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The article studies the symbolic one-to-all-target-subset reliability function of acyclic multi-state information networks (AMIN) using convolution universal generating function method (CUGFM). Findings suggest that symbolic reliability functions of the one-to-all-target-subset AMIN problem are more efficient than the best-known UGFM.

The article studies a new field-based compact capacitance model for general two-dimensional back-end-of-the-line (BEOL) interconnect structures. Findings reveal that new model has been conveniently adapted to incorporate advanced CMOS interconnect structures, such as the Cu diffusion layer and the air gap.

A study was conducted to examine the approach for interconnect modeling and analysis in designing advanced system-on-a-chip (SoC) design flow from design-automation point of view. Findings confirm the importance and perspective of design technology in manufacturing industries.

The article studies the electrical and thermal modeling and performance analysis for various carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) based interconnects. Findings reveal that single-walled, double-walled, and multiwalled CNTs could present better performance than Cu.

Many multipath routing schemes have recently been proposed to improve the performance of wireless networks. Multipath routing is supposed to reduce the end-to-end packet delay and increase the packet delivery ratio. Therefore, it can also improve the packet delivery ratio in vehicular ad hoc networks (VANETs) when the mobility of relaying vehicles is unknown. However, in wireless networks, multiple paths are exposed to mutual interference or path coupling, which impairs efficiency. The intriguing question is whether the node-disjoint multipath routing really helps. In this paper, we examine the performance of node-disjoint multipath routing in VANETs. Through extensive simulations, we explore the effect of mutual interference on the behavior of node-disjoint paths. It is shown that whether node-disjoint paths are able to improve performance, compared with the single path, is determined by path coupling and the source-destination distance. Results show that node-disjoint multipath routing can be applied to VANETs to substantially improve performance in terms of delay and packet delivery probability only if the node-disjoint paths are properly chosen. Index Terms--Interference, redundancy, reliability, routing.

Problem Statement: This study proposes a TCP layer protocol (Div-TCP) that aims to give a solution for communication over wireless mobile networks that have the occurrence of handoff at anytime. It describes a topology of wireless mobile network and the handoff process as an ordinary process in that type of networks which may cause segments losses. Approach: Wireless mobile networks have many weaknesses related to bit error, network congestion and weak signals that cause segments losses as well as handoff process. For this reason, wireless mobile network TCP cannot distinguish between losses caused by these weaknesses or by the handoff process. So in handoff case, segments losses will trigger congestion control algorithms that reduce the TCP connection's throughput performance. Results: However, in addition to the previous efforts that provide different algorithms and protocols which aim to come up with different solutions and enhancements for the TCP connection in wireless mobile networks when handoff occurs, I am providing in this study Div-TCP protocol that runs the ordinary TCP algorithms with adding more operations that are concerned to handoff. These operations aim to maintain a suitable RTO at each sender to avoid triggering congestions algorithms and also to maintain the sender's throughput by establishing a TCP connection prior to the handoff occurrence. Conclusions/Recommendations: The protocol's discussion shows how end-to-end TCP connection became more efficient since the new Div-TCP connection after handoff will have good and already built TCP connection and the RTO is too much high at all nodes so there is no fear of a that TCP considers congestion. Key word: TCP connection, mobile node, home agent, foreign agent, correspondent host, mobile IP, handoff, round trip time, retransmission time out, congestion control, exponential back off, INTRODUCTION In wireless 802.11 networking, communications take different shapes that connect end to end users using at least one non-wired part of the network. Actually, there are a lot of [...]

In a mobile telecommunications network, the location area (LA) of a mobile station (MS) is tracked by an LA update (LAU) mechanism. To reduce the LAU traffic caused by the ping-pong effect, the overlapping LA concept is introduced. In the overlapping LA configuration, an LA selection policy is required to select the new LA at an LAU when the MS enters a new cell covered by multiple LAs. This paper describes four LA selection policies and proposes an analytic model to study the performance of these LA selection policies. Our study provides guidelines to determine an appropriate degree of overlapping among the LAs. Index Terms--Location area (LA), location update, mobility management, overlapping LA, ping-pong effect.

A new error model for a special class of multiport vector network analyzers (VNAs) is presented in this paper. This model can be applied to multiport network analyzers with noncomplete reflectometers, i.e., when the measurement of the incident waves at each port is not always available. The method used to compute the error coefficients proposed here is based on a compact and easy formulation. This method is an extension of the already existing general theory for complete reflectometer multiport network analyzers. Furthermore, the new error model generalizes the theory for three-sampler two-port VNAs. The proposed model has been tested against the complete reflectometer one and exhibits the same accuracy level. Index Terms--Calibration models, multiport network analyzer, multiport network analyzer calibration, vectorial error correction, vector network analyzer (VNA), VNA calibration.

The unified service delivery process that is suggested for the next generation services (NGN) between end-to-end service delivery architecture (SDA) is discussed.

The most widely used standard for in-vehicle communication networks that interconnect electronic control units is the controller area network (CAN). However, the event-triggered architecture of CAN introduces several issues, such as predictability, signal jitter, and reliability. Different time-triggered networks are being developed to address these issues. In this paper, we focus on time-triggered CAN (TTCAN), which achieves time-triggered behavior by implementing time-division multiple access on the existing CAN network standard. The main task is thus to construct a message schedule for a given set of messages while fulfilling certain performance criteria. To this end, we provide a formal framework for the construction of feasible message schedules in TTCAN networks by considering several performance metrics, such as bandwidth utilization and jitter, as well as the hardware constraints of the TTCAN controller specification. Index Terms--Performance analysis, real time, scheduling, time-triggered controller area network (TTCAN), vehicular communication networks.

Capacity improvement from transmitter and receiver cooperation is investigated in a two-transmitter, two-receiver network with phase fading and full channel state information (CSI) available at all terminals. The transmitters cooperate by first exchanging messages over an orthogonal transmitter cooperation channel, then encoding jointly with dirty-paper coding. The receivers cooperate by using Wyner-Ziv compress-and-forward over an analogous orthogonal receiver cooperation channel. To account for the cost of cooperation, the allocation of network power and bandwidth among the data and cooperation channels is studied. It is shown that transmitter cooperation outperforms receiver cooperation and improves capacity over noncooperative transmission under most operating conditions when the cooperation channel is strong. However, a weak cooperation channel limits the transmitter cooperation rate; in this case, receiver cooperation is more advantageous. Transmitter-and-receiver cooperation offers sizable additional capacity gain over transmitter-only cooperation at low signal-to-noise ratio (SNR), whereas at high SNR transmitter cooperation alone captures most of the cooperative capacity improvement. Index Terms--Capacity, transmitter and receiver cooperation, dirty-paper coding, Wyner-Ziv compress-and-forward, power and bandwidth allocation, wireless ad hoc network.

In cooperative networks using a decode-and-forward strategy, the multiple relays effectively transmit a distributed space--time code, the performance of which can be severely degraded when timing synchronization among the relays is not assured (e.g., in cases of broadcast to dispersed recipients or in networks without a shared, high-quality timing reference). Recent work by Xia et al. and Hammons et al. have investigated the design of distributed space--time codes that are delay tolerant, in the sense that full spatial diversity is achieved regardless of timing offsets. In general, the previously known space--time block codes belonging to the class of C-linear codes, however, which are important because they achieve full spatial diversity and admit near-optimal lattice decoding algorithms, are not delay tolerant. In this paper, we present a new family of such codes that are fully delay tolerant. The new codes generalize the threaded algebraic space--time (TAST) codes introduced by El Gamal and Damen. Like their brethren, the new Distributed-TAST codes are effective and flexible, enabling use of different signaling constellations, transmission rates, numbers of transmit and receive antennas, and decoders of varying levels of complexity. Index Terms--Distributed, space--time codes, decode-and-forward, cooperation, multiple-input multiple-output (MIMO), cooperative networks, threaded algebraic space--time (TAST).

The relay channel with private messages (RCPM) is a generalized relay channel model where in addition to the traditional communication from source to destination (assisted by relay), the source has a private message for the relay, and the relay has a private message for the destination. This paper develops coding strategies for this channel based on decode-and-forward and compress-and-forward schemes. Achievable rate regions as well as outer bounds on the capacity region are obtained for the discrete memoryless relay channel with private messages. Then, the Gaussian versions of this channel are studied and achievable rate regions are characterized. Numerical results are provided that give insights into the trade-offs between private messaging and relayed messaging in this hybrid three-node network. Index Terms--Channel capacity, channel coding, relay channels, wireless networks.

n source and destination pairs randomly located in an area want to communicate with each other. Signals transmitted from one user to another at distance r apart are subject to a power loss of [r.sup.-[alpha] as well as a random phase. We identify the scaling laws of the information-theoretic capacity of the network when nodes can relay information for each other. In the case of dense networks, where the area is fixed and the density of nodes increasing, we show that the total capacity of the network scales linearly with n. This improves on the best known achievability result of [n.sup.2/3] of Aeron and Saligrama. In the case of extended networks, where the density of nodes is fixed and the area increasing linearly with n, we show that this capacity scales as [r.sup.2-[alpha]/2] for 2 [less than or equal to] < 3 and [square root]n for [alpha] [greater than or equal] 3. The best known earlier result of Xie and Kumar identified the scaling law for a > 4. Thus, much better scaling than multihop can be achieved in dense networks, as well as in extended networks with low attenuation. The performance gain is achieved by intelligent node cooperation and distributed multiple-input multiple-output (MIMO) communication. The key ingredient is a hierarchical and digital architecture for nodal exchange of information for realizing the cooperation. Index Terms--Ad hoc wireless networks, capacity scaling, digital communications, distributed multiple-input multiple-output (MIMO), hierarchical cooperation.

This paper describes techniques to decompose LT codes (a class of rateless erasure-correcting codes) into distributed LT (DLT) codes. DLT codes can be used to independently encode data from multiple sources in a network in such a way that, when the DLT-encoded packets are combined at a common relay, the resulting bit stream (called a modified LT (MLT) code) has a degree distribution approximating that of an LT code, with simulations indicating comparable performance. In essence, DLT codes are designed so that the final stage of encoding for erasure correction can be carried out by a low-complexity relay that selectively XORs the bit streams generated at each source and transmits the result to the sink. This paper presents results for two-source and four-source networks. It is shown that, when the relay-to-sink link is the bottleneck, the DLT/MLT approach can yield substantial performance benefits compared with a competing strategy wherein each of the sources uses its own independent LT encoder and the resulting bit streams are time-multiplexed through the relay. Index Terms--Distributed coding, erasure correction, LT codes, relay networks.

This paper addresses network coding in wireless networks in conjunction with medium access control (MAC). It is known that coding over wired networks enables connections with rates that cannot be achieved by routing. However, the properties of wireless networks (e.g., omnidirectional transmissions, destructive interference, single transceiver per node, finite energy) modify the formulation of time-varying network coding in a way that reflects strong interactions with underlying MAC protocols and deviates from the classical approach used in wired network coding. To perform network coding over conflict-free transmission schedules, predetermined network realizations are separately activated by a time-division mechanism and the content of network flows is derived through network coding to optimize performance measures such as achievable throughput and energy costs. A systematic method is presented to construct linear wireless network codes and interactions with MAC schedules are discussed under wireless assumptions. Network coding is also extended to operate with arbitrary (random or scheduled access based) MAC protocols. Alternatively, conflict-free transmission schedules are jointly constructed with network codes by decomposing wireless networks into subtrees and employing graph coloring on simplified subtree graphs. Finally, network coding and plain routing are compared in terms of throughput, energy and delay performance under different MAC solutions. Index Terms--Cross-layer design, energy efficiency, graph theory, medium access control (MAC), multiuser information theory, network coding, wireless ad hoc networks.

This paper proposes a network coding approach to cooperative diversity featuring the algebraic superposition of channel codes over a finite field. The scenario under consideration is one in which two "partners"--Node A and Node B--cooperate in transmitting information to a single destination; each partner transmits both locally generated information and relayed information that originated at the other partner. A key observation is that Node B already knows Node A's relayed information (because it originated at Node B) and can exploit that knowledge when decoding Node A's local information. This leads to an encoding scheme in which each partner transmits the algebraic superposition of its local and relayed information, and the superimposed codeword is interpreted differently at the two receivers--i.e., at the other partner and at the destination node--based on their different a priori knowledge. Decoding at the destination is then carried out by iterating between the codewords from the two partners. It is shown via simulation that the proposed scheme provides substantial coding gain over other cooperative diversity techniques, including those based on time multiplexing and signal (Euclidean space) superposition. Index Terms--Cooperative diversity, error control coding, fading channels, iterative decoding, network coding.

In this paper, a low-complexity cooperative protocol that significantly increases the average throughput of multihop upstream transmissions for wireless tree networks is developed and analyzed. A system in which transmissions are assigned to nodes in a collision free, spatial time division fashion is considered. The suggested protocol exploits the broadcast nature of wireless networks where the communication channel is shared between multiple adjacent nodes within interference range. For any upstream end-to-end flow in the tree, each intermediate node receives information from both one-hop and two-hop neighbors and transmits only sufficient information such that the next upstream one-hop neighbor will be able to decode the packet. This approach can be viewed as the generalization of the classical three node relay channel for end-to-end flows in which each intermediate node becomes successively source, relay and destination. The achievable rate for any regular tree network is derived and an optimal schedule that realizes this rate in most cases is proposed. Our protocol is shown to dramatically outperform the conventional scheme where intermediate nodes simply forward the packets hop by hop. At high signal-to-noise ratio (SNR), it yields approximately 66% throughput gain for practical scenarios. Index Terms--Fairness, relay channel, time division multiaccess, user cooperation, wireless networks.

The multiple-access channel with feedback and correlated sources (MACFCS) models a sensor network in which sensors collect and transmit correlated data to a common sink. We present four achievable rate regions and a capacity outer bound for the MACFCS. For the first achievable region, we construct a decode--forward based coding strategy. The sources first exchange their data, and then cooperate to send full information to the destination. We term this strategy full decoding at sources with decode-forward (FDS-DF). For two of the other achievable regions, we first perform Slepian--Wolf coding to remove the correlation among the source data. This is followed by either i) a compress--forward based coding strategy for the multiple-access channel with feedback, or ii) an existing coding strategy for the multiple-access channel. We also find another achievable region using a multihop coding strategy, which only uses point-to-point coding (no cooperation). From numerical computations, we see that different strategies perform better under certain source correlation structures and network topologies. More specifically, FDS-DF approaches the capacity when i) the inter-source distance decreases, or ii) the correlation among the sources gets higher. Furthermore, the cooperative coding strategies considered support larger achievable rate regions than the noncooperative multihop strategy. Index Terms--Achievable rates, capacity, correlated sources, generalized feedback, multiple-access channel, multiterminal networks.

The classic Bellman-Ford algorithm for calculating shortest paths can be easily adapted to a distributed environment in which the computations are performed locally by identical processors at each network node. […]

This paper proposes task-scheduling algorithms designed to save energy in ad hoc networks by using a novel concept of 'affinity' as the scheduling metric. This notion of affinity is used to represent the task-linking topology. For one-hop ad hoc networks, we define three types of affinity measures: node affinity, task affinity, and weighted affinity. Node affinity is defined as the weighted sum of incoming and outgoing task flows at each node, and task affinity as the sum of node affinities of source and destination nodes for each task. Based on these affinity measures, we consider three heuristic scheduling algorithms that are executable in real time: 1) affinity-first shortest task scheduling [Q.sup.at]; 2) task-size-first affinity-based scheduling [Q.sup.ta]; and 3) task-size weighted-affinity scheduling [Q.sup.wa]. These algorithms have the advantage of making the total duration of the doze state of all the nodes in the network longer than in other conventional schemes, thereby achieving significant power saving (PS). Our simulation experiments suggest that the PS performance of [Q.sup.wa] is comparable to optimal scheduling (which is not implementable in practice for realistic link topologies). We also present a framework for a PS medium-access-control (MAC) protocol in which our scheduling algorithm can be deployed, and we describe how to enhance the existing 802.11 PS MAC to implement our framework. Simulation results demonstrate that our enhanced PS MAC protocol combined with affinity-based scheduling improves power efficiency and throughput significantly over other existing schemes. Index Terms--Ad hoc network, affinity, medium-access control (MAC), power saving (PS), scheduling.

Active network tomography refers to an interesting class of large-scale inverse problems that arise in estimating the quality of service parameters of computer and communications networks. This article focuses on estimation of loss rates of the internal links of a network using end-to-end measurements of nodes located on the periphery. A class of flexible experiments for actively probing the network is introduced, and conditions under which all of the link-level information is estimable are obtained. Maximum likelihood estimation using the EM algorithm, the structure of the algorithm, and the properties of the maximum likelihood estimators are investigated. This includes simulation studies using the ns (network simulator) to obtain realistic network traffic. The optimal design of probing experiments is also studied. Finally, application of the results to network monitoring is briefly illustrated. KEY WORDS: EM algorithm; Inference on graphs; Network modeling; Network monitoring; Network tomography; Probing experiments.

Abstract--Ultra-wide band (UWB) communication is one of the most promising technologies for high data rate wireless networks for short range applications. This paper proposes a blind channel estimation method namely [...]

A routing algorithm named Shortest Path and Deflection Routing Algorithm (SPDRA) for the interconnection of multiple processors on the shortest-path and deflection-routing principles exhibits a performance advantage for a broad range of network sizes. The performance analyses compares SPDRA algorithm with limited set of multiprocessor systems and does not demonstrate the superiority over all systems with a fixed node-to-processor ratio and with growing node to ratio such as multistage network.