Communication techniques applying low-density parity-check code base graph selection

Wireless communication methods, systems, and devices capable of utilizing base graphs for error correction techniques. A base graph can be used to derive a low-density parity-check (LDPC) code used for encoding a retransmission of an original transmission in a wireless communication system. An exemplary method generally includes selecting, based on a modulation and coding scheme (MCS) and a resource allocation (RA) for transmitting a codeword, a base graph (BG), from which to derive a low density parity check (LDPC) code for use in encoding data bits in the codeword (e.g., encoding data bits of a bitstream such that some redundant bits are included in the codeword), encoding the data bits to generate the codeword using the LDPC code derived from the selected BG, and transmitting the codeword using the MCS via resources of the RA.

TECHNICAL FIELD

Certain aspects of the technology discussed below generally relate to wireless communications and, more particularly, to methods and apparatus for determining base graphs for deriving low-density parity-check (LDPC) codes for use in encoding and decoding data in transmissions. Embodiments can aid in encoding and decoding data by way of techniques associated with appropriate base graph selection.

INTRODUCTION

Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, data, message, broadcasts, and so on. These systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, time division synchronous CDMA (TD-SCDMA) systems, frequency division multiple access (FDMA) systems, single-carrier FDMA (SC-FDMA) systems, orthogonal FDMA (OFDMA), 3rdGeneration Partnership Project (3GPP) long term evolution (LTE) systems, and LTE Advanced (LTE-A) systems.

Multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of an emerging telecommunication standard is new radio (NR), for example, 5G radio access. NR is a set of enhancements to the LTE mobile standard promulgated by 3GPP. It is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using OFDMA with a cyclic prefix (CP) on the downlink (DL) and on the uplink (UL) as well as support beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation.

Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless nodes. Each node communicates with one or more base stations (BSs) via transmissions on forward and reverse links. The forward link (or downlink) refers to a communication link from BSs to nodes, and a reverse link (or uplink) refers to a communication link from nodes to base stations. Communication links may be established via a single-input single-output, multiple-input single-output, or a MIMO system.

In some examples, a wireless multiple-access communication system may include a number of BSs, each simultaneously supporting communication for multiple communication devices, otherwise known as user equipment (UEs). In an LTE or LTE-A network, a set of one or more BSs may define an e NodeB (eNB). In other examples (e.g., in a next generation, NR, or 5G network), a wireless multiple access communication system may include a number of distributed units (DUs) (e.g., edge units (EUs), edge nodes (ENs), radio heads (RHs), smart radio heads (SRHs), transmission reception points (TRPs), etc.) in communication with a number of central units (CUs) (e.g., central nodes (CNs), access node controllers (ANCs), etc.), where a set of one or more DUs, in communication with a CU, may define an access node (e.g., a BS, a NR BS, a 5G BS, a NB, an eNB, NR NB, a 5G NB, an access point (AP)), a network node, a gNB, a TRP, etc.). A BS, AN, or DU may communicate with a UE or a set of UEs on downlink channels (e.g., for transmissions from a BS or to a UE) and uplink channels (e.g., for transmissions from a UE to a BS, AN, or DU).

Binary values (e.g., ones and zeros), are used to represent and communicate various types of information, such as video, audio, statistical information, etc. Unfortunately, during storage, transmission, and/or processing of binary data, errors may be unintentionally introduced; for example, a “1” may be changed to a “0” or vice versa.

BRIEF SUMMARY

The following summarizes some aspects of the present disclosure to provide a basic understanding of the discussed technology. This summary is not an extensive overview of all contemplated features of the disclosure and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present some concepts of one or more aspects of the disclosure in summary form as a prelude to the more detailed description that is presented later. After considering this discussion, and particularly after reading the section entitled “Detailed Description” one will understand how the features of this disclosure provide advantages that include improved communications between access points and stations in a wireless network.

Generally, in the case of data transmission, a receiver observes each received bit in the presence of noise or distortion and only an indication of the bit's value is obtained. Under these circumstances, the observed values are interpreted as a source of “soft” bits. A soft bit indicates a preferred estimate of the bit's value (e.g., a 1 or a 0) together with some indication of the reliability of that estimate. While the number of errors may be relatively low, even a small number of errors or level of distortion can result in the data being unusable or, in the case of transmission errors, may necessitate retransmission of the data. In order to provide a mechanism to check for errors and, in some cases, to correct errors, binary data can be coded to introduce carefully designed redundancy. Coding of a unit of data produces what is commonly referred to as a codeword. Because of its redundancy, a codeword will often include more bits than the input unit of data from which the codeword was produced.

Redundant bits are added by an encoder to the transmitted bitstream to create a codeword. When signals arising from transmitted codewords are received or processed, the redundant information included in the codeword as observed in the signal can be used to identify and/or correct errors in or remove distortion from the received signal to recover the original data unit. Such error checking and/or correcting can be implemented as part of a decoding process. In the absence of errors, or in the case of correctable errors or distortion, decoding can be used to recover from the source data being processed, the original data unit that was encoded. In the case of unrecoverable errors, the decoding process may produce some indication that the original data cannot be fully recovered. Such indications of decoding failure initiate retransmission of the data.

Certain aspects of the present disclosure generally relate to methods and apparatus for determining a base graph used to derive a low-density parity-check (LDPC) code used for encoding a retransmission of an original transmission.

Certain aspects of the present disclosure provide a method for wireless communications that may be performed by a base station (BS) comprising a processor in electrical communication with a memory, the processor configured to obtain data from the memory in preparation for wireless communications. The method generally includes transmitting, by a transceiver circuit using one or more antenna elements in electrical communication with the transceiver circuit, a first codeword to a user equipment (UE), the first codeword encoded using a first low-density parity-check (LDPC) code derived from a base graph (BG) selected by the processor based on a code block size (CBS) and a first code rate of the transmission, obtaining, by the transceiver circuit, an indication that the UE did not receive the first codeword, selecting, by the processor, a second code rate for a retransmission of information bits of the first codeword, wherein the selection is from a restricted set of code rates designed to ensure the UE selects a same BG to decode the retransmission, and retransmitting, by the transceiver circuit using the one or more antenna elements, the information bits in a second codeword according to the selected second code rate.

Certain aspects of the present disclosure provide a method for wireless communications that may be performed by a base station (BS) comprising a processor in electrical communication with a memory, the processor configured to obtain data from the memory in preparation for wireless communications. The method generally includes selecting, by the processor and based on a modulation and coding scheme (MCS) and a resource allocation (RA) for transmitting a codeword, a base graph (BG) stored in said memory, from which to derive a low density parity check (LDPC) code for use in encoding data bits in the codeword, encoding, by an encoder circuit, the data bits to generate the codeword using the LDPC code derived from the selected BG, and transmitting, by a transceiver circuit, the codeword using the MCS via resources of the RA using one or more antenna elements in electrical communication with the transceiver circuit.

Certain aspects of the present disclosure provide a method for wireless communications that may be performed by a user equipment (UE) comprising a processor in electrical communication with a memory, the processor configured to obtain data from the memory in preparation for wireless communications. The method generally includes receiving, by a transceiver circuit using one or more antenna elements in electrical communication with the transceiver circuit, control information indicating a modulation and coding scheme (MCS) and resource allocation (RA) for transmission of a codeword, selecting, by the processor and based on the MCS and the RA, a base graph (BG) from which to derive a low density parity check (LDPC) code for use in decoding the codeword, receiving, by the transceiver circuit using the one or more antenna elements, the codeword via resources of the RA, and decoding, by a decoder circuit, the codeword using the LDPC code derived from the selected BG.

Certain aspects of the present disclosure provide a method for wireless communications that may be performed by a base station (BS) comprising a processor in electrical communication with a memory, the processor configured to obtain data from the memory in preparation for wireless communications. The method generally includes transmitting, by a transceiver circuit using one or more antenna elements in electrical communication with the transceiver circuit, control information indicating a base graph (BG) from which to derive a low density parity check (LDPC) code used in encoding data bits of a codeword, encoding, by an encoder circuit, the data bits to generate the codeword using the LDPC code derived from the selected BG, and transmitting, by the transceiver circuit using the one or more antenna elements, the codeword.

Certain aspects of the present disclosure provide a method for wireless communications that may be performed by a user equipment (UE) comprising a processor in electrical communication with a memory, the processor configured to obtain data from the memory in preparation for wireless communications. The method generally includes receiving, by a transceiver circuit using one or more antenna elements in electrical communication with the transceiver circuit, control information indicating a base graph (BG) from which to derive a low density parity check (LDPC) code used in encoding bits of a codeword, receiving, by the transceiver circuit using the one or more antenna elements, the codeword, and decoding, by a decoder circuit, the codeword using the LDPC code derived from the selected BG.

Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes a processor configured to cause the apparatus to transmit a first codeword to a user equipment (UE), the first codeword encoded using a first low-density parity-check (LDPC) code derived from a base graph (BG) selected based on a code block size (CBS) and a first code rate of the transmission, to obtain an indication that the UE did not receive the first codeword, to select a second code rate for a retransmission of information bits of the first codeword, wherein the selection is from a restricted set of code rates designed to ensure the UE selects a same BG to decode the retransmission, and to cause the apparatus to retransmit the information bits in a second codeword according to the selected second code rate.

Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes a processor configured to select, based on a modulation and coding scheme (MCS) and a resource allocation (RA) for transmitting a codeword, a base graph (BG) from which to derive a low density parity check (LDPC) code for use in encoding data bits in the codeword to encode the data bits to generate the codeword using the LDPC code derived from the selected BG, and to cause the apparatus to transmit the codeword using the MCS and via resources of the RA, and a memory coupled with the processor.

Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes a processor configured to cause the apparatus to receive control information indicating a modulation and coding scheme (MCS) and resource allocation (RA) for transmission of a codeword, to select a base graph (BG), from which to derive a low density parity check (LDPC) code for use in decoding the codeword, based on the MCS and the RA, to cause the apparatus to receive the codeword via resources of the RA, and to decode the codeword using the LDPC code derived from the selected BG, and a memory coupled with the processor.

Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes a processor configured to cause the apparatus to transmit control information indicating a base graph (BG) from which to derive a low density parity check (LDPC) code used in encoding bits of a codeword, to encode data bits to generate the codeword using the LDPC code derived from the selected BG, and to cause the apparatus to transmit the codeword.

Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes a processor configured to cause the apparatus to receive control information indicating a base graph (BG) from which to derive a low density parity check (LDPC) code used in encoding bits of a codeword, to cause the apparatus to receive the codeword, and to decode the codeword using the LDPC code derived from the selected BG, and a memory coupled with the processor.

Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes means for transmitting a first codeword to a user equipment (UE), the first codeword encoded using a first low-density parity-check (LDPC) code derived from a base graph (BG) selected based on a code block size (CBS) and a first code rate of the transmission, means for obtaining an indication that the UE did not receive the first codeword, means for selecting a second code rate for a retransmission of information bits of the first codeword, wherein the selection is from a restricted set of code rates designed to ensure the UE selects a same BG to decode the retransmission, and means for retransmitting the information bits in a second codeword according to the selected second code rate.

Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes means for selecting, based on a modulation and coding scheme (MCS) and a resource allocation (RA) for transmitting a codeword, a base graph (BG), from which to derive a low density parity check (LDPC) code for use in encoding data bits in the codeword, means for encoding the data bits to generate the codeword using the LDPC code derived from the selected BG, and means for transmitting the codeword using the MCS via resources of the RA.

Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes means for receiving control information indicating a modulation and coding scheme (MCS) and resource allocation (RA) for transmission of a codeword, means for selecting a base graph (BG), from which to derive a low density parity check (LDPC) code for use in decoding the codeword, based on the MCS and the RA, means for receiving the codeword via resources of the RA, and means for decoding the codeword using the LDPC code derived from the selected BG.

Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes means for transmitting control information indicating a base graph (BG) from which to derive a low density parity check (LDPC) code used in encoding bits of a codeword, means for encoding data bits to generate the codeword using the LDPC code derived from the selected BG, and means for transmitting the codeword.

Certain aspects of the present disclosure provide an apparatus for wireless communications. The apparatus generally includes means for receiving control information indicating a base graph (BG) from which to derive a low density parity check (LDPC) code used in encoding bits of a codeword, means for receiving the codeword, and means for decoding the codeword using the LDPC code derived from the selected BG.

Certain aspects of the present disclosure provide a computer-readable medium for wireless communications. The computer-readable medium includes instructions that, when executed by a processing system, cause the processing system to perform operations generally including transmitting a first codeword to a user equipment (UE), the first codeword encoded using a first low-density parity-check (LDPC) code derived from a base graph (BG) selected based on a code block size (CBS) and a first code rate of the transmission, obtaining an indication that the UE did not receive the first codeword, selecting a second code rate for a retransmission of information bits of the first codeword, wherein the selection is from a restricted set of code rates designed to ensure the UE selects a same BG to decode the retransmission, and retransmitting the information bits in a second codeword according to the selected second code rate.

Certain aspects of the present disclosure provide a computer-readable medium for wireless communications. The computer-readable medium includes instructions that, when executed by a processing system, cause the processing system to perform operations generally including selecting, based on a modulation and coding scheme (MCS) and a resource allocation (RA) for transmitting a codeword, a base graph (BG) from which to derive a low density parity check (LDPC) code for use in encoding data bits in the codeword, encoding the data bits to generate the codeword using the LDPC code derived from the selected BG, and transmitting the codeword using the MCS via resources of the RA.

Certain aspects of the present disclosure provide a computer-readable medium for wireless communications. The computer-readable medium includes instructions that, when executed by a processing system, cause the processing system to perform operations generally including receiving control information indicating a modulation and coding scheme (MCS) and resource allocation (RA) for transmission of a codeword, selecting, based on the MCS and the RA, a base graph (BG), from which to derive a low density parity check (LDPC) code for use in decoding the codeword, receiving the codeword via resources of the RA, and decoding the codeword using the LDPC code derived from the selected BG.

Certain aspects of the present disclosure provide a computer-readable medium for wireless communications. The computer-readable medium includes instructions that, when executed by a processing system, cause the processing system to perform operations generally including transmitting control information indicating a base graph (BG) from which to derive a low density parity check (LDPC) code used in encoding bits of a codeword, encoding data bits to generate the codeword using the LDPC code derived from the selected BG, and transmitting the codeword.

Certain aspects of the present disclosure provide a computer-readable medium for wireless communications. The computer-readable medium includes instructions that, when executed by a processing system, cause the processing system to perform operations generally including receiving control information indicating a base graph (BG) from which to derive a low density parity check (LDPC) code used in encoding bits of a codeword, receiving the codeword, and decoding the codeword using the LDPC code derived from the selected BG.

Other aspects, features, and embodiments of the present disclosure will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary aspects of the present disclosure in conjunction with the accompanying figures. While features of the present disclosure may be discussed relative to certain aspects and figures below, all aspects of the present disclosure can include one or more of the advantageous features discussed herein. In other words, while one or more aspects may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various aspects of the disclosure discussed herein. In similar fashion, while exemplary aspects may be discussed below as device, system, or method embodiments such exemplary embodiments can be implemented in various devices, systems, and methods.

DETAILED DESCRIPTION

Aspects of the present disclosure provide apparatuses, methods, processing systems, hardware components, and computer program products for determining a base graph (BG) that can be used for deriving a low-density parity-check (LDPC) code. An LPDC code can be used for encoding (and/or decoding) a codeword transmitted in a retransmission of data in a new radio (NR) access technology (e.g., 5G radio access) wireless communications system.

The term ‘New Radio’ (abbreviated NR) refers generally to a new type of communication network and related components for implementing 5G networks and beyond. NR may refer to radios configured to operate according to a new air interface or fixed transport layer. NR may include support for enhanced mobile broadband (eMBB) service targeting wide bandwidth (e.g., 80 MHz and wider) communications, millimeter wave (mmW) service targeting high carrier frequency (e.g., 27 GHz and higher) communications, massive machine type communications (mMTC) service targeting non-backward compatible machine type communications (MTC) techniques, and/or mission critical (MiCr) service targeting ultra-reliable low-latency communications (URLLC). These services may include latency and reliability requirements for a variety of uses, timing requirements, and other design considerations. NR may use low-density parity-check (LDPC) coding and/or polar codes.

NR standardization has introduced two low-density parity-check (LDPC) base graphs (BG1, BG2) from which an LDPC code may be derived for encoding data (see, e.g., TS 38.212, v 15.1.1, secs. 6.2.2 and 7.2.2). On each slot transmission, one of the base graphs is selected for usage, i.e., for deriving an LDPC code used to encode the transmission. The base graph (e.g., BG1 or BG2) used for encoding is implicitly indicated by code block size and code rate of the transmission.

It is therefore desirable to develop techniques for a UE to determine the BG used in a transmission. It is also desirable to develop techniques for a UE to determine the BG used in a retransmission in situations in which the UE misses (e.g., fails to properly decode, fails to receive) the control information for the original data transmission or the original data transmission.

According to aspects of the present disclosure, a BS transmits a choice of modulation and coding scheme (MCS) and a resource allocation (RA) in downlink control information (DCI). The DCI can correspond to a data transmission (e.g., a codeword) that the BS is transmitting or will transmit. A UE receives the DCI and, if the DCI is intended for the UE, then the UE can determine a transport block size (TBS) for the data transmission based on the MCS and RA and according to a network specification. Upon determination of the TBS, the UE can determine the LDPC BG the BS used to encode a data transmission based on values of the code block size and code rate implied by the TBS and the RA.

If the UE does not successfully receive the data transmission, then the BS may retransmit the data in a retransmission. For retransmissions, regardless of any new MCS and RA chosen for the retransmission, it is desirable for the BS to encode the data using the same BG as used for the original data transmission and for the UE to select the BG used in the original data transmission for decoding the retransmissions. Using the same BG for encoding and decoding the retransmissions may ensure proper hybrid automatic retransmission request (HARQ) combining (e.g., of the retransmission(s) and the original transmission) and LDPC decoding of the combination of the original data transmission and any retransmissions.

For clarity, while aspects may be described herein using terminology commonly associated with 3G and/or 4G or LTE wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems, such as 5G and later, including NR or 5G/NR technologies.

An Example Wireless Communication System

FIG. 1illustrates an example communications network100in which aspects of the present disclosure may be performed. Wireless communications network100may be a new radio (NR) or 5G network. Wireless communications network100may include a transmitting device such as a user equipment (UE)120or a base station (BS)110. Transmitting devices can communicate with one or more other devices and utilize techniques discussed herein to communicate efficiently and in a variety of manners as envisioned to be brought about by 5G communications technology.

Innovations discussed in this disclosure can be implemented for transmissions and receptions. In one example, a transmitting device may perform encoding according to aspects described herein using lifted LDPC codes that may be compactly described (e.g., determined/generated/stored). In another example, a receiving device (e.g., a UE120or a BS110) can perform corresponding decoding operations. In some aspects, a transmitting device can select at least one lifting size value for generating a group of lifted LDPC codes comprising copies of a base LDPC code defined by a base matrix having a first number of base variable nodes and a second number of base check nodes. The lifting size value is selected from a range of values. The transmitting device can generate a base matrix based on a lifting value of a set of lifting values associated with the selected lifting size value and generate a matrix for a different lifting size value in the group based on the base matrix.

As illustrated inFIG. 1, wireless communications network100may include a number of BSs110and other network entities. A BS may be a station that communicates with UEs. Each BS110may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to a coverage area of a Node B and/or a Node B subsystem serving this coverage area, depending on the context in which the term is used. In NR systems, the term “cell” and gNB, Node B, 5G NB, AP, NR BS, NR BS, TRP, etc., may be interchangeable. In some examples, a cell may not necessarily be stationary. And the geographic area of the cell may move according to the location of a mobile BS. In some examples, the BSs may be interconnected to one another and/or to one or more other BSs or network nodes (not shown) in wireless communications network100through various types of backhaul interfaces such as a direct physical connection, a virtual network, or the like using any suitable transport network.

A BS may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscription. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscription. A femto cell may cover a relatively small geographic area (e.g., a home) and may allow restricted access by UEs having association with the femto cell (e.g., UEs in a Closed Subscriber Group (CSG), UEs for users in the home, etc.). A BS for a macro cell may be referred to as a macro BS. A BS for a pico cell may be referred to as a pico BS. A BS for a femto cell may be referred to as a femto BS or a home BS. In the example shown inFIG. 1, BS110a, BS110b, and BS110cmay be macro BSs for the macro cell102a, macro cell102b, and macro cell102c, respectively. BS110xmay be a pico BS for pico cell102x. BS110yand BS110zmay be femto BS for the femto cell102yand femto cell102z, respectively. A BS may support one or multiple (e.g., three) cells.

Wireless communications network100may also include relay stations. A relay station is a station that receives a transmission of data and/or other information from an upstream station (e.g., a BS110or a UE120). A relay station can send a transmission of the data and/or other information to a downstream station (e.g., a UE120or a BS110). A relay station may also be a UE that relays transmissions for other UEs. In the example shown inFIG. 1, relay station110rmay communicate with BS110aand UE120rin order to facilitate communication between BS110aand UE120r. A relay station may also be referred to as a relay, a relay eNB, etc.

Wireless communications network100may be a heterogeneous network that includes BSs of different types, for example, macro BS, pico BS, femto BS, relays, etc. These different types of BSs may have different transmit power levels, different coverage areas, and different impact on interference in the wireless communications network100. For example, a macro BS may have a high transmit power level (e.g., 20 Watts) whereas pico BS, femto BS, and relays may have a lower transmit power level (e.g., 1 Watt).

Network controller130may couple to a set of BSs and provide coordination and control for these BSs. Network controller130may communicate with BSs110via a backhaul. BSs110may also communicate with one another, e.g., directly or indirectly via wireless or wireline backhaul.

Certain wireless networks (e.g., LTE) utilize orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, etc. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, the spacing of the subcarriers may be 15 kHz and the minimum resource allocation (called a “resource block” (RB)) may be 12 subcarriers (i.e., 180 kHz). Consequently, the nominal Fast Fourier Transform (FFT) size may be equal to 128, 256, 512, 1024 or 2048 for system bandwidth of 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, or 20 MHz, respectively. The system bandwidth may also be partitioned into subbands. For example, a subband may cover 1.08 MHz (i.e., 6 RBs), and there may be 1, 2, 4, 8 or 16 subbands for system bandwidth of 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, or 20 MHz, respectively.

NR may utilize OFDM with a CP on uplink and downlink and include support for half-duplex operation using TDD. A single component carrier bandwidth of 100 MHz may be supported. NR RBs may span 12 subcarriers with a subcarrier bandwidth of 75 kHz over a 0.1 ms duration. Each radio frame may consist of 2 half frames, each half frame consisting of 5 subframes, with a length of 10 ms. Consequently, each subframe may have a length of 1 ms. Each subframe may indicate a link direction (i.e., downlink or uplink) for data transmission and the link direction for each subframe may be dynamically switched. Each subframe may include DL/UL data as well as DL/UL control data. UL and DL subframes for NR may be as described in more detail below with respect toFIGS. 6 and 7. Beamforming may be supported and beam direction may be dynamically configured. MIMO transmissions with precoding may also be supported. MIMO configurations in the DL may support up to 8 transmit antennas with multi-layer DL transmissions up to 8 streams and up to 2 streams per UE. Multi-layer transmissions with up to 2 streams per UE may be supported. Aggregation of multiple cells may be supported with up to 8 serving cells. Alternatively, NR may support a different air interface, other than an OFDM-based.

In some examples, access to the air interface may be scheduled. For example, a scheduling entity (e.g., a BS110or UE120) allocates resources for communication among some or all devices and equipment within its service area or cell. Within the present disclosure, as discussed further below, the scheduling entity may be responsible for scheduling, assigning, reconfiguring, and releasing resources for one or more subordinate entities. That is, for scheduled communication, subordinate entities utilize resources allocated by the scheduling entity. BSs are not the only entities that may function as a scheduling entity. That is, in some examples, a UE may function as a scheduling entity, scheduling resources for one or more subordinate entities (e.g., one or more other UEs). In this example, the UE is functioning as a scheduling entity, and other UEs utilize resources scheduled by the UE for wireless communication. A UE may function as a scheduling entity in a peer-to-peer (P2P) network, and/or in a mesh network. In a mesh network example, UEs may optionally communicate directly with one another in addition to communicating with the scheduling entity.

The NR radio access network (RAN) may include one or more central units (CUs) and distributed units (DUs). A NR BS (e.g., a gNB, a 5G NB, a NB, a 5G NB, a transmission reception point (TRP), an AP) may correspond to one or multiple cells. NR cells can be configured as access cells (ACells) or data only cells (DCells). DCells may be cells used for carrier aggregation or dual connectivity, but not used for initial access, cell selection/reselection, or handover.

FIG. 2illustrates an example logical architecture of a distributed RAN200. In some aspects, the RAN200may be implemented in wireless communications system100illustrated inFIG. 1. 5G access node (AN)206may include access node controller (ANC)202. The ANC202may be a CU of distributed RAN200. A backhaul interface to next generation core network (NG-CN)204may terminate at ANC202. A backhaul interface to neighboring next generation access nodes (NG-ANs) may terminate at ANC202. ANC202may include one or more TRPs208.

TRPs208comprise DUs. TRPs208may be connected to one ANC (ANC202) or more than one ANC (not illustrated). For example, for RAN sharing, radio as a service (RaaS), and service specific AND deployments, the TRP may be connected to more than one ANC202. A TRP208may include one or more antenna ports. TRPs208may be configured to individually (e.g., dynamic selection) or jointly (e.g., joint transmission) serve traffic to a UE (e.g., a UE120).

Example logical architecture of the distributed RAN200may be used to illustrate fronthaul definition. The logical architecture may support fronthauling solutions across different deployment types. For example, the logical architecture may be based on transmit network capabilities (e.g., bandwidth, latency, and/or jitter). The logical architecture may share features and/or components with LTE. NG-AN210may support dual connectivity with NR. NG-AN210may share a common fronthaul for LTE and NR. The logical architecture may enable cooperation between and among TRPs208. For example, cooperation may be pre-configured within a TRP208and/or across TRPs208via ANC202. There may be no inter-TRP interface.

The logical architecture for distributed RAN200may include a dynamic configuration of split logical functions. As will be described in more detail with reference toFIG. 5, the Radio Resource Control (RRC) layer, Packet Data Convergence Protocol (PDCP) layer, Radio Link Control (RLC) layer, Medium Access Control (MAC) layer, and a Physical (PHY) layers may be placed at the DU (e.g., a TRP208) or the CU (e.g., ANC202).

FIG. 3illustrates an example physical architecture of a distributed RAN300, according to aspects of the present disclosure. As shown inFIG. 3, distributed RAN300includes centralized core network unit (C-CU)302, centralized RAN unit (C-RU)304, and DU306.

C-CU302may host core network functions. C-CU302may be centrally deployed. C-CU302functionality may be offloaded (e.g., to advanced wireless services (AWS)), in an effort to handle peak capacity. C-RU304may host one or more ANC functions. Optionally, C-RU304may host core network functions locally. C-RU304may have a distributed deployment. C-RU304may be located near an edge the network. DU306may host one or more TRPs (edge node (EN), an edge unit (EU), a radio head (RH), a smart radio head (SRH), or the like). DU306may be located at edges of the network with radio frequency (RF) functionality.

FIG. 4illustrates example components of the BS110and the UE120illustrated inFIG. 1. These components can be used to implement aspects of the present disclosure for high performance, flexible, and compact LDPC coding. One or more of the components of BS110and UE120illustrated inFIG. 4may be used to practice aspects of the present disclosure. For example, antenna(s)452a-454r, Demodulator(s)/Modulator(s)454a-454r, TX MIMO processor466, Receive Processor458, Transmit Processor464, and/or Controller/Processor480of UE120and/or antenna(s)434a-434t, Demodulator(s)/Modulator(s)432a-434t, TX MIMO Processors430, Transmit Processor420, Receive Processor438, and/or Controller/Processor440of BS110may be used to perform the operations1300-1700described herein and illustrated with reference toFIGS. 13-17, respectively.

For a restricted association scenario, BS110may be macro BS110cinFIG. 1, and UE120may be UE120y. BS110may also be a BS of some other type. BS110may be equipped with antennas434athrough434tand UE120may be equipped with antennas452athrough452r.

At BS110, transmit processor420may receive data from data source412and control information from controller/processor440. The control information may be for the Physical Broadcast Channel (PBCH), Physical Control Format Indicator Channel (PCFICH), Physical Hybrid ARQ Indicator Channel (PHICH), Physical Downlink Control Channel (PDCCH), or other control channel or signal. The data may be for the Physical Downlink Shared Channel (PDSCH), or other data channel or signal.

Transmit processor420may process (e.g., encode and symbol map) data and control information to obtain data symbols and control symbols, respectively. For example, transmit processor420may encode the information bits using LPDC code designs discussed in greater detail below. Transmit processor420may also generate reference symbols, for example, for the primary synchronization signal (PSS), secondary synchronization signal (SSS), and cell-specific reference signal (CRS). Transmit (TX) multiple-input multiple-output (MIMO) processor430may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs)432athrough432t. Each modulator432may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator432may further process (e.g., convert to analog, amplify, filter, and upconvert) an output sample stream to obtain a downlink signal. Downlink signals from modulators432athrough432tmay be transmitted via antennas434athrough434t, respectively.

At UE120, antennas452athrough452rmay receive downlink signals from BS110and may provide received signals to the demodulators (DEMODs)454athrough454r, respectively. Each demodulator454may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator454may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. MIMO detector456may obtain received symbols from one or more demodulators454athrough454r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. Receive processor458may process (e.g., demodulate, deinterleave, and decode) detected symbols, provide decoded data for UE120to a data sink460, and provide decoded control information to controller/processor480.

On the uplink, at UE120, transmit processor464may receive and process data (e.g., for the Physical Uplink Shared Channel (PUSCH) or other data channel or signal) from data source462and control information (e.g., for the Physical Uplink Control Channel (PUCCH) or other control channel or signal) from controller/processor480. Transmit processor464may also generate reference symbols for a reference signal. The symbols from transmit processor464may be precoded by TX MIMO processor466if applicable, further processed by demodulators454athrough454r(e.g., for SC-FDM, etc.), and transmitted to BS110. At BS110, the uplink signals from the UE120may be received by antennas434, processed by modulators432, detected by MIMO detector436if applicable, and further processed by receive processor438to obtain decoded data and control information sent by UE120. Receive processor438may provide the decoded data to data sink439and the decoded control information to controller/processor440.

The UE120can include additional components and features working in tandem with the controller/processor440. Memory442may store data and program codes for BS110and memory482may store data and program codes for UE120. Scheduler444may schedule UEs for data transmission on the downlink and/or uplink.

FIG. 5illustrates a diagram500showing examples for implementing a communications protocol stack per aspects of the present disclosure. The illustrated communications protocol stacks may be implemented by devices operating in a in a 5G system (e.g., a system that supports uplink-based mobility). Diagram500illustrates a communications protocol stack including RRC layer510, PDCP layer515, RLC layer520, MAC layer525, and PHY layer530. In an example, the layers of a protocol stack may be implemented as separate modules of software, portions of a processor or ASIC, portions of non-collocated devices connected by a communications link, or various combinations thereof. Collocated and non-collocated implementations may be used, for example, in a protocol stack for a network access device (e.g., ANs, CUs, and/or DUs) or a UE.

A first option505-ashows a split implementation of a protocol stack, in which implementation of the protocol stack is split between a centralized network access device (e.g., ANC202) and distributed network access device (e.g., DU208). In the first option505-a, RRC layer510and PDCP layer515may be implemented by the CU, and RLC layer520, MAC layer525, and PHY layer530may be implemented by the DU. In various examples, the CU and the DU may be collocated or non-collocated. The first option505-amay be useful in a macro cell, micro cell, or pico cell deployment.

A second option505-bshows a unified implementation of a protocol stack, in which the protocol stack is implemented in a single network access device (e.g., access node (AN), NR BS, a NR NBa network node (NN), TRP, gNB, etc.). In the second option, RRC layer510, PDCP layer515, RLC layer520, MAC layer525, and PHY layer530may each be implemented by the AN. The second option505-bmay be useful in a femto cell deployment.

Regardless of whether a network access device implements part or all of a protocol stack, a UE may implement the entire protocol stack505-c(e.g., RRC layer510, PDCP layer515, RLC layer520, MAC layer525, and PHY layer530).

FIG. 6is a diagram showing an example of a DL-centric subframe600. The DL-centric subframe600may include control portion602. Control portion602may exist in the initial or beginning portion of DL-centric subframe600. Control portion602may include various scheduling information and/or control information corresponding to various portions of DL-centric subframe600. In some configurations, control portion602may be a physical DL control channel (PDCCH), as shown inFIG. 6. DL-centric subframe600may also include DL data portion604. DL data portion604may be referred to as the payload of DL-centric subframe600. DL data portion604may include the communication resources utilized to communicate DL data from the scheduling entity (e.g., UE or BS) to the subordinate entity (e.g., UE). In some configurations, DL data portion604may be a physical DL shared channel (PDSCH).

DL-centric subframe600may also include common UL portion606. Common UL portion606may be referred to as an UL burst, a common UL burst, and/or various other suitable terms. Common UL portion606may include feedback information corresponding to various other portions of DL-centric subframe600. For example, common UL portion606may include feedback information corresponding to control portion602. Non-limiting examples of feedback information may include an acknowledgment (ACK) signal, a negative acknowledgment (NACK) signal, a HARQ indicator, and/or various other suitable types of information. Common UL portion606may additionally or alternatively include information, such as information pertaining to random access channel (RACH) procedures, scheduling requests (SRs), and various other suitable types of information. As illustrated inFIG. 6, the end of DL data portion604may be separated in time from the beginning of common UL portion606. This time separation may be referred to as a gap, a guard period, a guard interval, and/or various other suitable terms. This separation provides time for the switchover from DL communication (e.g., reception operation by the subordinate entity (e.g., UE)) to UL communication (e.g., transmission by the subordinate entity (e.g., UE)). The foregoing is merely one example of a DL-centric subframe and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

FIG. 7is a diagram showing an example of an UL-centric subframe700. UL-centric subframe700may include control portion702. Control portion702may exist in the initial or beginning portion of UL-centric subframe700. Control portion702inFIG. 7may be similar to control portion602described above with reference toFIG. 6. UL-centric subframe700may also include UL data portion704. UL data portion704may be referred to as the payload of UL-centric subframe700. UL data portion704may refer to the communication resources utilized to communicate UL data from the subordinate entity (e.g., UE) to the scheduling entity (e.g., UE or BS). In some configurations, control portion702may be a PDCCH.

As illustrated inFIG. 7, the end of control portion702may be separated in time from the beginning of UL data portion704. This time separation may be referred to as a gap, guard period, guard interval, and/or various other suitable terms. This separation provides time for the switchover from DL communication (e.g., reception operation by the scheduling entity) to UL communication (e.g., transmission by the scheduling entity). UL-centric subframe700may also include common UL portion706. Common UL portion706inFIG. 7may be similar to the common UL portion606described above with reference toFIG. 6. Common UL portion706may additionally or alternatively include information pertaining to channel quality indicator (CQI), sounding reference signals (SRSs), and various other suitable types of information. The foregoing is merely one example of an UL-centric subframe and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

Many communications systems use error-correcting codes. Error correcting codes generally compensate for the intrinsic unreliability of information transfer (e.g., over the air medium) in these systems by introducing redundancy into the data stream. Low-density parity-check (LDPC) codes are one type of error correcting codes which use an iterative coding system. Gallager codes are an example of “regular” LDPC codes. Regular LDPC codes are linear block codes in which most of the elements of its parity check matrix H are ‘0’.

LDPC codes can be represented by bipartite graphs (often referred to as “Tanner graphs”). In a bipartite graph, a set of variable nodes corresponds to bits of a codeword (e.g., information bits or systematic bits), and a set of check nodes correspond to a set of parity-check constraints that define the code. Edges in the graph connect variable nodes to check nodes. Thus, the nodes of the graph are separated into two distinctive sets and with edges connecting nodes of two different types, variable and check.

Graphs as used in LDPC coding may be characterized in a variety of manners. A lifted code is created by copying a bipartite base graph (G) (or a protograph), a number of times, Z. The number of times is referred to herein as the lifting, lifting size, or lifting size value. A variable node and a check node are considered “neighbors” if they are connected by an “edge” (i.e., the line connecting the variable node and the check node) in the graph. In addition, for each edge (e) of the bipartite base graph (G), a permutation (generally an integer value associated with the edge permutation that is represented by k and referred to as the lifting value) is applied to the Z copies of edge (e) to interconnect the Z copies of G. A bit sequence having a one-to-one association with the variable node sequence is a valid codeword if and only if, for each check node, the bits associated with all neighboring variable nodes sum to 0 modulo 2 (i.e., they include an even number of 1's). The resulting LDPC code may be quasi-cyclic (QC) if the permutations (liftings values) used are cyclic.

FIGS. 8-8Ashow graphical and matrix representations, respectively, of an example LDPC code, in accordance with certain aspects of the present disclosure. For example,FIG. 8shows a bipartite graph800representing an example LDPC code. Bipartite graph800includes a set of five variable nodes810(represented by circles) connected to four check nodes820(represented by squares). Edges in bipartite graph800connect variable nodes810to check nodes820(the edges are represented by the lines connecting variable nodes810to check nodes820). Bipartite graph800consists of |V|=5 variable nodes and |C|=4 check nodes, connected by |E|=12 edges.

Bipartite graph800may be represented by a simplified adjacency matrix, which may also be known as a parity check matrix (PCM).FIG. 8Ashows a matrix representation800A of bipartite graph800. Matrix representation800A includes a PCM H and a codeword vector x, where x1-x5represent bits of the codeword x. H is used for determining whether a received signal was normally decoded. H has C rows corresponding to j check nodes and V columns corresponding to i variable nodes (i.e., a demodulated symbol), where the rows represent the equations and the columns represents the bits of the codeword. InFIG. 8A, matrix H has four rows and five columns corresponding to four check nodes and five variable nodes, respectively. If a j-th check node is connected to an i-th variable node by an edge (i.e., the two nodes are neighbors), then there is a 1 in the i-th column and in the j-th row of the parity check matrix H. That is, the intersection of an i-th row and a j-th column contains a “1” where an edge joins the corresponding vertices and a “0” where there is no edge. The codeword vector x represents a valid codeword if and only if Hx=0, for example, if for each constraint node, the bits neighboring the constraint, via their association with variable nodes, sum to 0 modulo 2 (i.e., they comprise an even number of 1's). Thus, if the codeword is received correctly, then Hx=0 (mod 2). When the product of a coded received signal and the PCM H becomes ‘0’, this signifies that no error has occurred.

The number of demodulated symbols or variable nodes is the LDPC code length. The number of non-zero elements in a row (column) is defined as the row (column) weight d(c)d(v). The degree of a node refers to the number of edges connected to that node. For example, as shown inFIG. 8, the variable node801has three degrees of connectivity, with edges connected to check nodes811,812, and813. Variable node802has three degrees of connectivity, with edges connected to check nodes811,813, and814. Variable node803has two degrees of connectivity, with edges connected to check nodes811and814. Variable node804has two degrees of connectivity, with edges connected to check nodes812and814. And variable node805has two degrees of connectivity, with edges connected to check nodes812and813. This feature is illustrated in the matrix H shown inFIG. 8Awhere the number of edges incident to a variable node810is equal to the number of l's in the corresponding column and is called the variable node degree d(v). Similarly, the number of edges connected with a check node820is equal to the number of ones in a corresponding row and is called the check node degree d(c). For example, as shown inFIG. 8A, the first column in the matrix H corresponds to the variable node801and the corresponding entries in the column (1, 1, 1, 0) indicates the edge connections to the check nodes811,812, and813, while the 0 indicates that there is not an edge to check node814. The entries in the second, third, fourth, and fourth columns of H represent the edge connections of the variable nodes802,803,804, and805, respectively, to the check nodes.

A regular graph or a regular code is one for which all variable nodes have the same degree and all constraint nodes have the same degree. On the other hand, an irregular code has constraint nodes and/or variable nodes of differing degrees. For example, some variable nodes may be of degree 4, others of degree 3, and still others of degree 2.

“Lifting” enables LDPC codes to be implemented using parallel encoding and/or decoding implementations while also reducing the complexity typically associated with large LDPC codes. Lifting helps enable efficient parallelization of LDPC decoders while still having a relatively compact description. More specifically, lifting is a technique for generating a relatively large LDPC code from multiple copies of a smaller base code. For example, a lifted LDPC code may be generated by producing Z parallel copies of the base graph (e.g., protograph) and then interconnecting the parallel copies through permutations of edge bundles of each copy of the base graph. The base graph defines the (macro) structure of the code and consists of a number (K) of information bit columns and a number (N) of code bit columns. Lifting the base graph a number of liftings, Z, results in a final information block length of KZ. Some information bits can be shortened (set to 0) to realize information block lengths less than KZ.

Thus, a larger graph can be obtained by a “copy and permute” operation where multiple copies of the base graph are made and connected to form a single lifted graph. For the multiple copies, like edges that are a set of copies of a single base edge are permutated and connected to form a connected graph Z times larger than the base graph.

FIG. 9is a bipartite graph illustrating liftings of three copies of the bipartite graph800ofFIG. 8. Three copies may be interconnected by permuting like edges among the copies. If the permutations are restricted to cyclic permutations, then the resulting bipartite graph900corresponds to a quasi-cyclic LDPC with lifting Z=3. The original graph800from which three copies were made is referred to herein as the base graph. To obtain graphs of different sizes, “copy and permute” operation can be applied to the base graph.

A corresponding PCM of the lifted graph can be constructed from the parity check matrix of the base graph by replacing each entry in the base parity check matrix with a Z×Z matrix. The “0” entries (those having no base edges) are replaced with the 0 matrix and the 1 entries (indicating a base edge) are replaced with a Z×Z permutation matrix. In the case of cyclic liftings, the permutations are cyclic permutations.

A cyclically lifted LDPC code can also be interpreted as a code over the ring of binary polynomials modulo xz+1. In this interpretation, a binary polynomial, (x)=b0+b1x+b2x2++bz−1xz−1 may be associated to each variable node in the base graph. The binary vector (b0, b1, b2, . . . , bz−1) corresponds to the bits associated to Z corresponding variable nodes in the lifted graph, that is, Z copies of a single base variable node. A cyclic permutation by k (referred to as a lifting value associated to the edges in the graph) of the binary vector is achieved by multiplying the corresponding binary polynomial by xk where multiplication is taken modulo xz+1. A degree d parity check in the base graph can be interpreted as a linear constraint on the neighboring binary polynomials B1(x), . . . , Bd(x), written as xk1B1(x)+xk2B2(x)++xkdBd(x)=0xk1−B1(x)+xk2B2(x)++xkdBd(x)=0, the values, k1, . . . , kd are the cyclic lifting values associated to the corresponding edges.

This resulting equation is equivalent to the Z parity checks in the cyclically lifted Tanner graph corresponding to the single associated parity check in the base graph. Thus, the parity check matrix for the lifted graph can be expressed using the matrix for the base graph in which 1 entries are replaced with monomials of the form xk and 0 entries are lifted as 0, but now the 0 is interpreted as the 0 binary polynomial modulo xz+1. Such a matrix may be written by giving the value k in place of xk. In this case the 0 polynomial is sometimes represented as “−1” and sometimes as another character in order to distinguish it from x0.

Typically, a square submatrix of the parity check matrix represents the parity bits of the code. The complementary columns correspond to information bits that, at the time of encoding, are set equal to the information bits to be encoded. The encoding may be achieved by solving for the variables in the aforementioned square submatrix in order to satisfy the parity check equations. The parity check matrix H may be partitioned into two parts M and N, where M is the square portion. Thus, encoding reduces to solving Mc=s=Nd where c and d comprise x. In the case of quasi-cyclic codes, or cyclically lifted codes, the above algebra can be interpreted as being over the ring of binary polynomials modulo xz+1. In the case of the IEEE 802.11 LDPC codes, which are quasi-cyclic, the encoding submatrix M has an integer representation as shown inFIG. 10.

A received LDPC codeword can be decoded to produce a reconstructed version of the original codeword. In the absence of errors, or in the case of correctable errors, decoding can be used to recover the original data unit that was encoded. Redundant bits may be used by decoders to detect and correct bit errors. LDPC decoder(s) generally operate by iteratively performing local calculations and passing those results by exchanging messages within the bipartite graph along the edges, and updating these messages by performing computations at the nodes based on the incoming messages. These steps may be repeated several times. For example, each variable node810in the graph800may initially be provided with a “soft bit” (e.g., representing the received bit of the codeword) that indicates an estimate of the associated bit's value as determined by observations from the communications channel. Using these soft bits the LDPC decoders may update messages by iteratively reading them, or some portion thereof, from memory and writing an updated message, or some portion thereof, back to, memory. The update operations are typically based on the parity check constraints of the corresponding LDPC code. In implementations for lifted LDPC codes, messages on like edges are often processed in parallel.

LDPC codes designed for high speed applications often use quasi-cyclic constructions with large lifting factors and relatively small base graphs to support high parallelism in encoding and decoding operations. LDPC codes with higher code rates (e.g., the ratio of the message length to the codeword length) tend to have relatively fewer parity checks. If the number of base parity checks is smaller than the degree of a variable node (e.g., the number of edges connected to a variable node), then, in the base graph, that variable node is connected to at least one of the base parity checks by two or more edges (e.g., the variable node may have a “double edge”). If the number of base parity checks is smaller than the degree of a variable node (e.g., the number of edges connected to a variable node), then, in the base graph, that variable node is connected to at least one of the base parity checks by two or more edges. Having a base variable node and a base check node connected by two or more edges is generally undesirable for parallel hardware implementation purposes. For example, such double edges may result in multiple concurrent read and write operations to the same memory locations, which in turn may create data coherency problems. A double edge in a base LDPC code may trigger parallel reading of the same soft bit value memory location twice during a single parallel parity check update. Thus, additional circuitry is typically needed to combine the soft bit values that are written back to memory, so as to properly incorporate both updates. Eliminating double edges in the LDPC code helps to avoid this extra complexity.

LDPC code designs based on cyclic lifting can be interpreted, as codes over the ring of polynomials modulo may be binary polynomials modulo xZ−1, where Z is the lifting size (e.g., the size of the cycle in the quasi-cyclic code). Thus encoding such codes can often be interpreted as an algebraic operation in this ring.

In the definition of standard irregular LDPC code ensembles (degree distributions) all edges in the Tanner graph representation may be statistically interchangeable. In other words, there exists a single statistical equivalence class of edges. A more detailed discussion of lifted LDPC codes may be found, for example, in the book titled, “Modern Coding Theory,” published Mar. 17, 2008, by Tom Richardson and Ruediger Urbanke. For multi-edge LDPC codes, multiple equivalence classes of edges may be possible. While in the standard irregular LDPC ensemble definition, nodes in the graph (both variable and constraint) are specified by their degree, i.e., the number of edges they are connected to, in the multi-edge type setting an edge degree is a vector; it specifies the number of edges connected to the node from each edge equivalence class (type) independently. A multi-edge type ensemble is comprised of a finite number of edge types. The degree type of a constraint node is a vector of (non-negative) integers; the i-th entry of this vector records the number of sockets of the i-th type connected to such a node. This vector may be referred to as an edge degree. The degree type of a variable node has two parts although it can be viewed as a vector of (non-negative) integers. The first part relates to the received distribution and will be termed the received degree and the second part specifies the edge degree. The edge degree plays the same role as for constraint nodes. Edges are typed as they pair sockets of the same type. The constraint that sockets must pair with sockets of like type characterizes the multi-edge type concept. In a multi-edge type description, different node types can have different received distributions (e.g., the associated bits may go through different channels).

Puncturing is the act of removing bits from a codeword to yield a shorter codeword. Thus, punctured variable nodes correspond to codeword bits that are not actually transmitted. Puncturing a variable node in an LDPC code creates a shortened code (e.g. due to the removal of a bit), while also effectively removing a check node. Specifically, for a matrix representation of an LDPC code, including bits to be punctured, where the variable node to be punctured has a degree of one (such a representation may be possible through row combining provided the code is proper), puncturing the variable node removes the associated bit from the code and effectively removes its single neighboring check node from the graph. As a result, the number of check nodes in the graph is reduced by one.

FIG. 11is a simplified block diagram illustrating an encoder, in accordance with certain aspects of the present disclosure.FIG. 11is a simplified block diagram1100illustrating a portion of radio frequency (RF) modem1150that may be configured to provide a signal including an encoded message for wireless transmission. In one example, convolutional encoder1102in a BS110(or a UE120on the reverse path) receives message1120for transmission. Message1120may contain data and/or encoded voice or other content directed to the receiving device. Encoder1102encodes the message using a suitable modulation and coding scheme (MCS), typically selected based on a configuration defined by BS110or another network entity. Encoded bitstream1122produced by encoder1102may then be selectively punctured by puncturing module1104, which may be a separate device or component, or which may be integrated with encoder1102. Puncturing module1104may determine that bitstream1122should be punctured prior to transmission, or transmitted without puncturing. The decision to puncture bitstream1122is typically made based on network conditions, network configuration, RAN defined preferences and/or for other reasons. Bitstream1122may be punctured according to puncture pattern1112and used to encode message1120. Puncturing module1104provides output1124to mapper1106that generates a sequence of Tx symbols1126that are modulated, amplified and otherwise processed by Tx chain1108to produce an RF signal1128for transmission through antenna1110.

Output1124of puncturing module1104may be the unpunctured bitstream1122or a punctured version of the bitstream1122, according to whether modem portion1150is configured to puncture the bitstream1122. In one example, parity and/or other error correction bits may be punctured in output1124of encoder1102in order to transmit message1120within a limited bandwidth of the RF channel. In another example, the bitstream may be punctured to reduce the power needed to transmit message1120, to avoid interference, or for other network-related reasons. These punctured codeword bits are not transmitted.

The decoders and decoding algorithms used to decode LDPC codewords operate by exchanging messages within the graph along the edges and updating these messages by performing computations at the nodes based on the incoming messages. Each variable node in the graph is initially provided with a soft bit, termed a received value, that indicates an estimate of the associated bit's value as determined by observations from, for example, the communications channel. Ideally, the estimates for separate bits are statistically independent. This ideal may be violated in practice. A received word is comprised of a collection of received values.

FIG. 12is a simplified block diagram illustrating a decoder, in accordance with certain aspects of the present disclosure.FIG. 12is a simplified schematic1200illustrating a portion of a RF modem1250that may be configured to receive and decode a wirelessly transmitted signal including a punctured encoded message. The punctured codeword bits may be treated as erased. For example, the log-likelihood ratios (LLRs) of the punctured nodes may be set to 0 at initialization. De-puncturing may also include deshortening of shortened bits. These shortened bits are not included in a transmission and, at the receiver/decoder, shortened bits are treated as known bits. In various examples, modem1250receiving the signal may reside at the UE, at the BS, or at any other suitable apparatus or means for carrying out the described functions. Antenna1202provides an RF signal1220to a receiver. RF chain1204processes and demodulates RF signal1220and may provide a sequence of symbols1222to demapper1226, which produces a bitstream1224representative of the encoded message.

Demapper1206may provide a depunctured bitstream1224. In one example, demapper1206may include a depuncturing module that can be configured to insert null values at locations in the bitstream at which punctured bits were deleted by the transmitter. The depuncturing module may be used when the puncture pattern1210used to produce the punctured bitstream at the transmitter is known. Puncture pattern1210can be used to identify LLRs1228that may be ignored during decoding of bitstream1224by convolutional decoder1208. The LLRs may be associated with a set of depunctured bit locations in the bitstream1224. Accordingly, decoder1208may produce decoded message1226with reduced processing overhead by ignoring the identified LLRs1228. The LDPC decoder may include a plurality of processing elements to perform the parity check or variable node operations in parallel. For example, when processing a codeword with lifting size Z, the LDPC decoder may utilize a number (Z) of processing elements to perform parity check operations on all edges of a lifted graph, concurrently.

Processing efficiency of decoder1208may be improved by configuring decoder1208to ignore LLRs1228that correspond to punctured bits in a message transmitted in a punctured bitstream1222. The punctured bitstream1222may have been punctured according to a puncturing scheme that defines certain bits to be removed from an encoded message. In one example, certain parity or other error-correction bits may be removed. A puncturing pattern may be expressed in a puncturing matrix or table that identifies the location of bits to be punctured in each message. A puncturing scheme may be selected to reduce processing overhead used to decode the message1226while maintaining compliance with data rates on the communication channel and/or with transmission power limitations set by the network. A resultant punctured bitstream typically exhibits the error-correcting characteristics of a high rate error-correction code, but with less redundancy. Accordingly, puncturing may be effectively employed to reduce processing overhead at the decoder1208in the receiver when channel conditions produce a relatively high signal to noise ratio (SNR).

At the receiver, the same decoder used for decoding non-punctured bitstreams can typically be used for decoding punctured bitstreams, regardless of how many bits have been punctured. In conventional receivers, the LLR information is typically de-punctured before decoding is attempted by filling LLRs for punctured states or positions (de-punctured LLRs) with 0's. The decoder may disregard de-punctured LLRs that effectively carry no information based, at least in part, on which bits are punctured. The decoder may treat shortened bits as known bits (e.g., set to 0).

Example Low-Density Parity-Check Base Graph Selection for New Radio

NR standardization has introduced two low-density parity-check (LDPC) base graphs (BG1, BG2) from which an LDPC code may be derived for encoding data. On each slot transmission, one of the base graphs (BGs) is selected for usage, i.e., for deriving an LDPC code used to encode the transmission. The base graph (e.g., BG1 or BG2) used for the encoding is implicitly indicated by the code block size and code rate of the transmission.

In typical operation, a BS transmits a choice of modulation and coding scheme (MCS) and a resource allocation (RA) in downlink control information (DCI) corresponding to a data transmission (e.g., a codeword) that the BS is transmitting or will transmit. A UE receives the DCI and, if the DCI is intended for the UE, then the UE can determine a transport block size (TBS) for the data transmission based on the MCS and RA and according to a network specification. Upon determination of the TBS, the UE can determine the LDPC BG used to encode the data transmission based on values of the code block size and code rate implied by the TBS and RA. If the UE does not successfully receive the data transmission, then the BS may retransmit the data in a retransmission. For retransmissions, regardless of any new MCS and RA chosen for the retransmission, the BS encodes the data using the same BG as used for the original data transmission, and the UE selects the BG used in the original data transmission for decoding the retransmissions to ensure proper hybrid automatic retransmission request (HARQ) combining and LDPC decoding of the combined transmissions (e.g., the original data transmission and any retransmissions).

When a BS sends a retransmission, the BS uses a same BG for deriving a code for encoding the retransmission as used for deriving a code for encoding the original data transmission, but the BS may choose a different MCS and RA than used in the original data transmission. While the MCS and RA for the retransmission are selected by the BS to ensure that the implied TBS of the retransmission is the same as the TBS used for the original data transmission, the code rate and, hence, the indicated base graph may change from the code rate and BG indicated for the original transmission. If the UE then decodes with the wrong BG, the data channel will not be correctly received.

According to aspects of the present disclosure, techniques are provided for a UE to determine the BG used in a retransmission in situations in which the UE misses (e.g., fails to properly decode, fails to receive) the control information for the original data transmission or the original data transmission.

FIG. 13illustrates example operations1300for wireless communication, in accordance with certain aspects of the present disclosure. Operations1300may be performed, for example, by a base station (e.g., BS110ashown inFIG. 1) comprising a processor in electrical communication with a memory, the processor configured to obtain data from the memory in preparation for wireless communications.

Operations1300begin, at block1302, by the BS transmitting, by a transceiver circuit using one or more antenna elements in electrical communication with the transceiver circuit, a first codeword to a user equipment (UE), the first codeword encoded using a first low-density parity-check (LDPC) code derived from a base graph (BG) selected based on a code block size (CBS) and a first code rate of the transmission. For example, BS110atransmits a first codeword to UE120a, the first codeword encoded using a first LDPC code derived from a BG (e.g., BG1) selected (from a set of BG1 and BG2) based on a CBS and a first code rate of the transmission.

At block1304, the BS obtains, by the transceiver circuit using the one or more antenna elements, an indication that the UE did not receive the first codeword. Continuing the example from above, the BS obtains an indication that the UE did not receive the first codeword, such as the BS not receiving an acknowledgment (ACK) of the first codeword from the UE.

At block1306, the BS selects, by the processor, a second code rate for a retransmission of information bits of the first codeword, wherein the selection is from a restricted set of code rates designed to ensure the UE selects the same BG to decode the retransmission. Continuing the example, the BS selects a second code rate for a retransmission of information bits of the first codeword, wherein the selection is from a restricted set of code rates designed to ensure the UE selects the same BG (e.g., BG1 from the set of BG1 and BG2) to decode the retransmission.

At block1308, the BS retransmits, by the transceiver circuit using the one or more antenna elements, the information bits in a second codeword according to the selected second code rate. Continuing the example from above, the BS retransmits the information bits in a second codeword according to the rate selected in block1306.

According to aspects of the present disclosure, a BS may put a restriction on a code rate used for retransmissions, such that no ambiguity (e.g., ambiguity regarding which BG a UE should use in decoding the retransmissions) results. The operations1300, described above with reference toFIG. 13, are an example of one technique for putting a restriction on a code rate used for retransmissions.

In aspects of the present disclosure, a mapping of code block size and/or code rate to BG choice (e.g., BG1 or BG2) may be initially specified, but a transmitting device (e.g., a BS) may restrict selection of code rates so that no ambiguity can result. For example, an initial mapping may indicate:

CBS is less than or equal to a first threshold (e.g., CBS≤292 bits);

code rate is less than or equal to a second threshold (e.g., code rate≤0.25); or

CBS is less than or equal to a third threshold AND code rate is less than or equal to a fourth threshold (e.g., CBS≤3824 bits and code rate≤0.67);

In the example, for all original transmissions and retransmissions where the CBS is less than or equal to the third threshold (e.g., CBS≤3824 bits), the transmitting device (e.g., a BS) restricts the choice of MCS and/or RA on the original transmission and the retransmissions such that the code rate is always less than or equal to the fourth threshold (e.g., code rate≤0.67). Retransmissions will be guaranteed to have a same TBS sizing and therefore a same code block sizing. With the described additional restriction on code rate, choice of BG (e.g., BG1 or BG2) from which the receiving device is to derive an LDPC code to decode the retransmission becomes unambiguous. That is, a wireless device (e.g., a UE) that misses the original transmission and receives the retransmission will determine which BG to use based on the CBS and the code rate of the retransmission, and the transmitting device selects the MCS and/or RA for the original transmission and the retransmission such that the code rate for the original transmission and the retransmission always indicates the same BG (e.g., BG2).

FIG. 14illustrates example operations1400for wireless communication, in accordance with certain aspects of the present disclosure. Operations1400may be performed, for example, by a base station (e.g., BS110shown inFIG. 1) comprising a processor in electrical communication with a memory, the processor configured to obtain data from the memory in preparation for wireless communications.

Operations1400begin, at block1402, by the BS selecting, by the processor and based on a modulation and coding scheme (MCS) and a resource allocation (RA) for transmitting a codeword, a base graph (BG) stored in said memory, from which to derive a low density parity check (LDPC) code for use in encoding data bits in the codeword (e.g., encoding data bits of a bitstream such that some redundant bits are included in the codeword). For example, BS110selects, based on an MCS and a RA for transmitting a codeword, BG1 to derive an LDPC code for use in encoding data bits in the codeword.

At block1404, the BS encodes, by an encoder circuit, the data bits to generate the codeword using the LDPC code derived from the selected BG. Continuing the example from above, the BS encodes the data bits to generate the codeword using the LDPC code derived from BG1.

At block1406, the BS transmits, by a transceiver circuit, the codeword using the MCS via resources of the RA using one or more antenna elements in electrical communication with the transceiver circuit. Continuing the example from above, the BS transmits the codeword using the MCS via resources (e.g., time and frequency resources) of the RA.

FIG. 15illustrates example operations1500for wireless communication, in accordance with certain aspects of the present disclosure. Operations1500may be performed, for example, by a user equipment (e.g., UE120ashown inFIG. 1) comprising a processor in electrical communication with a memory, the processor configured to obtain data from the memory in preparation for wireless communications. Operations1500may be considered complementary to operations1400, described above with reference toFIG. 14.

Operations1500begin, at block1502, by the UE receiving, by a transceiver circuit using one or more antenna elements in electrical communication with the transceiver circuit, control information indicating a modulation and coding scheme (MCS) and a resource allocation (RA) for transmission of a codeword. For example, UE120areceives control information (e.g., a DCI from BS110a) indicating an MCS and an RA for transmission of a codeword.

At block1504, the UE selects, by the processor and based on the MCS and the RA, a base graph (BG), from which to derive a low density parity check (LDPC) code for use in decoding the codeword. Continuing the example from above, the UE selects, based on the MCS and the RA indicated in the control information received in block1502, BG1 to derive an LDPC code for use in decoding the codeword.

At block1506, the UE receives, by the transceiver circuit using the one or more antenna elements, the codeword via resources of the RA. Continuing the example from above, the UE receives the codeword via resources (e.g., time and frequency resources) of the RA indicated in the control information received in block1502.

At block1508, the UE decodes, by a decoder circuit, the codeword using the LDPC code derived from the selected BG. Continuing the example from above, the UE decodes the codeword using the LDPC code derived from BG1.

According to aspects of the present disclosure, BSs and UEs of a communications system may explicitly ensure that each TBS size always maps to a same BG choice regardless of code block size and code rate, thus ensuring that there is no ambiguity in selecting a BG when a BS transmits and a UE receives a retransmission.

In aspects of the present disclosure, a BS may use a same set of criteria for choosing BG as previously described above, i.e. choose BG2 if CBS is less than or equal to a first threshold (e.g., CBS≤292 bits), if code rate is less than or equal to a second threshold (e.g., code rate≤0.25), or if CBS is less than or equal to a third threshold AND code rate is less than or equal to a fourth threshold (e.g., CBS≤3824 bits AND code rate≤0.67); otherwise choose BG1.

According to aspects of the present disclosure, the BS and UE in a wireless communications system may determine a mapping of TBS sizes from MCS and RA selections. The BS and UE may consider all possible TBS sizes and map each TBS size to a particular BG1 or BG2 selection, regardless of code block size and code rate. The BS and UE may override the BG choice from above (i.e., BG choice based on CBS and code rate) with the choice of BG based on the TBS size. For the case where only one MCS and RA combination produces a TBS size, then there is no need to override the BG choice based on MCS and RA.

FIG. 16illustrates example operations1600for wireless communication, in accordance with certain aspects of the present disclosure. Operations1600may be performed, for example, by a base station (e.g., BS110shown inFIG. 1) comprising a processor in electrical communication with a memory, the processor configured to obtain data from the memory in preparation for wireless communications.

Operations1600begin, at block1602, with the BS transmitting, by a transceiver circuit using one or more antenna elements in electrical communication with the transceiver circuit, control information indicating a base graph (BG) from which to derive a low density parity check (LDPC) code used in encoding bits of a codeword. For example, BS110transmits control information (e.g., a DCI) indicating (e.g., in a field of the DCI) the BS used BG1 to derive an LDPC code used in encoding bits of a codeword (e.g., a codeword transmitted using resources indicated in the DCI).

At block1604, the BS encodes, by an encoder circuit, data bits to generate the codeword using the LDPC code derived from the selected BG. Continuing the example from above, the BS encodes data bits to generate the codeword using the LDPC code derived from BG1.

At block1606, the BS transmits, by the transceiver circuit using the one or more antenna elements, the codeword. Continuing the example from above, the BS transmits the codeword.

FIG. 17illustrates example operations1700for wireless communication, in accordance with certain aspects of the present disclosure. Operations1700may be performed, for example, by a user equipment (e.g., UE120ashown inFIG. 1) comprising a processor in electrical communication with a memory, the processor configured to obtain data from the memory in preparation for wireless communications. Operations1700may be considered complementary to operations1600, described above with reference toFIG. 16.

Operations1700begin, at block1702, with the UE receiving, by a transceiver circuit using one or more antenna elements in electrical communication with the transceiver circuit, control information indicating a base graph (BG) from which to derive a low density parity check (LDPC) code used in encoding bits of a codeword. For example, UE120areceives control information (e.g., a DCI) indicating (e.g., in a field of the DCI) BG1 to derive an LDPC code used in encoding bits of a codeword.

At1704, the UE receives, by the transceiver circuit using the one or more antenna elements, the codeword. Continuing the example from above, the UE receives the codeword.

At block1706, the UE decodes, by a decoder circuit, the codeword using the LDPC code derived from the selected BG. Continuing the example from above, the UE decodes the codeword received in block1704using the LDPC code derived from BG1.

According to aspects of the present disclosure, a BS may explicitly indicate a BG to use in decoding a transmission in a downlink control information (DCI). That is, a field and/or a bit in a DCI may directly indicate a BG to be used in decoding a data transmission scheduled by the DCI. Explicitly indicating a BG in a DCI clearly removes ambiguity, but at the expense of increasing control overhead in a wireless communications system.

In some cases, rather than actually transmitting a frame, a device may have an interface to output a frame for transmission. For example, a processor may output a frame, via a bus interface, to an RF front end for transmission. Similarly, rather than actually receiving a frame, a device may have an interface to obtain a frame received from another device. For example, a processor may obtain (or receive) a frame, via a bus interface, from an RF front end for transmission.

For example, means for encoding, means for determining, means for selecting, and/or means for generating may include one or more processors, such as the TX MIMO processor430, Transmit processor420, and/or the Controller/Processor440of the BS110illustrated inFIG. 4; the TX MIMO processor466, Transmit Processor464, and/or the Controller/Processor480of the UE120illustrated inFIG. 4; and/or the encoder1102of the encoder1100illustrated inFIG. 11. Means for puncturing may comprise a processing system, which may include one or more of processors ofFIG. 4, and/or the puncturing module1104of the encoder1100illustrated inFIG. 11. Means for transmitting includes a transmitter, which may include the Transmit processor420, TX MIMO processor430, modulator(s)432a-432t, and/or the antenna(s)434a-434tof the BS110illustrated inFIG. 4; the Transmit processor464, TX MIMO Processor466, modulator(s)454a-454r, and/or antenna(s)452a-452rof the UE120illustrated inFIG. 4; and/or the TX chain1108and antenna1110of the encoder1100illustrated inFIG. 11.