUM>-<NUM> and eNodeB <NUM>-<NUM>.

One aspect of the present disclosure provides base station-to-base station interference mitigation techniques. In this aspect of the disclosure, it is determined when uplink communications of a first user equipment (UE) experience interference from downlink communications of a base station. In one configuration, uplink communications of the first UE are scheduled based on the interference. For example, uplink control information may only be scheduled on subframes that do not experience interference from downlink communications of the base station. This can occur when the UE or the eNodeB is aware that it is seeing interference. The control information may include, but is not limited to, a rank indicator (RI), a channel quality indicator (CQI), a sounding reference signal (SRS), a scheduling request (SR), a physical random access channel (PRACH) message, or other link control information. The subframes with reduced likelihood of being received as uplink communications can include subframes that switch from uplink to downlink without the UE first being aware of the switch, for example when the eNodeB switches TDD configurations.

One aspect of the disclosure resolves base station-to-base station interference where certain uplink subframes see persistent interference from neighboring base stations (e.g., that renders those subframes unusable). In this example, improvements are provided for addressing downlink subframes for which it is known a priori that the corresponding ACK/NACK (Acknowledgement/Negative Acknowledgement) from the UE will be lost. In one aspect, a reduced size retransmission is employed to increase the likelihood of receiving the acknowledgement information. In another aspect, a later termination is targeted for downlink subframes for which it is known a priori that the corresponding ACK/NACK from the UE will be lost.

In another aspect, a random access channel (RACH) process is reconfigured to account for lost uplink subframes due to eNodeB to eNodeB interference. As noted, a random access preamble transmitted on uplink subframes that see eNodeB to eNodeB interference will be lost. The LTE specification, however, provides several physical random access channel (PRACH) configurations. In this example, a PRACH configuration is selected such that all PRACH resources are on uplink subframes that do not see any interference. This selected PRACH configuration should reduce or even minimize any delay in the RACH process, as shown in <FIG>.

In another example, scheduling restrictions are placed on the random access response to ensure that the scheduled transmission from the UE is sent on an uplink subframe that does not see eNodeB to eNodeB interference. For example, if the random access response is received on the nth subframe, the UE uses the first uplink subframe at time n+k (k>=<NUM>) when the uplink delay field is set to zero (<NUM>). Otherwise, the random access response is postponed until the next available uplink subframe when uplink delay field is set to one (<NUM>). Hence by selecting the subframe on which the random access response is transmitted and by controlling the uplink delay field, the eNodeB can control which uplink subframe gets used by the UE for the scheduled transmission.

In some cases, an uplink delay field that is set to zero may lead to the use of an uplink subframe with eNodeB to eNodeB interference, while an uplink delay field being set to one may lead to usage of the uplink subframe without eNodeB to eNodeB interference. Similarly, for a given choice of the uplink delay field, the uplink subframe that is used may or may not see eNodeB to eNodeB interference depending on the downlink subframe on which the random access response is sent. In another example, a restriction is imposed on scheduling the contention resolution, such that the ACK response from the UE is on an uplink subframe that sees no interference.

A very similar RACH issue also occurs in the case of TDD eIMTA, where UEs should be prevented from transmitting PRACH messages on uplink subframes under their LTE-TDD configuration, but could potentially be downlink subframes under the LTE-TDD configurations to which the eNodeB might switch. Legacy UEs are unaware of the set of LTE-TDD configurations that the eNodeB might switch among. In this example, it is assumed that new (e.g., non-legacy) UEs are aware of this set of LTE-TDD configurations among which the eNodeB switches. For example, the set of LTE-TDD configurations may be communicated to the new UEs through separate signaling.

For legacy UEs, one aspect of the present disclosure specifies that the eNodeB selects a PRACH configuration such that all PRACH resources are on subframes that are uplink for the entire set of configurations among which the eNodeB switches. It is noted that this configuration may be more stringent than the corresponding configuration for mitigating eNodeB to eNodeB interference discussed previously. In this configuration, all PRACH resources are restricted to a particular set of uplink subframes, whereas in the eNodeB to eNodeB interference case, it is only ensured that at least one PRACH resource belongs to a particular set of uplink subframes that do not see eNodeB to eNodeB interference.

For non-legacy UEs, another aspect of the present disclosure specifies new PRACH configurations such that all PRACH resources are on subframes that are uplink for the entire set (or a subset) of configurations that the eNodeB switches between. One among these new configurations is signaled to the UE (allows potential allocation of more PRACH resources than when restricted to existing PRACH configurations). For non-legacy UEs, another aspect specifies a modification to UE operation such that among the PRACH resources available under a particular PRACH configuration, the UE only uses those that fall on subframes that are uplink for all TDD configurations (or a subset of all TDD configurations) among which the eNodeB switches or are uplink subframes in the configuration being used by the eNodeB at that time.

One aspect of the disclosure ensures that the scheduled transmission (in response to the random access response) and the ACK for contention resolution are also sent on uplink subframes. For legacy UEs, one aspect specifies scheduling the random access response and contention resolution message on downlink subframes, such that the corresponding scheduled transmission and ACK for contention resolution are transmitted on subframes that are uplink for the entire set of TDD configurations (or a subset of TDD configurations) that the eNodeB might switch among. For new UEs, one configuration specifies new timelines for the scheduled transmission and ACK corresponding to contention resolution, such that they are transmitted on subframes that are uplink for all LTE-TDD configurations (or a subset of all TDD configurations) among which the eNodeB switches.

<FIG> illustrates a method <NUM> for mitigating base station-to-base station interference according to an aspect of the present disclosure. At block <NUM>, a set of subframes with a reduced likelihood of being received as uplink transmissions of a first user equipment (UE) are determined. For example, two adjacent cells deploying different time division duplex (TDD) configurations may have common subframes with an uplink (UL) and downlink (DL) mismatch resulting from the specified TDD configuration, for example, as shown in Table <NUM>. Alternatively, the uplink transmissions of the first UE may experience interference from downlink transmissions of a base station. In block <NUM>, uplink transmissions of the first UE are scheduled by scheduling uplink control information (UCI) on subframes other than the determined set of subframes. The uplink communications of the first UE may be scheduled based on the interference. For example, uplink control information may only be scheduled on subframes that do not experience interference from downlink communications of the base station. The uplink control information may include, but is not limited to, a rank indicator (RI), a channel quality indicator (CQI), a sounding reference signal (SRS), a scheduling request (SR), a physical random access channel (PRACH) message, or other link control information.

In another aspect, a physical random access channel (PRACH) configuration is selected such that at least some PRACH resources are on uplink subframes that do not see interference from the base station. In this aspect, a random access response and a contention resolution message of a PRACH process are scheduled on downlink subframes such that the corresponding scheduled transmission and acknowledgement (ACK) of the contention resolution are transmitted on uplink subframes that do not see interference from the base station.

UEs with different TDD configurations can coexist in a cell, and should be multiplexed carefully to avoid interfering with each other. eNodeB implementations are generally designed to address uplink channel collisions between UEs using the same configuration. One aspect of the present disclosure overcomes collisions across UEs using different TDD configurations. For example, uplink ACK collisions may occur when the ACK/NACKs corresponding to a physical downlink shared channel (PDSCH) on different downlink subframes are sent on the same uplink subframe and potentially the same resource. In one aspect, this scenario is avoided by orthogonalizing resources (e.g., using TDM (Time Division Multiplexing) and/or FDM (Frequency Division Multiplexing)) used by legacy and new UEs for a physical uplink control channel (PUCCH) using UE specific parameters. For example, uplink ACKs for the new and legacy UEs could be sent on a different set of resource blocks by using different PUCCH offsets. An alternative aspect defines a new mapping for the PUCCH for the new UEs. For example, an ACK can be based on a subframe and location within the PDCCH. In one example, the ACK is based on the subframe number (n) + <NUM>. In another example, which resource block (RB) to use is based on the location within the subframe.

Another aspect of the present disclosure overcomes downlink ACK collisions. For example, a downlink ACK collision may occur when ACK/NACKs corresponding to different uplink subframes are sent on the same downlink subframe and potentially the same resource. In one aspect, a DM-RS (Demodulation Reference Signal) sequence assignment as well as a resource block assignment are carefully planned at the eNodeB scheduler to prevent ACK collisions. That is, scheduling avoids collisions. This aspect does not involve a change to the LTE specification. An alternate aspect specifies a new mapping for PHICH (physical HARQ indicator channel) for new UEs. In one example, the new mapping is similar to the parameter IPHICH in the current version of the standard, where IPHICH can take a greater numbers of values than allowed in the current LTE specification. For example, more PHICH resources can be configured for use in the system and an existing IPHICH mechanism can address additional PHICH resources. Alternatively, IPHICH can take a non-zero value for TDD configurations other than configuration <NUM>, can take a non-zero value on subframes other than subframes <NUM> and <NUM> in TDD configuration <NUM>, and can take a value greater than or equal to <NUM> corresponding to subframes <NUM> and <NUM> in TDD configuration <NUM>. For example, IPHICH can be <NUM> for configurations other than <NUM>, <NUM> corresponding to subframes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> in configuration <NUM>, and <NUM> corresponding to subframes <NUM> and <NUM> in configuration <NUM>.

Yet another aspect of the present disclosure overcomes uplink data collisions. For example, a first transmission scheduled by an uplink grant (PDCCH (Physical Downlink Control Channel)) or retransmissions triggered by NACK (PHICH (Physical HARQ Indicator Channel)) of a UE using a first configuration could collide with a first transmission/retransmission of a UE using a different configuration. In one aspect, uplink grants are specified to avoid a PUSCH first transmission of a UE using a first configuration with a first PUSCH transmission of a UE using a second configuration. For example, when grants sent on a same downlink subframe cause a PUSCH collision on a particular uplink subframe, then the same constraints as in LTE Release <NUM> operations may apply. Where grants sent on different downlink subframes for the different UEs cause a PUSCH collision on a particular uplink subframe, one aspect specifies scheduling decisions for all UEs before the first downlink subframe containing the uplink grant.

Another aspect of the present disclosure avoids PUSCH retransmission of one UE from colliding with a PUSCH retransmission of second UE (using a different TDD configuration) by specifying an ACK and SUSPEND command for at least one UE. That is, an ACK is sent so that data is not retransmitted. Later, an uplink grant is issued to cause the data to be resent. For example, the eNodeB may prioritize not suspending the UEs whose ACK is sent first. A decision as to when a collision will occur is possible if decoding status for both UEs is available before the decision to send ACK/NACK for either UE. If it is determined that a collision will occur, the eNodeB may suspend one of the UEs. In one aspect, the UE whose transmission is suspended is based on a traffic condition (e.g., QoS (Quality of Service) level) of the two UEs. Another aspect may prioritize legacy UEs over new UEs depending on whether an advertised configuration is a true configuration or a configuration with more uplink subframes than the true configuration.

Another aspect avoids a first PUSCH transmission of a first UE from colliding with a PUSCH retransmission of second UE (e.g., using a different LTE-TDD configuration). For example, the PUSCH collision can be avoided by an acknowledgement and retransmission suspension of the second UE. Alternatively, the eNodeB may avoid scheduling the uplink grant for the first UE. Alternatively, the eNodeB may determine which UE to stop by using criteria similar to those described above. For example, the eNodeB may determine which UE to stop based on whether the downlink subframe containing the ACK is before or after the subframe containing the grant, whether the UE is a new or a legacy UE, QoS of the stream, or other like suspension criteria.

<FIG> illustrates a method <NUM> for multiplexing UEs with different time division duplex (TDD) configurations according to aspects of the present disclosure. At block <NUM> it is determined when a downlink acknowledgement (ACK) resource to a first UE, operating based on a first TDD configuration, could collide with a downlink ACK resource to a second UE. The second UE operates based on a second TDD configuration. In this aspect, the second TDD configuration is different from the first TDD configuration. At block <NUM>, uplink data resources are scheduled to avoid interference. Alternatively, a new mapping for ACK/NACK resources of at least one UE is defined to avoid the interference.

<FIG> is a diagram illustrating an example of a hardware implementation for an apparatus <NUM> employing an base station-to-base station interference mitigation system <NUM> according to one aspect of the present disclosure. The base station-to-base station interference mitigation system <NUM> may be implemented with a bus architecture, represented generally by a bus <NUM>. The bus <NUM> may include any number of interconnecting buses and bridges depending on the specific application of the base station-to-base station interference mitigation system <NUM> and the overall design constraints. The bus <NUM> links together various circuits including one or more processors and/or hardware modules, represented by a processor <NUM>, a determining module <NUM>, an adaptive scheduling module <NUM>, and a computer-readable medium <NUM>. The bus <NUM> 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 apparatus includes the base station-to-base station interference mitigation system <NUM> coupled to a transceiver <NUM>. The transceiver <NUM> is coupled to one or more antennas <NUM>. The transceiver <NUM> provides a means for communicating with various other apparatus over a transmission medium. The base station-to-base station interference mitigation system <NUM> includes the processor <NUM> coupled to the computer-readable medium <NUM>. The processor <NUM> is responsible for general processing, including the execution of software stored on the computer-readable medium <NUM>. The software, when executed by the processor <NUM>, causes the base station-to-base station interference mitigation system <NUM> to perform the various functions described supra for any particular apparatus. The computer-readable medium <NUM> may also be used for storing data that is manipulated by the processor <NUM> when executing software.

The base station-to-base station interference mitigation system <NUM> further includes the determining module <NUM>, e.g., for determining when uplink communications of a first user equipment (UE) experience interference from downlink communications of a base station. The base station-to-base station interference mitigation system <NUM> further includes the adaptive scheduling module <NUM>, e.g., for scheduling uplink communications of the first UE based on the interference. The determining module <NUM> and the adaptive scheduling module <NUM> may be software modules running in the processor <NUM>, resident/stored in the computer-readable medium <NUM>, one or more hardware modules coupled to the processor <NUM>, or combinations thereof. The base station-to-base station interference mitigation system <NUM> may be a component of the eNodeB <NUM> and/or the UE <NUM>.

In one aspect, the apparatus <NUM> for wireless communication includes means for determining and means for scheduling. The means may be the determining module <NUM>, the adaptive scheduling module <NUM> and/or the base station-to-base station interference mitigation system <NUM> of the apparatus <NUM> configured to perform the functions recited by the determining means and the scheduling means. In one aspect of the present disclosure, the determining means may be the controller/processor <NUM> and/or memory <NUM> configured to perform the functions recited by the determining means. In this aspect of the disclosure, the scheduling means may be the controller/processor <NUM> and/or memory <NUM> configured to perform the functions recited by the scheduling means. In another aspect of the present disclosure, the determining means may be the controller/processor <NUM> and/or memory <NUM> configured to perform the functions recited by the determining means. In this aspect of the disclosure, the scheduling means may be the controller/processor <NUM> and/or memory <NUM> configured to perform the functions recited by the scheduling means. In yet another aspect, the aforementioned means may be any module or any apparatus configured to perform the functions recited by the aforementioned means.

The examples above describe aspects implemented in LTE systems. The scope of the disclosure, however, is not so limited. Various aspects may be adapted for use with other communication systems, such as those that employ any of a variety of communication protocols including, but not limited to, CDMA systems, TDMA systems, FDMA systems, and OFDMA systems.

A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, PCM (phase change memory) memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

In one or more exemplary designs, the functions described may be implemented in hardware, software, or combinations thereof. A storage media may be any available media that can be accessed by a general purpose or special purpose 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.

Claim 1:
A method of wireless communication in a long term evolution-time division duplex, LTE-TDD system, wherein a base station switches among different TDD configurations, wherein uplink and downlink transmissions are orthogonalized in time, comprising:
modifying a behavior of non-legacy UEs arranged for adaptively changing their TDD configurations, while legacy UEs remain in an original TDD configuration to only use physical random access channel, PRACH resources that fall on subframes that are uplink for all TDD configurations among which the base station switches.