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Binary LDPC codes & decoder architectures
Published in Zhang Xinmiao, VLSI Architectures for Modern Error-Correcting Codes, 2017
The row and column weights, the length of the shortest cycle in the corresponding Tanner graph, which is also called the girth, as well as the distribution of the cycles, affect the error-correcting performance in the waterfall region and the error-floor of LDPC codes. The error-floor is a phenomenon that the error-correcting performance curve in high signal-to-ratio (SNR) region flattens out. It happens due to the presence of cycles in the Tanner graph. Apparently, the Tanner graph should not have 4-cycles, which are two variable nodes and two check nodes connected by four edges. This means that two rows of H should not have ‘1’s in the same two columns. Further discussions on the construction of LDPC codes for good waterfall region performance and low error floor is beyond the scope of this book. The interested reader is referred to [102, 103].
Basics on the Theory of Fading Channels and Diversity
Published in Athanasios G. Kanatas, Konstantina S. Nikita, Panagiotis Mathiopoulos, New Directions in Wireless Communications Systems, 2017
Vasileios M. Kapinas, Georgia D. Ntouni, George K. Karagiannidis
Even worse, in the case of transmission through a frequency-selective and/or fast fading channel, the system performance can exhibit an irreducible error-rate level, called error floor, due to the significant degradation induced by the ISI and/or Doppler spread.* In such a scenario, no amount of SNR can help achieve the desired level of performance, unless some forms of mitigation are first employed to reduce or even eliminate the signal distortion. In Section 4.4.1, a list of robust transmission techniques is given for the elimination of ISI and the associated performance error floor.
Coding
Published in Goff Hill, The Cable and Telecommunications Professionals' Reference, 2012
What is meant by an “error floor” is that the error probability of a given code does not approach 0 as quickly for medium to high SNR as it does at low SNR. Such error floors primarily affect codes with low-(Hamming-) weight codewords, such as LDPC and Turbo codes.
Parameter estimation of MIMO FSO systems using saddlepoint approximation
Published in Journal of Modern Optics, 2022
The on-off keying (OOK) modulation with intensity modulation and direct detection (IM/DD) is commonly used for FSO due to its simplicity and low implementation cost. However, the OOK IM/DD with a deterministic threshold suffers from the irreducible error floor in the high signal-to-noise ratio (SNR) regime [10]. Thus, numerous attempts have focused on the application of adaptive detection thresholds in order to overcome the irreducible error floors of OOK IM/DD systems. The adaptive detection of OOK signals can be classified into three categories: ideal adaptive detection, quasi-static adaptive detection, and electrical-SNR optimized detection. Note the electrical-SNR-optimized detection category does not require knowledge of the instantaneous channel state information; thus, these are relatively straightforward to implement in comparison to the other two categories [11]. Unfortunately, the success of such systems assumes the accurate knowledge of parameters in statistical models. Much research has been reported to tackle this challenge. For example, parameter estimation for the universal FSO channel models, namely Gamma–Gamma and lognormal–Rician channels, has been explored in [12–17]. Nevertheless, all of these results are limited to single-input single-output (SISO) FSO systems. To the best of our knowledge, no prior work has been carried out to study the parameter estimation in MIMO FSO systems.
Lattice-Based Coding to Enhance Error Performance of the Hidden Direct Sequence Spread Spectrum
Published in IETE Journal of Research, 2021
Nader Sanandaji, Abolfazl Falahati
In [1], a BCH linear block code is used with DSSS. This DSSS/BCH scheme can control the system error rate effectively in the presence of a co-band jammer. The same objective is also followed by Chen et al. [6] where, a DSSS is used together with a Luby Transform (LT) code. This DSSS/LT method is shown to be effective although its Bit Error Rate (BER) reaches an error floor value asymptotically by increasing the Signal to Noise Ratio (SNR), which could not be necessarily very low. A DSSS system together with a high rate convolutional code is introduced in [7]. In addition, the BER performance of a convolutional coded DSSS scheme is also studied in [8]. A Viterbi-based suboptimal decoding method such as a log-likelihood ratio is used in the system models of [7,8] and their error performances in the presence of interference are investigated. Furthermore, the results of another study on a DSSS/convolutional FEC indicate that a 4 dB enhancement can be achieved for a BER of 10−6 [9]. However, for a low structural delay, linear block codes with large block length could significantly outperform convolutional codes [10]. So in situations where the delay of the communication system is of priority, linear block codes might be more desirable than convolutional codes. A class of linear block codes involving good error control properties for large block length is “construction A” lattice codes [11]. “Construction A” lattice codes are created by lifting linear block codes to the Euclidean space [11,12]. Moreover, it is possible to provide mathematical means to draw decoding schemes for a Gaussian channel and study error performance by employing lattice fundamentals [13–15].
Overview of the challenges and solutions for 5G channel coding schemes
Published in Journal of Information and Telecommunication, 2021
Madhavsingh Indoonundon, Tulsi Pawan Fowdur
Garzon, Abdel and Douillard introduced an enhanced design of punctured Turbo codes in which the constituent code distance spectrum and the extrinsic information exchange using uniform interleavers are used to select the puncturing pattern (2018). The interleaver function was then defined by a graph-based approach. The proposed scheme provides a performance boost both at the waterfall and error floor regions when compared to the Turbo code used in LTE. At a frame error rate (FER) of 10−4 and a code-rate of 4/5, the proposed scheme provides an Eb/N0 gain of 1.2 dB over an AWGN channel and the gain keeps increasing with decreasing FER over the simulated range.