Patent Description:
The present disclosure relates generally to communication systems, and more particularly, to a technique for multiplexing downlink control information (DCI) signals for multiple user equipments (UEs) at an aggregation level (AL) by coding the DCI signals together in a control channel and transmitting the control channel.

Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency divisional multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

An example of an emerging telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). It is designed to better support mobile broadband Internet access by improving spectral efficiency, lower costs, improve services, make use of new spectrum, and better integrate with other open standards using OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. The following prior art documents relate to the multiplexing of downlink control signals for multiple user equipments thus being considered relevant to the present application: <CIT>, <CIT>, <CIT>, <CIT>.

According to aspects of the present disclosure, a BS may multiplex a first plurality of DCI signals directed to a first plurality of UEs at a first aggregation level coded together in a control channel (e.g., a PDCCH). The BS may multiplex a second plurality of DCI signals directed to a second plurality of UEs in a second control channel. The BS may transmit the control channels on separate time and frequency resources, or transmit the control channels at different power levels on the same time and frequency resources. A UE may receive the control channels and identify DCI signals directed to the UE based on identifier fields included with the DCI signals in the control channels.

These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as "elements").

Accordingly, in one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers.

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

The E-UTRAN includes the evolved Node B (eNB) <NUM> and other eNBs <NUM>. The eNB <NUM> provides user and control plane protocol terminations toward the UE <NUM>. The eNB <NUM> may be connected to the other eNBs <NUM> via an X2 interface (e.g., backhaul). The eNB <NUM> may also be referred to as a base station, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), or some other suitable terminology. The eNB <NUM> provides an access point to the EPC <NUM> for a UE <NUM>. Examples of UEs <NUM> include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, or any other similar functioning device. The UE <NUM> may also be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

The eNB <NUM> is connected by an S1 interface to the EPC <NUM>. The EPC <NUM> includes a Mobility Management Entity (MME) <NUM>, other MMEs <NUM>, a Serving Gateway <NUM>, and a Packet Data Network (PDN) Gateway <NUM>. The MME <NUM> is the control node that processes the signaling between the UE <NUM> and the EPC <NUM>. All user IP packets are transferred through the Serving Gateway <NUM>, which itself is connected to the PDN Gateway <NUM>. The PDN Gateway <NUM> is connected to the Operator's IP Services <NUM>. The Operator's IP Services <NUM> may include the Internet, the Intranet, an IP Multimedia Subsystem (IMS), and a PS Streaming Service (PSS).

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

The modulation and multiple access scheme employed by the access network <NUM> may vary depending on the particular telecommunications standard being deployed. In LTE applications, OFDM is used on the DL and SC-FDMA is used on the UL to support both frequency division duplexing (FDD) and time division duplexing (TDD). As those skilled in the art will readily appreciate from the detailed description to follow, the various concepts presented herein are well suited for LTE applications. However, these concepts may be readily extended to other telecommunication standards employing other modulation and multiple access techniques. By way of example, these concepts may be extended to Evolution-Data Optimized (EV-DO) or Ultra Mobile Broadband (UMB). EV-DO and UMB are air interface standards promulgated by the 3rd Generation Partnership Project <NUM> (3GPP2) as part of the CDMA2000 family of standards and employs CDMA to provide broadband Internet access to mobile stations. These concepts may also be extended to Universal Terrestrial Radio Access (UTRA) employing Wideband-CDMA (W-CDMA) and other variants of CDMA, such as TD-SCDMA; Global System for Mobile Communications (GSM) employing TDMA; and Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE <NUM> (Wi-Fi), IEEE <NUM> (WiMAX), IEEE <NUM>, and Flash-OFDM employing OFDMA. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from the 3GPP organization. CDMA2000 and UMB are described in documents from the 3GPP2 organization. The actual wireless communication standard and the multiple access technology employed will depend on the specific application and the overall design constraints imposed on the system.

The eNBs <NUM> may have multiple antennas supporting MIMO technology. The use of MIMO technology enables the eNBs <NUM> to exploit the spatial domain to support spatial multiplexing, beamforming, and transmit diversity. Spatial multiplexing may be used to transmit different streams of data simultaneously on the same frequency. The data steams may be transmitted to a single UE <NUM> to increase the data rate or to multiple UEs <NUM> to increase the overall system capacity. This is achieved by spatially precoding each data stream (i.e., applying a scaling of an amplitude and a phase) and then transmitting each spatially precoded stream through multiple transmit antennas on the DL. The spatially precoded data streams arrive at the UE(s) <NUM> with different spatial signatures, which enables each of the UE(s) <NUM> to recover the one or more data streams destined for that UE <NUM>. On the UL, each UE <NUM> transmits a spatially precoded data stream, which enables the eNB <NUM> to identify the source of each spatially precoded data stream.

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

In the detailed description that follows, various aspects of an access network will be described with reference to a MIMO system supporting OFDM on the DL. OFDM is a spread-spectrum technique that modulates data over a number of subcarriers within an OFDM symbol. The subcarriers are spaced apart at precise frequencies. The spacing provides "orthogonality" that enables a receiver to recover the data from the subcarriers. In the time domain, a guard interval (e.g., cyclic prefix) may be added to each OFDM symbol to combat inter-OFDM-symbol interference. The UL may use SC-FDMA in the form of a DFT-spread OFDM signal to compensate for high peak-to-average power ratio (PAPR).

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

<FIG> is a diagram <NUM> illustrating an example of an UL frame structure in LTE. The available resource blocks for the UL may be partitioned into a data section and a control section. The control section may be formed at the two edges of the system bandwidth and may have a configurable size. The resource blocks in the control section may be assigned to UEs for transmission of control information. The data section may include all resource blocks not included in the control section. The UL frame structure results in the data section including contiguous subcarriers, which may allow a single UE to be assigned all of the contiguous subcarriers in the data section.

A UE may be assigned resource blocks 410a, 410b in the control section to transmit control information to an eNB. The UE may also be assigned resource blocks 420a, 420b in the data section to transmit data to the eNB. The UE may transmit control information in a physical UL control channel (PUCCH) on the assigned resource blocks in the control section. The UE may transmit only data or both data and control information in a physical UL shared channel (PUSCH) on the assigned resource blocks in the data section. A UL transmission may span both slots of a subframe and may hop across frequency.

A set of resource blocks may be used to perform initial system access and achieve UL synchronization in a physical random access channel (PRACH) <NUM>. The PRACH <NUM> carries a random sequence and cannot carry any UL data/signaling. Each random access preamble occupies a bandwidth corresponding to six consecutive resource blocks. The starting frequency is specified by the network. That is, the transmission of the random access preamble is restricted to certain time and frequency resources. There is no frequency hopping for the PRACH. The PRACH attempt is carried in a single subframe (<NUM>) or in a sequence of few contiguous subframes and a UE can make only a single PRACH attempt per frame (<NUM>).

<FIG> is a diagram <NUM> illustrating an example of a radio protocol architecture for the user and control planes in LTE. The radio protocol architecture for the UE and the eNB is shown with three layers: Layer <NUM>, Layer <NUM>, and Layer <NUM>. Layer <NUM> (L1 layer) is the lowest layer and implements various physical layer signal processing functions. The L1 layer will be referred to herein as the physical layer <NUM>. Layer <NUM> (L2 layer) <NUM> is above the physical layer <NUM> and is responsible for the link between the UE and eNB over the physical layer <NUM>.

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

The PDCP sublayer <NUM> provides multiplexing between different radio bearers and logical channels. The PDCP sublayer <NUM> also provides header compression for upper layer data packets to reduce radio transmission overhead, security by ciphering the data packets, and handover support for UEs between eNBs. The RLC sublayer <NUM> provides segmentation and reassembly of upper layer data packets, retransmission of lost data packets, and reordering of data packets to compensate for out-of-order reception due to hybrid automatic repeat request (HARQ). The MAC sublayer <NUM> provides multiplexing between logical and transport channels. The MAC sublayer <NUM> is also responsible for allocating the various radio resources (e.g., resource blocks) in one cell among the UEs. The MAC sublayer <NUM> is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE and eNB is substantially the same for the physical layer <NUM> and the L2 layer <NUM> with the exception that there is no header compression function for the control plane. The control plane also includes a radio resource control (RRC) sublayer <NUM> in Layer <NUM> (L3 layer). The RRC sublayer <NUM> is responsible for obtaining radio resources (i.e., radio bearers) and for configuring the lower layers using RRC signaling between the eNB and the UE.

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

The TX processor <NUM> implements various signal processing functions for the L1 layer (i.e., physical layer). The signal processing functions includes coding and interleaving to facilitate forward error correction (FEC) at the UE <NUM> and mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded and modulated symbols are then split into parallel streams. Each stream is then mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. Each spatial stream is then provided to a different antenna <NUM> via a separate transmitter 618TX. Each transmitter 618TX modulates an RF carrier with a respective spatial stream for transmission. The TX processor may also perform or direct the eNB in performing operations described in this disclosure, for example, operation <NUM> described in <FIG>.

At the UE <NUM>, each receiver 654RX receives a signal through its respective antenna <NUM>. Each receiver 654RX recovers information modulated onto an RF carrier and provides the information to the receiver (RX) processor <NUM>. The RX processor <NUM> implements various signal processing functions of the L1 layer. The RX processor <NUM> performs spatial processing on the information to recover any spatial streams destined for the UE <NUM>. The symbols on each subcarrier, and the reference signal, is recovered and demodulated by determining the most likely signal constellation points transmitted by the eNB <NUM>. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the eNB <NUM> on the physical channel. The data and control signals are then provided to the controller/processor <NUM>. The RX processor may perform or direct the UE in performing operations described in this disclosure, for example, operation <NUM> described in <FIG>.

The controller/processor <NUM> implements the L2 layer. The controller/processor can be associated with a memory <NUM> that stores program codes and data. In the UL, the control/processor <NUM> provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the core network. The upper layer packets are then provided to a data sink <NUM>, which represents all the protocol layers above the L2 layer. Various control signals may also be provided to the data sink <NUM> for L3 processing. The controller/processor <NUM> is also responsible for error detection using an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support HARQ operations. The controller/processor may perform or direct the UE in performing operations described in this disclosure, for example, operation <NUM> described in <FIG>.

In the UL, a data source <NUM> is used to provide upper layer packets to the controller/processor <NUM>. The data source <NUM> represents all protocol layers above the L2 layer. Similar to the functionality described in connection with the DL transmission by the eNB <NUM>, the controller/processor <NUM> implements the L2 layer for the user plane and the control plane by providing header compression, ciphering, packet segmentation and reordering, and multiplexing between logical and transport channels based on radio resource allocations by the eNB <NUM>. The controller/processor <NUM> is also responsible for HARQ operations, retransmission of lost packets, and signaling to the eNB <NUM>.

Channel estimates derived by a channel estimator <NUM> from a reference signal or feedback transmitted by the eNB <NUM> may be used by the TX processor <NUM> to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor <NUM> are provided to different antenna <NUM> via separate transmitters 654TX. Each transmitter 654TX modulates an RF carrier with a respective spatial stream for transmission.

The UL transmission is processed at the eNB <NUM> in a manner similar to that described in connection with the receiver function at the UE <NUM>. Each receiver 618RX receives a signal through its respective antenna <NUM>. Each receiver 618RX recovers information modulated onto an RF carrier and provides the information to a RX processor <NUM>. The RX processor <NUM> may implement the L1 layer.

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

In current (e.g., LTE Release <NUM> (Rel-<NUM>)) wireless communications systems, a BS notifies UEs of scheduling grants for uplink and downlink transmissions by sending downlink control information (DCI) signals to the UEs. A DCI signal is included in a physical downlink control channel (PDCCH) that is transmitted to the UE scheduled in the DCI signal. A UE monitors search spaces in order to detect PDCCHs directed to the UE, and, as the number of CCEs for each of the PDCCHs may vary and is not signaled, attempts to blindly decode PDCCHs in the search spaces. To reduce the complexity of this process somewhat, certain restrictions on the aggregation of contiguous CCEs have been specified. For example, an aggregation of eight CCEs can only start on CCE numbers evenly divisible by <NUM>. If the UE successfully decodes a PDCCH directed to the UE, then the UE acquires the DCI signal and is informed of the scheduling grant.

A UE may monitor both a common search space and a UE-specific search space in a control region of a subframe. A search space may comprise a set of channel control element (CCE) locations where a UE may find its PDCCHs. All UEs served by a cell monitor the common search space, while a UE-specific search space is configured for an individual UE.

One or more CCEs are used to transmit each PDCCH. Sets of four consecutive physical resource elements (REs) are known as resource element groups (REGs), and nine REGs make up each CCE. Thus, one CCE equals <NUM> REs. The number of CCEs used for (e.g., to transmit) a PDCCH may be <NUM>, <NUM>, <NUM>, or <NUM>, known as an aggregation level (AL) of the PDCCH. An aggregation level is selected for a PDCCH transmission, by the transmitting BS, based on signal to interference and noise ratios (SINRs) experienced by UEs to which the PDCCH is directed. In other examples, aggregation level can be determined by the eNodeB on channel conditions other than signal to interference and noise ratios. That is, an aggregation level for a PDCCH directed to a single UE may be selected by a BS based on an SINR the UE has reported to the BS for transmissions from the BS, while an aggregation level for a PDCCH directed to several UEs may be selected by the BS based on SINRs reported by the several UEs. For example, when a PDCCH is intended for a UE under good downlink channel conditions (e.g. the UE is close to the eNodeB), then one CCE is likely to be sufficient, and the eNB may select aggregation level one for the PDCCH. However, when a PDCCH is intended for a UE under poor channel conditions (e.g. near the cell border) then up to eight CCEs may be used to achieve sufficient robustness and the eNB may select aggregation level eight for the PDCCH.

Each search space (i.e., the common search space and the UE-specific search spaces) comprises a group of consecutive CCEs that could be allocated to a PDCCH, called a PDCCH candidate. For each aggregation level, each UE has to try to decode more than one possible candidate. The CCE aggregation level determines the number of PDCCH candidates in a search space. Table <NUM> (reproduced from 3GPP TS <NUM> "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures" v8. <NUM>, which is publicly available and hereby incorporated by reference) gives the number of candidates and size of the search space for each aggregation level.

It can be observed in Table <NUM> that that there may be up to six PDCCH candidates in the common search space (i.e., four for control channel element (CCE) aggregation level <NUM>, and two for aggregation level <NUM>), and up to <NUM> candidates in the UE-specific search space (i.e., six for aggregation level <NUM>, six for aggregation level <NUM>, two for aggregation level <NUM>, and two for aggregation level <NUM>). The number of CCEs to be searched within each PDCCH candidate depends on the aggregation level. Thus, there are <NUM> PDCCH candidates in the common search space for aggregation level <NUM> and <NUM> PDCCH candidates for aggregation level <NUM>, though both sets of PDCCH candidates are sixteen CCEs in size. A UE monitors for PDCCHs directed to the UE in a set of PDCCH candidates in every subframe.

<FIG> illustrates an exemplary set <NUM> of CCEs. UE-specific search spaces are shown at <NUM> and <NUM>. Note that, as illustrated, UE-specific search spaces for different UEs may overlap. PDCCH candidates at different aggregation levels for a UE may also overlap. In addition, the common search space and UE-specific search space for a UE may overlap.

An overlap, if such occurs, may limit the possibility of scheduling a UE due to potential collision with other UEs. For example and with reference to <FIG>, if a BS schedules UE1 using the aggregation level <NUM> PDCCH at <NUM>, then the BS cannot schedule UE2 using either of the aggregation level <NUM> PDCCHs at <NUM> and <NUM>. If the other AL <NUM> and AL <NUM> PDCCH candidates for UE1 (recall from Table <NUM> above that there are two AL <NUM> PDCCH candidates in the UE-specific search space and <NUM> PDCCH candidates in the common search space) are also blocked and SINR conditions for UE1 require the use of AL <NUM> or AL <NUM> PDCCH transmissions to UE1, then the BS will not be able to schedule UE1 during that subframe.

A BS may attempt to schedule K (e.g., <NUM>-<NUM>) users of N (e.g., <NUM>) UEs being served in a cell during each subframe. The N users may experience varying SINR conditions when receiving from the BS. Because of the varying SINR conditions, PDCCHs to the scheduled UEs may be transmitted at varying aggregation levels. In some cases, a BS will be unable to transmit a PDCCH to a UE because all PDCCH candidates for the UE overlap with PDCCH candidates of other UEs to which the BS has scheduled PDCCH transmissions.

Each PDCCH transmitted by a BS includes a <NUM>-bit cyclic redundancy check (CRC). However, the transmitting BS masks the CRC with a radio network temporary identifier (RNTI) of a UE or UEs to which the PDCCH is directed. A UE determines that a PDCCH is directed to the UE by attempting blind decoding of PDCCH candidates. Blind decoding includes unmasking a CRC of a PDCCH candidate with one or more RNTIs assigned to the UE, and then checking that a CRC calculated against other (non-CRC) portions of the PDCCH candidate matches the unmasked CRC. Approximately <NUM>% of PDDCH transmissions are incorrectly decoded (e.g., due to interference) by a UE as being directed to a UE, commonly referred to as a "false alarm. " False alarms may reduce overall system throughput, as UEs experiencing false alarms may transmit at incorrect times or frequencies, possibly interfering with other transmissions. A UE experiencing a false alarm may receive at incorrect times or frequencies, possibly interfering with the operation of the UE (e.g., by causing the UE to miss a transmission on another frequency at that time).

Current PDCCH design (i.e., as described above) causes addition of new DCI formats to increase the number of blind decodes by UEs, as a UE must determine if each PDCCH candidate can be decoded for each possible DCI length. In Rel-<NUM> wireless communications systems, DCI formats <NUM>, 1A, <NUM>, 3A, and <NUM> have been designed to have the same length (in number of bits), to keep the number of blind decodes performed by UEs smaller. In some wireless communications systems, one or more UEs are configured to receive DCIs of only a limited number of formats, in order to reduce the number of blind decodes performed by those UEs.

According to aspects of the present disclosure, a BS may multiplex a plurality of DCI signals directed to a plurality of UEs at a first aggregation level (AL) coded together in a control channel (e.g., a PDCCH). A BS may determine aggregation level of a UE based on SINR conditions of the UE, for example, based on a channel quality indicator (CQI) report received from the UE. A BS operating according to disclosed techniques may avoid scheduling conflicts between UEs, in that DCIs for the UEs are multiplexed in the bit domain and not the symbol domain, allowing UEs to be scheduled in any CCE, rather than scheduling of a UE being limited to CCEs within search spaces configured for the UE. A BS may multiplex multiple DCIs for the UEs by concatenating the DCIs.

According to aspects of the present disclosure, new DCI formats may be easily defined, because four or more bits may be reserved in a DCI to indicate the format of the DCI. According to aspects of the present disclosure, DCIs (i.e., DCI signals) may be of variable length, as DCI signals multiplexed together in the bit domain are not required to all be of the same length.

According to aspects of the present disclosure, a BS may transmit multiple DCIs to a UE during a subframe. A BS may multiplex multiple DCIs to a UE in a control channel (e.g., a PDCCH) in a subframe by including an RNTI of the UE in each of the DCIs. For example, a BS may multiplex a first DCI for a first UE, a second DCI for a second UE, a third DCI for the first UE, a fourth DCI for a third UE, and a fifth DCI for the first UE in a single control channel. In the example, the BS may include a cell radio network temporary identifier (C-RNTI) of the first UE in the first, third, and fifth DCIs, while including a C-RNTI for the second UE in the second DCI and a C-RNTI for the third UE in the fourth DCI.

<FIG> illustrates an exemplary operation <NUM> that may be performed by a BS to multiplex DCIs of one AL by coding the DCIs together in a control channel, in accordance with certain aspects of the disclosure. The BS may include the eNodeBs <NUM>, <NUM> and/or <NUM>, for example.

Operation <NUM> may begin, at <NUM> where the BS groups a first plurality of UEs by a first aggregation level (AL). Next, at <NUM>, the BS multiplexes a first plurality of downlink control information (DCI) signals for a first plurality of user equipments (UEs) at a first aggregation level (AL) coded together in a first control channel. At <NUM>, the BS computes a CRC for the first control channel and includes the computed CRC in a field. At <NUM>, the BS transmits the first control channel using a selected MCS along with an indication of the MCS and/or a size of the control channel.

<FIG> illustrates an exemplary operation <NUM> that may be performed by a UE to receive a control channel including DCIs of one AL multiplexed together in a control channel, in accordance with certain aspects of the disclosure. The UE <NUM> may include UEs <NUM>, <NUM>, and/or <NUM>, for example.

Operation <NUM> may begin, at <NUM>, by the UE receiving a first control channel including a plurality of downlink control information (DCI) signals for a plurality of UEs at one aggregation level (AL) coded together. At <NUM>, the UE may identify a DCI signal within the first control channel directed to the UE.

According to aspects of the present disclosure, a BS (e.g., eNodeB <NUM>) scheduling control channel transmissions to UEs may group the UEs by aggregation level (AL) of the UEs. That is, a BS may multiplex DCI signals (DCIs) to multiple UEs that the BS transmits to at a same aggregation level in one control channel, as in block <NUM> in <FIG>. The BS may select a modulation and coding scheme (MCS) to use in transmitting the control channel, and transmit the control channel (as in block <NUM>) using the selected MCS, along with an indication of the MCS and/or the size of the control channel.

<FIG> is a block diagram illustrating exemplary multiplexing and transmission of DCI signals <NUM> and <NUM> in control channel <NUM>, according to aspects of the present disclosure. A BS may perform operation <NUM>, shown in <FIG>, in multiplexing the DCI signals and transmitting the control channels.

A BS may multiplex a first DCI signal <NUM> directed to UE1 with a second DCI signal <NUM> directed to UE2 in control channel <NUM>. In multiplexing together the DCI signals, the BS may also include DCI format or DCI# fields <NUM>, <NUM> and UE identifier (e.g., a cell radio network temporary identifier (C-RNTI)) fields <NUM>, <NUM>. A UE receiving the control channel may use the DCI format fields to determine the length of each DCI and hence, the starting point for a next field (e.g., a DCI# field) in the control channel. A UE receiving the control channel may use the identifier fields to determine which, if any, of the DCI signals in the control channel are directed to the UE. The BS may multiplex DCI signals for UEs (e.g., UE1 and UE2) that are at a same aggregation level (e.g., AL1) when the BS transmits to the UEs. Note that "AL1" in <FIG> is representative of a first aggregation level, and may refer to ALs equal to <NUM>, <NUM>, <NUM>, or <NUM>. The BS may also compute a CRC for all of the fields (e.g., DCI format fields <NUM> and <NUM>, UE identifier fields <NUM> and <NUM>, DCI signals <NUM> and <NUM>) and include the computed CRC in a CRC field <NUM> in the control channel. A UE receiving the control channel may use the CRC field to verify that the UE has received the control channel correctly.

While the exemplary control channel <NUM> shows the various fields concatenated together, other methods (e.g., interleaving) of combining the fields into a control channel are included in aspects of the disclosure. Similarly, while two DCI signals for two UEs are shown, other numbers of DCI signals for other numbers of UEs are also included in aspects of the disclosure. A BS may also aggregate multiple DCI signals for one UE in a control channel, according to aspects of the present disclosure.

The BS may then select a modulation and coding scheme (MCS) for transmitting the control channel to the UEs. The BS then performs coding and modulation, shown at <NUM>, on the control channel. Modulation and coding of the control channel results in one or more code words that may be transmitted. If the BS is not transmitting DCI signals to UEs at any other AL, then the BS may transmit an indication <NUM> of the size and/or MCS with the one or more code words <NUM> to the UEs (i.e., UE1 and UE2), as shown at <NUM>.

<FIG> is a block diagram illustrating exemplary multiplexing and transmission of DCI signals <NUM>, <NUM>, <NUM>, and <NUM> in control channels <NUM> and/or <NUM>, according to aspects of the present disclosure. A BS may perform operation <NUM>, shown in <FIG>, in multiplexing the DCI signals and transmitting the control channels.

Exemplary control channel <NUM> may be similar to exemplary control channel <NUM>, shown in <FIG>. If the BS is transmitting DCI signals to UEs at another AL, then the BS may also multiplex a third DCI signal <NUM> directed to UE3 with a fourth DCI signal <NUM> directed to UE4 in control channel <NUM>. As with control channel <NUM>, the BS may include DCI# fields <NUM>, <NUM> and UE identifier fields <NUM>, <NUM> in control channel <NUM>. Also as before, the BS may compute a CRC for the control channel <NUM> and include the computed CRC in a CRC field <NUM>. And, as with control channel <NUM>, the BS aggregates UEs at a same aggregation level (e.g., AL2) in control channel <NUM>. Similar to "AL1," "AL2" is representative of a second AL, and may refer to ALs equal to <NUM>, <NUM>, <NUM>, or <NUM>. The BS may then perform a separate coding modulation operation, shown at <NUM>, on the control channel <NUM>.

The BS may then transmit the code word(s) <NUM> for the first control channel <NUM> with an indication <NUM> of the size of the code words and/or the MCS used in transmitting the code words for the first control channel and the code word(s) <NUM> for the second control channel <NUM> with an indication <NUM> of the size of the code words and/or the MCS used in transmitting the code words for the second control channel.

When transmitting the code words <NUM>, <NUM> for the first and second control channels, the BS may transmit the code words using orthogonal multiple access (OMA), as at <NUM>, or non-orthogonal multiple access (NOMA), as at <NUM>. When transmitting the code words using OMA, the BS transmits each size and/or MCS indication 1140A, 1180A and code word 1142A, 1182A on a separate set of time and frequency resources. That is, each of the size/MCS indications and code words are transmitted on a set of CCEs that is not used for any other transmission by the BS. When transmitting the codewords using OMA, the BS transmits the second control channel at a starting CCE that may be determined based on the size/MCS indication 1140A of the first control channel.

When transmitting the code words using NOMA, as at <NUM>, the BS transmits the size/MCS indication 1140B and code words 1142B for one aggregation level combined with the size/MCS indication 1180B and code words 1182B for another aggregation level on one set of CCEs. The BS transmits the size/MCS indication 1140B and code words 1142B for the first control channel <NUM> at a first power level and the size/MCS indication 1180B and code words 1182B for the second control channel at a second power level lower than the first power level. When transmitting using NOMA, the first control channel <NUM> may contain DCIs directed to UEs at an AL (e.g., AL=<NUM>) that is higher than the AL (e.g., AL=<NUM>) of the UEs to which the DCIs in the second control channel <NUM> are directed. The BS may also include an indication of the first power level (PAL1) in a power level field <NUM> in the first control channel.

A UE receiving control channels (e.g., control channels <NUM>, <NUM>) transmitted using NOMA may identify one or more DCIs (e.g., DCIs <NUM>, <NUM>, <NUM>, <NUM>) in a control channel directed to the UE. If the BS transmits DCTs for the UE (e.g., UE1, UE2) using the first aggregation level (e.g., AL1), then the UE may identify one or more DCIs (e.g., DCIs <NUM>, <NUM>) directed to the UE by determining an identifier of the UE is in one or more UE identifier fields (e.g., UE identifier fields <NUM>, <NUM>) in the first control channel. Because the BS transmits DCIs for the UE at the first aggregation level, which, as described above, is higher than the second aggregation level, the UE may be able to decode the first control channel (e.g., control channel <NUM>) while ignoring the second control channel (e.g., control channel <NUM>), which was transmitted at a lower power level.

If the BS transmits DCIs for a UE (e.g., UE3, UE4) using NOMA and the second aggregation level (e.g., AL2), then the UE may use successive interference cancellation (SIC) to detect the second control channel (e.g., control channel <NUM>) within the transmission. The UE may receive the transmission and determine the power level used to transmit the first control channel (e.g., control channel <NUM>) from a power level field (e.g., power level field <NUM>) in the first control channel. The UE may use the received first control channel and the indicated power level to cancel the first control channel from the received transmission to make a second received transmission. The UE may then detect the second control channel (e.g., control channel <NUM>) within the second received transmission. If the UE is successful in detecting the second control channel (e.g., the CRC <NUM> for the second control channel matches a CRC computed by the UE for the second control channel), then the UE may identify DCIs (e.g., DCIs <NUM>, <NUM>) directed to the UE by determining an identifier of the UE is in one or more UE identifier fields (e.g., UE identifier fields <NUM>, <NUM>) in the second control channel.

While the above is described in terms of two control channels, the disclosure is not so limited. According to aspects of the present disclosure, a BS may transmit more than two (e.g., four) control channels, with each control channel directed to UEs at an aggregation level. When transmitting control channels using NOMA, the BS may transmit a power level field with each control channel except the control channel transmitted at the lowest power level.

According to aspects of the present disclosure, a BS (e.g., eNodeB 204A in <FIG>) may send (e.g., via an X2 interface) an indication of an aggregation level (e.g., AL=<NUM>) that the BS is going to use in transmitting to served UEs during a time period (e.g., a subframe) to a second BS (e.g., eNodeB 204F in <FIG>). The second BS may use the indication in determining aggregation levels of UEs that the second BS will transmit to during the time period. For example, a first BS may send to a second BS that the first BS is going to transmit to UEs using aggregation level <NUM> during a subframe. In the example, the second BS is a neighbor BS of the first BS. In the example, the second BS is able to determine that the first BS may be transmitting at a high power level to cell-edge UEs during the subframe, because aggregation level <NUM> is used for UEs in poor SINR conditions. Still in the example, the second BS may determine to transmit only to UEs at aggregation level <NUM>, both to avoid interference from the first BS and to avoid interfering with transmissions by the first BS. BSs in an area may cooperate to exchange information on aggregation levels used in transmissions in this manner, which may be referred to as inter-cell interference coordination (ICIC).

<FIG> illustrates an exemplary set of fields <NUM> that may be used when multiplexing DCIs in a control channel, according to aspects of the present disclosure described above. The MCS/size field <NUM> may be four to seven bits in size, depending on the system bandwidth and aggregation levels being used by the transmitting BS. For example, if a BS is supporting a system bandwidth of <NUM>, then the BS can transmit up to <NUM> CCEs in a subframe. In the example, if the BS is transmitting using aggregation level <NUM>, then the BS would transmit the size of the control channel in seven bits, as the control channel could be from <NUM> to <NUM> CCEs long, depending on the number of DCIs being transmitted.

The DCI format or DCI# field <NUM> may be four bits long, to allow up to sixteen different DCI formats. If it is determined (e.g., by a standards body) that more or fewer DCI formats should be supported, then the number of bits used for the DCI# field may be changed.

The C-RNTI field <NUM> may be from four to sixteen bits long, depending on the number of active UEs a BS may be supporting. For example, a BS may support <NUM>,<NUM> or fewer active UEs. In the example, the BS may define the C-RNTI field to be twelve bits, allowing the BS to address up to <NUM>,<NUM> UEs while conserving four bits for other fields. The C-RNTI field may contain other types of identifiers for UEs, for example, a BS may transmit an SI-RNTI in the C-RNTI field for a DCI conveying a system information (SI) change.

The DCI field <NUM> may be of variable length, depending on the information and/or commands being conveyed to the UE. The size of the DCI field may be determined from the format number conveyed in the DCI# field <NUM>.

The Power field <NUM> may be from four to six bits long and conveys the power level used for transmitting the control channel when the control channel is transmitted with NOMA with at least one other control channel at a lower aggregation level (and power level). As described above, the power field is used by receiving UEs in performing success interference cancellation to detect control channels at lower aggregation levels.

The CRC field <NUM> may be sixteen bits long. As described above, the CRC field is calculated by the transmitting BS based on the other fields of the control channel. Also as described above, a receiving UE verifies the CRC against the remainder of the control channel in order to ensure that the UE received the control channel correctly.

It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Further, some steps may be combined or omitted. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

" That is, unless specified otherwise or clear from the context, the phrase, for example, "X employs A or B" is intended to mean any of the natural inclusive permutations. That is, for example the phrase "X employs A or B" is satisfied by any of the following instances: X employs A; X employs B; or X employs both A and B.

Claim 1:
A method for wireless communications performed by a user equipment, UE (<NUM>, <NUM>, <NUM>), comprising:
receiving an indication of a modulation and coding scheme, MCS, and a size of a first control channel; receiving (<NUM>) a wireless transmission comprising the first control channel wherein the receiving comprises decoding at least a part of the first control channel using the indicated MCS and size,
wherein the first control channel includes a plurality of downlink control information, DCI, signals multiplexed in the bit domain for a plurality of UEs (<NUM>, <NUM>, <NUM>) within one or more control channel elements, CCE, at a first aggregation level, AL,
and wherein the first control channel includes a first downlink control information, DCI, signal at the first aggregation level, AL, and an indication of a first power level used for transmitting the first control channel;
identifying (<NUM>) the first DCI signal at the first AL within the first control channel directed to the UE (<NUM>, <NUM>, <NUM>);
receiving a second control channel from the wireless transmission, wherein the second control channel includes a second DCI signal at a second AL; and characterised in that the receiving comprises using successive interference cancellation, SIC, based on the indication of the first power level to cancel the first control channel from the wireless transmission and to detect the second control channel.