WO2015106456A1

WO2015106456A1 - Ack/nack feedback selection and management

Info

Publication number: WO2015106456A1
Application number: PCT/CN2014/070920
Authority: WO
Inventors: Jingxiu Liu; Yuyu YAN; Li Zhang; Peter Skov
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2014-01-20
Filing date: 2014-01-20
Publication date: 2015-07-23

Abstract

A method includes selecting, by a base station and based on one or more criteria, one of a number of feedback formats for individual ones of a number of UEs to use to report ack/nack information. More than one feedback format is used simultaneously by the base station for different user equipment within a single cell. The base station selects resources for the selected feedback formats. The base station informs UEs of corresponding selected feedback formats and resources to be used by the UEs to report the ack/nack information on the uplink channel. The base station receives transmissions on the uplink channel from the UEs based on corresponding selected feedback formats and in corresponding selected resources. Apparatus, computer programs, and program products are disclosed.

Description

ACK/NACK FEEDBACK SELECTION AND MANAGEMENT

TECHNICAL FIELD

[0001] This invention relates generally to wireless communications and, more specifically, relates to acknowledge (ACK)/not acknowledge (NACK) feedback.

BACKGROUND

[0002] This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section. Abbreviations that may be found in the specification and/or the drawing figures are defined below at the end of the specification but prior to the claims.

[0003] Generally speaking or in most of the universal realistic scenarios, the LTE system is an uplink-limited system, which means uplink may face more critical situations on link budget. For instance, it has been said that the LTE specification provides downlink peak rates of 300 Mbit/s, but uplink peak rates of 75 Mbit/s. It is believed this difference in design occurs because LTE designers were originally more concerned with getting more data, such as video, to users, and so the downlink was designed for this purpose.

However, with the explosion of video sharing applications, social networking, and the like, more people are uploading data, and the data they are uploading can require high data rates.

[0004] Furthermore between PUSCH and PUCCH, sometimes PUCCH is a bottleneck and sometimes PUSCH is a bottleneck, depending on PUSCH data rate requests. On the other hand, PUCCH performance will have a large impact on DL throughput, since ACK/NACK and SRs are carried by PUCCH.

[0005] As is known, A/N information is information indicative of whether a previous transmission was received correctly or not. Such A/N information is reported from a UE to an eNB on PUCCH. In 3GPP Rel-8, A/N multiplexing and A/N bundling are designed more specifically for LTE TDD, due to an unbalanced number of downlink and uplink subframes.

Furthermore, in 3GPP Rel-10, PUCCH format 3 is also introduced to cover multiple carrier (greater than two) scenarios for both FDD and TDD. That is, multiple carriers may be used for both downlink and uplink, including Ack/Nack information. The PUCCH format 3 in particular allows transmission of up to 10 Ack/Nack bits for FDD and up to 20 Ack/Nack bits for TDD. [0006] Although there have been improvements in the handling of Ack/Nack information, such as the PUCCH format 3, additional improvements could still be made.

SUMMARY

[0007] This section contains examples of possible implementations and is not meant to be limiting.

[0008] An exemplary embodiment is a method, comprising: selecting, by a base station and based on one or more criteria, one of a plurality of feedback formats for individual ones of a plurality of user equipment to use to report ack/nack information indicative of whether a previous transmission was received correctly or not by the individual user equipment, wherein more than one feedback format is used simultaneously by the base station for different user equipment within a single cell; selecting by the base station resources for the selected feedback formats; informing by the base station the plurality of user equipment of corresponding selected feedback formats and resources to be used by the user equipment to report the ack/nack information on the uplink channel; and receiving by the base station transmissions on the uplink channel from the plurality of user equipment based on corresponding selected feedback formats and in corresponding selected resources.

[0009] A method as above, wherein the one or more criteria comprise uplink load and selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment further comprises selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment based on the uplink load for the individual feedback formats on the uplink channel. A method as in this paragraph, wherein selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment based on uplink load for the individual feedback formats on the uplink channel further comprises in response to a feedback format x's physical resource block load being less than y percent, then reallocating physical resource blocks reserved for that feedback format x to at least one other feedback format or to a physical uplink shared channel, where x is one or three and y is a number greater than zero.

[0010] A method as above, wherein the one or more criteria comprise uplink load and selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment further comprises selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment based on uplink load for a physical uplink shared channel and in response to the uplink load for a physical uplink shared channel being greater than a threshold, selecting a feedback format with a smaller consumption per user than other ones of the plurality of feedback formats; [0011] A method as above, wherein the one or more criteria comprise carrier aggregation statuses of each of the plurality of user equipment and wherein selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises for a given user equipment that is not carrier aggregation capable, selecting as a selected feedback format one of ack/nack bundling or ack/nack multiplexing for the given user equipment.

[0012] A method as above, wherein the one or more criteria comprise carrier aggregation statuses of each of the plurality of user equipment and wherein selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises for a given user equipment that is carrier aggregation capable and has one serving cell, selecting as a selected feedback format one of ack/nack bundling or ack/nack multiplexing or format 3 for the given user equipment. A method as above, wherein the one or more criteria comprise carrier aggregation statuses of each of the plurality of user equipment and wherein selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises for a given user equipment that is carrier aggregation capable and has two serving cells, selecting as a selected feedback format one of format 3 or channel selection for the given user equipment. A method as above, wherein the one or more criteria comprise carrier aggregation statuses of each of the plurality of user equipment and wherein selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises for a given user equipment that is carrier aggregation capable and has more than two serving cells, selecting format 3 as a selected feedback format for the given user equipment.

[0013] A method as in the previous paragraph, wherein the uplink channel is a physical uplink control channel and wherein selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises performing the following: selecting format 3 for the selected ack/nack feedback format for the given user equipment in response to all of the following being true: the signal to interference noise ratio for the given user equipment supports format 3; the given user equipment is scheduled a predetermined number of times within one bundling window; a physical uplink shared channel resource utilization is below a threshold; and a resource is available on the physical uplink control channel; otherwise, selecting an ack/nack feedback format other than format 3 as the selected ack/nack feedback format for the given user equipment.

[0014] A method as above, wherein the one or more criteria comprise radio channel conditions of each of the plurality of user equipment and wherein different feedback formats have different required radio channel conditions, and wherein selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment further comprises considering for a given user equipment only those feedback formats for selection that have radio channel conditions for the given user equipment above the corresponding required signal to interference ratios. A method as in this paragraph, wherein signal to interference noise ratios for the plurality of user equipment are used as a metric of the radio channel conditions for the plurality of user equipment.

[0015] A method as above, wherein the uplink channel is a physical uplink control channel.

[0016] In another exemplary embodiment, an apparatus comprises: means for selecting, by a base station and based on one or more criteria, one of a plurality of feedback formats for individual ones of a plurality of user equipment to use to report ack/nack information indicative of whether a previous transmission was received correctly or not by the individual user equipment, wherein more than one feedback format is used simultaneously by the base station for different user equipment within a single cell; means for selecting by the base station resources for the selected feedback formats; means for informing by the base station the plurality of user equipment of corresponding selected feedback formats and resources to be used by the user equipment to report the ack/nack information on the uplink channel; and means for receiving by the base station

transmissions on the uplink channel from the plurality of user equipment based on corresponding selected feedback formats and in corresponding selected resources.

[0017] An apparatus as above, wherein the one or more criteria comprise uplink load and the means for selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment further comprises means for selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment based on the uplink load for the individual feedback formats on the uplink channel. An apparatus as in this paragraph, wherein the one or more criteria comprise uplink load and the means for selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment further comprises means for selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment based on uplink load for a physical uplink shared channel and means, in response to the uplink load for a physical uplink shared channel being greater than a threshold, for selecting a feedback format with a smaller consumption per user than other ones of the plurality of feedback formats;

[0018] An apparatus as above, wherein the one or more criteria comprise carrier aggregation statuses of each of the plurality of user equipment and wherein the means for selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises means, for a given user equipment that is not carrier aggregation capable, for selecting as a selected feedback format one of ack/nack bundling or ack/nack multiplexing for the given user equipment.

[0019] An apparatus as above, wherein the one or more criteria comprise carrier aggregation statuses of each of the plurality of user equipment and wherein the means for selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises means, for a given user equipment that is carrier aggregation capable and has one serving cell, for selecting as a selected feedback format one of ack/nack bundling or ack/nack multiplexing or format 3 for the given user equipment. An apparatus as above, wherein the one or more criteria comprise carrier aggregation statuses of each of the plurality of user equipment and wherein the means for selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises means, for a given user equipment that is carrier aggregation capable and has two serving cells, for selecting as a selected feedback format one of format 3 or channel selection for the given user equipment. An apparatus as above, wherein the one or more criteria comprise carrier aggregation statuses of each of the plurality of user equipment and wherein the means for selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises means, for a given user equipment that is carrier aggregation capable and has more than two serving cells, for selecting format 3 as a selected feedback format for the given user equipment.

[0020] An apparatus as in the previous paragraph, wherein the uplink channel is a physical uplink control channel and wherein the means for selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises the following: means for selecting format 3 for the selected ack/nack feedback format for the given user equipment in response to all of the following being true: the signal to interference noise ratio for the given user equipment supports format 3; the given user equipment is scheduled a predetermined number of times within one bundling window; a physical uplink shared channel resource utilization is below a threshold; and a resource is available on the physical uplink control channel; otherwise, using a means for selecting an ack/nack feedback format other than format 3 as the selected ack/nack feedback format for the given user equipment.

[0021] An apparatus as above, wherein the one or more criteria comprise radio channel conditions of each of the plurality of user equipment and wherein different feedback formats have different required radio channel conditions, and wherein the means for selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment further comprises means for considering for a given user equipment only those feedback formats for selection that have radio channel conditions for the given user equipment above the corresponding required signal to interference ratios. An apparatus as in this paragraph, wherein signal to interference noise ratios for the plurality of user equipment are used as a metric of the radio channel conditions for the plurality of user equipment.

[0022] Another exemplary embodiment is a system comprising the apparatus of any of the apparatus above.

[0023] In a further exemplary embodiment, a computer program comprises program code for executing the method according to any of the methods above. The computer program according to this paragraph, wherein the computer program is a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In the attached Drawing Figures:

[0025] FIG. 1 illustrates an exemplary system in which the exemplary

embodiments may be practiced;

[0026] FIG. 2 illustrates examples of A N bundling and multiplexing and when spatial multiplexing is used;

[0027] FIG. 3, including FIG. 3A and FIG. 3B, provides examples of A N feedback for carrier aggregation;

[0028] FIG. 4 is a graph of cumulative distribution function (CDF) versus UE SINR in dB;

[0029] FIG. 5 is a block diagram of an exemplary logic flow diagram for selecting format 3 over other formats; and

[0030] FIG. 6, including FIGS. 6A and 6B, is a block diagram of an exemplary logic flow diagram performed by a base station for ACK/NACK feedback selection and management that illustrates the operation of an exemplary method, a result of execution of computer program instructions embodied on a computer readable memory, and/or functions performed by logic implemented in hardware, in accordance with exemplary embodiments herein. DETAILED DESCRIPTION OF THE DRAWINGS

[0031] Before proceeding with description of additional problems with current Ack/Nack handling, reference is now made to FIG. 1 , which illustrates an exemplary system in which the exemplary embodiments may be practiced. In FIG. 1 , a user equipment (UE) 1 10-1 is in wireless communication with a wireless network 100 via a wireless link 1 15-1 with eNB 107, which is an LTE base station (in this example) providing access to and from the wireless network 100. It is assumed that there may be X UEs 1 10, each of which may be in wireless communication with the wireless network 100 using X wireless links 1 15-1 through 1 15-X, respectively.

[0032] It is further assumed that the UEs 1 10 are similar and therefore only an exemplary implementation of the UE 1 10-1 is shown. The user equipment 1 10-1 includes one or more antennas 128 (multiple antennas are shown), one or more processors 120, one or more memories 125, and one or more transceivers 130, interconnected using one or more buses 127. The one or more buses 127 may be any physical devices for interconnecting electronic elements, such as traces on a board, metal or other conductive runs on an integrated circuit, optic channels or elements, and the like. Each of the one or more transceivers 130 includes one or more transmitters (Tx) 131 , one or more receivers (RX) 132, or both. The one or more memories include computer program code 123. The UE 1 10-1 also includes an A/N feedback control process 180. The A/N feedback control process 180 may be implemented via the computer program code 123, such that the one or more memories 125 and the computer program code 123 are configured to, with the one or more processors 120, cause the eNB 107-1 to perform one or more of the operations as described herein. The A/N feedback control process 180 may be implemented as hardware logic, such as in an integrated circuit, a gate array or other programmable device, discrete circuitry, and the like. The A/N feedback control process 180 could be implemented through some combination of computer program code 123 and hardware logic. Regarding the A/N feedback control process 180, if this process is defined, this process shall only be used to receive the A/N configuration from the eNB 107, and control the UE to feedback A/N following the eNB's configuration. It is intended that the UE will not cause any impact to the eNB's decision making.

[0033] The wireless network 100 includes the eNB 107. The eNB 107includes one or more antennas 158. The eNB 107 further includes one or more processors 150, one or more memories 155, one or more network interfaces (N/W l/F(s)) 165, and one or more transceivers 160 (each comprising a transmitter, Tx, 161 and a receiver, Rx, 162) interconnected through one or more buses 157. The one or more buses 157 may be any physical devices for interconnecting electronic elements, such as traces on a board, metal or other conductive runs on an integrated circuit, optic channels or elements, and the like. The one or more transceivers are connected to the antennas 158. The one or more memories 155 include computer program code 153. The eNB 107 includes an A/N feedback control process 170. The A/N feedback control process 170 may be

implemented via the computer program code 153, such that the one or more memories 155 and the computer program code 153 are configured to, with the one or more processors 150, cause the eNB 107 to perform one or more of the operations as described herein. The A/N feedback control process 170 may be implemented as hardware logic, such as in an integrated circuit, a gate array or other programmable device, discrete circuitry, and the like. The A/N feedback control process 170 could be implemented through some combination of computer program code 153 and hardware logic.

[0034] The one or more network interfaces 165 communicate over networks such as the networks 173, 175. The eNB 107 may communicate with other eNBs using, e.g., network 173. The network 173 may be wired or wireless or both and may implement, e.g., an X2 interface. The eNB 107 may use the network 175 to communicate with a core portion of the wireless network 100 (e.g., and to other elements such as the Internet).

[0035] The eNB 107 is assumed to create one or more cells, of which cell 198 is illustrated. The edge 199 of the cell 198 is also shown. The cell 198 makes up part of an eNB. That is, there can be multiple cells 198 per eNB. For instance, there could be three cells 198 for a single eNB carrier frequency and associated bandwidth, each cell 198 covering one-third of a 360 degree area so that the single eNB's coverage area covers an approximate oval or circle. Furthermore, each cell 198 can correspond to a single carrier and an eNB may use multiple carriers. So if there are three 120 degree cells 198-1 , 198-2, and 198-3 per carrier C and two carriers C, then the eNB has a total of 6 cells. The example of FIG. 1 shows N carriers Ci through C_N.

[0036] The computer readable memories 125 and 155 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The processor(s) 120 and 150 may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, general or special purpose integrated circuits, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples.

[0037] Before proceeding with additional description of exemplary problems with conventional systems and exemplary embodiments herein to ameliorate or solve these problems, below are some considerations about PUCCH format 3, which is a brand new feedback container.

[0038] Regarding PRB resource selection, the following may be used for such selection:

[0039] Alternative 1 ) Fixed resource reservation, e.g., two PRBs, where the resource is located at the edge of current MaxPucchResourceSize (e.g., the largest possible size of PUCCH, in terms of PRBs); or [0040] Alternative 2) Resource reservation based on need (number of UEs configured to use format 3) or UL load (on PUSCH), where the resource is located around the center of the carrier.

[0041] Regarding UE configuration, the following are examples of such:

[0042] 1 ) A UE with more than two serving cells is configured to use format 3. If a UE is capable of aggregating three carriers and this feature is supported at eNB, it should be checked if the SINR required by format 3 (e.g., an eNB internal parameter, the exact value of which is out of the scope of this disclosure; an example can be 6 dB as shown in FIG. 4) is supported before the UE can be configured with three carriers. It should be noted that in TDD, it could happen that the payload size for three carriers is smaller than that for two carriers.

[0043] 2) A UE with two serving cells is selectively configured to use format 3. For instance, UEs are checked periodically, and for each UE a metric is calculated based on its SINR estimate (e.g., assuming worst case interference, and considering CoMP usage) and DL scheduling activity. If CoMP is considered, some mechanism (e.g., dummy UL grant) is needed to ensure PUSCH is always scheduled for A/N. A dummy UL grant is used to schedule PUSCH when the eNB determines the UE's buffer is empty. If scheduled, the UE will transmit PUSCH with only padding. The A/N information can be transmitted on PUSCH, or on PUCCH when PUSCH is not scheduled. In an exemplary embodiment, UEs are sorted with the calculated metric and placed into the total format 3 resources.

[0044] Regarding resource allocation, for each format 3 qualified UE, the four candidate resources should be allocated in the same PRB. There are five resources in each PRB, which may be allocated as follows:

[0045] Alternative 1 ) A random four resources are allocated; or

[0046] Alternative 2) Resources are split into two groups (e.g., {0,1 ,2,3} and {1 ,2,3,4}), and one of these groups is allocated.

[0047] Typically, each UE will be configured with four resources of format 3, and one of them will be selected for A/N feedback in each TTI. There are at most five resources per PRB as defined by 3GPP TS 36.21 1 , and that means at most five UEs can be multiplexed within one PRB. For format 1 , there can be at most 36 resources per PRB.

[0048] Concerning problems with conventional systems, the A/N bundling and multiplexing in a single carrier scenario are explained and compared in reference to FIG. 2. FIG. 2 illustrates examples of A/N bundling and multiplexing and when spatial multiplexing is used. FIG. 2 assumes two spatial streams (rank 2) per each downlink TTI. A number of subframes 220, 230 are shown, where "D" indicates DL, "U" indicates UL, and "S" indicates special. [0049] A/N bundling 250 is shown in the left of the figure. A/N bundling 250 is bundling performed in the time domain. With only one spatial stream 210, one bit A/N feedback is used for a cell-edge UE 1 10 (that is, a UE 1 10 near the edge 199). This bundling technique especially fits to the scenario when the timing correlation is large (e.g., for a slow moving UE). A slow moving UE could be, e.g., 3 Km/hr. In this example, an XOR operation is performed for A/N bits from the streams 210-1 in subframes 220-5, 220-6, 220-7, and 220-9 to create a single bit b(0) and another XOR operation is performed for A/N bits from the streams 210-2 in subframes 220-5, 220-6, 220-7, and 220-9 to create a single bit b(1 ).

[0050] Regarding A/N multiplexing 260, this is bundling in the spatial domain.

Regardless the number of spatial streams, two bits of A/N feedback is used for a cell center UE (that is, a UE near the eNB 107). A/N multiplexing 260 especially fits to the scenario when spatial correlation is large. Large spatial correlation can be caused when the spacing of antennas is small, for example. Such small antenna spacing could be, e.g., half lamba (λ ) spacing. In this example, XOR operations are performed for the streams 210-1 and 210-2, each creating a single A/N bit, for each of the subframes 230-5, 230-6, 230-7, and 230-9. After the A/N bits are created, there is a table mapping that occurs to map the A/N bits into bits b(0) and b(1 ). The " n_P ^l _{UCCH i} : location of PUCCH" in the figure indicates that the location of the PUCCH resource, which is used for transmission of b(0) and b(1 ), is also part of the table mapping.

[0051] FIG. 3 includes FIG. 3A and FIG. 3B and provides examples of A/N feedback for carrier aggregation. Under certain circumstance with carrier aggregation, eNBs will configure for each UE either format 3 or channel selection to be used for A/N feedback. FIG. 3A is directed to a TDD UL/DL configuration number one (config. #1 ) while FIG. 3B is directed to a TDD UL/DL configuration number two (config. #2). A single

UE-specific UL CC is configured semi-statically for carrying PUCCH ACK/NACK

corresponding to multiple DL CCs 310-1 and 310-2 in this example. Concerning channel selection, if the number of A/N bits is less than or equal to four, no bundling is used (called mode a). This is shown by reference 330, where two subframes 220-5 for component carriers 310-1 and 310-2 are multiplied by two codewords to create four bits. If the number of A/N bits is greater than four, time-domain bundling will be used (called mode b). This is shown by reference 340, where four subframes 220-1 , 220-2 for component carriers 310-1 and 310-2 are multiplied by two codewords to create eight bits.

[0052] For PUCCH format 3, this supports A/N payload size of up to 20 bits. An example is illustrated by reference 350, where eight subframes 220-1 , 220-2, 220-3 and 220-5 for component carriers 310-1 and 310-2 are multiplied by two codewords to create 16 bits. Spatial bundling is only used in the case of more than 20 bits.

[0053] An exemplary problem is that now only one kind of A N feedback will be used for the entire cell and the UE therein. This means either some users with good SINR will experience DL throughput drop if configured with A/N bundling and A/N multiplexing, or some users with poor SINR will lose connection due to being unable to support higher payload PUCCH, e.g., format 3.

[0054] Furthermore from FIG. 4, it can be seen that PUCCH format 3 can be supported by many users when inter-site distance (ISD) is not too big, and in this case it should be possible to optimize the configuration of different A/N feedback schemes. In this figure, "format 1 " is PUCCH format 1 (which uses a single bit for A/N feedback). Here, 12dB is the offset between the 10% (percent) SINR CDF percentile of case 1 and case 3. This implies in that in case 3, most of the UEs cannot support PUCCH format 3, whereas most UEs for case 1 can support PUCCH format 3. For a cell with large ISD (e.g., an example of which can be 1732m, as this value is commonly used in simulations as large ISD scenario), which is a power limited scenario, a UE will have a lower SINR than will a UE for a cell with small ISD. For small ISD, PUCCH format 3 can be supported by most of UEs since most of the UEs have high SINR. As indicated above the SINR required by format 3 is an eNB internal parameter, the exact value of which is out of the scope of this disclosure; an example can be 6 dB as shown in FIG. 4. For large ISD, where SINR is decreased relative to small ISD, then PUCCH format 3 may not be supported by most of UEs.

[0055] In order to improve these scenarios, the exemplary embodiments herein propose to enable more than one A/N feedback format for the same cell at the same time. Such A/N feedback formats include of A/N bundling, A/N multiplexing, PUCCH format 3, and channel selection. The eNB 107 may select an adequate scheme for each UE based on multiple factors in order, e.g., to optimize network performance and user satisfaction.

[0056] An exemplary aspect herein is which factors are to be used for selecting a feedback scheme. As different feedback formats require different SINR, it is important to ensure that a certain UE 1 10 will be able to achieve a high enough SINR on the assigned

PUCCH resource of the A/N feedback format to allow the UE to communicate reliably. Here, a need is highlighted to base the SINR estimation on the intended PUCCH resource, as SINR can be quite different for different PUCCH resources. It is noted that PUCCH SINR depends on a number of factors such as:

[0057] 1 ) Received power at the eNB, including the following:

[0058] i. Power control settings for the UE; and [0059] ii. CoMP. This is a scheme where the signal from one UE could be jointly processed by multiple base stations, hence the received SINR of that UE is improved over processing b a single base station.

[0060] 2) Intra-cell interference, including the following:

[0061] i. PUCCH muxing (multiplexing) level. In one cell, the PUCCH of different UEs could be code multiplexed. If only one UE is in the system, then there will be no intra-cell interference. Thus, the muxing level depends on how many UEs are code multiplexed;

[0062] ii. Radio channel orthogonality (e.g., the better the orthogonality, the less intra-cell interference there will be);

[0063] iii. Muxed users' power control settings; and

[0064] iv. IRC, IRC + CoMP (e.g., IRC provides reduced interference since interference from multiple signals from a single UE can be reduced and the multiple signals combined) .

[0065] 3) Inter-cell interference, including the following:

[0066] i. Neighbor cell PUCCH load (e.g., the higher the PUCCH load is on a neighbor cell, the more inter-cell interference there will be); and

[0067] ii. Neighbor cell PUCCH power control settings (e.g., the higher the power level for power control settings for PUCCH are, the higher the inter-cell

interference).

[0068] In addition, it is noted that different Ack/Nack feedback schemes will occupy varying amounts of PUCCH resources. So if uplink is a resource bottleneck, it may not be beneficial at the network level to trade more PUCCH PRBs for higher DL throughput. So uplink load might need to be included in the decision on feedback scheme selection.

[0069] Also, the benefit of having more Ack/Nacks is not significant if a same user is not scheduled multiple times within a bundling window, so this could be another condition to consider before selecting, e.g., format 3/Ack/Nack muxing.

[0070] Finally, it may not make sense to allocate new PUCCH PRBs for a certain format, e.g., if only one UE is using that format. Using a different format, meanwhile, may mean that there should be more users that can benefit from the different format.

[0071] Also, an example for allocating format 3 could be as illustrated by the following (and by FIG. 5, which begins in block 505):

[0072] 1 ) If UE SINR supports format 3 (block 510 = Yes) then next (block 515), else exit (block 510 = No, and the flow proceeds to block 535, where the flow ends);

[0073] 2) If the UE is scheduled often (e.g., twice or some other

predetermined number of times) within one bundling window (block 515 = Yes) then next (block 520), else exit (block 515 = No, and the flow proceeds to block 535) (e.g., if the UE is not scheduled often, format 3 will give similar DL performance as A/N multiplexing or channel selection, so there may not be a benefit to format 3). It is noted that a bundling window has a size of a number of downlink subframes associated with a single uplink subframe, applicable in TDD systems;

[0074] 3) If UL is not a bottleneck (e.g., PUSCH resource utilization is below a threshold) (block 520 = Yes) and a PUCCH resource is available (block 525 = Yes) then next (block 530), else exit (block 520 = No or block 525 = No, and the flow proceeds to block 535); and

[0075] 4) Allocate format 3 (block 530).

[0076] If an exit is taken above, it is checked if a next format (e.g., A/N multiplexing) can be allocated.

[0077] To monitor the load on different PUCCH formats and trigger reconfiguration based on the load, the following is proposed in an exemplary embodiment: If PUCCH format x's PRB load is < y% (percent) then reallocate PRBs reserved for that format x to other formats. The "x" may refer to 1 or 3, for instance, such that "PUCCH format x" is "PUCCH format 1 " or "PUCCH format 3", respectively. The PRB load is in percentage (e.g., of total possible PRB load). A possible value for y could be 20%, so when the utilization of PRBs reserved for format 3 is lower than 20%, no UE will be allocated to format 3, and the reserved PRBs will be used by other PUCCH formats (e.g., or PUSCH). It is noted that A/N bundling, A/N muxing and channel selection are all using format 1 .

[0078] Referring to FIG. 6, including FIGS. 6A and 6B, this figure is a block diagram of an exemplary logic flow diagram performed by a base station for ACK/NACK feedback selection and management. This figure illustrates the operation of an exemplary method, a result of execution of computer program instructions embodied on a computer readable memory, and/or functions performed by logic implemented in hardware, in accordance with exemplary embodiments herein. The blocks in the figure may be considered to be interconnected means for performing the functions in the blocks. It is assumed that FIG. 6 is performed by an eNB 107, e.g., under control of the A/N feedback control process 170.

[0079] In block 605, the eNB 107 determines SINRs of each of a plurality of UEs.

The plurality of UEs 1 10 are those UEs to which the ACK/NACK feedback selection and management is going to be applied. In general, the eNB 107 may have (as described above) multiple cells, each cell covering a certain number of degrees, e.g., in azimuth around the eNB, and multiple carriers, such that an eNB may control a number of cells 198, each cell using a carrier C. In block 610, the eNB 107 determines UL load (e.g., PRB load) on PUCCH. Determining UL load on PUCCH is currently performed at conventional eNBs, but the UL load is currently not used for A/N feedback mode selection. This UL load may be determined for each of the different PUCCH formats, as described above. In block 615, the eNB 107 determines the CA statuses of each of the plurality of UEs. For instance, a UE may not support CA, may support CA but have only one serving cell (a primary serving cell), or may support CA but have multiple serving cells (a primary serving cell and one or more secondary serving cells). A primary serving cell handles the RRC connection while the secondary serving cells do not.

[0080] In block 620, the eNB 107 selects, based on one or more criteria, one of a plurality of A/N feedback formats for individual ones of the plurality of UEs to use to report information indicative of whether a previous transmission was received correctly or not, wherein more than one feedback format is used simultaneously by the base station for different UEs within a single cell.

[0081] Block 680 shows one or more exemplary criteria 685 that may be used. For instance, criterion 685-21 indicates the selection in block 620 may be based on radio channel conditions for the UEs 1 10 and SINR is one possible metric of the radio channel conditions (e.g., as is pathloss). It should be noted that SINRs used to determine whether format 1 or format 3 A N feedback formats are supported are typically an eNB internal parameter, the exact value of which is out of the scope of this disclosure.

[0082] As indicated by criteria 685-2 and 685-3, UL load on the uplink channel may be used for selection in block 620. For criterion 685-2, UL load on the PUCCH, e.g., for each of the A/N feedback formats 631 may be used to determine which A/N feedback format 631 to select. For criterion 685-3, the UL load for PUSCH may be used. For instance, if PUSCH load is greater than a threshold, the eNB may select a feedback format with a smaller consumption per user than other ones of the plurality of feedback formats. Format 3 has a larger consumption per user than does all format 1 -based feedback formats (e.g., including A/N bundling, A/N muxing, and channel selection). In general, choosing between format 3 and a format 1 feedback format may be the only selection one can make to account for PUSCH load.

[0083] The criterion 685-4 is the carrier aggregation (CA) statuses of the UEs. Although it may be possible that all UEs in a cell might have the same CA statuses (and thus selection might not be based on CA statuses), but in general UEs may have different

CA statuses. According to 3GPP TS 36.213, e.g., section 10.1.3, a UE that is not CA capable (see reference 621 -1 ) (i.e., cannot support CA) can use A/N bundling (block 625) or A/N multiplexing (block 640), depending on RRC configuration; a UE that is CA capable but is only configured with one serving cell (see reference 621 -2) can use A/N bundling (block 625), A/N multiplexing (block 640) or format 3 (block 650), depending on RRC configuration; a UE that is CA capable and is configured with two serving cells (see reference 621-3) can use channel selection (block 660) or format 3 (block 650), depending on RRC configuration; and a UE that is CA capable and is configured with more than two serving cells (see reference 621-4) can only use format 3 (block 650). Thus, the eNB 107 takes into account the CA statuses 621 for each of the UEs 1 10, and the CA statuses 621 determine which A N feedback formats 631 may be selected by the eNB 107 for individual ones of the UEs 1 10 in blocks 625, 640, 650, and 660. Specifically, A/N feedback format 631-1 is A/N bundling, A/N feedback format 631-2 is A/N multiplexing, A/N feedback format 631-3 is format 3, and A/N feedback format 631-4 is channel selection.

[0084] If A/N bundling is selected in block 625 for a UE 1 10, the eNB 107 selects A/N bundling resources in block 630. If A/N multiplexing is selected in block 640 for a UE 1 10, the eNB 107 selects A/N multiplexing resources in block 645. If format 3 is selected in block 650 for a UE 1 10, the eNB 107 selects format 3 resources in block 655. If channel selection is selected in block 660 for a UE 1 10, the eNB 107 selects channel selection resources in block 665. Note that channel selection is defined in 3GPP TS 36.213, section 10.1.3.2.1 , entitled "PUCCH format 1 b with channel selection HARQ-ACK procedure".

[0085] In block 670, the eNB 107 informs (e.g., via PDCCH) the plurality of UEs of selected formats and corresponding resources (e.g., to be used by the UE on PUCCH to report the information). In block 675, the eNB 107 receives transmissions from UEs 1 10 based on corresponding selected formats and in corresponding selected resources (e.g., on PUCCH for one or more carrier(s)).

[0086] It should be noted that whenever format 3 could be selected from among multiple possible A/N feedback formats, e.g., CA statuses 621-2 and 621-3, the flow in FIG. 5 may be used as one possible implementation to select (or not select) format 3.

[0087] Embodiments of the present invention may be implemented in software (executed by one or more processors), hardware (e.g., an application specific integrated circuit), or a combination of software and hardware. In an example embodiment, the software (e.g., application logic, an instruction set) is maintained on any one of various conventional computer-readable media. In the context of this document, a

"computer-readable medium" may be any media or means that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer, with one example of a computer described and depicted, e.g., in FIG. 1 . A computer-readable medium may comprise a computer-readable storage medium (e.g., memory(ies) 155 or other device) that may be any media or means that can contain or store the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer. A computer readable storage medium does not, however, encompass propagating signals. [0088] If desired, the different functions discussed herein may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the above-described functions may be optional or may be combined.

[0089] Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claims.

[0090] It is also noted herein that while the above describes example embodiments of the invention, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the appended claims.

[0091] The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:

3GPP Third Generation Partnership Project

ACK or ack Acknowledge

A/N Ack/Nack

CA Carrier Aggregation

CC Component Carrier

CoMP Coordinated Multipoint

CW Codeword

DL Downlink (from a base station to a UE) eNB evolved Node B (e.g., LTE base station)

FDD Frequency Division Duplexing

hr hour

ISD Inter-Site Distance

IRC Interference Rejection Combining

Km Kilometer

LTE Long Term Evolution

Mbit/s megabits per second

muxing multiplexing

NACK or nack Not acknowledge

PRB Physical Resource Block

PUCCH Physical Uplink Control Channel

PUSCH Physical Uplink Shared Channel

Rel Release

Rx Reception or Receiver

SINR Signal to Interference Noise Ratio SR Scheduling Request

TDD Time Division Duplexing

TS Technical Standard

TTI Transmission Time Interval

Tx Transmission or Transmitter

UE User Equipment (e.g., mobile device)

UL Uplink (from a UE to a base station)

Claims

WHAT IS CLAIMED IS:

A method, comprising:

selecting, by a base station and based on one or more criteria, one of a plurality of feedback formats for individual ones of a plurality of user equipment to use to report ack/nack information indicative of whether a previous transmission was received correctly or not by the individual user equipment, wherein more than one feedback format is used simultaneously by the base station for different user equipment within a single cell;

selecting by the base station resources for the selected feedback formats;

informing by the base station the plurality of user equipment of corresponding

selected feedback formats and resources to be used by the user equipment to report the ack/nack information on the uplink channel; and receiving by the base station transmissions on the uplink channel from the plurality of user equipment based on corresponding selected feedback formats and in corresponding selected resources.

The method of claim 1 , wherein the one or more criteria comprise uplink load and selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment further comprises selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment based on the uplink load for the individual feedback formats on the uplink channel.

The method of claim 2, wherein selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment based on uplink load for the individual feedback formats on the uplink channel further comprises in response to a feedback format x's physical resource block load being less than y percent, then reallocating physical resource blocks reserved for that feedback format x to at least one other feedback format or to a physical uplink shared channel, where x is one or three and y is a number greater than zero.

The method of claim 1 , wherein the one or more criteria comprise uplink load and selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment further comprises selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment based on uplink load for a physical uplink shared channel and in response to the uplink load for a physical uplink shared channel being greater than a threshold, selecting a feedback format with a smaller consumption per user than other ones of the plurality of feedback formats.

The method of any one of claims 1 to 4, wherein the one or more criteria comprise carrier aggregation statuses of each of the plurality of user equipment and wherein selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises for a given user equipment that is not carrier aggregation capable, selecting as a selected feedback format one of ack/nack bundling or ack/nack multiplexing for the given user equipment.

The method of any one of claims 1 to 4, wherein the one or more criteria comprise carrier aggregation statuses of each of the plurality of user equipment and wherein selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises for a given user equipment that is carrier aggregation capable and has one serving cell, selecting as a selected feedback format one of ack/nack bundling or ack/nack multiplexing or format 3 for the given user equipment.

The method of any one of claims 1 to 4, wherein the one or more criteria comprise carrier aggregation statuses of each of the plurality of user equipment and wherein selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises for a given user equipment that is carrier aggregation capable and has two serving cells, selecting as a selected feedback format one of format 3 or channel selection for the given user equipment.

8. The method of any one of claims 1 to 4, wherein the one or more criteria comprise carrier aggregation statuses of each of the plurality of user equipment and wherein selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises for a given user equipment that is carrier aggregation capable and has more than two serving cells, selecting format 3 as a selected feedback format for the given user equipment.

The method of any one of claims 6 to 8, wherein the uplink channel is a physical uplink control channel and wherein selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises performing the following:

selecting format 3 for the selected ack/nack feedback format for the given user equipment in response to all of the following being true:

the signal to interference noise ratio for the given user equipment supports format 3;

the given user equipment is scheduled a predetermined number of times within one bundling window;

a physical uplink shared channel resource utilization is below a threshold; and

a resource is available on the physical uplink control channel; otherwise, selecting an ack/nack feedback format other than format 3 as the

selected ack/nack feedback format for the given user equipment.

The method of any one of claims 1 to 9, wherein the one or more criteria comprise radio channel conditions of each of the plurality of user equipment and wherein different feedback formats have different required radio channel conditions, and wherein selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment further comprises considering for a given user equipment only those feedback formats for selection that have radio channel conditions for the given user equipment above the corresponding required signal to interference ratios.

The method of claim 10, wherein signal to interference noise ratios for the plura of user equipment are used as a metric of the radio channel conditions for the plurality of user equipment.

2. The method of any of the above, wherein the uplink channel is a physical uplink control channel.

An apparatus, comprising:

means for selecting, by a base station and based on one or more criteria, one of a plurality of feedback formats for individual ones of a plurality of user equipment to use to report ack nack information indicative of whether a previous transmission was received correctly or not by the individual user equipment, wherein more than one feedback format is used simultaneously by the base station for different user equipment within a single cell;

means for selecting by the base station resources for the selected feedback

formats;

means for informing by the base station the plurality of user equipment of

corresponding selected feedback formats and resources to be used by the user equipment to report the ack nack information on the uplink channel; and

means for receiving by the base station transmissions on the uplink channel from the plurality of user equipment based on corresponding selected feedback formats and in corresponding selected resources.

The apparatus of claim 13, wherein the one or more criteria comprise uplink load and the means for selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment further comprises means for selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment based on the uplink load for the individual feedback formats on the uplink channel.

The apparatus of claim 13, wherein the one or more criteria comprise uplink load and the means for selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment further comprises means for selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment based on uplink load for a physical uplink shared channel and means, in response to the uplink load for a physical uplink shared channel being greater than a threshold, for selecting a feedback format with a smaller consumption per user than other ones of the plurality of feedback formats.

The apparatus of any one of claims 13 to 15, wherein the one or more criteria comprise carrier aggregation statuses of each of the plurality of user equipment and wherein the means for selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises means, for a given user equipment that is not carrier aggregation capable, for selecting as a selected feedback format one of ack/nack bundling or ack/nack multiplexing for the given user equipment.

17. The apparatus of any one of claims 13 to 15, wherein the one or more criteria

comprise carrier aggregation statuses of each of the plurality of user equipment and wherein the means for selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises means, for a given user equipment that is carrier aggregation capable and has one serving cell, for selecting as a selected feedback format one of ack/nack bundling or ack/nack multiplexing or format 3 for the given user equipment.

18. The apparatus of any one of claims 13 to 15, wherein the one or more criteria

comprise carrier aggregation statuses of each of the plurality of user equipment and wherein the means for selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises means, for a given user equipment that is carrier aggregation capable and has two serving cells, for selecting as a selected feedback format one of format 3 or channel selection for the given user equipment.

19. The apparatus of any one of claims 13 to 15, wherein the one or more criteria

comprise carrier aggregation statuses of each of the plurality of user equipment and wherein the means for selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises means, for a given user equipment that is carrier aggregation capable and has more than two serving cells, for selecting format 3 as a selected feedback format for the given user equipment.

20. The apparatus of any one of claims 17 to 19, wherein the uplink channel is a

physical uplink control channel and wherein the means for selecting by a base station one of a plurality of feedback formats for individual ones of the plurality of user equipment to use further comprises the following:

means for selecting format 3 for the selected ack/nack feedback format for the given user equipment in response to all of the following being true: the signal to interference noise ratio for the given user equipment supports format 3;

a physical uplink shared channel resource utilization is below a threshold; and a resource is available on the physical uplink control channel;

otherwise, using a means for selecting an ack nack feedback format other than format 3 as the selected ack/nack feedback format for the given user equipment.

21. The apparatus of any one of claims 13 to 20, wherein the one or more criteria

comprise radio channel conditions of each of the plurality of user equipment and wherein different feedback formats have different required radio channel conditions, and wherein the means for selecting one of a plurality of feedback formats for individual ones of the plurality of user equipment further comprises means for considering for a given user equipment only those feedback formats for selection that have radio channel conditions for the given user equipment above the corresponding required signal to interference ratios.

22. The apparatus of claim 21 , wherein signal to interference noise ratios for the

plurality of user equipment are used as a metric of the radio channel conditions for the plurality of user equipment.

23. A system comprising the apparatus of any one of claims 13 to 22.

24. A computer program comprising program code for executing the method according to any of claims 1 to 12.

25. The computer program according to claim 24, wherein the computer program is a computer program product comprising a computer-readable medium bearing computer program code embodied therein for use with a computer.