From the series:Understanding the 5G NR Standard
了解上行链路共享通道链,其中包括在下行链路共享信道链中找到的元素,包括LDPC编码,调制方案,层映射和两种类型的PUSCH映射。
视频遍历从下行链路共享信道区分上行链路共享信道的显着差异:层数限制为4,有可能使用可选的变换预编码,并且明确地指定MIMO预编码。
The video outlines the two possible types of MIMO precoding: codebook-based precoding and non-codebook-based precoding.
这是我们系列的“5G解释”中的一个新集。在此视频中,我们讨论了5G新无线电中的上行数据传输,我们查看了上行链路共享信道链,包括LDPC编码;物理上行链路共享信道链,包括可选变换预编码;和不同类型的PDSCH映射。上行链路共享通道或UL-SCH是携带用户数据的信道。它具有与下行链路共享信道非常类似的结构,具有CRC,代码块分段,使用LDPC,与LTE的关键差异和速率匹配。
The output of a coding chain is a codeword. Contrary to the downlink shared channel, it is limited to four layers, which means that uplink transmissions always use a single codeword. The coded data is then mapped to the physical uplink shared channel, or PUSCH. Here you can see how every stage of the uplink shared channel processing is mapped to functions in MathWorks 5G Toolbox. You can recognize CRC encoding, code block segmentation, LDPC coding, and rate matching.
在这里,链条类似于下行链路链,具有两个值得注意的差异。第一个是转换预编码的存在,DFT操作是将OFDM调制转换为OFDM或SC-OFDM的OFDM调制,有时被另一个名称,DFT扩展OFDM或DFT-S-OFDM。变换预编码是可选的,这意味着上行链路支持常规OFDM和SC-OFDM。金宝app
The second difference is that precoding is specified on the uplink, and we will see it can be of two types. I just mentioned transform precoding is an optional step. SC-FDMA provides lower PAPR, which means that less backoff is needed on the power amplifier. This helps with UEs that are in larger cells or have limited power.
Modulation schemes in the OFDM case are the same as for the downlink, ranging from QPSK to 256QAM. When transform recording is enabled, an additional modulation scheme. Pi/2-BPSK is also available to help with very low SNR transmission in a large cell or with low power.
Layer mapping on the uplink uses the same mechanism as on the downlink, a mechanism that is discussed in another episode of this "5G Explained" series, with one big difference. There can be a maximum of four layers. For that reason, the uplink always includes a single codeword. This single codeword is mapped to n layers, with n between 1 and 4, by mapping input blocks of n input bits to n layers, as shown here.
Precoding is the operation mapping layers' two antenna ports. As mentioned earlier, there are two precoding modes, codebook-based and non-codebook-based precoding. For non-codebook-based precoding, the UE determines the precoding matrix based on measurements it performs on downlink signals, typically the channel state information reference signals.
For codebook-based precoding, the UE simply applies the precoding matrix specified by the gNodeB. Here we have a closer look at the non-codebook-based precoding scheme. This is the mode where the UE makes its own decision about which precoding matrix to use. As just mentioned, the UE determines a suitable precoding matrix from CSI-RS measurements. It then applies the proposed precoding matrix to the SRS, or sounding reference signal. The gNodeB then informs the UE of which subset of the beamforming vectors it can use.
最后,问题可以pply the selected beamforming vectors to PUSCH transmission. In summary, in that mode, while the UE does propose a precoding matrix, the gNodeB can still veto some of the beamforming vectors, which would reduce the number of layers for transmission. For codebook-based precoding, the gNodeB determines the precoding matrix, based either on downlink measurements for TDD, or an uplink measurement of sounding reference signals.
然后,它将预编码信息发送到UE,用于上行链路的下行链路控制消息。UE只是在一系列表中查找矩阵。不同数量的层以及具有或不转换预编码的传输存在不同的表。在该“5G解释”视频系列的另一集中,详细描述了通道听起来和预编码的整个过程。
PUSCH符号使用两个映射类型,A或B中的一个映射到资源网格。这些与下行链路上的映射类型相同。映射A是指在插槽开始时开始的分配。然后将解调参考信号映射到符号2或3.映射类型B是为了分配通过时隙开始的分配,在这种情况下,DM-RS被映射到分配的第一符号。
这结束了这一关于上行链路数据传输的“5G解释”视频系列的一集。
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