Adaptive Optics in Ground Based Telescopes(electronics seminar topic)

Adaptive optics is a new technology which is being used now a days in ground based telescopes to remove atmospheric tremor and thus provide a clearer and brighter view of stars seen through ground based telescopes. Without using this system, the images obtained through telescopes on earth are seen to be blurred, which is caused by the turbulent mixing of air at different temperatures.

Adaptive optics in effect removes this atmospheric tremor. It brings together the latest in computers, material science, electronic detectors, and digital control in a system that warps and bends a mirror in a telescope to counteract, in real time the atmospheric distortion.

The advance promises to let ground based telescopes reach their fundamental limits of resolution and sensitivity, out performing space based telescopes and ushering in a new era in optical astronomy. Finally, with this technology, it will be possible to see gas-giant type planets in nearby solar systems in our Milky Way galaxy. Although about 100 such planets have been discovered in recent years, all were detected through indirect means, such as the gravitational effects on their parent stars, and none has actually been detected directly.

WHAT IS ADAPTIVE OPTICS ?

Adaptive optics refers to optical systems which adapt to compensate for optical effects introduced by the medium between the object and its image. In theory a telescope's resolving power is directly proportional to the diameter of its primary light gathering lens or mirror. But in practice , images from large telescopes are blurred to a resolution no better than would be seen through a 20 cm aperture with no atmospheric blurring. At scientifically important infrared wavelengths, atmospheric turbulence degrades resolution by at least a factor of 10.

Space telescopes avoid problems with the atmosphere, but they are enormously expensive and the limit on aperture size of telescopes is quite restrictive. The Hubble Space telescope, the world's largest telescope in orbit , has an aperture of only 2.4 metres, while terrestrial telescopes can have a diameter four times that size.

In order to avoid atmospheric aberration, one can turn to larger telescopes on the ground, which have been equipped with ADAPTIVE OPTICS system. With this setup, the image quality that can be recovered is close to that the telescope would deliver if it were in space. Images obtained from the adaptive optics system on the 6.5 m diameter telescope, called the MMT telescope illustrate the impact.

A 64 Point Fourier Transform Chip(electronics seminar topic)

Fourth generation wireless and mobile system are currently the focus of research and development. Broadband wireless system based on orthogonal frequency division multiplexing will allow packet based high data rate communication suitable for video transmission and mobile internet application. Considering this fact we proposed a data path architecture using dedicated hardwire for the baseband processor. The most computationally intensive part of such a high data rate system are the 64-point inverse FFT in the transmit direction and the viterbi decoder in the receiver direction. Accordingly an appropriate design methodology for constructing them has to be chosen a) how much silicon area is needed b) how easily the particular architecture can be made flat for implementation in VLSI c) in actual implementation how many wire crossings and how many long wires carrying signals to remote parts of the design are necessary d) how small the power consumption can be .This paper describes a novel 64-point FFT/IFFT processor which has been developed as part of a large research project to develop a single chip wireless modem.

ALGORITHM FORMULATION

The discrete fourier transformation A(r) of a complex data sequence B(k) of length N
where r, k ={0,1……, N-1} can be described as


Where WN = e-2?j/N . Let us consider that N=MT , ? = s+ Tt and k=l+Mm,where s,l ? {0,1…..7} and m, t ? {0,1,….T-1}. Applying these values in first equation and we get


This shows that it is possible to realize the FFT of length N by first decomposing it to one M and one T-point FFT where N = MT, and combinig them. But this results in in a two dimensional instead of one dimensional structure of FFT. We can formulate 64-point by considering M =T = 8

This shows that it is possible to express the 64-point FFT in terms of a two dimensional structure of 8-point FFTs plus 64 complex inter-dimensional constant multiplications. At first, appropriate data samples undergo an 8-point FFT computation. However, the number of non-trivial multiplications required for each set of 8-point FFT gets multiplied with 1. Eight such computations are needed to generate a full set of 64 intermediate data, which once again undergo a second 8-point FFT operation . Like first 8-point FFT for second 8-point again such computions are required. Proper reshuffling of the data coming out from the second 8-point FFT generates the final output of the 64-point FFT .

Fig. Signal flow graph of an 8-point DIT FFT.

For realization of 8-point FFT using the conventional DIT does not need to use any multiplication operation.

The constants to be multiplied for the first two columns of the 8-point FFT structure are either 1 or j . In the third column, the multiplications of the constants are actually addition/subtraction operation followed multiplication of 1/?2 which can be easily realized by using only a hardwired shift-and-add operation. Thus an 8-point FFT can be carried out without using any true digital multiplier and thus provide a way to realize a low- power 64-point FFT at reduced hardware cost. Since a basic 8-point FFT does not need a true multiplier. On the other hand, the number of non-trivial complex multiplications for the conventional 64-point radix-2 DIT FFT is 66. Thus the present approach results in a reduction of about 26% for complex multiplication compared to that required in the conventional radix-2 64-point FFT. This reduction of arithmetic complexity furthur enhances the scope for realizing a low-power 64-point FFT processor. However, the arithmetic complexity of the proposed scheme is almost the same to that of radix-4 FFT algorithm since the radix-4 64-point FFT algorithm needs 52 non-trivial complex multiplications.

Time Division Multiple Access (TDMA)

TDMA, or Time Division Multiple Access was one of the first cell phone digital standards available in the United States. It was the first successor to the original AMPS analog service that was popular throughout the country, and was in popular service from the early-mid 1990's up until roughly 2003 when the last of the TDMA carriers, Cingular and AT&T, switched to the GSM digital standard.

TDMA was a significant leap over the analog wireless service that was in place at the time, and it's chief benefit for carriers was that it used the available wireless spectrum much more efficiently than analog, allowing more phone calls to go through simultaneously. An additional benefit to carriers was that it virtually eliminated the criminal cell phone cloning that was popular at the time by encrypting the signal it's wireless signal.

The primary benefit for wireless users of the era was dramatically increased call quality over the scratchy, frequently garbled or "under water" sounds that analog users had become accustomed to. All manufacturers produced TDMA handsets during this period of time, but Nokia's ubiquitous model 5165 is probably the most popular example of TDMA technology.TDMA was replaced by GSM to permit the use of advanced, data intensive features such as text messaging and picture messaging, and to allow an even more efficient us e of bandwidth.

Asynchronous Transfer Mode (ATM)

Definition
These computers include the entire spectrum of PCs, through professional workstations up to 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.

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.

Analog-Digital Hybrid Modulation(electronics seminar topic)

This paper seeks to present ways to eliminate the inherent quantization noise component in digital communications, instead of conventionally making it minimal. It deals with a new concept of signaling called the Signal Code Modulation (SCM) Technique. The primary analog signal is represented by: a sample which is quantized and encoded digitally, and an analog component, which is a function of the quantization component of the digital sample. The advantages of such a system are two sided offering advantages of both analog and digital signaling. The presence of the analog residual allows for the system performance to improve when excess channel SNR is available. The digital component provides increased SNR and makes it possible for coding to be employed to achieve near error-free transmission.

Introduction

Let us consider the transmission of an analog signal over a band-limited channel. This could be possible by two conventional techniques: analog transmission, and digital transmission, of which the latter uses sampling and quantization principles. Analog Modulation techniques such as Frequency and Phase Modulations provide significant noise immunity as known and provide SNR improvement proportional to the square root of modulation index, and are thus able to trade off bandwidth for SNR.

The SCM Technique : An Analytical Approach
Suppose we are given a bandlimited signal of bandwidth B Hz, which needs to be transmitted over a channel of bandwidth Bc with Gaussian noise of spectral density N0 watts per Hz. Let the transmitter have an average power of P watts. We consider that the signal is sampled at the Nyquist rate of 2B samples per second, to produce a sampled signal x(n).

Next, let the signal be quantized to produce a discrete amplitude signal of M=2b levels. Where b is the no. of bits per sample of the digital symbol D, which is to be encoded. More explicitly, let the values of the 2b levels be, q1, q2, q3, q4…qM which are distributed over the range [-1, +1], where is the proportionality factor determined relative to the signal. Given a sample x(n) we find the nearest level qi(n). Here, qi(n) is the digital symbol and xa(n)= x(n)-qi(n) is the analog representation. The exact representation of the analog signal is given by x(n)=qi(n)+xa(n).

We can accomplish the transmission of this information over the noisy channel by dividing it into two channels: one for analog information and another for digital information. The analog channel bandwidth is Ba= aB, and the digital channel bandwidth being Bd= dB, where Ba+Bd=Bc, the channel bandwidth. Let =Bc/B, be the bandwidth expansion factor, i.e. the ratio of the bandwidth of the channel to the bandwidth of the signal.
Similarly, the variables a and d are the ratios of Ba/B and Bd/B. Here we will assume that a=1 so that d= -1. The total power is also divided amongst the two channels with fraction pa for the analog channel and fraction pd for the digital one, so that pa+pd=1.

Multisensor Fusion and Integration(electronics seminar topic)

Introduction
Sensor is a device that detects or senses the value or changes of value of the variable being measured. The term sensor some times is used instead of the term detector, primary element or transducer.

The fusion of information from sensors with different physical characteristics, such as light, sound, etc enhances the understanding of our surroundings and provide the basis for planning, decision making, and control of autonomous and intelligent machines.

Sensors Evolution

A sensor is a device that responds to some external stimuli and then provides some useful output. With the concept of input and output, one can begin to understand how sensors play a critical role in both closed and open loops.

One problem is that sensors have not been specified. In other words they tend to respond variety of stimuli applied on it without being able to differentiate one from another. Neverthless, sensors and sensor technology are necessary ingredients in any control type application. Without the feedback from the environment that sensors provide, the system has no data or reference points, and thus no way of understanding what is right or wrong g with its various elements.

Sensors are so important in automated manufacturing particularly in robotics. Automated manufacturing is essentially the procedure of remo0ving human element as possible from the manufacturing process. Sensors in the condition measurement category sense various types of inputs, condition, or properties to help monitor and predict the performance of a machine or system.

Multisensor Fusion And Integration

Multisensor integration is the synergistic use of the information provided by multiple sensory devices to assist in the accomplishment of a task by a system.

Multisensor fusion refers to any stage in the integration process where there is an actual combination of different sources of sensory information into one representational format.

Multisensor Integration

The diagram represents multisensor integration as being a composite of basic functions. A group of n sensors provide input to the integration process. In order for the data from each sensor to be used for integration, it must first be effectively modelled. A sensor model represents the uncertainty and error in the data from each sensor and provides a measure of its quality that can be 7used by the subsequent integration functions.

Mesh Radio

Governments are keen to encourage the roll-out of broadband interactive multimedia services to business and residential customers because they recognise the economic benefits of e-commerce, information and entertainment. Digital cable networks can provide a compelling combination of simultaneous services including broadcast TV, VOD, fast Internet and telephony. Residential customers are likely to be increasingly attracted to these bundles as the cost can be lower than for separate provision. Cable networks have therefore been implemented or upgraded to digital in many urban areas in the developed countries.

ADSL has been developed by telcos to allow on-demand delivery via copper pairs. A bundle comparable to cable can be provided if ADSL is combined with PSTN telephony and satellite or terrestrial broadcast TV services but incumbant telcos have been slow to roll it out and 'unbundling' has not proved successful so far. Some telcos have been accused of restricting ADSL performance and keeping prices high to protect their existing business revenues. Prices have recently fallen but even now the ADSL (and SDSL) offerings are primarily targeted at provision of fast (but contended) Internet services for SME and SOHO customers. This slow progress (which is partly due to the unfavourable economic climate) has also allowed cable companies to move slowly.

A significant proportion of customers in suburban and semi-rural areas will only be able to have ADSL at lower rates because of the attenuation caused by the longer copper drops. One solution is to take fibre out to street cabinets equipped for VDSL but this is expensive, even where ducts are already available.

Network operators and service providers are increasingly beset by a wave of technologies that could potentially close the gap between their fibre trunk networks and a client base that is all too anxious for the industry to accelerate the rollout of broadband. While the established vendors of copper-based DSL and fibre-based cable are finding new business, many start-up operators, discouraged by the high cost of entry into wired markets, have been looking to evolving wireless radio and laser options.

One relatively late entrant into this competitive mire is mesh radio, a technology that has quietly emerged to become a potential holder of the title 'next big thing'. Mesh Radio is a new approach to Broadband Fixed Wireless Access (BFWA) that avoids the limitations of point to multi-point delivery. It could provide a cheaper '3rd Way' to implement residential broadband that is also independent of any existing network operator or service provider. Instead of connecting each subscriber individually to a central provider, each is linked to several other subscribers nearby by low-power radio transmitters; these in turn are connected to others, forming a network, or mesh, of radio interconnections that at some point links back to the central transmitter.