Kui Cai

Kui Cai
Singapore University of Technology and Design · science and math cluster

About

207
Publications
13,024
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1,164
Citations
Additional affiliations
April 2015 - November 2017
Singapore University of Technology and Design
Position
  • Professor

Publications

Publications (207)
Conference Paper
In this work, given n,ϵ > 0, two efficient encoding (decoding) methods are presented for mapping arbitrary data to (from) n×n binary arrays in which the weight of every row and every column is within [(1/2–ϵ)n, (1/2+ϵ)n], which is referred to as the ϵ-balanced constraint. The first method combines the divide and conquer algorithm and a modification...
Conference Paper
Advances in synthesis and sequencing technologies have made DNA macromolecules an attractive medium for digital information storage. Compared with the ex vivo method that stores data in a non-biological environment, there have been considerations and attempts to store data in living organisms, also known as the in vivo method or live DNA due to sev...
Preprint
Full-text available
In this letter, we propose a two-stage design method to construct memory efficient mutual information-maximizing quantized min-sum (MIM-QMS) decoder for rate-compatible low-density parity-check (LDPC) codes. We first develop a modified density evolution to design a unique set of lookup tables (LUTs) that can be used for rate-compatible LDPC codes....
Preprint
Full-text available
In this paper, we present an explicit construction of list-decodable codes for single-deletion and single-substitution with list size two and redundancy 3log n+4, where n is the block length of the code. Our construction has lower redundancy than the best known explicit construction by Gabrys et al. (arXiv 2021), whose redundancy is 4log n+O(1).
Article
Resistive random-access memory is one of the most promising candidates for the next generation of non-volatile memory technology. However, its crossbar array structure causes severe “sneak-path" interference, which also leads to strong inter-cell correlation. Recent works have mainly focused on sub-optimal data detection schemes by ignoring inter-c...
Article
Full-text available
The error‐correcting performance of multi‐level‐cell (MLC) NAND flash memory is closely related to the block length of error‐correcting codes (ECCs) and log‐likelihood‐ratios of the read‐voltage thresholds. Driven by this issue, this paper optimizes the read‐voltage thresholds for MLC flash memory to improve the decoding performance of ECCs with fi...
Article
In this letter, we propose a two-stage design method to construct memory efficient mutual information-maximizing quantized min-sum (MIM-QMS) decoder for rate-compatible low-density parity-check (LDPC) codes. We first develop a modified density evolution to design a unique set of lookup tables (LUTs) that can be used for rate-compatible LDPC codes....
Article
The subblock energy-constrained codes (SECCs) and sliding window-constrained codes (SWCCs) have recently attracted attention due to various applications in communication systems such as simultaneous energy and information transfer. In a SECC, each codeword is divided into smaller non-overlapping windows, called subblocks, and every subblock is cons...
Preprint
Despite the great promises that the resistive random access memory (ReRAM) has shown as the next generation of non-volatile memory technology, its crossbar array structure leads to a severe sneak path interference to the signal read back from the memory cell. In this paper, we first propose a novel belief propagation (BP) based detector for the sne...
Article
Full-text available
We present coding methods for generating ℓ-symbol constrained codewords taken from a set, S, of allowed codewords. In standard practice, the size of the set S, denoted by M=|S|, is truncated to an integer power of two, which may lead to a serious waste of capacity. We present an efficient and low-complexity coding method for avoiding the truncation...
Article
Consider the computations at a node in a message passing algorithm. Assume that the node has incoming and outgoing messages x = (x1, x2, xn) and y = (y1, y2, yn), respectively. In this paper, we investigate a class of structures that can be adopted by the node for computing y from x, where each yj, j = 1, 2, ..., n is computed via a binary tree wit...
Article
Resistive random-access memory (ReRAM) is a promising non-volatile memory technology for achieving high-density and high-speed data storage. However, its crossbar array structure leads to a severe problem known as the sneak path interference (SPI), which is data dependent and correlated within a memory array. Meanwhile, variations of the memory fab...
Article
We investigate a basic decentralized caching network with coded prefetching under nonuniform requests and arbitrary file popularities, where a server containing $N$ files is connected to $K$ users, each with limited cache memory of $M$ files through a shared link. In the decentralized placement phase, the server encodes all files by the maxim...
Article
We propose coding techniques that simultaneously limit the length of homopolymers runs, ensure the GC-content constraint, and are capable of correcting a single edit error in strands of nucleotides in DNA-based data storage systems. In particular, for given ℓ, ϵ > 0, we propose simple and efficient encoders/decoders that transform binary sequences...
Conference Paper
Full-text available
In this work, given n, p>0 , efficient encoding/decoding algorithms are presented for mapping arbitrary data to and from n×n binary arrays in which the weight of every row and every column is at most pn. Such constraint, referred as p-bounded-weight-constraint, is crucial for reducing the parasitic currents in the crossbar resistive memory arrays,...
Article
In this article, under a general cost function $C$ , we present a dynamic programming (DP) method to obtain an optimal sequential deterministic quantizer (SDQ) for $q$ -ary input discrete memoryless channel (DMC). The DP method has complexity $O(q (N-M)^{2}\,\,M)$ , where $N$ and $M$ are the alphabet sizes of the DMC output and quantizer...
Article
As an emerging non-volatile memory (NVM) technology, spin-torque transfer magnetic random access memory (STT-MRAM) has received great attention in recent years since it combines the features of low switching energy, fast write/read speed, and high scalability. However, process variation and thermal fluctuation severely affect the data integrity of...
Article
Full-text available
We investigate a new approach for designing spectral shaping block codes with a target spectrum, H_t(f), that has been specified at a plurality of frequencies. We analyze the probability density function of the spectral power density function of uncoded n-symbol bipolar code words. We present estimates of the redundancy and the spectrum of spectral...
Preprint
Resistive random-access memory is one of the most promising candidates for the next generation of non-volatile memory technology. However, its crossbar structure causes severe "sneak-path" interference, which also leads to strong inter-cell correlation. Recent works have mainly focused on sub-optimal data detection schemes by ignoring inter-cell co...
Article
Resistive random-access memory (ReRAM) is a promising candidate for the next generation non-volatile memory technology due to its simple read/write operations and high storage density. However, its crossbar array structure causes a severe interference effect known as the “sneak path.” In this paper, we propose channel coding techniques that can mit...
Article
This paper proposes novel methods for designing two-dimensional (2-D) weight-constrained codes for reducing the parasitic currents in the crossbar resistive memory array. In particular, we present efficient encoding/decoding algorithms for capacity-approaching 2-D weight-constrained codes of size m×n, where each row has a weight pn with p < 1/2; an...
Article
An indel refers to a single insertion or deletion, while an edit refers to a single insertion, deletion or substitution. In this article, we investigate codes that correct either a single indel or a single edit and provide linear-time algorithms that encode binary messages into these codes of length n. Over the quaternary alphabet, we provide two l...
Preprint
Full-text available
In this paper, we propose a general framework of the mutual infomration-maximizing (MIM) quantized decoding for low-density parity-check (LDPC) codes, which can outperform the state-of-the-art lookup table (LUT) decoder by using simple mappings and fixed-point additions for the node updates. Our decoding method is generic in the sense that it can b...
Article
This paper investigates a cache-aided cloud radio access network (C-RAN), comprising a central unit, K base stations (BSs) each with N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> antennas, and M users each with N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3...
Article
Full-text available
Energy-harvesting sliding-window constrained block codes guarantee that within any prescribed window of ℓ consecutive bits the constrained sequence has at least t, t≥1, 1’s. Prior art code design methods build upon the finite-state machine description of the (ℓ,t) constraint, but as the number of states equals ℓ choose t, a code design becomes proh...
Article
Structured Gaussian elimination (SGE) is a class of methods for efficiently solving sparse linear systems. The key idea is to first triangulate the original linear systems. The maximum component (MC)-based strategies are widely used to implement the triangulation process. The most straightforward way to find the MC is through exhaustive search. Ins...
Article
The process of DNA-based data storage (DNA storage for short) can be mathematically modelled as a communication channel, termed DNA storage channel, whose inputs and outputs are sets of unordered sequences. To design error correcting codes for DNA storage channel, a new metric, termed the sequence-subset distance , is introduced, which generalize...
Preprint
Full-text available
The subblock energy-constrained codes (SECCs) and sliding window-constrained codes (SWCCs) have recently attracted attention due to various applications in communcation systems such as simultaneous energy and information transfer. In a SECC, each codewod is divided into smaller non-overlapping windows, called subblocks, and every subblock is constr...
Preprint
Consider the computations at a node in the message passing algorithms. Assume that the node has incoming and outgoing messages $\mathbf{x} = (x_1, x_2, \ldots, x_n)$ and $\mathbf{y} = (y_1, y_2, \ldots, y_n)$, respectively. In this paper, we investigate a class of structures that can be adopted by the node for computing $\mathbf{y}$ from $\mathbf{x...
Article
Thanks to its superior features of fast read/write speed and low power consumption, spin-torque transfer magnetic random access memory (STT-MRAM) has become a promising non-volatile memory (NVM) technology that is suitable for many applications. However, the reliability of STT-MRAM is seriously affected by the variation of the memory fabrication pr...
Article
Full-text available
We study properties and constructions of constrained binary codes that enable simultaneous energy and information transfer. We specifically study sliding-window constrained codes that guarantee that within any prescribed window of ℓ consecutive bits the constrained sequence has at least t, t > 1, 1’s. We present a K-state source, K = ℓ choose t, th...
Article
Decoders minimizing the Euclidean distance between the received word and the candidate codewords are known to be optimal for channels suffering from Gaussian noise. However, when the stored or transmitted signals are also corrupted by an unknown offset, other decoders may perform better. In particular, applying the Euclidean distance on normalized...
Preprint
Although studying in multiple-deletion correcting codes has made great progress in recent years, studying in codes correcting multiple deletions and substitutions simultaneously still in its beginning. Recent work by Smagloy et al. [12] gives a construction of single-deletion and single-substitution codes with redundancy 6log n + 8, where n is the...
Preprint
Motivated by the application of fountain codes in the DNA-based data storage systems, in this paper, we consider the decoding of fountain codes when the received symbols have a chance to be incorrect. Unlike the conventional scenario where the received symbols are all error-free, the maximum likelihood (ML) decoding and maximum a posterior probabil...
Conference Paper
The subblock energy-constrained codes (SECCs) have recently attracted attention due to various applications in communication systems such as simultaneous energy and information transfer. In a SECC, each codeword is divided into smaller subblocks, and every subblock is constrained to carry sufficient energy. In this work, we study SECCs under more g...
Conference Paper
In this paper, we first propose coding techniques for DNA-based data storage which account the maximum homopolymer runlength and the GC-content. In particular, for arbitrary $\ell,\epsilon > 0$, we propose simple and efficient $(\epsilon, \ell)$-constrained encoders that transform binary sequences into DNA base sequences (codewords), that satisfy t...
Preprint
Resistive random-access memory (ReRAM) is a promising candidate for the next generation non-volatile memory technology due to its simple read-write operation and high storage density. However, its crossbar array structure causes a server interference effect known as the "sneak path." In this paper, we address the sneak-path problem based on communi...
Preprint
Full-text available
The error correcting performance of multi-level-cell (MLC) NAND flash memory is closely related to the block length of error correcting codes (ECCs) and log-likelihood-ratios (LLRs) of the read-voltage thresholds. Driven by this issue, this paper optimizes the read-voltage thresholds for MLC flash memory to improve the decoding performance of ECCs...
Article
Power line communication (PLC) advances smart grid technology by offering a convenient and efficient data transmission service. However, due to the severe PLC channel condition and ever-growing traffic load in the PLC backhaul, reliable communications among widely distributed in-home PLC users is highly energy-consuming. In this paper, we put forth...
Article
Full-text available
We describe properties and constructions of constraint-based codes for DNA-based data storage which account for the maximum repetition length and AT/GC balance. Generating functions and approximations are presented for computing the number of sequences with maximum repetition length and AT/GC balance constraint. We describe routines for translating...
Article
The practical NAND flash memory suffers from various non-stationary noises that are difficult to be predicted. For example, the data retention noise induced channel offset is unknown during the readback process, and hence severely affects the reliability of data recovery from the memory cell. In this paper, we first propose a novel recurrent neural...
Preprint
The subblock energy-constrained codes (SECCs) have recently attracted attention due to various applications in communication systems such as simultaneous energy and information transfer. In a SECC, each codeword is divided into smaller subblocks, and every subblock is constrained to carry sufficient energy. In this work, we study SECCs under more g...
Article
Full-text available
We report on the feasibility of k-means clustering techniques for the dynamic threshold detection of encoded q-ary symbols transmitted over a noisy channel with partially unknown channel parameters. We first assess the performance of k-means clustering technique without dedicated constrained coding. We apply constrained codes which allows a wider r...
Preprint
Full-text available
Consider a centralized caching network with a single server and $K$ users. The server has a database of $N$ files with each file being divided into $F$ packets ($F$ is known as subpacketization), and each user owns a local cache that can store $\frac{M}{N}$ fraction of the $N$ files. We construct a family of centralized coded caching schemes with p...
Article
Full-text available
An efficient concatenation of error correction codes with constrained codes is proposed in this paper. Generally, constrained codes are designed to match specified channels, whereas error correction coding schemes are designed to correct the channel errors. They both play important roles to ensure the integrity of data in data storage systems. In t...
Article
A very low-complexity on-off division multiple access (ODMA) scheme is proposed for K-user non-orthogonal multiple access (NOMA) systems. At the transmission side, each user employs the same length-m channel code whose coded bits, after modulation, are sent in a random time-hopping manner. Specifically, m coded bits are randomly scheduled and sent...
Preprint
Full-text available
We propose coding techniques that limit the length of homopolymers runs, ensure the GC-content constraint, and are capable of correcting a single edit error in strands of nucleotides in DNA-based data storage systems. In particular, for given $\ell, {\epsilon} > 0$, we propose simple and efficient encoders/decoders that transform binary sequences i...
Article
Full-text available
The protograph low‐density parity‐check (LDPC) codes possess many attractive properties, such as the low encoding/decoding complexity and better error floor performance, and hence have been successfully applied to different types of communication and data storage channels. In this study, the authors design protograph LDPC codes for communication sy...
Article
Thanks to its superior features of non-volatility, fast read/write speed, high endurance, and low power consumption, spin-torque transfer magnetic random access memory (STT-MRAM) has become a promising candidate for the next generation non-volatile memories (NVMs) and storage class memories (SCMs). However, it has been found that the write errors a...
Article
As emerging memories such as spin-torque transfer magnetic random access memory (STT-MRAM) suffer from reliability issues caused by process variations and thermal fluctuations, the design of channel quantizer with the minimum number of quantization bits is critical to support effective error correction coding for ensuring high-density and high-spee...
Article
Full-text available
We analyze codes for DNA-based data storage which accounts for the maximum homopolymer repetition length and GC-AT balance. We present a new precoding method for translating words with a maximum run of k zeros into words with a maximum homopolymer run m = k + 1, which is atractive for securing GC-AT balance. Generating functions are presented for e...
Preprint
Mobile edge computing (MEC) provides computational services at the edge of networks by offloading tasks from user equipments (UEs). This letter employs an unmanned aerial vehicle (UAV) as the edge computing server to execute offloaded tasks from the ground UEs. We jointly optimize user association, UAV trajectory, and uploading power of each UE to...
Preprint
This letter studies a basic wireless caching network where a source server is connected to a cache-enabled base station (BS) that serves multiple requesting users. A critical problem is how to improve cache hit rate under dynamic content popularity. To solve this problem, the primary contribution of this work is to develop a novel dynamic content u...
Preprint
Full-text available
An indel refers to a single insertion or deletion, while an edit refers to a single insertion, deletion or substitution. In this paper, we investigate codes that combat either a single indel or a single edit and provide linear-time algorithms that encode binary messages into these codes of length n. Over the quaternary alphabet, we provide two line...
Preprint
Full-text available
An indel refers to a single insertion or deletion, while an edit refers to a single insertion, deletion or substitution. In this paper, we investigate codes that combat either a single indel or a single edit and provide linear-time algorithms that encode binary messages into these codes of length n. Over the quaternary alphabet, we provide two line...
Article
By accommodating overlapping transmissions over non-orthogonal resources, non-orthogonal multiple access (NOMA) integrated with massive multiple-input multiple-output (MIMO) can boost spectral efficiency and obtain vast diversity for wireless multiuser systems. However, NOMA requires channel state information (CSI) at the receiver for coherent dete...
Article
In this paper, we analyze the waterfall performance of finite-length low-density parity-check (LDPC) codes for asymmetric memoryless channels by considering variations of channel parameters: the observed bit error rate $P_{\text{obs}}$ and mutual information $I_{\text{obs}}$ during the real-time transmission. Moreover, we propose to use the var...
Article
This work aims to apply the mutual information-maximizing finite alphabet iterative decoding (MIM-FAID) method to decode low-density parity-check (LDPC) codes with high-order modulation. To this end, we propose an efficient model, through which our task becomes to design an MIM quantizer for a binary-input continuous memoryless channel (CMC) with l...
Preprint
Full-text available
First, a new perspective based on binary matrices of placement delivery array (PDA) design was introduced, by which the PDA design problem can be simplified. From this new perspective, and based on some families of combinatorial designs, new schemes with low subpacketization for centralized coded caching problem were constructed. We also give a tec...
Article
Full-text available
We apply the central limit theorem for deriving approximations to the auto-correlation function and power density function (spectrum) of second-order spectral null (dc2-balanced) codes. We show that the auto-correlation function of dc2-balanced codes can be accurately approximated by a cubic function. We show that the difference between the approxi...
Preprint
The practical NAND flash memory suffers from various non-stationary noises that are difficult to be predicted. Furthermore, the data retention noise induced channel offset is unknown during the readback process. This severely affects the data recovery from the memory cell. In this paper, we first propose a novel recurrent neural network (RNN)-based...
Book
Full-text available
In 1989 we organized the first Benelux‐Japan workshop on Information and Communication theory in Eindhoven, the Netherlands. This year, 2019 we celebrate 30 years of our friendship between Asian and European scientists at the AEW11 in Rotterdam, the Netherlands. Many of the 1989 participants are also present at the 2019 event. This year we have man...
Conference Paper
The process of DNA-based data storage (DNA storage for short) can be mathematically modelled as a communication channel, termed DNA storage channel, whose inputs and outputs are sets of unordered sequences. To design error correcting codes for DNA storage channel, a new metric, termed the sequence-subset distance, is introduced, which generalizes t...