The ntLDPC_5GNR Base Graph Encoder IP Core is defined in 3GPP TS 38.212 standard document and it is based on an implementation of QC-LDPC Quasi-Cyclic LDPC Codes. The specification defines two sets of LDPC Base Graphs and their respective derived Parity Check Matrices. Each Base Graph can be combined with 8 sets of lifting sizes (Zc) in a total of 51 different lifting sizes. This way by using the 2 Base Graphs, the 5G NR specification defines up to 102 possible distinct LDPC modes of operation to select from, for optimum decoding performance, depending on target application code block size and code rate (using the additional rate matching module features). For Base Graph 1 we have LDPC(N=66xZc,K=22xZc) sized code blocks, while for Base Graph 2 we have LDPC(N=50xZc,K=[6,8,9,10]xZc) sized code blocks.
The ntLDPCE_5GNR Encoder IP implements a multi-parallel systematic LDPC encoder. Parallelism depends on the selected lifting sizes subsets chosen for implementation. Shortened blocks are supported with granularity at lifting size Zc-bit boundaries. Customizable modes generation is also supported beyond the scope of the 5G-NR specification with features such as: “flat parity bits puncturing instead of Rate Matching Bit Selection”, “maintaining the first 2xZc payload bits instead of eliminating it before transmission”, etc.
The ntLDPCD_5GNR decoder IP implements a maximum lifting size of Zc_MAX-bit parallel systematic LDPC layered decoder. Each layer corresponds to Zc_MAX expanded rows of the original LDPC matrix. Each layer element corresponds to the active ZcxZc shifted identity sub-matrices within the layer. Each layer element is shifted accordingly and processed by the parallel decoding datapath unit, in order to update the layers LLR estimates and extrinsic information iteratively until the required number of decoding iterations has been run.
The decoder IP also features a powerful optional early termination (ET) criterion, to maintain practically equivalent error correction performance, while significantly increasing its throughput rate and/or reducing hardware cost. Additionally it reports how many decoding iterations have been performed when ET is activated, for system performance observation and calibration purposes. Finally a simple, yet robust, flow control handshaking mechanism is included in both IPs, which is used to communicate the IPs availability to adjacent system components. This logic is easily portable into any communication protocol, like AXI4 stream IF.
