Enhanced antenna management by a base station

Enhanced antenna management for nodes is described in which transmit antennas assigned to at least one first carrier are designated for usage in a second carrier. The nodes transmit various signals and reference signals using a set of antenna ports on the second carrier based on the combined physical antennas associated with the first inactive carriers and physical antennas associated with the second carrier.

BACKGROUND

Field

Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to enhanced antenna management by a base station.

Background

SUMMARY

In one aspect of the disclosure, a method of wireless communication includes designating, by a node, one or more transmit antennas of the node assigned to at least one first carrier for usage in a second carrier and transmitting at least one of a control channel, a data channel, or a reference signal with a set of antenna ports on the second carrier, wherein the set of antenna ports are based, at least in part, on a combination of the one or more transmit antennas assigned to the at least one first carrier and one or more transmit antennas of the node assigned to the second carrier.

In an additional aspect of the disclosure, a method of wireless communication includes receiving, at a mobile device, a reference signal on a carrier of a cell and a configuration of a first set of antenna ports and a second set of antenna ports, receiving an indication of one of the first set of antenna ports or the second set of antenna ports for the reference signal for a subframe, and processing the reference signal according to the configuration based on the indicated set of antenna ports for the reference signal in the subframe.

In an additional aspect of the disclosure, an apparatus configured for wireless communication includes means for designating, by a node, one or more transmit antennas of the node assigned to at least one first carrier for usage in a second carrier and means for transmitting at least one of a control channel, a data channel, or a reference signal with a set of antenna ports on the second carrier, wherein the set of antenna ports are based, at least in part, on a combination of the one or more transmit antennas assigned to the at least one first carrier and one or more transmit antennas of the node assigned to the second carrier.

In an additional aspect of the disclosure, an apparatus configured for wireless communication that includes means for receiving, at a mobile device, a reference signal on a carrier of a cell and a configuration of a first set of antenna ports and a second set of antenna ports, means for receiving an indication of one of the first set of antenna ports or the second set of antenna ports for the reference signal for a subframe, and means for processing the reference signal according to the configuration based on the indicated set of antenna ports for the reference signal in the subframe.

In an additional aspect of the disclosure, a computer program product has a computer-readable medium having program code recorded thereon. This program code includes code for causing a computer to designate, by a node, one or more transmit antennas of the node assigned to at least one first carrier for usage in a second carrier and code for causing the computer to transmit at least one of a control channel, a data channel, or a reference signal with a set of antenna ports on the second carrier, wherein the set of antenna ports are based, at least in part, on a combination of the one or more transmit antennas assigned to the at least one first carrier and one or more transmit antennas of the node assigned to the second carrier.

In an additional aspect of the disclosure, a computer program product has a computer-readable medium having program code recorded thereon. This program code includes code for causing a computer to receive, at a mobile device, a reference signal on a carrier of a cell and a configuration of a first set of antenna ports and a second set of antenna ports, code for causing the computer to receive an indication of one of the first set of antenna ports or the second set of antenna ports for the reference signal for a subframe, and code for causing the computer to process the reference signal according to the configuration based on the indicated set of antenna ports for the reference signal in the subframe.

In an additional aspect of the disclosure, an apparatus includes at least one processor and a memory coupled to the processor. The processor is configured to designate, by a node, one or more transmit antennas of the node assigned to at least one first carrier for usage in a second carrier and to transmit at least one of a control channel, a data channel, or a reference signal with a set of antenna ports on the second carrier, wherein the set of antenna ports are based, at least in part, on a combination of the one or more transmit antennas assigned to the at least one first carrier and one or more transmit antennas of the node assigned to the second carrier.

In an additional aspect of the disclosure, an apparatus includes at least one processor and a memory coupled to the processor. The processor is configured to receive, at a mobile device, a reference signal on a carrier of a cell and a configuration of a first set of antenna ports and a second set of antenna ports, to receive an indication of one of the first set of antenna ports or the second set of antenna ports for the reference signal for a subframe, and to process the reference signal according to the configuration based on the indicated set of antenna ports for the reference signal in the subframe.

DETAILED DESCRIPTION

The techniques described herein may be used for various wireless communication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other networks. The terms “network” and “system” are often used interchangeably. A CDMA network may implement a radio technology, such as Universal Terrestrial Radio Access (UTRA), Telecommunications Industry Association's (TIA's) CDMA2000®, and the like. The UTRA technology includes Wideband CDMA (WCDMA) and other variants of CDMA. The CDMA2000® technology includes the IS-2000, IS-95 and IS-856 standards from the Electronics Industry Alliance (EIA) and TIA. A TDMA network may implement a radio technology, such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology, such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, and the like. The UTRA and E-UTRA technologies are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are newer releases of the UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization called the “3rd Generation Partnership Project” (3GPP). CDMA2000® and UMB are described in documents from an organization called the “3rd Generation Partnership Project 2” (3GPP2). The techniques described herein may be used for the wireless networks and radio access technologies mentioned above, as well as other wireless networks and radio access technologies. For clarity, certain aspects of the techniques are described below for LTE or LTE-A (together referred to in the alternative as “LTE/-A”) and use such LTE/-A terminology in much of the description below.

FIG. 1shows a wireless network100for communication, which may be an LTE-A network. The wireless network100includes a number of evolved node Bs (eNBs)110and other network entities. An eNB may be a station that communicates with the UEs and may also be referred to as a base station, a node B, an access point, and the like. Each eNB110may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to this particular geographic coverage area of an eNB and/or an eNB subsystem serving the coverage area, depending on the context in which the term is used.

An eNB may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A pico cell would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A femto cell would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs for users in the home, and the like). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a pico cell may be referred to as a pico eNB. And, an eNB for a femto cell may be referred to as a femto eNB or a home eNB. In the example shown inFIG. 1, the eNBs110a,110band110care macro eNBs for the macro cells102a,102band102c, respectively. The eNB110xis a pico eNB for a pico cell102x. And, the eNBs110yand110zare femto eNBs for the femto cells102yand102z, respectively. An eNB may support one or multiple (e.g., two, three, four, and the like) cells.

The wireless network100also includes relay stations. A relay station is a station that receives a transmission of data and/or other information from an upstream station (e.g., an eNB, a UE, or the like) and sends a transmission of the data and/or other information to a downstream station (e.g., another UE, another eNB, or the like). A relay station may also be a UE that relays transmissions for other UEs. In the example shown inFIG. 1, a relay station110rmay communicate with the eNB110aand a UE120r, in which the relay station110racts as a relay between the two network elements (the eNB110aand the UE120r) in order to facilitate communication between them. A relay station may also be referred to as a relay eNB, a relay, and the like.

The wireless network100may support synchronous or asynchronous operation. For synchronous operation, the eNBs may have similar frame timing, and transmissions from different eNBs may be approximately aligned in time. For asynchronous operation, the eNBs may have different frame timing, and transmissions from different eNBs may not be aligned in time.

The UEs120are dispersed throughout the wireless network100, and each UE may be stationary or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, and the like. InFIG. 1, a solid line with double arrows indicates desired transmissions between a UE and a serving eNB, which is an eNB designated to serve the UE on the downlink and/or uplink. A dashed line with double arrows indicates interfering transmissions between a UE and an eNB.

LTE/-A utilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, or the like. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, K may be equal to 72, 180, 300, 600, 900, and 1200 for a corresponding system bandwidth of 1.4, 3, 5, 10, 15, or 20 megahertz (MHz), respectively. The system bandwidth may also be partitioned into sub-bands. For example, a sub-band may cover 1.08 MHz, and there may be 1, 2, 4, 8 or 16 sub-bands for a corresponding system bandwidth of 1.4, 3, 5, 10, 15, or 20 MHz, respectively.

FIG. 2shows a downlink frame structure used in LTE/-A. The transmission timeline for the downlink may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 milliseconds (ms)) and may be partitioned into 10 subframes with indices of 0 through 9. Each subframe may include two slots. Each radio frame may thus include 20 slots with indices of 0 through 19. Each slot may include L symbol periods, e.g., 7 symbol periods for a normal cyclic prefix (as shown inFIG. 2) or 6 symbol periods for an extended cyclic prefix. The 2L symbol periods in each subframe may be assigned indices of 0 through 2-L−1. The available time frequency resources may be partitioned into resource blocks. Each resource block may cover N subcarriers (e.g., 12 subcarriers) in one slot.

In LTE/-A, an eNB may send a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) for each cell in the eNB. The primary and secondary synchronization signals may be sent in symbol periods6and5, respectively, in each of subframes0and5of each radio frame with the normal cyclic prefix, as shown inFIG. 2. The synchronization signals may be used by UEs for cell detection and acquisition. The eNB may send a Physical Broadcast Channel (PBCH) in symbol periods0to3in slot1of subframe0. The PBCH may carry certain system information.

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

In addition to sending PHICH and PDCCH in the control section of each subframe, i.e., the first symbol period of each subframe, the LTE-A may also transmit these control-oriented channels in the data portions of each subframe as well. As shown inFIG. 2, these new control designs utilizing the data region, e.g., the Relay-Physical Downlink Control Channel (R-PDCCH) and Relay-Physical HARQ Indicator Channel (R-PHICH) are included in the later symbol periods of each subframe. The R-PDCCH is a new type of control channel utilizing the data region originally developed in the context of half-duplex relay operation. Different from legacy PDCCH and PHICH, which occupy the first several control symbols in one subframe, R-PDCCH and R-PHICH are mapped to resource elements (REs) originally designated as the data region. The new control channel may be in the form of Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), or a combination of FDM and TDM.

A number of resource elements may be available in each symbol period. Each resource element may cover one subcarrier in one symbol period and may be used to send one modulation symbol, which may be a real or complex value. Resource elements not used for a reference signal in each symbol period may be arranged into resource element groups (REGs). Each REG may include four resource elements in one symbol period. The PCFICH may occupy four REGs, which may be spaced approximately equally across frequency, in symbol period0. The PHICH may occupy three REGs, which may be spread across frequency, in one or more configurable symbol periods. For example, the three REGs for the PHICH may all belong in symbol period0or may be spread in symbol periods0,1and2. The PDCCH may occupy 9, 18, 32 or 64 REGs, which may be selected from the available REGs, in the first M symbol periods. Only certain combinations of REGs may be allowed for the PDCCH.

A UE may be within the coverage of multiple eNBs. One of these eNBs may be selected to serve the UE. The serving eNB may be selected based on various criteria such as received power, path loss, signal-to-noise ratio (SNR), etc.

A UE may be assigned resource blocks in the control section to transmit control information to an eNB. The UE may also be assigned resource blocks in the data section to transmit data to the eNode B. The UE may transmit control information in a Physical Uplink Control Channel (PUCCH) on the assigned resource blocks310aand310bin 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 blocks320aand320bin the data section. An uplink transmission may span both slots of a subframe and may hop across frequency as shown inFIG. 3.

Referring back toFIG. 1, the wireless network100uses the diverse set of eNBs110(i.e., macro eNBs, pico eNBs, femto eNBs, and relays) to improve the spectral efficiency of the system per unit area. Because the wireless network100uses such different eNBs for its spectral coverage, it may also be referred to as a heterogeneous network. The macro eNBs110a-care usually carefully planned and placed by the provider of the wireless network100. The macro eNBs110a-cgenerally transmit at high power levels (e.g., 5 W-40 W). The pico eNB110xand the relay station110r, which generally transmit at substantially lower power levels (e.g., 100 mW-2 W), may be deployed in a relatively unplanned manner to eliminate coverage holes in the coverage area provided by the macro eNBs110a-cand improve capacity in the hot spots. The femto eNBs110y-z, which are typically deployed independently from the wireless network100may, nonetheless, be incorporated into the coverage area of the wireless network100either as a potential access point to the wireless network100, if authorized by their administrator(s), or at least as an active and aware eNB that may communicate with the other eNBs110of the wireless network100to perform resource coordination and coordination of interference management. The femto eNBs110y-ztypically also transmit at substantially lower power levels (e.g., 100 mW-2 W) than the macro eNBs110a-c.

In operation of a heterogeneous network, such as the wireless network100, each UE is usually served by the eNB110with the better signal quality, while the unwanted signals received from the other eNBs110are treated as interference. While such operational principals can lead to significantly sub-optimal performance, gains in network performance are realized in the wireless network100by using intelligent resource coordination among the eNBs110, better server selection strategies, and more advanced techniques for efficient interference management.

A pico eNB, such as the pico eNB110x, is characterized by a substantially lower transmit power when compared with a macro eNB, such as the macro eNBs110a-c. A pico eNB will also usually be placed around a network, such as the wireless network100, in an ad hoc manner. Because of this unplanned deployment, wireless networks with pico eNB placements, such as the wireless network100, can be expected to have large areas with low signal to interference conditions, which can make for a more challenging RF environment for control channel transmissions to UEs on the edge of a coverage area or cell (a “cell-edge” UE). Moreover, the potentially large disparity (e.g., approximately 20 dB) between the transmit power levels of the macro eNBs110a-cand the pico eNB110ximplies that, in a mixed deployment, the downlink coverage area of the pico eNB110xwill be much smaller than that of the macro eNBs110a-c.

In the uplink case, however, the signal strength of the uplink signal is governed by the UE, and, thus, will be similar when received by any type of the eNBs110. With the uplink coverage areas for the eNBs110being roughly the same or similar, uplink handoff boundaries will be determined based on channel gains. This can lead to a mismatch between downlink handover boundaries and uplink handover boundaries. Without additional network accommodations, the mismatch would make the server selection or the association of UE to eNB more difficult in the wireless network100than in a macro eNB-only homogeneous network, where the downlink and uplink handover boundaries are more closely matched.

If server selection is based predominantly on downlink received signal strength, the usefulness of mixed eNB deployment of heterogeneous networks, such as the wireless network100, will be greatly diminished. This is because the larger coverage area of the higher powered macro eNBs, such as the macro eNBs110a-c, limits the benefits of splitting the cell coverage with the pico eNBs, such as the pico eNB110x, because, the higher downlink received signal strength of the macro eNBs110a-cwill attract all of the available UEs, while the pico eNB110xmay not be serving any UE because of its much weaker downlink transmission power. Moreover, the macro eNBs110a-cwill likely not have sufficient resources to efficiently serve those UEs. Therefore, the wireless network100will attempt to actively balance the load between the macro eNBs110a-cand the pico eNB110xby expanding the coverage area of the pico eNB110x. This concept is referred to as cell range extension (CRE).

The wireless network100achieves CRE by changing the manner in which server selection is determined. Instead of basing server selection on downlink received signal strength, selection is based more on the quality of the downlink signal. In one such quality-based determination, server selection may be based on determining the eNB that offers the minimum path loss to the UE. Additionally, the wireless network100provides a fixed partitioning of resources between the macro eNBs110a-cand the pico eNB110x. However, even with this active balancing of load, downlink interference from the macro eNBs110a-cshould be mitigated for the UEs served by the pico eNBs, such as the pico eNB110x. This can be accomplished by various methods, including interference cancellation at the UE, resource coordination among the eNBs110, or the like.

In a heterogeneous network with cell range extension, such as the wireless network100, in order for UEs to obtain service from the lower-powered eNBs, such as the pico eNB110x, in the presence of the stronger downlink signals transmitted from the higher-powered eNBs, such as the macro eNBs110a-c, the pico eNB110xengages in control channel and data channel interference coordination with the dominant interfering ones of the macro eNBs110a-c. Many different techniques for interference coordination may be employed to manage interference. For example, inter-cell interference coordination (ICIC) may be used to reduce interference from cells in co-channel deployment. One ICIC mechanism is adaptive resource partitioning. Adaptive resource partitioning assigns subframes to certain eNBs. In subframes assigned to a first eNB, neighbor eNBs do not transmit. Thus, interference experienced by a UE served by the first eNB is reduced. Subframe assignment may be performed on both the uplink and downlink channels.

For example, subframes may be allocated between three classes of subframes: protected subframes (U subframes), prohibited subframes (N subframes), and common subframes (C subframes). Protected subframes are assigned to a first eNB for use exclusively by the first eNB. Protected subframes may also be referred to as “clean” subframes based on the lack of interference from neighboring eNBs. Prohibited subframes are subframes assigned to a neighbor eNB, and the first eNB is prohibited from transmitting data during the prohibited subframes. For example, a prohibited subframe of the first eNB may correspond to a protected subframe of a second interfering eNB. Thus, the first eNB is the only eNB transmitting data during the first eNB's protected subframe. Common subframes may be used for data transmission by multiple eNBs. Common subframes may also be referred to as “unclean” subframes because of the possibility of interference from other eNBs.

At least one protected subframe is statically assigned per period. In some cases only one protected subframe is statically assigned. For example, if a period is 8 milliseconds, one protected subframe may be statically assigned to an eNB during every 8 milliseconds. Other subframes may be dynamically allocated.

Adaptive resource partitioning information (ARPI) allows the non-statically assigned subframes to be dynamically allocated. Any of protected, prohibited, or common subframes may be dynamically allocated (AU, AN, AC subframes, respectively). The dynamic assignments may change quickly, such as, for example, every one hundred milliseconds or less.

Heterogeneous networks may have eNBs of different power classes. For example, three power classes may be defined, in decreasing power class, as macro eNBs, pico eNBs, and femto eNBs. When macro eNBs, pico eNBs, and femto eNBs are in a co-channel deployment, the power spectral density (PSD) of the macro eNB (aggressor eNB) may be larger than the PSD of the pico eNB and the femto eNB (victim eNBs) creating large amounts of interference with the pico eNB and the femto eNB. Protected subframes may be used to reduce or minimize interference with the pico eNBs and femto eNBs. That is, a protected subframe may be scheduled for the victim eNB to correspond with a prohibited subframe on the aggressor eNB.

FIG. 4is a block diagram illustrating time division multiplexed (TDM) partitioning in a heterogeneous network according to one aspect of the disclosure. A first row of blocks illustrates subframe assignments for a femto eNB, and a second row of blocks illustrate subframe assignments for a macro eNB. Each of the eNBs has a static protected subframe during which the other eNB has a static prohibited subframe. For example, the femto eNB has a protected subframe (U subframe) in subframe0corresponding to a prohibited subframe (N subframe) in subframe0. Likewise, the macro eNB has a protected subframe (U subframe) in subframe7corresponding to a prohibited subframe (N subframe) in subframe7. Subframes1-6are dynamically assigned as either protected subframes (AU), prohibited subframes (AN), and common subframes (AC). During the dynamically assigned common subframes (AC) in subframes5and6, both the femto eNB and the macro eNB may transmit data.

Protected subframes (such as U/AU subframes) have reduced interference and a high channel quality because aggressor eNBs are prohibited from transmitting. Prohibited subframes (such as N/AN subframes) have no data transmission to allow victim eNBs to transmit data with low interference levels. Common subframes (such as C/AC subframes) have a channel quality dependent on the number of neighbor eNBs transmitting data. For example, if neighbor eNBs are transmitting data on the common subframes, the channel quality of the common subframes may be lower than the protected subframes. Channel quality on common subframes may also be lower for extended boundary area (EBA) UEs strongly affected by aggressor eNBs. An EBA UE may belong to a first eNB but also be located in the coverage area of a second eNB. For example, a UE communicating with a macro eNB that is near the range limit of a femto eNB coverage is an EBA UE.

Another example interference management scheme that may be employed in LTE/-A is the slowly-adaptive interference management. Using this approach to interference management, resources are negotiated and allocated over time scales that are much larger than the scheduling intervals. The goal of the scheme is to find a combination of transmit powers for all of the transmitting eNBs and UEs over all of the time or frequency resources that maximizes the total utility of the network. “Utility” may be defined as a function of user data rates, delays of quality of service (QoS) flows, and fairness metrics. Such an algorithm can be computed by a central entity that has access to all of the information used for solving the optimization and has control over all of the transmitting entities. This central entity may not always be practical or even desirable. Therefore, in alternative aspects a distributed algorithm may be used that makes resource usage decisions based on the channel information from a certain set of nodes. Thus, the slowly-adaptive interference algorithm may be deployed either using a central entity or by distributing the algorithm over various sets of nodes/entities in the network.

In deployments of heterogeneous networks, such as the wireless network100, a UE may operate in a dominant interference scenario in which the UE may observe high interference from one or more interfering eNBs. A dominant interference scenario may occur due to restricted association. For example, inFIG. 1, the UE120ymay be close to the femto eNB110yand may have high received power for the eNB110y. However, the UE120ymay not be able to access the femto eNB110ydue to restricted association and may then connect to the macro eNB110c(as shown inFIG. 1) or to the femto eNB110zalso with lower received power (not shown inFIG. 1). The UE120ymay then observe high interference from the femto eNB110yon the downlink and may also cause high interference to the eNB110yon the uplink. Using coordinated interference management, the eNB110cand the femto eNB110ymay communicate over the backhaul134to negotiate resources. In the negotiation, the femto eNB110yagrees to cease transmission on one of its channel resources, such that the UE120ywill not experience as much interference from the femto eNB110yas it communicates with the eNB110cover that same channel.

In addition to the discrepancies in signal power observed at the UEs in such a dominant interference scenario, timing delays of downlink signals may also be observed by the UEs, even in synchronous systems, because of the differing distances between the UEs and the multiple eNBs. The eNBs in a synchronous system are presumptively synchronized across the system. However, for example, considering a UE that is a distance of 5 km from the macro eNB, the propagation delay of any downlink signals received from that macro eNB would be delayed approximately 16.67 μs (5 km÷3×108, i.e., the speed of light, ‘c’). Comparing that downlink signal from the macro eNB to the downlink signal from a much closer femto eNB, the timing difference could approach the level of a time-to-live (TTL) error.

Additionally, such timing difference may impact the interference cancellation at the UE. Interference cancellation often uses cross correlation properties between a combination of multiple versions of the same signal. By combining multiple copies of the same signal, interference may be more easily identified because, while there will likely be interference on each copy of the signal, it will likely not be in the same location. Using the cross correlation of the combined signals, the actual signal portion may be determined and distinguished from the interference, thus, allowing the interference to be canceled.

FIG. 3shows a block diagram of a design of a base station/eNB110and a UE120, which may be one of the base stations/eNBs and one of the UEs inFIG. 1. For a restricted association scenario, the eNB110may be the macro eNB110cinFIG. 1, and the UE120may be the UE120y. The eNB110may also be a base station of some other type. The eNB110may be equipped with antennas334athrough334t, and the UE120may be equipped with antennas352athrough352r.

At the eNB110, a transmit processor320may receive data from a data source312and control information from a controller/processor340. The control information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for the PDSCH, etc. The transmit processor320may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor320may also generate reference symbols, e.g., for the PSS, SSS, and cell-specific reference signal. A transmit (TX) multiple-input multiple-output (MIMO) processor330may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs)332athrough332t. Each modulator332may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator332may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from modulators332athrough332tmay be transmitted via the antennas334athrough334t, respectively.

At the UE120, the antennas352athrough352rmay receive the downlink signals from the eNB110and may provide received signals to the demodulators (DEMODs)354athrough354r, respectively. Each demodulator354may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator354may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector356may obtain received symbols from all the demodulators354athrough354r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor358may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE120to a data sink360, and provide decoded control information to a controller/processor380.

On the uplink, at the UE120, a transmit processor364may receive and process data (e.g., for the PUSCH) from a data source362and control information (e.g., for the PUCCH) from the controller/processor380. The transmit processor364may also generate reference symbols for a reference signal. The symbols from the transmit processor364may be precoded by a TX MIMO processor366if applicable, further processed by the demodulators354athrough354r(e.g., for SC-FDM, etc.), and transmitted to the eNB110. At the eNB110, the uplink signals from the UE120may be received by the antennas334, processed by the modulators332, detected by a MIMO detector336if applicable, and further processed by a receive processor338to obtain decoded data and control information sent by the UE120. The processor338may provide the decoded data to a data sink339and the decoded control information to the controller/processor340.

The controllers/processors340and380may direct the operation at the eNB110and the UE120, respectively. The controller/processor340and/or other processors and modules at the eNB110may perform or direct the execution of various processes for the techniques described herein. The controllers/processor380and/or other processors and modules at the UE120may also perform or direct the execution of the functional blocks illustrated inFIGS. 6 and 7, and/or other processes for the techniques described herein. The memories342and382may store data and program codes for the eNB110and the UE120, respectively. A scheduler344may schedule UEs for data transmission on the downlink and/or uplink.

In LTE, each node is equipped one or more transmit antennas, making it possible to support DL MIMO operation. Each node may have multiple sectors in which one or more transmit antennas are designated for each sector that also support DL MIMO operations in each sector. For common reference signal (CRS) based DL transmissions, the number of CRS antenna ports can be 1, 2, or 4. An antenna port is a logical representation of an antenna and may map to one or more physical antenna elements. For UE reference signal (UE-RS) based DL transmissions, the number of UE-RS antenna ports can be up to 8 in currently defined mobile standards and potentially more in future standards.

A UE provides channel state information (CSI) feedback to support DL MIMO operation. The UE takes measurements and makes determinations of various criteria, such as channel quality, rank indicators, precoding matrix information, and the like, and sends this information to the serving nodes. Based on this CSI feedback, the serving node makes transmission determinations. Channel and interference measurements for CSI feedback may be based on CRS or CSI-RS, depending on the configuration for the UE. A UE may also be configured with one or more CSI-RS processes. For example, in coordinated multipoint (CoMP) operations, the communication with the UE may be coordinated across multiple cells and nodes. Each CSI-RS process may be associated with a particular cell or node. Each CSI-Norton RS process may also be associated with a set of parameters, e.g., number of antenna ports for CSI feedback, periodicity for CSI-RS feedback, and the like.

Each node may have two or more carriers that may be assigned to different frequencies. The two or more carriers may be intra-band, inter-band, or a combination thereof. Additionally, different nodes may have carriers assigned to the same carrier frequency. Each such carrier may be equipped with a certain number of transmit antennas at their respective node or nodes. The node broadcasts the number of antennas for different reference signals, which may be different depending on the type of reference signal. For example, in a node with four physical transmit antennas, the node may broadcast two CRS ports and four CSI-RS ports. However, in some circumstances there may be an occasion to turn off, either partially or completely, some of the carriers. For example, for energy savings, if overall system load in a node is not high, it may be beneficial to turn off some carriers, depending on the type of node. In another example, to implement interference management, some carriers in some nodes may be turned off which may benefit surrounding nodes since inter-cell interference is reduced. Additionally, the nodes providing service for small cells may periodically or occasionally enter a dormancy mode. In order to manage such dormancy/activation periods in small cells, it may be beneficial to either partially or completely deactivate certain carriers where some nodes may be actively managed to be off/on, for operations such as mobility enhancements, interference coordination, and the like.

It should be noted that such operations may also be experienced between sectors of a single node. For example, it may be beneficial to deactivate certain carriers in a first sector to manage interference in the other sectors, especially when the system load in the first sector is low.

Considering the potential for certain carriers to be either completely or partially deactivated, and the fact that transmit antennas are specifically assigned for carrier transmissions, there may be circumstances in which certain transmit antennas assigned to deactivated carriers are idle while other transmit antennas assigned to active carriers are operating under a heavy load.

FIG. 4Ais a block diagram illustrating transmission frames of two different carriers. In the illustrated example, Carrier1represents an LTE carrier, which may be a legacy carrier type (LCT) or a new carrier type (NCT), and Carrier2represents another LTE carrier of an NCT, where the NCT carrier of Carrier2is active once every 5 subframes. Thus, in the inactive subframes of Carrier2, the transmit antennas assigned to Carrier2will be idle, while the transmit antennas of Carrier1remain active.

FIG. 4Bis a block diagram illustrating transmission frames of two different carriers in which one of the two carriers remains inactive for certain durations. In this example, Carrier1, once again, remains active throughout the transmission frame, while Carrier2is in an inactive period for the duration of the illustrated time. Here again, the transmit antennas assigned for Carrier2remain idle during the same period of time in which the transmit carriers assigned to Carrier1are active.

FIG. 4Cis a block diagram illustrating transmission frames of two additional different carriers. In this example, Carrier1, which represents an LCT, once again, remains active throughout the transmission frame, while Carrier2, which also represents an LCT, operates in such a fashion where Carrier2is not active during a fraction of particular subframes. Such partial subframe activity may, in practice, occur in MBSFN regions of MBSFN subframes. Again, transmit antennas assigned to Carrier2will be inactive during periods in which the transmit antennas assigned to Carrier1are active. There should be no doubt that, during the inactivity of Carrier2, in any ofFIGS. 4A-4C, that the transmission efficiency of Carrier1may be increased by “borrowing” the idle transmit antennas that have been assigned to Carrier2.

Various aspects of the present disclosure are related to borrowing transmit antennas from at least one first carrier for usage with a second carrier and transmitting various signals and reference signals using a set of antenna ports on the second carrier based on the combined physical antennas associated with the first carrier and physical antennas associated with the second carrier.

FIG. 5Ais a block diagram illustrating transmission frames of two different carriers in a wireless communication system configured according to one aspect of the present disclosure. Carriers1and2are each transmitted in a single node having multiple antennas. In the illustrated example, the transmitting node has four physical transmit antennas in which two of the transmit antennas are assigned to Carrier1and two of the transmit antennas are assigned to Carrier2. In operation of the wireless communication system configured according to one aspect of the present disclosure, when both Carriers1and2are active, the node transmits using the assigned two transmit antennas for each of Carriers1and2. However, when Carrier2is inactive, the node borrows the idle transmit antennas assigned to Carrier2for transmissions in Carrier1. As such, during the inactive periods of Carrier2, the node transmits Carrier1using four antenna ports—two transmit antennas assigned to Carrier1and two transmit antennas assigned to and borrowed from Carrier2. Accordingly, the transmission efficiency of the node may be increased by utilizing the idle transmit antennas assigned to Carrier2for Carrier1transmissions.

FIG. 5Bis a block diagram illustrating transmission frames of two different carriers in another wireless communication system configured according to one aspect of the present disclosure. The various aspects of the present disclosure may also be applicable to implementations in which the second carrier is inactive for only portions of a particular subframe. As illustrated, Carrier2is active during the entire first and last illustrated subframes, but only a portion of the second and third illustrated subframes. While active, the node transmits on Carrier2using each of the assigned two transmit antennas. Correspondingly, while Carrier2is active and transmitting using two transmit antennas, Carrier1is also illustrated as active and will transmit using the two transmit antennas assigned to Carrier1. However, when Carrier2is inactive, even during the remaining portions of the second and third illustrated subframes, the node borrows the two transmit antennas assigned to Carrier2and uses them in transmitting Carrier1with four transmit antennas. Thus, considering a node having r total transmit antennas with two transmit antennas assigned for a first carrier, when additional carriers of the node are inactive, the node may combine transmit antennas for transmission of Carrier1, which can vary between two and r transmit antennas for the first carrier. When all carriers are active, the node uses the assigned transmit antennas for each carrier; however when one or more of the carriers is not active, the node may use the assigned transmit antennas for the active carrier plus any number of idle transmit antennas for the other inactive carriers.

With the increased number of transmit antennas, a carrier may perform better MIMO operations. For example, additional transmit antennas may allow for enhanced beamforming. Considering a node having N combined carriers in which two transmit antennas are assigned to each of the N carriers, a change from two transmit antennas to 2N transmit antennas where N−1 carriers are inactive at a time, a large beamforming gain is possible. Increased numbers of transmit antennas may also enhance multi-user MIMO (MU-MIMO) operation by creating an environment in which the node is more likely to perform MU-MIMO operation and achieve improved MU-MIMO performance with a greater number of transmit antennas. Increased numbers of transmit antennas may also enhance SU-MIMO operation by creating an environment in which a higher rank SU-MIMO operation is possible.

FIG. 6is a functional block diagram illustrating example blocks executed to implement one aspect of the present disclosure. At block600, a node designates one or more transmit antennas assigned to at least one first carrier for use in a second carrier. For example, a particular node may have six transmit antennas and use three carriers with two transmit antennas assigned for each of the three carriers. When a first carrier is inactive, the node may designate the two transmit antennas assigned to the first carrier for use in either the second or third carrier, such that the node may use four transmit carriers for the second or third carrier. When the first and second carriers are inactive, the node may designate the four transmit antennas assigned to the first and second carriers for use in the third carrier, such that the node may transmit using all six transmit carriers on the third carrier.

At block601, the node transmits a signal with a set of antenna ports on the second carrier where this set of antenna ports is based, at least in part, on the combination of the transmit antennas assigned to the at least one first carrier and the one or more antennas assigned to the second carrier. This signal may be any number of different signals transmitted by a node, such as a control channel, a data channel, a reference signal (e.g., CRS, CSI-RS, UE-RS, demodulation reference signals (DM-RS), etc.) for at least one control channel or data channel, and the like. For example, as noted above, as any other carrier is inactive, the node may combine the transmit antennas assigned to the inactive carrier or carriers with the transmit antennas assigned to the active carrier for transmission of the various signals on the active, second carrier.

A node may transmit a reference signal to reflect the combination of transmit antennas to surrounding UEs, such as by using a CSI-RS. In a first CSI-RS configuration, a UE may be indicated a first number of antenna ports (reflecting no combined operation), and in a second CSI-RS configuration, a UE may be indicated a second number of antenna ports (reflecting combined operation). In certain configurations, there may be more than two possible CSI-RS configurations, for example, when there may be more than two combinations of transmit antennas across carriers (e.g., considering three carriers in one subframe, there may be three CSI-RS configurations (1) all carriers active and no combination; (2) only one carrier active with combination of transmit antennas from two inactive carriers; and (3) two carriers active with combination of transmit antennas from one inactive carrier. The different configurations can be in a same subframe or different subframes. In general, the second configuration (combination) is in a subframe when there is combined transmit across antennas, while the first configuration (no combination) can be in any subframes.

The different configurations can be indicated to a UE simultaneously or on an ad hoc basis one at a time. The indication of the configurations may depend on the timescale of the inactivity. If the inactivity is semi-static, there may be one configuration for an extended duration, followed by another configuration for an extended duration when there is a change in inactivity on at least one carrier. In such a semi-static operation, the CSI-RS configuration may be indicated one at a time, on an ad hoc basis depending on the particular operation. If the inactivity is dynamic, two configurations can be enabled simultaneously for a UE. Thus, the UE should have access to select either configuration depending on the current state of inactivity. Moreover, different UEs can be configured differently, both with different configurations and having either semi-static or dynamic indications of the configurations.

A UE may provide CSI feedback according to the various CSI-RS antenna configurations. Where, in the dynamic inactivity operation, two configurations are configured simultaneously, a UE may provide CSI feedback for two or more CSI processes, and the CSI feedback can be periodic, aperiodic or a combination of both. The node will schedule the UE based on this CSI feedback and the transmit antenna availability accordingly.

FIG. 7is a functional block diagram illustrating example blocks executed to implement one aspect of the present disclosure. At block700, a UE receives a reference signal on a carrier and a configuration of multiple sets of antenna ports from a serving node. UEs routinely receive references signals from various serving and non-serving nodes. UEs utilize such reference signals to determine handover, analyze interference, perform measurements, and provide feedback to serving nodes. In the described aspect, the UE also receives antenna configurations that may indicate to the UE a number of transmit antennas or antenna ports that will be used by the serving node to transmit various signals, including reference signals.

At block701, the UE receives a dynamic indication of which of the configurations of the sets of antenna ports the node used for the reference signal received for a subframe. For example, the UE receives an indication of which CSI-RS configuration to select based on the number of transmit antennas used by the node in transmitting the reference signal for a subframe. The indication may also be received by the UE through downlink control information (DCI) transmitted from the serving node, or through various activation or deactivation messages from the serving node. The indication may be semi-static, dynamic, or a combination of both semi-static and dynamic. As an example, a UE may be configured with two or more CSI-RS configurations. Additionally, a UE may receive an activation of some of the two or more CSI-RS configurations.

At block702, the UE selects the indicated configuration for the particular set of antenna ports and processes the reference signal based on the indicated set of antenna ports. For example, after the UE receives the indication of which configuration to select, the UE selects to implement that transmit antenna configuration and processes the reference signal according to the selected antenna configuration.

As noted, the management of transmit antennas across carriers can be semi-static or dynamic. In an active (dynamic) transmit antenna management, there may be occasions in which there is a conflicting need regarding whether transmit antennas associated with a first carrier should be used for the first carrier or a second carrier at a given time.

FIG. 8is a block diagram illustrating a single subframe of two carriers in a wireless communication system configured according to one aspect of the present disclosure. The node transmitting Carriers1and2includes four transmit antennas. As illustrated, during the indicated subframe, the node shows that Carrier1is indicated to transmit using four transmit antennas while Carrier2is indicated to transmit using two transmit antennas. For example, Carrier1is scheduled to transmit a CSI-RS with four transmit ports (combined transmit antennas across the two carriers), while Carrier2determines to be active in the same subframe.

In order to resolve the conflict in the number of scheduled transmit antennas, the node may operate under several different alternatives. For example, in a first possible resolution, the node may force Carrier2to become inactive during the illustrated subframe. By forcing this inactivity in Carrier2, the node may use four transmit antenna ports for transmitting CSI-RS on Carrier1. In another example operation, the node may either completely omit CSI-RS on the conflicting subframe or use only the two transmit antenna ports assigned to Carrier1for transmitting CSI-RS in the subframe. In another example operation to resolve such a conflict, the node may transmit the CSI-RS using a time division multiplex (TDM) operation within the conflicting subframe, such that, on Carrier1, four transmit antenna ports are used to transmit CSI-RS in the symbols carrying CSI-RS, while two transmit antennas are used in other symbols for Carrier1. Consequently, the node will not transmit on Carrier2during those symbols carrying CSI-RS in Carrier1, and will transmit on Carrier2using two transmit antennas during the other symbols of the subframe.

In another example, the node may transmit both Carrier1with four antenna ports and Carrier2with two antenna ports in a same subframe. However, in order to address the issue that Carrier1only has two physical antennas but indicates transmission by four antenna ports, the node can logically map the two physical antennas to the four antenna ports. By doing so, transparent operation from the UE perspective can be realized. That is, no specific handling is necessary for a UE to handle the conflicting scenarios. Because two or more physical antenna ports are mapped to a same antenna port, there may be degraded performance associated with the corresponding reference signal, e.g., for CSI-RS-based channel feedback. However, such degraded performance can be handled by the node, since the node knows the actual mapping between the physical antennas and the indicated antenna ports.

It should be noted that the management of transmit antennas across carriers is not limited to LTE on licensed spectrum. Various aspects of the present disclosure may be applied to LTE communication operations on unlicensed spectrum, or WIFI communication on unlicensed spectrum (e.g., for carrier sense multiple access (CSMA)-based multiplexing), or a combination of both.

The functional blocks and modules inFIGS. 6 and 7may comprise processors, electronics devices, hardware devices, electronics components, logical circuits, memories, software codes, firmware codes, etc., or any combination thereof.