3GPP: TS 38.300 NR; Overall description - 1.物理层
下行
物理层中传输信道包括以下几步：
- Transport block CRC attachment (TBS超过3824比特24bitCRC，否则16bit CRC)
- Code block segmentation and code block, CRC attachement （24bit CRC）
- 信道编码：LDPC编码
- 物理层 HARQ处理和速率匹配
- Bit-interleaving
- 调制：QPSK，16QAM，6QAM， and 256QAM
- 层映射和预编码，layer mapping and pre-coding
- 资源映射和天线端口映射。
物理层控制信道：
物理层下行控制信道负责
- PDSCH的下行传输。下行任务包含调制，编码方式，资源分配和HARQ信息。
- PUSCH的上行传输。上行调度请求包括调制，编码方式，资源分配和HARQ信息。
控制信道是由控制信道元素组成（formed by aggregation of control channel elelments, each control element consisting of set of resource element groups）
Polar coding is used for PDCCH.
QPSK modulation is used for PDCCH.
同步信号和PBCH：
同步信号和PBCH包含PSS和SSS，每个占用1个符号127个子载波，PBCH占用三个符号240个子载波。结构如图。
Polar coding is used for PBCH
QPSK modulation is used for PBCH.
物理层过程：
链路自适应：AMC adaptive modulation and coding, 是为了适应PDSCH的不同的调制方式和编码速率。
同样的编码方式和调制方式适用于一个用户的MIMO同一个码字在一个TTI内的所有RBs。
为了估计信道状态，UE可以通过测量CSI-RS，将它上报给NB用于链路自适应。
上行
上行有两种传输方案：基于码本的传输和非码本的传输。
- 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.
物理层中上行共享信道的处理过程
- Transport Block CRC attachment (TBS above 3824 has 24 bit CRC, otherwise 16 bit CRC);
- Code block segmentation and Code Block CRC attachment (24 bit CRC);
- Channel coding: LDPC coding (base graph #1 or base graph #2);
- Bit-interleaving;
- Modulation: Pi/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.
物理层中上行控制信道
PUCCH携带Uplink Control Information UCI from UE to NB. PUCCH 有五种格式。
- Short PUCCH of 1 or 2 symbols with small UCI payloads of up to two bits with UE multiplexing in the same PRB;
- Short PUCCH of 1 or 2 symbols with large UCI payloads of more than two bits with no multiplexing in the same PRB;
- Long PUCCH of 4-14 symbols with small UCI payloads of up to two bits with multiplexing in the same PRB;
- Long PUCCH of 4-14 symbols with moderate UCI payloads with some multiplexing capacity in the same PRB;
- Long PUCCH of 4-14 symbols with large UCI payloads with no multiplexing capacity in the same PRB.
UCI包括以下信息：
- CSI
- ACK/NACK
- SR
QPSK modulation is used for long PUCCH with 2 or more bits of information, and short PUCCH with more than 2 bits of information. BPSK modulation is used for long PUCCH with 1 information bit.
Transform precoding is applied to long PUCCH.
Channel coding used for uplink control information is described in table 5.3.3-1.
随机接入
随机接入的sequence有两类，长的和短的。