The ntLDPC_Ghn IP Core is based on an implementation of QC-LDPC Quasi-Cyclic LDPC Codes. These LDPC codes are based on block-structured LDPC codes with circular block matrices. The entire parity check matrix can be partitioned into an array of block matrices; each block matrix is either a zero matrix or a right cyclic shift of an identity matrix. The parity check matrix designed in this way can be conveniently represented by a base matrix represented by cyclic shifts. The main
advantage of this feature is that they offer high throughput at low
implementation complexity.
The ntLDPCD_Ghn decoder IP Core may optionally implement one of two approximations of the log-domain LDPC iterative decoding algorithm (Belief propagation) known as either Layered Offset Min-Sum Algorithm or Layered Lambda-min Algorithm. Selecting between the two algorithms presents a decoding performance .vs. system resources utilization trade-off. The core is highly reconfigurable and fully compliant to the ITU-T G.9960 G.hn standard.
The ntLDPCE_Ghn encoder IP implements a 360-bit parallel systematic LDPC encoder. An off-line profiling Matlab script processes the original matrices and produces a set of constants that are associated with the matrix and hardcoded in the RTL encoder.
The ntLDPCD_Ghn decoder IP implements a 360-LLR parallel systematic LDPC layered decoder. A separate off-line profiling Matlab script is used to profile the layered matrices and resolve any possible memory access conflicts. Each layer corresponds to Z=[14, 80, 360, 60, 270, 48 or 216] expanded rows of the original LDPC matrix, depending on the mode selected expansion factor. Each layer element corresponds to the active ZxZ shifted identity sub-matrices, within a 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 executed. The decoder also IP features a powerful optional early termination (ET) criterion, to maintain practically the same error correction performance, while significantly increasing its throughput rate. 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 AXI.
