arXiv subjects

Qifa Yan

Publications and source records attributed to Qifa Yan.

27 records · Page 2Linked to original sources

arXiv2018

Constructions of Coded Caching Schemes with Flexible Memory Size

Coded caching scheme recently has become quite popular in the wireless network due to its effectively reducing the transmission amount (denote such an amount by $R$) during peak traffic times. However to realize a coded caching scheme, each file must be divided into $F$ packets which usually increases the computation complexity of a coded caching scheme. So we prefer to construct a caching scheme that decreases the order of $F$ for practical implementations. In this paper, we construct four classes of new schemes where two classes can significantly reduce the value of $F$ by increasing a little $R$ comparing with the well known scheme proposed by Maddah-Ali and Niesen, and $F$ in the other two classes grows sub-exponentially with $K$ by sacrificing more $R$. It is worth noting that a tradeoff between $R$ and $F$, which is a hot topic in the field of caching scheme, is proposed by our constructions. In addition, our constructions include all the results constructed by Yan et al., (IEEE Trans. Inf. Theory 63, 5821-5833, 2017) and some main results obtained by Shangguan et al., (arXiv preprint arXiv:1608.03989v1) as the special cases.

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arXiv2017

On the Placement Delivery Array Design for Coded Caching Scheme in D2D Networks

The coded caching scheme is an efficient technique as a solution to reduce the wireless network burden during the peak times in a Device-to-Device (D2D in short) communications. In a coded caching scheme, each file block should be divided into $F$ packets. It is meaningful to design a coded caching scheme with the rate and $F$ as small as possible, especially in the practice for D2D network. In this paper we first characterize coded caching scheme for D2D network by a simple array called D2D placement delivery array (DPDA in shot). Consequently some coded caching scheme for D2D network can be discussed by means of an appropriate DPDA. Secondly we derive the lower bounds on the rate and $F$ of a DPDA. According these two lower bounds, we show that the previously known determined scheme proposed by Ji et al., (IEEE Trans. Inform. Theory, 62(2): 849-869,2016) reaches our lower bound on the rate, but does not meet the lower bound on $F$ for some parameters. Finally for these parameters, we construct three classes of DPDAs which meet our two lower bounds. Based on these DPDAs, three classes of coded caching scheme with low rate and lower $F$ are obtained for D2D network.

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arXiv2017

On the Placement and Delivery Schemes for Decentralized Coded Caching System

Network based on distributed caching of content is a new architecture to alleviate the ongoing explosive demands for rate of multi-media traffic. In caching networks, coded caching is a recently proposed technique that achieves significant performance gains compared to uncoded caching schemes. In this paper, we derive a lower bound on the average rate with a memory constraint for a family of caching allocation placement and a family of XOR cooperative delivery. The lower bound inspires us how placement and delivery affect the rate memory tradeoff. Based on the clues, we design a new placement and two new delivery algorithms. On one hand, the new placement scheme can allocate the cache more flexibly compared to grouping scheme. On the other hand, the new delivery can exploit more cooperative opportunities compared to the known schemes. The simulations validate our idea.

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arXiv2017

Coded Caching Schemes with Low Rate and Subpacketizations

Coded caching scheme, which is an effective technique to increase the transmission efficiency during peak traffic times, has recently become quite popular among the coding community. Generally rate can be measured to the transmission in the peak traffic times, i.e., this efficiency increases with the decreasing of rate. In order to implement a coded caching scheme, each file in the library must be split in a certain number of packets. And this number directly reflects the complexity of a coded caching scheme, i.e., the complexity increases with the increasing of the packet number. However there exists a tradeoff between the rate and packet number. So it is meaningful to characterize this tradeoff and design the related Pareto-optimal coded caching schemes with respect to both parameters. Recently, a new concept called placement delivery array (PDA) was proposed to characterize the coded caching scheme. However as far as we know no one has yet proved that one of the previously known PDAs is Pareto-optimal. In this paper, we first derive two lower bounds on the rate under the framework of PDA. Consequently, the PDA proposed by Maddah-Ali and Niesen is Pareto-optimal, and a tradeoff between rate and packet number is obtained for some parameters. Then, from the above observations and the view point of combinatorial design, two new classes of Pareto-optimal PDAs are obtained. Based on these PDAs, the schemes with low rate and packet number are obtained. Finally the performance of some previously known PDAs are estimated by comparing with these two classes of schemes.

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arXiv2017

On the Gap Between Decentralized and Centralized Coded Caching Schemes

Caching is a promising solution to satisfy the ongoing explosive demands for multi-media traffics. Recently, Maddah-Ali and Niesen proposed both centralized and de-centralized coded caching schemes, which are able to attain significant performance gains over uncoded caching schemes. Particular, their work indicates that there exists a performance gap between the decentralized coded caching scheme and the centralized coded caching scheme. In this paper, we investigate this gap. As a result, we prove that the multiplicative gap (i.e., the ratio of their performances) is between 1 and 1:5. The upper bound tightens the original one of 12 by Maddah-Ali and Niesen, while the lower bound verifies the intuition that the centralized coded caching scheme always outperforms its decentralized counterpart. Notably, both bounds are achievable in some cases. Furthermore, we prove that the gap can be arbitrarily close to 1 if the number of users is large enough, which suggests the great potential in practical applications to use the less optimal but more practical decentralized coded caching scheme

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arXiv2017

The Optimal Placement Delivery Arrays

In wireless networks, coded caching is an effective technique to reduce network congestion during peak traffic times. Recently, a new concept called placement delivery array (PDA) was proposed to characterize the coded caching scheme. So far, only one class of PDAs by Maddah-Ali and Niesen is known to be optimal. In this paper, we mainly focus on constructing optimal PDAs. Firstly, we derive some lower bounds. Next, we present several infinite classes of PDAs, which are shown to be optimal with respect to the new bounds.

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arXiv2016

On the Placement Delivery Array Design in Centralized Coded Caching Scheme

Caching is a promising solution to satisfy the ever increasing demands for the multi-media traffics. In caching networks, coded caching is a recently proposed technique that achieves significant performance gains over the uncoded caching schemes. However, to implement the coded caching schemes, each file has to be split into $F$ packets, which usually increases exponentially with the number of users $K$. Thus, designing caching schemes that decrease the order of $F$ is meaningful for practical implementations. In this paper, by reviewing the Ali-Niesen caching scheme, the placement delivery array (PDA) design problem is firstly formulated to characterize the placement issue and the delivery issue with a single array. Moreover, we show that, through designing appropriate PDA, new centralized coded caching schemes can be discovered. Secondly, it is shown that the Ali-Niesen scheme corresponds to a special class of PDA, which realizes the best coding gain with the least $F$. Thirdly, we present a new construction of PDA for the centralized caching system, wherein the cache size of each user $M$ (identical cache size is assumed at all users) and the number of files $N$ satisfies $M/N=1/q$ or ${(q-1)}/{q}$ ($q$ is an integer such that $q\geq 2$). The new construction can decrease the required $F$ from the order $O\left(e^{K\cdot\left(\frac{M}{N}\ln \frac{N}{M} +(1-\frac{M}{N})\ln \frac{N}{N-M}\right)}\right)$ of Ali-Niesen scheme to $O\left(e^{K\cdot\frac{M}{N}\ln \frac{N}{M}}\right)$ or $O\left(e^{K\cdot(1-\frac{M}{N})\ln\frac{N}{N-M}}\right)$ respectively, while the coding gain loss is only $1$.

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arXiv2016

On the Coded Caching Delivery Design over Wireless Networks

Coded caching scheme is a promising technique to migrate the network burden in peak hours, which attains more prominent gains than the uncoded caching. The coded caching scheme can be classified into two types, namely, the centralized and the decentralized scheme, according to whether the placement procedures are carefully designed or operated at random. However, most of the previous analysis assumes that the connected links between server and users are error-free. In this paper, we explore the coded caching based delivery design in wireless networks, where all the connected wireless links are different. For both centralized and decentralized cases, we proposed two delivery schemes, namely, the orthogonal delivery scheme and the concurrent delivery scheme. We focus on the transmission time slots spent on satisfying the system requests, and prove that for both the centralized and the decentralized cases, the concurrent delivery always outperforms orthogonal delivery scheme. Furthermore, for the orthogonal delivery scheme, we derive the gap in terms of transmission time between the decentralized and centralized case, which is essentially no more than 1.5.

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arXiv2016

Placement Delivery Array Design through Strong Edge Coloring of Bipartite Graphs

The technique of coded caching proposed by Madddah-Ali and Niesen is a promising approach to alleviate the load of networks during busy times. Recently, placement delivery array (PDA) was presented to characterize both the placement and delivery phase in a single array for the centralized coded caching algorithm. In this paper, we interpret PDA from a new perspective, i.e., the strong edge coloring of bipartite graph. We prove that, a PDA is equivalent to a strong edge colored bipartite graph. Thus, we can construct a class of PDAs from existing structures in bipartite graphs. The class includes the scheme proposed by Maddah-Ali \textit{et al.} and a more general class of PDAs proposed by Shangguan \textit{et al.} as special cases. Moreover, it is capable of generating a lot of PDAs with flexible tradeoff between the sub-packet level and load.

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