Low latency operation with different hybrid automatic repeat request (HARQ) timing options

Methods, systems, and devices for wireless communication are described. A user equipment (UE) or a base station may identify a timing advance parameter and a processing parameter for the UE, and one or both may determine a hybrid automatic repeat request (HARQ) timing based on the identified parameters. For example, if the UE has a large timing advance or reduced processing capacity, a longer HARQ timing may be chosen. When the UE receives downlink (DL) transmissions from the base station, the UE may send an acknowledgement (ACK) or negative acknowledgement (NACK) based on the chosen HARQ timing. The base station may send a retransmission (in the case of a NACK) based on the HARQ timing. In some cases, the UE may request a specific HARQ timing, or request an updated timing advance. If HARQ synchronization is lost, the UE and the base station may default to a preconfigured HARQ timing.

BACKGROUND

The following relates generally to wireless communication, and more specifically to low latency operation with different hybrid automatic repeat request (HARQ) timing.

In some cases, a base station and a UE may operate based on a low latency physical (PHY) layer timing structure. Low latency operations (for example, operations based on a reduced transmission time interval (TTI)) may enable a reduction in the delay between a transmission and a HARQ response. However, the reduced delay may also reduce the time available for a UE to process a transmission and determine a response. For UEs with a large propagation delay (and hence, a large timing advance) this reduced processing time may not be sufficient.

SUMMARY

A user equipment (UE) or a base station, or both, may identify a timing advance parameter and a processing parameter for the UE and determine a hybrid automatic repeat request (HARQ) timing to the identified parameters. For example, if the UE has a large timing advance or reduced processing capacity, a longer HARQ timing may be chosen. When the UE receives downlink (DL) transmissions from the base station, the UE may send an acknowledgement (ACK) or negative acknowledgement (NACK) based on the chosen HARQ timing. The base station may then send a retransmission (in the case of a NACK) based on the HARQ timing. In some cases the UE may request a specific HARQ timing, or request an updated timing advance. If HARQ synchronization is lost, the UE and the base station may default to a preconfigured HARQ timing which may be based on a large timing advance.

A method of wireless communication is described. The method may include identifying a timing advance parameter and a processing parameter associated with a UE, determining a HARQ timing based at least in part on the timing advance parameter or the processing parameter, or both, and transmitting a HARQ response message based at least in part on the HARQ timing.

An apparatus for wireless communication is described. The apparatus may include means for identifying a timing advance parameter and a processing parameter associated with a UE, means for determining a HARQ timing based at least in part on the timing advance parameter or the processing parameter, or both, and means for transmitting a HARQ response message based at least in part on the HARQ timing.

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 and operable, when executed by the processor, to cause the apparatus to identify a timing advance parameter and a processing parameter associated with a UE, determine a HARQ timing based at least in part on the timing advance parameter or the processing parameter, or both, and transmit a HARQ response message based at least in part on the HARQ timing.

A non-transitory computer-readable medium storing code for wireless communication is described. The code may include instructions executable to identify a timing advance parameter and a processing parameter associated with a UE, determine a HARQ timing based at least in part on the timing advance parameter or the processing parameter, or both, and transmit a HARQ response message based at least in part on the HARQ timing.

DETAILED DESCRIPTION

In some cases, a wireless system may utilize low latency operations. This may be achieved by utilizing a reduced transmission time interval (TTI). UEs employing low latency operations may be affected by certain transmission timing, such as HARQ timing, more than other UEs. Accordingly, HARQ timing may need to be dynamically determined and adjusted to account for changing timing advance parameters and processing parameters associated with a UE.

During low latency operations, if different user equipment (UEs) are frequency multiplexed within an uplink subframe, it may be appropriate to have a UE-specific uplink (UL) timing advance (TA) such that the reception times for different UEs are substantially aligned at the base station. That is, a UE closer to the base station may have a smaller TA based on having a smaller propagation delay.

Accordingly, in some cases a system may be designed such that all UL traffic with a given TTI arrives at the base station at approximately the same time. This may enable a base station to use a single fast Fourier transform (FFT) processing without interference when frequency multiplexing different UL traffic in the same subframe. Low latency UL TA may be handled differently when low latency traffic coexists with other traffic. That is, low latency traffic may utilize different TA commands or different TA loops. For example, a base station may target different propagation areas for low latency and other traffic. This approach may also be used if low latency and other traffic can be time division multiplexed to avoid mutual interference.

In order to handle different UL TA impact, the link between a DL transmission and the corresponding UL feedback can be UE-specific. Similarly, the link between an UL transmission and the next DL response can also be UE-specific. That is, HARQ timing may depend on the UL TA for each UE, as well as on UE processing capability and load. Accordingly, a UE can indicate its processing capability to the base station. Additionally or alternatively, a UE can indicate its UL TA (either explicitly or implicitly). That is, a UE may transmit an explicit TA indication so the base station can adjust the HARQ timing accordingly. Alternatively, a UE may send an implicit TA indication. In some cases, a base station can indicate the UL TA commands, and possibly the response time options for a UE, as part of a random access procedure message.

A fallback operation may, for example, be configured such that there is a default timing operation that a UE and a base station may use, e.g., if synchronization is lost. In some cases, the default timing operation can assume the worst case UL TA. If low latency broadcast is supported, a common timing option may also be used (that is, a worst case UL TA for all possible UEs). Reference signal dependent TTI lengths may also be supported.

Aspects of the disclosure are initially described below in the context of a wireless communication system. Specific examples are then described for various UL/DL offset timing configurations based on different propagation delays. These and other aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to low latency operation with different hybrid automatic repeat request (HARQ) timing.

FIG. 1illustrates an example of a wireless communications system100in accordance with various aspects of the present disclosure. The wireless communications system100includes base stations105, user equipment (UEs)115, and a core network130. In some examples, the wireless communications system100may be a Long Term Evolution (LTE)/LTE-advanced (LTE-a) network. In some cases, wireless communications system100may utilize low latency operations and HARQ timing may be based on the timing advance of each UE115.

Base stations105may wirelessly communicate with UEs115via one or more base station antennas. Each base station105may provide communication coverage for a respective geographic coverage area110. 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. UEs115may be dispersed throughout the wireless communications system100, and each UE115may be stationary or mobile. A UE115may also be referred to as a mobile station, a subscriber station, a remote unit, a wireless device, an access terminal, a handset, a user agent, a client, or some other suitable terminology. A UE115may also be a cellular phone, a wireless modem, a handheld device, a personal computer, a tablet, a personal electronic device, a machine type communication (MTC) device or the like.

After the UE115decodes the system information from a base station105, it may transmit a random access channel (RACH) preamble to a base station105. This may be known as RACH message1. For example, the RACH preamble may be randomly selected from a set of 64 predetermined sequences. This may enable the base station105to distinguish between multiple UEs115trying to access the system simultaneously. The base station105may respond with a random access response (RAR), or RACH message2, that provides an uplink (UL) resource grant, a timing advance and a temporary cell radio network temporary identity (C-RNTI). The UE115may then transmit a radio resource control (RRC) connection request, or RACH message3, along with a temporary mobile subscriber identity (TMSI) (if the UE115has previously been connected to the same wireless network) or a random identifier. The RRC connection request may also indicate the reason the UE115is connecting to the network (e.g., emergency, signaling, data exchange, etc.). The base station105may respond to the connection request with a contention resolution message, or RACH message4, addressed to the UE115, which may provide a new cell radio network temporary identity (C-RNTI). If the UE115receives a contention resolution message with the correct identification, it may proceed with RRC setup. If the UE115does not receive a contention resolution message (e.g., if there is a conflict with another UE115) it may repeat the RACH process by transmitting a new RACH preamble.

Time intervals in LTE may be expressed in multiples of a basic time unit (e.g., the sampling period, Ts=1/30,720,000 seconds). Time resources may be organized according to radio frames of length of 10 ms (Tf=307200·Ts), which may be identified by a system frame number (SFN) ranging from 0 to 1023. Each frame may include ten 1 ms subframes numbered from 0 to 9. A subframe may be further divided into two 0.5 ms slots, each of which contains 6 or 7 modulation symbol periods (depending on the length of the cyclic prefix prepended to each symbol). Excluding the cyclic prefix, each symbol contains 2048 sample periods. In some cases the subframe may be the smallest scheduling unit, also known as a transmission time interval (TTI). In other cases, a TTI may be shorter than a subframe or may be dynamically selected (e.g., in short TTI bursts or in selected component carriers using short TTIs).

In some cases, a UE115will apply a negative timing offset (or timing advance (TA)) to each transmission (i.e., it may send the transmission before the beginning of a TTI) to account for the propagation delay between the UE115and the base station105. This may ensure that the base station105receives transmissions from different UEs115at substantially the same time. In some cases, a base station105may send a timing advance command (TAC) together with a RAR during a RACH procedure. The UE115may then set the TA based on the TAC. In some cases, the UE115may set the TA at a preconfigured time after receiving the TAC (e.g., during the 6th subframe following the TAC). A base station105may send subsequent TAC updates within media access control (MAC) control elements (CEs). In some cases, a UE115may set a TA timer after receiving a TAC. If the timer expires without receiving another TAC, the UE115may determine that it has lost synchronization (and, as a consequence, flush its HARQ buffers and release UL control resources.)

Wireless communications system100may improve the reliability of communication links125using hybrid automatic repeat request (HARQ) procedures. HARQ may include a combination of error detection (e.g., using a cyclic redundancy check (CRC)), forward error correction (FEC), and retransmission (e.g., automatic repeat request (ARQ)). HARQ may improve throughput at the medium access control (MAC) layer in poor radio conditions (e.g., 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. The chain of transmission, response and retransmission may be referred to as a HARQ process. In some cases, a limited number of HARQ processes may be used for a given communication link125. In some cases, the time between a transmission, a HARQ response (i.e., and acknowledgement (ACK) or negative ACK (NACK)), and retransmission may depend on the TA of each specific UE115.

In some cases, wireless communications system100may utilize one or more enhanced component carriers (eCCs). An enhanced component carrier (eCC) may be characterized by one or more features including: flexible bandwidth, different TTIs, and modified control channel configuration. In some cases, an eCC may be associated with a carrier aggregation (CA) configuration or a dual connectivity configuration (e.g., when multiple serving cells have a suboptimal backhaul link). An eCC may also be configured for use in unlicensed spectrum or shared spectrum (e.g., where more than one operator is licensed to use the spectrum). An eCC characterized by flexible bandwidth may include one or more segments that may be utilized by UEs115that do are not capable of monitoring the whole bandwidth or prefer to use a limited bandwidth (e.g., to conserve power).

In some cases, an eCC or a low latency component carrier (CC) may utilize a different TTI length than other CCs, which may include use of a reduced or variable symbol duration as compared with TTIs of the other CCs. The symbol duration may remain the same, in some cases, but each symbol may represent a distinct TTI. In some examples, an eCC may include multiple hierarchical layers associated with the different TTI lengths. For example, TTIs at one hierarchical layer may correspond to uniform 1 ms subframes, whereas in a second layer, variable length TTIs may correspond to bursts of short duration symbol periods. In some cases, a shorter symbol duration may also be associated with increased subcarrier spacing. In conjunction with the reduced TTI length, an eCC may utilize dynamic time division duplex (TDD) operation (i.e., it may switch from downlink (DL) to uplink (UL) operation for short bursts according to dynamic conditions.)

Flexible bandwidth and variable TTIs may be associated with a modified control channel configuration (e.g., an eCC may utilize an enhanced physical downlink control channel (ePDCCH) for DL control information). For example, one or more control channels of an eCC may utilize frequency-division multiplexing (FDM) scheduling to accommodate flexible bandwidth use. Other control channel modifications include the use of additional control channels (e.g., for evolved multimedia broadcast multicast service (eMBMS) scheduling, or to indicate the length of variable length UL and DL bursts), or control channels transmitted at different intervals. An eCC may also include modified or additional HARQ related control information.

FIG. 2illustrates an example of a wireless communications system200for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. Wireless communications system200may include UE115-a, UE115-b, and base station105-a, which may be examples of UEs115and a base station105described with reference toFIG. 1. Wireless communications system200illustrates an example in which UE115-ais closer to base station105-athan UE115-bis. Accordingly, communication link125-amay have a shorter propagation delay than communication link125-b. Thus, base station105-amay configure UE115-awith a shorter HARQ response time than UE115-b.

Wireless communications system200may utilize low latency operations. This may be achieved by utilizing a reduced TTI, such as a one symbol period TTI (˜71 μs for a normal cyclic prefix (CP) and ˜83 μs for an extended CP). This may enable wireless communications system200(which may be based on LTE) to achieve one-tenth of the over-the-air HARQ latency of systems that do not utilize low latency operations. That is, the HARQ latency may be approximately 300 μs rather than 4 ms. Low latency operations may reuse LTE numerology to minimize the impact on specifications and improve backward compatibility. For example, a low latency system may use 15 kHz tone spacing and a symbol duration approximately 71 μs (with a normal CP). This may enable smooth integration of low latency capable devices with devices that are not capable of low latency operation. For example wireless communications system200may achieve co-existence within a subframe via resource block level multiplexing. Low latency operations may be utilized for both small cells and for macro cells.

If UE115-aand UE115-bare frequency multiplexed within one or more uplink subframes, it may be appropriate to have a UE-specific UL TA such that the reception times for UE115-aand UE115-bat the base station105-aare substantially aligned. That is, UE115-a,being closer to base station105-a, may have a smaller TA based on having a smaller propagation delay. In the case of UE115-b, the propagation delay may be large. For example, for a 10 km distance between base station105-aand a UE115-b, the TA may be approximately 67 us. As a result, for a DL transmission with a 4-symbol turn-around time for a hybrid automatic repeat request (HARQ) response) the processing time available for UE115-bmay be reduced from 3 symbols to roughly 2 symbol periods. For larger distances, the processing time may be even further reduced. For example, with a 30 km distance (with a TA of 200 us), the actual processing time may be close to zero (less than one symbol period).

Wireless communications system200may be designed such that all UL traffic within a given TTI arrives at base station105-aat approximately the same time. This may enable base station105-ato use a single fast Fourier transform (FFT) processing without interference when frequency multiplexing different UL traffic in the same subframe. In some cases, low latency UL TA may be handled differently when low latency traffic coexists with other traffic. That is, low latency traffic may utilize different TA commands or different TA loops. For example, base station105-amay target different propagation areas for low latency and other traffic. This approach may also be used if low latency and other traffic can be time division multiplexed to avoid mutual interference.

In order to handle different UL TA impact, the link between a DL transmission and the corresponding UL feedback can be UE-specific. Similarly, the link between an UL transmission and the next DL response can also be UE-specific. That is, HARQ timing may depend on the UL TA for each UE115, as well as on UE processing capability and load. For example, with a 1 symbol TTI, UE115-amay be configured for a 4 symbol HARQ response time (that is, the ACK/NACK may be sent 4 symbols after the transmission), or if it has a relatively small amount of processing power available UE115-amay be configured with a 5 symbol response time; UE115-amay also be configured with a 5 symbol response time based on propagation delay or if it has relatively little processing power (or a very large UL TA) it may be configured with a 6 symbol response time. In some cases, the base station retransmission delay (i.e., the time between base station105-areceiving a NACK and retransmitting a block of data) may be configured such that the total delay between transmission and retransmission may be constant (e.g., 8 symbols). In other cases, the total delay may be based on the UE response time.

In cases when the HARQ timing depends on UE capabilities, UE115-aand UE115-bcan indicate their processing capability to the base station. Additionally or alternatively, UE115-aand UE115-bcan indicate their respective UL TAs (either explicitly or implicitly). That is, a UE115-aand UE115-bmay transmit explicit TA indications so base station105can adjust the HARQ timing accordingly. For example, if UE115-ais moving rapidly within a geographic coverage area110, it may anticipate a changing timing advance before a base station sends another timing advance command. Alternatively, UE115-aand UE115-bmay send implicit TA indications. For example, UE115-aand UE115-bmay simply send a request for a desired response timing. In some cases, base station105-amay provide a115-aor UE115-bwith one or more upper and lower bounds on the TA associated with different discrete response timing levels. In some cases, a hysteresis value can be provided to avoid ping-pong effect. For example, if UE115-bcurrently has TA of 40 us, it can indicate a desired response time of only if the propagation delay drops to 5 us (the hysteresis value) below a threshold of 30 us (that is, if it drops to 25 us). If the TA goes back up, UE115-bmay wait until the propagation delay gets 5 us above a threshold of 30 us (that is, if it increases to 35 us) prior to adjusting the TA and/or HARQ timing (or requesting an adjustment).

In some cases, base station105-acan indicate the UL TA commands, and possibly the response time options for UE115-aand UE115-bas part of a random access procedure message. For example, if the TA is large, the base station may indicate a 5 symbol response time; otherwise, a 4 symbol response time may be indicated. Base station105-amay then send an updated response time to the UE115-aor UE115-blater on based on other factors (e.g., past TA commands, scheduling needs, processing capabilities, etc.)

In some cases a fallback operation may be configured such that there is always a default timing operation such that UE115-aand base station105-amay use, e.g., if synchronization is lost. In some cases, the default timing operation can assume the worst case UL TA. If low latency broadcast is supported, a common timing option may also be used (that is, a worst case UL TA for all possible UEs115). It should be noted that the above discussion may be applicable to various TTI lengths (e.g., 1 symbol, 2 symbol, 1 slot, etc.). Reference signal dependent TTI lengths may also be supported. For example, for cell-specific reference signal (CRS) based low latency operation, a 1-symbol TTI length may be used; for demodulation reference signal (DM-RS) based ULL, a 2 symbol TTI length may be used (since in some cases it may be easier to design a DM-RS pattern with a 2-symbol TTI). The above discussion may also applicable to cases when the processing capability at the UE side is limited. For example, with a large number of component carriers (CCs) or CCs with large bandwidth (e.g., greater than 20 MHz), different UEs115may utilize different response time options.

FIG. 3Aillustrates an example of an offset timing configuration300-afor low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. Offset timing configuration300-amay represent a DL timing305-afor a base station105and an UL timing310-afor a UE115, which may be examples of a UE115and base station105described with reference toFIGS. 1-2. Offset timing configuration300-amay represent an example of low latency HARQ operation with a relatively small timing advance (TA)315-a.

UL timing310-amay be offset from DL timing305-aby TA312-ato account for a propagation delay between the corresponding UE115and base station105. This may enable UL transmissions from different UEs115to arrive substantially simultaneously at a base station105. According to the example of offset timing configuration300-a, a transmission315-amay be transmitted during DL subframe m. Based on the offset timing and the propagation delay, the transmission is received largely during symbol m+1 of the UE115. The receiving UE115may then process the transmission during processing period330-aand respond with a HARQ response320-a(either ACK or NACK). HARQ response320-amay be transmitted such that there is a HARQ delay335-aof 4 symbols. The base station105may then send retransmission 4 symbols later (at m+8).

FIG. 3Billustrates an example of an offset timing configuration300-bfor low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. Offset timing configuration300-bmay represent a DL timing305-bfor a base station105and an UL timing310-bfor a UE115, which may be examples of a UE115and base station105described with reference toFIGS. 1-2. Offset timing configuration300-bmay represent an example of low latency HARQ operation with a relatively large timing advance (TA)312-b.

UL timing310-bmay be offset from DL timing305-bby TA312-bto account for a propagation delay between the corresponding UE115and base station105. This may enable UL transmissions from different UEs115to arrive substantially simultaneously at a base station105. According to the example of offset timing configuration300-b, a transmission315-bmay be transmitted during DL subframe m and based on the offset timing and the propagation delay, the transmission is received largely during symbol m+1 and m+2 of the UE115. The receiving UE115may then process the transmission during processing period330-band respond with a HARQ response320-b(either ACK or NACK). HARQ response320-bmay be transmitted such that there is a HARQ delay335-bof 5 symbols. That is, HARQ delay335-bmay be lengthened to account for the large TA312-bwhile still providing a sufficient processing period330-b. In some cases, the HARQ delay225-bmay be configured based on both the TA312-band the desired processing period330-b(e.g., based on the UE processing capability and load).

The base station105may then send retransmission 4 symbols later (at m+8). That is, in some cases, the total HARQ period between transmission and retransmission may not depend on the HARQ delay335-b. In other cases, the total HARQ period may be adjusted. Offset timing configuration300-aand offset timing configuration300-brepresent two examples of how HARQ timing may depend on propagation delay or processing time, but other examples may also be possible (e.g., using different TTI lengths other than 1 symbol period).

FIG. 4illustrates an example of a process flow400for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. Process flow400may include a UE115-cand base station105-b, which may be examples of a UE115and base station105described with reference toFIGS. 1-2. Process flow400represents one example of how HARQ timing may be configured based on a timing advance or processing time, but other examples are also possible.

At405, UE115-cmay transmit a RACH preamble to base station105-b. At410, base station105-bmay calculate a timing advance based on the RACH preamble. At415, base station105-bmay also determine a HARQ timing. Thus, base station105-bmay receive a RACH message from UE115-c, such that the timing advance parameter may be identified based on the RACH message.

In some examples, the timing advance parameter is identified based on past timing advance commands or scheduling needs, or both. The HARQ timing may be based on low latency operation. In some examples, the low latency operation is based on a TTI duration. The TTI duration may be determined based on a reference signal type within the TTI. In some examples, the HARQ timing is based on a number of configured CCs, a number of scheduled CCs, a bandwidth of configured CCs, a bandwidth of scheduled CCs, or any combination thereof.

At420, base station105-bmay transmit a random access response including a timing advance command and, in some cases, the HARQ timing. In other cases, the HARQ timing may be configured with another message such as an RRC configuration message. Thus, base station105-bmay transmit signaling indicative of the HARQ timing to UE115-c. In some examples, the signaling may include a random access grant, the timing advance parameter, the HARQ timing, or any combination thereof. Similarly, UE115-cmay receive signaling indicative of the HARQ timing from base station105-b, such that the HARQ timing is determined based on the signaling. In some examples, the signaling includes the timing advance parameter.

At425, UE115-cmay identify the TA. At430, UE115-cmay identify the HARQ timing. UE115-cand base station105-bmay identify a timing advance parameter and a processing parameter associated with UE115-c. UE115-cand base station105-bmay determine a HARQ timing based on the timing advance parameter or the processing parameter, or both. In some examples, the processing parameter is associated with a processing capability of the UE or a processing load of the UE, or both.

In some cases (not shown) UE115-cmay transmit a HARQ timing preference to base station105-b, such that the HARQ timing is determined based on the HARQ timing preference. Similarly, base station105-bmay receive a HARQ timing preference from UE115-c. In some examples, the HARQ timing preference is received in a RACH message from UE115-c. In some cases, the HARQ timing preference is transmitted in a random access message. In some cases (not shown) UE115-cmay transmit a timing advance update message to base station105-b, such that the HARQ timing is determined based on the timing advance update message.

In some cases, UE115-cand base station105-bmay identify a set of timing advance threshold values, such that the HARQ timing is determined based on the set of timing advance threshold values. In some examples, the set of timing advance threshold values may include a hysteresis value, such that the timing advance parameter may be limited to a set duration offset based on the hysteresis value.

In some cases, UE115-cand base station105-bmay determine a HARQ synchronization error. UE115-cand base station105-bmay select a default HARQ timing based on the HARQ synchronization error determination. In some examples, the default HARQ timing is based on a greatest timing advance of a serving cell.

At435, base station105-bmay transmit a block of data to UE115-c. At440, UE115-cmay respond with an ACK or, as illustrated, a NACK using a delay based on the HARQ timing. Thus, base station105-bmay receive an ACK or a NACK from UE115-caccording to the HARQ timing, such that the HARQ response message is a retransmission of the data packet based on the received ACK or NACK.

At445, if the response is a NACK, base station105-bmay retransmit the data block. Thus, both UE115-cand base station105-bmay transmit a HARQ response message (i.e., either an ACK/NACK or a retransmission) based on the HARQ timing.

FIG. 5shows a block diagram of a wireless device500configured for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. Wireless device500may be an example of aspects of a UE115or base station105described with reference toFIGS. 1-4. Wireless device500may include a receiver505, a low latency HARQ timing module510, or a transmitter515. Wireless device500may also include a processor. Each of these components may be in communication with each other.

The receiver505may 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 low latency operation with different HARQ timing, etc.). Information may be passed on to the low latency HARQ timing module510, and to other components of wireless device500. In some cases, (e.g., for a UE115), the receiver505may receive signaling indicative of the HARQ timing from a serving cell, such that the HARQ timing is determined based on the signaling. In some examples, the signaling includes the timing advance parameter.

The low latency HARQ timing module510may identify a timing advance parameter and a processing parameter associated with a UE, determine a HARQ timing based on the timing advance parameter or the processing parameter, or both, and transmit a HARQ response message based on the HARQ timing.

The transmitter515may transmit signals received from other components of wireless device500. In some examples, the transmitter515may be collocated with the receiver505in a transceiver module. The transmitter515may include a single antenna, or it may include a plurality of antennas. In some cases, (e.g., for a base station105), the transmitter515may transmit signaling indicative of the HARQ timing to a UE115. In some examples, the signaling may include a random access grant, the timing advance parameter, the HARQ timing, or any combination thereof. In some examples, the transmitter515may transmit a data packet to a UE115.

FIG. 6shows a block diagram of a wireless device600for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. Wireless device600may be an example of aspects of a wireless device500, a base station105, or a UE115described with reference toFIGS. 1-5. Wireless device600may include a receiver505-a, a low latency HARQ timing module510-a, or a transmitter515-a. Wireless device600may also include a processor. Each of these components may be in communication with each other. The low latency HARQ timing module510-amay also include a timing parameter module605, a HARQ timing module610, and a HARQ response module615.

The receiver505-amay receive information which may be passed on to low latency HARQ timing module510-a, and to other components of wireless device600. The low latency HARQ timing module510-amay perform the operations described with reference toFIG. 5. The transmitter515-amay transmit signals received from other components of wireless device600.

The HARQ timing module610may determine a HARQ timing based on the timing advance parameter or the processing parameter, or both as described with reference toFIGS. 2-4. The HARQ timing module610may also select a default HARQ timing based on the HARQ synchronization error determination. In some examples, the default HARQ timing may be based on a greatest timing advance of a serving cell. In some examples, the HARQ timing may be based on a number of configured CCs, a number of scheduled CCs, a bandwidth of configured CCs, a bandwidth of scheduled CCs, or any combination thereof.

The HARQ response module615may transmit a HARQ response message based on the HARQ timing as described with reference toFIGS. 2-4. The HARQ response module615may also receive an ACK or a NACK from a UE115according to the HARQ timing, such that the HARQ response message is a retransmission of the data packet based on the received ACK or NACK.

FIG. 7shows a block diagram700of a low latency HARQ timing module510-bwhich may be a component of a wireless device500or a wireless device600for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. The low latency HARQ timing module510-bmay be an example of aspects of a low latency HARQ timing module510described with reference toFIGS. 5-6. The low latency HARQ timing module510-bmay include a timing parameter module605-a, a HARQ timing module610-a, and a HARQ response module615-a. Each of these modules may perform the functions described with reference toFIG. 6. The low latency HARQ timing module510-bmay also include a timing advance update module705, a timing preference module710, a HARQ synchronization module715, a RACH module720, and a low latency module725.

The timing advance update module705may transmit a timing advance update message to a serving cell, such that the HARQ timing is determined based on the timing advance update message as described with reference toFIGS. 2-4.

The timing preference module710may transmit a HARQ timing preference to a serving cell, such that the HARQ timing is determined based on the HARQ timing preference as described with reference toFIGS. 2-4. In some examples, the HARQ timing preference may be transmitted in a random access message. The timing preference module710may also receive a HARQ timing preference from a UE115, such that the HARQ timing is determined based on the HARQ timing preference. In some examples, the HARQ timing preference may be received in a RACH message from a UE115.

The HARQ synchronization module715may determine a HARQ synchronization error as described with reference toFIGS. 2-4.

The RACH module720may receive a RACH message from a UE115, such that the timing advance parameter is identified based on the RACH message as described with reference toFIGS. 2-4.

The low latency module725may be configured such that the HARQ timing may be based on low latency operation as described with reference toFIGS. 2-4. In some examples, the low latency operation may be based on a TTI duration. In some examples, the TTI duration may be determined based on a reference signal type within the TTI.

FIG. 8shows a diagram of a system800including a UE115configured for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. System800may include UE115-d, which may be an example of a wireless device500, a wireless device600, or a UE115described with reference toFIGS. 1, 2 and 5-7. UE115-dmay include a low latency HARQ timing module810, which may be an example of a low latency HARQ timing module510described with reference toFIGS. 5-7. UE115-dmay also include a low latency module825. UE115-dmay also include components for bi-directional voice and data communications including components for transmitting communications and components for receiving communications. For example, UE115-dmay communicate bi-directionally with base station105-e.

Low latency module825may enable UE115-dto communicate using a reduced HARQ latency, such as using a reduced TTI as described herein.

UE115-dmay also include a processor805, and memory815(including software (SW))820, a transceiver835, and one or more antenna(s)840, each of which may communicate, directly or indirectly, with one another (e.g., via buses845). The transceiver835may communicate bi-directionally, via the antenna(s)840or wired or wireless links, with one or more networks, as described above. For example, the transceiver835may communicate bi-directionally with a base station105or another UE115. The transceiver835may include a modem to modulate the packets and provide the modulated packets to the antenna(s)840for transmission, and to demodulate packets received from the antenna(s)840. While UE115-dmay include a single antenna840, UE115-dmay also have multiple antennas840capable of concurrently transmitting or receiving multiple wireless transmissions.

The memory815may include random access memory (RAM) and read only memory (ROM). The memory815may store computer-readable, computer-executable software/firmware code820including instructions that, when executed, cause the processor805to perform various functions described herein (e.g., low latency operation with different HARQ timing, etc.). Alternatively, the software/firmware code820may not be directly executable by the processor805but cause a computer (e.g., when compiled and executed) to perform functions described herein. The processor805may include an intelligent hardware device, (e.g., a central processing unit (CPU), a microcontroller, an application specific integrated circuit (ASIC), etc.)

FIG. 9shows a diagram of a system900including a base station105configured for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. System900may include base station105-d, which may be an example of a wireless device500, a wireless device600, or a base station105described with reference toFIGS. 1, 2 and 6-8. Base station105-dmay include a base station low latency HARQ timing module910, which may be an example of a base station low latency HARQ timing module910described with reference toFIGS. 6-8. 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-eor 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-eand base station105-fvia 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-eor105-futilizing base station communications module925. In some examples, base station communications module925may provide an X2 interface within an LTE/LTE-A wireless communication network technology to provide communication between some of the base stations105. In some examples, base station105-dmay communicate with other base stations through core network130. In some cases, base station105-dmay communicate with the core network130through network communications module930.

The base station105-dmay include a processor905, memory915(including software (SW)920), transceiver935, and antenna(s)940, which each may be in communication, directly or indirectly, with one another (e.g., over bus system945). The transceivers935may be configured to communicate bi-directionally, via the antenna(s)940, with the UEs115, which may be multi-mode devices. The transceiver935(or other components of the base station105-d) may also be configured to communicate bi-directionally, via the antennas940, with one or more other base stations (not shown). The transceiver935may include a modem configured to modulate the packets and provide the modulated packets to the antennas940for transmission, and to demodulate packets received from the antennas940. The base station105-dmay include multiple transceivers935, each with one or more associated antennas940. The transceiver may be an example of a combined receiver505and transmitter515ofFIG. 5.

The memory915may include RAM and ROM. The memory915may also store computer-readable, computer-executable software code920containing instructions that are configured to, when executed, cause the processor905to perform various functions described herein (e.g., low latency operation with different HARQ timing, selecting coverage enhancement techniques, call processing, database management, message routing, etc.). Alternatively, the software code920may not be directly executable by the processor905but be configured to cause the computer, e.g., when compiled and executed, to perform functions described herein. The processor905may include an intelligent hardware device, e.g., a CPU, a microcontroller, an ASIC, etc. The processor905may 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 module925may manage communications with other base stations105. In some cases, a 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 module925may coordinate scheduling for transmissions to UEs115for various interference mitigation techniques such as beamforming or joint transmission.

FIG. 10shows a flowchart illustrating a method1000for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. The operations of method1000may be implemented by a device such as a UE115, a base station105, or their components as described with reference toFIGS. 1-9. For example, the operations of method1000may be performed by the low latency HARQ timing module510as described with reference toFIGS. 5-8. 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 the functions described below using special-purpose hardware.

At block1005, the device may identify a timing advance parameter and a processing parameter associated with a UE as described with reference toFIGS. 2-4. In certain examples, the operations of block1005may be performed by the timing parameter module605as described with reference toFIG. 6.

At block1010, the device may determine a HARQ timing based at least in part on the timing advance parameter or the processing parameter, or both as described with reference toFIGS. 2-4. In certain examples, the operations of block1010may be performed by the HARQ timing module610as described with reference toFIG. 6.

At block1015, the device may transmit a HARQ response message based at least in part on the HARQ timing as described with reference toFIGS. 2-4. In certain examples, the operations of block1015may be performed by the HARQ response module615as described with reference toFIG. 6.

FIG. 11shows a flowchart illustrating a method1100for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. The operations of method1100may be implemented by device such as a UE115, or its components as described with reference toFIGS. 1-9. For example, the operations of method1100may be performed by the low latency HARQ timing module510as described with reference toFIGS. 5-8. In some examples, a UE115may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally or alternatively, the UE115may perform aspects the functions described below using special-purpose hardware. The method1100may also incorporate aspects of method1000ofFIG. 10.

At block1105, the UE115may identify a timing advance parameter and a processing parameter associated with a UE as described with reference toFIGS. 2-4. In certain examples, the operations of block1105may be performed by the timing parameter module605as described with reference toFIG. 6.

At block1110, the UE115may receive signaling indicative of the HARQ timing from a serving cell, such that a HARQ timing is determined based at least in part on the signaling as described with reference toFIGS. 2-4. In certain examples, the operations of block1110may be performed by the receiver505as described with reference toFIG. 5.

At block1115, the UE115may determine a HARQ timing based at least in part on the timing advance parameter or the processing parameter, or both as described with reference toFIGS. 2-4. In certain examples, the operations of block1115may be performed by the HARQ timing module610as described with reference toFIG. 6.

At block1120, the UE115may transmit a HARQ response message based at least in part on the HARQ timing as described with reference toFIGS. 2-4. In certain examples, the operations of block1120may be performed by the HARQ response module615as described with reference toFIG. 6.

FIG. 12shows a flowchart illustrating a method1200for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. The operations of method1200may be implemented by a UE115or its components as described with reference toFIGS. 1-9. For example, the operations of method1200may be performed by the low latency HARQ timing module510as described with reference toFIGS. 5-8. In some examples, a UE115may execute a set of codes to control the functional elements of the UE115to perform the functions described below. Additionally or alternatively, the UE115may perform aspects the functions described below using special-purpose hardware. The method1200may also incorporate aspects of methods1000, and1100ofFIGS. 10-11.

At block1205, the UE115may identify a timing advance parameter and a processing parameter associated with a UE as described with reference toFIGS. 2-4. In certain examples, the operations of block1205may be performed by the timing parameter module605as described with reference toFIG. 6.

At block1210, the UE115may transmit a HARQ timing preference to a serving cell, such that a HARQ timing is determined based at least in part on the HARQ timing preference as described with reference toFIGS. 2-4. In certain examples, the operations of block1210may be performed by the timing preference module710as described with reference toFIG. 7.

At block1215, the UE115may determine a HARQ timing based at least in part on the timing advance parameter or the processing parameter, or both as described with reference toFIGS. 2-4. In certain examples, the operations of block1215may be performed by the HARQ timing module610as described with reference toFIG. 6.

At block1220, the UE115may transmit a HARQ response message based at least in part on the HARQ timing as described with reference toFIGS. 2-4. In certain examples, the operations of block1220may be performed by the HARQ response module615as described with reference toFIG. 6.

FIG. 13shows a flowchart illustrating a method1300for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. The operations of method1300may be implemented by device such as a UE115, a base station105, or their components as described with reference toFIGS. 1-9. For example, the operations of method1300may be performed by the low latency HARQ timing module510as described with reference toFIGS. 5-8. 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 the functions described below using special-purpose hardware. The method1300may also incorporate aspects of methods1000,1100, and1200ofFIGS. 10-12.

At block1305, the device may identify a timing advance parameter and a processing parameter associated with a UE as described with reference toFIGS. 2-4. In certain examples, the operations of block1305may be performed by the timing parameter module605as described with reference toFIG. 6.

At block1310, the device may identify a set of timing advance threshold values, such that a HARQ timing is determined based at least in part on the set of timing advance threshold values as described with reference toFIGS. 2-4. In certain examples, the operations of block1310may be performed by the timing parameter module605as described with reference toFIG. 6.

At block1315, the device may determine a HARQ timing based at least in part on the timing advance parameter or the processing parameter, or both as described with reference toFIGS. 2-4. In certain examples, the operations of block1315may be performed by the HARQ timing module610as described with reference toFIG. 6.

At block1320, the device may transmit a HARQ response message based at least in part on the HARQ timing as described with reference toFIGS. 2-4. In certain examples, the operations of block1320may be performed by the HARQ response module615as described with reference toFIG. 6.

FIG. 14shows a flowchart illustrating a method1400for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. The operations of method1400may be implemented by device such as a UE115, a base station105, or their components as described with reference toFIGS. 1-9. For example, the operations of method1400may be performed by the low latency HARQ timing module510as described with reference toFIGS. 5-8. 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 the functions described below using special-purpose hardware. The method1400may also incorporate aspects of methods1000,1100,1200, and1300ofFIGS. 10-13.

At block1405, the device may identify a timing advance parameter and a processing parameter associated with a UE as described with reference toFIGS. 2-4. In certain examples, the operations of block1405may be performed by the timing parameter module605as described with reference toFIG. 6.

At block1410, the device may determine a HARQ timing based at least in part on the timing advance parameter or the processing parameter, or both as described with reference toFIGS. 2-4. In certain examples, the operations of block1410may be performed by the HARQ timing module610as described with reference toFIG. 6.

At block1415, the device may transmit a HARQ response message based at least in part on the HARQ timing as described with reference toFIGS. 2-4. In certain examples, the operations of block1415may be performed by the HARQ response module615as described with reference toFIG. 6.

At block1420, the device may determine a HARQ synchronization error as described with reference toFIGS. 2-4. In certain examples, the operations of block1420may be performed by the HARQ synchronization module715as described with reference toFIG. 7.

At block1425, the device may select a default HARQ timing based at least in part on the HARQ synchronization error determination as described with reference toFIGS. 2-4. In certain examples, the operations of block1425may be performed by the HARQ timing module610as described with reference toFIG. 6.

FIG. 15shows a flowchart illustrating a method1500for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. The operations of method1500may be implemented by a base station105or its components as described with reference toFIGS. 1-9. For example, the operations of method1500may be performed by the low latency HARQ timing module510as described with reference toFIGS. 5-8. In some examples, a base station105may execute a set of codes to control the functional elements of the base station105to perform the functions described below. Additionally or alternatively, the base station105may perform aspects the functions described below using special-purpose hardware. The method1500may also incorporate aspects of methods1000,1100,1200,1300, and1400ofFIGS. 10-14.

At block1505, the base station105may receive a RACH message from a UE, such that a timing advance parameter is identified based at least in part on the RACH message as described with reference toFIGS. 2-4. In certain examples, the operations of block1505may be performed by the RACH module720as described with reference toFIG. 7.

At block1510, the base station105may identify a timing advance parameter and a processing parameter associated with a UE as described with reference toFIGS. 2-4. In certain examples, the operations of block1510may be performed by the timing parameter module605as described with reference toFIG. 6.

At block1515, the base station105may determine a HARQ timing based at least in part on the timing advance parameter or the processing parameter, or both as described with reference toFIGS. 2-4. In certain examples, the operations of block1515may be performed by the HARQ timing module610as described with reference toFIG. 6.

At block1520, the base station105may transmit signaling indicative of the HARQ timing to the UE as described with reference toFIGS. 2-4. In certain examples, the operations of block1520may be performed by the transmitter515as described with reference toFIG. 5.

At block1525, the base station105may transmit a HARQ response message based at least in part on the HARQ timing as described with reference toFIGS. 2-4. In certain examples, the operations of block1525may be performed by the HARQ response module615as described with reference toFIG. 6.

FIG. 16shows a flowchart illustrating a method1600for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. The operations of method1600may be implemented by a base station105or its components as described with reference toFIGS. 1-9. For example, the operations of method1600may be performed by the low latency HARQ timing module510as described with reference toFIGS. 5-8. In some examples, a base station105may execute a set of codes to control the functional elements of the base station105to perform the functions described below. Additionally or alternatively, the base station105may perform aspects the functions described below using special-purpose hardware. The method1600may also incorporate aspects of methods1000,1100,1200,1300,1400, and1500ofFIGS. 10-15.

At block1605, the base station105may identify a timing advance parameter and a processing parameter associated with a UE as described with reference toFIGS. 2-4. In certain examples, the operations of block1605may be performed by the timing parameter module605as described with reference toFIG. 6.

At block1610, the base station105may receive a HARQ timing preference from the UE, such that a HARQ timing is determined based at least in part on the HARQ timing preference as described with reference toFIGS. 2-4. In certain examples, the operations of block1610may be performed by the timing preference module710as described with reference toFIG. 7.

At block1615, the base station105may determine a HARQ timing based at least in part on the timing advance parameter or the processing parameter, or both as described with reference toFIGS. 2-4. In certain examples, the operations of block1615may be performed by the HARQ timing module610as described with reference toFIG. 6.

At block1620, the base station105may transmit a HARQ response message based at least in part on the HARQ timing as described with reference toFIGS. 2-4. In certain examples, the operations of block1620may be performed by the HARQ response module615as described with reference toFIG. 6.

FIG. 17shows a flowchart illustrating a method1700for low latency operation with different HARQ timing in accordance with various aspects of the present disclosure. The operations of method1700may be implemented by a base station105or its components as described with reference toFIGS. 1-9. For example, the operations of method1700may be performed by the low latency HARQ timing module510as described with reference toFIGS. 5-8. In some examples, a base station105may execute a set of codes to control the functional elements of the base station105to perform the functions described below. Additionally or alternatively, the base station105may perform aspects the functions described below using special-purpose hardware. The method1700may also incorporate aspects of methods1000,1100,1200,1300,1400,1500, and1600ofFIGS. 10-16.

At block1705, the base station105may identify a timing advance parameter and a processing parameter associated with a UE as described with reference toFIGS. 2-4. In certain examples, the operations of block1705may be performed by the timing parameter module605as described with reference toFIG. 6.

At block1710, the base station105may determine a HARQ timing based at least in part on the timing advance parameter or the processing parameter, or both as described with reference toFIGS. 2-4. In certain examples, the operations of block1710may be performed by the HARQ timing module610as described with reference toFIG. 6.

At block1715, the base station105may transmit a data packet to the UE as described with reference toFIGS. 2-4. In certain examples, the operations of block1715may be performed by the transmitter515as described with reference toFIG. 5.

At block1720, the base station105may receive an ACK or a NACK from the UE according to the HARQ timing, such that the HARQ response message is a retransmission of the data packet based at least in part on the received ACK or NACK as described with reference toFIGS. 2-4. In certain examples, the operations of block1720may be performed by the HARQ response module615as described with reference toFIG. 6.

At block1725, the base station105may transmit a HARQ response (i.e., retransmission) message based at least in part on the HARQ timing as described with reference toFIGS. 2-4. In certain examples, the operations of block1725may be performed by the HARQ response module615as described with reference toFIG. 6.

Thus, methods1000,1100,1200,1300,1400,1500,1600, and1700may provide for low latency operation with different HARQ timing. It should be noted that methods1000,1100,1200,1300,1400,1500,1600, and1700describe 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 methods1000,1100,1200,1300,1400,1500,1600, and1700may be combined.

The description herein provides examples, and is not limiting of the scope, applicability, or examples set forth in the claims. Changes may be made in the function and arrangement of elements discussed without departing from the scope of the disclosure. Various examples may omit, substitute, or add various procedures or components as appropriate. Also, features described with respect to some examples may be combined in other examples.

The downlink transmissions described herein may also be called forward link transmissions while the uplink transmissions may also be called reverse link transmissions. Each communication link described herein—including, for example, wireless communications system100and200ofFIGS. 1 and 2—may 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). 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 links described herein (e.g., communication links125ofFIG. 1) may 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 frequency division duplex (FDD) (e.g., frame structure type1) and TDD (e.g., frame structure type2).