Showing posts with label Electronics Engineering. Show all posts
Showing posts with label Electronics Engineering. Show all posts

Aeronautical Communications

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In the future, airliners will provide a variety of entertainment and communications equipment to the passenger. Since people are becoming more and more used to their own communications equipment, such as mobile phones and laptops with Internet connection, either through a network interface card or dial-in access through modems, business travellers will soon be demanding wireless access to communication services.  Specifically it focus on wireless services such as UMTS and W-LAN in aircraft cabins that connect the passenger via satellite to terrestrial infrastructure. Current trends are towards high data rate communication services, in particular internet applications.  In an aeronautical scenario global coverage is essential for providing continuous service.  Therefore satellite communication became indispensable, and together with ever increasing data rate requirements of applications, aeronautical satellite communication meets an expensive market. Certain features of UMTS and W-LAN that helps to provide these services are also explained.
INTRODUCTION
                 The demand for making air traveling more ‘pleasant, secure and productive for passengers is one of the winning factors for airlines and aircraft industry. Current trends are towards high data rate communication services, in particular Internet applications. In an aeronautical scenario global coverage is essential for providing continuous service. Therefore satellite communication becomes indispensable, and together with the ever increasing data rate requirements of applications, aeronautical satellite communication meets an expansive market.
                Wireless Cabin (IST -2001-37466) is looking into those radio access technologies to be transported via satellite to terrestrial backbones .  The project will provide UMTS services, W-LAN IEEE 802.11 b and Blue tooth to the cabin passengers. With the advent of new services a detailed investigation of the expected traffic is necessary in order to plan the needed capacities to fulfill the QoS demands. This paper will thus describe a methodology for the planning of such system.
            

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Smart Memories

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Trends in VLSI technology scaling demand that future computing devices be narrowly focused to achieve high performance and high efficiency, yet also target the high volumes and low costs of widely applicable general-purpose designs. To address these conflicting requirements, here propose a modular reconfigurable architecture called Smart Memories, targeted at computing needs in the 0.1mm technology generation. A Smart Memories chip is made up of many processing tiles, each containing local memory, local interconnect, and a processor core. For efficient computation under a wide class of possible applications, the memories, the wires, and the computational model can all be altered to match the applications. To show the applicability of this design, two very different machines at opposite ends of the architectural spectrum, the Imagine stream processor and the Hydra speculative multiprocessor, are mapped onto the Smart Memories computing substrate. Simulations of the mappings show that the Smart Memories architecture can successfully map these architectures with only modest performance degradation.
INTRODUCTION

            The continued scaling of integrated circuit fabrication technology will dramatically affect the architecture of future computing systems. Scaling will make computation cheaper, smaller, and lower power, thus enabling more sophisticated computation in a growing number of embedded applications. This spread of low-cost, low power computing can easily be seen in today’s wired (e.g. gigabit Ethernet or DSL) and wireless communication devices, gaming consoles, and handheld PDAs. These new applications have different characteristics from today’s standard workloads, often containing highly data-parallel streaming behavior. While the applications will demand ever-growing compute performance, power (ops/W) and computational efficiency (ops/$) are also paramount; therefore, designers have created narrowly focused custom silicon solutions to meet these needs.

                 However, the scaling of process technologies makes the construction of custom solutions increasingly difficult due to the increasing complexity of the desired devices. While designer productivity has improved over time, and technologies like system-on-a-chip help to manage complexity, each generation of complex machines is more expensive to design than the previous one. High non-recurring fabrication costs (e.g. mask generation) and long chip manufacturing delays mean that designs must be all the more carefully validated, further increasing the design costs. Thus, these large complex chips are only cost-effective if they can be sold in large volumes. This need for a large market runs counter to the drive for efficient, narrowly- focused, custom hardware solutions.

                 To fill the need for widely applicable computing designs, a number of more general-purpose processors are targeted at a class of problems, rather than at specific applications. Tri-media, Equator, Mpact, IRAM, and many other projects are all attempts to create general purpose computing engine for multi-media applications. However, these attempts to create more universal computing elements have some limitations. First, these machines have been optimized for applications where the parallelism can be expressed at the instruction level using either VLIW or vector engines. However, they would not be very efficient for applications that lacked parallelism at this level, but had, for example, thread level parallelism. Second, their globally shared resource models (shared multi-ported registers and memory) will be increasingly difficult to implement in future technologies in which on-chip communication costs are appreciable. Finally, since these machines are generally compromise solutions between true signal processing engines and general-purpose processors, their efficiency at doing either task suffers.

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Modelling of Delay Lines on Pcbs

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Designers of printed circuit boards often face the problem illustrated by the example in Figure 1.It is desired to transmit signals 1, 2 and 3 from one chip to the other with precisely the same transmission delay. However, with the routing pattern in Figure 1a, signal 3 has a longer path and will arrive later. The conventional solution, shown in Figure 1b, artificially extends the paths of signals 1 and 2 to match the lengths of all wires.
An example where meander lines might be used is as a bus between a processor and memory. Another example is a clock distribution tree between a clock synthesizer and target clocked circuits.

Traces such as those for signals 1 and 2 are called serpentine lines or meander lines. In the past, meander lines have been used with the assumption that the extra wire length is electrically identical to a straight section, and no parasitics were introduced. As trace dimensions become smaller and signal frequencies increase, that assumption may no longer be valid.

In this report, we present measurements of the time delay through, and characteristic impedance of meander lines as compared to an equivalent length of straight line.

It is seen that the delay through a meander line is shorter than the delay through an equivalent length of straight trace. This is because coupling between the segments of the meander lines shortens the electrical path.

The remainder of this report is organized as follows. Section 2 gives the physical background of transmission lines and meander lines, and defines terms used in the rest of the report. Section 3 discusses our measurement methods and reports experimental results. In Section 4, we discuss the results, and Section 5 gives a model for the observed effects. Finally, Section 6 gives conclusions.



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Smart Dust

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The ‘Smart Dust’ project is aiming to build an autonomous sensing, computing, and communication system packed into a cubic-millimeter mote, to form the basis of integrated, massively distributed sensor networks.  So, this device will be around the size of a grain of sand and will contain sensors, computational ability, bidirectional wireless communications, and power supply, while being inexpensive enough to deploy by the hundreds.  Smart Dust requires evolutionary and revolutionary advances in integration, miniaturization and energy management.
If the project is successful, clouds of smart dust could one day be used in an astonishing array of application, from following enemy troop movements and hunting send missiles to detecting toxic chemicals in the environment and monitoring weather patters around the globe.
INTRODUCTION
The current ultramodern technologies are focusing on automation and miniaturization.  The decreasing computing device size, increased connectivity and enhanced interaction with the physical world have characterized computing’s history.  Recently, the popularity of small computing devices, such as hand held computers and cell phones; rapidly flourishing internet group and the diminishing size and cost of sensors and especially transistors have accelerated these strengths.  The emergence of small computing elements, with sporadic connectivity and increased interaction with the environment, provides enriched opportunities to reshape interactions between people and computers and spur ubiquitous computing researches.  
Smart dust is tiny electronic devices designed to capture mountains of information about their surroundings while literally floating on air.  Nowadays, sensors, computers and communicators are shrinking down to ridiculously small sizes.  If all of these are packed into a single tiny device, it can open up new dimensions in the field of communications.
The idea behind ‘smart dust’ is to pack sophisticated sensors, tiny computers and wireless communicators in to a cubic-millimeter mote to form the basis of integrated, massively distributed sensor networks.  They will be light enough to remain suspended in air for hours.  As the motes drift on wind, they can monitor the environment for light, sound, temperature, chemical composition and a wide range of other information, and beam that data back to the base station, miles away.

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Real-time systems

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Real-time systems play a considerable role in our society, and they cover a spectrum from the very simple to the very complex. Examples of current real-time systems include the control of domestic appliances like washing machines and televisions, the control of automobile engines, telecommunication switching systems, military command and control systems, industrial process control, flight control systems, and space shuttle and aircraft avionics.
All of these involve gathering data from the environment, processing of gathered data, and providing timely response. A concept of time is the distinguishing issue between real-time and non-real-time systems. When a usual design goal for non-real-time systems is to maximize system’s throughput, the goal for real-time system design is to guarantee, that all tasks are processed within a given time. The taxonomy of time introduces special aspects for real-time system research.                                            
Real-time operating systems are an integral part of real-time systems. Future systems will be much larger, more widely distributed, and will be expected to perform  a  constantly  changing  set  of duties  in  dynamic  environments. This also sets more requirements for future real-time operating systems.
This seminar has the humble aim to convey the main ideas on Real Time System and Real Time Operating System design and implementation.
INTRODUCTION
Timeliness is the single most important aspect of a real -time system. These systems  respond to a series of external inputs, which arrive in an unpredictable fashion. The  real-time systems process these inputs, take appropriate decis ions and also generate  output necessary to control the peripherals connected to them. As defined by Donald  Gillies “A real-time system is one in which the correctness of the computations not only  depends upon the logical correctness of the computation but  also upon the time in  which the result is produced. If the timing constraints are not met, system failure is said  to have occurred.”
It is essential that the timing constraints of the system are guaranteed to be met.  Guaranteeing timing behaviour requires that the system be predictable.
The design of a real -time system must specify the timing requirements of the system  and ensure that the system performance is both correct and timely. There are three  types of time constraints:
Ø  Hard:  A late response is incor rect and implies a system failure. An example of such a system is of medical equipment monitoring vital functions of a human body,  where a late response would be considered as a failure.
Ø  Soft:  Timeliness requirements are defined by using an average respons e time. If a single computation is late, it is not usually significant, although repeated late  computation can result in system failures. An example of such a system includes  airlines reservation systems.
Ø  Firm:  This is a combination of both hard and soft t imeliness requirements. The computation has a shorter soft requirement and a longer hard requirement. For  example, a patient ventilator must mechanically ventilate the patient a certain  amount in a given time period. A few seconds’ delay in the initiation  of breath is  allowed, but not more than that. 
One need to distinguish between on -line systems such as an airline reservation system,  which operates in real-time but with much less severe timeliness constraints than, say, a missile control system or a telephone switch. An interactive system with better response  time is not a real-time system. These types of systems are often referred to as soft real time systems. In a soft real -time  system  (such  as  the  airline  reservation  system)  late  data is still good dat a. However, for hard real -time systems, late data is bad data. In  this paper we concentrate on the hard and firm real-time systems only.
Most real -time systems interface with and control hardware directly. The software for  such systems is mostly custom -developed. Real -time Applications can be either  embedded applications or non -embedded (desktop) applications. Real -time systems  often do not have standard peripherals associated with a desktop computer, namely the  keyboard, mouse or conventional display monitors. In most instances, real-time systems  have a customized version of these devices.

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Quantum Dot Lasers

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The infrastructure of the Information Age has to date relied upon advances in microelectronics to produce integrated circuits that continually become smaller, better, and less expensive.  The emergence of photonics, where light rather than electricity is manipulated, is posed to further advance the Information Age.  Central to the photonic revolution is the development of miniature light sources such as the Quantum dots(QDs).  Today, Quantum Dots manufacturing has been established to serve new datacom and telecom markets. 
Recent progress in microcavity physics, new materials, and fabrication technologies has enabled a new generation of high performance QDs.  This presentation will review commercial QDs and their applications as well as discuss recent research, including new device structures such as composite resonators and photonic crystals
Semiconductor lasers are key components in a host of widely used technological products, including compact disk players and laser printers, and they will play critical roles in optical communication schemes. The basis of laser operation depends on the creation of non-equilibrium populations of electrons and holes, and coupling of electrons and holes to an optical field, which will stimulate radiative emission. . Other benefits of quantum dot active layers include further reduction in threshold currents and an increase in differential gain-that is, more efficient laser operation.
Since the 1994 demonstration of a quantum dot (QD) semiconductor laser, the research progress in developing lasers based on QDs has been impressive. Because of their fundamentally different physics that stem from zero-dimensional electronic states, QD lasers now surpass the established planar quantum well laser technology in several respects. These include their minimum threshold current density, the threshold dependence on temperature, and range of wavelengths obtainable in given strained layer material systems. Self-organized QDs are formed from strained-layer epitaxy. Upon reaching such conditions, the growth front can spontaneously reorganize to form 3-dimensional islands. The greater strain relief provided by the 3-dimensionally structured crystal surface prevents the formation of dislocations. When covered with additional epitaxy, the coherently strained islands form the QDs that trap and isolate individual electron-hole pairs to create efficient light emitters.

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Laser Communication

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Laser communications offer a viable alternative to RF communications for inter satellite links and other applications where high-performance links are a necessity. High data rate, small antenna size, narrow beam divergence, and a narrow field of view are characteristics of laser communications that offer a number of potential advantages for system design.
Lasers have been considered for space communications since their realization in 1960. Specific advancements were needed in component performance and system engineering particularly for space qualified hardware. Advances in system architecture, data formatting and component technology over the past three decades have made laser communications in space not only viable but also an attractive approach into inter satellite link applications.
Information transfer is driving the requirements to higher data rates, laser cross -link technology explosions, global development activity, increased hardware, and design maturity. Most important in space laser communications has been the development of a reliable, high power, single mode laser diode as a directly modulable laser source. This technology advance offers the space laser communication system designer the flexibility to design very lightweight, high bandwidth, low-cost communication payloads for satellites whose launch costs are a very strong function of launch weigh. This feature substantially reduces blockage of fields of view of most desirable areas on satellites. The smaller antennas with diameter typically less than 30 centimeters create less momentum disturbance to any sensitive satellite sensors. Fewer on board consumables are required over the long lifetime because there are fewer disturbances to the satellite compared with heavier and larger RF systems. The narrow beam divergence affords interference free and secure operation.

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BLAST

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BLAST is a wireless communications technique which uses multi-element antennas at both transmitter and receiver to permit transmission rates far in excess of those possible using conventional approaches.
In wireless systems, radio waves do not propagate simply from transmit antenna to receive antenna, but bounce and scatter randomly off objects in the environment. This scattering known as multipath, as it results in multiple copies (“images”) of the transmitted sign arriving at the receiver via different scattered paths. In conventional wireless system multipath represents a significant impediment to accurate transmission, because the image arrive at the receiver at slightly different times and can thus interfere destructively, canceling each other out. For this reason, multipath is traditionally viewed as a serious impairment. Using the BLAST approach however, it is possible toexploit multipath, that is, to use the scattering characteristics of the propagation environment to enhance, rather than degrade transmission accuracy by treating the multiplicity of scattering paths as separate parallel sub channels.
INTRODUCTION
                    The explosive growth of both the wireless industry and the Internet is creating a huge market opportunity for wireless data access. Limited internet access, at very low speeds, is already available as an enhancement to some existing cellular systems. However those systems were designed with purpose of providing voice services and at most short messaging, but not fast data transfer. Traditional wireless technologies are not very well suited to meet the demanding requirements of providing very high data rates with the ubiquity, mobility and portability characteristics of cellular systems. Increased use of antenna arrays appears to be the only means of enabling the type of data rates and capacities needed for wireless internet and multimedia services. While the deployment of  base station arrays is becoming universal it is really the simultaneous deployment of base station and terminal arrays that can unleash unprecedented  levels of performance by opening up multiple spatial signaling dimensions .Theoretically, user data rates as high as 2 Mb/sec will be supported in certain environments, although recent studies have shown that approaching those might only be feasible under extremely favorable conditions-in the vicinity of the base station and with no other users competing for band width. Some fundamental barriers related to the nature of radio channel as well as to the limited band width availability at the frequencies of interest stand in the way of high data rates and low cost associated with wide access.

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ATM

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Nowadays, most us are surrounded by powerful computer systems with graphics oriented input and output.
These computers include the entire spectrum of PCs, through professional workstations upto super-computers.  As the performance of computers has increased, so too has the demand for communication between all systems for exchanging data, or between central servers and the associated host computer system.
The replacement of copper with fiber and the advancement sin digital communication and encoding are at the heart of several developments that will change the communication infrastructure. The former development has provided us with huge amount of transmission bandwidth.  While the latter has made the transmission of all information including voice and video through a packet switched network possible.
With continuously work sharing over large distances, including international communication, the systems must be interconnected via wide area networks with increasing demands for higher bit rates.
For the first time, a single communications technology meets LAN and WAN requirements and handles a wide variety of current and emerging applications.  ATM is the first technology to provide a common format for bursts of high speed data and the ebb and flow of the typical voice phone call.  Seamless ATM networks provide desktop-to-desktop multimedia networking over single technology, high bandwidth, low latency network, removing the boundary between LAN WAN.
ATM is simply a Data Link Layer protocol.  It is asynchronous in the sense that the recurrence of the cells containing information from an individual user is not necessarily periodic.  It is the technology of choice for evolving B-ISDN (Board Integrated Services Digital Network), for next generation LANs and WANs. ATM supports transmission speeds of 155Mbits / sec.  In the future.  Photonic approaches have made the advent of ATM switches feasible, and an evolution towards an all packetized, unified, broadband telecommunications and data communication world based on ATM is taking place.

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BLAST

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BLAST is a wireless communications technique which uses multi-element antennas at both transmitter and receiver to permit transmission rates far in excess of those possible using conventional approaches.
In wireless systems, radio waves do not propagate simply from transmit antenna to receive antenna, but bounce and scatter randomly off objects in the environment. This scattering known as multipath, as it results in multiple copies (“images”) of the transmitted sign arriving at the receiver via different scattered paths. In conventional wireless system multipath represents a significant impediment to accurate transmission, because the image arrive at the receiver at slightly different times and can thus interfere destructively, canceling each other out. For this reason, multipath is traditionally viewed as a serious impairment. Using the BLAST approach however, it is possible toexploit multipath, that is, to use the scattering characteristics of the propagation environment to enhance, rather than degrade transmission accuracy by treating the multiplicity of scattering paths as separate parallel sub channels.
INTRODUCTION
                    The explosive growth of both the wireless industry and the Internet is creating a huge market opportunity for wireless data access. Limited internet access, at very low speeds, is already available as an enhancement to some existing cellular systems. However those systems were designed with purpose of providing voice services and at most short messaging, but not fast data transfer. Traditional wireless technologies are not very well suited to meet the demanding requirements of providing very high data rates with the ubiquity, mobility and portability characteristics of cellular systems. Increased use of antenna arrays appears to be the only means of enabling the type of data rates and capacities needed for wireless internet and multimedia services. While the deployment of  base station arrays is becoming universal it is really the simultaneous deployment of base station and terminal arrays that can unleash unprecedented  levels of performance by opening up multiple spatial signaling dimensions .Theoretically, user data rates as high as 2 Mb/sec will be supported in certain environments, although recent studies have shown that approaching those might only be feasible under extremely favorable conditions-in the vicinity of the base station and with no other users competing for band width. Some fundamental barriers related to the nature of radio channel as well as to the limited band width availability at the frequencies of interest stand in the way of high data rates and low cost associated with wide access.

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Blue Eyes

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Imagine yourself in a world where humans interact with computers. You are sitting in front of your personal computer that can listen, talk, or even scream aloud. It has the ability to gather information about you and interact with you through special techniques like facial recognition, speech recognition, etc. It can even understand your emotions at the touch of the mouse. It verifies your identity, feels your presents, and starts interacting with you .You ask the computer to dial to your friend at his office. It realizes the urgency of the situation through the mouse, dials your friend at his office, and establishes a connection.
Human cognition depends primarily on the ability to perceive, interpret, and integrate audio-visuals and sensoring information. Adding extraordinary perceptual abilities to computers would enable computers to work together with human beings as intimate partners. Researchers are attempting to add more capabilities to computers that will allow them to interact like humans, recognize human presents, talk, listen, or even guess their feelings.
The BLUE EYES technology aims at creating computational machines that have perceptual and sensory ability like those of human beings. It uses non-obtrusige sensing method, employing most modern video cameras and microphones to identifies the users actions through the use of imparted sensory abilities . The machine can understand what a user wants, where he is looking at, and even realize his physical or emotional states.
EMOTION MOUSE
One goal of human computer interaction (HCI) is to make an adaptive, smart computer system. This type of project could possibly include gesture recognition, facial recognition, eye tracking, speech recognition, etc. Another non-invasive way to obtain information about a person is through touch. People use their computers to obtain, store and manipulate data using their computer. In order to start creating smart computers, the computer must start gaining information about the user. Our proposed method for gaining user information through touch is via a computer input device, the mouse. From the physiological data obtained from the user, an emotional state may be determined which would then be related to the task the user is currently doing on the computer. Over a period of time, a user model will be built in order to gain a sense of the user’s personality. The scope of the project is to have the computer adapt to the user in order to create a better working environment where the user is more productive. The first steps towards realizing this goal are described here.

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BiCMOS Technology

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  The need for high-performance, low-power, and low-cost systems for network transport and wireless communications is driving silicon technology toward higher speed, higher integration, and more functionality. Further more, this integration of RF and analog mixed-signal circuits into high-performance digital signal-processing (DSP) systems must be done with minimum cost overhead to be commercially viable. While some analog and RF designs have been attempted in mainstream digital-only complimentary metal-oxide semiconductor (CMOS) technologies, almost all designs that require stringent RF performance use bipolar or semiconductor technology. Silicon integrated circuit (IC) products that, at present, require modern bipolar or BiCMOS silicon technology in wired application space include the essential optical network (SONET) and synchronous digital hierarchy (SDH) operating at 10 Gb/s and higher.
           The viability of a mixed digital/analog. RF chip depends on the cost of making the silicon with the required elements; in practice, it must approximate the cost of the CMOS wafer, Cycle times for processing the wafer should not significantly exceed cycle times for a digital CMOS wafer. Yields of the SOC chip must be similar to those of a multi-chip implementation. Much of this article will examine process techniques that achieve the objectives of low cost, rapid cycle time, and solid yield.

INTRODUCTION

              The history of semiconductor devices starts in 1930’s when Lienfed and Heil first proposed the mosfet. However it took 30 years before this idea was applied to functioning devices to be used in practical applications, and up to the late 1980 this trend took a turn when MOS technology caught up and there was a cross over between bipolar and MOS share.CMOS was finding more wide spread use due to its low power dissipation, high packing density and simple design, such that by 1990 CMOS covered more than 90% of total MOS scale.
              In 1983 bipolar compatible process based on CMOS technology was developed and BiCMOS technology with both the MOS and bipolar device fabricated on the same chip was developed and studied. The objective of the BiCMOS is to combine bipolar and CMOS so as to exploit the advantages of both at the circuit and system levels. Since 1985, the state-of-the-art bipolar CMOS structures have been converging. Today BiCMOS has become one of the dominant technologies used for high speed, low power and highly functional VLSI circuits especially when the BiCMOS process has been enhanced and integrated in to the CMOS process without any additional steps. Because the    process step required for both CMOS and bipolar are similar, these steps cane be shared for both of them.

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Boiler Instrumentation and Controls

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 Instrumentation and controls in a boiler plant encompass an enormous range of equipment from simple in the small industrial plant to the complex in the large utility station. Boiler Instrumentation Control is the control over the industrial boilers. It consists of several control loops to control various systems related to a boiler. The main control of boilers   include combination control and feed water control. To do the various operations in control different hardware methods are used.
Virtually any boiler-old or new, industrial or utility can benefit from or several control system modifications available today either by introducing advanced control schemes adding to existing control schemes
INTRODUCTION
Instrumentation and controls in a boiler plant encompass an enormous range of equipment from simple industrial plant to the complex in the large utility station. 
The boiler control system is the means by which the balance of energy & mass into and out of the boiler are achieved. Inputs are fuel, combustion air, atomizing air or steam &feed water. Of these, fuel is the major energy input. Combustion air is the major mass input, outputs are steam, flue gas, blowdown, radiation & soot blowing.
CONTROL LOOPS
Boiler control systems contain several variable with interaction occurring among the control loops for fuel, combustion air, & feedwater . The overall system generally can be treated as a series of basic control loops connected together. for safety purposes, fuel addition should be limited by the amount of combustion air and it may need minimum limiting for flame stability.
Combustion controls
              Amounts of fuel  and air must be carefully regulated to keep excess air within close tolerances-especially over the loads. This is critical to efficient boiler operation no matter what the unit size, type of fuel fired or control system used.
Feedwater control
           Industrial boilers are subject to wide load variations and require quick responding control to maintain constant drum level. Multiple element feed water control can help faster and more accurate control response…

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Cable Modems

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A cable modem is a digital device, which connects the computer system to the Internet, via a coaxial cable, usually the same as used in a cable television network. It converts digital information into modulated RF signals(upstream) and RF signals back to digital information (downstream) across cable TV networks. Cable modem allows high-speed access to the Internet via a cable TV network. A cable modem will typically have two connections, one to the cable wall outlet and one to a computer. Most cable modems are external devices that connect to the PC through a standard 10Base-T Ethernet card and twisted-pair wiring. Cable modem speeds vary widely, depending on the cable modem system, cable network architecture, and traffic load. In the downstream direction (from the network to the computer), network speeds can be anywhere up to 27 Mbps, an aggregate amount of bandwidth that is shared by users. In the upstream direction (from computer to network), speeds can be up to 10 Mbps. However, most modem producers have selected a more optimum speed between 500 Kbps and 2.5 Mbps. An asymmetric scheme is used in most cable modems.
The term ‘Cable Modem’ is quite new and refers to a modem that operates over the ordinary cable TV network cables. Basically you just connect the Cable Modem to the TV outlet for your cable TV, and the cable TV operator connects a Cable Modem Termination System (CMTS) in his end (the Head-End).
Actually the term “Cable Modem” is a bit misleading, as a Cable Modem works more like a Local Area Network (LAN) interface than as a modem.
Cable modems allow consumers access to the Internet at higher speeds and at a fraction of the time it takes traditional telephone modems.
This is true for two reasons:
1.      Broadband networks make the connection up to a hundred times faster
2.      The service is “always on,” meaning customers get the information they want, when they want it.
Unlike telephone modems, cable modems allow consumers to keep their telephone lines open for voice conversations.

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Distributed Wireless Communication

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With the rapid progress in telecommunications, more and more services are provided on the basis of broadband communications, such as video services and high-speed Internet. With worldwide fundamental construction of a backbone network based on optical fiber providing almost unlimited communications capability, the limited throughput of the subscriber loop becomes one of the most stringent bottlenecks.Compared to the capacity of the backbone network, which is measured by tens of gigabits per second, the throughput of the subscriber loop is much lower, only up to hundreds of megabits per second for wired systems (including fixed wireless access). However, for mobile access the throughput is even lower, and depends on the mobility of the terminal. For example, the peak data rate is only 2 Mb/s for 3G systems. Since there will be more and more need for mobile services, the poor throughput of mobile access not only limits user applications based on interconnection, but also wastes the capability of the backbone network. This case is quite similar to the traffic conditions shown in Fig. a, which is an image of an ultra-wide expressway with a few narrow entrances. Since the little paths are rough, narrow, and crowded, the problems in Fig. a are:
Terminals are far away from the expressway, which will consume much power.
Too many cars converge into the same narrow paths.
Little paths converge several times before going into the expressway.
The expressway is used insufficiently, since few cars are running on it.
In telecommunications, the optical fiber network (expressway) is relatively much cheaper than the wireless spectrum (little paths), while the capability of the former is much greater than that of the later. As shown in Fig. b, besides the backbone expressway, there are some dedicated sub expressways used to provide direct entrance for distributed subscribers. The above example implies that the high-capacity wired network, being so cheap, can help us solve the problem of wireless access(too many users crowded in a very narrow bandwidth). The key issue is to provide each mobile user a direct or one-hop connection to an optical network.This structure also follows the trend in network evolution: the hierarchical or tree-like structure of traditional networks will be gradually flattened to simple single-layer ones. 

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Free Space Optics

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Free space optics or FSO, free space photonics or optical wireless, refers to the transmission of modulated visible or infrared beams through the atmosphere to obtain optical communication. FSO systems can function over distances of several kilometers. FSO is a line-of-sight technology, which enables optical transmission up to 2.5 Gbps of data, voice and video communications, allowing optical connectivity without deploying fiber optic cable or securing spectrum licenses. Free space optics require light, which can be focused by using either light emitting diodes (LED) or LASERS(light amplification by stimulated emission of radiation). The use of lasers is a simple concept similar to optical transmissions using fiber-optic cables, the only difference being the medium.

As long as there is a clear line of sight between the source and the destination and enough transmitter power, communication is possible virtually at the speed of light. Because light travels through air faster than it does through glass, so it is fair to classify FSO as optical communications at the speed of light. FSO works on the same basic principle as infrared television remote controls, wireless keyboards or wireless palm devices.

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Electrophysiological Interactive Computer Systems

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New interactive computing applications are continually being developed in a bid to support people’s changing work and recreational activities.  As research focuses on one particular class interactive systems, high level models of interaction are formulated and requirements emerge that reflect shared features or common functionality among those systems.  The existence of models of interaction and shared functional requirements mean that support tools can be created which ease the subsequent development of these systems.  The type of tool that interactive systems developers are most familiar with is a library of reusable code that can be used for prototyping and building interactive applications and their interfaces.
A new class of interactive system  is identified, based on shared requirements for detection, processing and presentation of human physiological information.  This is electro physiological interactive computers systems.  It is envisaged that the work will serve as a jumping of point for others interested in exploring the potential of incorporating physiological information into the human machine relationship.  A method of hands free of human computer interaction currently under investigation is based on the detection of consciously controllable human physiological information.  This physiological information can be processed electrically and thereafter transformed into computer control signals and commands. 
INTRODUCTION
EPICS is a new class of interactive system based on detection, processing and presentation of human physiological information .A user physically manipulates an electromechanical device to initiate a computer operation requires the periodic dedication one or both hands. Unfortunately many people work in environments where their hands are fully occupied with other physical tasks. Examples include surgeons, fitters, maintenance engineers, aircraft flight crew and drivers of heavy goods, passenger and private vehicles. In all of these situations, access to information would be better served by alternative, hands-free access control. A further limitation of existing mechanical models of interaction is that they exclude access to those individuals for whom normal physical control is either difficult or impossible. It is clear that supplemental methods of human-machine interaction to those currently available are needed.
EPICS are interactive systems in which the physiological information can be processed electrically and thereafter transformed into computer control signals and commands. Using specialised electronic sensing equipment it is possible to both detect and make available in digital format information pertaining to a wide range of human physiology. Physiological sensing equipment can be used in order to train individuals to gain conscious control over a range of physiological parameters including heart rate, muscle tension and brain activity. The process of making physiological information available to a subject who is being trained to control some aspect of his or her own physiology is known as bio feed back. After training, physiological signals can be applied to hands free human machine control. It can utilize electrical brain activity to directly control a cursor on a computer screen and to input alphanumeric character using a soft keyboard….

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HAAPS

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Affordable bandwidth will be as essential to the Information Revolution in the21 st century as inexpensive power was to the Industrial Revolution in the 18 th and 19 th centuries. Today’s global communications infrastructures of landlines, cellular towers, and satellites are inadequately equipped to support the increasing worldwide demand for faster, better, and less expensive service. At a time when conventional ground and satellite systems are facing increasing obstacles and spiraling costs, a low cost solution is being advocated.
This paper focuses on airborne platforms- airships, planes, helicopters or some hybrid solutions which could operate at stratospheric altitudes for significant periods of time, be low cost and be capable of carrying sizable multipurpose communications payloads. This report briefly presents an overview about the internal architecture of a High Altitude Aeronautical Platform and the various HAAPS projects.
HAAPS
 High Altitude Aeronautical Platform Stations (HAAPS) is the name of a technology for providing wireless narrowband and broadband telecommunication services as well as broadcasting services with either airships or aircrafts. The HAAPS are operating at altitudes between 3 to 22 km. A HAPS shall be able to cover a service area of up to 1′000 km diameter, depending on the minimum elevation angle accepted from the user’s location. The platforms may be airplanes or airships (essentially balloons) and may be manned or un-manned with autonomous operation coupled with remote control from the ground. While the term HAP may not have a rigid definition, we take it to mean a solar-powered and unmanned airplane or airship, capable of long endurance on-station –possibly several years.
Various types of platform options exist: SkyStation™, the Japanese Stratospheric Platform Project, the European Space Agency (ESA) and others suggest the use of airships/blimps/dirigibles. These will be stationed at 21km and are expected to remain aloft for about 5 years. Angel Technologies (HALO™), AeroVironment/ NASA (Helios) and the European Union (Heliplat) propose the use of high altitude long endurance aircraft. The aircraft are either engine or solar powered and are stationed at 16km (HALO) or 21km (Helios). Helios is expected to stay aloft for a minimum of 6 months whereas HALO will have 3 aircraft flying in 8- hour shifts. Platforms Wireless International is implementing a tethered aerostat situated at ~6km.
A high altitude telecommunication system comprises an airborne platform – typically at high atmospheric or stratospheric altitudes – with a telecommunications payload, and associated ground station telecommunications equipment. The combination of altitude, payload capability, and power supply capability makes it ideal to serve new and metropolitan areas with advanced telecommunications services such as broadband access and regional broadcasting. The opportunities for applications are virtually unlimited. The possibilities range from narrowband services such as paging and mobile voice to interactive broadband services such as multimedia and video conferencing. For future telecommunications operators such a platform could provide blanket coverage from day one with the added advantage of not being limited to a single service. Where little or unreliable infrastructure exists, traffic could be switched through air via the HAPS platform. Technically, the concept offers a solution to the propagation and rollout problems of terrestrial infrastructure and capacity and cost problems of satellite networks. Recent developments in digital array antenna technology make it possible to construct 100+ cells from one platform. Linking and switching of traffic between multiple high altitude platforms, satellite networks and terrestrial gateways are also possible. Economically it provides the opportunity for developing countries to have satellite-like infrastructure without the funds flowing out of the country due to gateways and control stations located outside of these countries.

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Landmine detection using impulse ground penetrating radar

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 Landmines are affecting the lives and livelihood of millions of people around the world. The video impulse ground penetrating radar system for detection for small and shallow buried objects has been developed. The hardware combines commercially available components with components specially developed or modified for being used in the system. The GPR system has been desired to measure accurately electromagnetic field backscattered from subsurface targets in order to allow identification of detected targets through the solution of the inverse scattering problem. The GPR has been tested in different environmental conditions and has proved its ability to detect small and shallow buried targets.
INTRODUCTION               
Landmines and unexploded ordnance (UXO) are a legacy of war, insurrection, and guerilla activity. Landmines kill and maim approximately 26,000 people annually. In Cambodia, whole areas of arable land cannot be farmed due to the threat of landmines. United Nations relief operations are made more difficult and dangerous due to the mining of roads. Current demining techniques are heavily reliant on metal detectors and prodders.
Technologies are used for landmine detection are:
·       Metal detectors— capable of finding even low-metal content mines in mineralized soils.
·       Nuclear magnetic resonance, fast neutron activation and thermal neutron activation.
·       Thermal imaging and electro-optical sensors— detect evidence of buried objects.
·       Biological sensors such as dogs, pigs, bees and birds.
·       Chemical sensors such as thermal fluorescence— detect airborne and waterborne presence of explosive vapors.
 In this discussion, we will concentrate on Ground Penetrating Radar (GPR). This ultra wide band radar provides centimeter resolution to locate even small targets. There are two distinct types of GPR, time-domain and frequency domain. Time domain or impulse GPR transmites discrete pulses of nanosecond duration and digitizes the returns at GHz sample rates. Frequency domain GPR systems transmit single frequencies either uniquely, as a series of frequency steps, or as a chirp. The amplitude and phase of the return signal is measured. The resulting data is converted to the time domain. GPR operates by detecting the dielectric contrasts in the soils, which allows it to locate even non metallic mines.
In this discussion we deal with buried anti-tank (AT) and anti-personnel (AP) landmines which require close approach or contact to activate. AT mines range from about 15 to 35 cm in size. They are typically buried up to 40cm deep, but they can also be deployed on the surface of a road to block a column of machinery. AP mines range from about 5 to 15cm in size. AT mines which are designed to impede the progress of destroy vehicles and AP mines which are designed to kill and maim people.

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