Replication Strategies in Non-Uniform Membership Federated Data Grid Systems

Replica management is currently a major topic to data grid community. This paper first proposed a replication strategy model for federated data grid systems in which sub data grid is not equal-sized. Then, we investigated what is the optimal way to replicate data in non- uniform membership federated data grid, that is, system with storage constraints should make how many replicas for every data to minimize average access latency. Furthermore, we considered the impact of non-uniform membership on system performance. For a replication strategy, we built a mechanism to compare the performance between two data grids. The simulation results showed that the strategy proposed in this paper is superior to LRU strategy, uniform replication strategy, proportional replication strategy and square root replication strategy in wide area network bandwidth requirement and in average access latency of data.     

Resource allocation for multiuser two-way OFDMA relay networks with user rate constraints

This paper studies the resource allocation for a multi-user two-way amplify-and-forward (AF) relay network over orthogonal frequency-division multiplexing (OFDM) technology,where all users communicate with their pre-assigned partners.Using convex optimization techniques,an optimal solution tominimize the total transmit power while satisfy each user-pair’s data rate requirements is proposed.We divide the resource allocation problem into two subproblems:(1) power optimization within user-pair and relay in each subcarrier.(2) optimal subcarrier allocation and sum power assignment among N parallel OFDM subcarriers.Closed-form expressions of the power among user-pair and relay can be obtained in subproblem (1),and so the proposed algorithm decreases the variable dimensionality of the objective function to reduce the complexity of this optimization problem.To solve it,a three-step suboptimal approach is proposed to assign the resources to user-pairs:Firstly,decompose each user-pair into two sub user-pairs which have one-way and two-way relaying transmission modes.Secondly,allocate the subcarriers to the new mode user-pairs and assign the transmit power to each carrier.Thirdly,distribute the assigned power to three nodes allocated in the subcarrier.Simulation results demonstrate the significant power is saved with the proposed solutions,as compared to a fixed subcarrier allocation.     

放大转发协作中继是否提升OFDM/OFDMA遍历容量?(英)

The ergodic information rate for Orthogonal Frequency-Division Multiplexing/ Orthogonal Frequency-Division Multiple Access with amplify-and-forward(AF)relaying systems in the presence of frequency offsets is evaluated.Unlike previous work,per-subcarrier adaptive power allocation is performed on each relay to optimize the system ergodic information rate.For a given frequency offset and total number of relays M,the AF ergodic information rate is proven to be a monotonically increasing function of a(the ratio of the power allocated to the source node and the total transmit power),implying that the maximum ergodic information rate can be obtained at α=1(i.e.,there is no cooperative relay).Furthermore,the proof of "cooperative relays cannot improve the AF ergodic information rate in a quasi-static wireless channel" is also provided in this letter.     

Does Amplify-and-Forward Cooperative Relay Improve OFDM/OFDMA Ergodic Capacity？

The ergodic information rate for Orthogonal Frequency-Division Multiplexing / Orthogonal Frequency-Division Multiple Access with amplify-and-forward （AF） relaying systems in the presence of frequency offsets is evaluated. Unlike previous work, per-subcarrier adaptive power allocation is performed on each relay to optimize the system ergodic information rate. For a given frequency offset and total number of relays M, the AF ergodic information rate is proven to be a monotonically increasing function of α （the ratio of the power allocated to the source node and the total transmit power）, implying that the maximum ergodic information rate can be obtained at α=1 （i.e., there is no cooperative relay）. Furthermore, the proof of ＂cooperative relays cannot improve the AF ergodic information rate in a quasi-static wireless channel＂ is also provided in this letter.     

Optimal power allocation for two-way relaying over OFDM using physical-layer network coding

In this paper,a network scenario of two-way relaying over orthogonal frequency division multiplexing(OFDM) is considered,in which two nodes intend to exchange the information via a relay using physical-layer network coding(PLNC).Assuming that the full channel knowledge is available,an optimization problem,which maximizes the achievable sum rate under a sum-power constraint,is investigated.It is shown that the optimization problem is non-convex,which is difficult to find the global optimum solution in terms of the computational complexity.In consequence,a low-complexity optimal power allocation scheme is proposed for practice implementation.A link capacity diagram is first employed for power allocation on each subcarrier.Subsequently,an equivalent relaxed optimization problem and Karush-Kuhn-Tucker(KKT) conditions are developed for power allocation among each subcarrier.Simulation results demonstrate that the substantial capacity gains are achieved by implementing the proposed schemes efficiently with a low-complexity computational effort.     

Control Structure Analysis and Recovery of Embedded Binaries

Existing decompilers use rule-based algorithms to transform unstructured Control flow graph (CFG) into equivalent high-level programming language constructs with "goto" statements. One problem of such approaches is that they generate a large number of "goto"s in the output code, which reduce the readability and hinder the understanding of input binaries. A global search algorithm is proposed based on structural analysis. This algorithm restructures a CFG and generates fewer number of "goto" statements than the rule-based algorithm does. We also present a Genetic algorithm (GA) for the global search approach to locate near optimal solutions for large CFGs. Evaluation results on a set of real CFGs show that the genetic algorithm-based heuristic for global search is capable of finding high-quality solutions.     

Subcarrier assignment considering path loss for multiuser OFDM systems with proportional fairness

This article studies downlink subcarrier assignment problem to maximize rate-sum capacity subject to total power and proportional rate constraints in orthogonal frequency division multiplexing （OFDM） systems. Previous algorithms assume that the initial power is equally distributed over all subcarriers. The presence of path loss makes the assumption not correct any more. This article proposes a novel subcarrier assignment algorithm which makes full use of path loss and rate proportionality information to improve rate-sum capacity. The proposed algorithm determines optimal initial power allocation according to path losses and rate proportionalities of different users, assigns subcarriers to users in a greedy fashion, and then exchanges subcarfiers between users to obtain fairer rate distribution. Simulation results show that the proposed algorithm approximately achieves double the capacity of static assignment schemes, such as fixed frequency band approach, and obtains better performance than previous subcarrier assignment algorithms in the presence of different path losses and proportional rate requirements..     

Coalition-based downlink resource allocation for LTE system with divide-and-conquer approach

To take advantage of the multiuser diversity resulted from the variation in channel conditions among the users,it has become an interesting and challenging problem to efficiently allocate the resources such as subcarriers,bits,and power.Most of current research concentrates on solving the resource-allocation problem for all users together in a centralized way,which brings about high computational complexity and makes it impractical for real system.Therefore,a coalitional game framework for downlink multi-user resource allocation in long term evolution(LTE) system is proposed,based on the divide-and-conquer idea.The goal is to maximize the overall system data rate under the constraints of each user’s minimal rate requirement and maximal transmit power of base station while considering the fairness among users.In this framework,a coalitional formation algorithm is proposed to achieve optimal coalition formation and a two-user bargaining algorithm is designed to bargain channel assignment between two users.The total computational complexity is greatly reduced in comparison with conventional methods.The simulation results show that the proposed algorithms acquire a good tradeoff between the overall system throughout and fairness,compared to maximal rate and max-min schemes.     

Optimal and Suboptimal Access and Transmission Polices for Dynamic Spectrum Access over Fading Channels in Cognitive Radio Networks

We propose a cross-layer optimal access and transmission framework for dynamic spectrum access to maximize expected long-term average throughput under power and collision constraints by a dynamic programming method namely Constrained Markov decision process （CMDP）. The optimal policy for CMDP is capable of guiding transmitter to choose an available channel and transmission rate at the beginning of each frame for its long-term goals according to current channel sensing results and prior channel fading information. The complexity of finding the optimal policy by Linear programming （LP） approach increases exponentially with the number of channels and fading levels, which incurs so-called curse of dimensionality. Therefore we propose two complexity- reduced suboptimal policies, namely, policy separation and heuristic algorithms. Finally, we compare the performances of policies by numerical results.     

Utility-Based Joint Scheduling Approach Supporting Multiple Services for Co MP-SUMIMO in LTE-A System

In this paper, we study utility-based resource allocation for users supporting multiple services in a LTE-A system with coordinated multi-point transmission for single-user multi-input multi-output(Co MP-SU-MIMO). We designed Joint Transmission Power Control(JTPC) for the selected clusters for minimizing power consumption in LTE-A systems. The objective of JTPC is to calculate the optimal transmission power for each scheduled user and subcarrier. Moreover, based on the convex optimization theory, we propose the dynamic sector selection method in which the average sector throughput and cell-edge users(UEs) rates are performed to achieve the optimal solution. Simulation results show that the system performance achieved by using the proposed suboptimal algorithm is close to that achieved by the dual decomposition method.     

Optimal Rate Allocation Based on Cross-Layer Design and End-to-End Congestion Control in WCDMA Networks

In this paper, a novel idea for rate allocation combining both vertical coupling and horizontal coupling constraints is proposed, and a unified utility function to balance two paradoxical issues: efficiency and fairness, revenue and cost is elaborated in WCDMA networks. Then, the optimal rate allocation problem is formulated as a network utility maximization(NUM) model based on cross-layer design and end-to-end congestion control, aiming at exploring the impacts of wired networks and the characteristics of radio access networks(RANs) on rate allocation. Furthermore, a distributed algorithm is derived, which can effectively match load states between RANs and wired networks, followed by a detailed illustration of the practical implementations. Numerical results demonstrate a signifi cant performance improvement in the end-to-end throughput.     

多天线系统中的二次注水功率分配

Aiming at the problem of resource allocation in multiuser multi-input multi-output （MIMO） systems, a new power allocation algorithm based on dual waterfilling is proposed. Block diagonalization is adopted to cancel the inter-user interference, and then the complete diagonalization method is employed to derive the spatial sub-channels for each user. The overall power of the system is divided among users based on each user＇s large scale fading; then the power of each user is further allocated to its spatial sub-channels based on the small scale fading. Simulation results show that compared with the existing resource allocation strategies, the proposed algorithm can provide more ergodic capacity for multi-user MIMO systems. When the total transmit power is 100w, it has 15% capacity advantage over the traditional waterfilling method.     

Improving Resilience against DDoS Attack in Unstructured P2P Networks

In unstructured peer-to-peer （P2P） systems such as Gnutella, a general routing search algorithm is used to blindly flood a query through network among peers. But unfortunately, malicious nodes could easily make use of the search approach launching distributed denial of service （DDoS） attack which aims at the whole network. In order to alleviate or minimize the bad effect due to behavior of malicious nodes using the flooding search mechanism, the paper proposes a Markov-based evaluation model which exerts the trust and reputation mechanism to computing the level of trustworthy of nodes having the information requested by evaluation of the nodes＇ history behavior. Moreover, it can differentiate malicious nodes as early as possible for isolating and controlling the ones＇ message transmitted. The simulation results of the algorithm proposed show that it could effectively isolate malicious nodes, and hold back the transmission of vicious messages so that it could enhance tolerance of DDoS based on flooding in Guutella-like P2P network.     

Clustering compressed sensing based on image block similarities

Compressed sensing （CS） algorithm enables sampling rates significantly under classical Nyquist rate without sacrificing reconstructed image quality. It is known that, a great number of images have many similar areas which are composed by the same number of grayscale or color. A new CS scheme, namely clustering compressed sensing （CCS）, was proposed for image compression, and it introduces clustering algorithm onto framework of CS based on similarity of image blocks. Instead of processing the image as a whole, the image is firstly divided into small blocks, and then the clustering algorithm was proposed to cluster the similar image blocks. Afterwards, the optimal public image block in each category is selected as the representative for transmission. The discrete wavelet transform （DWT） and Gaussian random matrix are applied to each optimal public image block to obtain the random measurements. Different from equal measurements, the proposed scheme adaptively selects the number of measurements based on different sparsity of image blocks. In order to further improve the performance of the CCS algorithm, the unequal-CCS algorithm based on the characteristics of wavelet coefficients was proposed as well. The low frequency coefficients are retained to ensure the quality of reconstructed image, and the high frequency coefficients are compressed by the CCS algorithm. Experiments on images demonstrate good performances of the proposed approach.     

OFDMA分布式无线接入网络中基于共享标准的资源分布研究

Distributed radio access network (DRAN) is a novel wireless access architecture and can solve the problem of the available spectrum scarcity in wireless communications. In this paper, we investigate resource allocation for the downlink of OFDMA DRAN. Unlike previous exclusive criterion based algorithms that allocate each subcarrier to only one user in the system, the proposed algorithms are based on shared criterion that allow each subcarrier to be allocated to multiple users through different antennas and to only one user through same antenna. First, an adaptive resource allocation algorithm based on shared criterion is proposed to maximize total system rate under each user’s minimal rate and each antenna’s maximal power constraints. Then we improve the above algorithm by considering the influence of the resource allocation scheme on single user. The simulation results show that the shared criterion based algorithm provide much higher total system rate than that of the exclusive criterion based algorithm at the expense of the outage performance and the fairness, while the improved algorithm based on shared criterion can achieve a good tradeoff performance.     

State Estimation for Linear Constrained Systems with Unknown Input

This paper deals with the filtering problem for linear discrete constrained dynamic systems with unknown input. The constraint matrix and constraint vector in this system are allowed to vary in the value and in the dimension. The original full state is separated into two parts, and the estimate of the state is reduced to find the optimal estimate of a singular system. The estimable condition is researched and a recursive estimator for the original full state is presented. A rigorous mathematical induction is given to compare the performance of our approach to that of the existing method without constraint. A numerical example is presented to demonstrate the effectiveness of the new method.     

Optimal transmission mode proportion for heterogeneous networks of cellular and device-to-device communications

This paper discusses about the optimal mode allocation for the heterogeneous networks, in which the network can schedule users working in the device-to-device （D2D） mode or cellular mode. The D2D user is allowed to reuse the uplink resource of cellular system and the problem is formed as a sum-capacity optimization issue with outage constraints for both cellular and D2D links. The method for the optimal user proration is proved to be divided into three cases according to the total user density： when the total user density is small, the optimal proration trends to all users utilizing one mode; when the total user density is large, the optimal proration is all of users choosing D2D mode; and when the total user density situates in the between, there is a unique optimal transmission mode proportion for the hybrid networks to maximize its sumcapacity. The simulation results demonstrate the validity of the conclusions in the analysis part.     

Theil Utility Based Multi-Device Cooperation Mechanism for Service Quality Equilibrium in Ubiquitous Stub Environments

An approach to make heterogeneous devices cooperate with each other to provide ubiquitous service remains a longstanding challenge in ubiquitous environments. In addition, when multi-user request ubiquitous services simultaneously, the arbitrariness in resource allocation process easily leads to non-equilibrium of qualities of multi- user＇s services. Thus, How to design an effective heterogeneous devices cooperation mechanism that meet the QoS requirements and also equilibrate QoS among multi-user＇s services becomes a very tough problem. In the paper, Equilibrium Index and Theil Utility function are imported to establish a multi- device equilibrium cooperation model, which is benefit for resource allocation in ubiquitous environments. Then a Theil-Equilibrium based Cooperation Mechanism for multi-service is proposed. Firstly, in order to simplify calculating, a dimensionless processing is introduced. After that, a cooperation approach with Theil-Utility Heuristic algorithm is designed to choose the best solution for the simplified model. At last, the mechanism is simulated in a smart home scenario. The simulation results show that this mechanism outperforms non-equilibrium method by improving almost 40% in internal equilibrium with just reducing 0-2% in the total utility of all the requested ubiquitous services. These data show that the proposed mechanism performs well in equilibrating qualities of multi-user＇s ubiquitous services.     

Dynamic subcarrier and power allocation based on cooperative game theory in symmetric cooperative OFDMA networks

In order to improve the efficiency and fairness of radio resource utilization,a scheme of dynamic cooperative subcarrier and power allocation based on Nash bargaining solution(NBS-DCSPA) is proposed in the uplink of a three-node symmetric cooperative orthogonal frequency division multiple access(OFDMA) system.In the proposed NBS-DCSPA scheme,resource allocation problem is formulated as a two-person subcarrier and power allocation bargaining game(SPABG) to maximize the system utility,under the constraints of each user’s maximal power and minimal rate,while considering the fairness between the two users.Firstly,the equivalent direct channel gain of the relay link is introduced to decide the transmission mode of each subcarrier.Then,all subcarriers can be dynamically allocated to the two users in terms of their selected transmission mode.After that,the adaptive power allocation scheme combined with dynamic subcarrier allocation is optimized according to NBS.Finally,computer simulation is conducted to show the efficiency and fairness performance of the proposed NBS-DCSPA scheme.     

A Scalable Peer-to-Peer Web Services Overlay for Semantic Discovery

The growing number of web services advocates distributed discovery infrastructures which are semantics-enabled. We introduce a novel approach for semantic discovery of web services in structured P2P-based （Peer-to-Peer） registries. We partition concepts into different CGs （Concept groups） and index these ordered concept sets in a two-phase semantic routing mechanism. Each node and query has one concept set as its unique ID. For each concept in the query, current node first route the query to a node with nodeID that shares a prefix as long as with the query, but a longer CG. Second, the query will be routed to a node sharing a longer prefix than that of the current node. Combining with semantic similarity calculation, our proposal guarantees that most existing services matching a query will be found with bounded costs in terms of number of nodes involved. The scalability and reliability of our approach are also confirmed through emulation tests.