Fountain HARQ for reliable low latency communication

A wireless device may transmit a data block based on a low latency operational mode. The device may then transmit a number of redundancy versions of the data block prior to determining whether an acknowledgement (ACK) has been received. In some examples the ACK may be an augmented ACK, which may be based on the number of redundancy versions received prior to successfully decoding the data block, and which may include an additional resource request. In some examples, the device may select an updated modulation and coding scheme (MCS) based on the augmented ACK. In some examples, the device may increase a number of frequency resources (e.g., component carriers) used for transmission based on the augmented ACK.

BACKGROUND

Field of Disclosure

The following relates generally to wireless communication, and more specifically to fountain hybrid automatic repeat request (HARQ) for reliable low latency communication.

Description of Related Art

By way of example, a wireless multiple-access communications system may include a number of base stations, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UEs). A base station may communicate with the communication devices on downlink channels (e.g., for transmissions from a base station to a UE) and uplink channels (e.g., for transmissions from a UE to a base station). In some cases, UEs may also communicate directly with each other.

In some cases, a wireless device may send HARQ feedback such as an acknowledgement (ACK) or a negative acknowledgment (NACK) to indicate whether a transmission was correctly received. If the transmitter of the message receives a NACK, it may retransmit the message to ensure successful delivery of the data. However, the HARQ process may take a significant amount of time based on the decoding time and the round trip time for the NACK and retransmission. This may contribute to latency in communication between devices, which may interfere with the data rate and reliability of the wireless link.

SUMMARY

The present disclosure may relate generally to wireless communications systems, and more particularly to improved systems, methods, or apparatuses associated with fountain hybrid automatic repeat request (HARQ) for reliable low latency communication. A wireless device may transmit a data block based on a low latency operational mode. The device may then transmit a number of redundancy versions of the data block prior to determining whether an acknowledgement (ACK) has been received. In some examples the ACK may be an augmented ACK, which may be based on the number of redundancy versions received prior to successfully decoding the data block, and which may include an additional resource request. In some examples, the device may select an updated modulation and coding scheme (MCS) based on the augmented ACK. In some examples, the device may increase a number of frequency resources (e.g., component carriers) used for transmission based on the augmented ACK.

A method of wireless communication is described. The method may include transmitting a data block using a first set of resources based on a low latency operational mode, and transmitting a number of redundancy versions of the data block using a second set of resources based on the low latency operational mode, the number of redundancy versions of the data block being transmitted prior to determining whether an ACK is received for the data block.

An apparatus for wireless communication is described. The apparatus may include means for transmitting a data block using a first set of resources based on a low latency operational mode, and means for transmitting a number of redundancy versions of the data block using a second set of resources based on the low latency operational mode, the number of redundancy versions of the data block being transmitted prior to determining whether an ACK is received for the data block.

A further apparatus for wireless communication is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory, wherein the instructions are executable by the processor to transmit a data block using a first set of resources based on a low latency operational mode, and transmit a number of redundancy versions of the data block using a second set of resources based on the low latency operational mode, the number of redundancy versions of the data block being transmitted prior to determining whether an ACK is received for the data block.

A non-transitory computer-readable medium storing code for wireless communication is described. The code may include instructions executable to transmit a data block using a first set of resources based on a low latency operational mode, and transmit a number of redundancy versions of the data block using a second set of resources based on the low latency operational mode, the number of redundancy versions of the data block being transmitted prior to determining whether an ACK is received for the data block.

Some examples of the method, apparatuses, or non-transitory computer-readable medium described above may further include selecting an initial MCS based at least in part on a channel condition or a size of the data block, wherein transmitting the data block is based on the initial MCS. Additionally or alternatively, in some examples the ACK is an augmented ACK based at least in part on the number of redundancy versions and comprising an additional resource request, and selecting an updated MCS based at least in part on the augmented ACK.

Some examples of the method, apparatuses, or non-transitory computer-readable medium described above may further include receiving the ACK on a reduced symbol duration uplink (UL) control channel based on the low latency operational mode. Additionally or alternatively, some examples may include receiving a number of NACKs corresponding to the number of redundancy versions on the reduced symbol duration UL control channel.

Some examples of the method, apparatuses, or non-transitory computer-readable medium described above may further include refraining from transmitting an additional redundancy version of the data block based on the ACK. Additionally or alternatively, in some examples the low latency operational mode comprises a reduced transmission time interval (TTI) time period.

In some examples of the method, apparatuses, or non-transitory computer-readable medium described above, the second set of resources is contiguous to the first set of resources in time. Additionally or alternatively, some examples may include transmitting control information on a reduced symbol duration downlink (DL) control channel based on the low latency operational mode.

A method of wireless communication is described. The method may include receiving a data block using a first set of resources based on a low latency operational mode, computing a first set of LLRs for the data block, determining that a first set of decoded bits from the first set of LLRs does not pass a CRC, receiving a number of redundancy versions of the data block based on the low latency operational mode using a second set of resources prior to transmitting a NACK, computing an updated set of LLRs for the data block based on the number of redundancy versions, determining that a second set of decoded bits from the updated set of LLRs passes the CRC, and transmitting an ACK for the data block based on the determination that the updated set of LLRs passes the CRC.

An apparatus for wireless communication is described. The apparatus may include means for receiving a data block using a first set of resources based on a low latency operational mode, means for computing a first set of LLRs for the data block, means for determining that a first set of decoded bits from the first set of LLRs does not pass a CRC, means for receiving a number of redundancy versions of the data block based on the low latency operational mode using a second set of resources prior to transmitting a NACK, means for computing an updated set of LLRs for the data block based on the number of redundancy versions, means for determining that a second set of decoded bits from the updated set of LLRs passes the CRC, and means for transmitting an ACK for the data block based on the determination that the updated set of LLRs passes the CRC.

A further apparatus for wireless communication is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory, wherein the instructions are executable by the processor to receive a data block using a first set of resources based on a low latency operational mode, compute a first set of LLRs for the data block, determine that a first set of decoded bits from the first set of LLRs does not pass a CRC, receive a number of redundancy versions of the data block based on the low latency operational mode using a second set of resources prior to transmitting a NACK, compute an updated set of LLRs for the data block based on the number of redundancy versions, determine that a second set of decoded bits from the updated set of LLRs passes the CRC, and transmit an ACK for the data block based on the determination that the updated set of LLRs passes the CRC.

A non-transitory computer-readable medium storing code for wireless communication is described. The code may include instructions executable to receive a data block using a first set of resources based on a low latency operational mode, compute a first set of LLRs for the data block, determine that a first set of decoded bits from the first set of LLRs does not pass a CRC, receive a number of redundancy versions of the data block based on the low latency operational mode using a second set of resources prior to transmitting a NACK, compute an updated set of LLRs for the data block based on the number of redundancy versions, determine that a second set of decoded bits from the updated set of LLRs passes the CRC, and transmit an ACK for the data block based on the determination that the updated set of LLRs passes the CRC.

In some examples of the method, apparatuses, or non-transitory computer-readable medium described above, receiving the data block comprises receiving the data block using an initial MCS based at least in part on a channel condition or a size of the data block. Additionally or alternatively, in some examples the ACK is an augmented ACK based at least in part on the number of redundancy versions and comprising an additional resource request.

Some examples of the method, apparatuses, or non-transitory computer-readable medium described above may further include receiving a subsequent data block using an updated MCS based at least in part on the augmented ACK. Additionally or alternatively, in some examples the additional resource request is based at least in part on one or more reliability metrics.

In some examples of the method, apparatuses, or non-transitory computer-readable medium described above, the ACK is transmitted on a reduced symbol duration UL control channel based on the low latency operational mode. Additionally or alternatively, some examples may include transmitting a number of NACKs corresponding to the number of redundancy versions on the reduced symbol duration UL control channel.

Some examples of the method, apparatuses, or non-transitory computer-readable medium described above may further include receiving control information on a reduced symbol duration DL control channel based on the low latency operational mode. Additionally or alternatively, in some examples the low latency operational mode comprises a reduced TTI time period.

In some examples of the method, apparatuses, or non-transitory computer-readable medium described above, the second set of resources is contiguous to the first set of resources in time. Additionally or alternatively, in some examples receiving the number of redundancy versions of the data block comprises receiving the number of redundancy versions of the data block over a plurality of symbols.

Some examples of the method, apparatuses, or non-transitory computer-readable medium described above may further include determining that an accumulated quality metric for the updated set of LLRs exceeds a threshold. Additionally or alternatively, some examples may include performing a decoding operation based on the updated set of LLRs and the determination that the accumulated quality metric exceeds the threshold, wherein the second set of decoded bits is an output of the decoding operation.

In some examples of the method, apparatuses, or non-transitory computer-readable medium described above, the decoding operation is based in part on an intermediate set of LLRs or an intermediate set of decoded bits.

DETAILED DESCRIPTION

The described features generally relate to improved systems, methods, or apparatuses associated with fountain HARQ for reliable low latency communication. Some wireless systems (e.g., most 3GPP/3GPP2 standards) may employ an interlaced hybrid automatic repeat request (HARQ) structure. Such a structure may avoid stalling (i.e., due to decoding/acknowledgement latency) by efficiently multiplexing multiple packets. However, in a delay sensitive communication with small payload size, interlaced HARQ may introduce a significant delay and may significantly decrease the link-budget. Thus, a wireless communication system may use a fountain HARQ to mitigate the resulting latency.

In a fountain HARQ scheme, a transmitter may select a rate/modulation scheme as well as a targeted latency based on channel conditions, payload size, etc. The transmitter may continue to send the data (e.g., redundancy versions) in back-to-back transmit time intervals (TTIs) until an ACK is received. The receiver may accumulate the multiple received data symbols, compute log-likelihood (LLRs), and send an ACK to stop transmission whenever the computed LLRs pass a cyclic redundancy check (CRC). As a result, there may be no use of NACK signals.

In some instances, the receiver may convey additional feedback requests on the ACK (i.e., an augmented ACK). The feedback may include update requests for bandwidth (BW), additional carriers, coordinated multi-point transmission/reception (COMP), an updated precoding matrix indicator (PMI), or an updated rank indicator (RI). In other words, the augmented ACK may be used to request additional resources, additional coordination, or adjustment to the transmission scheme. In some instances, channel quality information may be derived using information such as a channel estimate, demodulation LLR values, or decoder LLR values. Thus, in some examples, the ACK may be based on channel estimate quality, demodulation LLR quality, and decoder LLR quality. In some cases, a thin control channel (e.g., a control channel with a reduced symbol duration) may be used to improve feedback and control efficiency (e.g., overhead due to decoding/HARQ retransmission time).

FIG. 1illustrates an example of a wireless communications system100in accordance with various aspects of the present disclosure. The wireless communications system100includes base stations105, at least one UE115, and a core network130. The core network130may provide user authentication, access authorization, tracking, internet protocol (IP) connectivity, and other access, routing, or mobility functions. The base stations105interface with the core network130through backhaul links132(e.g., S1, etc.). The base stations105may perform radio configuration and scheduling for communication with the UEs115, or may operate under the control of a base station controller (not shown). In various examples, the base stations105may communicate, either directly or indirectly (e.g., through core network130), with each other over backhaul links134(e.g., X1, etc.), which may be wired or wireless communication links.

In some examples, the wireless communications system100is a Long Term Evolution (LTE)/LTE-Advanced (LTE-A) network. In LTE/LTE-A networks, the term evolved node B (eNB) may be generally used to describe the base stations105, while the term UE may be generally used to describe the UEs115. The wireless communications system100may be a heterogeneous LTE/LTE-A network in which different types of eNBs provide coverage for various geographical regions. For example, each eNB or base station105may provide communication coverage for a macro cell, a small cell, or other types of cell. The term “cell” is a 3GPP term that can be used to describe a base station, a carrier or component carrier associated with a base station, or a coverage area (e.g., sector, etc.) of a carrier or base station, depending on context.

A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs115with service subscriptions with the network provider. A small cell is a lower-powered base station, as compared with a macro cell, that may operate in the same or different (e.g., licensed, unlicensed, etc.) frequency bands as macro cells. Small cells may include pico cells, femto cells, and micro cells according to various examples. A pico cell, for example, may cover a small geographic area and may allow unrestricted access by UEs115with service subscriptions with the network provider. A femto cell may also cover a small geographic area (e.g., a home) and may provide restricted access by UEs115having an association with the femto cell (e.g., UEs115in a closed subscriber group (CSG), UEs115for users in the home, and the like). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a small cell may be referred to as a small cell eNB, a pico eNB, a femto eNB, or a home eNB. An eNB may support one or multiple (e.g., two, three, four, and the like) cells (e.g., component carriers).

The communication networks that may accommodate some of the various disclosed examples may be packet-based networks that operate according to a layered protocol stack. In the user plane, communications at the bearer or packet data convergence protocol (PDCP) layer may be IP-based. A radio link control (RLC) layer may perform packet segmentation and reassembly to communicate over logical channels. A medium access control (MAC) layer may perform priority handling and multiplexing of logical channels into transport channels. The MAC layer may also use HARQ to provide retransmission at the MAC layer to improve link efficiency. In the control plane, the radio resource control (RRC) protocol layer may provide establishment, configuration, and maintenance of an RRC connection between a UE115and the base stations105. The RRC protocol layer may also be used for core network130support of radio bearers for the user plane data. At the physical (PHY) layer, the transport channels may be mapped to physical channels.

The communication links125shown in wireless communications system100may include uplink (UL) transmissions from a UE115to a base station105, or downlink (DL) transmissions, from a base station105to a UE115. The downlink transmissions may also be called forward link transmissions while the uplink transmissions may also be called reverse link transmissions. Each communication link125may include one or more carriers, where each carrier may be a signal made up of multiple sub-carriers (e.g., waveform signals of different frequencies) modulated according to the various radio technologies described above. Each modulated signal may be sent on a different sub-carrier and may carry control information (e.g., reference signals, control channels, etc.), overhead information, user data, etc. The communication links125may transmit bidirectional communications using frequency division duplex (FDD) (e.g., using paired spectrum resources) or time division duplex (TDD) operation (e.g., using unpaired spectrum resources). Frame structures may be defined for FDD (e.g., frame structure type 1) and TDD (e.g., frame structure type 2).

Wireless communication links125may also be established between UEs115in a configuration known as device-to-device (D2D) communications. One or more of a group of UEs115utilizing D2D communications may be within the coverage area110of a cell. Other UEs115in such a group may be outside the coverage area110of a cell, or otherwise unable to receive transmissions from a base station105. In some cases, groups of UEs115communicating via D2D communications may utilize a one-to-many (1:M) system in which each UE115transmits to every other UE115in the group. In some cases, a base station105facilitates the scheduling of resources for D2D communications. In other cases, D2D communications are carried out independent of a base station105.

In some embodiments of the wireless communications system100, base stations105or UEs115may include multiple antennas for employing antenna diversity schemes to improve communication quality and reliability between base stations105and UEs115. Additionally or alternatively, base stations105or UEs115may employ multiple input multiple output (MIMO) techniques that may take advantage of multi-path environments to transmit multiple spatial layers carrying the same or different coded data.

HARQ may be a method of ensuring that data is received correctly over a wireless communication link125. HARQ may include a combination of error detection (e.g., using a cyclic redundancy check (CRC)), forward error correction (FEC), and retransmission (i.e., automatic repeat request (ARQ)). HARQ may improve throughput at the MAC layer in poor radio conditions (e.g., poor signal-to-noise conditions). In Incremental Redundancy HARQ, incorrectly received data may be stored in a buffer and combined with subsequent transmissions to improve the overall likelihood of successfully decoding the data. In some cases, redundancy bits are added to each message prior to transmission. This may be especially useful in poor conditions. In other cases, redundancy bits are not added to each transmission, but are retransmitted after the transmitter of the original message receives a negative acknowledgement (NACK) indicating a failed attempt to decode the information.

According to the present disclosure, a wireless device such as a UE115or a base station105may transmit a data block based on a low latency operational mode. The device may then transmit a number of redundancy versions of the data block prior to determining whether an ACK has been received. In some examples the ACK may be an augmented ACK, which may be based on the number of redundancy versions received prior to successfully decoding the data block, and which may include an additional resource request. In some examples, the device may select an updated modulation and coding scheme (MCS) based on the augmented ACK. In some examples, the device may increase a number of frequency resources (e.g., component carriers) used for transmission based on the augmented ACK.

FIG. 2illustrates an example of a wireless communications subsystem200associated with fountain HARQ for reliable low latency communication in accordance with various aspects of the present disclosure. Wireless communications subsystem200may include UE115-a, which may be an example of a UE115described above with reference toFIG. 1. Wireless communications subsystem200may also include a base station105-a, which may be an example of a base station105described above with reference toFIG. 1. Base station105-amay communicate with any UE115within its coverage area110-avia downlink205and uplink210, as generally described above with respect toFIG. 1.

For example, base station105-amay transmit data to UE115-aon downlink205, and UE115-amay send HARQ acknowledgments and negative-acknowledgments (ACK/NACKs) on uplink210informing base station105-aof the reception status of the data. According to the present disclosure, base station105-amay continuously transmit redundancy versions of a data block to UE115-auntil base station105-areceives an ACK from UE115-a(i.e., base station105may implement a fountain HARQ procedure). In some examples, UE115-amay implement fountain HARQ on uplink210, or in D2D communications with another UE115(not shown).

In a first HARQ scheme, base station105-amay use a first transmit time interval (TTI) to send a data block to UE115-a. Base station105-amay then wait for an ACK/NACK response from UE115-a. Upon reception of a NACK, base station105-amay transmit a redundancy version (e.g., the same data encoded differently) to UE115-a. In the event UE115-acorrectly receives the data block, UE115-amay transmit (and base station105-amay receive) an ACK indicating to base station105-athat additional redundancy versions are not requested. In some examples the ACK/NACKs may be interlaced (e.g., multiple packets are multiplexed) to reduce stall due to decoding/ACK latency. However, the round trip time for a NACK and the following retransmission may introduce significant latency for delay-sensitive communications. Thus, wireless communications subsystem200may use a second HARQ scheme such as a fountain HARQ scheme.

The second HARQ scheme may be associated with bursts based on a reduced TTI. For example, base station105-amay transmit a data block to UE115-aduring a short TTI burst220. In some cases, short TTI burst220may include a number of contiguous TTIs which may be embedded within and have a shorter length than default TTIs215. After the initial transmission of the data block in short TTI burst220, base station105-amay transmit redundancy versions of the data in subsequent short TTIs within short TTI burst220until base station105-areceives an ACK from UE115-aover uplink210.

Accordingly, UE115-amay accumulate the received data blocks and send an ACK after a successful cyclic redundancy check (CRC). In some cases, UE115-amay send an augmented ACK which conveys additional feedback for base station105-a. For example, the augmented ACK may request adjustment of the transmission scheme, additional bandwidth (e.g., carriers), resources, and coordination. Upon reception of the augmented ACK, base station105-amay adjust communication parameters based on the augmented ACK feedback and cease transmission of the data redundancy versions.

Although described in conjunction with the fountain HARQ scheme, bursts of short TTIs may be used for any HARQ scheme, including the first HARQ scheme described above. Furthermore, a communication link may include any number of short TTI bursts, which may be variable in length, and may include any number of short TTIs, which also may be variable in length. Different TTI lengths may also be used for different component carriers. For example, one or more component carriers may utilize short TTIs while other component carriers may utilize longer default TTIs215.

Thus, UE115-aor a base station105-amay transmit a data block based on a low latency (e.g., short TTI) operational mode. The transmitting device may then send a number of redundancy versions of the data block prior to determining whether an ACK has been received. In some examples the ACK may be an augmented ACK, which may be based on the number of redundancy versions received prior to successfully decoding the data block, and which may include an additional resource request. In some examples, the transmitting device may select an updated modulation and coding scheme (MCS) or increase a number of frequency resources (e.g., component carriers) used for transmission based on the augmented ACK.

FIG. 3illustrates an example of a fountain HARQ timeline300associated with reliable low latency communication in accordance with various aspects of the present disclosure. Fountain HARQ timeline300may be used for data transmission between a UE115and a base station105, such as those described above with reference toFIGS. 1-2. Fountain HARQ timeline300includes a downlink control channel305and an uplink control channel310, which may be aspects of downlink205and uplink210such as described above with reference toFIG. 2. The fountain HARQ design illustrated by fountain HARQ timeline300may also be applied to UL data transmissions and to D2D communications.

Additionally, fountain HARQ timeline300depicts component carrier315-a, component carrier315-b, and component carrier315-c. In some cases, the number of redundancy versions in a fountain HARQ scheme may introduce overhead. Thus, a control channel (e.g., downlink control channel305and/or uplink control channel310) may be configured to include a reduced symbol period (i.e., the control channel may be a thin control channel) to mitigate the impact of the additional HARQ overhead.

A base station105may convey a downlink grant320-ato a UE115via downlink control channel305. In the same or subsequent TTI, the base station105may transmit data block325on component carrier315-a. In some instances the TTI may be part of a burst of short TTIs, such as described with reference toFIG. 2. To improve reception of data block325, base station105may transmit redundancy versions of the data block325until the UE115responds with an ACK. In one example the base station105may transmit redundancy versions330-(athroughe) of data block325. For each redundancy version of data block325, the UE115may compute log-likelihood ratios (LLRs) to estimate the transmitted bits. The UE115may use the updated decoded bits to perform redundancy cyclic checks (CRC) until one passes. After a successful CRC, the UE115may transmit an ACK335-aon uplink control channel310to the base station105. In some cases, based on the timing of ACK335-a, the base station105may transmit one more redundancy version330-ebefore terminating transmission of redundancy versions330. That is, the base station105may transmit redundancy version330-eat the same time as ACK335-a. Although described with references to a base station105and a UE115, fountain HARQ timeline300may be an example of a HARQ timeline for UL data transmissions or between two UEs115.

In some instances, ACK335-amay be an augmented ACK. An augmented ACK may be based on the number of redundancy versions330which have been received at the UE115prior to successfully decoding a data block. In some cases, augmented ACK335-amay convey feedback information or an additional resource request from the UE115to the base station105. For example, augmented ACK335-amay request additional bandwidth (e.g., carriers). Thus, the base station105may receive augmented ACK335-aand make adjustments to the transmission scheme based on the information. For instance, upon transmission of downlink grant320-a, the base station105may allocate component carrier315-a, component carrier315-b, and component carrier315-cfor UE115. Consequently, a downlink data transmission may include data block version340-aon component carrier315-a, data block version340-bon component carrier315-b, and data block version340-con component carrier315-c. The UE115may receive data block versions340(a through c) and perform a successful CRC, thus triggering the transmission of ACK335-b. In some cases ACK335-bmay also be an augmented ACK. Based on the reception time of ACK335-b, base station105may cease transmission of redundancy versions. In some cases, an additional set of redundancy versions340-(dthroughf) of data block versions340(a through c) may be transmitted concurrently with ACK335-b.

In some cases, the base station105may select an initial modulation and coding scheme (MCS) for downlink transmissions. The MCS may be based in part on a channel condition or the size of the data to be transmitted. In some examples, the transmission of the data block325may be based on the initial MCS. In the cases in which an augmented ACK335-ahas been received at the base station105, the base station may update the MCS for transmission of data block340.

FIG. 4illustrates an example of a process flow400associated with fountain HARQ for reliable low latency communication in accordance with various aspects of the present disclosure. Process flow diagram400may include UE115-b, which may be an example of a UE115described above with reference toFIGS. 1-2. Process flow diagram400may also include a base station105-b, which may be an example of a base station105described above with reference toFIGS. 1-2. Process flow diagram400may utilize a data transmission scheme between a UE115and a base station105, as described above with reference toFIG. 3. The fountain HARQ process illustrated by process flow400may also be applied to UL data transmissions and to D2D communications.

At step405, base station105-bmay transmit (and UE115-bmay receive) a data block using a first set of resources based on a low latency operation mode. For example, base station105-bmay transmit a data block using a first set of resources based on a low latency operational mode. Base station105-bmay also select an initial modulation and coding scheme (MCS) based at least in part on a channel condition or a size of the data block

At step410UE115-bmay calculate a set of LLRs for the data block. At step415, UE115-bmay determine that the LLRs do not pass CRC check (i.e., UE115-bmay have only received a portion of the data block, or the data block may have experienced corruption).

Subsequently, at step420and step425, base station105-bmay transmit and UE115-bmay receive a number of redundancy versions of the data block using a second set of resources based on the low latency operational mode prior to base station105-bdetermining whether an ACK is received for the data block. In some examples, the second set of resources may be contiguous to (i.e., immediately following) the first set of resources in time. In some cases, UE115-bmay transmit a number of NACKs corresponding to the number of redundancy versions.

At step430, UE115-bmay compute an updated set of LLRs for the data block based on the number of redundancy versions. At step435, UE115-bmay determine that the updated set of LLRs passes a CRC check.

Subsequently, at step440, UE115-bmay transmit an ACK for the data block based on the determination that the updates set of LLRs passed the CRC check. In some examples the ACK is an augmented ACK based at least in part on the number of redundancy versions and comprising an additional resource request. In some examples, the ACK may be transmitted on a reduced symbol duration (and/or TTI duration) UL control channel.

Upon reception of the ACK from UE115-b, base station105-bmay cease transmission of the redundancy version of the data block at step445. Base station105-bmay also select an updated MCS based on receiving an augmented ACK.

At step450, base station105-bmay transmit a different data block using resources based on feedback information carried on the ACK. For example, base station105-bmay transmit the data block (with redundancy versions) on multiple component carriers as described above with reference toFIG. 3.

FIG. 5illustrates an example of a low latency physical layer structure500associated with fountain HARQ for reliable low latency communication in accordance with various aspects of the present disclosure. Low latency physical layer structure500may be used for communication between a UE115and a base station105, or between multiple UE115as described above with reference toFIGS. 1-4. Low latency physical layer structure500may be used in conjunction with a fountain HARQ scheme as described above with reference toFIGS. 2-4. Low latency physical layer structure500illustrates one example of a low latency structure, but other structures may also be used in conjunction with a fountain HARQ scheme. For example, a low latency structure could incorporate band pairing, and ACKs could be provided on any symbol after the first transmission.

In some cases, a wireless communications system (e.g., wireless communications system100ofFIG. 1) may have more than one hierarchical physical layer structure. For example, a second hierarchical layer may have lower latency compared to the first hierarchical layer. A radio frame510may include ten 1 ms subframes that include DL subframes525, special subframes530, and UL subframes535, each of which may be used to transmit data symbols. A number of DL subframes525may be replaced with burst subframes540which may be transmitted according to a different hierarchical layer than DL subframes525, special subframes530, and UL subframes535(e.g., in the second layer). In some examples, burst subframes540may include a greater number of symbols than subframes in the first hierarchical layer (e.g., 88 symbols rather than 14 symbols), and may include DL symbols545, special symbols550, and UL symbols555. In some cases, the symbols545,550, and555may have a reduced symbol duration relative to the symbols transmitted according to the first hierarchical layer. The reduced symbol duration may enable acknowledgment of transmissions with a reduced latency.

In first layer TDD frame510, a UE115may receive a DL transmission in DL subframe525and transmit an acknowledgement (ACK) according to a first layer HARQ scheme in which ACKs are transmitted in a first available subframe at or after k+4 subframes following the receipt of a DL transmission. In some cases, subframe k+4 from DL subframe525may be another DL subframe, and an ACK/NACK560may be transmitted in following UL subframe565. Thus, in this example, there is a 7 ms delay between DL subframe525and the ACK/NACK560associated with the subframe. In the event that a retransmission is appropriate (e.g., after receiving a NACK), the retransmission may be scheduled for a subsequent DL subframe. The retransmission timing may result in a relatively long round trip time (RTT) (e.g., a minimum of 11 ms). If an acknowledgment is sent in the fourth subframe following a DL transmission (in FDD mode ACK/NACK may be consistently transmitted in subframe k+4), the minimum RTT may be 8 ms.

Within burst subframes540, the latency for providing ACKs may be less than the latency for transmissions in the first hierarchical layer. In some cases, transmissions using the second hierarchical layer may utilize similar HARQ techniques as with first layer transmissions. That is, ACKs may be provided in symbol k+4 (where k represents the original symbol transmission), or in a first available symbol for transmission afterward. For example, a UE115may receive a DL transmission in symbol545and provide an ACK/NACK570in UL symbol555, which is five symbols after the receipt of DL transmission in DL symbol545(because the fourth symbol following the transmission is a special symbol550). Thus, the UE115may provide ACK/NACK570of the DL transmission within the burst subframe540, which is less than 1 ms following the receipt of the DL transmission in DL symbol545. In some examples, similarly as discussed above with respect toFIG. 3A, the symbol duration for symbols in the burst subframe540may be 11.36 μs, resulting in an acknowledgment being provided in this example 56.8 μs following the DL symbol545transmission. The eNB may then schedule any required retransmission and thus may provide, in some examples, a resulting RTT of approximately 100 μs or less.

While ACK/NACK570is described with respect to a UE115receiving a DL symbol545, similar functions may be performed for UL transmissions. For example, a UE may transmit an UL symbol580to an eNB, which may be acknowledged by the eNB through ACK/NACK575that is provided in DL symbol585. In the event that a retransmission is necessary, such a retransmission may be provided in a subsequent UL symbol from the UE and thus may again provide, in some examples, a resulting RTT of approximately 100 μs or less. Accordingly, latency associated with transmissions in burst subframes540may be significantly reduced. Such reduced latency may enable enhanced data rates, through reduced RTTs which may reduce overall retransmission times.

FIG. 6shows a block diagram600of a device601configured for fountain HARQ and reliable low latency communication in accordance with various aspects of the present disclosure. Device601may be an example of aspects of a UE115or a base station105described with reference toFIGS. 1-5. Device601may include a receiver605, a fountain HARQ module610, or a transmitter615. Device601may also include a processor. Each of these components may be in communication with each other.

The receiver605may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to fountain HARQ for reliable low latency communication, etc.). Information may be passed on to the fountain HARQ module610, and to other components of device601.

The fountain HARQ module610may transmit a data block using a first set of resources based on a low latency operational mode, and transmit a number of redundancy versions of the data block using a second set of resources based on the low latency operational mode, the number of redundancy versions of the data block being transmitted prior to determining whether an ACK is received for the data block.

The transmitter615may transmit signals received from other components of device601. In some embodiments, the transmitter615may be collocated with the receiver605in a transceiver module. The transmitter615may include a single antenna, or it may include a plurality of antennas.

FIG. 7shows a block diagram700of a device601-aconfigured for fountain HARQ and reliable low latency communication in accordance with various aspects of the present disclosure. Device601-amay be an example of aspects of a UE115or base station105described with reference toFIGS. 1-6. Device601-amay include a receiver605-a, a fountain HARQ module610-a, or a transmitter615-a. Device601-amay also include a processor. Each of these components may be in communication with each other. The fountain HARQ module610-amay also include a low latency (LL) data module705, and a redundancy module710.

The receiver605-amay receive information which may be passed on to fountain HARQ module610-a, and to other components of device601-a. The fountain HARQ module610-amay perform the operations described above with reference toFIG. 6. The transmitter615-amay transmit signals received from other components of device601-a.

The LL data module705may transmit a data block using a first set of resources based on a low latency operational mode as described above with reference toFIGS. 2-5. In some examples, the low latency operational mode comprises a reduced TTI time period. The LL data module705may also receive a data block using a first set of resources based on a low latency operational mode. In some examples, the low latency operational mode comprises a reduced TTI time period.

The redundancy module710may transmit a number of redundancy versions of the data block using a second set of resources based on the low latency operational mode, the number of redundancy versions of the data block being transmitted prior to determining whether an ACK is received for the data block as described above with reference toFIGS. 2-5. The redundancy module710may also refrain from transmitting an additional redundancy version of the data block based on the ACK. In some examples, the second set of resources may be contiguous to the first set of resources in time. In some examples, the redundancy module710may also receive a number of redundancy versions of the data block based on the low latency operational mode using the second set of resources prior to transmitting a NACK. In some examples, receiving the number of redundancy versions of the data block comprises receiving the number of redundancy versions of the data block over a plurality of symbols.

FIG. 8shows a block diagram800of a fountain HARQ module610-bconfigured for fountain HARQ and reliable low latency communication in accordance with various aspects of the present disclosure. The fountain HARQ module610-bmay be an example of aspects of a fountain HARQ module610described with reference toFIGS. 6-7. The fountain HARQ module610-bmay include an LL data module705-a, and a redundancy module710-a. Each of these modules may perform the functions described above with reference toFIG. 7. The fountain HARQ module610-bmay also include an MCS module805, an augmented ACK module810, a HARQ module815, an LLR module820, a CRC module825, and a decoder830.

The MCS module805may select an initial MCS based at least in part on a channel condition or a size of the data block, wherein transmitting the data block is based on the initial MCS as described above with reference toFIGS. 2-5. The MCS module805may also select an updated MCS based at least in part on the augmented ACK. In some examples, receiving a data block comprises receiving the data block using the initial MCS based at least in part on a channel condition or a size of the data block. The MCS module805may also be configured to receive a subsequent data block using an updated MCS based at least in part on the augmented ACK.

The augmented ACK module810may generate an augmented ACK based at least in part on the number of redundancy versions (e.g., the number received prior to successfully decoding a data block). The augmented ACK may comprise an additional resource request as described above with reference toFIGS. 2-5. In some examples, the additional resource request may be based at least in part on one or more reliability metrics.

The HARQ module815may receive an ACK (e.g., on a reduced symbol duration UL control channel based on the low latency operational mode) as described above with reference toFIGS. 2-5. The HARQ module815may also receive a number of NACKs (corresponding to the number of redundancy versions) on the reduced symbol duration UL control channel. The HARQ module815may also transmit an ACK for a data block based on a determination that a set of LLRs passes the CRC. In some examples, the ACK may be transmitted on a reduced symbol duration UL control channel based on a low latency operational mode. The HARQ module815may also transmit a number of NACKs corresponding to the number of redundancy versions on the reduced symbol duration UL control channel.

The LLR module820may compute a first set of LLRs for the data block as described above with reference toFIGS. 2-5. The LLR module820may also compute an updated set of LLRs for the data block based on the number of redundancy versions received. The LLR module820may also determine that an accumulated quality metric for the updated set of LLRs exceeds a threshold (e.g., to determine whether to proceed with processing the bits).

The CRC module825may determine that a first set of decoded bits from the first set of LLRs does not pass a CRC as described above with reference toFIGS. 2-5. The CRC module825may also determine that a second set of decoded bits from the updated set of LLRs passes the CRC.

The decoder830may perform a decoding operation based on an initial or on an updated set of LLRs and, in some cases, based on the determination that an accumulated quality metric exceeds the threshold as described above with reference toFIGS. 2-5. In some examples, the decoding operation may be based in part on an intermediate set of LLRs or an intermediate set of decoded bits.

FIG. 9shows a diagram of a system900including a UE115configured for fountain HARQ and reliable low latency communication in accordance with various aspects of the present disclosure. System900may include UE115-c, which may be an example of a UE115described above with reference toFIGS. 1-8. UE115-cmay include a fountain HARQ module910, which may be an example of a fountain HARQ module610described with reference toFIGS. 6-8. UE115-cmay also include a LL control module925. UE115-cmay also include components for bi-directional voice and data communications including components for transmitting communications and components for receiving communications. For example, UE115-cmay communicate bi-directionally with UE115-dor base station105-c.

The LL control module925may be configured to transmit data or control information on a reduced symbol duration DL channel based on the low latency operational mode as described above with reference toFIGS. 2-5. The LL control module925may also receive data and control information on a reduced symbol duration DL channel based on the low latency operational mode. The low latency channels may be configured as described above with reference toFIG. 5.

UE115-cmay also include a processor module905, and memory915(including software (SW))920, a transceiver module935, and one or more antenna(s)940, each of which may communicate, directly or indirectly, with each other (e.g., via buses945). The transceiver module935may communicate bi-directionally, via the antenna(s)940or wired or wireless links, with one or more networks, as described above. For example, the transceiver module935may communicate bi-directionally with a base station105or another UE115. The transceiver module935may include a modem to modulate the packets and provide the modulated packets to the antenna(s)940for transmission, and to demodulate packets received from the antenna(s)940. While UE115-cmay include a single antenna940, UE115-cmay also have multiple antennas940capable of concurrently transmitting or receiving multiple wireless transmissions.

The memory915may include random access memory (RAM) and read only memory (ROM). The memory915may store computer-readable, computer-executable software/firmware code920including instructions that, when executed, cause the processor module905to perform various functions described herein (e.g., fountain HARQ for reliable low latency communication, etc.). Alternatively, the software/firmware code920may not be directly executable by the processor module905but cause a computer (e.g., when compiled and executed) to perform functions described herein. The processor module905may include an intelligent hardware device, (e.g., a central processing unit (CPU), a microcontroller, an ASIC, etc.)

FIG. 10shows a diagram of a system1000including a base station105configured for fountain HARQ and reliable low latency communication in accordance with various aspects of the present disclosure. System1000may include base station105-d, which may be an example of a base station105described above with reference toFIGS. 1-9. Base station105-dmay include a base station fountain HARQ module1010, which may be an example of a base station fountain HARQ module1010described with reference toFIGS. 7-9. Base station105-dmay also include components for bi-directional voice and data communications including components for transmitting communications and components for receiving communications. For example, base station105-dmay communicate bi-directionally with UE115-eand UE115-f.

In some cases, base station105-dmay have one or more wired backhaul links Base station105-dmay have a wired backhaul link (e.g., S1 interface, etc.) to the core network130. Base station105-dmay also communicate with other base stations105, such as base station105-mand base station105-nvia inter-base station backhaul links (e.g., an X2 interface). Each of the base stations105may communicate with UEs115using the same or different wireless communications technologies. In some cases, base station105-dmay communicate with other base stations such as105-mor105-nutilizing base station communications module1025. In some embodiments, base station communications module1025may provide an X2 interface within an LTE/LTE-A wireless communication network technology to provide communication between some of the base stations105. In some embodiments, base station105-dmay communicate with other base stations through core network130. In some cases, base station105-dmay communicate with the core network130through network communications module1035.

The base station105-dmay include a processor module1005, memory1015(including software (SW)1020), transceiver modules1030, and antenna(s)1040, which each may be in communication, directly or indirectly, with each other (e.g., over bus system1045). The transceiver modules1030may be configured to communicate bi-directionally, via the antenna(s)1040, with the UEs115, which may be multi-mode devices. The transceiver module1030(or other components of base station105-d) may also be configured to communicate bi-directionally, via the antennas1040, with one or more other base stations (not shown). The transceiver module1030may include a modem configured to modulate the packets and provide the modulated packets to the antennas1040for transmission, and to demodulate packets received from the antennas1040. The base station105-dmay include multiple transceiver modules1030, each with one or more associated antennas1040. The transceiver module may be an example of a combined receiver605and transmitter615ofFIG. 6.

The memory1015may include RAM and ROM. The memory1015may also store computer-readable, computer-executable software code1020containing instructions that are configured to, when executed, cause the processor module1005to perform various functions described herein (e.g., fountain HARQ for reliable low latency communication, selecting coverage enhancement techniques, call processing, database management, message routing, etc.). Alternatively, the software1020may not be directly executable by the processor module1005but be configured to cause the computer, e.g., when compiled and executed, to perform functions described herein. The processor module1005may include an intelligent hardware device, e.g., a CPU, a microcontroller, an ASIC, etc. The processor module1005may include various special purpose processors such as encoders, queue processing modules, base band processors, radio head controllers, digital signal processor (DSPs), and the like.

The base station communications module1025may manage communications with other base stations105. The communications management module may include a controller or scheduler for controlling communications with UEs115in cooperation with other base stations105. For example, the base station communications module1025may coordinate scheduling for transmissions to UEs115for various interference mitigation techniques such as beamforming or joint transmission.

FIG. 11shows a flowchart illustrating a method1100associated with fountain HARQ for reliable low latency communication in accordance with various aspects of the present disclosure. The operations of method1100may be implemented by a wireless device which may be an example of a UE115or base station105or its components as described with reference toFIGS. 1-10. For example, the operations of method1100may be performed by the fountain HARQ module610as described with reference toFIGS. 6-10. In some examples, the device may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally or alternatively, the device may perform aspects of the functions described below using special-purpose hardware.

At block1105, the device may transmit a data block using a first set of resources based on a low latency operational mode as described above with reference toFIGS. 2-5. In certain examples, the operations of block1105may be performed by the LL data module705as described above with reference toFIG. 7.

At block1110, the device may transmit a number of redundancy versions of the data block using a second set of resources based on the low latency operational mode, the number of redundancy versions of the data block being transmitted prior to determining whether an ACK is received for the data block as described above with reference toFIGS. 2-5. In certain examples, the operations of block1110may be performed by the redundancy module710as described above with reference toFIG. 7.

FIG. 12shows a flowchart illustrating a method1200associated with fountain HARQ for reliable low latency communication in accordance with various aspects of the present disclosure. The operations of method1200may be implemented by a wireless device which may be an example of a UE115or base station105or its components as described with reference toFIGS. 1-10. For example, the operations of method1200may be performed by the fountain HARQ module610as described with reference toFIGS. 6-10. In some examples, a device may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally or alternatively, the device may perform aspects of the functions described below using special-purpose hardware. The method1200may also incorporate aspects of method1100ofFIG. 11.

At block1205, the device may select an initial MCS based at least in part on a channel condition or a size of a data block, wherein transmitting the data block is based on the initial MCS as described above with reference toFIGS. 2-5. In certain examples, the operations of block1205may be performed by the MCS module805as described above with reference toFIG. 8.

At block1210, the device may transmit the data block using a first set of resources based on a low latency operational mode as described above with reference toFIGS. 2-5. In certain examples, the operations of block1210may be performed by the LL data module705as described above with reference toFIG. 7.

At block1215, the device may transmit a number of redundancy versions of the data block using a second set of resources based on the low latency operational mode, the number of redundancy versions of the data block being transmitted prior to determining whether an ACK is received for the data block as described above with reference toFIGS. 2-5. In certain examples, the operations of block1215may be performed by the redundancy module710as described above with reference toFIG. 7.

At block1220, the device may receive an ACK. In some cases, the ACK is an augmented ACK based at least in part on the number of redundancy versions and comprising an additional resource request as described above with reference toFIGS. 2-5. In certain examples, the operations of block1220may be performed by the augmented ACK module810as described above with reference toFIG. 8.

At block1225, the device may select an updated MCS based at least in part on the augmented ACK as described above with reference toFIGS. 2-5. In certain examples, the operations of block1225may be performed by the MCS module805as described above with reference toFIG. 8.

FIG. 13shows a flowchart illustrating a method1300associated with fountain HARQ for reliable low latency communication in accordance with various aspects of the present disclosure. The operations of method1300may be implemented by a wireless device which may be an example of a UE115or base station105or its components as described with reference toFIGS. 1-10. For example, the operations of method1300may be performed by the fountain HARQ module610as described with reference toFIGS. 6-10. In some examples, a device may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally or alternatively, the device may perform aspects of the functions described below using special-purpose hardware. The method1300may also incorporate aspects of methods1100, and1200ofFIGS. 11-12.

At block1305, the device may transmit a data block using a first set of resources based on a low latency operational mode as described above with reference toFIGS. 2-5. In certain examples, the operations of block1305may be performed by the LL data module705as described above with reference toFIG. 7.

At block1310, the device may transmit a number of redundancy versions of the data block using a second set of resources based on the low latency operational mode, the number of redundancy versions of the data block being transmitted prior to determining whether an ACK is received for the data block as described above with reference toFIGS. 2-5. In certain examples, the operations of block1310may be performed by the redundancy module710as described above with reference toFIG. 7.

At block1315, the device may receive the ACK on a reduced symbol duration UL control channel based on the low latency operational mode as described above with reference toFIGS. 2-5. In certain examples, the operations of block1315may be performed by the HARQ module815as described above with reference toFIG. 8.

At block1320, the device may refrain from transmitting an additional redundancy version of the data block based on the ACK as described above with reference toFIGS. 2-5. In certain examples, the operations of block1320may be performed by the redundancy module710as described above with reference toFIG. 7.

FIG. 14shows a flowchart illustrating a method1400associated with fountain HARQ for reliable low latency communication in accordance with various aspects of the present disclosure. The operations of method1400may be implemented by a wireless device which may be an example of a UE115or base station105or its components as described with reference toFIGS. 1-10. For example, the operations of method1400may be performed by the fountain HARQ module610as described with reference toFIGS. 6-10. In some examples, a device may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally or alternatively, the device may perform aspects of the functions described below using special-purpose hardware. The method1400may also incorporate aspects of methods1100,1200, and1300ofFIGS. 11-13.

At block1405, the device may receive a data block using a first set of resources based on a low latency operational mode as described above with reference toFIGS. 2-5. In certain examples, the operations of block1405may be performed by the LL data module705as described above with reference toFIG. 7.

At block1410, the device may compute a first set of LLRs for the data block as described above with reference toFIGS. 2-5. In certain examples, the operations of block1410may be performed by the LLR module820as described above with reference toFIG. 8.

At block1415, the device may determine that a first set of decoded bits from the first set of LLRs does not pass a CRC as described above with reference toFIGS. 2-5. In certain examples, the operations of block1415may be performed by the CRC module825as described above with reference toFIG. 8.

At block1420, the device may receive a number of redundancy versions of the data block based on the low latency operational mode using a second set of resources prior to transmitting a NACK as described above with reference toFIGS. 2-5. In certain examples, the operations of block1420may be performed by the redundancy module710as described above with reference toFIG. 7.

At block1425, the device may compute an updated set of LLRs for the data block based on the number of redundancy versions as described above with reference toFIGS. 2-5. In certain examples, the operations of block1425may be performed by the LLR module820as described above with reference toFIG. 8.

At block1430, the device may determine that a second set of decoded bits from the updated set of LLRs passes the CRC as described above with reference toFIGS. 2-5. In certain examples, the operations of block1430may be performed by the CRC module825as described above with reference toFIG. 8.

At block1435, the device may transmit an ACK for the data block based on the determination that the updated set of LLRs passes the CRC as described above with reference toFIGS. 2-5. In certain examples, the operations of block1435may be performed by the HARQ module815as described above with reference toFIG. 8.

FIG. 15shows a flowchart illustrating a method1500associated with fountain HARQ for reliable low latency communication in accordance with various aspects of the present disclosure. The operations of method1500may be implemented by a wireless device which may be an example of a UE115or base station105or its components as described with reference toFIGS. 1-10. For example, the operations of method1500may be performed by the fountain HARQ module610as described with reference toFIGS. 6-10. In some examples, a device may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally or alternatively, the device may perform aspects of the functions described below using special-purpose hardware. The method1500may also incorporate aspects of methods1100,1200,1300, and1400ofFIGS. 11-14.

At block1505, the device may receive a data block using a first set of resources based on a low latency operational mode as described above with reference toFIGS. 2-5. In certain examples, the operations of block1505may be performed by the LL data module705as described above with reference toFIG. 7.

At block1510, the device may compute a first set of LLRs for the data block as described above with reference toFIGS. 2-5. In certain examples, the operations of block1510may be performed by the LLR module820as described above with reference toFIG. 8.

At block1515, the device may determine that a first set of decoded bits from the first set of LLRs does not pass a CRC as described above with reference toFIGS. 2-5. In certain examples, the operations of block1515may be performed by the CRC module825as described above with reference toFIG. 8.

At block1520, the device may receive a number of redundancy versions of the data block based on the low latency operational mode using a second set of resources prior to transmitting a NACK as described above with reference toFIGS. 2-5. In certain examples, the operations of block1520may be performed by the redundancy module710as described above with reference toFIG. 7.

At block1525, the device may compute an updated set of LLRs for the data block based on the number of redundancy versions as described above with reference toFIGS. 2-5. In certain examples, the operations of block1525may be performed by the LLR module820as described above with reference toFIG. 8.

At block1530, the device may determine that a second set of decoded bits from the updated set of LLRs passes the CRC as described above with reference toFIGS. 2-5. In certain examples, the operations of block1530may be performed by the CRC module825as described above with reference toFIG. 8.

At block1535, the device may transmit an ACK for the data block based on the determination that the updated set of LLRs passes the CRC as described above with reference toFIGS. 2-5. The ACK may be an augmented ACK based at least in part on the number of redundancy versions and comprising an additional resource request. In certain examples, the operations of block1535may be performed by the HARQ module815as described above with reference toFIG. 8.

At block1540, the device may receive a subsequent data block using an updated MCS based at least in part on the augmented ACK as described above with reference to FIGS.2-5. In certain examples, the operations of block1540may be performed by the MCS module805as described above with reference toFIG. 8.

FIG. 16shows a flowchart illustrating a method1600associated with fountain HARQ for reliable low latency communication in accordance with various aspects of the present disclosure. The operations of method1600may be implemented by a wireless device which may be an example of a UE115or base station105or its components as described with reference toFIGS. 1-10. For example, the operations of method1600may be performed by the fountain HARQ module610as described with reference toFIGS. 6-10. In some examples, a device may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally or alternatively, the device may perform aspects of the functions described below using special-purpose hardware. The method1600may also incorporate aspects of methods1100,1200,1300,1400, and1500ofFIGS. 11-15.

At block1605, the device may receive a data block using a first set of resources based on a low latency operational mode as described above with reference toFIGS. 2-5. In certain examples, the operations of block1605may be performed by the LL data module705as described above with reference toFIG. 7.

At block1610, the device may compute a first set of LLRs for the data block as described above with reference toFIGS. 2-5. In certain examples, the operations of block1610may be performed by the LLR module820as described above with reference toFIG. 8.

At block1615, the device may determine that a first set of decoded bits from the first set of LLRs does not pass a CRC as described above with reference toFIGS. 2-5. In certain examples, the operations of block1615may be performed by the CRC module825as described above with reference toFIG. 8.

At block1620, the device may receive a number of redundancy versions of the data block based on the low latency operational mode using a second set of resources prior to transmitting a NACK as described above with reference toFIGS. 2-5. In certain examples, the operations of block1620may be performed by the redundancy module710as described above with reference toFIG. 7.

At block1625, the device may compute an updated set of LLRs for the data block based on the number of redundancy versions as described above with reference toFIGS. 2-5. In certain examples, the operations of block1625may be performed by the LLR module820as described above with reference toFIG. 8.

At block1630, the device may perform a decoding operation based on the updated set of LLRs and the determination that the accumulated quality metric exceeds the threshold, wherein the second set of decoded bits is an output of the decoding operation as described above with reference toFIGS. 2-5. In certain examples, the operations of block1630may be performed by the decoder830as described above with reference toFIG. 8.

At block1635, the device may determine that a second set of decoded bits from the updated set of LLRs passes the CRC as described above with reference toFIGS. 2-5. In certain examples, the operations of block1635may be performed by the CRC module825as described above with reference toFIG. 8.

At block1640, the device may transmit an ACK for the data block based on the determination that the updated set of LLRs passes the CRC as described above with reference toFIGS. 2-5. In certain examples, the operations of block1640may be performed by the HARQ module815as described above with reference toFIG. 8.

Thus, methods1100,1200,1300,1400,1500, and1600may provide for wireless communications associated with fountain HARQ for reliable low latency communication. It should be noted that methods1100,1200,1300,1400,1500, and1600describe possible implementation, and that the operations and the steps may be rearranged or otherwise modified such that other implementations are possible. In some examples, aspects from two or more of the methods1100,1200,1300,1400,1500, and1600may be combined.