arXiv subjects

Dianhua Wu

Publications and source records attributed to Dianhua Wu.

9 recordsLinked to original sources

arXiv2026

A Construction Framework of Coded Caching Scheme for Multi-Access MISO Systems via Knapsack Problem

This paper investigates the coded caching problem in a multi-access multiple-input single-output (MAMISO) network with the combinatorial topology. The considered system consists of a server containing $N$ files, $Λ$ cache nodes, and $K$ cache-less users, where each user can access a unique subset of $r$ cache nodes. The server is equipped with $L$ transmit antennas. Our objective is to design a caching scheme that simultaneously achieves a high sum Degree of Freedom (sum-DoF) and low subpacketization complexity. To address this challenge, we formulate the design of multi-antenna placement delivery arrays (MAPDA) as a $0$--$1$ knapsack problem to maximize the achievable DoF, thereby transforming the complex combinatorial caching structure into a tractable optimization framework that yields efficient cache placement and flexible delivery strategies. Theoretical and numerical analyses demonstrate that: for networks with combinatorial topologies, the proposed scheme achieves a higher sum-DoF than existing schemes. Under identical cache size constraints, the subpacketization level remains comparable to existing linear subpacketization schemes. Moreover, under specific system conditions, the proposed scheme attains the theoretical maximum sum-DoF of $\min\{L+KM/N, K\}$ while achieving further reductions subpacketization. For particular combinatorial structures, we further derive optimized constructions that achieve even higher sum-DoF with lower subpacketization. ```

cs.IT↗

arXiv2025

Rack-Aware MSR Codes with Linear Field Size and Smaller Sub-Packetization for Tolerating Multiple Erasures

In an $(n,k,d)$ rack-aware storage model, the system consists of $n$ nodes uniformly distributed across $\bar{n}$ successive racks, such that each rack contains $u$ nodes of equal capacity and the reconstructive degree satisfies $k=\bar{k}u+v$ where $0\leq v\leq u-1$. Suppose there are $h\geq1$ failed nodes in a rack (called the host rack). Then together with its surviving nodes, the host rack downloads recovery data from $\bar{d}$ helper racks and repairs its failed nodes. In this paper, we focus on studying the rack-aware minimum storage generating (MSR) codes for repairing $h$ failed nodes within the same rack. By using the coupled-layer construction with the alignment technique, we construct the first class of rack-aware MSR codes for all $\bar{k}+1\leq\bar{d}\leq\bar{n}-1$ which achieve the small sub-packetization $l=\bar{s}^{\lceil\bar{n}/\bar{s}\rceil}$ where the field size $q$ increases linearly with $n$ and $\bar{s}=\bar{d}-\bar{k}+1$. In addition, these codes achieve optimal repair bandwidth for $1\leq h\leq u-v$, and asymptotically optimal repair bandwidth for $u-v+1\leq h\leq u$. In particular, they achieve optimal access when $h=u-v$. It is worth noting that the existing rack-aware MSR codes which achieve the same sub-packetization $l=\bar{s}^{\lceil\bar{n}/\bar{s}\rceil}$ are only known for the special case of $\bar{d}=\bar{n}-1$, $h=1$, and the field size is much larger than ours. Then, based on our first construction we further develop another class of explicit rack-aware MSR codes with even smaller sub-packetization $l=\bar{s}^{\lceil\bar{n}/(\bar{s}+1)\rceil}$ for all admissible values of $\bar{d}$.

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arXiv2025

Explicit Constructions for Rack-Aware Minimum Storage Partially Cooperative Regenerating Codes

The rack-aware storage model improves repair efficiency by exploiting locality within racks to minimize cross-rack traffic in a distributed storage system. While the partially cooperative repair model presents a solution for multiple node failures that reduces the need to exchange data with all other host racks (defined as racks containing failed nodes), thus enhancing system flexibility. In this paper, we focus on rack-aware minimum storage partially cooperative regenerating (MSPCR) codes for repairing multiple node failures. We first derive the lower bound on the repair bandwidth for rack-aware MSPCR codes using extremal combinatorics, and then explicitly construct the first class of (asymptotically) optimal repair schemes for rack-aware MSPCR codes with a sub-packetization level of $(\bar{s}+\bar{h}-δ)\bar{s}^{\bar{n}}$, which is smaller than that of the known rack-aware minimum-storage cooperative regenerating (MSCR) codes when $δ\geq 2$. By utilizing the grouping technique, we explicitly construct the second class of (asymptotically) optimal repair schemes for rack-aware MSPCR codes with a sub-packetization level of $2^{\bar{n}}$. In particular, when $δ=1$, our second codes reduce to rack-aware MSCR codes, while achieving an $(\bar{h}+1)$-fold reduction in sub-packetization level compared to the known rack-aware MSCR codes.

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arXiv2025

Order Optimal Cascaded Code Distributed Computing With Low Complexity and Improved Flexibility

Coded distributed computing (CDC), proposed by Li \emph{et al.}, offers significant potential for reducing the communication load in MapReduce computing systems. In cascaded CDC with $K$ nodes, $N$ input files, and $Q$ output functions, each input file will be mapped by $r\geq 1$ nodes and each output function will be computed by $s>1$ nodes such that coding techniques can be applied to generate multicast opportunities. However, a significant limitation of most existing coded distributed computing schemes is their requirement to split the original data into a large number of input files (or output functions) that grows exponentially with $K$, which significantly increases the coding complexity and degrades the system performance. In this paper, we focus on the case of $K/s\in\mathbb{N}$, deliberately designing the strategy of data placement and output functions assignment, such that a low-complexity CDC scheme is achievable. The main advantages of the proposed scheme include: 1) the multicast gains equal to $(r+s-1)(1-1/s)$ and $r+s-1$ which is approximately $r+s-1$ when $s$ is relatively large, and the communication load potentially better than the well-known scheme proposed by Li \emph{et al.}; 2) the proposed scheme requires significantly less input files and output functions; 3) all the operations are implemented over the binary field $\mathbb{F}_2$ with the one-shot fashion (i.e., each node can decode its requested content immediately upon receiving the multicast message during the current time slot). Finally, we derive a new information-theoretic converse bound for the cascaded CDC framework under the proposed strategies of data placement and output functions assignment. We demonstrate that the communication load of the proposed scheme is order optimal within a factor of $2$; and is also approximately optimal when $K$ is sufficiently large for a given $r$.

cs.IT↗

arXiv2023

Asymptotically Optimal Coded Distributed Computing via Combinatorial Designs

Coded distributed computing (CDC) introduced by Li \emph{et al.} can greatly reduce the communication load for MapReduce computing systems. In the general cascaded CDC with $K$ workers, $N$ input files and $Q$ Reduce functions, each input file will be mapped by $r$ workers and each Reduce function will be computed by $s$ workers such that coding techniques can be applied to achieve the maximum multicast gain. The main drawback of most existing CDC schemes is that they require the original data to be split into a large number of input files that grows exponentially with $K$, which can significantly increase the coding complexity and degrade system performance. In this paper, we first use a classic combinatorial structure $t$-design, for any integer $t\geq 2$, to develop a low-complexity and asymptotically optimal CDC with $r=s$. The main advantages of our scheme via $t$-design are two-fold: 1) having much smaller $N$ and $Q$ than the existing schemes under the same parameters $K$, $r$ and $s$; and 2) achieving smaller communication loads compared with the state-of-the-art schemes. Remarkably, unlike the previous schemes that realize on large operation fields, our scheme operates on the minimum binary field $\mathbb{F}_2$. Furthermore, we show that our construction method can incorporate the other combinatorial structures that have a similar property to $t$-design. For instance, we use $t$-GDD to obtain another asymptotically optimal CDC scheme over $\mathbb{F}_2$ that has different parameters from $t$-design. Finally, we show that our construction method can also be used to construct CDC schemes with $r\neq s$ that have small file number and Reduce function number.

cs.IT↗

arXiv2022

Holey Schröder Designs of Type $\bf 3^n u^1$

A holey Schröder design of type $h_1^{n_1}h_4^{n_2}\cdots h^{n_k}_k$ (HSD$(h_1^{n_1}h_4^{n_2}\cdots h^{n_k}_k))$ is equivalent to a frame idempotent Schröder quasigroup (FISQ$(h_1^{n_1}h_4^{n_2}\cdots h^{n_k}_k))$ of order $n$ with $n_i$ missing subquasigroups (holes) of order $h_i, 1 \le i \le k$, which are disjoint and spanning (i.e., $\sum_{1\le i \le k}n_ih_i = n$). The existence of HSD$(h^nu^1)$ for $h=1, 2, 4$ has been known. In this paper, we consider the existence of HSD$(3^nu^1)$ and show that for $0\le u \le 15$, an HSD$(3^nu^1)$ exists if and only if $n(n + 2u -1) \equiv 0~(mod~4)$, $n\ge 4$ and $n\ge 1+2u/3$. For $0 \le u \le n$, an HSD$(3^nu^1)$ exists if and only if $n(n + 2u -1) \equiv 0~(mod~4)$ and $n \ge 4$, with possible exceptions of $n = 29, 43$. We have also found six new HSDs of type $(4^nu^1)$.

math.CO↗

arXiv2021

Constructions and Applications of Perfect Difference Matrices and Perfect Difference Families

Perfect difference families (PDFs for short) are important both in theoretical and in applications. Perfect difference matrices (PDMs for short) and the equivalent structure had been extensively studied and used to construct perfect difference families, radar array and related codes. The necessary condition for the existence of a PDM$(n,m)$ is $m\equiv 1\pmod2$ and $m\geq n+1$. So far, PDM$(3,m)$s exist for odd $5\leq m\leq 201$ with two definite exceptions of $m=9,11$. In this paper, new recursive constructions on PDM$(3,m)$s are investigated, and it is proved that there exist PDM$(3,m)$s for any odd $5\leq m<1000$ with two definite exceptions of $m=9,11$ and $33$ possible exceptions. A complete result of $(g,\{3,4\},1)$-PDFs with the ratio of block size $4$ no less than $\frac{1}{14}$ is obtained. As an application, a complete class of perfect strict optical orthogonal codes with weights $3$ and $4$ is obtained.

cs.IT↗

arXiv2021

On balanced $(Z_{4u}\times Z_{8v},\{4,5\},1)$ difference packings

Let $K$ be a set of positive integers and let $G$ be an additive group. A $(G, K, 1)$ difference packing is a set of subsets of $G$ with sizes from $K$ whose list of differences covers every element of $G$ at most once. It is balanced if the number of blocks of size $k\in K$ does not depend on $k$. In this paper, we determine a balanced $(Z_{4u}\times Z_{8v},{4,5},1)$ difference packing of the largest possible size whenever $uv$ is odd. The corresponding optimal balanced $(4u, 8v,\{4,5\},1)$ optical orthogonal signature pattern codes are also obtained.

math.CO↗

arXiv2014

Multimedia IPP Codes with Efficient Tracing

Binary multimedia identifiable parent property codes (binary $t$-MIPPCs) are used in multimedia fingerprinting schemes where the identification of users taking part in the averaging collusion attack to illegally redistribute content is required. In this paper, we first introduce a binary strong multimedia identifiable parent property code (binary $t$-SMIPPC) whose tracing algorithm is more efficient than that of a binary $t$-MIPPC. Then a composition construction for binary $t$-SMIPPCs from $q$-ary $t$-SMIPPCs is provided. Several infinite series of optimal $q$-ary $t$-SMIPPCs of length $2$ with $t = 2, 3$ are derived from the relationships among $t$-SMIPPCs and other fingerprinting codes, such as $\overline{t}$-separable codes and $t$-MIPPCs. Finally, combinatorial properties of $q$-ary $2$-SMIPPCs of length $3$ are investigated, and optimal $q$-ary $2$-SMIPPCs of length $3$ with $q \equiv 0, 1, 2, 5 \pmod 6$ are constructed.

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