WO2020042161A1

WO2020042161A1 - Incremental redundancy hybrid automatic repeat request transmissions for polar coded systems

Info

Publication number: WO2020042161A1
Application number: PCT/CN2018/103613
Authority: WO
Inventors: Kai Zhu; Yu Chen
Original assignee: Nokia Shanghai Bell Co., Ltd.; Nokia Solutions And Networks Oy; Nokia Technologies Oy
Priority date: 2018-08-31
Filing date: 2018-08-31
Publication date: 2020-03-05
Also published as: CN112640335B; CN112640335A

Abstract

Embodiments of the present disclosure relate to a device, method, apparatus and computer readable storage media for incremental redundancy hybrid automatic repeat request (IR-HARQ) transmissions of polar coded systems. In example embodiments, polar encoding is performed on an information bit sequence based on a reference coding rate to generate a first reference parity bit sequence. A plurality of parity bit sequences are generated for a plurality of transmissions at least in part based on the first reference parity bit sequence, where a parity bit sequence for a transmission of the plurality of transmissions is contained in a parity bit sequence for a later transmission of the plurality of transmissions. A plurality of coded bit sequences are generated for the plurality of transmissions by cascading the information bit sequence and the respective parity bit sequence.

Description

INCREMENTAL REDUNDANCY HYBRID AUTOMATIC REPEAT REQUEST TRANSMISSIONS FOR POLAR CODED SYSTEMS

FIELD

Embodiments of the present disclosure generally relate to the field of communications, and in particular, to a device, method, apparatus and computer readable storage media for incremental redundancy hybrid automatic repeat request (IR-HARQ) transmissions.

BACKGROUND

New Radio (NR) Ultra-Reliable and Low Latency Communications (URLLC) is currently under development in the 3rd Generation Partnership Project (3GPP) . NR URLLC requires higher reliability of Block Error Rate (BLER) down to 1E-6 and shorter latency in the order of 0.5 to 1 ms. Such requirements are more challenging compared with Enhanced Mobile Broadband (eMBB) . To meet these requirements, channel codes designed for eMBB need to be improved in the terms of physical layer enhancements.

Choice of coding scheme for data channel is a key aspect of URLLC. For eMBB Low Density Parity Check code (LDPC) base-graph 2 (BG2) , the error floor aronnd BLER of 1E-4～1E-5 is observed in simulations with short block sizes (for example, a typical URLLC payload size of 200, 400, 600 or 1000 bits) , under Additive White Gaussian Noise (AWGN) channel. Therefore, eMBB LDPC seems incapable of meeting the high reliability requirement imposed by URLLC. On the other hand, polar code seems a favorable candidate for URLLC data channels, since Cyclic Redundancy Check (CRC) -aided list decoding offers extraordinary error performance outperforming LDPC and many other codes.

In addition, hybrid automatic repeat request (HARQ) is a combination of forward error correction (FEC) and automatic repeat request (ARQ) . With the HARQ technology, if data transmitted by a transmitter is missing or cannot be decoded at a receiver, the transmitter can retransmit the data. Chase combining HARQ and Incremental Redundancy HARQ (IR-HARQ) are two typical HARQ technologies. Chase combining HARQ allows the initial transmitted data and retransmitted data to be combined at the receiver for joint decoding. Typically, the same set of coded bits is transmitted in each retransmission as in the original transmission.

On the contrary, IR-HARQ allows additional parity bits for later transmissions in order to provide extra redundancy incrementally during each step of retransmissions. The introduced extra redundancy enables the combined signal out of multiple Redundancy Versions (RVs) to be able to offer an increased error correction capability compared with Chase combining HARQ. Hence, for the ultra-high reliability scenario (for example, URLLC) , IR-HARQ is preferable than Chase combining HARQ. In order to be qualified for the URLLC data channel, a HARQ scheme for polar codes has been discussed. Some conventional designs of the polar IR-HARQ scheme for URLLC are typically based on non-systematic polar codes, which causing the computing complexity relatively high.

SUMMARY

In general, example embodiments of the present disclosure provide a device, method, apparatus and computer readable storage media for IR-HARQ transmissions.

In a first aspect, a device is provided at least one processor and at least one memory including computer program code. The at least one memory and the computer program code are configured to, with the at least one processor, cause the device to perform polar encoding on an information bit sequence based on a reference coding rate to generate a first reference parity bit sequence. The device is also caused to generate a plurality of parity bit sequences for a plurality of transmissions at least in part based on the first reference parity bit sequence. A parity bit sequence for a transmission of the plurality of transmissions is contained in a parity bit sequence for a later transmission of the plurality of transmissions. The device is further caused to generate a plurality of coded bit sequences for the plurality of transmissions by cascading the information bit sequence and the respective parity bit sequence.

In a second aspect, a method is provided. In the method, polar encoding is performed on an information bit sequence based on a reference coding rate to generate a first reference parity bit sequence. A plurality of parity bit sequences are generated for a plurality of transmissions at least in part based on the first reference parity bit sequence, where a parity bit sequence for a transmission of the plurality of transmissions is contained in a parity bit sequence for a later transmission of the plurality of transmissions. A plurality of coded bit sequences are generated for the plurality of transmissions by cascading the information bit sequence and the respective parity bit sequence.

In a third aspect, there is provided an apparatus comprising means for performing the method according to the second aspect.

In a fourth aspect, there is provided a computer readable storage medium that stores a computer program thereon. The computer program, when executed by a processor of a device, causes the device to perform the method according to the second aspect.

It is to be understood that the summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Some example embodiments will now be described with reference to the accompanying drawings, where:

FIG. 1 illustrates an example incremental freezing-based process in accordance with some embodiments of the present disclosure;

FIG. 2 illustrates an example environment in which embodiments of the present disclosure can be implemented;

FIG. 3 illustrates an example structure of systematic polar IR-HARQ codewords according to some embodiments of the present disclosure;

FIG. 4 illustrates an example nested structure of different redundancy versions (RVs) according to some other embodiments of the present disclosure;

FIG. 5 illustrates a flowchart of an example method in accordance with some embodiments of the present disclosure;

FIG. 6 illustrates an example process of generating the parity bit sequence for a subsequent transmission in accordance with some embodiments of the present disclosure;

FIG. 7 illustrates Eb/N0 v.s. bit error rate (BER) for the proposed systematic polar IR-HARQ scheme and the Chase combining HARQ scheme in accordance with some embodiments of the present disclosure;

FIG. 8 illustrates Eb/N0 v.s. block error rate (BLER) for the proposed systematic polar IR-HARQ scheme and the Chase combining HARQ scheme in accordance with some embodiments of the present disclosure; and

FIG. 9 illustrates a simplified block diagram of a device that is suitable for implementing embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

As used herein, the term “network device” refers to any suitable device at a network side of a communication network. The network device may include any suitable device in an access network of the communication network, for example, including a base station (BS) , a relay, an access point (AP) , a node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a NR NodeB (gNB) , a Remote Radio Module (RRU) , a radio header (RH) , a remote radio head (RRH) , a low power node such as a femto, a pico, and the like.

As used herein, the term “terminal device” refers to a device capable of, configured for, arranged for, and/or operable for communications with a network device or a further terminal device in a communication network. The communications may involve transmitting and/or receiving wireless signals using electromagnetic signals, radio waves, infrared signals, and/or other types of signals suitable for conveying information over air. In some embodiments, the terminal device may be configured to transmit and/or receive information without direct human interaction. For example, the terminal device may transmit information to the network device on predetermined schedules, when triggered by an internal or external event, or in response to requests from the network side.

Examples of the terminal device include, but are not limited to, user equipment (UE) such as smart phones, wireless-enabled tablet computers, laptop-embedded equipment (LEE) , laptop-mounted equipment (LME) , and/or wireless customer-premises equipment (CPE) . For the purpose of discussion, some embodiments will be described with reference to UEs as examples of the terminal devices, and the terms “terminal device” and “user equipment” (UE) may be used interchangeably in the context of the present disclosure.

As used herein, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable) : (i) a combination of analog and/or digital hardware circuit (s) with software/firmware and (ii) any portions of hardware processor (s) with software (including digital signal processor (s) ) , software, and memory (ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) hardware circuit (s) and or processor (s) , such as a microprocessor (s) or a portion of a microprocessor (s) , that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

As used herein, the singular forms “a” , “an” , and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term “includes” and its variants are to be read as open terms that mean “includes, but is not limited to” . The term “based on” is to be read as “based at least in part on” . The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment” . The term “another embodiment” is to be read as “at least one other embodiment” . Other definitions, explicit and implicit, may be included below.

eMBB standardized polar code schemes do not have the feature of HARQ. To be qualified for the URLLC data channel, the HARQ scheme for polar codes has been discussed. The conventional design of polar IR-HARQ solutions is typically based on non-systematic polar codes.

The typical IR-HARQ scheme for non-systematic polar codes relies on the technique termed “incremental freezing” . Owing to the IR-HARQ process, the retransmitted coded bit sequence (also referred to as the codeword sequence) , for example, RV1, RV2...RVN, are getting extended in length incrementally. Incremental freezing means that if some locations in the extended sequence are found to be more reliable, then information bits are copied to these new locations. The locations, from which the information bits are copied from, are used to transmit frozen or Parity Check (PC) bits.

An example incremental freezing-based process will be discussed below with reference to FIG. 1. As shown, during the initial transmission (M ₁ = 8) , 8 bits [u ₇u ₆u ₅u ₄u ₃u ₂u ₁u ₀] are multiplied with a generation matrix of polar codes G ₈ to derive a coded sequence [c ₇c ₆c ₅c ₄c ₃c ₂c ₁c ₀] . The locations u ₀ to u ₄ in the sequence are used for carrying information bits (represented by I) , and the locations u ₅ to u ₇ in the sequence are used for frozen bits (represented by F) .

During the first retransmission in response to the initial transmission being failed (M ₂ = 12) , 12 bits [u ₁₁u ₁₀u ₉u ₈u ₇u ₆u ₅u ₄u ₃u ₂u ₁u ₀] , including 8 bits from the previous transmission and 4 bits newly added to this retransmission, are multiplied by G ₁₂ to generate a coded sequence [c ₁₁c ₁₀c ₉c ₈c ₇c ₆c ₅c ₄c ₃c ₂c ₁c ₀] . Before this retransmission, the reliability of the new bit u8 is determined to be higher than that of u ₄. Accordingly, the information bit is copied from u ₄ to u ₈. A PC bit (represented by P) is placed in the location of u ₄. Similarly, during the second retransmission (M ₃ = 16) , 16 bits [u ₁₅u ₁₄u ₁₃u ₁₂u ₁₁u ₁₀u ₉u ₈u ₇u ₆u ₅u ₄u ₃u ₂u ₁u ₀] , including 12 bits from the previous transmission and 4 bits newly added to this retransmission, are multiplied by G ₁₆ to generate a coded sequence [c ₁₅c ₁₄c ₁₃c ₁₂c ₁₁c ₁₀c ₉c ₈c ₇c ₆c ₅c ₄c ₃c ₂c ₁c ₀] . At this time, the reliability of individual bits at the extended locations u ₁₂, u ₁₃, u ₁₄ and u ₁₅ is not found to be higher than any bits at the locations [u ₀～u ₁₁] , and therefore no bit copying occurs.

In this example, only 1 bit is copied from u ₄ to u ₈ for the purpose of illustration. However, in practice, the coded sequence may vary from a few hundred bits to thousands bits if several HARQ processes are performed before correct receiving. In this case, the amount of copying is significant. This copying introduces massive operations and requires a lot of memory addressing and accessing, and therefore may degrade the latency performance of URLLC applications which target at overall latency as low as 0.5ms.

In addition, according to channel polarization theory, the reliability corresponding to the individual bits of the coded sequence is distinct, and therefore information bits are allocated to the specific locations in the sequence having higher reliability, in the order of high to low reliability. During the preparation of the IR-HARQ codewords (or coded bits) , the reliability calculated previously may be shifted as the RV number becomes larger.

For each of different RVs, the reliability order needs to be determined for the individual bits. In the scenario with poor signal qualities due to deep fading, up to 8 retransmissions may occur in the HARQ process. This implies that massive reliability computations and comparisons are involved in order to perform the “incremental freezing” scheme as described above. Such comparison is typically performed after the rate matching, and therefore the length of the coded bit sequence may be ranging from dozens to thousands of bits. It is very difficult to employ pre-defined values to bypass online computation. Moreover, online computation using density evolution based Gaussian approximation incurs very heavy workload.

The inventor notices that the design philosophy of the conventional polar IR-HARQ schemes follows the nested structure of non-systematic polar codes. The inventor also finds that according to classic coding theory, for every non-systematic linear block code, equivalent systematic versions of the original code exist. Note that, in essence, systematic and non-systematic polar codes are equivalent, and they are just two different types of representation of the polar code. The nested structure can also be achieved in systematic polar codes, which guarantees straightforward combining and joint decoding at the receiver side.

Embodiments of the present disclosure provide a novel IR-HARQ scheme for systematic polar codes. With this scheme, a reference parity bit sequence is generated by performing polar encoding on an information bit sequence based on a reference coding rate. Using the reference parity bit sequence, a plurality of parity bit sequences are generated for a plurality of transmissions. The parity bit sequence for a transmission is contained in the parity bit sequence for a later transmission. Further, a plurality of coded bit sequences are generated for the plurality of transmissions by cascading the information bit sequence and the respective parity bit sequence.

In one aspect, the generated coded sequence has a systematic structure like many other systematic linear block codes, where the information bits and the parity bits are completely separated and transparent. Owing to the unique characteristic of the systematic polar codes, the IR-HARQ scheme becomes fairly simple with low processing latency. For example, extensive copying can be avoided to reduce the processing latency. Moreover, compared with the non-systematic polar codes, the systematic polar codes offer superior bit error performance which is crucial in high reliability applications such as URLLC.

In another aspect, the generated coded sequence has inherited the nested feature of non-systematic polar codes. That allows additional parity bits to be appended to the end of coded sequence transmitted earlier in order to form a new coded sequence for next retransmission. For example, the codewords (or coded bits) transmitted during the initial transmission (represented by RV0) is concatenated with a few extra parity bits in the tail to generate the codewords to be transmitted during the first retransmission (represented by RV1) . Similarly, the codewords for the second retransmission (represented by RV2) is generated by concatenating RV1 with further extra parity bits in the tail. The codewords for the third retransmission (represented by RV3) and the codewords for the fourth retransmission (represented by RV4) can be generated in the similar way, and so on. This nested feature guarantees the performance of the IR-HARQ polar codes outperforming that of Chase Combining polar codes, for example.

FIG. 2 shows an example environment 200 in which embodiments of the present disclosure can be implemented. The environment 200, which may be a part of a communication network, comprises a network device 210 and a terminal device 220. It is to be understood that one network device 210 and one terminal device 220 are shown in the environment 200 only for the purpose of illustration, without suggesting any limitation to the scope of the present disclosure. The environment 200 may include any suitable number of network devices and terminal devices adapted for implementing embodiments of the present disclosure.

The terminal device 220 can communicate with the network device 210 or with another terminal device (not shown) directly or via the network device 210. The communication may follow any suitable communication standards or protocols such as Universal Mobile Telecommunications System (UMTS) , long term evolution (LTE) , LTE-Advanced (LTE-A) , the fifth generation (5G) NR, Wireless Fidelity (Wi-Fi) and Worldwide Interoperability for Microwave Access (WiMAX) standards, and employs any suitable communication technologies, including, for example, Multiple-Input Multiple-Output (MIMO) , Orthogonal Frequency Division Multiplexing (OFDM) , time division multiplexing (TDM) , frequency division multiplexing (FDM) , code division multiplexing (CDM) , Bluetooth, ZigBee, and machine type communication (MTC) , enhanced mobile broadband (eMBB) , massive machine type communication (mMTC) and ultra-reliable low latency communication (URLLC) technologies.

The IR-HARQ scheme is applied to the communications in the environment 200. For example, if the initial transmission with RV0 from a transmitter is missed at a receiver due to deep fading or incorrect decoding that causes CRC check failure, RV1 containing extra redundancy, equivalently a lower-rate coded version of RV0, will be transmitted in the next available transmission time slot, for example. At the receiver, RV0 received during the initial transmission is stored in the buffer for future processing. After RV1 is received during the first retransmission, RV1 and RV0 are combined in a sequential bit-by-bit manner to obtain a relatively higher effective Signal to Noise Ratio (SNR) such that the transmitted information has better chance to be successfully recovered. If repeated failures occur during the reception of RV1 and RV2, RV3 with an even lower coding rate will be transmitted in turn. This retransmission process continues until the decoded bits are deemed correct if the CRC check is passed, or the maximum number of HARQ is reached.

According to embodiments of the present disclosure, the polar IR-HARQ codewords are systematic and nested. FIG. 3 shows an example structure 300 of systematic polar IR-HARQ codewords according to some embodiments of the present disclosure.

As shown, n coded bit sequences 305-1, 305-2 ... 305-n (collectively referred to as coded bit sequences 305) are transmitted during n transmissions. n represents a positive integer greater than 2. Each of the coded bit sequences 305 are systematic, which consists of two parts, including an information bit sequence (also known as a systematic bit sequence) 310 and the respective parity bit sequence 315-1, 315-2 ... 315-n (collectively referred to as parity bit sequences 315) . The information bit sequence 310 contains the replication of uncoded information bits. As shown, all redundancy introduced by polar encoding forms the parity bit sequences 315 utilized at the receiver to correct errors.

For the different coded bit sequences 305-1, 305-2 ... 305-n with different redundancy RV0, RV1 ... RVN (corresponding to the Nth retransmission, where N presents a positive integer greater than 1) , respectively, the redundancy portion is incrementally attached to the coded bit sequence used in previous transmission. In this nested structure, RV0 is a sub-code of RV1, RV1 is a sub-code of RV2, and so on, as shown in FIG. 4. It is to be understood that more than two transmissions are shown only for the purpose of illustration, without suggesting any limitation. In some embodiments, only the initial transmission and the first retransmission may be needed for successful decoding at the receiver.

The parity bit sequence 315 for each transmission may be determined using Equation (1) :

where u represents the information bit sequence 310 (i.e. payload) , and Kronecker n-th power

represents the polarizing matrix, A represents a set of indices to indicate the locations in a given sequence where the information bits are carried,

represents a set of indices to indicate locations of frozen bits, and G _AA indicates a sub-matrix of the polarizing matrix G with the element fromi-th row, j-th column defined by G _ij, i ∈ A, j ∈ A.

The sets A and

may be determined based on the reliability sorting using density evolution based Gaussian approximation algorithm. For example, the specific locations in a given sequence with higher reliabilities may be used to transmit the information bits, and the corresponding index numbers of the locations form the set A.

is the complementary set of A.

The inventor finds that v in Equation (1) may be an arbitrary vector. The inventor also finds that

is always a null matrix independent of the dimension of G and the choice of the set A. As a consequence, the equivalence of Equation (1) may be formulated as Equation (2) :

In Equation (2) , the dependence between u and

is eliminated, which allows the IR-HARQ design for systematic polar codes much simpler.

FIG. 5 shows a flowchart of an example method 500 in accordance with some embodiments of the present disclosure. The method 500 can be implemented by a transmitter such as a network device 210 or a terminal device 220 as shown in FIG. 2 for IR-HARQ transmissions with systematic polar codes. In the method 500, the coded bit sequence can be structured as shown in FIG. 3. For the purpose of discussion, the method 500 will be described with reference to FIG. 3.

At block 505, the polar encoding is performed on an information bit sequence based on a reference coding rate to generate a reference parity bit sequence (referred to as a first reference parity bit sequence) . In some embodiments, the reference coding rate may be a coding rate (referred to as a first coding rate) for an initial transmission of a plurality of transmissions. The first coding rate for the initial transmission may be determined in any suitable way. For example, if the transmitter has some data payloads to transmit, the transmitter may select the first coding rate R _RV0 for the initial transmission from a Modulation and Coding Scheme (MCS) table based on channel quality measurement feedback, such as a Channel Quality Indicator (CQI) or a Rank Indicator (RI) .

In some other embodiments, the transmitter may select a coding rate below a predetermined threshold as the reference coding rate. For example, the lowest coding rate to be used in the entire HARQ process may be determined as the reference coding rate.

Based on the reference coding rate, the information bit sequence may be polar-encoded using Equation (2) , for example. The set A defined in TS 38.212 may be used. Other choices of A are also possible. For example, the set A may be determined based on the reliability sorting of the individual locations of a codeword sequence having a given length. The scope of the present disclosure will not be limited in this regards. The derived parity bit sequence is considered as the first reference parity bit sequence.

At block 510, a plurality of parity bit sequences 315 are generated for a plurality of transmissions at least in part based on the first reference parity bit sequence. The parity bit sequence 315-1 for a transmission of the plurality of transmissions is contained in the parity bit sequence 315-2 or 315-n for a later transmission of the plurality of transmissions, as shown in FIG. 3.

In the embodiments where the reference coding rate is the first coding rate for the initial transmission of the plurality of transmissions, the first reference parity bit sequence may be determined as a parity bit sequence for the initial transmission. The parity bit sequences for at least one subsequent transmission of the plurality of transmissions may be determined based on the first reference parity bit sequence. An example process of determining the parity bit sequences for the subsequent transmissions will be discussed below with reference to FIG. 6.

FIG. 6 shows an example process 600 of generating the parity bit sequence 315 for a subsequent transmission in accordance with some embodiments of the present disclosure.

As shown, at block 605, a coding rate (referred to as a second coding rate) is determined for the subsequent transmission in case that the initial transmission is unsuccessful. For example, in the IR-HARQ process, the coding rate for a retransmission may be selected to be no greater than the rate of previous transmissions to reinforce the effective received SNR, that is, R _RV0 ≥ R _RV1 ≥ R _RV2 ..... ≥ R _RVN. The specific coding rate may be predefined or scheduled by the network or system.

At block 610, based on the second coding rate for the subsequent transmission, the polar encoding is performed on the information bit sequence 310 to generate a further reference parity bit sequence (referred to as a second reference parity bit sequence) . The polar encoding may also be performed using Equation (2) by using the set A as defined in TS 38.212, although other choices of A are also possible. The scope of the present disclosure will not be limited in this regards.

At block 615, a frozen bit sequence is determined based on the second reference parity bit sequence and a reference parity bit sequence (referred to as a third reference parity bit sequence) where the third reference parity bit sequence is determined for a transmission immediately prior to the current transmission. The third reference parity bit sequence may also be generated using Equation (2) . If the current transmission is the first retransmission immediately subsequent to the initial transmission, the third reference parity bit sequence is the first reference parity bit sequence generated based on the coding rate for the initial transmission.

The frozen bit sequence may be related to the information bit sequence 310 and the transmission number t (t>=1) . For the initial transmission, the transmission number t=0. In some embodiments, the frozen bit sequence f _t may be determined using Equation (3) as below:

c _RVt (as the second reference parity bit sequence) and c _RVt-1 (as the third reference parity bit sequence) may be calculated using Equation (2) with v = φ, where φ represents a zero-matrix or null matrix. c _RVt-1 is padded with zeros to enforce two operands have identical lengths. For example, the information bit sequence 310 is encoded based on the individual coding rates R _RV0 ≥ R _RV1 ≥ R _RV2 ... ≥ R _RVN by using Equation (2) with v = φ to obtain the reference parity bit sequences c _RVt (t>=1) . The encoding may be start from the highest coding rate to be used for the plurality of transmissions.

At block 620, the second reference parity bit sequence is adjusted based on the frozen bit sequence to generate a parity bit sequence 315 for the current transmission. For example, the parity bit sequence 315 for the current transmission may be computed as

equivalent to:

where

is equivalent to

with the arbitrary vector v set to be a suitable vector.

In preparing the codewords for the transmission number t (0＜=t＜=N) (or RVt) , the parity bit sequence 315 to be transmitted may be determined in the order of c _RV0, c′ _RV1, c′ _RV2, ...... c′ _RVN. As such, the parity bit sequence 315-1 generated after the polar encoding for a specific transmission is contained in the parity bit sequence 315-2 or 315-n generated for a later transmission.

In the embodiments where the reference coding rate is determined to be the lowest coding rate to be used for the entire HARQ process, the parity bit sequences 315 for all the transmissions be generated based on the first reference parity bit sequence generated using the reference coding rate. In this case, the first reference parity bit sequence may be used for the last transmission.

For example, for one of the transmissions, after a coding rate (referred to as a third coding rate) is determined, a sub-sequence of the first reference parity bit sequence may be extracted from the beginning of the first reference parity bit sequence based on the third coding rate. By utilizing such encoding rule, the resulting parity bits generated for a specific transmission are inherently contained in the parity bits to be used in a later transmission.

In this way, the longest transmitted parity sequence c _RVN may be used as a template for generating the remaining parity bit sequence c′ _RVN-1 .... c′ _RV1, c′ _RV0 to be used in the HARQ process. Thus, the encoding processes for other coding rates R _RVN-1, ... R _RV1, R _RV0 could be skipped to further reduce the processing latency.

In this case, the frozen bit sequence during the initial encoding step may be selected as the all-zero or null vector φ. The corresponding frozen bit sequence for the remaining transmission number t (0＜=t＜=N) could be obtained by

where c′ _RVt-1 is padded with zeroes to enforce two operands have identical lengths. During actual transmission, the order of the parity bits to be attached to the tail of the information bit sequence 310 may be reversed, like c′ _RV0, c′ _RV1, c′ _RV2, ...... c′ _RVN.

Still with reference to FIG. 5, at block 515, a plurality of coded bit sequences 305 are generated for the plurality of transmissions by cascading the information bit sequence 310 and the respective parity bit sequence 315. As such, each of the parity bit sequences 315 is attached to the tail of data payload (or the information bit sequence 305) such that each of the coded bit sequences 305 has the systematic structure, as shown in FIG. 3.

At the receiver, multiple RVs could be received and combined together using any suitable combining technique. The combined signal may be treated by the decoder as a conventional systematic polar code, with no need of special modification.

The systematic polar IR-HARQ scheme according to embodiments of the present disclosure offers flexible IR-HARQ support from the code domain in the sense that the generated polar parity bits are inherently and implicitly IR-HARQ-compatible. It is to be understood that the proposed systematic polar IR-HARQ scheme is not limited to any specific system architecture, and may be applicable to both Physical Uplink Shared Channel (PUSCH) in uplink (UL) and Physical Downlink Shared Channel PDSCH in downlink (DL) . Similar to conventional HARQ schemes, the proposed IR-HARQ scheme relies on an indicator to keep track of the RV number as well as a feedback channel to send Acknowledgement (ACK) /Non-acknowledgement (NACK) messages to identify the successful reception of data payload. The signalling between UE and gNB, which is known or to be developed in the future, may be applicable to the proposed IR-HARQ scheme. For example, the eMBB signalling may be reused for the proposed IR-HARQ scheme.

The proposed systematic polar IR-HARQ scheme has better performance compared with the Chase combining HARQ scheme especially in the URLLC scenario. The performances of the above two HARQ schemes are compared in the simulations where the payload is light and the coding rate is low to medium, for instance, 128 bits are transmitted at rate of 0.1～0.5. In the simulations, the receiver is battery-powered with limited processing capability, and hence the choice of list size is simplified to 1, that is, generic successive cancellation algorithm is used in decoding. The rate-matching scheme (puncturing) designed for eMBB polar codes is reused.

It is ensured that the effective coding rate is identical when comparing the performance of Chase Combining and IR HARQ schemes. Effective coding rate is defined as the ratio of a payload size and the total number of transmitted codewords before successful decoding. For example, it is assumed that for the initial transmission, a total of 256 coded bits are transmitted, half of which is information bits. Hence, the effective rate is 1/2 for the initial transmission. With the first retransmission (RV1) , it is assumed that the number of coded bits is the same (256) , the combined block (RV0+RV1) would be 256+256=512 bits. Then, the effective rate is 128/512 = 1/4 after the first retransmission. Similarly, after the second retransmission, it is 128/ (3*256) = 1/6. Note that, under such assumption, the number of transmitted codewords is exactly the same for every Chase combining RVs, whilst this number varies among the individual IR-HARQ RVs.

The rate allocation for systematic polar IR-HARQ and Chase combining HARQ performance comparison is shown in Table 1.

Table 1

RV#	IR-HARQ	Chase Combining	Effective Rate
RV0	0.5	0.5	0.5
RV0+RV1	[0.5 0.3333]	[0.4 0.4]	0.2
RV0+RV1+RV2	[0.5 0.3333 0.25]	[0.3333 0.3333 0.3333]	0.1111

Detailed simulation configuration is summarized in Table 2.

Table 2

Channel	AWGN channel
Modulation	QPSK
Rate-matching	TS38.212

Decoding algorithm	Successive cancellation
Transmitted frames	10 ⁶ frames

FIGS. 7 and 8 show Eb/N0 v.s. bit error rate (BER) and Eb/N0 v.s. block error rate (BLER) for the proposed systematic polar IR-HARQ scheme and the Chase combining HARQ scheme. In FIGS. 7 and 8, the BER and BLER performances of the proposed systematic polar IR-HARQ scheme are plotted for the initial transmission as well as the first and second retransmissions. It can be seen that the systematic polar IR-HARQ scheme performs significantly better for every (re) transmission. The achieved gain is roughly 1dB.

In some embodiments, an apparatus capable of performing the method 500 may comprise means for performing the respective steps of the method 500. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some embodiments, the apparatus capable of performing the method 500 comprises: means for performing polar encoding on an information bit sequence based on a reference coding rate to generate a first reference parity bit sequence; means for generating a plurality of parity bit sequences for a plurality of transmissions at least in part based on the first reference parity bit sequence, wherein a parity bit sequence for a transmission of the plurality of transmissions is contained in a parity bit sequence for a later transmission of the plurality of transmissions; and means for generating a plurality of coded bit sequences for the plurality of transmissions by cascading the information bit sequence and the respective parity bit sequence.

In some embodiments, the plurality of transmissions may comprise an initial transmission and at least one subsequent transmission, and the reference coding rate is a first coding rate for the initial transmission.

In some embodiments, the means for generating the plurality of parity bit sequences may comprise means for determining the first reference parity bit sequence as a parity bit sequence for the initial transmission.

In some embodiments, the means for generating the plurality of parity bit sequences may further comprise: means for determining a second coding rate for a transmission of the at least one subsequent transmission; means for performing the polar encoding on the information bit sequence based on the second coding rate to generate a second reference parity bit sequence; means for determining a frozen bit sequence based on the second reference parity bit sequence and a third reference parity bit sequence for a transmission of the plurality of transmissions immediately prior to the transmission of the at least one subsequent transmission; and means for adjusting the second reference parity bit sequence based on the frozen bit sequence to generate a parity bit sequence for the transmission of the at least one subsequent transmission.

In some embodiments, the transmission of at least one subsequent transmission may be immediately subsequent to the initial transmission. In these embodiments, the third reference parity bit sequence may be the first reference parity bit sequence.

In some embodiments, the reference coding rate may be below a predetermined threshold. For example, the lowest coding rate to be used in the entire HARQ process may be used as the reference coding rate.

In some embodiments, the means for generating the plurality of parity bit sequences may comprise: means for determining a third coding rate for a transmission of the plurality of transmissions; and means for selecting, based on the third coding rate, from the beginning of the first reference parity bit sequence, a sub-sequence of the first reference parity bit sequence as a parity bit sequence for the transmission. In this case, the first reference parity bit sequence may be used for the last transmission.

FIG. 9 is a simplified block diagram of a device 900 that is suitable for implementing embodiments of the present disclosure. The device 900 can be implemented at or at least as a part of the transmitter such as the network device 210 or the terminal device 220 as shown in FIG. 2.

As shown, the device 900 includes a processor 910, a memory 920 coupled to the processor 910, a communication module 930 coupled to the processor 910, and a communication interface (not shown) coupled to the communication module 930. The memory 920 stores at least a program 940. The communication module 930 is for bidirectional communications. The communication interface may represent any interface that is necessary for communication.

The program 940 is assumed to include program instructions that, when executed by the associated processor 910, enable the device 900 to operate in accordance with the embodiments of the present disclosure, as discussed herein with reference to FIGS. 2-8. The embodiments herein may be implemented by computer software executable by the processor 910 of the device 900, or by hardware, or by a combination of software and hardware. The processor 910 may be configured to implement various embodiments of the present disclosure.

The memory 920 may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology, such as a non-transitory computer readable storage medium, semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one memory 920 is shown in the device 900, there may be several physically distinct memory modules in the device 900. The processor 910 may be of any type suitable to the local technical network, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 900 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

All operations and features as described above with reference to FIGS. 2-8 are likewise applicable to the device 900 and have similar effects. For the purpose of simplification, the details will be omitted.

Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the method 500 and the process 600 as described above with reference to FIGS. 2-8. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

In the context of the present disclosure, the computer program codes or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable media.

The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , Digital Versatile Disc (DVD) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in languages specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Various embodiments of the techniques have been described. In addition to or as an alternative to the above, the following examples are described. The features described in any of the following examples may be utilized with any of the other examples described herein.

Claims

A device for incremental redundancy hybrid automatic repeat request, IR-HARQ, transmissions comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the device to:

perform polar encoding on an information bit sequence based on a reference coding rate to generate a first reference parity bit sequence;

generate a plurality of parity bit sequences for a plurality of transmissions at least in part based on the first reference parity bit sequence, wherein a parity bit sequence for a transmission of the plurality of transmissions is contained in a parity bit sequence for a later transmission of the plurality of transmissions; and

generate a plurality of coded bit sequences for the plurality of transmissions by cascading the information bit sequence and the respective parity bit sequence.
The device of claim 1, wherein the plurality of transmissions comprise an initial transmission and at least one subsequent transmission, and the reference coding rate is a first coding rate for the initial transmission.
The device of claim 2, wherein the device is caused to generate the plurality of parity bit sequences as follows:

determine the first reference parity bit sequence as a parity bit sequence for the initial transmission.
The device of claim 3, wherein the device is further caused to generate the plurality of parity bit sequences as follows:

determine a second coding rate for a transmission of the at least one subsequent transmission;

perform the polar encoding on the information bit sequence based on the second coding rate to generate a second reference parity bit sequence;

determine a frozen bit sequence based on the second reference parity bit sequence and a third reference parity bit sequence for a transmission of the plurality of transmissions immediately prior to the transmission of the at least one subsequent transmission; and

adjust the second reference parity bit sequence based on the frozen bit sequence to generate a parity bit sequence for the transmission of the at least one subsequent transmission.
The device of claim 4, wherein the transmission of at least one subsequent transmission is immediately subsequent to the initial transmission, and the third reference parity bit sequence is the first reference parity bit sequence.
The device of claim 1, wherein the reference coding rate is below a predetermined threshold.
The device of claim 6, wherein the device is caused to generate the plurality of parity bit sequences as follows:

determine a third coding rate for a transmission of the plurality of transmissions; and

select, based on the third coding rate, from the beginning of the first reference parity bit sequence, a sub-sequence of the first reference parity bit sequence as a parity bit sequence for the transmission.
A method of incremental redundancy hybrid automatic repeat request, IR-HARQ, transmissions, comprising:

performing polar encoding on an information bit sequence based on a reference coding rate to generate a first reference parity bit sequence;

generating a plurality of parity bit sequences for a plurality of transmissions at least in part based on the first reference parity bit sequence, wherein a parity bit sequence for a transmission of the plurality of transmissions is contained in a parity bit sequence for a later transmission of the plurality of transmissions; and

generating a plurality of coded bit sequences for the plurality of transmissions by cascading the information bit sequence and the respective parity bit sequence.
The method of claim 8, wherein the plurality of transmissions comprise an initial transmission and at least one subsequent transmission, and the reference coding rate is a first coding rate for the initial transmission.
The method of claim 9, wherein generating the plurality of parity bit sequences comprises:

determining the first reference parity bit sequence as a parity bit sequence for the initial transmission.
The method of claim 10, wherein generating the plurality of parity bit sequences further comprises:

determining a second coding rate for a transmission of the at least one subsequent transmission;

performing the polar encoding on the information bit sequence based on the second coding rate to generate a second reference parity bit sequence;

detennining a frozen bit sequence based on the second reference parity bit sequence and a third reference parity bit sequence for a transmission of the plurality of transmissions immediately prior to the transmission of the at least one subsequent transmission; and

adjusting the second reference parity bit sequence based on the frozen bit sequence to generate a parity bit sequence for the transmission of the at least one subsequent transmission.
The method of claim 11, wherein the transmission of at least one subsequent transmission is immediately subsequent to the initial transmission, and the third reference parity bit sequence is the first reference parity bit sequence.
The method of claim 8, wherein the reference coding rate is below a predetermined threshold.
The method of claim 13, wherein generating the plurality of parity bit sequences comprises:

determining a third coding rate for a transmission of the plurality of transmissions; and

selecting, based on the third coding rate, from the beginning of the first reference parity bit sequence, a sub-sequence of the first reference parity bit sequence as a parity bit sequence for the transmission.
An apparatus for incremental redundancy hybrid automatic repeat request, IR-HARQ, transmissions, comprising:

means for performing polar encoding on an information bit sequence based on a reference coding rate to generate a first reference parity bit sequence;

means for generating a plurality of parity bit sequences for a plurality of transmissions at least in part based on the first reference parity bit sequence, wherein a parity bit sequence for a transmission of the plurality of transmissions is contained in a parity bit sequence for a later transmission of the plurality of transmissions; and

means for generating a plurality of coded bit sequences for the plurality of transmissions by cascading the information bit sequence and the respective parity bit sequence.
The apparatus of claim 15, wherein the plurality of transmissions comprise an initial transmission and at least one subsequent transmission, and the reference coding rate is a first coding rate for the initial transmission.
The apparatus of claim 16, wherein the means for generating the plurality of parity bit sequences comprises:

means for determining the first reference parity bit sequence as a parity bit sequence for the initial transmission.
The apparatus of claim 17, wherein the means for generating the plurality of parity bit sequences further comprises:

means for determining a second coding rate for a transmission of the at least one subsequent transmission;

means for performing the polar encoding on the information bit sequence based on the second coding rate to generate a second reference parity bit sequence;

means for determining a frozen bit sequence based on the second reference parity bit sequence and a third reference parity bit sequence for a transmission of the plurality of transmissions immediately prior to the transmission of the at least one subsequent transmission; and

means for adjusting the second reference parity bit sequence based on the frozen bit sequence to generate a parity bit sequence for the transmission of the at least one subsequent transmission.
The apparatus of claim 18, wherein the transmission of at least one subsequent transmission is immediately subsequent to the initial transmission, and the third reference parity bit sequence is the first reference parity bit sequence.
The apparatus of claim 15, wherein the reference coding rate is below a predetermined threshold.
The apparatus of claim 20, wherein the means for generating the plurality of parity bit sequences comprises:

means for determining a third coding rate for a transmission of the plurality of transmissions; and

means for selecting, based on the third coding rate, from the beginning of the first reference parity bit sequence, a sub-sequence of the first reference parity bit sequence as a parity bit sequence for the transmission.
The apparatus of any of claims 15-21, wherein the means comprises:

at least one processor; and

at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.
A computer readable storage medium comprising program instructions stored thereon, the instructions, when executed by a processor of a device, causing the device to perform actions comprising:

performing polar encoding on an information bit sequence based on a reference coding rate to generate a first reference parity bit sequence;

generating a plurality of parity bit sequences for a plurality of transmissions at least in part based on the first reference parity bit sequence, wherein a parity bit sequence for a transmission of the plurality of transmissions is contained in a parity bit sequence for a later transmission of the plurality of transmissions; and

generating a plurality of coded bit sequences for the plurality of transmissions by cascading the information bit sequence and the respective parity bit sequence.
The computer readable storage medium of claim 23, wherein the plurality of transmissions comprise an initial transmission and at least one subsequent transmission, and the reference coding rate is a first coding rate for the initial transmission.
The computer readable storage medium of claim 24, wherein generating the plurality of parity bit sequences comprises:

determining the first reference parity bit sequence as a parity bit sequence for the initial transmission.
The computer readable storage medium of claim 25, wherein generating the plurality of parity bit sequences further comprises:

determining a second coding rate for a transmission of the at least one subsequent transmission;

performing the polar encoding on the information bit sequence based on the second coding rate to generate a second reference parity bit sequence;

determining a frozen bit sequence based on the second reference parity bit sequence and a third reference parity bit sequence for a transmission of the plurality of transmissions immediately prior to the transmission of the at least one subsequent transmission; and

adjusting the second reference parity bit sequence based on the frozen bit sequence to generate a parity bit sequence for the transmission of the at least one subsequent transmission.
The computer readable storage medium of claim 26, wherein the transmission of at least one subsequent transmission is immediately subsequent to the initial transmission, and the third reference parity bit sequence is the first reference parity bit sequence.
The computer readable storage medium of claim 23, wherein the reference coding rate is below a predetermined threshold.
The computer readable storage medium of claim 28, wherein generating the plurality of parity bit sequences comprises:

determining a third coding rate for a transmission of the plurality of transmissions; and

selecting, based on the third coding rate, from the beginning of the first reference parity bit sequence, a sub-sequence of the first reference parity bit sequence as a parity bit sequence for the transmission.