In recent years, quality of experience (QoE) has been investigated and proved to have both influential factors on user's visual quality and perceptual quality, while the perceptual quality means user's requirement on personalized content should be acquired in optimized quality. That's to say, those segments holding user interested content such as highlights need to be allocated more network resource in a resource-limited streaming scenario. However, all the existing HTTP-based adaptive methods only focus the content-agnostic bitrate adaptation according to limited network resources or energy resource, since they ignored user perceived semantics on some important segments, which suffered less quality on the important segments than on those ordinary ones, so as to hurt the overall QoE. In this paper, we have proposed a new semantic-aware adaptation scheme for MPEG-DASH services, which decides how to preserve bandwidth and buffering time depending on content descriptors for the perceived important content to users. Further, a semantic-aware probe and adaptation (SMA-PANDA) algorithm has been implemented in a DASH client to compare with conventional bitrate adaptions. Preliminary results show that SMA-PANDA achieves better QoE and flexibility on streaming user's interested content on MPEG-DASH platform, and it also aggressively helps user interested content compete more resource to deliver high quality presentation.

Network coding (NC) consists of intelligently aggregating data packets by means of binary or linear combinations. NC has been considered as one of the possible solutions to the current low throughput, energy consumption, packet loss, non-connectivity and mobility support problems in MANETs. Sliding-window Network Coding is a variation of NC that is an addition to TCP/IP and improves the throughput of TCP on wireless networks. In this paper, we propose a Variable Length Sliding Window-based Network Coding algorithm in MANETs (VLSW-NC). The performance of this VLSW-NC is studied using NS2 and evaluated in terms of the throughput, packet loss probability, and decoding delay when packet is transmitted. The simulations results shows that the VLSW-NC achieved with our proposition can significantly improve the network performance and reliability.

The paper presents novel content-aware adaptation schemes for QoE optimized HTTP-based adaptive video streaming services. In recent years, content type has been investigated and proofed to have a deep influence on user's acceptable quality of experience (QoE). However, most of the existing HTTP-based adaptive video strategies only conduct bitrate switching according to network resources without a consideration of video content types. This may cause a non-optimal network resource allocation which may not achieve the optimized QoE for delivered video streaming services. In this paper, we proposed two content-aware adaptation schemes, named as Content-aware Probe and Adapt (C-PANDA) and Content-aware Dynamic Programming (C-DP), which are able to decide the video bitrate for the next video segment, based on not only the available bandwidth, the existing buffer capacity, but also the video content type. We implemented both content-aware adaptation algorithms in player prototypes based on libdash 3.0 library. Preliminary results show that content-aware adaptation schemes achieve better QoE when compared with conventional PANDA scheme. The proposed schemes are able to optimize QoE according to contents. They can achieve higher than acceptable QoE for most attractive contents such as those with high motion intensity to improve user experience for the most interesting scenes; select same video representations for segments belonging to a scene to avoid quality oscillation; and reserve buffer resource during low motion scenes to avoid stalling for the following high motion scenes. The work will be helpful in designing QoE-aware DASH schemes in the future.

Emerging non-volatile memory technologies, especially flash-based solid state drives (SSDs), have increasingly been adopted in the storage stack. They provide numerous advantages over traditional mechanically rotating hard disk drives (HDDs) and have a tendency to replace HDDs. Due to the long existence of HDDs as primary building blocks for storage systems, however, much of the system software has been specially designed for HDD and may not be optimal for non-volatile memory media. Therefore, in order to realistically leverage its superior raw performance to the maximum, the existing upper layer software has to be re-evaluated or re-designed. To this end, in this paper, we propose PASS, an optimized I/O scheduler at the Linux block layer to accommodate the changing trend of underlying storage devices toward flash-based SSDs. PASS takes the rich internal parallelism in SSDs into account when dispatching requests to the device driver in order to achieve high performance. Specifically, it partitions the logical storage space into fixed-size regions (preferably the component package sizes) as scheduling units. These scheduling units are serviced in a round-robin manner and for every chance that the chosen dispatching unit issues only a batch of either read or write requests to suppress the excessive mutual interference. Additionally, the requests are sorted according to their visiting addresses while waiting in the dispatching queues to exploit high sequential performance of SSD. The experimental results with a variety of workloads have shown that PASS outperforms the four Linux off-the-shelf I/O schedulers by a degree of 3% up to 41%, while at the same time it improves the lifetime significantly, due to reducing the internal write amplification.

Due to the ignorance of the relation between different collisions, traditional medium access control protocols cant achieve their anticipated collision resolution results. This paper proposes a novel way to distribute MAC accesses in MANETs based on collision classification approach and modified backoff schemes. The idea is to avoid cross collisions through dynamically allocated elementary windows which prevent intersection of spaces in which the backoff counters are decremented. It develops a policy to select an appropriate backoff value as a function of retransmission attempts, observed number of collisions etc. to minimize repeated collisions, and thus improves throughput, delay jitter, as well as fairness. The performance improvement is demonstrated convincingly using a wide range of simulations.

Traditional backoff algorithms in distributed contention-based MAC protocols adopt contention window scheme for collision resolution. Collided nodes are redistributed in extended windows to avoid further collision. However, collision may still occur due to intersecting window ranges. In this paper, we propose an effective backoff algorithm featuring collision-free collision classification resolution (CF-CCR) based on collision classification model to resolve different collisions with different manners. Under the schedule of CF-CCR, the network will ultimately converges to a collision free state, in which nodes access channel sequentially with no collision occurred. The simulation results show that CF-CCR outperforms IEEE 802.11 DCF in collision times, throughput, delay and fairness.

Backoff algorithms in traditional distributed contention-based MAC protocols concentrate on adjusting contention window size to resolve collision. However, collision may still occur as long as these windows intersect with each other. In order to solve this problem, we put forward a collision classification model to classify collisions into cross collision and intra collision and suggest to solve them with different manners. Based on this model, we propose collision classification resolution (CCR) algorithm to dynamically allocate discrete distribution windows for collided nodes to avoid cross collision, and the intra collision is resolved with an appropriate distribution window size to achieve a tradeoff between delay and collision probability. The extensive simulations performed demonstrate that compared to IEEE 802.11 DCF, CCR algorithm consistently excels, in terms of collision times, throughput, delay and fairness.

In many applications of sensor networks, security is a very important issue. To be resistant against the various attacks, nodes in a sensor network can establish pairwise secret keys[5], [6], [10], authenticate all communications with cryptographic functions[8], and also apply secure information aggregation schemes[13] or hop-by-hop filtering methods[14], [16]. However, these security measures can take considerable overhead in terms of storage, communication and computation, which are scarce resources in sensor nodes. Previously proposed security measures can only resist against a limited number of compromised nodes, which we define as the resistance level. In this paper, we propose a separate solution to any security measure. This technique either significantly reduces the overhead, or increases the resistance level without increasing overhead. The solution is based on a new "Mixed Multi-Channel" (MMC) architecture. In this design, each node can only use one fixed channel. The whole network is thus divided into multiple "planes" by the different planes. Exploiting the characteristics of multi-channel communication, a series of methods are proposed, such as MMC-1, MMC-k and MMC-r. We then present designs to integrate the methods with current security measures, and analyze their resistance level and energy conservation.

Surveillance has been a typical application of wireless sensor networks. To conduct surveillance of a given area in real life, one can use stationary watch towers, or can also use patrolling sentinels. Comparing them to solutions in sensor network surveillance, all current coverage based methods fall into the first category. In this paper, we propose and study patrol-based surveillance operations in sensor networks. Two patrol models are presented: the coverage-oriented patrol and the on-demand patrol. They achieve one of the following goals, respectively, i) to achieve surveillance of the entire field with low power drain but still bounded delay of detection; ii) to use an on-demand manner to achieve user initiated surveillance only to interested places. We propose the "SENSTROL" protocol to fulfill the patrol setup procedure for both models. With the implementation in the GloMoSim simulator, it is shown that patrol on arbitrary path can be set up in a network where each node follows a 98%-time-sleep-2%-time-wake power schedule.

A Mobile Ad hoc NETwork (MANET) is an autonomous system of mobile nodes connected by wireless links. There is no static infrastructure such as base station as that was in cell mobile communication. Due to the dynamic nature of the network topology and restricted resources, quality of service (QoS) and multicast routing in MANET is a challenging task. In this paper, we present an entropy-based model to support QoS multicast routing optimization algorithm in mobile ad hoc networks (EQMOA). The basic motivations of the proposed modeling approach stem from the commonality observed in the location uncertainty in mobile ad hoc wireless networks and the concept of entropy. The simulation results demonstrate that the proposed approach and parameters provide an accurate and efficient method of estimating and evaluating the route stability in dynamic mobile networks.

Many potential applications of mobile ad hoc networks (MANETs) involve group communications among the nodes. Multicasting is an useful operation that facilitates group communications. Efficient and scalable multicast routing in MANETs is a difficult issue. In addition to the conventional multicast routing algorithms, recent protocols have adopted the following new approaches: overlays, backbone-based, and stateless. In this paper, we study these approaches from the protocol state management point of view, and compare their scalability behaviors. To enhance performance and enable scalability, we have proposed a framework for hierarchical multicasting in MANET environments. Two classes of hierarchical multicasting approaches, termed as domain-based and overlay-based, are proposed. We have considered a variety of approaches that are suitable for different mobility patterns and multicast group sizes. Results obtained through simulations demonstrate enhanced performance and scalability of the proposed techniques

Target tracking is an important application of wireless sensor networks. In this application, the sensor nodes collectively monitor and track the movement of an event or target object. The network operations have two states: the surveillance state during the absence of any event of interest, and the tracking state which is in response to any moving targets. Thus, the power saving operations, which is of critical importance for extending network lifetime, should be operative in two different modes as well. In this paper, we study the power saving operations in both states of network operations. During surveillance state, a set of novel metrics for quality of surveillance is proposed specifically for detecting moving objects. In the tracking state, we propose a collaborative messaging scheme that wakes up and shuts down the sensor nodes with spatial and temporal preciseness. This study, which is a combination of theoretical analysis and simulated evaluations, quantifies the trade-off between power conservation and quality of surveillance while presenting guidelines for efficient deployment of sensor nodes for target tracking application.

On demand routing protocols provide scalable and cost-effective solutions for packet routing in mobile wireless ad hoc networks. The paths generated by these protocols may deviate far from the optimal because of the lack of knowledge about the global topology and the mobility of nodes. Routing optimality affects network performance and energy consumption, especially when the load is high. In this paper, we define routing optimality using different metrics such as path length, energy consumption along the path, and energy aware load balancing among the nodes. We then propose a framework of Self-Healing and Optimizing Routing Techniques (SHORT) for mobile ad hoc networks. While using SHORT, all the neighboring nodes monitor the route and try to optimize it if and when a better local sub-path is available. Thus SHORT enhances performance in terms of bandwidth and latency without incurring any significant additional cost. In addition, SHORT can be also used to determine paths that result in low energy consumption or optimize the residual battery power. Thus, we have detailed two broad classes of SHORT algorithms: Path-Aware SHORT and Energy-Aware SHORT. Finally, we evaluate SHORT using the ns-2 simulator. The results demonstrate that the performance of existing routing schemes can be significantly improved using the proposed SHORT algorithms.

Overlay multicast protocol builds a virtual mesh spanning all member nodes of a multicast group. It employs standard unicast routing and forwarding to fulfill multicast functionality. The advantages of this approach are robustness and low overhead. However, efficiency is an issue since the generated multicast trees are normally not optimized in terms of total link cost and data delivery delay. In this paper, we propose an efficient overlay multicast protocol to tackle this problem in MANET environment. The virtual topology gradually adapts to the changes in underlying network topology in a fully distributed manner. A novel source-based Steiner tree algorithm is proposed for constructing the multicast tree. The multicast tree is progressively adjusted according to the latest local topology information. Simulations are conducted to evaluate the tree quality. The results show that our approach solves the efficiency problem effectively.