Protection of broadcast signals in heterogeneous networks

Certain aspects of the disclosure provide for the protection of broadcast signals in heterogeneous networks. As described herein, a first set of resources used for downlink transmission in a first cell may overlap with a second set of resources used for broadcast signals in a second cell. The broadcast signals may be protected by allocating a third set of resources for the downlink transmission in the first cell, wherein the third set of resources is based, at least in part, on the overlapping set of resources.

BACKGROUND

1. Field of the Invention

This disclosure generally relates to communication and, more specifically, to power control in a multi-carrier wireless communication network.

A wireless communication network may include a number of base stations that can support communication for a number of user equipments (UEs). A UE may communicate with a base station via the downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station.

A base station may transmit data to one or more UEs on the downlink and may receive data from one or more UEs on the uplink. On the downlink, a data transmission from the base station may observe interference due to data transmissions from neighbor base stations. On the uplink, a data transmission from a UE may observe interference due to data transmissions from other UEs communicating with the neighbor base stations. For both the downlink and uplink, the interference due to the interfering base stations and the interfering UEs may degrade performance.

SUMMARY

Certain aspects of the disclosure provide a method for wireless communications in a wireless communications network. The method generally includes determining a first set of resources for downlink transmission to one or more first user equipments (UEs) in a first cell, determining a second set of resources for use in transmitting broadcast signals to one or more second UEs in a second cell, where the first and the second set of resources comprise an overlapping set of resources that at least partially overlap in time and frequency, and allocating a third set of resources for the downlink transmission in the first cell, wherein the third set of resources is based, at least in part, on the overlapping set of resources.

Certain aspects of the disclosure provide an apparatus for wireless communications in wireless communications network. The apparatus generally includes means for determining a first set of resources for downlink transmission to one or more first user equipments (UEs) in a first cell, means for determining a second set of resources for use in transmitting broadcast signals to one or more second UEs in a second cell, where the first and the second set of resources comprise an overlapping set of resources that at least partially overlap in time and frequency, and means for allocating a third set of resources for the downlink transmission in the first cell, wherein the third set of resources is based, at least in part, on the overlapping set of resources.

Certain aspects of the disclosure provide an apparatus for wireless communications in wireless communications network. The apparatus generally includes at least one processor configured to determine a first set of resources for downlink transmission to one or more first user equipments (UEs) in a first cell, determine a second set of resources for use in transmitting broadcast signals to one or more second UEs in a second cell, where the first and the second set of resources comprise an overlapping set of resources that at least partially overlap in time and frequency, and allocate a third set of resources for the downlink transmission in the first cell, wherein the third set of resources is based, at least in part, on the overlapping set of resources; and a memory coupled with the at least one processor.

Certain aspects of the disclosure provide a computer-program product for wireless communications comprising a computer-readable storage medium having instructions stored thereon. The instructions generally executable by a processor for determining a first set of resources for downlink transmission to one or more first user equipments (UEs) in a first cell, determining a second set of resources for use in transmitting broadcast signals to one or more second UEs in a second cell, where the first and the second set of resources comprise an overlapping set of resources that at least partially overlap in time and frequency, allocating a third set of resources for the downlink transmission in the first cell, wherein the third set of resources is based, at least in part, on the overlapping set of resources.

DETAILED DESCRIPTION

Various aspects are now described with reference to the drawings. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects. It will be recognized, however, that such aspect(s) may be practiced without these specific details.

The techniques described herein may be used for various wireless communication networks such as Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, Single-Carrier FDMA (SC-FDMA) networks, etc. The terms “networks” and “systems” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), CDMA 2000, etc. UTRA includes Wideband-CDMA (W-CDMA) and Low Chip Rate (LCR). CDMA2000 covers IS-2000, IS-95 and IS-856 standards. 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), IEEE 802.11, IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM are part of Universal Mobile Telecommunication System (UMTS). Long Term Evolution (LTE) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). CDMA2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). These various radio technologies and standards are known in the art. For clarity, certain aspects of the techniques are described below for LTE, and LTE terminology is used in much of the description below.

Single carrier frequency division multiple access (SC-FDMA), which utilizes single carrier modulation and frequency domain equalization has similar performance and essentially the same overall complexity as those of OFDMA system. SC-FDMA signal has lower peak-to-average power ratio (PAPR) because of its inherent single carrier structure. SC-FDMA has drawn great attention, especially in uplink communications where lower PAPR benefits the mobile terminal in terms of transmit power efficiency.

FIG. 1illustrates an example heterogeneous wireless network100, in which various aspects of the disclosure may be practiced.

The wireless communication network100may be an LTE network or some other wireless network. Wireless network100may include a number of evolved Node Bs (eNBs)110and other network entities. An eNB may be an entity that communicates with the UEs and may also be referred to as a base station, a Node B, an access point, etc. Each eNB may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to a coverage area of an eNB and/or an eNB subsystem serving this 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 may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscription. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscription. A femto cell may cover a relatively small geographic area (e.g., a home) and may allow restricted access by UEs having association with the femto cell (e.g., UEs in a Closed Subscriber Group (CSG)). 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. An eNB for a femto cell may be referred to as a home eNB (HeNB) or a femto eNB. In the example shown inFIG. 1, an eNB110amay be a macro eNB for a macro cell102a, an eNB110bmay be a pico eNB for a pico cell102b, and an eNB110cmay be a femto eNB for a femto cell102c. An eNB may support one or multiple (e.g., three) cells. The terms “eNB”, “base station”, and “cell” may be used interchangeably herein.

Wireless network100may also include relays. A relay may be an entity that can receive a transmission of data from an upstream station (e.g., an eNB or a UE) and send a transmission of the data to a downstream station (e.g., a UE or an eNB). A relay may also be a UE that can relay transmissions for other UEs. In the example shown inFIG. 1, a relay110dmay communicate with macro eNB110avia a backhaul link and with a UE120dvia an access link in order to facilitate communication between eNB110aand UE120d. A relay may also be referred to as a relay eNB, a relay station, a relay base station, etc.

Wireless network100may be a heterogeneous network that includes eNBs of different types, e.g., macro eNBs, pico eNBs, femto eNBs, relay eNBs, etc. These different types of eNBs may have different transmit power levels, different coverage sizes, and different impact on interference in wireless network100. For example, macro eNBs may have a high transmit power level (e.g., 5 to 40 Watts) whereas pico eNBs, femto eNBs, and relays may have lower transmit power levels (e.g., 0.1 to 2 Watts).

A network controller130may couple to a set of eNBs and may provide coordination and control for these eNBs. Network controller130may comprise a single network entity or a collection of network entities. Network controller130may communicate with the eNBs via a backhaul. The eNBs may also communicate with one another, e.g., directly or indirectly via a wireless or wireline backhaul.

UEs120may be dispersed throughout wireless network100, and each UE may be stationary or mobile. A UE may also be referred to as a mobile station, a terminal, an access terminal, a subscriber unit, a station, etc. A UE may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a smart phone, a netbook, a smartbook, etc. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, etc. A UE may also be able to communicate peer-to-peer (P2P) with another UE. In the example shown inFIG. 1, UEs120eand120fmay communicate directly with each other without communicating with an eNB in wireless network100. P2P communication may reduce the load on wireless network100for local communications between UEs. P2P communication between UEs may also allow one UE to act as a relay for another UE, thereby enabling the other UE to connect to an eNB.

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.

A UE may be located 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 signal strength, received signal quality, pathloss, etc. Received signal quality may be quantified by a signal-to-noise-and-interference ratio (SINR), or a reference signal received quality (RSRQ), or some other metric.

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, UE120cmay be close to femto eNB110cand may have high received power for eNB110c. However, UE120cmay not be able to access femto eNB110cdue to restricted association and may then connect to macro eNB110awith lower received power. UE120cmay then observe high interference from femto eNB110con the downlink and may also cause high interference to femto eNB110con the uplink.

A dominant interference scenario may also occur due to range extension, which is a scenario in which a UE connects to an eNB with lower pathloss and possibly lower SINR among all eNBs detected by the UE. For example, inFIG. 1, UE120bmay be located closer to pico eNB110bthan macro eNB110aand may have lower pathloss for pico eNB110b. However, UE120bmay have lower received power for pico eNB110bthan macro eNB110adue to a lower transmit power level of pico eNB110bas compared to macro eNB110a. Nevertheless, it may be desirable for UE120bto connect to pico eNB110bdue to the lower pathloss. This may result in less interference to the wireless network for a given data rate for UE120b.

Various interference management techniques may be used to support communication in a dominant interference scenario. These interference management techniques may include semi-static resource partitioning (which may be referred to as inter-cell interference coordination (ICIC)), dynamic resource allocation, interference cancellation, etc. Semi-static resource partitioning may be performed (e.g., via backhaul negotiation) to allocate resources to different cells. The resources may comprise subframes, subbands, carriers, resource blocks, transmit power, etc. Each cell may be allocated a set of resources that may observe little or no interference from other cells or their UEs. Dynamic resource allocation may also be performed (e.g., via exchange of over-the-air messages between cells and UEs) to allocate resources as needed to support communication for UEs observing strong interference on the downlink and/or uplink. Interference cancellation may also be performed by UEs to mitigate interference from interfering cells.

Wireless network100may support hybrid automatic repeat request (HARQ) for data transmission on the downlink and uplink. For HARQ, a transmitter (e.g., an eNB) may send one or more transmissions of a packet until the packet is decoded correctly by a receiver (e.g., a UE) or some other termination condition is encountered. For synchronous HARQ, all transmissions of the packet may be sent in subframes of a single HARQ interlace, which may include every Q-th subframes, where Q may be equal to 4, 6, 8, 10, or some other value. For asynchronous HARQ, each transmission of the packet may be sent in any subframe.

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.

Wireless network100may utilize FDD or TDD. For FDD, the downlink and uplink may be allocated separate frequency channels, and downlink transmissions and uplink transmissions may be sent concurrently on the two frequency channels. For TDD, the downlink and uplink may share the same frequency channel, and downlink and uplink transmissions may be sent on the same frequency channel in different time periods.

Protection of Broadcast Signals in Heterogeneous Networks

As illustrated, according to certain aspects, different eNBs in the heterogeneous wireless network100may be configured to “extend” the resources allocated to a physical downlink shared channel (PDSCH) for its UEs via the application of extension carriers and/or carrier segments. As illustrated, macro eNB110amay allocate resources, via a PDCCH132, in a manner that extends the PDSCH for a UE120cby allocating a portion of a component carrier used by UEs served in the Femto cell102c. Similarly, macro eNB110bmay allocate resources, via a PDCCH134, in a manner that extends the PDSCH for a UE120bby allocating a portion of a component carrier used by UEs served in the Macro cell102a.

As will be described in greater detail below, the allocation may be done in a manner designed to “protect” broadcast signals that a UE needs to reliably decode for proper operation. This protection may be accomplished by carefully allocating resources used for downlink transmission in a first cell (an “interfering cell”) that overlap with resources allocated for broadcast signals in a second cell (an “interfered cell”).

As an example, for a carrier exploiting case, the transmission of certain broadcast signals (e.g., PBCH/PSS/SSS) of some cells (e.g., low power class nodes) may be protected from some interfering cells (e.g., high power class nodes) by allocating resources such that downlink transmissions from the interfering cells avoid using resource blocks (RBs) used for the broadcast signals. As will be described in detail below, there may be various options for accomplishing this protection.

As one illustrative but not limiting example, a first cell may utilize resources of a first component carrier (CC) for a physical downlink shared channel (PDSCH) and “extend” the PDSCH by utilizing resources of a second CC. The resources of the second CC used for the extended PDSCH may overlap with resources used for transmitting broadcast signals in a second cell. Therefore, the broadcast signals may be protected by allocating resources of the second CC used to extend the PDSCH in a manner that attempts to avoid interference with the resources used for the broadcast signals in the second cell.

FIG. 2is a block diagram200showing example components of an exemplary base station210and access terminal250in an example wireless system200. The base station210can be an access point or eNB such as one of the eNBs110illustrated inFIG. 1and the access terminal250can be a user equipment such as one of the UEs120illustrated inFIG. 1.

At the base station210, traffic data for a number of data streams is provided from a data source212to a transmit (TX) data processor214. A processor230may generate control information to be transmitted to the AT250. As illustrated, the processor230may receive resource allocation information indicating how different resources are allocated between different cells in a heterogeneous network. According to certain aspects, the resource allocation information may indicate a set of resources used for transmitting broadcast signals in a different cell (e.g., an “interfered cell”). As will be described below, this information may be used to protect the broadcast signals by allocating resources for downlink transmission in the current cell so they do not interfere with the broadcast signals in the other cell.

The resource allocation information may be exchanged, for example, over a backhaul connection (not shown inFIG. 2) and may be the result of resource negotiations. As such, the resource allocation information may vary over time as negotiations change with varying network conditions. In any case, the processor230may utilize this information to generate an appropriate PDCCH sent in a downlink transmission to allocate resources to the AT250for use as a PDSCH (or extended PDSCH).

A TX data processor214formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data. The coded data for the data streams and control information may be multiplexed with pilot data using OFDM techniques.

The pilot data is typically a known data pattern that is processed in a known manner and may be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream is then modulated (e.g., symbol mapped) based on a particular modulation scheme (e.g., Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), M-PSK in which M is generally a power of two, or M-QAM (Quadrature Amplitude Modulation)) selected for that data stream to provide modulation symbols. The data rate, coding and modulation for each data stream may be determined by instructions performed by processor230that may be coupled with a memory232.

The modulation symbols for all data streams are then provided to a TX MIMO processor220, which may further process the modulation symbols (e.g., for OFDM). TX MIMO processor220then provides NTmodulation symbol streams to NTtransmitters (TMTR)222athrough222t. In certain aspects, TX MIMO processor220applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted.

Transmitters222receive and process symbol streams for each downlink component carrier to provide one or more analog signals, and further condition (e.g., amplify filter, and upconvert) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. NTmodulated signals from transmitters222athrough222tare then transmitted from NTantennas224athrough224t, respectively.

A RX data processor260then receives and processes the NRreceived symbol streams from NRreceivers254based on a particular receiver processing technique to provide NT“detected” symbol streams. The RX data processor260then demodulates, deinterleaves and decodes each detected symbol stream for each configured component carrier to recover the traffic data and control information, for example, including PDSCH and broadcast signals (which may be protected by careful resource allocation in potentially interfering cells as described herein).

The processing by RX data processor260may be complementary to that performed by TX MIMO processor220and TX data processor214at transmitter system210. A processor270, coupled to a memory272, periodically determines which pre-coding matrix to use (discussed below). Processor270formulates an uplink message comprising a matrix index portion and a rank value portion.

The processor270may receive resource allocation information, for example, for a PDSCH (or extended PDSCH) and broadcast signals. The processor270may determine which resources are used for these signals based on this information.

An uplink (reverse link) message may comprise various types of information regarding the communication link and/or the received data stream. The uplink message may then processed by a TX data processor238, which also receives traffic data for a number of data streams from a data source236, modulated by a modulator280, conditioned by transmitters254athrough254r.

At transmitter system210, the uplink transmissions from access terminal250are received by antennas224, conditioned by receivers222, demodulated by a demodulator240and processed by a RX data processor242to extract the reserve link message transmitted by the receiver system250. Processor230can then determine various parameters, such as which pre-coding matrix to use for determining beamforming weights, and continue processing the extracted message.

As noted above, in systems where multi-carrier operation is supported, a UE may be configured to monitor and be served by two or more component carriers (CCs). In such systems, cross-carrier signaling may be supported in an effort to provide for efficient control. This may be particularly desirable in the context of heterogeneous networks—where different types of cells (e.g., macro, pico, and Femto-cells) are overlayed that have access points that transmit with varying levels of power.

There may be different types of CCs, for example, to provide backward compatibility to UEs compatible earlier versions of a standard (“legacy” UEs). Such a combination of CCs may bring not only enhanced UE throughput, but also more efficient interference management especially for heterogeneous networks. As described herein, a portion of resources of a CC (e.g., a carrier segment or extended carrier) may be used to extend the PDSCH of a (non-legacy) UE.

According to certain aspects, care may be taken in an effort to reduce interference between portions of a CC used for downlink transmissions in a first cell and resources of that same CC used to transmit broadcast signals in a second cell. These broadcast signals may include, for example, Physical Broadcast Channel (PBCH), Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS), Common Reference Signal (CRS), Channel State Information Reference Signal (CSI-RS), and the like.

FIG. 3illustrates an example communication system300capable of protecting broadcast transmissions on CCs in one cell that are also used for downlink transmissions in one or more other cells. As noted above, this may be achieved by coordinated resource allocation, in which different sets of resources are allocated in an effort to reduce interference between downlink transmissions in the other cells with the broadcast signals. As withFIG. 1, interfering transmissions are indicated with a dashed line.

As illustrated, system300includes a base station302of a first cell (referred to herein as an “interfering base station”) and a base station304of a second cell (referred to herein as an “interfered base station”). The base stations302/304and UE306may, each of which may operate in a similar manner to the base stations and UEs described in connection withFIGS. 1-2. According to certain aspects, for multi-carrier operation, the base station302or base station304may generate allocation information for extending the PDSCH of the UE304across multiple carriers. In such cases, the allocation may be performed in an effort to reduce interference between the extended PDSCH and broadcast signals in other cells transmitted using resources in the same CC.

As illustrated, transmissions from interfering base station302may interfere with transmissions from interfered base station304, for example, hindering the ability of a User Equipment (UE)306to properly decode signals transmitted from the interfered base station304. Although not shown, it is contemplated that any number of base stations similar to interfering base station302and/or interfered base station304may be included in system300and/or any number of UEs similar to UE306can be included in system300.

System300may be a heterogeneous network, in which different power classes of nodes (e.g., base stations such as interfering base station302and interfered based station304) co-exist. In such systems, UEs (e.g., UE306or disparate UE not shown) may observe strong interference in the downlink from nodes from different power class cells. An example is in a closed-subscriber-group (CSG) cell, a Macro UE may not be allowed to access the CSG cell, but the Macro UE may observe strong downlink (DL) interference from the CSG cell, effectively creating a coverage hole for the Macro UE.

Various techniques may be employed to manage such interference attempt to reduce such interference in the context of co-channel deployment. As an example, blank or “almost-blank” subframes (ABSF), where one or more base stations avoid or limit transmissions on one or more subframes (so they appear blank), may allow Time Division Multiplexing (TDM)-based resource management. Interference from interfering cells can be reduced via blank subframes. With “almost” blank subframes, the data region can be completely blank, while the control region may only have Physical Control Format Indicator Channel (PCFICH), omitting transmission of Physical HARQ ACK/NAK Indicator Channel (PHICH)/Physical Downlink Control Channel (PDCCH). Further, transmit power of higher power class nodes may be reduced, to approximate homogeneous networks, albeit at the risk of potentially shrinking Macro cell coverage.

The use of multiple carriers may also help reduce interference. Following this example, interfering base station302can include a carrier aggregation component308and interfered base station304can include a carrier aggregation component310. Carrier aggregation component308and carrier aggregation component310may enable the aggregation of contiguous and/or non-contiguous spectrum for UEs to have access to corresponding Physical Layer (PHY) resources. According to certain aspects, resource allocation from one carrier to another carrier may be enabled via the use of the agreed ‘carrier indicator field’ embedded in PDCCH. Carrier aggregation component308and carrier aggregation component310may implement one or more non-backward-compatible concepts such as, for instance, carrier extension (segments) and extension carriers.

As illustrated, the interfered base station304can further include a broadcast component312that can send broadcast signals over a downlink on a particular CC. Unfortunately, downlink data transmission using Physical Downlink Shared Channel (PDSCH) sent by the interfering base station302may overlap with resources used to transmit the broadcast signals.

In an effort to avoid interference between PDSCH transmissions and the broadcast signals of the interfered base station304, the interfering base station302may include an interference management component314that can manage interference using techniques described herein. According to certain aspects, the interference management component314may exchange information regarding resources utilized by the interfered base station304for transmitting broadcast signals via a backhaul link320.

FIG. 4illustrates example operations400that may be performed, for example, by an interfering base station304, for protecting broadcast signals, in accordance with certain aspects of the disclosure. A base station performing these operations may be as described in connection with any ofFIGS. 1-3. For instance, exemplary operations400may be directed by one or more processors (such as processor230), or by one or more components (such as components308-314).

At402, the base station determines a first set of resources for downlink transmission to one or more first user equipments (UEs) in a first cell. At404, the base station determines a second set of resources for use in transmitting broadcast signals to one or more second UEs in a second cell, where the first and the second set of resources comprise an overlapping set of resources that at least partially overlap in time and frequency. At406, the base station allocates a third set of resources for the downlink transmission in the first cell, wherein the third set of resources is based, at least in part, on the overlapping set of resources. According to certain aspects, the third set of resources may comprise a subset of the first set of resources. According to certain aspects, transmission utilizing resources in the first set (but not resources in the third set) may be performed with zero-power (thus conventional mapping may be utilized, but with power control to protect broadcast signals).

The techniques presented herein may be used to protect broadcast signals in one cell from interference by downlink transmissions in another cell. This protection may be achieved by careful allocation of resources for downlink transmissions in an interfering (or potentially interfering) cell, based on knowledge of resources allocated for transmitting the broadcast signals in the interfered cell (or potentially interfered cell).

In various systems, such as LTE “Advanced” (LTE-A), carrier aggregation enables the aggregation of contiguous or non-contiguous spectrum for UEs to have access to corresponding PHY resources. Resource allocation from one carrier to another carrier may be enabled. As an example, it can be enabled via the use of an agreed-upon carrier indicator field (CIF) embedded in the PDCCH. As another example, it can be enabled by treating the carriers in aggregation as one carrier in terms of resource assignment, especially in the case of carrier extensions detailed below.

In order to extend PDSCH, different mechanisms outside a primary CC may be used, such as carrier extension (segments) and extension carriers. As used herein, the term carrier segments generally refers to segments that are defined as bandwidth extensions of an existing (e.g., LTE Rel-8 compatible) component carrier (which is typically no larger than 110 RBs in total). A carrier segment may allow utilization of frequency resources in case new transmission bandwidths are needed in a backwards compatible way complementing carrier aggregation means. This mechanism may reduce additional PDCCH transmissions that would be required in a carrier aggregation setting and also reduce the use of small TB sizes for the part corresponding to the segment. Thus, a carrier segment may allow aggregating additional resource blocks to a component carrier, while still retaining the backward compatibility of the original carrier bandwidth. Carrier segments may be defined as always adjacent and linked to one component carrier (and not used “stand-alone”). Carrier segments may also be limited in their use, for example, not providing synchronization signals, system information, or paging.

Diagram510inFIG. 5illustrates example carrier segments (Segment1and Segment2) adjacent to a component carrier (Carrier0), illustratively backward-compatible with LTE Rel. 8. As noted, the segments are an extension of the CC and, thus, the CC with extension(s) may be considered a single HARQ entity. Allocation of one or more of the extensions for use in extending the PDSCH may be made in the PDCCH in Carrier0.

Extension carriers may be designed with a similar philosophy as carrier segments. However, an extension carrier may be an actual component carrier itself, which may or may not be backward compatible (with Rel-8 UEs). The backward compatible carrier and the extension carrier, being two different component carriers, may assume independent H-ARQ processes and transport blocks.

Diagram520inFIG. 5illustrates example extension carrier (Carrier1) linked to a backward-compatible component carrier (Carrier0). As noted, the extension carrier may be an actual component carrier and, thus, may be treated as an independent HARQ entity. Again, allocation of the extension carrier for use in extending the PDSCH may be made in the PDCCH in Carrier0.

As shown inFIG. 5, extension carriers and carrier segments may be linked to a backward compatible component carrier and, in some cases, may not be used in a stand-alone manner. Use of the extension carriers and/or segments may be limited to prohibit their use for conveying synchronization signals, system information, paging for UEs, and various control channels, such as Rel-8 PDCCH, Rel-8 PHICH, and Rel-8 PCFICH. Further, these extension mechanisms may be prohibited for use in random access or UE camping. Extension carriers and segments may not be recognized and/or accessible by LTE Rel 8 (“legacy”) UEs.

The use of these carrier aggregation mechanisms in heterogeneous networks (HetNets) proposed herein may allow semi-static partitioning of spectrum for high power nodes (e.g., macro UEs) and low power nodes (e.g., femto/pico nodes UEs). According to certain aspects, extension carriers and carrier segments may be suitable for interference management for HetNets. In this case, different portions of the spectrum may be interpreted differently by different type of nodes.

For example, as illustrated in the resource diagram610ofFIG. 6, an extended PDSCH for a high power node may comprise one backward compatible carrier (CC1) and an extended PDSCH region comprising at least one carrier segment (CS1) or extension carrier (EC2) which may be of a second component carrier (CC2). According to certain aspects, legacy UEs (e.g., Rel-8 or older) may be served within CC1only, while non-legacy UEs (Rel-9 or higher) may be served by both CC1and CS1/EC2. As illustrated, however, the allocation of resources in CS1/EC2may be via the control region612in CC1.

It should be noted that the diagram610inFIG. 6represents an example interpretation of available spectrum from the perspective of a high power node. Diagram650, on the other hand, represents an example interpretation of the same spectrum from the perspective of a low power node. As illustrated, from the perspective of the low power node, the extended PDSCH may include one backward compatible carrier (CC2), and extension carrier(s) EC1or carrier segment(s) CS2or a component carrier (CC1). In this example, CC2, being backward compatible, carries the control region, and can signal the resources for EC1/CS2/CC1. The mapping of PDSCH in EC1/CS2/CC1in this case assigned from CC2starts from an OFDM symbol conveyed by CC2to the UE (or at a fixed OFDM symbol). In this example, EC1/CS2does not carry control region, rather CC1carries the regular control channel.

As illustrated above, with this arrangement, different parts of the spectrum may be interpreted differently by different type of node. In general, high power nodes and low power nodes may be arranged such that low power nodes using CC2is free of interference in the control region, if the high power nodes do not transmit in the symbols using CS1or EC2colliding with the control region of the lower nodes using CC2.

According to certain aspects, resources for the “extended PDSCH” may be allocated in a manner that attempts to avoid high power node data interfering with low power node broadcast signals (e.g., since legacy broadcast signals may be transmitted on CC2by low power nodes). According to certain aspects, symbols in resource blocks (RBs) used for transmitting the broadcast signals (or the entire RBs) may be avoided when transmitting the extended PDSCH.

For example, by exchanging resource partitioning information (e.g., via backhaul connections), node Bs may be able to schedule resources in this manner to avoid interference between broadcast signals sent in the control region624(e.g., corresponding to control region of the high power node) and an extended PDSCH of the high power node. Interference avoidance may be accomplished, for example, by avoiding RBs used to transmit broadcast signals by a low power node in CC2when allocating resources for an extended PDSCH for another node.

While CS1or EC2of the high power nodes may be transparent to “legacy UEs” (e.g., those compatible with LTE Rel-8 or earlier), “non-legacy UEs” (e.g., those compatible with later releases, such as Rel-10 or higher) may be scheduled with PDCCH transmitted on CC1of the high power nodes (cross-carrier signaling). Depending on interference management schemes, the transmit power of the data region of CS1or EC2can be significantly higher than that of CC2, consequently causing severe interference to CC2. To mitigate the issue, backhaul information exchange or resource allocation information may be used to coordinate the involved cells.

For the low power class nodes, UEs served by CC2may need to reliably decode various broadcast signals transmitted from CC2for proper operation. These broadcast signals can include PBCH, PSS, SSS, CRS, etc. The transmission of PBCH, PSS and SSS typically occupy some of the symbols in the center six Resource Blocks of the system. This is illustrated inFIG. 7, which shows an example radio frame depicting resources utilized for PBCH, PSS, and SSS in an FDD system.

According to an example, broadcast signals may be protected by having a (potentially) interfering base station avoid transmitting on the downlink using those symbols in the center 6 RBs (or the entire group of these RBs) in the subframes that would collide with those symbols/subframes carrying PBCH/PSS/SSS of the interfered cells (e.g., as sent by broadcast component312of interfered base station304). If interfering base station302schedules PDSCH overlapping with these 6 RBs, then interference management component314can rate-match around or puncture these 6 RBs and within these 6 RBs, using only the remaining symbols, or avoiding these RBs in their entirety.

As another example of protecting broadcast signals, if (demodulation of) the colliding PDSCH on interfering base station302is based on CRS, then interference management component314may be configured to cause PDSCH to be rate-matched around the symbols colliding with those of PBCH/PSS/SSS of the interfered cells (e.g., as sent by broadcast component312of interfered base station304). On the other hand, if (demodulation of) the colliding PDSCH on interfering base station302is based on UE-RS, then the interference management component314may be configured to cause PDSCH to be rate-matched around or the entire overlapping RBs can be punctured.

As another example, interfering base station302can transmit those PDSCH which is rate matched around CRS tones for the interfered cells. Thus, interference management component314can cause interfering base station302to signal to UEs associated therewith.

Interfering base station302may transmit PDSCH and puncture those tones where CRS tones are transmitted for the interfered cells. This operation may be transparent to the UEs associated with interfering base station302. Interfering base station302may selectively puncture those CRS tones based on projected interference to those interfered cells. In other words, interfering base station302may at least reserve those symbols in the corresponding subframes colliding with those of PBCH/PSS/SSS/CRS of the cells requiring interference protection. This may allow reliable broadcast signal (e.g., PBCH/PSS/SSS) detection for the UEs served by the interfered cells.

Whether an interfering base station chooses to reserve some symbols or RBs for the purpose of minimizing interference to protect transmission of broadcast signals from other cells may depend on various factors, such as a difference in power class, antenna gain, proximity among the involving cells, UE distributions/channel conditions in the involving cells, scheduling algorithms, Quality of Service (QoS) requirements, and/or one or more resource management schemes. The reservation information may also be exchanged over a backhaul link between involved cells for more efficient interference management.

It should be noted that in some synchronous systems, broadcast signals from different cells may collide with each other. Alternatively, the broadcast signals of different cells may not occur in the same subframes, and/or not be completely overlap in a single subframe. Thus, resource reservation described herein to protect broadcast signals may span more than one subframe in the interfered cell.

According to other aspects, the above techniques described with reference to PBCH, PSS, and SSS may also be applied to Channel State Information-Reference Signal (CSI-RS) that may be introduced in later releases (e.g., Rel-10).

It may also be noted that the interfering cells need to accommodate protection of broadcast signals for more than one interfered cell, if these interfered cells do not have the same REs for broadcast signals. In such cases, according to certain aspects, the interfering cells may choose to perform the RE reservation only one (or only a selected set) of the interfered cells. According to certain aspects, this selection may be based on various factors, such as channel conditions, loading, QoS, and the like. Such information may be exchanged over backhaul.

As an example of this selection, if a first cell (Cell1) interferes with second and third cells (Cell2and Cell3), the reservation can be such that cell1only reserves REs in a manner that protects broadcast transmissions on Cell2, but not Cell3. Such a decision may be based on a condition such as, for example, that Cell2is more sensitive than Cell3to interference from Cell1. According to another example, if Cell1interferes with Cell2and Cell3, the reservation may be such that Cell1protects broadcast transmissions on both Cell2and Cell3(e.g., by reserves REs for both).

The disclosure provides for the application of extension carriers and carrier segments in the context of heterogeneous networks, while protecting broadcast signal transmission by other nodes. As described herein, different parts of the spectrum may be interpreted differently by different type of nodes.

For example, such a device can be coupled to a server to facilitate the transfer of means for performing the methods described herein. Alternatively, various methods described herein can be provided via storage means (e.g., RAM, ROM, a physical storage medium such as a compact disc (CD) or floppy disk, etc.), such that a user terminal and/or base station can obtain the various methods upon coupling or providing the storage means to the device. Moreover, any other suitable technique for providing the methods and techniques described herein to a device can be utilized.

While the foregoing is directed to aspects of the disclosure, other and further aspects of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.