Artificial neural networks (ANNs) constitute a class of flexible nonlinear models designed to mimic biological neural systems. In this entry, we introduce ANN using familiar econometric terminology and provide an overview of ANN modeling approach and its implementation methods. † Correspondence: Chung-Ming Kuan, Institute of Economics, Academia Sinica, 128 Academia Road, Sec. 2, Taipei 115, Taiwan; ckuan@econ.sinica.edu.tw. †† I would like to express my sincere gratitude to the editor, Professor Steven Durlauf, for his patience and constructive comments on early drafts of this entry. I also thank Shih-Hsun Hsu and Yu-Lieh Huang for very helpful suggestions. The remaining errors are all mine.

Artificial neural networks

Digital processing of speech signals

Wireless sensor network (WSN) has emerged as one of the most promising technologies for the future. This has been enabled by advances in technology and availability of small, inexpensive, and smart sensors resulting in cost effective and easily deployable WSNs. However, researchers must address a variety of challenges to facilitate the widespread deployment of WSN technology in real-world domains. In this survey, we give an overview of wireless sensor networks and their application domains including the challenges that should be addressed in order to push the technology further. Then we review the recent technologies and testbeds for WSNs. Finally, we identify several open research issues that need to be investigated in future.

Our survey is different from existing surveys in that we focus on recent developments in wireless sensor network technologies. We review the leading research projects, standards and technologies, and platforms. Moreover, we highlight a recent phenomenon in WSN research that is to explore synergy between sensor networks and other technologies and explain how this can help sensor networks achieve their full potential. This paper intends to help new researchers entering the domain of WSNs by providing a comprehensive survey on recent developments.

Wireless sensor networks: a survey on recent developments and potential synergies

Space-air-ground integrated network (SAGIN), as an integration of satellite systems, aerial networks, and terrestrial communications, has been becoming an emerging architecture and attracted intensive research interest during the past years. Besides bringing significant benefits for various practical services and applications, SAGIN is also facing many unprecedented challenges due to its specific characteristics, such as heterogeneity, self-organization, and time-variability. Compared to traditional ground or satellite networks, SAGIN is affected by the limited and unbalanced network resources in all three network segments, so that it is difficult to obtain the best performances for traffic delivery. Therefore, the system integration, protocol optimization, resource management, and allocation in SAGIN is of great significance. To the best of our knowledge, we are the first to present the state-of-the-art of the SAGIN since existing survey papers focused on either only one single network segment in space or air, or the integration of space-ground, neglecting the integration of all the three network segments. In light of this, we present in this paper a comprehensive review of recent research works concerning SAGIN from network design and resource allocation to performance analysis and optimization. After discussing several existing network architectures, we also point out some technology challenges and future directions.

Space-Air-Ground Integrated Network: A Survey

Consider a discrete source producing a sequence of message letters from a finite alphabet. A single-letter distortion measure is given by a non-negative matrix (d ij ). The entryd ij measures the ?cost? or ?distortion? if letteriis reproduced at the receiver as letterj. The average distortion of a communications system (source-coder-noisy channel-decoder) is taken to bed= ? i.j P ij d ij whereP ij is the probability ofibeing reproduced asj. It is shown that there is a functionR(d) that measures the ?equivalent rate? of the source for a given level of distortion. For coding purposes where a leveldof distortion can be tolerated, the source acts like one with information rateR(d). Methods are given for calculatingR(d), and various properties discussed. Finally, generalizations to ergodic sources, to continuous sources, and to distortion measures involving blocks of letters are developed. In this paper a study is made of the problem of coding a discrete source of information, given afidelity criterionor ameasure of the distortionof the final recovered message at the receiving point relative to the actual transmitted message. In a particular case there might be a certain tolerable level of distortion as determined by this measure. It is desired to so encode the information that the maximum possible signaling rate is obtained without exceeding the tolerable distortion level. This work is an expansion and detailed elaboration of ideas presented earlier [1], with particular reference to the discrete case. We shall show that for a wide class of distortion measures and discrete sources of information there exists a functionR(d) (depending on the particular distortion measure and source) which measures, in a sense, the equivalent rateRof the source (in bits per letter produced) whendis the allowed distortion level. Methods will be given for evaluatingR(d) explicitly in certain simple cases and for evaluatingR(d) by a limiting process in more complex cases. The basic results are roughly that it is impossible to signal at a rate faster thanC/R(d) (source letters per second) over a memoryless channel of capacityC(bits per second) with a distortion measure less than or equal tod. On the other hand, by sufficiently long block codes it is possible to approach as closely as desired the rateC/R(d) with distortion leveld. Finally, some particular examples, using error probability per letter of message and other simple distortion measures, are worked out in detail.

Coding Theorems for a Discrete Source With a Fidelity CriterionInstitute of Radio Engineers, International Convention Record, vol. 7, 1959.

This paper evaluates the effects of bandwidth asymmetry introduced in a geostationary DVB-RCS satellite architecture on the round trip time of the transmission control protocol (TCP). In particular, it shows the analytical approximation of the round trip time (RTT) of a TCP connection and defines a bandwidth asymmetry index, which is the key point of the work. The final goal is the provision of analytical equations approximating the RTT behavior over asymmetric satellite networks in strict dependence on the asymmetry index. It can help design DVB-RCS system and evaluate their performance. The results are compared with the values obtained through the ns-2 simulator

/pdf/analysis-of-the-tcp-round-trip-time-over-asymmetric-dvb-rcs-3zoubvvt18.pdf

Analysis of the TCP round trip time over asymmetric DVB-RCS systems

This chapter contains the description of a simulative/emulative platform developed by the authors and called the “Hybrid Simulative-Emulative Platform (HySEP).” It has been designed and built to simulate long term evolution (LTE) networks by using Network Simulator 3 (ns-3) and to emulate a backhaul network that implements the Differentiated Service (DiffServ) solution to guarantee Quality of Service (QoS). The former composes the Simulated Network Segment (SNS), the latter the Emulated Network Segment (ENS). The use of ns-3 assures a detailed LTE simulative model and an effective mechanism to connect the simulated scenario with real network nodes and links. Moreover, this platform enables the creation of a heterogeneous network through the exploitation of personal computers and free software without using any ad-hoc hardware. HySEP makes possible testing different network configurations, limiting costs and using technologies such as LTE whose real implementation is hardly applicable inside a research laboratory. The tool can be completely configured and used remotely through Internet connections.

An Ns-3 based simulative and emulative platform

Context information is fundamental for mobile application. A system able to detect if a smartphone is indoors or outdoors can give useful information to upper-level applications, permitting to improve their performance or reduce the computational load and consequently the lifetime of the smartphone battery. For example, GPS provides an accurate location reference in the outdoor environment while it performs poorly inside buildings. The proposed Indoor/Outdoor (IO) detector can provide a useful essential information to a localization application that can check whether the user is outdoors before turning on the GPS interface and decide not to turn it on and use other localization methods if the user is detected indoors. In mobile data services, mobile phones normally observe more WiFi access points (APs) with strong signals inside buildings, whereas it is unlikely to have good WiFi connections in outdoor environments. Therefore, knowing whether the smartphone is indoors or outdoors can help to make smarter decisions regarding whether to perform or not AP scans. Although it is clear that various applications may benefit from accurate and prompt indoor/outdoor information, the research work on indoor/outdoor detection of mobile devices is still lacking. There are mainly two techniques to perform such detection. One is to use GPS and its signal quality as a cue to infer if the user is indoor. This technique is proven to be highly power consuming. Another technique is to leverage the sensors which the smartphone is equipped with. IO detection can be done by exploiting lightweight sensors such as the light sensor, the radio interface and the magnetism sensor [1]. The proposed IO detector is an active system. The phone periodically emits an ultrasonic ping using its in-built speakers and continuously listens for the echoes through its microphone. It is impossible to identify the direction of the echoes being the microphone (as well as the phone speakers) non-directional. The idea is that indoors the number and the intensity of the echoes should be higher than outdoors due to the higher number of obstacles. Translating such an idea into a practical Indoor/Outdoor detector means finding those features that model such behaviour. The proposed

Poster: Detecting if a Smartphone is Indoors or Outdoors with Ultrasounds

In-home physical therapy is one of the best options for many individuals and families thanks to its convenience and because it makes possible to receive professional care in the comfort of your own home. To enable this therapeutic approach, this paper proposes the employment of a smartphone-centric platform for in-home rehabilitation. The platform helps physicians to monitor the patients remotely so avoiding hospitalization therapies that can be stressful. In more detail, the work is focused on the Movement Recognition (MR) functionality of the aforementioned platform. It compares algorithms, which process the signal provided by the embedded accelerometer sensor of the smartphone, able to recognize if a patient had performed the movements requested by the physicians. The provided performance comparison of different MR techniques shows that Support Vector Machine-based approaches have very good accuracy (up to 99.3%), thus making the in-home physical therapy reliable.

Enabling smartphone-centric platforms for in-home rehabilitation: A comparison among movement recognition approaches

In Satellite-based Sensor Networks (SSN), earth stations represent the sink nodes of the sensor field and they may be simultaneously used to sent messages from the sensors to the remote monitoring hosts where data are stored and managed. In this environment, the choice of the sink may play a crucial role and represent a interesting field of investigation. The work includes: an introduction of the network scenario considered; a brief description of the Sink selection methods aimed at guaranteeing the optimization of the energy consumption and, simultaneously, of the message transfer delay; a performance investigation of the proposals, which represents the main contribution of this paper, carried out by simulation.

Igor Bisio

Papers

Analysis of the TCP round trip time over asymmetric DVB-RCS systems

An Ns-3 based simulative and emulative platform

Poster: Detecting if a Smartphone is Indoors or Outdoors with Ultrasounds

Enabling smartphone-centric platforms for in-home rehabilitation: A comparison among movement recognition approaches

Multi Attribute Sink Selection Techniques in Satellite Sensor Networks: Study and Performance Evaluation