Francis C. M. Lau

The Hong Kong Polytechnic University | PolyU · Department of Electronic and Information Engineering

The original online fountain codes discard a large number of symbols that do not meet the requirements at the decoder. To improve channel utilization, this article proposes a new online fountain code. In the completion phase, the proposed code improves the receiving rules of encoded symbols, that is, the encoded symbols discarded in the original on...

In this paper, we investigate the performance of physical-layer network coding (PNC) with hierarchical modulation (HM) over a two-way relay channel (TWRC). While Gray mapping is the optimal for bit-interleaved coded modulation (BICM) systems in point-to-point communications, the superimposed constellation at the relay in PNC transmission does not m...

In this paper, we construct non-binary codes of length N which correct errors under a non-binary segment-N maxburst-D deletion and maxburst-S insertion (NB-SBDI( $N,D,S$ )) channel without knowing the codeword boundaries. In this NB-SBDI( $N,D,S$ ) channel, at most a single non-binary burst (a block of consecutive bits/symbols) of deletions or in...

In this paper, the joint downlink delay-aware scheduling in a large time span, where the rotation of User Equipments (UEs) may lead to significant channel variation, is investigated via a novel approximate Markov Decision Process (MDP) method. Specifically, we consider the joint downlink power allocation and receiving UE selection of a number of su...

Wireless sensor networks (WSNs) leveraging millimeter wave (mmWave) communication for bandwidth-demanding applications is considered in this paper. Despite the large bandwidth, the delivery of delay-sensitive information collected by sensors may still face significant latency due to the vulnerability to intermittent link blockage. Hence, the guaran...

In this paper, we present a coding method called expanding-window zigzag decodable fountain code with unequal error protection property (EWF-ZD UEP code) to achieve scalable multimedia transmission. The key idea of the EWF-ZD UEP code is to utilize bit-shift operation and expanding-window strategy to improve the decoding performance of the high-pri...

In this paper, we propose a novel joint source-channel code (JSCC) called spatially-coupled double-protograph-based low-density parity-check (SC-DP-LDPC) code. The SC-DP-LDPC code consists of a source spatially-coupled protograph-based low-density parity-check (SC-P-LDPC) code and a channel SC-P-LDPC code. Moreover, the two corresponding protomatri...

In this paper, we first propose a novel joint source-channel block code (JSC-BC) in which two protograph-based low-density parity-check (P-LDPC) block codes are connected not only by a source-variable-channel-check (SVCC) linking matrix, but also by a source-check-channel-variable (SCCV) linking matrix that consists of a zero matrix and a lower or...

We propose the use of a lower or upper triangular sub-base matrix to replace the identity matrix in the source-check-channel-variable linking protomatrix of a double-protograph low-density parity-check joint-source-channel code (DP-LDPC JSCC). The elements along the diagonal of the proposed lower or upper triangular sub-base matrix are assigned as...

In this work, we develop a pair of rate-diverse encoder and decoder for a two-user Gaussian multiple access channel (GMAC). The proposed scheme enables the users to transmit with the same codeword length but different coding rates under diverse user channel conditions. First, we propose the row-combining (RC) method and row-extending (RE) method to...

Device-to-device (D2D) communications can allow different devices to communicate in short range, which greatly meets the demand of effective transmissions. In this paper, a spectral and energy-efficient carrier index keying-aided M -ary differential chaos cyclic shift keying (CIK-MDCCSK) system is proposed for D2D communications, where multiple c...

Protograph-based low-density parity-check Hadamard codes (PLDPC-HCs) are a new type of ultimate-Shannon-limit-approaching codes. In this paper, we propose a hardware architecture for the PLDPC-HC layered decoders. The decoders consist mainly of random address memories, Hadamard sub-decoders and control logics. Two types of pipelined structures are...

In this paper, we propose a doping approach to lower the error floor of Low-Density Parity-Check (LDPC) codes. The doping component is a short block code in which the information bits are selected from the coded bits of the dominant trapping sets of the LDPC code. Accordingly, an algorithm for selecting the information bits of the short code is pro...

Spectrum sharing in a cognitive radio system involves a secondary user updating transmit power for sharing spectrum with a primary user. The deep $Q$ -network in the framework of deep reinforcement learning achieves transmit power control by a deep neural network for learning a nonlinear mapping from states to $Q$ -values. Since a deep neural n...

Heterogeneous cellular networks (HetNets), where low-power low-complexity base stations (Pico-BSs) are deployed inside the coverage of macro base stations (Macro-BSs), can significantly improve the spectrum efficiency by Pico- and Macro base station collaboration. Due to cross-tier interference, joint detection of uplink signals is widely adopted s...

In this letter, we study turbo product codes with quadratic residue codes (called QR-TPCs) as the component codes. We propose an efficient decoder based on Chase-II algorithm with two convergence conditions for the iterative decoding of QR-TPCs. For each row and column, the Chase-II decoder will stop immediately when one of the conditions is met. T...

Combining powerful error-correction codes (ECCs) with multipulse pulse-position modulation (MPPM) has great potential to realize high-throughput and high-reliability transmissions in free-space optical (FSO) communication systems. This paper conducts an insightful investigation on protograph low-density parity-check (PLDPC)-coded MPPM systems over...

We propose a new type of ultimate-Shannon-limit-approaching codes called spatially coupled protograph-based low-density parity-check Hadamard convolutional codes (SC-PLDPCH-CCs), which are constructed by spatially coupling PLDPC-Hadamard block codes. We develop an efficient decoding algorithm that combines pipeline decoding and layered scheduling f...

In this paper, a low-complexity decoder based on a neural network is proposed to decode binary quadratic residue (QR) codes. The proposed decoder is based on the neural min-sum algorithm and the modified random redundant decoder (mRRD) algorithm. This new method has the same asymptotic time complexity as the min-sum algorithm, which is much lower t...

By combining bit‐shift and exclusive‐or operations, a weighted zigzag decodable fountain code is proposed to achieve an unequal error protection property. In the proposed scheme, the input symbols of different importance levels are first pre‐coded into variable nodes using low‐density parity‐check codes. Then, bit‐shift operations prior to exclusiv...

Device-to-device (D2D) communication is a promising technology which can improve the spectrum efficiency of cellular networks. Despite abundant research on resource allocation and interference cancellation for D2D communication, few works discuss how D2D is realized within cellular communication. In this paper, we propose a symmetric cooperative co...

As an established bandwidth-efficient coded modulation technique, bit-interleaved coded modulation (BICM) can achieve very desirable error performance with relatively low implementation complexity for a large number of communication and storage systems. It attracted considerable attention from the research community in the past three decades. The B...

A low overhead fountain code with an unequal error protection property, called duplicated-zigzag unequal-error-protection (DZ-UEP) code, is proposed. Using low-density-parity-check codes of different code rates, input symbols of different important levels are first precoded into variable nodes. Based on predefined duplication factors, these variabl...

Recent studies have revealed that neural combinatorial optimization (NCO) has advantages over conventional algorithms in many combinatorial optimization problems such as routing, but it is less efficient for more complicated optimization tasks such as packing which involves mutually conditioned action spaces. In this paper, we propose a Recurrent C...

The huge amount of data produced in the 6G networks not only brings new challenges to the reliability and efficiency of mobile devices but also drives rapid development of new storage techniques. With the benefits of fast access speed and high reliability, NAND flash memory has become a promising storage solution for the 6G networks. In this paper,...

Recent studies have revealed that neural combinatorial optimization (NCO) has advantages over conventional algorithms in many combinatorial optimization problems such as routing, but it is less efficient for more complicated optimization tasks such as packing which involves mutually conditioned action spaces. In this paper, we propose a Recurrent C...

Protograph-based low-density parity-check Hadamard codes (PLDPC-HCs) are a new type of ultimate-Shannon-limit-approaching codes. In this paper, we propose a hardware architecture for the PLDPC-HC layered decoders. The decoders consist mainly of random address memories, Hadamard sub-decoders and control logics. Two types of pipelined structures are...

In this paper, we propose a new type of ultimate-Shannon-limit-approaching codes called spatially coupled protograph-based low-density parity-check Hadamard convolutional codes (SC-PLDPCH-CCs), which are constructed by spatially coupling PLDPC-Hadamard block codes. We also develop an efficient decoding algorithm that combines pipeline decoding and...

Job dispatching is a fundamental problem in edge computing for load balancing among multiple edge servers. When implementing an edge computing system with distributed job dispatchers in a sizable network, such as a metropolitan area network (MAN), the highly dynamic transmission latency is nonnegligible, which could lead to outdated information bei...

Humankind is generating digital data at an exponential rate. These data are typically stored using electronic, magnetic or optical devices, which require large physical spaces and cannot last for a very long time. Here we report the use of peptide sequences for data storage, which can be durable and of high storage density. With the selection of su...

The Bulk Synchronous Parallel (BSP) paradigm is gaining tremendous importance recently due to the popularity of computations as distributed machine learning and graph computation. In a typical BSP job, multiple workers concurrently conduct iterative computations, where frequent synchronization is required. Therefore, the workers should be scheduled...

In this paper, we investigate distributed broadcasting in dynamic networks, where the topology changes continually over time. We propose a network model that captures the dynamicity caused by both churn and mobility of nodes. In contrast to existing work on dynamic networks, our model defines the dynamicity in terms of localized topological changes...

From the beginning of civilization, the media for storing data have been continuously evolving from such as stone tablets, animal bones and bamboo tablets to paper, with improvements on data density over time. Since the invention of electronics in the last century, the percentage of data stored in digital form has been increasing rapidly to almost...

In this paper, we propose a new method to design low-density parity-check Hadamard (LDPC-Hadamard) codes — a type of ultimate-Shannon-limit approaching channel codes. The technique is based on applying Hadamard constraints to the check nodes in a generalized protograph-based LDPC code, followed by lifting the generalized protograph. We name the cod...

In this paper, we study distributed algorithms to realize efficient communications under the Rayleigh-fading model. This model extends the popular deterministic SINR model using stochastic propagations to address the fading effects observed in reality. Stochastic propagations can greatly increase the difficulty of handling interference and collisio...

The huge amount of data produced in the fifth-generation (5G) networks not only brings new challenges to the reliability and efficiency of mobile devices but also drives rapid development of new storage techniques. With the benefits of fast access speed and high reliability, NAND flash memory has become a promising storage solution for the 5G netwo...

In this work, we develop a pair of rate-diverse encoder and decoder for a two-user Gaussian multiple access channel (GMAC). The proposed scheme enables the users to transmit with the same codeword length but different coding rates under diverse user channel conditions. First, we propose the row-combining (RC) method and row-extending (RE) method to...

In this paper, we propose a layered decoding algorithm for protograph-based low-density parity-check Hadamard codes (PLDPC-HCs), which have been shown to be ultimate-Shannon-limit approaching. Compared with the standard decoding algorithm, the layered decoding algorithm improves the convergence rate by about two times. At a bit error rate of 2.0 ×...

In this paper, we investigate online distributed job dispatching in an edge computing system residing in a Metropolitan Area Network (MAN). Specifically, job dispatchers are implemented on access points (APs) which collect jobs from mobile users and distribute each job to a server at the edge or the cloud. A signaling mechanism with periodic broadc...

A joint carrier-code index modulation aided Mary differential chaos shift keying (JCCIM-MDCSK) system is proposed in this paper. In the proposed JCCIM-MDCSK system, the carrier and code indices are used to transmit extra carrier and code index bits, respectively. Moreover, the modulating bits are input to multiple M-ary DCSK modulators, and the res...

In a joint source-channel coding (JSCC) system, excessive source compression can cause an error floor. In the original JSCC scheme based on double protograph LDPC (DPLDPC) codes, only connections exist between check nodes (CNs) of the source protograph and variable nodes (VNs) of the channel protograph, and error floors are observed. In this paper,...

In this paper, we propose a new method to design low-density parity-check Hadamard (LDPC-Hadamard) codes, a type of ultimate-Shannon-limit approaching channel codes. The technique is based on applying Hadamard constraints to the check nodes in a generalized protograph-based LDPC code, followed by lifting the generalized protograph. We name the code...

Mobile sensor networks (MSNs) are good candidates for large-scale unattended surveillance applications. However, it is challenging to track moving targets due to their complex dynamic behaviors. Semiflocking algorithms have been proven to be efficient in controlling MSNs in both area coverage and target tracking applications. While many existing li...

Cognitive radio networks (CRNs) have been proposed to solve the spectrum scarcity problem. One of their fundamental procedures is to construct a communication link on a common channel for the users, which is referred to as rendezvous . In reality, the capability to sense the spectrum may vary from user to user. We study distributed rendezvous for...

Dynamicity is one of the most challenging, yet, key aspects of wireless networks. It can come in many guises, such as churn (node insertion/deletion) and node mobility. Although the study of dynamic networks has been popular in distributed computing domain, previous works considered only partial factors causing dynamicity. In this work, we propose...

In this work we introduce an automatic stream computing re-optimization flow from ASICs to FPGAs. Complex VLSI designs need to be prototyped and/or emulated on Field Programmable Gate Arrays (FPGA). The main problem that we address in this work is that configurations optimized when targeting ASICs are often, as we will show in this work, highly un-...

Synthetic deoxyribonucleic acid (DNA) is a good medium for storing digital data for a long period due to its achievable high data storage density and outstanding longevity. However, synthesizing and sequencing DNA sequences in a DNA storage system are prone to a wide variety of errors, including insertion, deletion and mutation errors. At the same...

Both turbo Hadamard codes and concatenated zigzag Hadamard codes are ultimate-Shannonlimit-approaching channel codes. The former one requires the use of Bahl-Cocke-Jelinek-Raviv (BCJR) in the iterative decoding process, making the decoder structure more complex and limiting its throughput. The latter one, however, does not involve BCJR decoding. He...

A turbo-Hadamard code (THC) is a type of low-rate channel code with capacity approaching the ultimate Shannon limit, i.e., -1.59 dB. In this brief, we investigate the hardware design of a turbo-Hadamard encoder/decoder system. The entire system has been implemented on an FPGA board. A bit error rate (BER) of 10 <sup xmlns:mml="http://www.w3.org/199...

In edge-cloud computing, a set of servers (called edge servers) are deployed near the mobile devices to allow these devices to offload their jobs to and subsequently obtain their results from the edge servers with low latency. One fundamental problem in edge-cloud systems is how to dispatch and schedule the jobs so that the job response time (defin...

As a typical example of bandwidth-efficient techniques, bit-interleaved coded modulation with iterative decoding (BICM-ID) provides desirable spectral efficiencies in various wireless communication scenarios. In this paper, we carry out a comprehensive investigation on tail-biting (TB) spatially coupled protograph (SCP) low-density parity-check (LD...

As a typical example of bandwidth-efficient techniques, bit-interleaved coded modulation with iterative decoding (BICM-ID) provides desirable spectral efficiencies in various wireless communication scenarios. In this paper, we carry out a comprehensive investigation on tail-biting (TB) spatially coupled protograph (SC-P) low-density parity-check (L...

In this letter, a joint shuffled scheduling decoding algorithm for double-protograph low-density parity-check (DP-LDPC) codes-based joint source-channel coding (JSCC) schemes is presented. The proposed algorithm adopts the shuffled scheduling method to both source decoder and channel decoder, and can improve convergence speed and reduce the decodin...

This paper presents a nonbinary adaptive 2D scheduling-based majority logic decoding (NB-ATS-MLGD) algorithm for NAND flash memory. The proposed algorithms provide considerable tradeoff between error-correcting capability and decoding complexity, and make the NB-MLGD decoding more attractive for practical purposes in the multi-level cells (MLC) NAN...

This paper proposes a cooperative nonorthogonal multiple access (CNOMA) scheme in a full-duplex (FD) relaying cognitive radio network (CRN), where a primary user (PU) communicates with the base station under the assistance of a secondary user (SU), in order to sufficiently utilize both idle and underutilized spectrum resources. When the PU does not...

As a bandwidth-efficient technique, bit-interleaved coded modulation with iterative demapping and decoding (BICM-ID) has attracted much research attention in the field of wireless communication. In this paper, we put forth a joint design of root-protograph (RP) low-density parity-check (LDPC) codes and BICM-ID, referred to as RP-based BICM-ID (RP-B...

One of the advantages of High-Level Synthesis (HLS), also called C-based VLSI-design, over traditional RT-level VLSI design flows, is that multiple micro-architectures of unique area vs. performance can be automatically generated by setting different synthesis options, typically in the form of synthesis directives specified as pragmas in the source...

Mobile sensor networks (MSNs) are utilized in many sensing applications that require both target seeking and tracking capabilities. Dynamics of mobile agents and the interactions among them introduce new challenges in designing robust cooperative control mechanisms. In this paper, a distributed semiflocking algorithm inspired by Temnothorax albipen...

Neighbor discovery is a crucial operation frequently executed throughout the life cycle of a Wireless Sensor Network (WSN). Various protocols have been proposed to minimize the discovery latency or to prolong the lifetime of sensors. However, none of them have addressed that all the critical concerns stemming from real WSNs, including communication...

A block-fading (BF) channel, also known as a slow-fading channel, is a type of simple and practical channel model that can characterize the primary feature of a number of wireless-communication applications with low to moderate mobility. Although BF channels have received significant research attention in the past 20 years, designing low-complexity...

In this letter, we develop an efficient linear programming (LP) decoding algorithm for low-density parity-check (LDPC) codes. The LP relaxation is formulated based on a check-node decomposition approach. Our main contributions are as follows: first, we propose an algorithm based on the alternating direction method of multipliers (ADMM) technique to...

Block-fading (BF) channel, also known as slow-fading channel, is a type of simple and practical channel model that can characterize the primary feature of a number of wireless-communication applications with low to moderate mobility. Although the BF channel has received significant research attention in the past twenty years, designing low-complexi...

To increase program-and-erase (PE) cycles for the multi-level-cell (MLC) NAND flash memory, a page-based dynamic partitioning scheduling (DPS) algorithm for low-density parity-check (LDPC) codes is proposed in this paper. The proposed scheme provides a dynamic scheduling metric to obtain variable nodes (VNs) with the highest erroneous probabilities...

This paper investigates the decoding performance of channel-coded ship-based satellite communications on-themove (SSCOTM) between ships and satellites. In practical communications, ship antennas deviated from satellites by wind waves suffer rapid channel degradation with serious burst errors and even losing all the data. To address this issue, we f...

In this letter, we develop an efficient linear programming (LP) decoding algorithm for low-density parity-check (LDPC) codes. We first relax the maximum likelihood (ML) decoding problem to a LP problem by using check-node decomposition. Then, to solve the resulting LP problem, we propose an efficient iterative algorithm based on the alternating dir...

In this paper, a novel full-duplex cooperative nonorthogonal multiple access (FD CNOMA) system is proposed, where users intend to exchange messages with the assistance of a decode-and-forward relay. To characterize the potential performance gain brought by the proposed FD CNOMA scheme, the outage probability and ergodic rate are analyzed. Specifica...

Uniformly inserting points on the sphere has been found useful in many scientific and engineering fields. Different from the offline version where the number of points is known in advance, we consider the online version of this problem. The requests for point insertion arrive one by one and the target is to insert points as uniformly as possible. T...

In channels that introduce substitution, insertion and deletion errors, one challenging problem for a code designer to overcome is to avoid false code-synchronization. In other words, the probability of a false codeword occurring should be minimized with appropriate code designs. In this paper, we propose a new class of systematic comma-free code c...