WO2021062880A1

WO2021062880A1 - Harq for long propagation delay

Info

Publication number: WO2021062880A1
Application number: PCT/CN2019/109831
Authority: WO
Inventors: Tzu-Chung Frank Hsieh; Pingping Wen
Original assignee: Nokia Shanghai Bell Co., Ltd.; Nokia Solutions And Networks Oy; Nokia Technologies Oy
Priority date: 2019-10-04
Filing date: 2019-10-04
Publication date: 2021-04-08
Also published as: CN114503642B; CN114503642A

Abstract

In accordance with some embodiments, a method comprises transmitting, by a user equipment, at least one indication of a fixed change of channel quality indicator (CQI). The method further comprises measuring, by the user equipment, at least one CQI change rate. The method further comprises transmitting, by the user equipment, at least one downlink channel gain correlation time indication. The method further comprise transmitting, by the user equipment, at least one sounding reference signal.

Description

HARQ FOR LONG PROPAGATION DELAY

BACKGROUND: Field:

Certain embodiments may relate to communication systems. For example, some embodiments may relate to random access procedures.

Description of the Related Art:

3rd Generation Partnership Project (3GPP) release (Rel) -16 includes a study item on how fifth generation (5G) new radio (NR) standards may support non-terrestrial network (NTN) deployments using satellites and high altitude platform stations (HAPS) to provide connectivity across a wide service area. In many NTN deployment scenarios, the round trip signal propagation time may be considerably longer compared to ordinary cellular networks intended for NR interfaces. As a result, these longer propagation delays may pose a challenge to hybrid automatic repeat request (HARQ) protocols in the physical layer for retransmission of erroneous packets. One objective of the study item for the physical layer of NR is to enhance HARQ for NTN operations, which continues to be studied in 3GPP RAN1 and RAN2 meetings.

SUMMARY:

In accordance with some embodiments, a method may include transmitting, by a user equipment, at least one indication of a fixed change of channel quality indicator (CQI) . The method may further include measuring, by the user equipment, at least one CQI change rate. The method may further include transmitting, by the user equipment, at least one downlink channel gain correlation time indication. The method may further include transmitting, by the user equipment, at least one sounding reference signal.

In accordance with some embodiments, an apparatus may include means for transmitting at least one indication of a fixed change of channel quality indicator (CQI) . The apparatus may further include means for measuring at least one CQI change rate. The apparatus may further include means for transmitting at least one downlink channel gain correlation time indication. The apparatus may further include means for transmitting at least one sounding reference signal.

In accordance with some embodiments, an apparatus may include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code can be configured to, with the at least one processor, cause the apparatus to at least transmit at least one indication of a fixed change of channel quality indicator (CQI) . The at least one memory and the computer program code can be further configured to, with the at least one processor, cause the apparatus to at least measure. The at least one memory and the computer program code can be further configured to, with the at least one processor, cause the apparatus to at least transmit at least one downlink channel gain correlation time indication. The at least one memory and the computer program code can be further configured to, with the at least one processor, cause the apparatus to at least transmit at least one sounding reference signal.

In accordance with some embodiments, a non-transitory computer readable medium can be encoded with instructions that may, when executed in hardware, perform a method. The method may include transmitting at least one indication of a fixed change of channel quality indicator (CQI) . The method may further include measuring at least one CQI change rate. The method may further include transmitting at least one downlink channel gain correlation time indication. The method may further include transmitting at least one sounding reference signal.

In accordance with some embodiments, a computer program product may perform a method. The method may include transmitting at least one indication of a fixed change of channel quality indicator (CQI) . The method may further include measuring at least one CQI change rate. The method may further include transmitting at least one downlink channel gain correlation time indication. The method may further include transmitting at least one sounding reference signal.

In accordance with some embodiments, an apparatus may include circuitry configured to transmit at least one indication of a fixed change of channel quality indicator (CQI) . The circuitry may further be configured to measure at least one CQI change rate. The circuitry may further be configured to transmit at least one downlink channel gain correlation time indication. The circuitry may further be configured to transmit at least one sounding reference signal.

In accordance with some embodiments, a method may include receiving, by a network entity, at slot t, at least one acknowledgement of packet reception failure after m transmissions for a HARQ process at slot t’= t –RTT. The method may further include identifying, by the network entity, at least one HARQ process transmitting within interval between slot t′and slot t′+T _C-1. The method may further include determining, by the network entity, at least one HARQ process P _i whose number of transmissions is less than or equal to m. The method may further include scheduling, by the network entity, P _i for retransmission.

In accordance with some embodiments, an apparatus may include means for receiving at slot t, at least one acknowledgement of packet reception failure after m transmissions for a HARQ process at slot t’= t –RTT. The apparatus may further include means for identifying at least one HARQ process transmitting within interval between slot t′and slot t′+T _C-1. The apparatus may further include means for determining at least one HARQ process P _i whose number of transmissions is less than or equal to m. The apparatus may further include means for scheduling P _i for retransmission.

In accordance with some embodiments, an apparatus may include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code can be configured to, with the at least one processor, cause the apparatus to at least receive, at slot t, at least one acknowledgement of packet reception failure after m transmissions for a HARQ process at slot t’= t –RTT. The at least one memory and the computer program code can be further configured to, with the at least one processor, cause the apparatus to at least identify at least one HARQ process transmitting within interval between slot t′and slot t′+T _C-1. The at least one memory and the computer program code can be further configured to, with the at least one processor, cause the apparatus to at least determine at least one HARQ process P _i whose number of transmissions is less than or equal to m. The at least one memory and the computer program code can be further configured to, with the at least one processor, cause the apparatus to at least schedule P _i for retransmission.

In accordance with some embodiments, a non-transitory computer readable medium can be encoded with instructions that may, when executed in hardware, perform a method. The method may include receiving, at slot t, at least one acknowledgement of packet reception failure after m transmissions for a HARQ process at slot t’= t –RTT. The method may further include identifying at least one HARQ process transmitting within interval between slot t′and slot t′+T _C-1. The method may further include determining at least one HARQ process P _i whose number of transmissions is less than or equal to m. The method may further include scheduling P _i for retransmission.

In accordance with some embodiments, a computer program product may perform a method. The method may include receiving, at slot t, at least one acknowledgement of packet reception failure after m transmissions for a HARQ process at slot t’= t –RTT. The method may further include identifying at least one HARQ process transmitting within interval between slot t′and slot t′+T _C-1. The method may further include determining at least one HARQ process P _i whose number of transmissions is less than or equal to m. The method may further include scheduling P _i for retransmission.

In accordance with some embodiments, an apparatus may include circuitry configured to receive at slot t, at least one acknowledgement of packet reception failure after m transmissions for a HARQ process at slot t’= t –RTT. The circuitry may further be configured to identify at least one HARQ process transmitting within interval between slot t′and slot t′+T _C-1. The circuitry may further be configured to determine at least one HARQ process P _i whose number of transmissions is less than or equal to m. The circuitry may further be configured to schedule P _i for retransmission.

In accordance with some embodiments, a method may include decoding, by a user equipment, at least one DCI of slot i. The method may further include determining, by the user equipment, whether at least one allocated ERF starts from slot i. The method may further include, upon determining that no allocated ERF starts from slot i, determining, by the user equipment, whether at least one allocated asynchronous HARQ is associated with slot i. The method may further include, upon determining that at least one allocated ERF starts from slot i, processing, by the user equipment, soft combining and decoding for N slots of the ERF. The method may further include, upon determining that at least one allocated asynchronous HARQ is associated with slot i, processing, by the user equipment, soft combining and decoding for at least one current slot. The method may further include, upon determining that no allocated asynchronous HARQ is associated with slot i; set i = i + N upon decoding N slots of ERF; or set i = i + 1 upon decoding the at least one current slot, re-decoding, by the user equipment, DCI of slot i.

In accordance with some embodiments, an apparatus may include means for decoding at least one DCI of slot i. The apparatus may further include means for determining whether at least one allocated ERF starts from slot i. The apparatus may further include means for, upon determining that no allocated ERF starts from slot i, determining whether at least one allocated asynchronous HARQ is associated with slot i. The apparatus may further include means for, upon determining that at least one allocated ERF starts from slot i, processing soft combining and decoding for N slots of the ERF. The apparatus may further include means for, upon determining that at least one allocated asynchronous HARQ is associated with slot i, processing soft combining and decoding for at least one current slot. The apparatus may further include means for, upon determining that no allocated asynchronous HARQ is associated with slot i; set i = i + N upon decoding N slots of ERF; or set i = i + 1 upon decoding the at least one current slot, re-decoding DCI of slot i.

In accordance with some embodiments, an apparatus may include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code can be configured to, with the at least one processor, cause the apparatus to at least decode at least one DCI of slot i. The at least one memory and the computer program code can be further configured to, with the at least one processor, cause the apparatus to at least determine whether at least one allocated ERF starts from slot i. The at least one memory and the computer program code can be further configured to, with the at least one processor, cause the apparatus to at least, upon determining that no allocated ERF starts from slot i, determine whether at least one allocated asynchronous HARQ is associated with slot i. The at least one memory and the computer program code can be further configured to, with the at least one processor, cause the apparatus to at least, upon determining that at least one allocated ERF starts from slot i, process soft combining and decoding for N slots of the ERF. The at least one memory and the computer program code can be further configured to, with the at least one processor, cause the apparatus to at least, upon determining that at least one allocated asynchronous HARQ is associated with slot i, process soft combining and decoding for at least one current slot. The at least one memory and the computer program code can be further configured to, with the at least one processor, cause the apparatus to at least, upon determining that no allocated asynchronous HARQ is associated with slot i; set i = i + N upon decoding N slots of ERF; or set i = i + 1 upon decoding the at least one current slot, re-decode DCI of slot i.

In accordance with some embodiments, a non-transitory computer readable medium can be encoded with instructions that may, when executed in hardware, perform a method. The method may include decoding at least one DCI of slot i. The method may further include determining whether at least one allocated ERF starts from slot i. The method may further include, upon determining that no allocated ERF starts from slot i, determining whether at least one allocated asynchronous HARQ is associated with slot i. The method may further include, upon determining that at least one allocated ERF starts from slot i, processing soft combining and decoding for N slots of the ERF. The method may further include, upon determining that at least one allocated asynchronous HARQ is associated with slot i, processing soft combining and decoding for at least one current slot. The method may further include, upon determining that no allocated asynchronous HARQ is associated with slot i; set i = i + N upon decoding N slots of ERF; or set i = i + 1 upon decoding the at least one current slot, re-decoding DCI of slot i.

In accordance with some embodiments, a computer program product may perform a method. The method may include decoding at least one DCI of slot i. The method may further include determining whether at least one allocated ERF starts from slot i. The method may further include, upon determining that no allocated ERF starts from slot i, determining whether at least one allocated asynchronous HARQ is associated with slot i. The method may further include, upon determining that at least one allocated ERF starts from slot i, processing soft combining and decoding for N slots of the ERF. The method may further include, upon determining that at least one allocated asynchronous HARQ is associated with slot i, processing soft combining and decoding for at least one current slot. The method may further include, upon determining that no allocated asynchronous HARQ is associated with slot i; set i = i + N upon decoding N slots of ERF; or set i = i + 1 upon decoding the at least one current slot, re-decoding DCI of slot i.

In accordance with some embodiments, an apparatus may include circuitry configured to decode at least one DCI of slot i. The circuitry may further be configured to determine whether at least one allocated ERF starts from slot i. The circuitry may further be configured to, upon determining that no allocated ERF starts from slot i, determine whether at least one allocated asynchronous HARQ is associated with slot i. The circuitry may further be configured to, upon determining that at least one allocated ERF starts from slot i, process soft combining and decoding for N slots of the ERF. The circuitry may further be configured to, upon determining that at least one allocated asynchronous HARQ is associated with slot i, process soft combining and decoding for at least one current slot. The circuitry may further be configured to upon determining that no allocated asynchronous HARQ is associated with slot i;set i = i + N upon decoding N slots of ERF; or set i = i + 1 upon decoding the at least one current slot, re-decode DCI of slot i.

BRIEF DESCRIPTION OF THE DRAWINGS:

For proper understanding of this disclosure, reference should be made to the accompanying drawings, wherein:

FIG. 1 illustrates a table showing round trip signal propagation delay for typical GEO and LEO satellite deployments.

FIG. 2 illustrates a chart of channel gain variation in a fast fading channel.

FIG. 3 illustrates a channel gain variation in a slow fading channel.

FIG. 4 illustrates an example of a method performed by a user equipment according to certain embodiments.

FIG. 5 (a) illustrates an example of determination of repetition factor k for early retransmission.

FIG. 5 (b) illustrates an example of an early retransmission frame.

FIG. 6 (a) illustrates an example of slots for asynchronous HARQ inserted between two early retransmission frames.

FIG. 6 (b) illustrates an example of multiple transmissions of the same packet between two early retransmission frames for determination of ERF repetition factor.

FIG. 7 illustrates an example of cross-process retransmission when a NACK bit is received.

FIG. 8 illustrates an example of a method performed by a network entity according to certain embodiments.

FIG. 9 illustrates an example of a method performed by a user equipment according to certain embodiments.

FIG. 10 illustrates an example of a system according to certain embodiments.

DETAILED DESCRIPTION:

Hybrid automatic repeat request (HARQ) is a physical layer retransmission mechanism to reliably transport encoded packets. Each HARQ process employs a stop-and-wait protocol, and receives feedback including acknowledgement (ACK) and non-acknowledgement (NACK) bits from the receiver. After an encoded packet is sent, the transmitter waits for feedback, and transmits a subsequent new packet when an ACK bit is received indicating the successfully decoding of the previously transmitted packet.

In contrast, when a NACK bit is received by the transmitter, the transmitter will send a redundant version of the encoded packet, which may be soft combined by the receiver with the coded bits previously received for the decoding of the packet. Multiple HARQ processes may be required to run in parallel so that data may be continuously transmitted by an available process while other processes are decoding packets or awaiting feedback. In a fast fading channel, HARQ is an effective technique for minimizing errors and inaccuracy of adaptive modulation and coding rate (AMC) selection.

In NTN scenarios, the long distance between a satellite and a UE near the near the Earth’s surface may result in a much longer round trip time between the transmitter sending a packet and receiving the feedback for a HARQ process. When a packet error does occur, for example, when the receiver fails to decode an encoded packet, another RTT is required in reattempting to decode the encoded packet. Furthermore, the CQI report and SRS from the UE may take longer to be received by the network entity, resulting in the AMC link adaptation being less responsive to channel condition changes and leading to a higher likelihood of packet errors occurring. As a result, data services may have a much longer latency period for NTN.

Another challenge for HARQ when applied with long RTT scenario is the need for a large number of processes to continuously transmit data. Since the RTT includes both propagation delay and data processing time, the required number of processes is RTT/transmission time interval (TTI) , wherein TTI is the interval for transmitting one packet. For example, in the example of transparent GEO shown in the table of FIG. 1, more than 540 processes are required for 1ms TTI using 15 KHz SCS OFDM waveform, which is significantly higher compared to the maximum number of 16 HARQ processes for NR. The long RTT may increase the soft buffer size requirement for the operation of HARQ.

In order to avoid excessive latencies in a link with long propagation times, the first transmission may be made more reliable to reduce the probability of HARQ retransmissions. For example, this may be accomplished by lowering target BLER in AMC, such as from 10%to 1%, and/or selecting a lower MCS. However, seeking such a high reliability in a single transmission may degrade the spectral efficiency. This problem may be further compounded when the propagation time is even longer since additional margin may need to be added in MCS selection for the inaccuracy of CQI due to feedback delay.

Another technique for reducing latency may be through the use of blind retransmission, where the transmitter always sends redundant versions of the packet before a NACK bit is received. This may be implemented by NR’s asynchronous HARQ by the network entity, with DCI carrying HARQ-related information, such as NDI, process ID, and RV. Alternatively, RRC protocol may allow slot segregation to be configured semi-statically, wherein consecutive slots may be used to transmit one transport block (TB) with different RVs. For systems involving long distance service links such as NTN, these two approaches may reduce latency, but at the expense of wasted network resources. Thus, while conventional HARQ may be spectrally efficient, there are significant drawbacks from associated large latencies.

Certain embodiments described herein may improve data service latency in a long distance communication link with more efficient utilization of resources. For example, various embodiments discussed below may reduce data service latencies, provide for the efficient use of resources during data delivery, reduce signalling overhead required for HARQ, and/or may reduce the required soft buffer size for the receiver. Certain embodiments are, therefore, directed to improvements in computer-related technology, specifically, by conserving network resources and reducing power consumption of network entities and/or user equipment located within the network.

Described herein are techniques which provide HARQ with extended propagation delays. Specifically, a signaling mechanism may be employed to determine a channel correlation time that may be used to configure HARQ transmissions of data packets, and a frame structure with a build-in early retransmission pattern may be adapted to the channel variation. This may further include low overhead HARQ signalling for multiple slots of the early retransmission frame, as well as cross-process asynchronous HARQ retransmissions which may be based on a single NACK and/or the channel correlation time. Currently in NR, UE reports its CQI measurement using a 4-bit codeword. However, the granularity of the reported CQI is insufficient to determine a correlation time T _C; thus, in the following embodiments, DL channel gain correlation time may be reported by the UE, while UL channel gain correlation time measurements may be performed by the network entity.

In order to determine if a decoding outcome among consecutive time slots is correlated, the rate of change of the channel gain may be determined. For example, when the change rate is small, as illustrated in FIG. 3, a relatively long period of time may be required for the channel to experience a fixed small variation of gain. In contrast, when the change rate is relatively large, as shown in FIG. 2, the same amount of channel variation may occur in a much shorter time span. The small amount of channel gain variation may be represented by a fixed small change of short-term (or instantaneous) CQI, denoted as ΔCQI.

FIG. 4 illustrates an example of a signalling diagram according to some embodiments. User equipment (UE) 410 may be similar to UE 1010, and network entity (NE) 420 may be similar to NE 1020, both illustrated in FIG. 10. Although only a single UE and NE are illustrated, a communications network may contain one or more of each of these entities.

In step 401, NE 420 may transmit to UE 410 at least one ΔCQI, wherein ΔCQI denotes the fixed change of short-term (or instantaneous) CQI. In various embodiments, the value of ΔCQI may be predetermined so that, within this range of channel variation, decoding outcome of packets of the same MCS (i.e., transport format) may be correlated above a predetermined threshold. As illustrated in FIG. 2, the time period for the channel to have a variation ΔCQI may have a correlation time, denoted as T _C, for packet detection to have the same outcome.

In various embodiments, when at least one connection between UE 410 and NE 420 is established, NE 420 may configure UE 410 according to at least one criteria to report at least one DL correlation time T _c, such as one or more of at least one threshold for CQI variation ΔCQI and at least one SRS configuration, such as the time-frequency allocation of SRS, for at least one UL correlation time T _c according to RRC signalling.

In step 403, UE 410 may measure at least one CQI change rate. If the correlation time corresponding to the measured at least one CQI change rate is below at least one predetermined threshold, such as one or two slots, slot aggregation or blind retransmission may be applied to reduce service latency. However, if the correlation time corresponding to the measured at least one CQI change rate is at or above at least one predetermined threshold, latency and resource efficiency may be improved from these measurements.

In step 405, UE 410 may transmit to NE 420 at least one downlink (DL) channel gain correlation time indication (T _c) , which may associated with at least one CSI/CQI measurement. In certain embodiments, the DL T _c measurement may be made on one or more of at least one SSB and at least one CSI-RS signal. In some embodiments, the at least one DL T _c may be sent back in the unit of slot time corresponding to the ΔCQI on PUCCH and/or PUSCH.

In various embodiments, correlation time T _c may change over time. For example, NE 420 may request UE 410 to report downlink T _c periodically, and/or when the difference from the previously reported value is greater than a predetermined number of slots. Additionally or alternatively, NE 420 may update UL T _c from the channel estimation of at least one uplink signal.

In step 407, UE 410 may transmit at least one SRS to NE 420 according to the configuration in step 401 as the reference signal for UL T _c measurement. In step 409, NE 420 may perform at least one uplink (UL) channel gain correlation time measurement (T _c) , which may be performed on one or more of at least one SRS and at least one other UL signal associated with UE 410.

For early retransmissions, a repetition factor k may be determined, for example, by the NE determining how many transmissions should be made for a packet. In some embodiments, this determination may be performed by scheduling consecutive slots for multiple redundant versions (RV) of the same packet, and setting repetition k, according to the HARQ feedback for these slots. For example, in the illustration of FIG. 5 (a) , the same packet may be transmitted in 4 slots with different RV and HARQ feedback consisting of two NACK bits and two ACK bits. The NE may then assume that if the packet in the current channel condition requires three transmissions to be successfully decoded, the proper repetition factor may be k = 3.

Upon determining repetition factor k, the NE may transmit at least one packet in repetition in consecutive slots before HARQ feedback is received. For example, this may be performed in an “Early Retransmission Frame” (ERF) over a period of T _c slots where channel variation is expected to be small. During an ERF frame, all slots may use fixed MCS, repetition factor k, and the same set of redundant versions. Consecutive slots may then be allocated for the transmission of the same packet allowing the NE to know if the packet has been decoded correctly after k times of transmission. Each packet may be assigned a separate HARQ process for soft combining. If a packet may be successfully decoded before the end of the consecutive k slots, the memory used by the process in the soft buffer may be flushed, thus reducing the soft buffer size requirement when the RTT is long.

As an example, the downlink ERF structure of FIG. 5 (b) illustrates six packets being transmitted with a repetition factor k=3 in six separate HARQ processes, resulting in a frame spanning a period of 3x6=18 slots. The number of HARQ processes in an ERF may be estimated from the repetition factor k so that the total number of slots is close to the measured correlation time T _c. Since the HARQ related information, such as MCS and RV, is the same, it may be signaled in the DCI of the first slot of the frame. After the DCI is decoded, the HARQ process ID and RV of each slot may follow a predictable pattern. For example, the receiver may operate the same way as in a synchronous HARQ within the frame, but HARQ-related fields in the DCI of an individual slot may no longer be needed, reducing L1 control overhead. For an ERF, the required DCI fields in the first slot may contain at least one ERF ID, a number of HARQ processes in the frame, repetition factor k, redundancy versions for k transmissions, MCS level, and/or allocated PRBs, as shown in FIG. 5 (b) . The redundant versions for different retransmissions may alternatively be pre-configured in RRC to reduce the signaling bits. The operation of UL ERF may be similar to DL, wherein DCI may indicate the structure of UL synchronous HARQ during the ERF with the same timing offset for the first slot of ERF as the rest of the UL transmission.

Following an ERF, one or more slots may be scheduled for the retransmissions of previously transmitted packet which may not have been received correctly, as illustrated in FIG. 6 (a) . For example, retransmission in these slots may be asynchronous (without a specific order of HARQ processes) using the DCI of each slot to indicate the HARQ process of the transmission. Once these asynchronous retransmissions are completed, another set of new packets may be scheduled in the next ERF. Between two ERFs, multiple transmissions of the same packet may also be inserted, as illustrated in FIG. 6 (b) , for an estimation of ERF repetition factors from the corresponding HARQ feedback.

If a NACK bit for DL transmission is received and/or an UL data packet fails to be decoded, a network entity may schedule retransmission in an asynchronous HARQ slot after an ERF, as shown in FIG. 6 (a) . Unlike conventional HARQ where packet retransmission is sent in the same process of the NACK, the network entity may determine if other processes need retransmission with its knowledge of the correlation time T _c, and proactively schedule retransmission for those processes even before their HARQ feedback has been received.

As illustrated in FIG. 7, where a NACK bit is received at slot t, acknowledging a DL packet sent at slot t’= t –RTT. Since the decoding outcome may be correlated within the time T _c, the received NACK for slot t’ may be used to infer the outcome of packets sent in the interval between slot t′and slot t′+T _C-1, as well as the processes in these slots which may need retransmission. In some embodiments, if slot t’ is the m ^th transmission of a packet, then the processes in the interval [t′, t′+T _C-1] whose number of transmissions is less or equal to m may be expected to receive a NACK; thus, retransmission for those processes may be scheduled. For example, if the 2 ^nd transmission was sent at slot t’ for which a NACK was received RTT later at slot t, then all processes between t’ and t’ + T _c –1 whose most recent transmission is either the 1 ^st or the 2 ^nd should be scheduled for retransmission. Thus, the number of transmissions of a packet may be directly compared in the retransmission decision without considering MCS since the MCS is not expected to charge much in an interval of T _c.

For UL transmissions, the network entity may schedule the asynchronous HARQ slots in a similar manner directly based on the transport block decoding failures instead of NACK feedback.

The process of scheduling retransmissions in asynchronous slots with indication of a DL NACK bit or a UL packet error is illustrated in FIG. 8. FIG. 8 illustrates an example of a method performed by a network entity, such as network entity 1020 in FIG. 10. In step 801, the NE may receive HARQ feedback for the m ^th transmission in at least one process at slot t’= t –RTT from a UE, which may be similar to UE 1010 in FIG. 10. In step 803, the NE may identify one or more processes (P ₁, P ₂, …, P _n) transmitting in the interval between slot t′and slot t′+T _C-1. In step 805, the NE may determine at least one process P _i whose number of transmissions is less than or equal to m. In step 807, the NE may schedule the process P _i for retransmission.

The UE operation of this HARQ enhancement is shown in FIG. 9. Thus, the action of the UE may be driven by DCI, which may perform soft combining and packet decoding either in synchronous mode of HARQ during an ERF or in an asynchronous mode based on per-slot HARQ information in the DCI. In any case, an ACK/NACK bit is transmitted at every decoding attempt as the conventional HARQ. The techniques described herein may be applied when the channel gain varies slowly, which may be used with NTN due to the required LOS condition and/or the use of directional antenna. The ERF with its duration and repetition factor determined by the channel condition may reduce packet delivery delay with a more efficient user of resource compared to traditional blind retransmissions. The retransmission patterns in ERF may minimize the soft buffer size requirement for the receiver. In addition to ERF, some embodiments may further ensure robustness of the link.

FIG. 9 illustrates an example of a method performed by a user equipment, such as UE 1010 in FIG. 10. In some embodiments, the NE may control at least one HARQ process configured to schedule both uplink and downlink transmissions. To reduce HARQ latency, the NE may schedule retransmissions of a packet before a HARQ feedback is received in case of DL, and/or before a scheduled packet is decoded in case of UL.

In step 901, the UE may decode at least one DCI of slot i. In step 903, the UE may determine whether at least one allocated ERF starts from slot i. In step 905, upon determining that no allocated ERF starts from slot i, the UE may determine whether at least one allocated asynchronous HARQ is associated with slot i. In step 907, upon determining that at least one allocated ERF starts from slot i, the UE may process soft combining and decoding for N slots of the ERF. In step 909, upon determining that at least one allocated asynchronous HARQ is associated with slot i, the UE may process soft combining and decoding for at least one current slot. In step 911, upon determining that no allocated asynchronous HARQ is associated with slot i; set i = i + N upon decoding N slots of ERF; or set i = i + 1 upon decoding the at least one current slot, the UE may re-decode DCI of slot i.

FIG. 10 illustrates an example of a system according to certain embodiments. In one embodiment, a system may include multiple devices, such as, for example, user equipment 1010 and/or network entity 1020.

User equipment 1010 may include one or more of a mobile device, such as a mobile phone, smart phone, personal digital assistant (PDA) , tablet, or portable media player, digital camera, pocket video camera, video game console, navigation unit, such as a global positioning system (GPS) device, desktop or laptop computer, single-location device, such as a sensor or smart meter, or any combination thereof.

Network entity 1020 may be one or more of a base station, such as a mmWave antenna, an evolved node B (eNB) or 5G or New Radio node B (gNB) , a serving gateway, a server, and/or any other access node or combination thereof. Furthermore, user equipment 1010 and/or network entity 1020 may be one or more of a citizens broadband radio service device (CBSD) .

One or more of these devices may include at least one processor, respectively indicated as 1011 and 1021.

Processors

1011 and 1021 may be embodied by any computational or data processing device, such as a central processing unit (CPU) , application specific integrated circuit (ASIC) , or comparable device. The processors may be implemented as a single controller, or a plurality of controllers or processors.

At least one memory may be provided in one or more of devices indicated at 1012 and 1022. The memory may be fixed or removable. The memory may include computer program instructions or computer code contained therein.

Memories

1012 and 1022 may independently be any suitable storage device, such as a non-transitory computer-readable medium. A hard disk drive (HDD) , random access memory (RAM) , flash memory, or other suitable memory may be used. The memories may be combined on a single integrated circuit as the processor, or may be separate from the one or more processors. Furthermore, the computer program instructions stored in the memory and which may be processed by the processors may be any suitable form of computer program code, for example, a compiled or interpreted computer program written in any suitable programming language. Memory may be removable or non-removable.

Processors

1011 and 1021 and

memories

1012 and 1022 or a subset thereof, may be configured to provide means corresponding to the various blocks of FIGS. 1-9. Although not shown, the devices may also include positioning hardware, such as GPS or micro electrical mechanical system (MEMS) hardware, which may be used to determine a location of the device. Other sensors are also permitted and may be included to determine location, elevation, orientation, and so forth, such as barometers, compasses, and the like.

As shown in FIG. 10,

transceivers

1013 and 1023 may be provided, and one or more devices may also include at least one antenna, respectively illustrated as 1014 and 1024. The device may have many antennas, such as an array of antennas configured for multiple input multiple output (MIMO) communications, or multiple antennas for multiple radio access technologies. Other configurations of these devices, for example, may be provided.

Transceivers

1013 and 1023 may be a transmitter, a receiver, or both a transmitter and a receiver, or a unit or device that may be configured both for transmission and reception.

The memory and the computer program instructions may be configured, with the processor for the particular device, to cause a hardware apparatus such as user equipment to perform any of the processes described below (see, for example, FIGS. 1-9) . Therefore, in certain embodiments, a non-transitory computer-readable medium may be encoded with computer instructions that, when executed in hardware, perform a process such as one of the processes described herein. Alternatively, certain embodiments may be performed entirely in hardware.

In certain embodiments, an apparatus may include circuitry configured to perform any of the processes or functions illustrated in FIGS. 1-9. For example, circuitry may be hardware-only circuit implementations, such as analog and/or digital circuitry. In another example, circuitry may be a combination of hardware circuits and software, such as a combination of analog and/or digital hardware circuit (s) with software or firmware, and/or any portions of hardware processor (s) with software (including digital signal processor (s) ) , software, and at least one memory that work together to cause an apparatus to perform various processes or functions. In yet another example, circuitry may be hardware circuit (s) and or processor (s) , such as a microprocessor (s) or a portion of a microprocessor (s) , that include software, such as firmware for operation. Software in circuitry may not be present when it is not needed for the operation of the hardware.

The features, structures, or characteristics of certain embodiments described throughout this specification may be combined in any suitable manner in one or more embodiments. For example, the usage of the phrases “certain embodiments, ” “some embodiments, ” “other embodiments, ” or other similar language, throughout this specification refers to the fact that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present invention. Thus, appearance of the phrases “in certain embodiments, ” “in some embodiments, ” “in other embodiments, ” or other similar language, throughout this specification does not necessarily refer to the same group of embodiments, and the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

One having ordinary skill in the art will readily understand that certain embodiments discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention. In order to determine the metes and bounds of the invention, therefore, reference should be made to the appended claims.

Partial Glossary

3GPP 3rd Generation Partnership Project

5G 5th Generation Wireless System

ACK Acknowledgement

AMC Adaptive Modulation and Coding

BLER Block Error Rate

CQI Channel Quality Indicator

CSI Channel State Information

CSI-RS Channel State Information Reference Signal

DCI Downlink Control Information

DL Downlink

eMTC Enhanced Machine Type Communications

eNB evolved Node B

ERF Early Retransmission Frame

E-UTRAN Evolved Universal Mobile Telecommunications System Terrestrial Radio Access Network

GEO Geostationary Earth Orbiting

HAPS High Altitude Platform Stations

HARQ Hybrid Automatic Repeat Request

IoT Internet of Things

gNB Next Generation Node B

LEO Low Earth Orbiting

LOS Line-of-Sight

LTE Long Term Evolution

MCS Modulation and Coding Scheme

MEO Medium Earth Orbiting

MME Mobility Management Entity

NACK Negative Acknowledgement

NAS Non-Access Stratum

NDI New Data Indicator

NE Network Entity

NLOS Non-Line-of-Sight

NR New Radio (5G)

NTN Non-Terrestrial Network

OFDM Orthogonal Frequency Division Multiplex

PRB Physical Resource Block

PDSCH Physical Downlink Data Channel

PUCCH Physical Uplink Control Channel

PUSCH Physical Uplink Shared Channel

RRC Radio Resource Control

RTT Round Trip Time

RV Redundant Version

SCS Sub-Carrier Spacing

SRS Sounding Reference Signal

SSB Synchronization Signal Block

TB Transport Block

TTI Transmission Time Interval

UL Uplink

UE User Equipment

Claims

A method, comprising:

receiving, by a user equipment, at least one indication of a fixed change of channel quality indicator (CQI) ;

measuring, by the user equipment, at least one CQI change rate;

transmitting, by the user equipment, at least one downlink channel gain correlation time indication; and

transmitting, by the user equipment, at least one sounding reference signal.
A method, comprising:

receiving, by a network entity, at slot t, at least one acknowledgement of packet reception failure after m transmissions for a HARQ process at slot t’ = t –RTT;

identifying, by the network entity, at least one HARQ process transmitting within interval between slot t′ and slot t′ + T _C - 1;

determining, by the network entity, at least one HARQ process P _i whose number of transmissions is less than or equal to m; and

scheduling, by the network entity, P _i for retransmission.
The method of claim 2, further comprising:

scheduling, by the network entity, based upon at least one received downlink channel gain correlation time indication, at least one early retransmission frame, wherein HARQ signaling is associated with a first slot downlink control information, consecutive slots are used in the same process, and a plurality of processes are associated with synchronous HARQ reception.
A method, comprising:

decoding, by a user equipment, at least one DCI of slot i;

determining, by the user equipment, whether at least one allocated ERF starts from slot i;

upon determining that no allocated ERF starts from slot i, determining, by the user equipment, whether at least one allocated asynchronous HARQ is associated with slot i;

upon determining that at least one allocated ERF starts from slot i, processing, by the user equipment, soft combining and decoding for N slots of the ERF;

upon determining that at least one allocated asynchronous HARQ is associated with slot i, processing, by the user equipment, soft combining and decoding for at least one current slot; and

upon determining that no allocated asynchronous HARQ is associated with slot i; set i = i + N upon decoding N slots of ERF; or set i = i + 1 upon decoding the at least one current slot, re-decoding, by the user equipment, DCI of slot i.
An apparatus, comprising at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to perform a process according to any of claims 1-4.
A non-transitory computer-readable medium encoding instructions that, when executed in hardware, perform a process according to any of claims 1-4.
An apparatus comprising means for performing a process according to any of claims 1-4.
An apparatus comprising circuitry configured to cause the apparatus to perform a process according to any of claims 1-4.
A computer program product encoded with instructions for performing a process according to any of claims 1-4.