Download Full Article QUANTUM_DOT_LASERS

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.

Download Full Article QUANTUM_DOT_LASERS

Download Full Article Real-time systems

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.

 Download Full Article Real-time systems

Download Full Article SOFTWARE RADIO IN CELL PHONES

The memory hierarchy of high performance and embedded processors has been shown to be one of the major energy consumers. Extrapolating the current trends, this portion is likely to be increased in the near future. In this paper, a technique is proposed which uses an additional mini cache, called the L0-cache, located between the I-cache and the CPU core. This mechanism can provide the instruction stream to the data path, and when managed properly, it can efficiently eliminate the need for high utilization of the more expensive I-cache.

Five techniques are proposed and evaluated which are used to the dynamic analysis of the program instruction access behavior and to proactively guide the L0-cache. The basic idea is that only the most frequently executed portion of the code should be stored in the L0-cache, since this is where the program spends most of its time.

Results of the experiments indicate that more than 60% of the dissipated energy in the I-cache subsystem can be saved.

INTRODUCTION

                  In recent years, power dissipation has become one of the major design concerns for the microprocessor industry. The shrinking device size and the large number of devices packed in a chip die coupled with large operating frequencies, have led to unacceptably high levels of power dissipation. The problem of wasted power caused by unnecessary activities in various parts of the CPU during code execution has traditionally been ignored in code optimization and architectural design.

                       Higher frequencies and large transistor counts more than offset the lower voltages and the smaller the devices and they result in large power consumption in a newest version in a processor family.

Download Full Article SOFTWARE RADIO IN CELL PHONES

Download Full Article Steganography - The Art of Hiding Information

Steganography, from the Greek, means covered or secret writing, and is a long-practiced form of hiding information. Although related to cryptography, they are not the same. Steganography’s intent is to hide the existence of the message, while cryptography scrambles a message so that it cannot be understood.

More precisely, 

“the goal of steganography is to hide messages inside other harmless messages in a way that does not allow any enemy to even detect that there is a second secret message present.”

Steganography includes a vast array of techniques for hiding messages in a variety of media. Among these methods are invisible inks, microdots, digital signatures, covert channels and spread-spectrum communications. Today, thanks to modern technology, steganography is used on text, images, sound, signals, and more.

The advantage of steganography is that it can be used to secretly transmit messages without the fact of the transmission being discovered. Often, using encryption might identify the sender or receiver as somebody with something to hide. For example, that picture of your cat could conceal the plans for your company’s latest technical innovation.

However, steganography has a number of disadvantages as well. Unlike encryption, it generally requires a lot of overhead to hide a relatively few bits of information. However, there are ways around this. Also, once a steganographic system is discovered, it is rendered useless. This problem, too, can be overcome if the hidden data depends on some sort of key for its insertion and extraction.

In fact, it is common practice to encrypt the hidden message before placing it in the cover message. However, it should be noted that the hidden message does not need to be encrypted to qualify as steganography. The message itself can be in plain English and still be a hidden message. However, most steganographers like the extra layer of protection that encryption provides. If your hidden message is found, and then at least make it as protected as possible.

This seminar aims to outline a general introduction to steganography - what it is, and where it comes from. Methods for hiding data in three varied media (text, image, and audio) will be described, and some guidelines for users of steganography will be provided where necessary. In addition, we will take a brief look at steganalysis, the science of detecting steganography, and destroying it.

Introduction to Terms used

In the field of steganography, some terminology has developed.

The adjectives cover, embedded and stego were defined at the Information Hiding Workshop held in Cambridge, England. The term “cover” is used to describe the original, innocent message, data, audio, still, video and so on. When referring to audio signal steganography, the cover signal is sometimes called the “host” signal.

The information to be hidden in the cover data is known as the “embedded” data. The “stego” data is the data containing both the cover signal and the “embedded” information. Logically, the processing of putting the hidden or embedded data, into the cover data, is sometimes known as embedding. Occasionally, especially when referring to image steganography, the cover image is known as the container.

Steganography under Various Media

In the following three sections we will try to show how steganography can and is being used through the media of text, images, and audio.

Often, although it is not necessary, the hidden messages will be encrypted. This meets a requirement posed by the “Kerckhoff principle” in cryptography. This principle states that the security of the system has to be based on the assumption that the enemy has full knowledge of the design and implementation details of the steganographic system. The only missing information for the enemy is a short, easily exchangeable random number sequence, the secret key. Without this secret key, the enemy should not have the chance to even suspect that on an observed communication channel, hidden communication is taking place. Most of the software that we will discuss later meets this principle.

When embedding data, it is important to remember the following restrictions and features:

• The cover data should not be significantly degraded by the embedded data, and the embedded data should be as imperceptible as possible. (This does not mean the embedded data needs to be invisible; it is possible for the data to be hidden while it remains in plain sight.)
• The embedded data should be directly encoded into the media, rather than into a header or wrapper, to maintain data consistency across formats.
• The embedded data should be as immune as possible to modifications from intelligent attacks or anticipated manipulations such as filtering and resampling.
• Some distortion or degradation of the embedded data can be expected when the cover data is modified. To minimize this, error correcting codes should be used.
• The embedded data should be self-clocking or arbitrarily re-entrant. This ensures that the embedded data can still be extracted when only portions of the cover data are available. For example, if only a part of image is available, the embedded data should still be recoverable.

 Download Full Article Steganography - The Art of Hiding Information