Predictive Caching Strategy for On-Demand Routing Protocols in Wireless Ad Hoc Networks

Route caching strategy is important in on-demand routing protocols in wireless ad hoc networks. While high routing overhead usually has a significant performance impact in low bandwidth wireless networks, a good route caching strategy can reduce routing overheads by making use of the available route information more efficiently. In this paper, we first study the effects of two cache schemes, link cache and path cache, on the performance of on-demand routing protocols through simulations based on the Dynamic Source Routing (DSR) protocol. Since the path cache DSR has been extensively studied, we focus in this paper on the link cache DSR in combination with timer-based stale link expiry mechanisms. The effects of different link lifetime values on the performance of routing protocol in terms of routing overhead, packet delivery ratio and packet latency are investigated. A caching strategy incorporating adaptive link timeout is then proposed, which aims at tracking the optimal link lifetime under various node mobility levels by adaptively adjusting the link lifetime based on the real link lifetime statistics. The performance of the proposed strategy is then compared with the conventional path cache DSR. The results show that without a timeout mechanism, a link cache scheme may suffer severe performance degradation due to the use of broken routes, while the proposed adaptive link cache strategy achieves significantly improved performance by reducing the routing overhead when the network traffic load is high.     

Mobility Management for Hierarchical Wireless Networks

In this paper, we consider the mobility management in large, hierarchically organized multihop wireless networks. The examples of such networks range from battlefield networks, emergency disaster relief and law enforcement etc. We present a novel network addressing architecture to accommodate mobility using a Home Agent concept akin to mobile IP. We distinguish between the physical routing hierarchy (dictated by geographical relationships between nodes) and logical hierarchy of subnets in which the members move as a group (e.g., company, brigade, battalion in the battlefield). The performance of the mobility management scheme is investigated through simulation.     

Microsystems Engineering: A Great Stride Forward in Microelectronics Technology

The development of new-generation technological and engineering concepts by the example of microsystems technology and microsystems engineering approaches is considered.     

The Future Generations of Mobile Communications Based on Broadband Access Methods

The forthcoming mobile communication systems are expected to provide much variety of services from high quality voice to high definition videos through high data rate wireless channels at anywhere in the world. High data rate requires broad frequency bands, and sufficient broadband can be achieved in higher frequency bands such as microwave, Ka-band and millimeter-wave. Broadband wireless channels have to be connected to broadband fixed networks such as the Internet and local area networks. The future generation systems will include not only cellular phones, but also many new types of communication systems such as broadband wireless access systems, millimeter-wave LAN, intelligent transport systems (ITS) and high altitude stratospheric platform station (HAPS) systems. The key words in the future generations of mobile communications are multimedia communications, wireless access to broadband fixed networks and seamless roaming among different systems. This article discusses the future generations mobile communication systems.     

Floor acquisition multiple access (FAMA) in single‐channel wireless networks

The FAMANCS protocol is introduced for wireless LANs and adhoc networks that are based on a single channel and asynchronous transmissions (i.e., no time slotting). FAMANCS (for floor acquisition multiple access with nonpersistent carrier sensing) guarantees that a single sender is able to send data packets free of collisions to a given receiver at any given time. FAMANCS is based on a threeway handshake between sender and receiver in which the sender uses nonpersistent carrier sensing to transmit a requesttosend (RTS) and the receiver sends a cleartosend (CTS) that lasts much longer than the RTS to serve as a busy tone that forces all hidden nodes to back off long enough to allow a collisionfree data packet to arrive at the receiver. It is shown that carrier sensing is needed to support collisionfree transmissions in the presence of hidden terminals when nodes transmit RTSs asynchronously. The throughput of FAMANCS is analyzed for singlechannel networks with and without hidden terminals; the analysis shows that FAMANCS performs better than ALOHA, CSMA, and all prior proposals based on collision avoidance dialogues (e.g., MACA, MACAW, and IEEE 802.11 DFWMAC) in the presence of hidden terminals. Simulation experiments are used to confirm the analytical results.     

A unified partitioning and scheduling scheme for mapping multi-stage regular iterative algorithms onto processor arrays

This paper addresses the partitioning and scheduling problems in mapping multi-stage regular iterative algorithms onto fixed size distributed memory processor arrays. We first propose a versatile partitioning model which provides a unified framework to integrate various partitioning schemes such as locally sequential globally parallel, locally parallel globally sequential and multi-projection. To alleviate the run time data migration overhead—a crucial problem to the mapping of multi-stage algorithms, we further relax the widely adopted atomic partitioning constraint in our model such that a more flexible partitioning scheme can be achieved. Based on this unified partitioning model, a novel hierarchical scheduling scheme which applies separate schedules at different processor hierarchies is then developed. The scheduling problem is then formulated into a set of ILP problem and solved by the existing software package for optimal solutions. Examples indicate that our partitioning model is a superset of the existing schemes and the proposed hierarchical scheduling scheme can outperform the conventional one-level linear schedule.     

Quality Determination for Gate Delay Fault Tests Considering Three-State Elements

Most industrial digital circuits contain three-state elements besides pure logic gates. This paper presents a gate delay fault simulator for combinational circuits that can handle three-state elements like bus drivers, transmission gates and pulled busses. The well known delay faults--slow-to-rise and slow-to-fall--are considered as well as delayed transitions from isolating signal state high impedance to binary states 0 and 1 and vice versa. The presented parallel delay fault simulator distinguishes between non-robust, robust and hazard free tests and determines the quality of a test. Experimental results for ISCAS85/89 benchmark circuits are presented as well as results for industrial circuits containing three-state elements.     

Perspectives on Analytical Modeling of Small Geometry MOSFETs in SPICE for Low Voltage/Low Power CMOS Circuit Design

The present state of the art in analytical MOSFET modeling for SPICE circuit simulation is reviewed, with emphasis on the circuit design usage of these models. It is noted that the model formulation represents an upper limit of what is possible from any type of model, but that good parameter extraction is required to most closely approach that limit. The individual model types presently in common use are examined, with discussion of the behavior of each model, its strengths and weaknesses, its applicability to certain types of circuits, and criteria that a circuit design consumer can employ to judge a model before using it for circuit design. Some related issues, such as node charge and gate capacitance modeling, charge conservation, and statistical simulation of process variations, are also evaluated. Finally, new trends, directions, and requirements of MOSFET modeling for circuit simulation are considered.     

Simulation‐based performance evaluation of routing protocols for mobile ad hoc networks

In this paper we evaluate several routing protocols for mobile, wireless, ad hoc networks via packetlevel simulations. The ad hoc networks are multihop wireless networks with dynamically changing network connectivity owing to mobility. The protocol suite includes several routing protocols specifically designed for ad hoc routing, as well as more traditional protocols, such as link state and distance vector, used for dynamic networks. Performance is evaluated with respect to fraction of packets delivered, endtoend delay, and routing load for a given traffic and mobility model. Both small (30 nodes) and medium sized (60 nodes) networks are used. It is observed that the new generation of ondemand routing protocols use much lower routing load, especially with small number of peertopeer conversations. However, the traditional link state and distance vector protocols provide, in general, better packet delivery and endtoend delay performance.     

Computational experience with an effective heuristic for some capacity expansion problems in local access networks

We present a heuristic for multiplexer location problems in local access networks. The effectiveness of the heuristic is demonstrated on several real-life problem instances.Partially funded by an NSF PYI award, a consulting agreement with Bellcore, and an equipment grant from IBM.     

A necessary and sufficient condition for right coprime factorization of nonlinear feedback systems

In this short note, we establish a simple, yet precise, necessary and sufficient condition for the right coprime factorization of a nonlinear feedback control system. As a consequence, we also obtain similar conditions for the stable right coprime factorizations of the nonlinear feedback control system.     

Input-output systems whose transmission operators furnish nearly best approximations to a given map

Let {S(A):A A}, whereA is a subset of an infinite-dimensional normed linear spaceL, be a class of general nonlinear input-output systems that are governed by operator equations relating the input, state, and output, all of which are in extended spaces. IfQ is a given operator from a specified set ¯D _i, of inputs into the space of outputs ¯H ₀, the problem we consider is to find, for a given >0, a parameterA A such that the transmission operatorR(A ) ofS(A ) furnishes a nearly best (or -best) approximation toQ from allR(A),A A. Here the distance betweenQ andR(A) is defined as the supremum of distances betweenQz andR(A)z taken over allz ¯D _i. In Theorems 2 through 5 we show that ifS(A) is normal (Definition 2),A satisfies some mild requirement andL contains a fundamental sequence, then establishingA A reduces to minimizing a certain continuous functional on a compact subset ofR ⁿ, and thus can be carried out by conventional methods. The applications of results are illustrated by the example of a model-matching problem for a nonlinear system, and of optimal tracking.     

Biasing a differential pair in low-voltage analog circuits: a systematic approach

This paper deals with a systematic approach to the common mode and the differential mode biasing of a differential transistor pair. Four different variants will be shown, two of these variants show practical importance; a practical circuit of one of these variants turns out to be the traditional long-tailed pair. This variant is mainly suited, if the input signal operates at voltage level, whereas another variant has great advantages if operation at current level occurs. Besides, the latter variant turns out to be very favorable in circuits operating with a single low supply voltage. Two practical circuits based on this variant are given.     

Optical-LSP Establishment and a QoS Maintenance Scheme Based on Differentiated Optical QoS Classes in OVPNs

A virtual private network (VPN) over Internet has the benefit of being cost-effective and flexible. However, it has difficulties providing sufficient QoS and adequate transmission capacity for high bandwidth services. Given the increasing demand for high bandwidth Internet and the demand for QoS assurances in a VPN over Internet, IP/generalized multi-protocol label switching (GMPLS) based on a control plane combined with a high-bandwidth, dense-wavelength division multiplexing (DWDM) optical network is seen as a very favorable approach for realizing the future optical VPN (OVPN) over IP/GMPLS over DWDM. Within this architecture, providing QoS guaranteed multimedia services with a differentiated QoS guaranteed protocol framework with QoS recovery is one of the key issues to implement. Therefore, we suggest in this paper optical-label switched path (O-LSP) establishment and its QoS maintenance scheme based on differentiated optical QoS-service (DOQoS) classes. They are the key components for this DOQoS framework in assuring end-to-end QoS in an OVPN over IP/GMPLS over DWDM architecture.     

2-D harmonic retrieval using higher-order statistics

We consider the problem of estimating the harmonics of a noisy 2-D signal. The observed data is modeled as a 2-D sinusoidal signal, with either random or deterministic phases, plus additive Gaussian noise ofunknown covariance. Our method utilizes recently defined higher-order statistics, referred to as mixed-cumulants, which permit a formulation that is applicable to both the random and deterministic case. In particular, we first estimate the frequencies in each dimension using an overdetermined Yule-Walker type approach. Then, the 1-D frequencies are paired using a matching criterion. To support our theory, we examine the performance of the proposed method via simulations.     

The Complex Bootstrap Algorithm for Blind Separation of QAM Multiuser CDMA Signals

The bootstrap separator for multiuser signals is principally composed of cancelers, each one using the output of the other cancelers to facilitate control of its adaptive weight. In fact, such a structure performs as a signal separator rather than an interference canceler. Since for its separation there is no need for a reference signal (as in LMS cancelers), it is sometimes justifiably called a Blind Separator. However, for its operation the bootstrap separator requires a signal distinguisher termed discriminator. The algorithm was used in the past in applications such as dually polarized satellite communications and microwave terrestrial links. It was particularly reported for multiuser CDMA signal separating, with the signum function as discriminator. Especially for QAM signals, complex presentation is important. Therefore, we will concentrate in this report on what we call the Complex Bootstrap Algorithm. It is an extension to the previously reported bootstrap structure of [5]. We will examine its performance and emphasize the hardware saving in its implementation, and the ease of using it in simulation.     

On minimum cost isolated failure immune networks

A telecommunications network is isolated failure immune (IFI) if and only if communication between operative sites can be completed as long as network failures are isolated. It is known that the class of minimal IFI networks is equivalent to the class of spanning 2-trees. To the best of our knowledge, this work is the first computational study dealing with the construction of a minimum cost IFI network. The problem is known to be NP-complete. We develop a tabu search based heuristic for solving the minimum cost spanning 2-tree (MCS2T) problem. The complex structure of 2-trees makes the tabu search heuristic highly dependent on the starting solution. We develop four heuristic algorithms to obtain diversified good starting solutions. They are: completion of a 2-tree from a spanning tree, two greedy approaches, and a method based on the recursive definition of a 2-tree. We also formulate an integer programming problem (IP) whose objective function value is a lower bound to the MCS2T problem. We solve the IP by developing a constraint generation scheme. The algorithms were tested on complete random graphs with Euclidean distances and on two real data sets (Civil Aeronautics Board) with instances of 10, 15, 20 and 25 nodes. As a result of this research for small problems (10 and 15 nodes), the heuristic solutions are on average within 0.8% from the optimal solution and for large problems (20 and 25 nodes), the average error is less than 2.8%.     

Tree multicast strategies in mobile,multihop wireless networks

Tree multicast is a well established concept in wired networks. Two versions, persource tree multicast (e.g., DVMRP) and shared tree multicast (e.g., Core Based Tree), account for the majority of the wireline implementations. In this paper, we extend the tree multicast concept to wireless, mobile, multihop networks for applications ranging from ad hoc networking to disaster recovery and battlefield. The main challenge in wireless, mobile networks is the rapidly changing environment. We address this issue in our design by: (a) using soft state (b) assigning different roles to nodes depending on their mobility (2level mobility model); (c) proposing an adaptive scheme which combines shared tree and persource tree benefits, and (d) dynamically relocating the shared tree Rendezvous Point (RP). A detailed wireless simulation model is used to evaluate various multicast schemes. The results show that persource trees perform better in heavy loads because of the more efficient traffic distribution; while shared trees are more robust to mobility and are more scalable to large network sizes. The adaptive tree multicast scheme, a hybrid between shared tree and persource tree, combines the advantages of both and performs consistently well across all load and mobility scenarios. The main contributions of this study are: the use of a 2level mobility model to improve the stability of the shared tree, the development of a hybrid, adaptive persource and shared tree scheme, and the dynamic relocation of the RP in the shared tree.     

Gaussian radial basis functions and inner product spaces

An approximation result is given concerning Gaussian radial basis functions in a general inner product space. Applications are described concerning the classification of the elements of disjoint sets of signals, and also the approximation of continuous real functions defined on all of ⁿ using radial basis function (RBF) networks. More specifically, it is shown that an important large class of classification problems involving signals can be solved using a structure consisting of only a generalized RBF network followed by a quantizer. It is also shown that Gaussian radial basis functions defined on ⁿ can uniformly approximate arbitrarily well over all of ⁿ any continuous real functionalf on ⁿ that meets the condition that |f(x)|0 as x.     

Personal Imaging and lookpainting as tools for personal documentary and investigative photojournalism

A means and apparatus for covert capture of extremely highresolution photorealistic images is presented. The apparatus embodies a new form of userinterface – instead of the traditional point and click metaphor which was thought to be the simplest photography had to offer, what is proposed is a look metaphor in which images are generated through the natural process of looking around, in a manner that does not require conscious thought or effort. These lookpaintings become photographic/videographic memories that may, at times, exceed the quality attainable with even large and cumbersome professional photographic film cameras, yet they may be captured through a device that resembles ordinary sunglasses. The method is based on longterm psychophysical adaptation using a covert sunglassbased realitymediating apparatus, together with two new results in image processing. The first new result is a means of estimating the true projective coordinate transformation between successive pairs of images, and the second is that of estimating, to within a single unknown scalar constant, the quantity of light arriving at the image plane. Furthermore, what is captured is more than just a picture. The resulting environment map may be explored by one or more remote participants who may also correspond and interact with the wearer during the actual shooting process, giving rise to computer supported collaborative (collective) photography, videography, shared photographic/videographic memory, etc.