 such that the first column has weight three, C is a zero matrix, D corresponds to single parity check rows, and E is an identity matrix for the base graph [55]. The rate matching for the LDPC code uses a circular buffer similar to LTE. The circular buffer is filled with an ordered sequence of systematic bits and parity bits. For HARQ-IR, each RV RV is assigned a starting bit location Si in the circular buffer. For HARQ-IR retransmission of RVi, the coded bits are read out sequentially from the circular buffer, start- ing with the bit location Si. Limited buffer rate matching is further supported. Before code block segmentation, LCRC = 24 TB-level CRC bits are attached to the end of the transport block. The value of LCRC was determined to satisfy the probability of misdetection of the TB with BLER < 10-6 as well as the inherent error detection of LDPC codes. LDPC code word Parity bits Systematic bits Base graph structure Figure 4.50 Structure of 3 GPP NR base graphs with dual diagonal property [55]. New Radio Access Physical Layer Aspects (Part 2) 533 The NR LDPC coding chain includes code block segmentation, CRC attachment, LDPC encoding, rate matching, and systematic-bit-priority interleaving. More specifically, code block segmentation allows very large transport blocks (MAC PDUs) to be divided into mul- tiple smaller sized code blocks that can be efficiently processed by the LDPC encoder/ decoder. The CRC bits are then attached for error detection purposes. When combined with the inherent error detection of the LDPC codes through the parity check equations, very low probability of undetected errors can be achieved. The rectangular interleaver with number of rows equal to the QAM order improves the performance by making systematic bits more reliable than parity bits for the initial transmission of the code blocks. The NR LDPC codes use a QC structure, where the PC matrix is defined by a smaller base graph. Each entry of the base graph represents either a zero matrix or a shifted ZXZ identity matrix, where a cyc