Reference signal configuration for extension carriers and carrier segments

Reference signals configured for use with extension carriers and/or carrier segments are described. Reference signals for extension carriers and/or carrier segments may include demodulation reference signals (e.g., user equipment-specific reference signals), cell-specific reference signals, and channel-state information reference signals. Methods, systems and apparatuses for configuring extension carriers and/or carrier segments with one or more of the reference signals (e.g., positioning one or more reference signal symbols in extension carriers and/or carrier segments) are described.

BACKGROUND

A wireless communication network, for example a wireless network configured in accordance with Third Generation Partnership Project (3GPP) standards, may support transmission of signals (e.g., voice and/or data signals) over a carrier (e.g., a primary carrier) that may be established between one or more components of a core network (CN) of the wireless communications network and user equipment (UE) associated with the wireless communications network. One or both of the CN and the UE may transmit reference signals over the carrier that may be used, for example, to perform channel estimation of the carrier.

A respective portion of wireless communication network bandwidth that may be made available for use by a UE may be expanded, for example by employing one or more carrier expansion techniques. Carrier expansion techniques may include employing one or more extension carriers configured to supplement the primary carrier. Signaling schemes that may be employed for a primary carrier, for example positions of reference signals within the primary carrier, may not provide optimal performance if employed for an extension carrier.

SUMMARY

As described herein, reference signals may be positioned in various locations within respective resource elements of an extension carrier and/or a carrier segment, for instance such that transmission performance between a CN and a UE over the extension carrier and/or carrier segment may be optimized.

A method may include transmitting a first timeslot of a subcarrier. The first timeslot may have a first plurality of resource elements that may be ordered from a first resource element to a last resource element. Transmitting the first timeslot may include transmitting a first symbol in a select one of the first plurality of resource elements that may not be the last resource element. The first symbol may be a user equipment-specific demodulation reference signal. Transmitting the first timeslot may include transmitting a second symbol in the last resource element of the first plurality of resource elements. The second symbol may be other than a user equipment-specific demodulation reference signal.

A wireless transmit/receive unit (WTRU) may include a processor that may cause the WTRU to transmit a first timeslot of a subcarrier. The first timeslot may have a first plurality of resource elements that are ordered from a first resource element to a last resource element. The WTRU may transmit the first timeslot by transmitting a first symbol in a select one of the first plurality of resource elements that may not be the last resource element. The first symbol may be a user equipment-specific demodulation reference signal. The WTRU may transmit the first timeslot by transmitting a second symbol in the last resource element of the first plurality of resource elements. The second symbol may be other than a user equipment-specific demodulation reference signal.

DETAILED DESCRIPTION

FIG. 1Ais a diagram of an example communications system100in which one or more disclosed embodiments may be implemented. For example, a wireless network (e.g., a wireless network comprising one or more components of the communications system100) may be configured such that bearers that extend beyond the wireless network (e.g., beyond a walled garden associated with the wireless network) may be assigned QoS characteristics.

As shown inFIG. 1A, the communications system100may include at least one wireless transmit/receive unit (WTRU), such as a plurality of WTRUs, for instance WTRUs102a,102b,102c, and102d, a radio access network (RAN)104, a core network106, a public switched telephone network (PSTN)108, the Internet110, and other networks112, though it should be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. Each of the WTRUs102a,102b,102c,102dmay be any type of device configured to operate and/or communicate in a wireless environment. By way of example, the WTRUs102a,102b,102c,102dmay be configured to transmit and/or receive wireless signals and may include user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, consumer electronics, and the like.

FIG. 1Cis a system diagram of an embodiment of the communications system100that includes a RAN104aand a core network106athat comprise example implementations of the RAN104and the core network106, respectively. As noted above, the RAN104, for instance the RAN104a, may employ a UTRA radio technology to communicate with the WTRUs102a,102b, and102cover the air interface116. The RAN104amay also be in communication with the core network106a. As shown inFIG. 1C, the RAN104amay include Node-Bs140a,140b,140c, which may each include one or more transceivers for communicating with the WTRUs102a,102b,102cover the air interface116. The Node-Bs140a,140b,140cmay each be associated with a particular cell (not shown) within the RAN104a. The RAN104amay also include RNCs142a,142b. It should be appreciated that the RAN104amay include any number of Node-Bs and RNCs while remaining consistent with an embodiment.

The core network106ashown inFIG. 1Cmay include a media gateway (MGW)144, a mobile switching center (MSC)146, a serving GPRS support node (SGSN)148, and/or a gateway GPRS support node (GGSN)150. While each of the foregoing elements is depicted as part of the core network106a, it should be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator.

As noted above, the core network106amay also be connected to the networks112, which may include other wired or wireless networks that are owned and/or operated by other service providers.

FIG. 1Dis a system diagram of an embodiment of the communications system100that includes a RAN104band a core network106bthat comprise example implementations of the RAN104and the core network106, respectively. As noted above, the RAN104, for instance the RAN104b, may employ an E-UTRA radio technology to communicate with the WTRUs102a,102b, and102cover the air interface116. The RAN104bmay also be in communication with the core network106b.

The RAN104bmay include eNode-Bs140d,140e,140f, though it should be appreciated that the RAN104bmay include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs140d,140e,140fmay each include one or more transceivers for communicating with the WTRUs102a,102b,102cover the air interface116. In one embodiment, the eNode-Bs140d,140e,140fmay implement MIMO technology. Thus, the eNode-B140d, for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU102a.

Each of the eNode-Bs140d,140e, and140fmay be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the uplink and/or downlink, and the like. As shown inFIG. 1D, the eNode-Bs140d,140e,140fmay communicate with one another over an X2 interface.

The core network106bshown inFIG. 1Dmay include a mobility management gateway (MME)143, a serving gateway145, and a packet data network (PDN) gateway147. While each of the foregoing elements is depicted as part of the core network106b, it should be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator.

The MME143may be connected to each of the eNode-Bs140d,140e, and140fin the RAN104bvia an S1 interface and may serve as a control node. For example, the MME143may be responsible for authenticating users of the WTRUs102a,102b,102c, bearer activation/deactivation, selecting a particular serving gateway during an initial attach of the WTRUs102a,102b,102c, and the like. The MME143may also provide a control plane function for switching between the RAN104band other RANs (not shown) that employ other radio technologies, such as GSM or WCDMA.

The serving gateway145may be connected to each of the eNode Bs140d,140e,140fin the RAN104bvia the S1 interface. The serving gateway145may generally route and forward user data packets to/from the WTRUs102a,102b,102c. The serving gateway145may also perform other functions, such as anchoring user planes during inter-eNode B handovers, triggering paging when downlink data is available for the WTRUs102a,102b,102c, managing and storing contexts of the WTRUs102a,102b,102c, and the like.

The serving gateway145may also be connected to the PDN gateway147, which may provide the WTRUs102a,102b,102cwith access to packet-switched networks, such as the Internet110, to facilitate communications between the WTRUs102a,102b,102cand IP-enabled devices.

The core network106bmay facilitate communications with other networks. For example, the core network106bmay provide the WTRUs102a,102b,102cwith access to circuit-switched networks, such as the PSTN108, to facilitate communications between the WTRUs102a,102b,102cand traditional land-line communications devices. For example, the core network106bmay include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the core network106band the PSTN108. In addition, the core network106bmay provide the WTRUs102a,102b,102cwith access to the networks112, which may include other wired or wireless networks that are owned and/or operated by other service providers.

FIG. 1Eis a system diagram of an embodiment of the communications system100that includes a RAN104cand a core network106cthat comprise example implementations of the RAN104and the core network106, respectively. The RAN104, for instance the RAN104c, may be an access service network (ASN) that employs IEEE 802.16 radio technology to communicate with the WTRUs102a,102b, and102cover the air interface116. As described herein, the communication links between the different functional entities of the WTRUs102a,102b,102c, the RAN104c, and the core network106cmay be defined as reference points.

As shown inFIG. 1E, the RAN104cmay include base stations102a,102b,102c, and an ASN gateway141, though it should be appreciated that the RAN104cmay include any number of base stations and ASN gateways while remaining consistent with an embodiment. The base stations102a,102b,102cmay each be associated with a particular cell (not shown) in the RAN104cand may each include one or more transceivers for communicating with the WTRUs102a,102b,102cover the air interface116. In one embodiment, the base stations140g,140h,140imay implement MIMO technology. Thus, the base station140g, for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU102a. The base stations140g,140h,140imay also provide mobility management functions, such as handoff triggering, tunnel establishment, radio resource management, traffic classification, quality of service (QoS) policy enforcement, and the like. The ASN Gateway141may serve as a traffic aggregation point and may be responsible for paging, caching of subscriber profiles, routing to the core network106c, and the like.

The air interface116between the WTRUs102a,102b,102cand the RAN104cmay be defined as an R1 reference point that implements the IEEE 802.16 specification. In addition, each of the WTRUs102a,102b, and102cmay establish a logical interface (not shown) with the core network106c. The logical interface between the WTRUs102a,102b,102cand the core network106cmay be defined as an R2 reference point, which may be used for authentication, authorization, IP host configuration management, and/or mobility management.

The communication link between each of the base stations140g,140h,140imay be defined as an R8 reference point that includes protocols for facilitating WTRU handovers and the transfer of data between base stations. The communication link between the base stations140g,140h,140iand the ASN gateway141may be defined as an R6 reference point. The R6 reference point may include protocols for facilitating mobility management based on mobility events associated with each of the WTRUs102a,102b,102c.

As shown inFIG. 1E, the RAN104cmay be connected to the core network106c. The communication link between the RAN104cand the core network106cmay defined as an R3 reference point that includes protocols for facilitating data transfer and mobility management capabilities, for example. The core network106cmay include a mobile IP home agent (MIP-HA)144, an authentication, authorization, accounting (AAA) server156, and a gateway158. While each of the foregoing elements is depicted as part of the core network106c, it should be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator.

The MIP-HA may be responsible for IP address management, and may enable the WTRUs102a,102b, and102cto roam between different ASNs and/or different core networks. The MIP-HA154may provide the WTRUs102a,102b,102cwith access to packet-switched networks, such as the Internet110, to facilitate communications between the WTRUs102a,102b,102cand IP-enabled devices. The AAA server156may be responsible for user authentication and for supporting user services. The gateway158may facilitate interworking with other networks. For example, the gateway158may provide the WTRUs102a,102b,102cwith access to circuit-switched networks, such as the PSTN108, to facilitate communications between the WTRUs102a,102b,102cand traditional landline communications devices. In addition, the gateway158may provide the WTRUs102a,102b,102cwith access to the networks112, which may include other wired or wireless networks that are owned and/or operated by other service providers.

Although not shown inFIG. 1E, it should be appreciated that the RAN104cmay be connected to other ASNs and the core network106cmay be connected to other core networks. The communication link between the RAN104cthe other ASNs may be defined as an R4 reference point, which may include protocols for coordinating the mobility of the WTRUs102a,102b,102cbetween the RAN104cand the other ASNs. The communication link between the core network106cand the other core networks may be defined as an R5 reference point, which may include protocols for facilitating interworking between home core networks and visited core networks.

A WTRU operating within a single serving cell of an LTE system (e.g., in accordance with 3GPP Releases 8, 9, 10 and/or future releases (hereinafter “R8+”)) may support transmission rates up to 100 Mbps for transmissions on a downlink (DL), and up to 50 Mbps for transmissions on an uplink (UL) for a 2×2 (e.g., dual-antenna MIMO) configuration. The DL transmission scheme of an LTE system may be based on an OFDMA air interface. In accordance with R8+, an LTE system may support scalable transmission bandwidth. For example, transmission bandwidth may scale up and/or down using any of a defined set of bandwidths, for instance 1.4 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz or 20 MHz within which roughly 6, 15, 25, 50, 75, 100 resource blocks, respectively, may be transmitted.

In R8+LTE systems, (e.g., systems in accordance with 3GPP Releases 10 and/or future releases (hereinafter “R10+”) that may support carrier aggregation), each radio frame may have a duration of approximately 10 milliseconds (ms), and may be formed from ten substantially equally-sized sub-frames, such subframe SF1depicted inFIG. 2. Each subframe may have a duration of approximately 1 ms. Each sub-frame may be formed from two substantially equally-sized timeslots, such as TS1and TS2of SF1. Each timeslot may have a duration of approximately 0.5 ms. Each timeslot may comprise (and may be decomposed into) a respective number of symbols, for example seven OFDM symbols in accordance with a regular cyclic prefix (CP) length, six OFDM symbols in accordance with an extended cyclic prefix (CP) length, or the like.

Each subframe may comprise a first resource block (RB) and a second RB, such as RB1and RB2, respectively, that may define a resource block pair. Each resource block of each pair may be associated with a particular timeslot of each subframe. Each subframe, may comprise (and may be decomposed into) twelve subcarriers, such as subcarriers SC1-SC12. The twelfth subcarrier (SC12) may be referred to as the last subcarrier of the subframe. The subcarriers may be configured in accordance with predefined subcarrier spacing. For instance, in accordance with R8 and R9 LTE systems, the subcarrier spacing may be 15 kHz. In an alternative, reduced sub-carrier spacing mode, the sub-carrier spacing may be 7.5 kHz.

Each subcarrier may comprise (and may be decomposed into) a plurality of resource elements. Each resource element (RE) may correspond to a select sub-carrier during a select OFDM symbol interval. Twelve consecutive subcarriers during a timeslot may form one RB. In accordance with an example of normal CP length, each RB, such as each of RB1and RB2, may comprise 84 REs, (12 subcarriers×7 OFDM symbols). Accordingly, each subcarrier may include a plurality of REs in accordance with the CP length employed, for instance SC1-SC12each comprising RE1-RE7associated with RB1and RE1-RE7associated with RB2.

In each timeslot of each subcarrier, respectively, each RE1may be referred to as a first resource element of the timeslot, each RE2may be referred to as a second resource element of the timeslot, each RE3may be referred to as a third resource element of the timeslot, each RE4may be referred to as a fourth resource element of the timeslot, each RE5may be referred to as the third resource element of the timeslot, each RE6may be referred to as the sixth resource element of the timeslot, and each RE7may be referred to as one or both of the seventh resource element of the timeslot and the last resource element of the timeslot. In this regard, each timeslot may comprise a respective plurality of resource elements (e.g., RE1-RE7) that are ordered from a first resource element (e.g., RE1) to a last resource element (e.g., RE7). If extended CP is employed, each timeslot may only contain six REs, and each RE6may therefore be referred to as one or both of the sixth resource element of the timeslot and the last resource element of the timeslot.

A carrier (e.g., a DL carrier) may include a scalable number of resource blocks, for instance from 6 RBs to 110 RBs. The number of RBs may be scaled up and/or down in accordance with overall scalable transmission bandwidth, for instance in accordance with any herein described pre-defined bandwidth.

A basic time-domain unit for dynamic scheduling may be one subframe (e.g., two consecutive timeslots), and may be referred to as a resource block pair.

Select subcarriers on some OFDM symbols may be allocated to carry pilot signals in the time-frequency grid. A select number of subcarriers at edges of the transmission bandwidth may not be transmitted, for example, to comply with spectral mask requirements.

A number of multi-antenna transmission modes may be supported. In LTE systems, each multi-antenna transmission modes may be referred to as a select transmission mode (TM). The TMs may differ relative to each other, for example in input-to-antenna-port mapping and/or in what reference signals may be used for demodulation. Transmission modes defined for Downlink Shared Channel (DL-SCH) transmissions may include: TM1(single-antenna transmission); TM2(transmit diversity); TM3(open-loop codebook-based precoding if more than one layer, else transmit diversity if rank-one transmission); TM4(closed-loop codebook-based precoding); TM5(multi-user-MIMO version of TM4); TM6(codebook-based precoding limited to single layer transmission); TM7(R8 non-codebook-based precoding with single layer transmission); TM8(R9 non-codebook-based precoding supporting up to two layers) and TM9(R10 non-codebook-based precoding supporting up to eight layers).

In R8+LTE systems, a UE may receive one or more reference signals (RS) on the DL. Reference signals may include cell-specific reference signals (CRS), demodulation reference signals (DM-RS) that may be UE-specific, and/or channel state information (CSI) RS (CSI-RS).

A UE may use a CRS for channel estimation for coherent demodulation of any DL physical channel. An exception may include a Physical Multicast data Channel (PMCH) and/or a Physical Data Shared Channel (PDSCH), which may be configured with TM7, TM8or TM9. A UE may use a CRS for channel state information (CSI) measurements. A UE may use a CRS for cell-selection and/or mobility-related measurements. A CRS may be received in any subframe. There may be one CRS for each antenna ports (e.g., 1, 2, or 4). A CRS may occupy at least the first and third-to-last OFDM symbol of each time slot.

A DM-RS may be specific to a select UE. A UE may use a DM-RS for channel estimation, for example for demodulation of a PDSCH configured with TM7, TM8or TM9. A DM-RS may be transmitted in resource blocks assigned to the PDSCH transmission for a select UE.

A UE may use a CSI-RS for CSI measurements. CSI-RSs may only be used for TM9, and may be less densely transmitted by a network than CRSs.

A UE may be configured with one or more carrier segments for a given serving cell. If carrier aggregation is configured, the serving cell may be any of a Primary Cell (PCell) and a Serving Cell (SCell) of the UE's configuration. Each carrier segment may define a set of physical RBs available to the UE that may not be members of an addressable set of RBs supported for the given serving cell. Each of the carrier segments may be appended to the supported set of RBs (supported-RB set) and/or to other carrier segments. Carrier segments may be appended in a number of ways. For example, carrier segments may be appended so as to form a contiguous bandwidth extension to the supported-RB set (and/or to other carrier segments appended to the supported-RB set and/or other carrier segments).

Referring toFIG. 3, a block diagram illustrating an example DL RB-grid structure for a WTRU configured with a plurality of carrier segments is shown. This DL RB-grid structure may define an addressable superset of RBs that includes the supported-RB set and two carrier segments appended as contiguous bandwidth extensions to the supported-RB set. The illustrated DL RB-grid structure (hereinafter “extended-RB-superset structure”) may be part of, integrated into and/or associated with a UE physical resource map on which transmissions (uplink or downlink) may be scheduled by the network.

As shown inFIG. 3, the extended-RB-superset structure may have a carrier bandwidth, B. The bandwidth B may be an aggregation of carrier bandwidths B0, BDand BUof the supported-RB set, carrier SEGMENT1and carrier SEGMENT2, respectively. The supported-RB bandwidth B0may be a bandwidth supported for the given serving cell, and may be defined by a standard to which the associated serving cell conforms. When configured to operate on the associated serving cell, the UE may initially operate using the supported-RB bandwidth B0. The UE may be subsequently configured to operate using one or both of the carrier-segment bandwidths BD, BUin addition to (or at least partially, in lieu of) supported-RB bandwidth B0.

A UE may be configured with one or more serving cells on which it operates according to one or more extension carriers; each of which may be a frequency on which the UE may operate. The serving cells may include a SCell of the UE's multicarrier configuration. The SCell may be configured with uplink resources (e.g., SCell DL and SCell UL), without uplink resources (e.g., SCell DL only) and/or only uplink resources (e.g., SCell UL only). The SCell may be configured with SCell UL only, when, for example, the SCell UL is in substantially the same band as the PCell of the UE's configuration.

The UE may perform one or more of the following for a SCell configured as an extension carrier. The may receive downlink transmissions, such as SCell DL (e.g., on PDSCH). The UE may perform uplink transmissions, such as SCell UL (e.g., on PUSCH). The UE may receive reference signals (e.g., one or more cell-specific CRSs, one or more UE-specific DM-RSs, and/or one or more CSI-RSs). The UE may transmit Sounding and Reference Signals (SRS) signals.

The UE may not perform one or more of the following for a serving cell configured as an extension carrier. The UE may receive primary synchronization signals (PSS) and/or secondary synchronization signals (SSS). The UE may receive broadcasted System Information (SI) (e.g., on a broadcast channel (BCCH) if present). The UE may receive and/or decode downlink control signaling on physical control channels of the associated serving cell (e.g., a Physical Data Control Channel (PDCCH) and/or a Physical Hybrid ARQ Indicator Channel (PHICH) and/or a Physical Control Format Indicator Channel (PCFICH) if present).

A component carrier (CC) may include a frequency on which a UE operates. A UE may receive one or more transmissions on a downlink CC (DL CC). A DL CC may include at least one DL physical channel, such as a plurality of DL physical channels. For an LTE system, downlink physical channels may include a Physical Control Format Indicator Channel (PCFICH), a Physical Hybrid ARQ Indicator Channel (PHICH), a Physical Data Control Channel (PDCCH), a Physical Multicast data Channel (PMCH) and/or a Physical Data Shared Channel (PDSCH). On the PCFICH, the UE may receive control data (e.g., indicating the size of a control region of the DL CC). On the PHICH, a UE may receive control data (e.g., indicating HARQ Acknowledgement/Negative Acknowledgement (HARQ A/N, HARQ ACK/NACK, or HARQ-ACK) feedback for a previous uplink transmission. On a PDCCH, a UE may receive downlink control information (DCI) messages, which may be used for scheduling of downlink and/or uplink resources. On a PDSCH, a UE may receive user and/or control data.

A UE may perform one or more transmissions on an uplink CC (UL CC). An UL CC may include at least one UL physical channel, such as a plurality of UL physical channels. A UE may transmit on an uplink CC (UL CC). For an LTE system, uplink physical channels may include a Physical Uplink Control Channel (PUCCH) and/or a Physical Uplink Shared Channel (PUSCH). On a PUSCH, a UE may transmit user and/or control data. On a PUCCH, and in some cases on a PUSCH, the UE may transmit uplink control information (e.g., CQI/PMI/RI or SR) and/or hybrid automatic repeat request (HARQ) acknowledgement/negative acknowledgement (ACK/NACK) feedback. On a UL CC, the UE may be allocated dedicated resources for transmission of Sounding and Reference Signals (SRS).

A cell may comprise a DL CC that may be linked to a UL CC, for instance based on the system information (SI) received by the UE broadcasted on the DL CC and/or using dedicated configuration signaling from the network. For example, when broadcasted on the DL CC, the UE may receive the uplink frequency and bandwidth of the linked UL CC as part of the system information element (e.g., when in RRC_IDLE for LTE, or when in idle/CELL_FACH for WCDMA (when the WTRU does not yet have a radio resource connection to the network)).

A Primary Cell (PCell) may comprise a cell operating on a primary frequency in which the UE performed initial access to the system (e.g., in which the UE performed an initial connection establishment procedure or initiated a connection re-establishment procedure), a cell indicated as a primary cell in a handover procedure, or the like. A PCell may correspond to a frequency indicated as part of a radio resource connection configuration procedure. Some functions may be only supported on a PCell. For example, the UL CC of a PCell may correspond to a CC whose physical uplink control channel resources may be configured to carry HARQ ACK/NACK feedback for a given UE.

For example, in LTE systems, a UE may use a PCell to derive parameters for security functions and/or for upper layer system information such as NAS mobility information. Other functions that may be supported on a PCell DL include system information (SI) acquisition, change monitoring procedures on a broadcast channel (BCCH), paging, and the like.

A Secondary Cell (SCell) may include a cell operating on a secondary frequency that may be configured once a radio resource control connection is established and that may be used to provide additional radio resources. System information relevant for operation in a SCell may be provided using dedicated signaling (e.g., when a SCell is added to the UE's configuration). Although associated parameters may have different values than those broadcast on the downlink of a SCell using the system information (SI) signaling, this information may be referred to as SI of the concerned SCell, independently of how the UE acquires the information.

PCell DL and PCell UL may correspond to the DL CC and the UL CC of the PCell, respectively. SCell DL and SCell UL may correspond to the DL CC and the UL CC (if configured) of a SCell, respectively.

A serving cell may include a primary cell (PCell) or a secondary cell (SCell). For a UE that is not configured with a SCell or that does not support operation on multiple component carriers (e.g., does not support carrier aggregation), there may be only one serving cell comprising the PCell. For a UE that is configured with at least one SCell, serving cells may include a set of one or more cells comprising the PCell and one or more configured SCells.

When a UE is configured with at least one SCell, there may be one PCell DL and one PCell UL and, for each configured SCell, there may be one SCell DL and one SCell UL (if configured).

In accordance with a LTE R10 DL, for a given antenna port, DM-RS may be transmitted only on resource blocks that a corresponding PDSCH is mapped to, and may be transmitted only in a predefined set of OFDM symbols in a subframe. For example, as depicted inFIG. 4, using normal CP for antenna ports A and B (which may be any of antenna ports7,8. . . and/or,14), DM-RSs may be transmitted in the sixth and seventh OFDM symbol (e.g., RE6and RE7) in each timeslot in a subframe.

The illustrated locations of OFDM symbols for DM-RS may be used because other physical channels and/or signals (e.g., PDCCH and CRS) may be mapped to other OFDM symbols. For example, a PDCCH region may be expanded to REs in one or more, up to the first three OFDM symbols (e.g., RE1up to RE3) in at least the first timeslot in a subframe. As such, it may not be desirable to locate DM-RS in any of the first three OFDM symbols in the first timeslot where PDCCH may be transmitted. In addition, the CRS for one or more antenna ports (e.g., 0, 1, 2, 3) may be placed in REs in one or more of the first, second, and/or fourth OFDM symbols (e.g., RE1, RE2, and RE4) in each timeslot in a subframe. As such, the sixth and seventh symbols (e.g., in the first timeslot (TS1)) may be desirable locations for DM-RS transmission in a DL.

In accordance with locating DM-RSs in the sixth and seventh OFDM symbols, channel estimation for the first OFDM symbol through the fifth OFDM symbol in the first timeslot may have to be performed (e.g., using an extrapolation based on DM-RS in the sixth and seventh OFDM symbols in the first timeslot). Extrapolation based channel estimation may result in PDSCH performance degradation. As described herein, DM-RS locations for extension carriers and/or carrier segments may be adapted (e.g., to perform channel estimation in extension carriers and/or carrier segments without using extrapolation based channel estimation).

In the absence of synchronization signals (e.g., PSS/SSS) in extension carriers, synchronization operation in an associated serving cell may not be performed properly, unless there is a signal which may be used to assist the synchronization operation. Various CRS for extension carriers and/or carrier segments may be adapted for several purposes, including, for example, synchronization.

In a DL resource grid structure (e.g., in accordance with LTE R10), the RE locations for DM-RSs for respective configured antenna ports (e.g., RE6and RE7) may be selected based at least in part upon exclusion of RE positions reserved for the PDCCH region and CRS of a serving cell. As described herein, one or more extension carriers and/or carrier segments may be configured with various mappings of RE locations to DM-RSs for one or more configured antenna ports for a UE. The RE-to-DM-RS mappings for extension carriers and/or carrier segments may be configured in an absence of LTE R10 restrictions (e.g., selecting RE positions for DM-RSs based upon PDCCH and/or CRS), for instance because the PDCCH and/or CRS may not be configured for extension carriers and/or carrier segments. RE locations for DM-RSs may take precedence over the RE positioning for one or both of the PDCCH and/or CRS.

With continued reference toFIG. 4, DM-RSs may be located in the sixth and seventh OFDM symbols (e.g., RE6and RE7) in each timeslot (e.g., TS1and TS2) of a subframe, for example, for two antenna ports A and B, respectively, and using normal CP, where an orthogonal cover code (OCC) sequence of 4 bits may be applied to two pairs of two consecutive reference symbols, for example to separate multiple RSs, for example, on antenna port7and8.

It may be assumed that DM-RS based channel estimation for data demodulation operates on a per subframe basis (e.g., no interpolation technique is used between adjacent subframes for channel estimation). Accordingly, channel estimation for OFDM symbols prior to the sixth OFDM symbol in the first timeslot in a subframe may be carried out using some form of extrapolation based channel estimation. However extrapolation based channel estimation may cause performance of the PDSCH to be degraded. In extension carriers and/or carrier segments, the PDSCH may start from the first OFDM symbol in the first timeslot.

Use of extrapolation based channel estimation in extension carriers and/or carrier segments, which may be collectively referred to as extension resource carriers, may be avoided. For example, mapping of REs to OFDM symbols for DM-RS in extension resource carriers, which may be referred to as extension DM-RS structure and/or mapping (e.g. in the first timeslot in a subframe), may include mapping DM-RSs to RE positions that may correspond to earlier OFDM symbols (e.g., REs used for the PDCCH and/or CRS in LTE R10). Any suitable component of a communications system may be configured to employ extension DM-RS structure and/or mapping (e.g., a UE, a component of a CN, or the like).

Referring now toFIG. 5, in accordance with an example of extension DM-RS structure and/or mapping, DM-RSs for antenna ports A and B (e.g., antenna ports7and8of a corresponding UE with normal CP) may be positioned in (e.g., inserted into, appended to, etc.) REs in one or more respective OFDM symbols (e.g., RE1and RE2) in the first timeslot (e.g., TS1) of at least one subcarrier (e.g., SC2, SC7, and/or SC12). The DM-RSs may be positioned in the first timeslot at any time relative to transmission of the subcarrier (e.g., prior to transmission, substantially at the time of transmission, etc.). The subcarrier may be transmitted by any suitable component of a communication system (e.g., by an eNB).

In this regard, extension DM-RS structure and/or mapping may include transmitting a first timeslot (e.g., TS1) of a subcarrier (e.g., SC2). The first timeslot may have a first plurality of resource elements that are ordered from a first resource element to a last resource element (e.g., RE1-RE7). Transmitting the first timeslot may include transmitting a first symbol in a select one of the first plurality of resource elements (e.g., RE1) that may not be the last resource element. The first symbol may be a demodulation reference signal (e.g., a UE-specific DM-RS). Transmitting the first timeslot may include transmitting a second symbol in the last resource element of the first plurality of resource elements (e.g., RE7), wherein the second symbol is other than a demodulation reference signal (e.g., not a UE-specific DM-RS). For example, the second symbol may include OFDM symbols comprising voice and/or data information. Transmitting the first timeslot may include transmitting a third symbol in a second select one of the first plurality of resource elements (e.g., RE2) that may not be the last resource element. The third symbol may be a demodulation reference signal (e.g., a UE-specific DM-RS).

In accordance with the illustrated example of extension DM-RS structure and/or mapping, the first and second select ones of the plurality of resource elements (e.g., RE1and RE2), respectively, may be adjacent to one another in the first timeslot.

Further in accordance with the illustrated example of extension DM-RS structure and/or mapping, DM-RSs for antenna ports A and B (e.g., antenna ports7and8of a corresponding UE with normal CP) may be positioned in REs in one or more respective OFDM symbols (e.g., RE6and RE7) in the second timeslot (e.g., TS2) of at least one subcarrier (e.g., SC2, SC7, and/or SC12).

In this regard, extension DM-RS structure and/or mapping may include transmitting a second timeslot (e.g., TS2) of the subcarrier (e.g., SC2). The second timeslot may have a second plurality of resource elements that are ordered from a first resource element to a last resource element (e.g., RE1-RE7). Transmitting the second timeslot may include transmitting a fourth symbol in a select one of the second plurality of resource elements (e.g., RE6). The fourth symbol may be a demodulation reference signal (e.g., a UE-specific DM-RS). Transmitting the second timeslot may include transmitting a fifth symbol in a select one of the second plurality of resource elements (e.g., RE7). The fifth symbol may be a demodulation reference signal (e.g., a UE-specific DM-RS).

The UE-specific DM-RSs of the first and second timeslots may be located in different RE locations (e.g., RE1and RE2of TS1and RE6and RE7of TS2). The UE-specific DM-RSs of the first timeslot (e.g., TS1) may be located in a first position relative to the plurality of resource elements of the first timeslot (which may be referred to as a first plurality of reference elements) and the UE-specific DM-RSs of the second timeslot may be located in a second position relative to the second plurality of resource elements of the second timeslot TS2, such that the first position may be different relative to the first position. In this regard, the first symbol and the third symbol may be located in different positions relative to the first and second pluralities of resource elements, respectively.

In the illustrated example of extension DM-RS structure and/or mapping, an interval between two pairs of consecutive reference symbols (e.g., in time) within a subframe may be longer with respect to the DM-RS structure illustrated inFIG. 4. However the illustrated extension DM-RS structure and/or mapping may enable interpolation-based channel estimation (e.g., for PDSCH demodulation to be carried out).

FIG. 6depicts another example of extension DM-RS structure and/or mapping for antenna ports A and B (e.g., antenna ports7and8of a corresponding UE with normal CP). In accordance with the illustrated example, DM-RSs may be positioned in (e.g., inserted into, appended to, etc.) REs in one or more respective OFDM symbols (e.g., RE3and RE4) in the first timeslot (e.g., TS1) and REs in one or more respective OFDM symbols (e.g., RE4and RE5) in the second timeslot (e.g., TS2) of at least one subcarrier (e.g., SC2, SC7, and SC12). The illustrated extension DM-RS structure and/or mapping may enable interpolation based channel estimation (e.g., for PDSCH demodulation to be carried out).

FIG. 7depicts another example of extension DM-RS structure and/or mapping for antenna ports A and B (e.g., antenna ports7and8of a corresponding UE with normal CP). In accordance with the illustrated example, DM-RSs may be positioned in (e.g., inserted into, appended to, etc.) REs in one or more respective OFDM symbols (e.g., RE1and RE2) in the first timeslot (e.g., TS1) of a first subcarrier (e.g., SC2) and REs in one or more respective OFDM symbols (e.g., RE6and RE7) in the second timeslot (e.g., TS2) of the first subcarrier. In a second subcarrier (e.g., SC7) DM-RSs may be positioned in different OFDM symbol locations than in the first subcarrier. For example, DM-RSs may be positioned in REs in one or more respective OFDM symbols (e.g., RE5and RE6) in the first timeslot (e.g., TS1) and in REs in one or more respective OFDM symbols (e.g., RE2and RE3) in the second timeslot (e.g., TS2) of the second subcarrier.

In this regard, extension DM-RS structure and/or mapping may include transmitting a first timeslot (e.g., TS1) of a first subcarrier (e.g., SC2). The first timeslot of the first subcarrier may have a first plurality of resource elements that are ordered from a first resource element to a last resource element (e.g., RE1-RE7). Transmitting the first timeslot of the first subcarrier may include transmitting a first symbol in a select one of the first plurality of resource elements (e.g., RE1) that may not be the last resource element. The first symbol may be a demodulation reference signal (e.g., a UE-specific DM-RS). Transmitting the first timeslot of the first subcarrier may include transmitting a second symbol in the last resource element of the first plurality of resource elements (e.g., RE7), wherein the second symbol is other than a demodulation reference signal (e.g., not a UE-specific DM-RS). For example, the second symbol may include OFDM symbols comprising voice and/or data information.

In accordance with the illustrated example, extension DM-RS structure and/or mapping may include transmitting a first timeslot of a second subcarrier (e.g., SC7). The first timeslot of the second subcarrier may have a plurality of resource elements (which may be referred to as a second plurality of resource elements) that are ordered from a first resource element to a last resource element (e.g., RE1-RE7). Transmitting the first timeslot of the second subcarrier may include transmitting a third symbol in a select one of the second plurality of resource elements (e.g., RE5) of the first timeslot of the second subcarrier. The third symbol may be a demodulation reference signal (e.g., a UE-specific DM-RS). Transmitting the first timeslot of the second subcarrier may include transmitting a fourth symbol in the last resource element of the second plurality of resource elements (e.g., RE7), wherein the fourth symbol is other than a demodulation reference signal (e.g., not a UE-specific DM-RS). For example, the fourth symbol may include OFDM symbols comprising voice and/or data information.

In a third subcarrier (e.g., SC12) DM-RSs may be positioned in different OFDM symbol locations than in the second subcarrier. For example, DM-RSs may be positioned in REs in one or more respective OFDM symbols (e.g., RE1and RE2) in the first timeslot (e.g., TS1) of the third subcarrier and in REs in one or more respective OFDM symbols (e.g., RE6and RE7) in the second timeslot (e.g., TS2) of the third subcarrier. In this regard, the DM-RS symbols of the third subcarrier may be located in substantially the same locations relative to the DM-RS symbols of the first subcarrier. The first, second, and third subcarriers may be staggered with respect to each other, such that at least one subcarrier that may not have DM-RSs may disposed between the first and second subcarriers and/or at least one other subcarrier that may not have DM-RS symbols may be disposed between the second and third subcarriers.

The UE-specific DM-RSs of the first and second subcarriers (e.g., SC2and SC7) may be located in different RE locations (e.g., RE1and RE2of SC12and RE5and RE6of SC7), the UE-specific DM-RSs of the first subcarrier may be located in a first position relative to the plurality of resource elements of the first timeslot TS1of the first subcarrier (which may be referred to as a first plurality of reference elements) and the UE-specific DM-RSs of the second subcarrier may be located in a second position relative to the second plurality of resource elements of the first timeslot of the second subcarrier, such that the first position may be different relative to the first position. In this regard, the first symbol and the third symbol may be located in different positions relative to the first and second pluralities of resource elements, respectively. The UE-specific DM-RS symbols of the first subcarrier and the UE-specific DM-RS symbols of the second subcarrier may be located in different positions relative to the first and second pluralities of resource elements, respectively. The UE-specific DM-RS symbols of the second subcarrier and the UE-specific DM-RS symbols of the third subcarrier may be located in different positions relative to the respective pluralities of resource elements of first timeslots of the second and third subcarriers. The UE-specific DM-RS symbols of the first subcarrier and the UE-specific DM-RS symbols of the third subcarrier may be located in substantially the same positions relative to the respective pluralities of resource elements of first timeslots of the first and third subcarriers.

With continuing reference toFIG. 7, the illustrated extension DM-RS structure and/or mapping may comprise a pair-wise time-domain staggering of N OFDM symbols within a subframe. Pair-wise time-domain staggering may provide accurate channel estimation and/or measurements when channels vary non-monotonically in both time and frequency domains (e.g., channel peak or sink occurs in the middle of the RB). A frequency-domain staggering of M subcarriers for the RS within a RB and/or a subframe may be applied. A combination of time-domain staggering and frequency-domain staggering may be applied.

In the examples of extension DM-RS structure and/or mapping depicted inFIGS. 5-7, DM-RSs may be positioned in REs in two consecutive OFDM symbols (in time) (e.g., RE1and RE2inFIG. 5) in each timeslot in a subframe. The consecutive OFDM symbols may be paired. Two pairs of consecutive reference symbols (e.g., four reference symbols in a single subcarrier) in a subframe may be covered (e.g., spread and/or multiplied) by a 4-bit OCC sequence, so that Extension DM-RSs for multiple antenna ports (e.g., antenna ports7and8) may be separated (e.g., using CDM in the receiver). Alternatively, a set of the OCC sequences (e.g., OCC sequences used for LTE R10 DM-RS) may be applied for extension DM-RS structure and/or mapping (e.g., as depicted in shown inFIGS. 5-7).

FIG. 8depicts another example of extension DM-RS structure and/or mapping for antenna ports A and B (e.g., antenna ports7and8of a corresponding UE with normal CP). In accordance with the illustrated example, DM-RSs may be separated from each other by one or more non-DM-RS OFDM symbols, such that no two DM-RSs are consecutive in time. For example, DM-RSs may be positioned in (e.g., inserted into, appended to, etc.) REs in one or more respective OFDM symbols (e.g., RE1and RE5) in the first timeslot (e.g., TS1) of at least one subcarrier (e.g., SC2, SC7, and SC12) and in REs in one or more respective OFDM symbols (e.g., RE2and RE7) in the second timeslot (e.g., TS2) of the at least one subcarrier. In this regard, first and second select ones of a first plurality of resource elements of the first timeslot that carry respective DM-RSs (e.g., RE1and RE5) respectively, are spaced apart from one another in the first timeslot, and first and second select ones of a second plurality of resource elements of the second timeslot that carry respective DM-RSs (e.g., RE2and RE7) respectively, are spaced apart from one another in the second timeslot.

The illustrated example of extension DM-RS structure and/or mapping may provide channel estimation using an interpolation technique. Because the four DM-RSs symbols are not consecutive in time, a DM-RS orthogonality property might not be maintained in, for example, fast varying channel conditions (e.g., for high mobility UEs).

FIGS. 9A-Bdepicts an example of extension DM-RS structure and/or mapping for multiple antenna ports A, B, C, and D (e.g., antenna ports7,8,9, and10of a corresponding UE with normal CP). In accordance with the illustrated example, DM-RSs for antenna port A may be positioned in (e.g., inserted into, appended to, etc.) REs in one or more respective OFDM symbols (e.g., RE5) in the first timeslot (e.g., TS1) of at least one subcarrier (e.g., SC4and SC10) and in REs in one or more respective OFDM symbols (e.g., RE5) in the second timeslot (e.g., TS2) of the at least one subcarrier. The first and second subcarriers may be staggered with respect to each other. DM-RSs for antenna port B may be positioned in REs in one or more respective OFDM symbols (e.g., RE1) in the first timeslot (e.g., TS1) of a first subcarrier (e.g., SC1) and in REs in one or more respective OFDM symbols (e.g., RE1) in the second timeslot (e.g., TS2) of the first subcarrier and may be positioned in REs in one or more respective OFDM symbols (e.g., RE5) in the first timeslot (e.g., TS1) of a second subcarrier (e.g., SC10) and in REs in one or more respective OFDM symbols (e.g., RE5) in the second timeslot (e.g., TS2) of the second subcarrier. The first and second subcarriers may be staggered with respect to each other.

In this regard, extension DM-RS structure and/or mapping may include transmitting a first timeslot (e.g., TS1) of a subcarrier (e.g., SC4). The first timeslot may have a first plurality of resource elements that are ordered from a first resource element to a last resource element (e.g., RE1-RE7). Transmitting the first timeslot may include transmitting a first symbol in a select one of the first plurality of resource elements (e.g., RE5) that may not be the last resource element. The first symbol may be a demodulation reference signal (e.g., a UE-specific DM-RS). Transmitting the first timeslot may include transmitting a second symbol in the last resource element of the first plurality of resource elements (e.g., RE7), wherein the second symbol is other than a demodulation reference signal (e.g., not a UE-specific DM-RS).

Extension DM-RS structure and/or mapping may include transmitting a second timeslot (e.g., TS2) of the subcarrier (e.g., SC4). The second timeslot may have a second plurality of resource elements that are ordered from a first resource element to a last resource element (e.g., RE1-RE7). Transmitting the second timeslot may include transmitting a third symbol in a select one of the second plurality of resource elements (e.g., RE5). The third symbol may be a demodulation reference signal (e.g., a UE-specific DM-RS).

The UE-specific DM-RSs of the first and second timeslots may be located in substantially the same locations relative to their respective pluralities of reference elements (e.g., RE5of TS1and RE5of TS2). Stated differently, the UE-specific DM-RS of the first timeslot may be located in a first position relative to the plurality of resource elements of the first timeslot TS1(which may be referred to as a first plurality of reference elements) and the UE-specific DM-RS of the second timeslot may be located in a second position relative to the second plurality of resource elements of the second timeslot TS2, such that the first position may be substantially the same relative to the first position. In this regard, the first symbol and the third symbol may be located in substantially equivalent positions relative to the first and second pluralities of resource elements, respectively.

Transmitting a first timeslot of a second subcarrier (e.g., SC10) may include transmitting a fourth symbol in a select one of a first plurality of resource elements (e.g., RE5) of the first timeslot of the second subcarrier. The fourth symbol may be a demodulation reference signal (e.g., a UE-specific DM-RS). Transmitting a second timeslot of the second subcarrier (e.g., SC10) may include transmitting a fifth symbol in a select one of a second plurality of resource elements (e.g., RE5) of the second timeslot of the second subcarrier. The fifth symbol may be a demodulation reference signal (e.g., a UE-specific DM-RS).

Further in accordance with the illustrated example of extension DM-RS structure and/or mapping, overhead of DM-RS may be limited (e.g., in PDSCH transmission on an extension carrier and/or carrier segments). For example, extension DM-RS structure and/or mapping for one or more antenna ports (e.g., antenna ports9and10) may be transmitted using a lower DM-RS density in the time and/or the frequency domains. For example, DM-RSs for antenna port C may be positioned in REs in one or more respective OFDM symbols (e.g., RE2) in the first timeslot (e.g., TS1) of a first subcarrier (e.g., SC1) and may be positioned in REs in one or more respective OFDM symbols (e.g., RE2) in the second timeslot (e.g., TS2) of a second subcarrier (e.g., SC10). The first and second subcarriers may be staggered with respect to each other. DM-RSs for antenna port D may be positioned in REs in one or more respective OFDM symbols (e.g., RE2) in the first timeslot (e.g., TS1) of a first subcarrier (e.g., SC10) and may be positioned in REs in one or more respective OFDM symbols (e.g., RE2) in the second timeslot (e.g., TS2) of a second subcarrier (e.g., SC1). The first and second subcarriers may be staggered with respect to each other.

It should be appreciated that extension DM-RS (e.g., UE-specific DM-RS) structure and/or mapping is not limited to the examples illustrated and described herein, and that extension DM-RS structure and/or mapping may include any other combinations of DS-RSs varied in one or both of the time and frequency domains (e.g., using the RE resource grid).

One or more (e.g., all) of the herein disclosed extension DM-RS structure and/or mapping examples, configurations, and/or patterns may be used to configure UEs. UEs may be configured with any of the set (e.g., all) of the Extension DM-RS structure and/or mapping configurations and/or patterns. For example, a UE (e.g., in response to being configured with extension carriers and/or carrier segments) may be configured with any of the set (e.g., all) of the Extension DM-RS structure and/or mapping configurations and/or patterns (e.g., via L1 signaling and/or L2/3 signaling). A UE previously configured with extension carriers and/or carrier segments and/or any of the extension DM-RS structure and/or mapping configurations and/or patterns may be reconfigured with any of the set (e.g., all) of the extension DM-RS structure and/or mapping configurations and/or patterns via L1 signaling and/or L2/3 signaling.

Extension DM-RS structure and/or mapping configurations and/or patterns may be configured per UE and/or per extension carrier and/or carrier segment. DM-RSs may be transmitted only in RBs upon which a corresponding PDSCH is mapped. The configuration may depend on the CP type (e.g., normal CP vs. extended CP). For example, as defined in TS 36.211, for antenna ports p=7, 8, or p=7, 8, . . . , v+6, in a PRB with frequency-domain index, nPRB, assigned for s corresponding PDSCH, a part of the reference sequence r(m) may be mapped to complex-valued modulation symbols, ak,l, in a subframe as follows:

The OCC sequencewp(i) may be found, for example, in TS. 36.211.

For the extension DM-RS structure and/or mapping depicted inFIG. 6,

For the Extension DM-RS structure and/or mapping depicted inFIG. 6,

For extended CP, respective modification rules that may be substantially the same as those for normal CP may be applied. However different CP types may require one or more different rules for modifying one or more corresponding extension DM-RS structures and/or mappings.

In addition to extension DM-RS structure and/or mapping, the following DM-RS related parameters and/or variables may be configured and/or modified for extension DM-RS structure and/or mapping. OCC sequences (e.g., wp(l)) may be configured and/or modified (e.g., for all DM-RSs), including, for example, DM-RSs that are not consecutive in the time domain. Different sets and/or tables of the OCC sequences may be defined for different DM-RS structures and/or mappings. For each antenna port, p (e.g. in LTE R10), the OCC sequences and the order of their elements may be the same for three different subcarriers/REs (e.g., m′=0, 1 or 2) in an RB as shown in the expression of
ak,l(p)=wp(l′)·r(3·l′·NRBmax,DL+3·nPRB+m′).
Channel estimation from de-spreading of OCC at the receiver may only take place along the time domain for each of three subcarriers where the DM-RS symbols reside. Channel estimation of other frequency-time location within the RB may be done by interpolation and/or extrapolation (e.g., from those three estimations). The channel estimation based on this method may not be accurate for channels varying in both the time domain and the frequency domain within a RB.

For extension DM-RS structure and/or mapping, the order of the OCC sequence may be changed in the middle subcarrier (e.g., m′=1) such that de-spreading over both the frequency domain and the time domain may be possible. Accordingly, for normal cyclic prefix:

FIG. 10depicts an example OCC distribution for Extension DM-RS, which may be referred to as an Extension OCC Distribution. The Extension OCC Distribution may be a modification of OCC sequence distribution (e.g., using the example extension DM-RS structure and/or mapping depicted inFIG. 7. Seven different channel estimation values based on de-spreading of the OCC may be obtained. The channel estimation values may be used to represent channels in seven different time-frequency locations within a RB. A two dimensional interpolation and/or extrapolation may be used to obtain a channel estimation for any RE within the RB.

For reference signal (RS) mapping in the frequency domain, a mapping pattern in the frequency domain of the reference signal sequence r(m) may be modified (e.g., using subcarrier index, k, in the RS to RE mapping equation). For example,
ak,l(p)=wp(l′)·r(3·l′·NRBmax,DL+3·nPRB+m′).
for antenna ports p=7, p=8, or p=7, 8, . . . , v+6, and normal CP where k may be determined for the above mapping equation as:

For extension carriers and/or carrier segments, k may be modified, for example for frequency hopping such that frequency hopping of the set of, or a subset of, subcarriers used for the DM-RS transmission for a given UE may be performed on a subframe and/or radio frame basis. Frequency hopping for the DM-RS transmission may be configured (e.g., including enable and/or disable) per extension carrier and/or carrier segment and/or per UE.

k=5⁢⁢m′+nscRB⁢nPRB+k′k′={1+vshift1p∈{7,8,11,13}0+vshift2p∈{9,10,12,14}
where vshift1and vshift2may be cell-specific and/or UE-specific frequency shifts, may be a function of the cell-ID and/or UE ID, and/or may be set to a same value. For antenna port5(e.g., TM5), the cell-specific frequency shift, vshift, may be modified.

DM-RS performance may be improved. For example, the density of extension DM-RS may be increased by increasing the number of OFDM symbols used for DM-RS transmission, by increasing the number of REs mapped for the DM-RS in a RB, and/or by increasing both the number of OFDM symbols and the number of REs.

In order to reduce DM-RS overhead (e.g., for extension carriers and/or carrier segments, the density of Extension DM-RS may get lower in the time domain and/or the frequency domain (e.g., as depicted inFIGS. 9A-B).

In an MBSFN subframe, if a PDSCH for a given UE is transmitted in the carrier segments configured for a serving cell, the Extension DM-RS may be transmitted as in the corresponding carrier segments of a non-MBSFN subframe. The extension DM-RS defined for extended CP may be used for the carrier segments.

DM-RS transmission may be configured per extension carrier and/or per WTRU (e.g., depending upon the TM configured for the extension carrier). DM-RS transmission may be configured per carrier segments of a serving cell and/or per UE (e.g., depending on the TM configured for the carrier segments).

Extension DM-RS (e.g., UE-specific DM-RS structure and/or mapping) may be used when the use of extension carrier and/or carrier segments is configured for a UE and/or when extension DM-RS is activated for a UE.

CRS may be used for several purposes in extension carriers and/or carrier segments, including data demodulation, for example, for TM1˜6, and/or CQI reporting for TM1˜8. CRS may be used for assisting synchronization operation at a UE.

CRS may be transmitted on extension carrier and/or carrier segments when the extension carrier and/or carrier segments are configured, and/or when the extension carrier and/or carrier segments are activated.

CRS may be transmitted on extension carrier and/or carrier segments, for example so that a UE configured with extension carriers and/or carrier segments may perform measurements based on CRS, for example, to acquire CSI and/or carrier-specific time and/or frequency tracking and/or synchronization.

CSI-RS may be transmitted on extension carriers and/or carrier segments. For example, a UE may be configured with an extension carrier and/or carrier segments of a serving cell. If the UE is configured with a TM capable of supporting CSI-RS (e.g., TM9) on the extension carrier and/or carrier segments, then CSI for the UE may be transmitted on the extension carrier. Examples of configuring CRS for extension carriers and/or carrier segments may be described herein.

A CRS (e.g., the structure thereof) in an extension carrier and/or carrier segment may include fewer OFDM symbols used for CRS transmission in a subframe than the number of OFDM symbols that may be used a primary carrier CRS structure (e.g., a CRS in LTE R10).

FIGS. 11-13depict example CRS mappings and/or configurations for implementing CRSs (depicted as CS in the FIGS.) in extension carriers and/or carrier segments. The example mappings and/or configurations are depicted in terms of respective numbers of OFDM symbols that may be occupied with CRS in a subframe (e.g., using four antenna ports and normal CP).

In the example CRS mapping and/or configuration depicted inFIG. 12, CRSs may be transmitted only in the second timeslot (e.g., TS2) in a subframe, which may result in approximately a 50% CRS overhead reduction (e.g., relative to LTE R10). The number of REs used for CRS transmission per RB may be configured for each antenna port and/or for some of the antenna ports. For example, antenna ports0and1may be configured to use 4 REs per RB for CRS transmission and antenna ports2and3may be configured to use 2 REs per RB for CRS transmission. A CRS configuration may be provided for one or more UEs configured with an extension carrier and/or carrier segment (e.g., via RRC signaling and/or broadcast signaling). Configuration signaling may be provided from a serving cell linked to the extension carrier and/or from a PCell.

For extension carriers and/or carrier segments, CRS transmission with a lower density in the time domain and/or the frequency domain may perform some UE measurements, for example CQI reporting, timing tracking and/or synchronization, and/or frequency tracking and/or synchronization.

CRS may be configured to be transmitted only in certain subframes in an extension carrier and/or carrier segment (e.g. in certain subframes of one or more radio frames in an extension carrier and/or carrier segment). For example, the periodicity of CRS transmission may be configured for an extension carrier and/or carrier segment and may be provided for one or more UEs configured with the extension carrier and/or carrier segment (e.g., via RRC signaling and/or broadcast signaling). The periodicity may comprise a parameter of a configuration received by the one or more UEs. The parameter may indicate the periodicity of subframes that carry CRS. The configuration signaling may be provided from a serving cell linked to the extension carrier and/or from a PCell. One or more extension carriers and/or carrier segments may be configured not to carry CRS (e.g., by setting the periodicity of CRS transmission on the carrier to an infinite value and/or by setting a parameter for the carrier).

Transmission subframes and/or antenna ports for CRS may be configured similarly CSI-RS, for example to reduce overhead.

CRS transmission on an extension carrier and/or carrier segment may be configured dependent on the transmission mode, or modes, that the extension carrier and/or carrier segment may support. For example, if the extension carrier and/or carrier segment supports only TM9, then Extension CRS may not be transmitted on the carrier. In accordance with another example, if the extension carrier and/or carrier segment supports multiple TMs, then CRS may be configured to be transmitted on the extension carrier and/or carrier segment. Configuration signaling may be provided from a serving cell linked to the extension carrier.

The number of antenna ports for the Extension CRS transmission may be configured for each extension carrier and/or carrier segment. The antenna configuration may be provided to one or more UEs configured with the extension carrier and/or carrier segment (e.g., via RRC signaling and/or broadcast signaling). The configuration signaling may be provided from a serving cell linked to the extension carrier and/or from a PCell. An antenna configuration for the CRS transmission on the carrier may be independent of that for DM-RS and/or CSI-RS on the same carrier. A set of antenna ports for CRS transmission may be limited, for example to only two antenna ports (e.g. antenna ports0and1), for extension carriers and/or carrier segments. The antenna configuration for the linked serving cell and/or the PCell may be applied to one or more extension carriers and/or carrier segments.

Rather than transmitting CRS over an entirety of the bandwidth of an extension carrier and/or carrier segment, CRS for the carrier may be transmitted only on a limited set of RBs (e.g., including RBs upon which one or more corresponding PDSCHs for a UE or a group of UEs configured with the carrier may be mapped). The bandwidth in which the Extension CRS may be transmitted may be configured and/or provided for the UE, or group of UEs (e.g., via RRC signaling and/or broadcast signaling from the serving cell linked to the extension carrier and/or from a PCell).

Other CRS parameters may be configured for extension carriers and/or carrier segments. For example, the variable, v, and cell-specific frequency shift, vshift, which may define a position in the frequency domain for the different CRSs, may be determined differently for an extension carrier. For example, vshiftmay be set to zero for extension carriers. Accordingly, for an extension carrier and/or carrier segment, the CRS mapping pattern and/or position in the frequency domain may be different (e.g., relative to LTE R10).

The density of the CRS in the frequency domain (e.g. the number of REs to which CRS may be mapped within a RB) may be configured for an extension carrier. For example, one RE per RB per OFDM symbol may be used for CRS transmission on an extension carrier.

CRS transmission and/or a set of CRS related parameters may be configured per extension carrier and/or carrier segment, or per a group of extension carriers and/or carrier segments). CRS transmission on extension carriers and/or carrier segments may be configured depending on the CP type (e.g., normal CP or extended CP) used for the extension carrier and/or carrier segment. Configuration related signaling may be provided from a serving cell linked to the extension carrier, /or from a PCell, and/or from another serving Cell.

CRS, if configured, may be transmitted on extension carriers and/or carrier segments in an MBSFN subframe (e.g., if PMCH may not be carried on any extension carrier and/or carrier segment). In an MBSFN subframe, if PDSCH is transmitted in the carrier segments configured for a serving cell, the PDSCH transmission may use substantially the same CRS configuration for carrier segments corresponding to a non-MBSFN subframe. CRS may not be transmitted in OFDM symbols of carrier segments corresponding to the MBSFN region of the MBSFN subframe, or may not be transmitted in carrier segments in any MBSFN subframe. In an MBSFN subframe, Extension CRS defined for extension CP may be used for carrier segments.

CRS transmission may be configured per extension carrier (e.g., depending on a TM supported for the extension carrier). CRS transmission may be configured per carrier segments of a serving cell (e.g., depending on a TM supported for the carrier segments). It should be appreciated that any combination of the herein described CRS configurations may be applied for CRS configuration of one or more extension carriers and/or carrier segments.

A set of CRS structure and/or mapping configurations and/or patterns (e.g., as described herein) may be pre-defined, and may be configurable, for extension carriers and/or carrier segments. CRS structure and/or mapping configurations and/or patterns (e.g., a set of CRS structure and/or mapping configurations and/or patterns) may be used to configure one or more UEs. For example, a UE, in response to being configured with extension carriers and/or carrier segments, may be configured with one or more (e.g., a set of) CRS structure and/or mapping configurations and/or patterns (e.g., via RRC signaling and/or broadcast signaling). A UE previously configured with extension carriers and/or carrier segments and/or any CRS structure and/or mapping configurations and/or patterns may be reconfigured with one or more (e.g., a set of) CRS structure and/or mapping configurations and/or patterns (e.g., via RRC signaling and/or broadcast signaling).

CSI-RS structure and/or design may be configured for extension carriers and/or carrier segments. For example CSI-RS may be used for assisting synchronization operation for extension carriers and/or carrier segments at a UE.

Antenna ports may be redefined for CSI-RS. CSI-RS transmission may be configured per extension carrier and/or per UE (e.g., depending on a TM configured for the extension carrier. CSI-RS transmission may be configured per carrier segments of a serving cell and/or per UE (e.g., depending on a TM configured for the carrier segments).

A set of CSI-RS structure and/or mapping configurations and/or patterns (e.g., as described herein) may be pre-defined, and may be configurable, for extension carriers and/or carrier segments. CSI-RS structure and/or mapping configurations and/or patterns (e.g., a set of CSI-RS structure and/or mapping configurations and/or patterns) may be used to configure one or more UEs. For example, a UE, in response to being configured with extension carriers and/or carrier segments, may be configured with one or more (e.g., a set of) CSI-RS structure and/or mapping configurations and/or patterns (e.g., via L1 signaling or L2/3 signaling). A UE previously configured with extension carriers and/or carrier segments and/or any CRS structure and/or mapping configurations and/or patterns may be reconfigured with one or more (e.g., a set of) CSI-RS structure and/or mapping configurations and/or patterns (e.g., via L1 signaling or L2/3 signaling).