A modified Gradient Descent Bit Flipping (GDBF) algorithm is proposed for decoding Low Density Parity Check (LDPC) codes on the binary-input additive white Gaussian noise channel. The new algorithm, called Noisy GDBF (NGDBF), introduces a random perturbation into each symbol metric at each iteration. The noise perturbation allows the algorithm to escape from undesirable local maxima, resulting in improved performance. A combination of heuristic improvements to the algorithm are proposed and evaluated. When the proposed heuristics are applied, NGDBF performs better than any previously reported GDBF variant, and comes within 0.5 dB of the belief propagation algorithm for several tested codes. Unlike other previous GDBF algorithms that provide an escape from local maxima, the proposed algorithm uses only local, fully parallelizable operations and does not require computing a global objective function or a sort over symbol metrics, making it highly efficient in comparison. The proposed NGDBF algorithm requires channel state information which must be obtained from a signal to noise ratio (SNR) estimator. Architectural details are presented for implementing the NGDBF algorithm. Complexity analysis and optimizations are also discussed.
In addition to recent work on low-complexity decoding, there has also been some exploration of noise-perturbed decoding using traditional MS and BP algorithms. demonstrated a beneficial effect of noise perturbations for the BP algorithm, using a method called dithered belief propagation @cite_1 . Kameni examined the effect of noise perturbations on MS decoders and found beneficial effects under certain conditions @cite_26 . The authors of @cite_14 offered the conjecture that noise perturbations assist the MS algorithm in escaping from spurious fixed-point attractors, similar to the hypothesis offered in this paper to motivate the NGDBF algorithm.
@cite_14 @cite_26 @cite_1
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This paper deals with Low-Density Parity-Check decoders running on noisy hardware. This represents an unconventional paradigm in communication theory, since it is traditionally assumed that the error correction decoder operates on error-free devices and the randomness (in the form of noise and or errors) exists only in the transmission channel. However, with the advent of nanoelectronics, it starts to be widely accepted that the future generations of circuits and systems will need to reliability compute and solve statistical inferences, by making use of unreliable “noisy” components. It is then critical to properly evaluate the robustness of the existing decoders in the presence of an additional source of noise at the circuit level. To this end, we first introduce a new error model approach and carry out the “noisy” density evolution analysis of the fixed-point Min-Sum decoding. Then, for different parameters of the noisy components of the decoder, we determine the range of the signal-to-noise ratio values for which the decoder is able to achieve a target bit error rate performance. Finally, we evaluate the finite-length performance of the Min-Sum and two other Min-Sum-based decoders running on noisy hardware. This paper investigates the behavior of the noisy Min-Sum decoder over binary symmetric channels. A noisy decoder is a decoder running on a noisy device, which may introduce errors during the decoding process. We show that in some particular cases, the noise introduce by the device can help the Min-Sum decoder to escape from fixed points attractors, and may actually result in an increased correction capacity with respect to the noiseless decoder. We also reveal the existence of a specific threshold phenomenon, referred to as functional threshold. The behavior of the noisy decoder is demonstrated in the asymptotic limit of the code-length, by using “noisy” density evolution equations, and it is also verified in the finite-length case by Monte-Carlo simulation. We introduce two dithered belief propagation decoding algorithms to lower the error floor with a minimal hardware overhead. One of the algorithms can additionally improve the decoding performance in the waterfall region using a large iteration limit but with a negligible increase in the average time complexity.