Adaptive control channel design for balancing data payload size and decoding time

A method of wireless communication includes allocating transport blocks to a control channel region as a function of the size of the transport block. The user equipment (UE) monitors at least two different control regions in a subframe for control information. The monitored control regions do not overlap in time. The UE receives a subframe including control information in at least one of the two different control regions.

BACKGROUND

Field

Aspects of the present disclosure relate generally to wireless communication systems, and more particularly to allocating transport blocks to a control channel region as a function of the size of the transport block.

Background

SUMMARY

In one aspect, a method of wireless communication is disclosed. The method includes monitoring at least two different control regions in a subframe for control information, were the two control regions do not overlap in time. The method also includes receiving the subframe including control information in at least one of the two different control regions.

Another aspect discloses a method of wireless communication including determining a control region to use for transmitting control information to a receiver based on a transport block size. The method also includes transmitting control information in the determined control region.

In another aspect, a wireless communication having a memory and at least one processor coupled to the memory is disclosed. The processor(s) is configured to monitor at least two different control regions in a subframe for control information. The two control regions do not overlap in time. The processor(s) is also configured to receive the subframe including control information in at least one of the two different control regions.

Another aspect discloses wireless communication having a memory and at least one processor coupled to the memory. The processor(s) is configured to determine a control region to use for transmitting control information to a receiver based on a transport block size. The processor(s) is also configured to transmit control information in the determined control region.

In another aspect, a computer program product for wireless communications in a wireless network having a non-transitory computer-readable medium is disclosed. The computer readable medium has non-transitory program code recorded thereon which, when executed by the processor(s), causes the processor(s) to perform operations of monitoring at least two different control regions in a subframe for control information, in which the two control regions do not overlap in time. The program code also causes the processor(s) to receive the subframe including control information in at least one of the two different control regions.

Another aspect discloses a computer program product for wireless communications in a wireless network having a non-transitory computer-readable medium is disclosed. The computer readable medium has non-transitory program code recorded thereon which, when executed by the processor(s), causes the processor(s) to perform operations of determining a control region to use for transmitting control information to a receiver based on a transport block size. The program code also causes the processor(s) to transmit control information in the determined control region.

In another aspect, an apparatus including means for monitoring at least two different control regions in a subframe for control information is disclosed. The monitored control regions do not overlap in time. Also included is a means for receiving the subframe including control information in at least one of the two different control regions.

Another aspect discloses an apparatus including means for determining a control region to use for transmitting control information to a receiver based on a transport block size. Also included is a means for transmitting control information in the determined control region.

DETAILED DESCRIPTION

The E-UTRAN includes the evolved Node B (eNodeB)106and other eNodeBs108. The eNodeB106provides user and control plane protocol terminations toward the UE102. The eNodeB106may be connected to the other eNodeBs108via a backhaul (e.g., an X2 interface). The eNodeB106may 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 eNodeB106provides an access point to the EPC110for a UE102. Examples of UEs102include 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 UE102may 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 eNodeB106is connected to the EPC110via, e.g., an S1 interface. The EPC110includes a Mobility Management Entity (MME)112, other MMEs114, a Serving Gateway116, and a Packet Data Network (PDN) Gateway118. The MME112is the control node that processes the signaling between the UE102and the EPC110. Generally, the MME112provides bearer and connection management. All user IP packets are transferred through the Serving Gateway116, which itself is connected to the PDN Gateway118. The PDN Gateway118provides UE IP address allocation as well as other functions. The PDN Gateway118is connected to the Operator's IP Services122. The Operator's IP Services122may include the Internet, the Intranet, an IP Multimedia Subsystem (IMS), and a PS Streaming Service (PSS).

FIG. 2is a diagram illustrating an example of an access network200in an LTE network architecture. In this example, the access network200is divided into a number of cellular regions (cells)202. One or more lower power class eNodeBs208may have cellular regions210that overlap with one or more of the cells202. The lower power class eNodeB208may be a remote radio head (RRH), a femto cell (e.g., home eNodeB (HeNodeB)), pico cell, or micro cell. The macro eNodeBs204are each assigned to a respective cell202and are configured to provide an access point to the EPC110for all the UEs206in the cells202. There is no centralized controller in this example of an access network200, but a centralized controller may be used in alternative configurations. The eNodeBs204are responsible for all radio related functions including radio bearer control, admission control, mobility control, scheduling, security, and connectivity to the serving gateway116.

FIG. 4is a diagram400illustrating an example of an uplink frame structure in LTE. The available resource blocks for the uplink 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 uplink 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 blocks410a,410bin the control section to transmit control information to an eNodeB. The UE may also be assigned resource blocks420a,420bin the data section to transmit data to the eNodeB. The UE may transmit control information in a physical uplink 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 uplink shared channel (PUSCH) on the assigned resource blocks in the data section. An uplink transmission may span both slots of a subframe and may hop across frequency.

FIG. 6is a block diagram of an eNodeB610in communication with a UE650in an access network. In the downlink, upper layer packets from the core network are provided to a controller/processor675. The controller/processor675implements the functionality of the L2 layer. In the downlink, the controller/processor675provides header compression, ciphering, packet segmentation and reordering, multiplexing between logical and transport channels, and radio resource allocations to the UE650based on various priority metrics. The controller/processor675is also responsible for HARQ operations, retransmission of lost packets, and signaling to the UE650.

Adaptive Control Channel Design for Balancing Data Payload Size and Decoding Time

In LTE Release 8, 9, and 10, the physical downlink control channel (PDCCH) is located within the first several symbols (e.g., one, two, three, or four) in a subframe and is fully distributed across the entire system bandwidth. Additionally, the physical downlink control channel is time domain multiplexed (TDM'ed) with a shared control channel, such as PDSCH, which effectively divides a subframe into a control region and a data region.

In Release 11, coordinated multipoint transmission (CoMP) schemes are supported. This feature provides an interference mitigation technique for improving overall communication performance. With CoMP, multiple base stations (e.g., eNodeBs110) collaborate to transmit data on the downlink and/or to receive on the uplink to/from one or more UEs. Downlink CoMP and uplink CoMP can be separately or jointed enabled for a UE. Some examples of CoMP schemes are described as follows. In joint transmission (directed to downlink CoMP), multiple eNodeBs transmit the same data meant for a UE. In joint reception (directed to uplink CoMP), multiple eNodeBs receive the same data meant for a UE. In coordinated beam forming, an eNodeB transmits to its UE using beams that are chosen to reduce interference to UEs in neighboring cells. In dynamic point(s) selection, the cell(s) involved in data transmissions may change from subframe to subframe. CoMP may exist in homogeneous networks and/or heterogeneous networks (HetNet). The connection between the nodes involved in CoMP can be X2 or fiber. In heterogeneous network CoMP, low power nodes may include remote radio heads (RRH).

The conventional physical downlink control channel does not include sufficient control capacity for coordinated multi-point (CoMP) scenarios. In particular, CoMP scenario4occurs when a macro eNodeB and connected remote radio heads (RRHs) use the same cell identification but transmit potentially different data in a coordinated fashion.

An enhanced physical downlink control channel (ePDDCH) may improve control link performance for downlink coverage enhancements and may also provide a control channel solution for extension carriers. Extension carriers are non-standalone carriers that may not specify a legacy control region.

Those skilled in the art will appreciate that physical downlink control channel enhancement techniques have included using a new control region, linking efficiency gain with beamforming, using higher order modulation to conserve resources, and multiple user-multiple input multiple output (MU-MIMO) multiplexing.

LTE Release 11 includes an enhanced physical downlink control channel and other channels, such as an enhanced PCFICH (ePCFICH) and an enhanced PHICH (ePHICH). In contrast to the conventional PDCCH (e.g., legacy PDCCH), which occupies the first several control symbols in a subframe, the enhanced physical downlink control channel occupies the data region of the subframe, similar to the PDSCH. The enhanced physical downlink control channel may increase control channel capacity, support frequency-domain inter-cell interference coordination (ICIC), improve spatial reuse of control channel resources, support beamforming and/or diversity, and operate on the new carrier type and in MBSFN subframes. Furthermore, the enhanced physical downlink control channel may coexist on the same carrier as legacy UEs.

FIG. 7illustrates various enhanced physical downlink control channel structures (Alt1-Alt5). For example, in some cases, the enhanced physical downlink control channel structure may be the same as an R-PDCCH structure (Alt1). Alternately, the enhanced physical downlink control channel may be frequency division multiplexed (FDM'ed) with a data region (Alt2). Moreover, in an alternate structure, the enhanced physical downlink control channel structure may be time division multiplexed (TDM'ed) with the data region (Alt3). Alternately, the enhanced physical downlink control channel may be similar, but not the same as R-PDCCH (Alt4). In another alternate structure, the enhanced physical downlink control channel may combine TDM and FDM (Alt5). For example, the downlink grants may be time division multiplexed with the data region whereas the uplink grants may be frequency division multiplexed with the data region.

The present disclosure provides aspects for the mapping an enhanced physical downlink control channel in the presence of other signals. The other signals may potentially include common reference signals (CRSs), a legacy control region, PSS/SSS, PBCH, PRSs (positioning reference signals), channel state information reference signals (CSI-RSs), and/or demodulation reference signals (DM-RSs).

FIG. 8illustrates a block diagram illustrating resource arrangements according to an aspect of the present disclosure. The block includes data subframes810and control subframes812. The control subframe812comprises two slots814and816, and each slot814and816includes resource elements. That is, each slot includes seven OFDM symbols in the time domain and twelve subcarriers in a frequency domain, and each slot comprises resource elements that may be grouped as resource blocks (RBs). Within a slot of the control subframe812, as previously discussed, the legacy control region (PDCCH) is allocated to the first one, two, or three OFDM symbols. In some cases, such as the 1.4 MHz bandwidth, the legacy control region is allocated to the first four OFDM symbols. According to an aspect of the present disclosure, the new control region (ePDCCH) is allocated to resource elements of one or more slots that are not allocated by the legacy control region, a CRS, or a DM-RS.

As shown inFIG. 8, according to an aspect, the legacy control region is allocated to the first three OFDM symbols of the control subframe812. Furthermore, some of the resource elements of the first and second slots814and816are allocated to the CRS and the DM-RS. Finally, the new control region is allocated to the remaining resource elements of the first slot814and also the remaining resource elements of the second slot816. The remaining resource elements refer to resource elements that are not allocated to the legacy control region, the CRS, or the DM-RS.

AlthoughFIG. 8illustrates the new control region occupying all of the remaining resource elements of the first and second slots, the present disclosure is not limited to the new control region occupying all of the remaining resource elements of a subframe. Specifically, the new control region may be allocated to some or all of the remaining resource elements of the first slot and/or the second slot. Furthermore, aspects of the present disclosure provide for the new control region occupying resource elements of one or two slots, however, the new control region may be divided into other sizes, and is not limited to the two slots of a subframe.

In LTE Release 8, 9, and 10, the turnaround time for UE acknowledgement (ACK) is 4 ms. For example, the UE may transmit a positive or negative ACK in subframe n+4 if the PDCCH and PDSCH are transmitted to a UE in subframe n. According to an aspect, the decoding time for the new control region is reduced. For example, the decoding time may be reduced to 2.5-3 ms. In particular, the decoding time is reduced to about 3 ms if the new control region only occupies the unoccupied resource elements of the first slot. Additionally, the decoding time is reduced to approximately 2.5-3 ms if new control region occupies the unoccupied resource elements of the second slot, or the unoccupied resource elements of both the first and second slots.

It should be noted that in a conventional system, the reduced decoding times is only available via a redesign of the demodulation back end hardware. Accordingly, aspects of the present disclosure provide for a reduced decoding time without hardware modifications.

In one aspect, the maximum transport block size (TBS) is limited as a function of the available decoding time. For example, for a legacy control region, the maximum transport block size (Max_TBS) maybe be expressed as:
Max_TBS=Cmax(1)

For the new control region, when the new control region occupies resource elements of only the first slot, the maximum transport block size may be expressed as:
Max_TBS=Cmax/x(2)

Furthermore, for the new control region, when the new control region occupies resource elements of the first slot and the second slot, the maximum transport block size may be expressed as:
Max_TBS=Cmax/y(3)

In EQUATIONS 1, 2, and 3, Cmaxis the maximum transport block size allowed by the UE category. Parameters x and y are chosen parameters, with both x and y being greater than or equal to one. The parameters x and y may be selected based on various factors, such as, the new control region decoding time, symbol pre-processing time, MIMO mode, transmission rank, or use of UE interference cancellation.

Although the maximum transport size specifies which slot may be used, the specification is not exclusive. For example, the transport block may be allocated to the first slot or the legacy control region even if the maximum transport size designates the second slot for the new control region. Similarly, the transport block may be allocated to the legacy control region even if the first slot is designated for the new control region.

In some cases, up to two transport blocks (TBs) may be used in a multiple input multiple output (MIMO) system. Thus, the combined MIMO transport block size may be considered. Alternatively, the transport block size may be compared with a different Cmaxwhen allocating MIMO transport blocks.

In one aspect, the common search space control messages may be transmitted in the legacy control region. Because legacy UEs may be present in a network, the legacy control region is specified for all or most subframes. The legacy control region and the new control region may be present in the same subframe. Still, when the new control region is specified for a subframe, the number of OFDM symbols allocated to the legacy subframe may be reduced in comparison to the number of OFDM symbols occupied with the new control region is not used. The number of OFDM symbol occupied is reduced due to control off-load.

A UE may be semi-statically configured to monitor a UE-specific search space in either the legacy control region or the new control region. The UE may also be requested to monitor both the legacy control region and the new control region. The control may be sent based on the size of the transport block. Furthermore, the decoding time specified for a large transport block may be greater than the decoding time specified for a small transport block.

In some cases, so as not to increase the number of blind decodes performed by the UE, the UE-specific search space may be in either the legacy control region or the new control region. The common search space would remain in the legacy control region.

In another aspect, the search space may be divided based on an aggregation size. For example, when an aggregation level is one, the UE may first monitor two decoding hypotheses (i.e. decoding candidates) in the legacy control region and then monitor four decoding hypotheses in the new control region. Furthermore, when the aggregation level is two, the UE can first monitor two decoding hypotheses (i.e. decoding candidates) in the legacy control region and then monitor four decoding hypotheses in the new control region. Furthermore, when the aggregation level is four the UE can first monitor one decoding hypothesis in the legacy control region and then monitor one decoding hypothesis in the new control region. Moreover, when the aggregation level is eight the UE may only monitor the legacy control region. The aggregation level dependent division of the decoding hypotheses (decoding candidates) may be specified in the standard or semi-statically configured for the UE. Still, the common search space (e.g., broadcast SIBs (system information blocks) may remain in the legacy control region.

According to aspects of the present disclosure, the existing demodulating hardware can be reused by limiting the maximum transport block size (TBS) as a function of the E-PDCCH duration. Furthermore, the decoding time is reduced for a small transport block size, and therefore, the new control region may be specified. For a large transport block size, the control information may be specified in the legacy control region because there are only a few UEs scheduled due to the limitation represented by cell capacity.

In some cases, when the new control region is used with beamforming for coverage extension purposes, the signal to noise ratio (SNR) is moderate. Therefore, maximum transport block size may be naturally limited. Accordingly, the decoding time may be reduced and the use of the new control region is viable.

FIG. 9Aillustrates a method901for monitoring control regions. In block910, a UE (user equipment) monitors at least two different control regions in a subframe for control information. The control regions do not overlap in time. In block912, the UE receives a subframe including control information in at least one of the two different control regions.

FIG. 9Billustrates a method902for limiting transport block size. In block920, an eNodeB determines a control region to use for transmitting control information to a receiver based on a transport block size. In block922, the eNodeB transmits control information in the determined control region.

In one configuration, the eNodeB610is configured for wireless communication including means for determining. In one aspect, the determining means may be the controller/processor675and memory676configured to perform the functions recited by the determining means. The eNodeB610is also configured to include a means for transmitting. In one aspect, the transmitting means may be the transmit processor616, modulators618and antenna620configured to perform the functions recited by the transmitting means. In another aspect, the aforementioned means may be any module or any apparatus configured to perform the functions recited by the aforementioned means.

In one configuration, the UE650is configured for wireless communication including means for monitoring. In one aspect, the monitoring means may be the controller/processor659, receive processor656, modulators654, and antenna652configured to perform the functions recited by the monitoring means. The UE650is also configured to include a means for receiving. In one aspect, the receiving means may be the controller/processor659, receive processor656, modulators654, and antenna652configured to perform the functions recited by the receiving means. In another aspect, the aforementioned means may be any module or any apparatus configured to perform the functions recited by the aforementioned means.

FIG. 10is a conceptual data flow diagram illustrating the data flow between different modules/means/components in an exemplary apparatus1000. The apparatus1000includes a monitoring module1002that monitors at least two different control regions in a subframe for control information. The monitoring module1002monitors the control regions of subframes received via the receiving module1006. The receiving module1006receives subframes on a signal1010. Furthermore, the receiving module1006may also receive a subframe including control information in at least one of the two different control regions. The apparatus may include additional modules that perform each of the steps of the algorithm in the aforementioned flow chartsFIGS. 9A and 9B. As such, each step in the aforementioned flow chartsFIGS. 9A and 9Bmay be performed by a module and the apparatus may include one or more of those modules. The modules may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof.

FIG. 11is a conceptual data flow diagram illustrating the data flow between different modules/means/components in an exemplary apparatus1100. The apparatus1100includes a determining module1102that determines a control region to use for transmitting control information to a receiver based on a transport block size. The determining module1102may then control a transmission module1108to transmit control information in the determined control region. The control information may be transmitted via a signal1112transmitted via the transmission module1108. The apparatus may include additional modules that perform each of the steps of the algorithm in the aforementioned flow chartsFIGS. 9A and 9B. As such, each step in the aforementioned flow chartsFIGS. 9A and 9Bmay be performed by a module and the apparatus may include one or more of those modules. The modules may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof.

FIG. 12is a diagram illustrating an example of a hardware implementation for an apparatus1200employing a processing system1214. The processing system1214may be implemented with a bus architecture, represented generally by the bus1224. The bus1224may include any number of interconnecting buses and bridges depending on the specific application of the processing system1214and the overall design constraints. The bus1224links together various circuits including one or more processors and/or hardware modules, represented by the processor1222the modules1202,1204,1206and the computer-readable medium1226. The bus1224may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

The apparatus includes a processing system1214coupled to a transceiver1230. The transceiver1230is coupled to one or more antennas1220. The transceiver1230enables communicating with various other apparatus over a transmission medium. The processing system1214includes a processor1222coupled to a computer-readable medium1226. The processor1222is responsible for general processing, including the execution of software stored on the computer-readable medium1226. The software, when executed by the processor1222, causes the processing system1214to perform the various functions described for any particular apparatus. The computer-readable medium1226may also be used for storing data that is manipulated by the processor1222when executing software.

The processing system1214includes a monitoring module1202for monitoring at least two different control regions in a subframe for control information. The processing system1214also includes a receiving module1204for receiving a subframe including control information in at least one of the two different control regions. The modules may be software modules running in the processor1222, resident/stored in the computer-readable medium1226, one or more hardware modules coupled to the processor1222, or some combination thereof. The processing system1214may be a component of the UE650and may include the memory660, and/or the controller/processor659.

FIG. 13is a diagram illustrating an example of a hardware implementation for an apparatus1300employing a processing system1314. The processing system1314may be implemented with a bus architecture, represented generally by the bus1324. The bus1324may include any number of interconnecting buses and bridges depending on the specific application of the processing system1314and the overall design constraints. The bus1324links together various circuits including one or more processors and/or hardware modules, represented by the processor1322the modules1302,1304,1306and the computer-readable medium1326. The bus1324may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

The apparatus includes a processing system1314coupled to a transceiver1330. The transceiver1330is coupled to one or more antennas1320. The transceiver1330enables communicating with various other apparatus over a transmission medium. The processing system1314includes a processor1322coupled to a computer-readable medium1326. The processor1322is responsible for general processing, including the execution of software stored on the computer-readable medium1326. The software, when executed by the processor1322, causes the processing system1314to perform the various functions described for any particular apparatus. The computer-readable medium1326may also be used for storing data that is manipulated by the processor1322when executing software.

The processing system1314includes a determining module1302for determining a control region to use for transmitting control information to a receiver based on a transport block size. The processing system1314also includes a transmitting module1304for transmitting control information in the determined control region. The modules may be software modules running in the processor1322, resident/stored in the computer-readable medium1326, one or more hardware modules coupled to the processor1322, or some combination thereof. The processing system1314may be a component of the eNodeB610and may include the memory676, and/or the controller/processor675.