TS 38.300 物理层（译）

持续更新ing...updated in 2019.7.18

目录

5. 物理层

5.1 波形，Numerology（子载波间隔&CP长度）以及帧结构

5.2 下行

5.2.1 下行传输方案

5.2.2 PDSCH的物理层处理

5.2.3 物理下行控制信道

5.2.4 同步信号和PBCH块

5.2.5 物理层过程

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5. 物理层

5.1 波形，Numerology（子载波间隔&CP长度）以及帧结构

下行传输波形用的是传统的使用了循环前缀的OFDM。上行传输波形也是传统的使用循环前缀的OFDM，以及一个转换预编码器进行DFT扩展，这个转换预编码器功能是可选的。

Numerology基于指数可伸缩的子载波间隔，如果是PSS,SSS以及PBCH信道的话 ，否则如果是其他信道。所有的子载波间隔都支持普通CP, 只有子载波支持扩展CP。12个连续的子载波构成一个PRB，一个载波上最多支持有275个PRB。

在一个成员载波上，UE可以被配置一个或者多个带宽部分，但是同一时间只能有一个带宽部分被激活。这个激活的带宽定义了在小区工作带宽内UE的工作带宽。对于初始接入，UE使用从系统信息中检测得到的初始带宽，直到UE收到小区的配置信息。

上下行传输是以10ms长度的帧结构进行的，一个帧包括10个1ms的子帧。每一个帧又分为两个同样大小的5ms半帧。一个slot包括14个符号（普通CP）或者12个符号（扩展CP），一个slot的时间长度和使用的子载波间隔有关，所以一个子帧（1ms）总是由整数个slot组成。（e.g. 15kHz: 1 subframe = 1 slot; 30kHz: 1 subframe = 2 slots;60kHz: 1 subframe = 4 slots)

时间提前量被用作调整相对于下行的上行帧时间。

支持工作在对称和非对称频谱，也即FDD和TDD。

5.2 下行

5.2.1 下行传输方案

物理下行共享信道（PDSCH）支持基于闭环DMRS的空分复用。对于type 1和type 2 DMRS类型分别支持最多8个和12个下行DMRS端口。SU-MIMO用户支持最多8个正交的下行DMRS端口，MU-MIMO用户支持最多4个正交的下行DMRS端口。对于SU-MIMO，1-4层传输支持1个码子，2-5层传输支持2个码子。

DMRS和对应的PDSCH传输使用相同的预编码矩阵，UE解调DMRS时不需要知道预编码矩阵。发射端可以传输带宽的不同部分使用不同的预编码矩阵，也就是频率选择性的与编码。UE也同样可以假设一组PRB（i.e., precoding resource block group, PRG）使用相同的预编码矩阵。

一个slot中支持2-14个符号的传输时长。

支持多个slot进行TB的重复传输。

5.2.2 PDSCH的物理层处理

传输信道的下行物理层处理包括以下步骤：

• 传输块加CRC（为了检错）
• 码块分割以及分割后码块加CRC（为信道编码作准备）
• 信道编码：LDPC码（数据信道LDPC, 控制信道polar）
• 物理层混合-ARQ处理(生成RV, 冗余版本，环形)
• 速率匹配（各个冗余版本进行速率匹配）
• 扰码
• 调制：QPSK, 16QAM,64QAM and 256QAM
• 层映射
• 映射到分配的资源以及端口上

在PDSCH传输给一个UE的每一层上，UE可以假设在这层上至少存在一个OFDM符号，其中包含DMRS，其次，最多3个额外DMRS可以被高层配置。

PTRS可以在额外的符号上传输，用于帮助接收端进行相位追踪。

5.2.3 物理下行控制信道

物理下行控制信道（PDCCH）可以被用作调度在PDSCH上的下行传输以及在PUSCH上的上行传输，调度的DCI存在于PDCCH中，包含：

• 下行分配信息包含至少调制编码格式，资源分配，DL-SCH相关的混合自动请求重传信息
• 上行调度许可包含至少调制编码格式，资源分配，UL-SCH相关的混合自动请求重传信息

除了调度功能，PDCCH还被用作：

• 基于配置许可的PUSCH传输的激活与去激活
• PDCSH半静态传输的激活与去激活
• 通知一个或多个UE的slot格式
• 通知一个或多个UE在哪些PRB和OFDM上UE应该假设没有传输
• 发送TPC命令给PUCCH和PUSCH
• 发送一个或多个TPC命令给一个或多个UE的SRS传输
• 切换一个UE的激活带宽部分
• 启动随机接入过程

UE根据相应的搜索空间配置，在配置的一个或多个CORESET的检测场合上监测一组PDCCH候选。

一个CORESET由一组PRB组成，时间上占据1-3OFDM符号。一个CORESET里定义了资源单位：REG以及CCE，没一个CCE包含一组REG。控制信道由一些CCE聚合而成。控制信道的不同码率由聚合不同数量的CCE来实现。一个CORESET里支持交织和非交织的CCE-REG映射。

PDCCH信道编码使用Polar码。

每一个包含PDCCH的REG都有自己的DMRS。

PDCCH使用QPSK的调制格式。

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补充一些概念：

• RE(Resource Element）：时间上一个OFDM符号，频率上一个子载波
• REG(Resource Element Group): 时间上一个OFDM符号。频率上一个RB（12个连续的子载波）
• CCE(Control Channel Element): 由6个REG组成（REG可以组成REG bundle再由REG bundle组成CCE）
• PDCCH: 由若干个CCE组成一个PDCCH（根据聚合等级配置）

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5.2.4 同步信号和PBCH块

同步信号和PBCH块也叫做SSB由主同步信号和辅同步信号以及PBCH组成，其中PSS以及SSS分别占据1个OFDM符号以及127个子载波，PBCH占据3个OFDM符号以及240个子载波，其中第二个符号中间一部分留空给SSS使用。SSB在一个半帧中的可能位置由子载波间隔决定，SSB出现的半帧周期由网络配置。在一个半帧中，多个可能位置的SSB可以向不同的空分方向传输。

在一个载波的不同频率位置可以到有多个SSB，这些SSB的PCI可以不是一样的，也就是说不同频率上的SSB可以有不同的PCI。当一个SSB和一个RMSI对应上了，这个SSB就和一个特定小区关联上了，就有一个独一无二的NCGI。这样的SSB被称作小区定义的SSB(CD-SSB)。一个PCell在同步栅格上总是和一个CD-SSB关联。

PBCH使用Polar编码。

UE可以假设在一个频带内SSB都使用一个子载波间隔，除非UE被网络配置使用了不同的子载波。

PBCH符号承载了他自己的频分DMRS。

PBCH使用QPSK调制。

5.2.5 物理层过程

5.2.5.1 链路适应

PDSCH应用了包含多种调制方案和信道编码率的链路适应技术（AMC: 适应的调至编码）。在一个传输时间和一个MIMO码字内，同样的编码和调至方案应用于所有属于同一个被调度给一个用户的L2 PDU资源块

为了信道状态估计，UE可以被配置去测量CSI-RS以及基于测量结果去估计下行信道状态。测量UE把测量的信道状态反馈给基站用于链路适应

5.2.5.2 功率控制

可以使用下行功率控制

5.2.5.3 小区搜索

小区搜索是UE获得与小区的时间以及频率同步，以及检测小区ID的过程。NR 小区搜索是基于主同步信号以及辅同步信号，以及PBCH DMRS的

5.2.5.4 HARQ

Asynchronous Incremental Redundancy Hybrid ARQ is supported. The gNB provides the UE with the HARQ-ACK feedback timing either dynamically in the DCI or semi-statically in an RRC configuration.

The UE may be configured to receive code block group based transmissions where retransmissions may be scheduled to carry a sub-set of all the code blocks of a TB.

5.2.5.5          Reception of SIB1

The Master Information Block (MIB) on PBCH provides the UE with parameters (e.g. CORESET#0 configuration) for monitoring of PDCCH for scheduling PDSCH that carries the System Information Block 1 (SIB1). PBCH may also indicate that there is no associated SIB1, in which case the UE may be pointed to another frequency from where to search for an SSB that is associated with a SIB1 as well as a frequency range where the UE may assume no SSB associated with SIB1 is present. The indicated frequency range is confined within a contiguous spectrum allocation of the same operator in which SSB is detected.

5.3              Uplink

5.3.1          Uplink transmission scheme

Two transmission schemes are supported for PUSCH: codebook based transmission and non-codebook based transmission.

For codebook based transmission, the gNB provides the UE with a transmit precoding matrix indication in the DCI. The UE uses the indication to select the PUSCH transmit precoder from the codebook. For non-codebook based transmission, the UE determines its PUSCH precoder based on wideband SRI field from the DCI.

A closed loop DMRS based spatial multiplexing is supported for PUSCH. For a given UE, up to 4 layer transmissions are supported. The number of code words is one. When transform precoding is used, only a single MIMO layer transmission is supported.

Transmission durations from 1 to 14 symbols in a slot is supported.

Aggregation of multiple slots with TB repetition is supported.

Two types of frequency hopping are supported, intra-slot frequency hopping, and in case of slot aggregation, inter-slot frequency hopping.

PUSCH may be scheduled with DCI on PDCCH, or a semi-static configured grant may be provided over RRC, where two types of operation are supported:

-    The first PUSCH is triggered with a DCI, with subsequent PUSCH transmissions following the RRC configuration and scheduling received on the DCI, or

-    The PUSCH is triggered by data arrival to the UE's transmit buffer and the PUSCH transmissions follow the RRC configuration.

5.3.2          Physical-layer processing for physical uplink shared channel

The uplink physical-layer processing of transport channels consists of the following steps:

-    Transport Block CRC attachment;

-    Code block segmentation and Code Block CRC attachment;

-    Channel coding: LDPC coding;

-    Physical-layer hybrid-ARQ processing;

-    Rate matching;

-    Scrambling;

-    Modulation: π/2 BPSK (with transform precoding only), QPSK, 16QAM, 64QAM and 256QAM;

-    Layer mapping, transform precoding (enabled/disabled by configuration), and pre-coding;

-    Mapping to assigned resources and antenna ports.

The UE transmits at least one symbol with demodulation reference signal on each layer on each frequency hop in which the PUSCH is transmitted, and up to 3 additional DMRS can be configured by higher layers.

Phase Tracking RS may be transmitted on additional symbols to aid receiver phase tracking.

The UL-SCH physical layer model is described in TS 38.202 [20].

5.3.3          Physical uplink control channel

Physical uplink control channel (PUCCH) carries the Uplink Control Information (UCI) from the UE to the gNB. Five formats of PUCCH exist, depending on the duration of PUCCH and the UCI payload size.

-    Format #0: Short PUCCH of 1 or 2 symbols with small UCI payloads of up to two bits with UE multiplexing capacity of up to 6 UEs with 1-bit payload in the same PRB;

-    Format #1: Long PUCCH of 4-14 symbols with small UCI payloads of up to two bits with UE multiplexing capacity of up to 84 UEs without frequency hopping and 36 UEs with frequency hopping in the same PRB;

-    Format #2: Short PUCCH of 1 or 2 symbols with large UCI payloads of more than two bits with no UE multiplexing capability in the same PRBs;

-    Format #3: Long PUCCH of 4-14 symbols with large UCI payloads with no UE multiplexing capability in the same PRBs;

-    Format #4: Long PUCCH of 4-14 symbols with moderate UCI payloads with multiplexing capacity of up to 4 UEs in the same PRBs.

The short PUCCH format of up to two UCI bits is based on sequence selection, while the short PUCCH format of more than two UCI bits frequency multiplexes UCI and DMRS. The long PUCCH formats time-multiplex the UCI and DMRS. Frequency hopping is supported for long PUCCH formats and for short PUCCH formats of duration of 2 symbols. Long PUCCH formats can be repeated over multiple slots.

UCI multiplexing in PUSCH is supported when UCI and PUSCH transmissions coincide in time, either due to transmission of a UL-SCH transport block or due to triggering of A-CSI transmission without UL-SCH transport block:

-    UCI carrying HARQ-ACK feedback with 1 or 2 bits is multiplexed by puncturing PUSCH;

-    In all other cases UCI is multiplexed by rate matching PUSCH.

UCI consists of the following information:

-    CSI;

-    ACK/NAK;

-    Scheduling request.

QPSK and π/2 BPSK modulation can be used for long PUCCH with more than 2 bits of information, QPSK is used for short PUCCH with more than 2 bits of information and BPSK and QPSK modulation can be used for long PUCCH with up to 2 information bits.

Transform precoding is applied to long PUCCH.

Channel coding used for uplink control information is described in table 5.3.3-1.

Table 5.3.3-1: Channel coding for uplink control information

Uplink Control Information size including CRC, if present	Channel code
1	Repetition code
2	Simplex code
3-11	Reed Muller code
>11	Polar code

 

5.3.4          Random access

Random access preamble sequences, of two different lengths are supported. Long sequence length 839 is applied with subcarrier spacings of 1.25 and 5 kHz and short sequence length 139 is applied with subcarrier spacings of 15, 30, 60 and 120 kHz. Long sequences support unrestricted sets and restricted sets of Type A and Type B, while short sequences support unrestricted sets only.

Multiple PRACH preamble formats are defined with one or more PRACH OFDM symbols, and different cyclic prefix and guard time. The PRACH preamble configuration to use is provided to the UE in the system information.

The UE calculates the PRACH transmit power for the retransmission of the preamble based on the most recent estimate pathloss and power ramping counter.

The system information provides information for the UE to determine the association between the SSB and the RACH resources. The RSRP threshold for SSB selection for RACH resource association is configurable by network.

5.3.5          Physical layer procedures

5.3.5.1          Link adaptation

Four types of link adaptation are supported as follows:

-    Adaptive transmission bandwidth;

-    Adaptive transmission duration;

-    Transmission power control;

-    Adaptive modulation and channel coding rate.

For channel state estimation purposes, the UE may be configured to transmit SRS that the gNB may use to estimate the uplink channel state and use the estimate in link adaptation.

5.3.5.2          Uplink Power control

The gNB determines the desired uplink transmit power and provides uplink transmit power control commands to the UE. The UE uses the provided uplink transmit power control commands to adjust its transmit power.

5.3.5.3          Uplink timing control

The gNB determines the desired Timing Advance setting and provides that to the UE. The UE uses the provided TA to determine its uplink transmit timing relative to the UE's observed downlink receive timing.

5.3.5.4          HARQ

Asynchronous Incremental Redundancy Hybrid ARQ is supported. The gNB schedules each uplink transmission and retransmission using the uplink grant on DCI.

The UE may be configured to transmit code block group based transmissions where retransmissions may be scheduled to carry a sub-set of all the code blocks of a transport block.

5.4              Carrier aggregation

5.4.1          Carrier aggregation

In Carrier Aggregation (CA), two or more Component Carriers (CCs) are aggregated. A UE may simultaneously receive or transmit on one or multiple CCs depending on its capabilities:

-    A UE with single timing advance capability for CA can simultaneously receive and/or transmit on multiple CCs corresponding to multiple serving cells sharing the same timing advance (multiple serving cells grouped in one TAG);

-    A UE with multiple timing advance capability for CA can simultaneously receive and/or transmit on multiple CCs corresponding to multiple serving cells with different timing advances (multiple serving cells grouped in multiple TAGs). NG-RAN ensures that each TAG contains at least one serving cell;

-    A non-CA capable UE can receive on a single CC and transmit on a single CC corresponding to one serving cell only (one serving cell in one TAG).

CA is supported for both contiguous and non-contiguous CCs. When CA is deployed frame timing and SFN are aligned across cells that can be aggregated. The maximum number of configured CCs for a UE is 16 for DL and 16 for UL.

5.4.2          Supplementary Uplink

In conjunction with a UL/DL carrier pair (FDD band) or a bidirectional carrier (TDD band), a UE may be configured with additional, Supplementary Uplink (SUL). SUL differs from the aggregated uplink in that the UE may be scheduled to transmit either on the supplementary uplink or on the uplink of the carrier being supplemented, but not on both at the same time.

5.5              Transport Channels

The physical layer offers information transfer services to MAC and higher layers. The physical layer transport services are described by how and with what characteristics data are transferred over the radio interface. An adequate term for this is "Transport Channel". This should be clearly separated from the classification of what is transported, which relates to the concept of logical channels at MAC sublayer.

Downlink transport channel types are:

1.   Broadcast Channel (BCH) characterised by:

-    fixed, pre-defined transport format;

-    requirement to be broadcast in the entire coverage area of the cell, either as a single message or by beamforming different BCH instances.

2.   Downlink Shared Channel (DL-SCH) characterised by:

-    support for HARQ;

-    support for dynamic link adaptation by varying the modulation, coding and transmit power;

-    possibility to be broadcast in the entire cell;

-    possibility to use beamforming;

-    support for both dynamic and semi-static resource allocation;

-    support for UE discontinuous reception (DRX) to enable UE power saving.

3.   Paging Channel (PCH) characterised by:

-    support for UE discontinuous reception (DRX) to enable UE power saving (DRX cycle is indicated by the network to the UE);

-    requirement to be broadcast in the entire coverage area of the cell, either as a single message or by beamforming different BCH instances;

-    mapped to physical resources which can be used dynamically also for traffic/other control channels.

Uplink transport channel types are:

1.   Uplink Shared Channel (UL-SCH) characterised by:

-    possibility to use beamforming;

-    support for dynamic link adaptation by varying the transmit power and potentially modulation and coding;

-    support for HARQ;

-    support for both dynamic and semi-static resource allocation.

2.   Random Access Channel(s) (RACH) characterised by:

-    limited control information;

-    collision risk.

Association of transport channels to physical channels is described in TS 38.202 [20].