Patent Description:
Wireless communication networks are widely deployed to provide various communication content such as voice, video, packet data, messaging, broadcast, etc. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Examples of such multiple- access networks include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (EDMA) networks, Orthogonal EDMA (OEDMA) networks, and Single-Carrier EDMA (SC-EDMA) networks.

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. <CIT> describes changing between primary and secondary serving cells using preconfigured serving cell information upon receipt of a handover indication. <CIT> describes dynamic switching between DC-HSDPA and SFDC-HSDPA. <CIT> describes resource allocation and transmission for coordinated multi-point transmission. <CIT> describes an architecture to support network wide multiple in multiple out wireless communication over an uplink. <CIT>, which is an Article <NUM>(<NUM>) EPC document, describes a method and apparatus for aggregating carriers of multiple radio access technologies. <CIT> describes a handover method for mobile communication. <CIT> describes a wireless transmit/receive unit that activates a primary uplink carrier and a primary downlink carrier and activates or deactivates a secondary uplink carrier based on a signal from a network or upon detection of a pre-configured condition.

The invention is defined by the method and apparatuses of the independent claims.

Techniques for communicating in a HetNet with carrier aggregation are disclosed herein. These techniques may be used for various wireless communication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other wireless networks. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband CDMA (WCDMA), Time Division Synchronous CDMA (TD-SCDMA), and other variants of CDMA. cdma2000 includes IS-<NUM>, IS-<NUM> and IS-<NUM> standards. An OFDMA network may implement a radio technology such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE <NUM> (Wi-Fi and Wi-Fi Direct), IEEE <NUM> (WiMAX), IEEE <NUM>, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A), in both frequency division duplexing (FDD) and time division duplexing (TDD), are recent releases of UMTS that use E-UTRA, which employs OFDMA on the downlink and SC-FDMA on the uplink. UTRA, E-UTRA, GSM, UMTS, LTE and LTE-A are described in documents from an organization named "3rd Generation Partnership Project" (3GPP). For clarity, certain aspects of the techniques are described below for LTE, and LTE terminology is used in much of the description below.

<FIG> shows a wireless communication network <NUM>, which may be an LTE network or some other wireless network. Wireless network <NUM> may include a number of evolved Node Bs (eNBs) <NUM> and other network entities. An eNB may be a station or node that communicates with the UEs and may also be referred to as a base station, a Node B, an access point, etc. Each eNB <NUM> 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 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)). In the example shown in <FIG>, eNBs 110a, 110b and 110c may be macro eNBs for macro cells 102a, 102b and 102c, respectively. eNB 110d may be a pico eNB for a pico cell 102d. eNBs 110e and 110f may be home eNBs for femto cells 102e and 102f, respectively. An eNB may support one or multiple (e.g., three) cells. The terms "eNB", "cell", and "base station" may be used interchangeably.

Wireless network <NUM> may also include relays. A relay may be a station or node that receives a transmission of data from an upstream station (e.g., an eNB or a UE) and sends a transmission of the data to a downstream station (e.g., a UE or an eNB). A relay may also be a UE that relays transmissions for other UEs. In the example shown in <FIG>, a relay <NUM> may communicate with eNB 110a and a UE 120r in order to facilitate communication between eNB 110a and UE 120r. Relay <NUM> may appear like a UE to eNB 110a and may appear like an eNB to UE 120r.

Wireless network <NUM> may also include remote radio heads (RRHs). An RRH may be a remote unit that can support radio frequency (RF) transmission and reception. An eNB may include one or more RRHs, which may be located away from the eNB. The eNB may be coupled to the RRHs via a wireline backhaul (e.g., fiber optics) using standard interface. The eNB may communicate with UEs via the RRHs.

Wireless network <NUM> may also include other network entities. For example, a network controller <NUM> may couple to a set of eNBs and provide coordination and control for these eNBs. Network controller <NUM> may communicate with the eNBs via a backhaul. The eNBs may also communicate with one another, e.g., directly or indirectly via wireless or wireline backhaul.

Wireless network <NUM> may be a HetNet that includes network nodes of different types. A network node may be a macro eNB/cell, a pico eNB/cell, a home eNB/femto cell, a relay, an RRH, etc. For example, wireless network <NUM> may include macro eNBs/cells, pico eNBs/cells, home eNBs/femto cells relays, RRHs, etc., which may have different transmit power levels, different coverage areas, and different impact on interference in wireless network <NUM>. Macro eNBs/cells may have a high transmit power level (e.g., <NUM> to <NUM> Watts) whereas pico eNBs/cells, home eNBs/femto cells, and relays may have lower transmit power levels (e.g., <NUM> to <NUM> Watts). Wireless network <NUM> may be a dense or a very dense HetNet. The density of a HetNet may be quantified by an eNB-to-UE ratio, and a very dense HetNet may have a low eNB-to-UE ratio approaching <NUM>:<NUM> (or possibly exceeding <NUM>:<NUM> with more eNBs than UEs).

UEs <NUM> may be dispersed throughout wireless network <NUM>, and each UE may be stationary or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, etc. A UE may be a cellular phone, a smartphone, a tablet, 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, etc. A UE may be able to communicate with one or more network nodes (e.g., one or more macro cells, pico cells, femto cells, relays, RRHs, etc.) at any given moment.

Wireless network <NUM> may support data transmission with hybrid automatic retransmission (HARQ) in order to improve reliability. For HARQ, a transmitter (e.g., an UE) may send an initial transmission of a packet of data and may send one or more additional transmissions of the packet, if needed, until the packet is decoded correctly by a receiver (e.g., an eNB/cell), or the maximum number of transmissions of the packet has occurred, or some other termination condition is encountered. After each transmission of the packet, the receiver may decode all received transmissions of the packet to attempt to recover the packet. The receiver may send an acknowledgement (ACK) if the packet is decoded correctly or a negative acknowledgement (NAK) if the packet is decoded in error. The transmitter may send another transmission of the packet if a NAK is received and may terminate transmission of the packet if an ACK is received. Data may be transmitted based on an HARQ timeline, which may indicate when to send ACK/NAK feedback and when to send a retransmission for a given transmission of data sent at a particular time. For example, an HARQ timeline of <NUM> milliseconds (ms) may be used in which, for a given transmission of data sent at time t, ACK/NAK feedback may be sent <NUM> later at time t + <NUM> , and a retransmission may be sent <NUM> later at time t + <NUM>.

<FIG> shows an exemplary frame structure <NUM> for FDD in LTE. Each radio frame may have a predetermined duration (e.g., <NUM> milliseconds (ms)) and may be partitioned into <NUM> subframes with indices of <NUM> through <NUM>. Each subframe may include two slots. Each radio frame may thus include <NUM> slots with indices of <NUM> through <NUM>. Each slot may include L symbol periods, e.g., seven symbol periods for a normal cyclic prefix (as shown in <FIG>) or six symbol periods for an extended cyclic prefix. The <NUM> symbol periods in each subframe may be assigned indices of <NUM> through <NUM>-<NUM>.

A cell may transmit a Physical Control Format Indicator Channel (PCFICH), a Physical HARQ Indicator Channel (PHICH), a Physical Downlink Control Channel (PDCCH), and/or other physical channels in a control region of a subframe for the downlink (or downlink subframe). The PCFICH may convey the number of symbol periods (M) used for the control region of the downlink subframe, where M may be equal to <NUM>, <NUM> or <NUM> and may change from subframe to subframe. The PDCCH may carry downlink control information (DCI) such as downlink grants, uplink grants, etc. The PHICH may carry ACK/NAK feedback for data transmission sent on the uplink with HARQ. The cell may also transmit a Physical Downlink Shared Channel (PDSCH) and/or other physical channels in a data region of a downlink subframe. The PDSCH may carry data for UEs scheduled for data transmission on the downlink.

A UE may transmit either a Physical Uplink Control Channel (PUCCH) in a control region of a subframe for the uplink (or uplink subframe) or a Physical Uplink Shared Channel (PUSCH) in a data region of the uplink subframe. The PUCCH may carry uplink control information (UCI) such as channel state information (CSI), ACK/NAK feedback, scheduling request, etc. The PUSCH may carry data and/or UCI. The various signals and channels in LTE are described in 3GPP TS <NUM>, entitled "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation," which is publicly available.

Wireless network <NUM> may support operation on multiple component carriers (CCs), which may be referred to as carrier aggregation (CA) or multi-carrier operation. A CC may refer to a range of frequencies used for communication and may be associated with certain characteristics. For example, a CC may be associated with system information defining operation on the CC. A CC may also be referred to as a carrier, a frequency channel, a cell, etc..

A UE may be configured with multiple CCs for the downlink and one or more CCs for the uplink for carrier aggregation. A cell may send data and control information on one or more CCs to the UE. The UE may send data and control information on one or more CCs to the cell.

<FIG> shows an example of continuous carrier aggregation. Multiple (K) CCs may be available for communication and may be adjacent to each other, where K may be any integer value.

<FIG> shows an example of non-continuous carrier aggregation. Multiple (K) CCs may be available for communication and may be separated from each other.

In LTE Release <NUM>, a UE may be configured with up to five CCs for carrier aggregation. Each CC may have a bandwidth of up to <NUM> and may be backward compatible with LTE Release <NUM>. The UE may thus be configured with up to <NUM> for up to five CCs in LTE Release <NUM>. One CC may be designated as a primary CC (PCC), and each remaining CC may be designated as a secondary CC (SCC). A cell may send a control information on the PDCCH on the PCC to the UE. The UE may send control information on the PUCCH on the PCC to the cell. In LTE Release <NUM>, a UE may communicate with a single network node (e.g., a serving cell) on all CCs configured for that UE.

In an aspect of the disclosure, carrier aggregation may be used to support communication in a dense HetNet. A dense HetNet may refer to a deployment of many network nodes of different types in a relatively small geographic area. These network nodes may include macro cells, pico cells, relays, RRHs, etc. For example, many pico cells, relays, and/or RRHs may be widely deployed (e.g., on light poles, within buildings and homes, inside stores, etc.) throughout the coverage of a macro cell. A dense HetNet may then include the macro cell as well as the pico cells, relays, and/or RRHs within the coverage of the macro cell. For example, the macro cell may have a coverage area of <NUM> to <NUM> kilometers (km) radius and may include hundreds of pico cells, relays, and/or RRHs. Deployment of network nodes of different types may greatly increase the capacity of the HetNet. Multiple CCs may be used to support communication with the network nodes in the HetNet in order to further increase network capacity. For example, in some instances, network capacity of the dense HetNet may be hundreds or thousand times greater than network capacity of a single macro cell.

<FIG> shows an exemplary HetNet <NUM> with carrier aggregation. In <FIG>, a cell 110x may be a macro cell or a pico cell and may support communication for UEs within its coverage area. Cell 110x may include a centralized baseband unit and/or a centralized control unit. A cell 110y may be a pico cell located within the coverage area of cell 110x. A relay 112x may relay transmissions for cell 110x, which may be a donor cell for relay 112x. An RRH 114x may support RF transmission and reception for cell 110x. On the downlink, RRH 114x may receive data from cell 110x, generate a downlink signal comprising the data, and transmit the downlink signal to UEs. On the uplink, RRH 114x may receive uplink signals sent by UEs, process the uplink signals to obtain symbol estimates or decoded data, and send the symbol estimates or decoded data to cell 110x.

A UE 120x may communicate with cell 110x via a direct link <NUM> at time T1. UE 120x may be one of the UEs in <FIG>. UE 120x may also communicate with cell 110x via relay 112x at time T1. Relay 112x may communicate with UE 120x via an access link <NUM> and with cell 110x via a backhaul link <NUM>. Backhaul link <NUM> may typically be a wireless link but may also be a wireline link. UE 120x may be mobile and may move to a new location at time T2, which may be K1 seconds or minutes later than time T1, where K1 may be any value. At time T2, UE 120x may communicate with cell 110x via a direct link <NUM> and also with RRH 114x via a secondary link <NUM>. RRH 114x may communicate with cell 110x via a wireline (e.g., fiber optics) backhaul <NUM>. UE 120x may move to a new location at time T3, which may be K2 seconds or minutes later than time T2, where K2 may be any value. At time T3, UE 120x may communicate with cell 110x via a direct link <NUM> and also with cell 110y via a direct link <NUM>.

In one aspect of the disclosure, a UE may concurrently communicate with multiple network nodes via different CCs for carrier aggregation. In one design, the UE may communicate with a serving cell via a PCC and zero or more SSCs and may also communicate with one or more other network nodes via one or more SCCs. The use of multiple CCs may improve capacity and performance, especially in a dense HetNet.

In the example shown in <FIG>, two CCs may be available and may include a PCC at frequency f1 and an SCC at frequency f2. Cell 110x may be a serving cell of UE 120x. At time T1, UE 120x may communicate with cell 110x via the PCC on frequency f1 and may communicate with relay 112x via the SCC on frequency f2. Relay 112x may communicate with cell 110x via the PCC. At time T2, UE 120x may communicate with cell 110x via the PCC and may communicate with RRH 114x via the SCC. RRH 114x may communicate with cell 110x via a wireline backhaul. At time T3, UE 120x may communicate with cell 110x via the PCC and may communicate with pico cell 110y via the SCC.

There may be many network nodes in a dense HetNet. A UE may rapidly move in and out of coverage of different cells within the HetNet. If the UE performs handover to the strongest cell at any given moment, then the UE may perform handover frequently as the UE moves about the dense HetNet. Each handover may be associated with signaling and other overhead. It may be desirable to minimize the number of handovers performed by the UE as it moves about the dense HetNet.

In another aspect of the disclosure, a PCC may be maintained for a UE for communication with a network node (e.g., a serving cell), and SCCs may be added to or removed from a configuration of the UE. The UE may perform handover whenever there is a change in PCC from one network node to another network node. By maintaining the PCC while adding and/or removing SCCs, the number of handovers for the UE may be reduced.

In the example shown in <FIG>, UE 120x may communicate with cell 110x via the PCC at times T1, T2 and T3. The PCC may thus remain the same for UE 120x from time T1 to time T3. UE 120x may communicate with different network nodes via the SCC at different times. In particular, UE 120x may communicate with relay 112x via the SCC at time T1, then with RRH 114x via the SCC at time T2, and then with pico cell 110y via the SCC at time T3. UE 120x may add the SCC from relay 112x, then remove the SCC from relay 112x and add the SCC from RRH 114x, and then remove the SCC from RRH 114x and add the SCC from pico cell 110y. However, UE 120x may avoid performing handover since the PCC has not changed from time T1 to time T3 even though the SCC has changed multiple times.

In general, a PCC and an SCC may have the same bandwidth or different bandwidths. The PCC and SCC may be contiguous (e.g., as shown in <FIG>) or non-contiguous (e.g., as shown in <FIG>).

In general, any information may be sent via a PCC and an SCC. In one design, designated control information (e.g., scheduling/grant information, ACK/NAK feedback, etc.) may be sent on the PCC. In another design, certain types of traffic/data may be sent on the PCC, and other types of traffic/data may be sent on the SCC. For example, voice traffic may be sent on the PCC whereas best-effort traffic may be sent on the SCC. The PCC and SCC may be associated with different quality-of-service (QoS) levels. In this case, the PCC and SCC may be more suitable for carrying different types of traffic/data based on the QoS requirements of the different traffic/data types.

In yet another aspect of the disclosure not forming part of the invention, soft combining and/or HARQ may be enabled or disabled for uplink transmissions, e.g., depending on whether multiple CCs are enabled on the uplink and whether communication on a CC is via an RRH or a relay. Soft combining refers to combining of symbol estimates from different sources (e.g., different network nodes, different antennas, etc.) prior to decoding. The symbol estimates may be estimates of transmitted modulation symbols. Soft combining may result in accumulation of more energy for the transmitted modulation symbols, which may improve decoding performance.

Referring to <FIG>, at time T2, UE 120x may concurrently send a first uplink transmission on the PCC to cell 110x and a second uplink transmission on the SCC to RRH 114x. Cell 110x may receive the first uplink transmission intended for cell 110x as well as the second uplink transmission intended for RRH 114x. Cell 110x may derive first symbol estimates based on the first uplink transmission received on the PCC and second symbol estimates based on the second uplink transmission received on the SCC. Similarly, RRH 114x may receive the second uplink transmission intended for RRH 114x as well as the first uplink transmission intended for cell 110x. RRH 114x may derive third symbol estimates based on the second uplink transmission received on the SCC and fourth symbol estimates based on the first uplink transmission received on the PCC. RRH 114x may forward the third and fourth symbol estimates to cell 110x via backhaul <NUM>.

Cell 110x may obtain the first symbol estimates determined by cell 110x for the first uplink transmission and the fourth symbol estimates determined by RRH 114x for first uplink transmission. Cell 110x may combine the first and fourth symbol estimates in a manner known in the art to obtain first combined symbol estimates for the first uplink transmission. Cell 110x may then decode the first combined symbol estimates to recover data sent by UE 120x in the first uplink transmission. Similarly, cell 110x may obtain the second symbol estimates determined by cell 110x for the second uplink transmission and the third symbol estimates determined by RRH 114x for second uplink transmission. Cell 110x may combine the second and third symbol estimates to obtain second combined symbol estimates for the second uplink transmission. Cell 110x may then decode the second combined symbol estimates to recover data sent by UE 120x in the second uplink transmission. Soft combining the first and fourth symbol estimates may improve the likelihood of correctly decoding the data sent by UE 120x in the first uplink transmission. Soft combining the second and third symbol estimates may improve the likelihood of correctly decoding the data sent by UE 120x in the second uplink transmission.

UE 120x may typically adjust its transmit timing independently for each network node receiving an uplink transmission from UE 120x. In the example shown in <FIG>, at time T2, UE 120x may adjust its transmit timing for the first uplink transmission to cell 110x based on first timing adjustments from cell 110x. Cell 110x may determine the first timing adjustments for UE 120x such that the first uplink transmission from UE 120x is properly time-aligned at cell 110x. Similarly, UE 120x may adjust is transmit timing for the second uplink transmission to RRH 114x based on second timing adjustments RRH 114x. RRH 114x may determine the second timing adjustments for UE 120x such that the second uplink transmission from UE 120x is properly time-aligned at RRH 114x.

In one design, the transmit timing of a UE for uplink transmissions to multiple network nodes may be adjusted such that good performance can be achieved for soft combining on the uplink. In the example shown in <FIG>, the first timing adjustments from cell 110x and the second timing adjustments from RRH 114x may be determined for UE 120x such that good performance can be obtained for (i) soft combining of symbol estimates determined by cell 110x and RRH 114x for the first uplink transmission on the PCC and/or (ii) soft combining of symbol estimates determined by cell 110x and RRH 114x for the second uplink transmission on the SCC. For example, the transmit timing of UE 120x for the first uplink transmission may be set to t1 if adjusted based solely on timing adjustments from cell 110x. The transmit timing of UE 120x for the second uplink transmission may be set to t2 if adjusted based solely on timing adjustments from RRH 114x. The difference between t1 and t2 may be relatively large for various reasons. The transmit timing of UE 120x for the first uplink transmission may be skewed toward t2, and the transmit timing of UE 120x for the second uplink transmission may be skewed toward t1 in order to improve performance of soft combining on the uplink. The amount of skew may be dependent on various factors such as the difference between t1 and t2, the loading at cell 110x and the loading at RRH 114x, the received power of UE 120x at cell 110x and RRH 114x, etc. In one design, the amount of skew may be dependent on a weighted average of the received uplink transmissions at cell 110x and RRH 114x. For example, the uplink timing of UE 120x may be skewed more toward a target uplink timing of UE 120x for a network node (e.g., cell 110x or RRH 114x) having a higher received power or a higher received signal quality for an uplink transmission from UE 120x.

HetNet <NUM> in <FIG> may have one or more of the following characteristics:.

<FIG> shows an exemplary HetNet <NUM> with carrier aggregation. HetNet <NUM> includes macro/pico cell 110x, pico cell 110y, relay 112x, and RRH 114x in HetNet <NUM> in <FIG>. HetNet <NUM> further includes an access point 116x, which may implement IEEE <NUM> (Wi-Fi), Hiperlan, etc..

At time T0, UE 120x may communicate with cell 110x via direct link <NUM> and within access point 116x via a secondary link <NUM>. At time T1, which may be K0 seconds or minutes later than time T0, UE 120x may communicate with cell 110x via direct link <NUM> and also with relay 112x via secondary link <NUM>. At time T2, UE 120x may communicate with cell 110x via direct link <NUM> and also with RRH 114x via secondary link <NUM>. At time T3, UE 120x may communicate with cell 110x via direct link <NUM> and also with cell 110y via direct link <NUM>.

In the example shown in <FIG>, two CCs may be available and may include a PCC at frequency f1 and an SCC at frequency f2. Cell 110x may be a serving cell of UE 120x. At time T0, UE 120x may communicate with cell 110x via the PCC on frequency f1 and may communicate with access point 116x via an unlicensed frequency, which may be referred to as an unlicensed SCC. The unlicensed frequency may be in an ISM band at <NUM> or some other band. UE may communicate with cell 110x, relay 112x, RRH 114x, and pico cell 110y as described above for <FIG>.

In general, a UE may concurrently communicate with a network node via a PCC and with any number of additional network nodes via any number of SCCs. The UE may communicate with a single additional network node via a single SCC, as shown in <FIG>. The UE may also communicate with a single additional network node via multiple SCCs. The UE may also communicate with multiple additional network nodes via multiple SCCs.

In one design, an SCC may be used for both the downlink and uplink, as shown in <FIG>, with two-ended arrows being shown for secondary links <NUM>, <NUM> and <NUM>. This design may allow for soft combining of an uplink transmission sent by a UE on a CC and received at different network nodes. For example, RRH 114x may send symbol estimates for a first uplink transmission sent by UE 120x to cell 110x as well as symbol estimates for a second uplink transmission sent by UE 120x to RRH 114x. The symbol estimates determined by RRH 114x may be combined with symbol estimates determined by cell 110x for the first and second uplink transmissions from UE 120x, as described above.

In the invention, an SCC is used for only the downlink, which may be referred to as supplemental downlink. In this design, control information for data transmission on the PCC as well as the SCC is sent on the PCC since the SCC is not available for uplink transmission. For example, UE 120x may receive a first downlink transmission from cell 110x via the PCC and a second downlink transmission from RRH 114x via the SCC. UE 120x may send ACK/NAK for the first downlink transmission as well as ACK/NAK for the second downlink transmission on the PCC to cell 110x. Cell 110x may forward the ACK/NAK for the second downlink transmission to RRH 114x. Since cell 110x may perform common baseband processing for downlink transmissions from cell 110x and RRH 114x, the same HARQ timeline may be used for downlink transmissions by cell 110x and RRH 114x to UE 120x. An SCC used for only the downlink may also be operated as a simplified SCC carrying broadcast traffic/data and unacknowledged mode (UM) traffic/data. UM traffic/data may include unicast data with no HARQ and no ACK/NAK feedback. An example of UM traffic/data may be Voice-over-Internet Protocol (VoIP).

In one design, a PCC and an SCC for different network nodes may be associated with the same cell identity (ID). For example, the PCC for cell 110x and the SCC for RRH 114x in <FIG> may be associated with the same cell ID. In this case, RRH 114x may appear like a different antenna of cell 110x. In this design, control information may be sent in the control region of a downlink subframe on both the PCC and SCC.

In another design, a PCC and an SCC for different network nodes may be associated with different cell IDs. For example, the PCC for cell 110x in <FIG> may be associated with a first cell ID, and the SCC for RRH 114x may be associated with a second cell ID. In this case, RRH 114x may appear like a different cell than cell 110x. In this design, different control information may be sent in the control region of a downlink subframe on the PCC and SCC. The control space for the downlink may increase via use of different cell IDs for the PCC and SCC.

In one design, centralized scheduling may be used for UEs served by different network nodes on different CCs. For example, in <FIG>, cell 110x may serve one or more UEs on the PCC, and RRH 114x may serve one or more UEs on the SCC. RRH 114x may be associated with cell 110x, which may perform baseband processing for both cell 110x and RRH 114x. A central scheduler may jointly schedule UEs communicating with only cell 110x, UEs communicating with only RRH 114x, and UEs communicating with both cell 110x and RRH 114x such that good overall performance can be achieved. Overall performance may be quantified by various metrics related to throughput, latency, etc..

In another design, de-centralized scheduling may be used for UEs served by different network nodes on different CCs. For example, in <FIG>, cell 110x may serve one or more UEs, and relay 112x may serve one or more UEs. Relay 112x may have cell 110x as its donor cell. A scheduler for cell 110x may schedule the UEs served by cell 110x such that good performance can be achieved. Another scheduler for relay 112x may schedule the UEs served by relay 112x such that good performance can be achieved.

Carrier aggregation may be used for various dense HetNets. Some exemplary dense HetNets with carrier aggregation are show below.

<FIG> shows an exemplary HetNet <NUM> including macro/pico cell 110x and multiple RRHs <NUM> with carrier aggregation. In <FIG>, cell 110x may be a macro cell or a pico cell and may support communication for UEs within its coverage area. RRHs 114x, 114y and 114z may support RF transmission and reception for cell 110x.

At time T1, UE 120x may communicate with cell 110x via a direct link <NUM> and also with RRH 114x via a secondary link <NUM>. RRH 114x may communicate with cell 110x via a wireline backhaul <NUM>. At time T2, UE 120x may communicate with cell 110x via a direct link <NUM> and also with RRH 114y via a secondary link <NUM>. RRH 114y may communicate with cell 110x via a wireline backhaul <NUM>. At time T3, UE 120x may communicate with cell 110x via a direct link <NUM> and also with RRH 114z via a secondary link <NUM>. RRH 114z may communicate with cell 110x via a wireline backhaul <NUM>.

Different network nodes may serve UE 120x via different CCs. In the example shown in <FIG>, two CCs may be available and may include a PCC at frequency f1 and an SCC at frequency f2. At time T1, UE 120x may communicate with cell 110x via the PCC on frequency f1 and may communicate with RRH 114x via the SCC on frequency f2. At time T2, UE 120x may communicate with cell 110x via the PCC and may communicate with RRH 114y via the SCC. At time T3, UE 120x may communicate with cell 110x via the PCC and may communicate with RRH 114z via the SCC.

As also shown in <FIG>, the PCC may remain the same for UE 120x, and the SCC may be added to or removed from a configuration of UE 120x. In the example shown in <FIG>, UE 120x may communicate with cell 110x via the PCC at times T1, T2 and T3. The PCC may thus remain the same for UE 120x from time T1 to time T3, and no handover may be performed by UE 120x. UE 120x may communicate with different network nodes such as RRHs 114x, 114y and 114z via the SCC at different times.

<FIG> shows an exemplary HetNet <NUM> including macro/pico cell 110x and multiple relays <NUM> with carrier aggregation. In <FIG>, cell 110x may be a macro cell or a pico cell and may support communication for UEs within its coverage area. Relays 112x, 112y and 112z may be coupled to cell 110x and may relay transmissions for cell 110x.

At time T1, UE 120x may communicate with cell 110x via a direct link <NUM> and also with relay 112x via an access link <NUM>. Relay 112x may communicate with cell 110x via a backhaul link <NUM>. At time T2, UE 120x may communicate with cell 110x via a direct link <NUM> and also with relay 112y via an access link <NUM>. Relay 112y may communicate with cell 110x via a backhaul link <NUM>. At time T3, UE 120x may communicate with cell 110x via a direct link <NUM> and also with relay 112z via an access link <NUM>. Relay 112z may communicate with cell 110x via a backhaul link <NUM>.

Different network nodes may serve UE 120x via different CCs. In the example shown in <FIG>, two CCs may be available and may include a PCC at frequency f1 and an SCC at frequency f2. At time T1, UE 120x may communicate with cell 110x via the PCC on frequency f1 and may communicate with relay 112x via the SCC on frequency f2. Relay 112x may communicate with cell 110x via the PCC. At time T2, UE 120x may communicate with cell 110x via the PCC and may communicate with relay 112y via the SCC. Relay 112y may communicate with cell 110x via the PCC. At time T3, UE 120x may communicate with cell 110x via the PCC and may communicate with relay 112z via the SCC. Relay 112z may communicate with cell 110x via the PCC.

As shown in <FIG>, the PCC may remain the same for UE 120x, while the SCC may be added to or removed from a configuration of UE 120x. In the example shown in <FIG>, UE 120x may communicate with cell 110x via the PCC at times T1, T2 and T3. The PCC may thus remain the same for UE 120x from time T1 to time T3, and no handover may be performed by UE 120x. UE 120x may communicate with different network nodes such as relays 112x, 112y and 112z via the SCC at different times.

As long as UE 120x maintains connection to cell 110x via the PCC, no handover for UE 120x is triggered when communication via the SCC shifts from various additional network nodes, such as relays 112x, 112y, and 112z from times T1-T3. This feature reduces the additional overhead due to handover procedures, while maintaining the beneficial features of carrier aggregation through SCC communications.

In additional aspects, as UE 120x communicates via SCC with relays 112x, 112y, and 112z, relays 112x, 112y, and 112z communicate with cell 110x using a non-standard backhaul <NUM>, <NUM>, and <NUM>, such as a non-fiber communication link. SCC communication through relays 112x, 112y, and 112z may then be coordinated through cell 110x.

<FIG> shows example blocks executed to implement one aspect for communicating on multiple CCs of the present disclosure. The example aspect may be performed by a UE (as described below) or by some other entity. The UE may communicate with a first network node via a PCC and a second network node via a SCC at a first time (block <NUM>). The PCC may carry designated control information and possibly data and/or other information for the UE. The SCC may carry data and/or other information for the UE. In one design, the PCC and SCC may be independently configured for the UE. The first network node may comprise a serving cell of the UE. The second network node may comprise a pico cell, a relay, a remote radio head, or some other network entity. The second network node may also comprise an access point, and the SCC may be within an unlicensed band, e.g., as shown in <FIG>.

The UE may establish communication with a third network node via the SCC at a second time (block <NUM>). The UE maintains communication with the first network node via the PCC without triggering handover at the UE while establishing communication with the third network node (block <NUM>). Thus, the UE may switch communication from the second network node to the third network node on the SCC without the added overhead of handover.

In one design of blocks <NUM> and <NUM>, the UE may send data to and receive data from the first network node via the PCC. The UE may also send data to and receive data from the second network node via the SCC. In this design, the SCC may serve as supplementary downlink and uplink for the UE. In another design of blocks <NUM> and <NUM>, the UE may send data to and receive data from the first network node via the PCC. However, the UE may only receive data from the second network node via the SCC. In this design, the SCC may serve as a supplementary downlink for the UE.

The UE may receive at least one grant for data transmission on the PCC and SCC. In one design, scheduling of data transmission on the first and second CCs for the UE may be centralized. In another design, scheduling of data transmission on the PCC and SCC for the UE may be de-centralized.

The PCC and SCC may be used for data transmission in various manners. In general, any type of traffic/data may be sent on each CC, and data may be sent with or without HARQ on each CC. In one design, each type of traffic may be sent on each CC. In another design, different types of traffic may be sent on the PCC and SCC. For example, the PCC may carry traffic carrier, and the SCC may carry broadcast data. In one design, HARQ may be used for each CC. In another design, HARQ may be used for one CC and not for the other CC. In the invention, data is sent with HARQ on the PCC and without HARQ on the SCC.

<FIG> shows example blocks executed to implement one aspect for communicating on multiple CCs of the present disclosure. The example aspect may be performed by a UE (as described below) or by some other entity. The UE may communicate at a first time with a first network node via a PCC and a second network node via a SCC (block <NUM>). The PCC may be maintained for the UE during the entire first time period. The UE may communicate with at least one additional network node via at least one additional SCC at the first time, where each of the additional SCCs are added to or removed from a configuration of the UE during the first time (block <NUM>). In one design, the PCC and the additional SCC(s) may be independently configured for the UE. The first network node may comprise a serving cell of the UE. The additional network node(s) may comprise a pico cell, a relay, a remote radio head, and/or other network entities. The additional network node(s) may also comprise an access point, and the additional SCC(s) may comprise a CC within an unlicensed band, e.g., as shown in <FIG>.

The UE may add an SCC for a second network node to the configuration of the UE during the first time period. Alternatively or additionally, the UE may remove the SCC for the second network node from the configuration of the UE during the first time period. The at least one additional SCC may comprise the SCC, and the at least one additional network node may comprise the second network node. The UE may not perform handover during the first time period while the UE communicates with the first network node on the PCC.

The UE may establish communication with a third network node via the SCC at a second time (block <NUM>). The UE maintains communication with the first network node via the PCC also without triggering handover at the UE while establishing communication with the third network node in the second time (block <NUM>). The PCC may carry designated control information and/or data of a first type (e.g., voice traffic, etc.) for the UE. The SCC(s) may carry data of a second type (e.g., best-effort traffic, broadcast traffic, etc.) and/or other information for the UE.

In one design of blocks <NUM>-<NUM>, the UE may send data to and receive data from the first network node via the PCC. The UE may also send data to and receive data from the additional network node(s) via the additional SCC(s). In this design, the additional SCC(s) may serve as supplementary downlink and uplink for the UE. In another design of blocks <NUM>-<NUM>, the UE may send data to and receive data from the first network node via the PCC. However, the UE may only receive data from the additional network node(s) via the additional SCC(s). In this design, the additional SCC(s) may serve as a supplementary downlink for the UE.

The UE may receive a first grant for data transmission on the PCC. The UE may receive at least one additional grant for data transmission on the additional SCC(s). In one design, scheduling of data transmission on the PCC and additional SCC(s) for the UE may be de-centralized. In another design, scheduling of data transmission on the PCC and additional SCC(s) for the UE may be centralized.

<FIG> shows example blocks executed to implement one aspect for supporting communication on multiple CCs of the present disclosure. The example aspect may be performed by a network node (as described below) or by some other entity. A UE may be configured with a PCC for communication with a first network node at a first time and a SCC for communication with a second network node (block <NUM>). The UE may be configured with the SCC for communication with a third network node at a second time after the first time (block <NUM>). The UE may also be configured to maintain communication with the first network node via the PCC while configuring the UE for communication with the third network node, wherein handover is not performed for the UE while the UE communicates with the first network node via the PCC (block <NUM>).

In one design, the PCC and SCC may be independently configured for the UE. The first network node may comprise a serving cell of the UE. The second network node may comprise a pico cell, a relay, or a remote radio head. In another design, a grant may be sent to the UE for data transmission on the PCC and SCC. In another design, a first grant may be sent to the UE for data transmission on the PCC, and a second grant may be sent to the UE for data transmission on the SCC. In one design, the UE may be scheduled for data transmission on the PCC and SCC with centralized scheduling. In another design, the UE may be scheduled for data transmission on the PCC and SCC with de-centralized scheduling. The PCC may carry designated control information and/or data of a first type for the UE. The SCC may carry data of a second type and/or other information for the UE.

In one design, the SCC may serve as supplementary downlink and uplink for the UE. In this design, the UE may (i) send data to and receive data from the first network node via the PCC and (ii) send data to and receive data from the second network node via the SCC. In another design, the SCC may serve as supplementary downlink for the UE. In this design, the UE may (i) send data to and receive data from the first network node via the first CC and (ii) only receive data from the second network node via the SCC.

The PCC and SCC may be used for data transmission in various manners. In general, any type of traffic/data may be sent on each CC, and data may be sent with or without HARQ on each CC. In one design, each type of traffic may be sent on each CC. In another design, different types of traffic may be sent on the PCC and SCC. For example, the PCC may carry traffic carrier, and the SCC may carry broadcast data. In one design, HARQ may be used for each CC. In another design, HARQ may be used for one CC and not for the other CC. For example, data may be sent with HARQ on the PCC and without HARQ on the SCC.

<FIG> shows a design of a process <NUM> for supporting communication not forming part of the invention. Process <NUM> may be performed by a first network node, which may be a serving cell of a UE or some other entity. The first network node may obtain first symbol estimates for a first uplink transmission sent on a first CC from the UE to the first network node (block <NUM>). The first network node may also obtain second symbol estimates for the first uplink transmission from a second network node, which may also receive the first uplink transmission sent to the first network node (block <NUM>). The second network node may comprise another cell, a relay, a remote radio head, etc. The first UE may concurrently communicate with the first network node on the first CC and also with the second network node on a second CC. The first network node may combine the first and second symbol estimates to obtain first combined symbol estimates for the first uplink transmission (block <NUM>). The first network node may decode the first combined symbol estimates to recover data sent in the first uplink transmission by the UE (block <NUM>).

The first network node may obtain third symbol estimates for a second uplink transmission sent on the second CC from the UE to the second network node and received by the first network node (block <NUM>). The first network node may also obtain fourth symbol estimates for the second uplink transmission from the second network node, which may be the intended recipient of the second uplink transmission (block <NUM>). The first network node may combine the third and fourth symbol estimates to obtain second combined symbol estimates for the second uplink transmission (block <NUM>). The first network node may decode the second combined symbol estimates to recover data sent in the second uplink transmission by the UE (block <NUM>).

First transmit timing of the UE for the first uplink transmission may be adjusted, e.g., via timing adjustments sent by the first network node to the UE. Second transmit timing of the UE for the second uplink transmission may also be adjusted, e.g., via timing adjustments sent by the second network node to the UE. In one design, the first transmit timing and the second transmit timing of the UE may be adjusted to improve performance of uplink soft combining, e.g., to improve decoding performance of combined symbol estimates obtained from symbol estimates determined by the first and second network nodes for uplink transmissions sent by the UE.

<FIG> shows a block diagram of a design of a network node 110u and a UE 120u. Network node 110u may be one of the eNBs in <FIG> and/or may be the cell 110x in <FIG>. UE 120u may be one of the UEs in <FIG> and/or UE 120x in <FIG>.

Within network node 110u, a module <NUM> may determine configurations of UE 120u and/or other UEs, e.g., determine which CCs are configured for UE 120u and which network node is communicating with UE 120u on each configured CC. A module <NUM> may schedule UE 120u and other UEs for data transmission on the downlink and uplink. A module <NUM> may adjust the transmit timing of UE 120u. A module <NUM> may support communication with UE 120u and/or other UEs on a PCC, e.g., support data transmission to the UEs and data reception from the UEs on the PCC. A module <NUM> may support communication with UE 120u and/or other UEs on one or more SCCs. A module <NUM> may perform soft combining for uplink transmissions sent by UE 120u and/or other UEs. These uplink transmissions may be intended for network node 110u and/or other network nodes. A transmitter <NUM> may generate one or more downlink signals for the PCC and/or SCC(s). A receiver <NUM> may receive and process uplink signals transmitted by UE 120u and/or other UEs on the PCC and/or SCC(s). A controller/processor <NUM> may direct the operation of various modules within network node 110u. A memory <NUM> may store data and program codes for network node 110u.

Within UE 120u, a receiver <NUM> may receive and process downlink signals from network node 110u and/or other network nodes. A transmitter <NUM> may generate one or more uplink signals comprising the uplink transmissions intended for network node 110u and/or other network nodes. A module <NUM> may determine a configuration of UE 120u, e.g., determine which CCs are configured for UE 120u and which network node to communicate with on each configured CC. A module <NUM> may receive grants that schedule UE 120u for data transmission on the downlink and uplink. A module <NUM> may adjust the transmit timing of UE 120u for each configured CC and/or each network node with which UE 120u is in communication. A module <NUM> may support communication for UE 120u on a PCC, e.g., support data transmission to network nodes and data reception from the network nodes. A module <NUM> may support communication for UE 120u on one or more SCCs. A controller/processor <NUM> may direct the operation of various modules within UE 120u. A memory <NUM> may store data and program codes for UE 120u.

The modules in <FIG> may comprise processors, electronic devices, hardware devices, electronic components, logical circuits, memories, software codes, firmware codes, etc., or any combination thereof.

<FIG> shows a block diagram of a design of a network node 110v and a UE 120v. Network node 110v may be one of the eNBs in <FIG> and/or may be for cell 110x in <FIG>. UE 120v may be one of the UEs in <FIG> and/or UE 120x in <FIG>. Network node 110v may be equipped with T antennas 1234a through 1234t, and UE 120v may be equipped with R antennas 1252a through 1252r, where in general T ≥ <NUM> and R ≥ <NUM>.

At network node 110v, a transmit processor <NUM> may receive data from a data source <NUM> for one or more UEs, process (e.g., encode and modulate) the data for each UE based on one or more modulation and coding schemes selected for that UE, and provide data symbols for all UEs. Transmit processor <NUM> may also process control information (e.g., for configuration messages, grants, etc.) and provide control symbols. Processor <NUM> may also generate reference symbols for reference signals. A transmit (TX) multiple-input-multiple-output (MIMO) processor <NUM> may precode the data symbols, the control symbols, and/or the reference symbols (if applicable) and may provide T output symbol streams to T modulators (MOD) 1232a through 1232t. Each modulator <NUM> may process its output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator <NUM> may further condition (e.g., convert to analog, amplify, filter, and upconvert) its output sample stream to obtain a downlink signal. The downlink signal from each modulator <NUM> may comprise data and control information sent on one or more CCs configured for each UE scheduled for data transmission on the downlink. T downlink signals from modulators 1232a through 1232t may be transmitted via T antennas 1234a through 1234t, respectively.

At UE 120v, antennas 1252a through 1252r may receive the downlink signals from network node 110v and/or other network nodes and may provide received signals to demodulators (DEMODs) 1254a through 1254r, respectively. Each demodulator <NUM> may condition (e.g., filter, amplify, downconvert, and digitize) its received signal to obtain input samples. A MIMO detector <NUM> may obtain received symbols from all R demodulators 1254a through 1254r, perform MIMO detection, and provide detected symbols. A receive processor <NUM> may process (e.g., demodulate and decode) the detected symbols, provide decoded data for UE 120v to a data sink <NUM>, and provide decoded control information to a controller/processor <NUM>.

At UE 120v, a transmit processor <NUM> may receive and process data from a data source <NUM> and control information from controller/processor <NUM>. Processor <NUM> may also generate reference symbols for one or more reference signals. The symbols from transmit processor <NUM> may be precoded by a TX MIMO processor <NUM> if applicable, further processed by modulators 1254a through 1254r (e.g., for SC-FDM, OFDM, etc.), and transmitted. The uplink signal from each modulator <NUM> may comprise data and control information sent on one or more CCs configured for UE 110v.

At network node 110v, the uplink signals from UE 120v and other UEs may be received by antennas <NUM>, processed by demodulators <NUM>, detected by a MIMO detector <NUM> if applicable, and further processed by a receive processor <NUM> to obtain decoded data and control information sent by UE 120v and other UEs. Processor <NUM> may perform soft combining for uplink transmissions sent by UE 120v and received by multiple network nodes including network node 110v. Processor <NUM> may provide the decoded data to a data sink <NUM> and the decoded control information to controller/processor <NUM>.

Controllers/processors <NUM> and <NUM> may direct the operation at network node 110v and UE 120v, respectively. Processor <NUM> and/or other processors and modules at network node 110v may perform or direct process <NUM> in <FIG>, process <NUM> in <FIG>, and/or other processes for the techniques described herein. Processor <NUM> and/or other processors and modules at UE 120v may perform or direct process <NUM> in <FIG>, process <NUM> in <FIG>, and/or other processes for the techniques described herein. Memories <NUM> and <NUM> may store data and program codes for network node 110v and UE 120v, respectively. A scheduler <NUM> may schedule UEs for data transmission.

Claim 1:
A method for wireless communication, comprising:
communicating (<NUM>) at a first time, by a user equipment, UE, with a first network node via a primary component carrier, PCC, and a second network node via a secondary CC, SCC, wherein the second network node is remotely located with respect to the first network node and the SCC is only used for downlink communication, wherein data is sent with hybrid automatic retransmission, HARQ, on the PCC and without HARQ on the SCC;
switching, communication, by the UE, from the second network node to a third network node via the SCC at a second time, wherein the third network node is remotely located with respect to the second network node and the first network node and
maintaining (<NUM>) communication with the first network node via the PCC without triggering handover at the UE during the establishing communication with the third network node.