In this paper, we propose a new localization algorithm and improve the DV-Hop algorithm by using a differential error correction scheme that is designed to reduce the location error accumulated over multiple hops. This scheme needs no additional hardware support and can be implemented in a distributed way. The proposed method can improve location accuracy without increasing communication traffic and computing complexity. Simulation results show the performance of the proposed algorithm is superior to that of the DV-Hop algorithm.

End-to-end delay and loss measurement is an efficient way for a host to examine the network performance. Unnoticed clock errors that influence the accuracy of the timestamp may result in fatal system errors. In this paper, we discuss the characteristics and defects of the existing clock distortion adjustment algorithms. Those algorithms are not applicable to process a long-term delay trace, which contains periodical NTP clock adjustment. Therefore, we propose a relatively robust algorithm to resolve the problem. The algorithm employs window function to partition the long-term trace into short segments, improves the precision of the estimation of the time and amount of NTP clock adjustment To evaluate the performance of our proposed algorithm, we practice it in adjusting the clock distortion of the real delay traces collected from Internet. The results indicate that our proposed algorithm has excellent effect on the removal of the clock distortion from the long-term delay traces.

WDM optical networks represent the future direction of high capacity wide-area network applications. By creating optical paths between several nodes in the core networks, a logical topology can be created over the physical topology. By reconfiguring the logical topology, network resource utilization can be optimized corresponding to traffic pattern changes. From the viewpoint of network operation, the complexity of reconfiguration should be minimized as well. In this paper we consider the logical topology reconfiguration in arbitrary topology IP over WDM networks with balancing between network performance and operation complexity. The exact formulation of the logical topology reconfiguration problem is usually represented as Mixed Integer Linear Programming, but it grows intractable with increasing network size. Here we propose a simulated annealing approach in order to both determine the target topology with a smaller logical topology change and also satisfy the performance requirement. A threshold on the congestion performance requirement is used to balance the optimal congestion requirement and operation complexity. This is achieved by tuning this threshold to a feasible value. For effective solution discovery, a two-stage SA algorithm is developed for multiple objectives optimization.

Collecting environmental sound by utilizing high-end mobile phones provides us opportunities to capture rich contextual information in real world. The gathered information can be used for various purposes, ranging from academic research to livelihood support. Furthermore, mobility of mobile phones opens a door for easily forming a dynamic sensing infrastructure, in order to gather fine-grained, but still large-scale data from both spatial and temporal perspectives. However, collecting, analyzing, storing, and sharing of sound data usually involve large energy consumption than scalar data, and like any battery-operated device, mobile phones also face the reality of energy constraints. Because people's first priorities are naturally to use mobile phones for their own purposes, there are occasions when people will not be inclined to allow their mobile phones to be used as sensing devices fearing that they will run out of batteries. Therefore, our research focuses on energy-efficient sensing, to reduce average energy consumption and to extend overall system lifetime. In this paper, we propose a node scheduling scheme for mobile nodes. By applying this scheme, optimized sensing schedules (ACTIVE/SLEEP duty cycles) will be periodically generated at each node. Following the provided schedule during sensing, energy-efficiency can be realized while original Quality of Service (i.e. coverage rate) is retained. Unlike most previous works which were based on ideal binary disk coverage model, our proposal is designed under a probabilistic disk coverage model which takes the characteristic of sound propagation into consideration. Furthermore, this is the first scheme that is adaptable to large-scale mobile sensor networks where topology dynamically changes. An accurate energy consumption model is adopted for evaluating the proposed scheme. Simulation results show that our scheme can reduce up to 48% energy consumption in an ideal environment and up to 31% energy consumption in a realistic environment. The robustness of our scheme is also verified against different type of sensing terrains and communication environments.

Participatory sensing is an emerging system that allows the increasing number of smartphone users to share effectively the minute statistical information collected by themselves. This system relies on participants' active contribution including intentional input data. However, a number of privacy concerns will hinder the spread of participatory sensing applications. It is difficult for resource-constrained mobile phones to rely on complicated encryption schemes. We should prepare a privacy-preserving participatory sensing scheme with low computation complexity. Moreover, an environment that can reassure participants and encourage their participation in participatory sensing is strongly required because the quality of the statistical data is dependent on the active contribution of general users. In this article, we present MNS-RRT algorithms, which is the combination of negative surveys and randomized response techniques, for preserving privacy in participatory sensing, with high levels of data integrity. By using our method, participatory sensing applications can deal with a data having two selections in a dimension. We evaluated how this scheme can preserve the privacy while ensuring data integrity.

Wavelength division multiplexed (WDM) routed optical networks represent the direction towards future high-capacity wide-area network applications. A serious issue in WDM-routed networks, though, is light-path allocation which requires a combination of optical routing and wavelength assignment. While near-optimal-routing and wavelength-assignment algorithms aimed at minimizing network wavelength requirements have been reported, the practicability of wavelength-routed optical networks depends on the number of wavelengths required to satisfy a given traffic demand. In this paper, we proposed two symmetrical routing and wavelength-assignment methods for optical networks with a Grid or ShuffleNet physical topology. Here, we consider the case of non-adaptive wavelength routing systems, where the operations performed in nodes are independent of the network traffic load. In this case, the routing differs somewhat from that in adaptive routing networks where the routing function may produce different results at different times. The path followed by a wavelength never changes in non-adaptive wavelength-routing networks. When all N(N-1) node-pairs are to be connected, our methods lower the wavelength requirement to (or close to) its calculated minimum. Symmetry is a basic feature of both these regular topologies, but there are differences in the features within the topologies. Our goal has been to try to make use of the symmetry, and the differences in the native symmetry features, of these regular topologies to yield a lower wavelength requirement.

There is an increasing requirement for supporting complex multidimensional queries in Peer-to-Peer systems. In the centralized spatial database world, R-Trees and its variant structures are widely accepted due to their capabilities to manage complex multidimensional queries. In this paper, we propose a new multidimensional indexing structure for P2P systems, called Distributed Hilbert R-Trees (DHR-Trees), in which peers organize themselves into an overlay network, dynamically maintain routing tables with region information and collaboratively execute complex multidimensional queries, such as range query and k-nearest neighbors query, efficiently. DHR-Trees has similar topology to the P-Trees P2P system. The peers' routing tables are enhanced with spatial region information, which allow multidimensional query predicates to be adapted into P2P systems with minor modification. The structure design and two major multidimensional query algorithms are presented. Our experimental results demonstrate that it performs well on range queries and k-nearest neighbors queries with multidimensional data set.

Ad hoc networks have recently become a hot topic. In ad hoc networks, battery power is an important resource, since most terminals are battery powered. Terminals consume extra energy when their network interfaces are in the idle state or when they overhear packets not destined for them. They should, therefore, switch off their radio when they do not have to send or receive packets. IEEE802.11 features a power saving mechanism (PSM) in Distributed Coordination Function(DCF). In PSM for DCF, nodes must stay awake for a fixed time, called ATIM window (Ad-Hoc Traffic Indication Map window). If nodes do not have data to send or receive, they enter the doze state except for during ATIM window. However, ad hoc networks with PSM have longer end-to-end delays to deliver packets and suffer lower throughput than the standard IEEE802.11. To solve this problem, this paper proposes a protocol that reduces delay and achieves high throughput and energy efficiency. Simulation results show that our proposal outperforms other PSMs in terms of throughput, end-to-end delay and energy efficiency.

A Time-Division Multiplexed (TDM) Hierarchical Switching System (HSS), proposed by Eng and Acampora [5], provides any size of bandwidth for a number of subscribers by allocating proper number of time-slots in a frame. In this paper, we present a binary time-slot assignment (TSA) algorithm by which a proper size of time-slots in the frame are allocated to each subscriber so as to meet its bandwidth requests. The time complexity of the proposed algorithm is O(NLlog2 L) in which N is the number of input/output links of the central switch and L is the number of time-slots allotted to each link in the frame. As the authors know, the most efficient algorithm proposed in the literature has time complexity of O(min(L, M2)min(N, M)M2), in which M is the number of subscribers that is larger than N in TDM/HSS system. To give a clear idea of relative efficiency between two algorithms, let us give a typical situation of M = L = O(N2). In this configuration our algorithm makes a significant improvement in time complexity by the order of O(M2/log2M).

Compatibility of conventional lossless discrete cosine transforms (LDCTs) with the discrete cosine transform (DCT) is not high due to rounding operations. In this paper, we design an LDCT which has high compatibility with the DCT. We first design an 8-point DCT (DCT3) by changing the order of row of the transform matrix and also the way of decomposing the DCT in order to obtain an 8-point LDCT which has high compatibility with the DCT. Next we design an 88-point nonseparable 2D LDCT based on a 4-point lossless Walsh-Hadamard Transform (LWHT) which is multiplier-free. The DCT3 is used, when the nonseparable 2D LDCT is designed. Simulation results show that compatibility of the nonseparable 2D LDCT with the separable 2D DCT is high. We also design an 88-point nonseparable 2D LWHT which is multiplier-free and indicate that its compatibility with the separable 2D Walsh-Hadamard Transform is high.

Havihg modified and extended the routing algorithm used in our previously proposed Bidirectional Shuffle Ring Network (BSRN), we here provide some adaptive routing algorithms that can relieve the congestion caused by bottlenecks when nonuniform traffic exists. As to preserve the transmission order of cells associated with a message which may otherwise arrive at the destination out of sequence if they are forwarded along different routing paths, two control schemes are also devised. The BSRN proves to be highly reliable and robust since countermeasures against node or link failure can also easily be realized.

In recent years, the reduced cost and increased capacity of memory have resulted in a growing number of buffers in switches and routers. Consequently, today's networks suffer from bufferbloat, a term that refers to excess frame buffering resulting in high latency, high jitter, and low throughput. Although ring aggregation is an efficient topology for forwarding traffic from multiple, widely deployed user nodes to a core network, a fairness scheme is needed to achieve throughput fairness and avoid bufferbloat, because frames are forwarded along ring nodes. N Rate N+1 Color Marking (NRN+1CM) was proposed to achieve per-flow fairness in ring aggregation networks. The key idea of NRN+1CM is to assign a color that indicates the dropping priority of a frame according to the flow-input rate. When congestion occurs, frames are selectively discarded based on their color and the frame-dropping threshold. Through the notification process for the frame-dropping threshold, frames are discarded at upstream nodes in advance, avoiding the accumulation of a queuing delay. The performance of NRN+1CM was analyzed theoretically and evaluated with computer simulations. However, its ability to avoid bufferbloat has not yet been proven mathematically. This paper uses an M(n)/M/1/K queue model to demonstrate how bufferbloat is avoided with NRN+1CM's frame-dropping threshold-notification process. The M(n)/M/1/K queue is an M/M/1/K queuing system with balking. The state probabilities and average queue size of each ring node were calculated with the model, proving that the average queue size is suppressed in several frames, but not in the most congested queue. Computer simulation results confirm the validity of the queue model. Consequently, it was logically deducted from the proposed M(n)/M/1/K model that bufferbloat is successfully avoided with NRN+1CM independent of the network conditions including the number of nodes, buffer sizes, and the number and types of flows.

In this paper, we present Scalable Data Collection (SDC) protocol, a tree-based protocol for collecting data over multi-hop, wireless sensor networks. The design of the protocol aims to satisfy the requirements of sensor networks that every sensor transmits sensed data to a sink node periodically or spontaneously. The sink nodes construct the tree by broadcasting a HELLO packet to discover the child nodes. The sensor receiving this packet decides an appropriate parent to which it will attach, it then broadcasts the HELLO packet to discover its child nodes. Based on this process, the tree is quickly created without flooding of any routing packets. SDC avoids periodic updating of routing information but the tree will be reconstructed upon node failures or adding of new nodes. The states required on each sensor are constant and independent of network size, thereby SDC scales better than the existing protocols. Moreover, each sensor can make forwarding decisions regardless of the knowledge on geographical information. We evaluate the performance of SDC by using the ns-2 simulator and comparing with Directed Diffusion, DSR, AODV, and OLSR. The simulation results demonstrate that SDC achieves much higher delivery ratio and lower delay as well as scalability in various scenarios.

Because of the large scale of wireless sensor networks, the configuration needs to be done autonomously. In this paper, we present Scalable Data Collection (SDC) protocol, a tree-based protocol for collecting data over multi-hop, wireless sensor networks. The design of the protocol aims to satisfy the requirements of sensor networks that every sensor transmits sensed data to a sink node periodically or spontaneously. The sink nodes construct the tree by broadcasting a solicit packet to discover the child nodes. The sensor receiving this packet decides on an appropriate parent to which it will attach, it then broadcasts the same packet to discover its child nodes. Through this process, the tree is created autonomously without any flooding of the routing packets. SDC avoids periodic updating of routing information but the tree need to be reconstructed upon node failures or adding of new nodes. The states required on each sensor are constant and independent of network size, therefore SDC scales better than the existing protocols. Moreover, each sensor can make forwarding decisions regardless of the knowledge on geographical information. We evaluated the performance of SDC by using the ns-2 simulator and comparing with Directed Diffusion, DSR, AODV, and OLSR. The simulation results demonstrate that SDC achieves much higher delivery ratio, shorter delay, as well as high scalability in various scenarios.

Efficiently locating nodes and allocating demand has been a significant problem for telecommunication network carriers. Most of location models focused on where to locate nodes and how to assign increasing demand with optical access networks. However, the population in industrialized countries will decline over the coming decades. Recent advance in the optical amplifier technology has enabled node integration; an excess telecommunication node is closed and integrated to another node. Node integration in low-demand areas will improve the efficiency of access networks in this approaching age of depopulation. A dynamic node integration problem (DNIP) has been developed to organize the optimal plan for node integration. The problem of the DNIP was that it cannot consider the requirements of network carriers. In actual situations, network carriers often want to specify the way each node is managed, regardless of the mathematical optimality of the solution. This paper proposes a requirement modeling language (RML) for the DNIP, with which the requirements of network carriers can be described. The described statements are used to solve the DNIP, and consequently the calculated optimal solution always satisfies the requirements. The validity of the proposed method was evaluated with computer simulations in a case study.

Recently there has been a great deal of research on using mobility in sensor networks to assist their sensing tasks. In this paper, we propose a policy-based session control protocol for Multi-Robot Sensor Networks (MRSNs) called Billiards. In a MRSN, all messages are transported by the physical motion of participants (mobile nodes) in the network. When a large volume of data or continuous data is required to be transferred, there exists a problem determining how the data is fragmented and how the mobile nodes are formed for carrying the data to the destination. To overcome the issues, we propose a suitable method of session control which is determined based on a state of surrounding mobile nodes such as number, maximum-velocity and buffer-size. Billiards also takes a system policy of delay minimization into consideration. In this paper, we describe the protocol and model of Billiards and analyze the model. We evaluated the performance of Billiards utilizing mobile robots which are equipped with MICA2 mote and comparing with non optimized method. The experimental results demonstrate that Billiards achieves less delay than non optimized method at every velocity and buffer-size of each robot.

We propose a new multicast ATM switching network, called the Cascade Clos Broadcast Switching Network (CCB-SN). It has the following features. Firstly, the CCB-SN is robust not only for unicast calls but also for multicast calls. Therefore, deterioration of traffic handling performance due to a non-uniform traffic pattern does not occur. Secondly, in the CCB-SN, the cells are replicated after they are partly routed. And so, the delay time caused by the increment of replicas of cells is kept to a minimum.

The IEEE802.11e is a standard developed by a Task Group E of the IEEE802.11 working group and defines a MAC protocol, which provides EDCA (enhanced distributed channel access) and HCCA (HCF controlled channel access) to support differentiation service over WLAN (wireless LAN). In IEEE802.11e WLAN, real-time application such as VoIP (Voice over IP) can have more chances to access the WM (wireless medium) than non real-time application. In addition to QoS support in WLAN, power consumption is a critical issue when WLAN is used in handheld devices. For power saving in the use of real-time applications like VoIP under EDCA, U-APSD (Unscheduled Automatic Power Save Delivery) was proposed in [2] and [4]. In fact, it can save power consumption and works well when it is used for bi-directional voice connections generated at constant bit rate. However, when it is used for real-time applications like ON-OFF traffic, buffering delay at AP (access point) increases. To reduce the buffering delay, this paper proposes two mechanisms. Simulation results show that they can alleviate buffering delay generated at AP.

Lossless block transforms and filter banks that map integers to integers are important for unified lossless and lossy image coding systems. In this paper, we present simple yet effective methods for designing lossless versions of block transforms and FIR filter banks. First, an N-point lossless transform and a lossless interpolative prediction are introduced. Next, we demonstrate that filter banks can be decomposed into 2-point transforms or interpolative predictions. Lastly, lossless versions of block transforms and filter banks are obtained by replacing every constituent module by the corresponding lossless version. Lossless versions of 8-point discrete cosine transform (DCT), 8-point Walsh-Hadamard transform (WHT) and several filter banks are designed and their lossless compression performance is evaluated.