High performance nb-ldpc decoder with reduction of message exchange
- 1. A High-Performance FIR Filter Architecture for Fixed and Reconfigurable Applications High-Performance NB-LDPC Decoder With Reduction of Message Exchange Abstract: This paper presents a novel algorithm based on trellis min–max for decoding non-binary low- density parity check (NB-LDPC) codes. This decoder reduces the number of messages exchanged between check node and variable node processors, which decreases the storage resources and the wiring congestion and, thus, increases the throughput of the decoder. Our frame error rate performance simulations show that the proposed algorithm has a negligible performance loss for high rate codes with GF(16) and GF(32), and a performance loss smaller than 0.07 dB for high-rate codes over GF(64). The proposed architecture of this paper analysis the logic size, area and power consumption using Xilinx 14.2. Enhancement of the project: Existing System: The first algorithm proposed to decode NB-LDPC codes was the Q-ary sum-of-product algorithm (QSPA), which was developed as a generalization of the SPA for binary LDPC codes. Further improvements, such as fast Fourier transform SPA, log-SPA, and max-log-SPA, were proposed to reduce the complexity of the CN processing equations without introducing any performance loss. More recently, a trellisbased implementation for QPSA (T-max-log-QSPA) was proposed, offering a solution that increases the throughput with respect to previous solutions based on QPSA. Its main drawback is that the required area is prohibitive for real applications in communications and storage systems. Extended min-sum (EMS) and min–max algorithms were presented as the approximations of the QSPA, so that they reduce considerably the CN complexity, which only requires additions and/or comparisons. In addition, EMS and min–max algorithms utilize forward–backward metrics to derive the CN output messages. These metrics involve serial computations that limit the throughput of the derived hardware architectures. Trellis EMS (T-EMS) algorithm was proposed with the aim of enabling parallel processing of the messages in the CN. The input messages are organized in a trellis structure, while the output messages are generated in parallel by means of an extra column included in the trellis. Trellis min–max (T-MM) algorithm in adapts the idea of T-EMS to min–max algorithm. One minimum only T-MM (OMO T-MM) is an approximation of T-MM that reduces the complexity of the CN by obtaining only one minimum and estimating the second one. All these algorithms
- 2. A High-Performance FIR Filter Architecture for Fixed and Reconfigurable Applications exchange q × dc reliability values between CN and variable node (VN) processors. This amount of exchanged messages is large enough to cause wiring congestion, and this limits the maximum throughput, especially for high-rate NB-LDPC codes and high-order GFs. In addition, in decoder architectures with a layered schedule, the CN output messages are stored to be used in the next iteration. So, the required memory, which is the main part of the area in NB-LDPC decoder architectures, is too high. Disadvantages: Area coverage is high Throughput is low Proposed System: MODIFIED TRELLIS MIN–MAX ALGORITHM: Reformulation of Trellis Min–Max Algorithm: We reformulate the T-MM algorithm as a first step to define our proposal. As can be seen in Algorithm 2, Steps 4 and 5 are the ones reformulated. The function ψ’ in Step 4 obtains, which path in the trellis was used to obtain ΔQ (a), that is, the most reliable path. Considering that a maximum of two deviations is evaluated, the function returns the two GF symbols that define this path, η∗ 1(a) and η∗ 2(a). Algorithm 1 T-MM Algorithm
- 3. A High-Performance FIR Filter Architecture for Fixed and Reconfigurable Applications Fig. 1 includes an example of trellis with GF(4) and dc = 5. It shows the CN input messages before (Qmn(a)) and after (ΔQmn(a)) delta domain transformation. The hard-decision symbols are z = {α1, α0, 0, α0, 0}. After the normal-to-delta domain transformation, the reliabilities ΔQ mn(a) in the first row of the trellis are equal to 0.
- 4. A High-Performance FIR Filter Architecture for Fixed and Reconfigurable Applications Fig. 1. Top: example of CN input messages in normal domain. Bottom: messages in delta domain and organized in trellis way including the extra column Q(a) (bottom size). Example for GF(4) and dc = 5. NB-LDPC DECODER IMPLEMENTATION We describe the architecture designed to implement the proposed mT-MM algorithm. CN Architecture for mT-MM Algorithm The main characteristic of the proposed mT-MM Algorithm is to move part of the complexity of the CN processor to the VN processor. In this way, the number of exchanged messages between them and also the storage resources of the decoder are reduced. Therefore, the CN architecture presented in this section requires less functional blocks than a conventional implementation of the T-MM algorithm. Fig. 2 shows the block diagram for the top-level CN architecture, where each block corresponds to a step in the mT-MM algorithm.
- 5. A High-Performance FIR Filter Architecture for Fixed and Reconfigurable Applications Fig. 2. Proposed CN block diagram. The complete block diagram for the proposed decoder is presented in Fig. 3. As can be seen, there is only one CN processor and one VN processor, which processes one row of H per clock cycle. A layered schedule requires to store the CN output messages from one iteration to be used in the next one. This is done by means of a shift register with M stages (SR in Fig. 3). Fig. 3. Top-level proposed decoder architecture. Advantages: Improve area and throughput. Software implementation: Modelsim Xilinx ISE