4G Technology : 4th Generation Technology

The fourth generation of mobile networks will truly turn the current mobile phone networks, in to end to end IP based networks, couple this with the arrival of IPv6, every device in the world will have a unique IP address, which will allow full IP based communications from a mobile device, right to the core of the internet, and back out again. If 4G is implemented correctly, it will truly harmonise global roaming, super high speed connectivity, and transparent end user performance on every mobile communications device in the world.

4G is set to deliver 100mbps to a roaming mobile device globally, and up to 1gbps to a stationary device. With this in mind, it allows for video conferencing, streaming picture perfect video and much more.

It wont be just the phone networks that need to evolve, the increased traffic load on the internet as a whole (imagine having 1 billion 100mb nodes attached to a network over night) will need to expand, with faster backbones and oceanic links requiring major upgrade.

4G wont happen over night, it is estimated that it will be implemented by 2010, and if done correctly, should take off rather quickly.

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WiMAX Introduction

WiMax (Worldwide Interoperability for Microwave Access) is a wireless broadband technology, which supports point to multi-point (PMP) broadband wireless access.

WiMax is basically a new shorthand term for IEEE Standard 802.16, which was designed to support the European standards. 802.16's predecessors (like 802.11a) were not very acc ommodative of the European standards, per se.

The IEEE wireless standard has a range of up to 30 miles, and can deliver broadband at around 75 megabits per second. This is theoretically, 20 times faster than a commercially available wireless broadband.

The 802.16, WiMax standard was published in March 2002 and provided updated information on the Metropolitan Area Network (MAN) technology. The extension given in the March publication, extended the line-of-sight fixed wireless MAN standard, focused solely on a spectrum from 10 GHz to 60+ GHz.

This extension provides for non-line of sight access in low frequency bands like 2 - 11 GHz. These bands are sometimes unlicensed. This also boosts the maximum distance from 31 to 50 miles and supports PMP (point to multipoint) and mesh technologies.

The IEEE approved the 802.16 standards in June 2004, and three working groups were formed to evaluate and rate the standards.

WiMax can be used for wireless networking like the popular WiFi. WiMax, a second-generation protocol, allows higher data rates over longer distances, efficient use of bandwidth, and avoids interference almost to a minimum. WiMax can be termed partially a successor to the Wi-Fi protocol, which is measured in feet, and works, over shorter distances.

Manpreet Singh Bindra

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OPTICAL CHARACTERISTICS OF LEDS

The radiation from an LED can be characterized by radiometric and spectroradiometric
quantities. If the LED emits visible radiation, then photometric and colorimetric quantities
are also required to quantify its effect on the human eye. Note that for every radiometric
quantity there is a photometric analog. The only difference is that, for radiometric quantities
the radiation is evaluated in energy units, while for photometric quantities the radiation is
weighted against the photopic response of the human eye.

3.1 Spectral Properties of Light Emitting Diodes

The spectral distribution of the optical radiation emitted by LEDs distinguish them from
typical element sources. The radiant power is neither monochromatic (as emitted by lasers),
nor broadband (as found with incandescent lamps), but rather something between the two.
The light output of a typical LED has a narrowband spectral bandwidth between 20nm and
50nm and a peak wavelength somewhere in the near UV, the visible, or near infrared regions
of the spectrum.

Sample LED Spectral Distributions

The spectral properties of an LED are important to aid
manufacturers in their design efforts and process control.
End-users use these values in determining the correct LED
for their application. An overview of the spectral parameters
of an LED is listed below:
Peak Wavelength λp:
Wavelength at the maximum spectral power . The peak wavelength has little significance for
practical purposes since two LEDs may have the same peak
wavelength but different color perception.
Full Width Half Max (FWHM):
The spectral bandwidth at half peak λ 0.5 is calculated from
the two wavelengths λ'0.5 and λ''0.5 on either side of λp.
λ 0.5 = λ'0.5 - λ''0.5 (Reference Figure 3.0).
Center Wavelength λ m:
The center wavelength is the wavelength halfway between the half-wavelengths λ'0.5 - λ''0.5.
Centroid Wavelength λc:
The centroid wavelength is the center of moment or the mean of the spectral power
distribution.
Dominant Wavelength:
The dominant wavelength is determined from drawing a straight line through the color
coordinates of the reference illuminant (usually arbitrarily chosen as illuminant E) and
the measured chromaticity coordinates of the LED in the International Commission on
Illumination (CIE) 1931 chromaticity diagram. The intersection of this straight line on
the boundary of the chromaticity diagram gives the dominant wavelength. It is a measure
of the hue sensation produced in the human eye by the LED.
Purity:
Purity is defined as the ratio of the distance from reference illuminant (usually arbitrarily
chosen as Illuminant E) to the measured chromaticity coordinates and the distance from
reference illuminant to the intersection with the boundary of the chromaticity diagram.
Most LEDs are narrow band radiators, with a purity of nearly 100%, i.e. the color cannot
be distinguished from a monochromatic beam. Polychromatic sources have low purity
approaching zero.
Full Width Half Max Angle , Viewing Angle or Beam Angle:
The total cone apex angle in degrees encompassing the central, high luminous intensity
portion of a directional beam, from the on-axis peak out to the off-axis angles in both
directions at which the source's relative intensity is 1/2.
Half-Angle:
The included angle in degrees between the peak and the point on one side of the beam
axis at which the luminous intensity is 50% of maximum or half of the beam angle.
Note: Peak Wavelength, Full Width Half Max, Center Wavelength, and Centroid
Wavelength are all plotted on a scale of (power / λ) vs. (λ).
0.5
(2θ1/2)
4

Theoretical V(λ) function, relative
spectral flux output of a blue LED,
relative spectral distribution of a
typical tungsten incandescent lamp,
typical response of photopic detector
with f1’ response of 4%.
3.2 Comparison of Photometers and Spectroradiometers
Photometers use a broadband detector in conjunction with an optical filter in an effort to
simulate the spectral luminous efficiency curve of the human eye, V(λ), which is referenced
using CIE 15.2 Colorimetry. The detection process involves a change in the
characteristics of the detector caused by the absorption of visible photons. The electrical
signal generated by the detector is a response to the visible radiation incident on the detector
active area. For example, a photometer designed to measure illuminance may be calibrated
in photocurrent per lux.
Spectroradiometers can be calibrated to measure the radiant energy or radiant flux from an
LED as a function of wavelength. These instruments separate or disperse polychromatic light
into its constituent monochromatic components usually by means of prisms or gratings. The
photometric value may then be computed (usually by software) from this measured spectrum.
This basic difference between spectroradiometers and photometers is extremely important in
LED metrology.
A disadvantage of a photometer is the difficulty in designing a filter that, when combined
with a detector, fits the spectral luminous efficiency curve of the eye exactly. Because of
available filter materials, a mismatch is particularly prevalent in the blue portion of the
spectrum. Though corrections can be applied, these corrections require knowledge of the
LED spectral distribution and are usually approximations. Figure 3.1 shows the theoretical
V(λ) function, the relative spectral flux output of a blue LED, the relative spectral distribution
of a typical tungsten incandescent lamp, and the typical response of a photopic detector.
A typical photopic detector with an f1' response of 4% can have a spectral mismatch as great
as a factor of 2 at 470nm between the V(λ) function and the response of a photopic detector.
If an incandescent source or a source similar in spectral content is measured, the correction
for the slopes of the photopic detector to the V(λ) curve is minimal since the light is
continuous and there is relatively little light in the
blue portion of the spectrum in relation to the
higher wavelengths. A mismatch in the response
curves results in only a slight error of the measured
photometric value.
LEDs, however, have a completely different spectral
power distribution, which tends to be narrowband
Gaussian with a specific peak and a FWHM of a
couple of tens of nanometers. The relatively poor
match of the photopic detector to the V(λ) function,
can result in large deviations in the measured photometric
quantities. This is particularly true for blue
and red LEDs. Errors exceeding a hundred percent
are not unusual for blue LEDs. Spectroradiometers
avoid these errors because the photometric quantities
are calculated from the spectral data and defined CIE
functions. It should be noted that photometers can
be used to compare sources having identical spectral
distribution, or to measure illumination of the same spectral distribution as that of the source
with which it was calibrated. LEDs can have so much variation from one to another, spectroradiometers
or photometers fabricated with specially designed filtering should be used for
LED metrology.
5
3.3 Color and Dominant Wavelength
Often used for determining the color of an LED, dominant wavelength is actually a
measure of the hue sensation produced in the human eye. Hue designates the basic color
being referenced; such as, red, yellow or blue-green. The hue refers to the color impression
that a sample makes. Two LEDs can have the same hue, but it is possible for one to appear
washed out. For example, one can look red and one can look pink.
In order to guarantee a match in color from one LED to another both dominant wavelength
and purity should be referenced. Purity is a characteristic of chroma (also referred to as
saturation), which is the degree of color saturation, or the amount of pure color added to
obtain the sample. The purer colors of a particular hue sample are placed nearer to the
boundary of the chromaticity diagram.
In order to calculate the color properties of an LED, the spectral properties of the LED
must be known. Therefore, a photometer cannot be used. In choosing a spectroradiometer
with which to calculate these values, it should be noted that the optical bandwidth of a
spectroradiometer artificially broadens the spectral shape of any source. For LEDs, this
can introduce errors, especially in the calculated chromaticity coordinates and dominant
wavelength. A 10nm bandwidth spectroradiometer, measuring 20nm full width half max
LEDs, can cause errors as high as:
0.005 in x
0.007 in y
2nm in λd
On the other hand, error contributions on color for spectroradiometers with bandwidths
of 5nm have been documented to be less than about 0.002 in x,y (0.001 in u',v') and 0.2nm
in dominant wavelength. Bandwidths of 1nm or less have no appreciable error contribution.
In choosing a spectroradiometer one should be aware of these errors. Spectroradiometers
with bandwidths of 5nm or less are accepted for most practical measurements of LEDs
of all colors.
3.4 Influence of Temperature on Radiation
Initial Light-up:
The light output of an LED is a function of Vf and If,
where the LED junction temperature under constant current
operation heavily influences Vf. At constant current.
the forward voltage of an LED stabilizes as the junction
temperature (Tj) stabilizes. The junction temperature of
the LED is determined by Tj =Ta + Pd * Rth (j-a). Where
Ta is ambient temperature, Pd is power dissipation (Vf *I f)
and Rth(j-a) is the thermal resistance (junction to ambient
temperature). During initial light-up, the temperature of
the junction increases due to electrical power consumed
by the LED chip and then stabilizes at a temperature
value > Ta. Because of this effect, the emitted light is not
stabilized until thermal equilibrium has been reached.
After thermal equilibrium, the junction value is governed
by the heat transfer to the surroundings, which takes
place through the leads of the LED. As a consequence,
the thermal properties of the electrical contacts used to
supply the LED, the length of the wires between the chip, and when used the heat sink can
significantly affect the output. Figure 3.2 shows the stabilization over time of a green LED.
The relative spectral flux and the forward voltage is measured every 5 seconds with a constant
current of 20ma flowing through the LED, until a near constant forward voltage is achieved. The stabilization procedure can take several minutes and will be
influenced by the properties of the specific LED measured. Depending on the LED type,
spectral distribution effects from junction temperature, as presented in the graph, can create
6 shifts in dominant wavelength

Example of LED
Stabilization Over Time
as great as 0.7nm and decreases in luminous flux as great as
3.5%. Since the dominant wavelength is dependent upon
the intersection on the spectrum locus of the 1931 CIE
chromaticity diagram, small spectral distribution changes
in "red" and "blue" LEDs can create relatively large changes
in dominant wavelength.
Thermal Equilibrium:
Once thermal equilibrium has been reached, the spectral
distribution of an LED is dependent upon the ambient
temperature surrounding the chip. For a typical LED as the
power is stabilized and the ambient temperature rises, there
will be a slight change in the shape of the spectrum, and the
peak wavelength will shift about 0.1 to 0.3nm/K. For blue
LEDs, the shift in most cases is towards shorter wavelengths.
For other LEDs, the whole distribution will shift in the
direction of longer wavelengths. The luminous efficacy and color of LEDs can be changed by
relatively small ambient temperature changes, making it difficult to achieve constant photometric
or radiometric measurement results. Figure 3.3 depicts the spectral radiant flux output
of a "green" LED run at 23°C and 30°C. For this example, a 1.1nm shift in peak wavelength
resulted in a 0.2nm change in dominant wavelength. As previously described, shifts in the
spectra of red and blue LEDs, because of their location on the color curve, will create greater
changes in dominant wavelength. Since the spectral distribution of an LED depends on both
the junction temperature of the chip and stabilization of current, temperature offers the best
way of controlling the operating conditions and maintaining a constant spectral distribution.

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STRUCTURED CABLES IN TELECOMMUNICATION

Cable is the highway used to deliver all of you organization's information. A system that is poorly designed, ineffectively installed, or out of date hinders the performance, profitability and client satisfaction in your organization

TNSI has the experience and capability to tie your cabling needs together for maximum efficiency in a cost effective manner, in your building or in a campus environment.

Voice: Structured wiring for voice, modem, terminal, fax and other applications.

Data: Structured wiring systems for local area networks, host terminal, data collection, factory automation. Category 5 and 6 copper twisted pair, patch panels, ladder and system racks, network services access, building connection, and many other applications.

Fiber Optics: Backbone and workstation cable systems using single or mutimode fiber. We offer a variety of fiber optic systems for unique applications.

High Speed Internet Access: Access the information Super Highway using a high speed internet connection.

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AIRTEL Success Story

Airtel’s solutions provider, Bharti Telesoft, designed a unique televoting application that uses Short Messages as the media for polling votes. The application was developed on open standards. Televoting effectively enables Airtel’s mobile subscribers to participate in various SMS contests aired on both KBC & Indian Idol. The system handles tremendous peak loads of mobile-originated (MO) messages generated by subscribers and processes it according to a pre-configured format specified by the two TV programs. The application caters to subscriber traffic across millions of users in seven different Airtel Circles over a pre-defined short code (646).

“When we first decided to evaluate Linux, apprehensions were raised immediately. People began to say that the system would choke and not be able to handle the load,” explains Vatsal.

“But in our simulations, Linux proved its detractors completely wrong. The pilot Enterprise Linux server could handle a peak load of 1000 TPS with superb ease. People soon began to realize that Linux is in fact ideally suited for high throughputs. Since our transactions needed to be recorded into a log file on-the-fly, Linux, with its high performance, was the perfect fit,” he adds.

Security was also another critical factor that swung the decision in the favor of Enterprise Linux. “Microsoft Windows is prone to viruses that affect its filesystem easily, whereas Linux remains unaffected,” he adds. In fact, Windows was never on the selection radar at all. “We didn’t even evaluate it for our server requirements,” adds Vatsal.

At Airtel, Enterprise Linux runs on low cost, dual Intel Xeon servers. The servers run both the Televoting application and a MySQL database at each of the seven different locations across the country. A central server, again powered by Red Hat Enterprise Linux, functions as a host. “The central server generates MIS reports and also acts as an FTP server for the other seven distributed machines,” explains Uttam Kumar, Project Head, Airtel.

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Wireless Code Division Multiple Access (CDMA)

Code Division Multiple Access (CDMA) is a radically new concept in wireless communications. It has gained widespread international acceptance by cellular radio system operators as an upgrade that will dramatically increase both their system capacity and the service quality. It has likewise been chosen for deployment by the majority of the winners of the United States Personal Communications System spectrum auctions. It may seem, however, mysterious for those who aren't familiar with it. This site is provided in an effort to dispel some of the mystery and to disseminate at least a basic level of knowledge about the technology.

CDMA is a form of spread-spectrum , a family of digital communication techniques that have been used in military applications for many years. The core principle of spread spectrum is the use of noise-like carrier waves, and, as the name implies, bandwidths much wider than that required for simple point-to-point communication at the same data rate. Originally there were two motivations: either to resist enemy efforts to jam the communications (anti-jam, or AJ), or to hide the fact that communication was even taking place, sometimes called low probability of intercept (LPI). It has a history that goes back to the early days of World War II.

The use of CDMA for civilian mobile radio applications is novel. It was proposed theoretically in the late 1940's, but the practical application in the civilian marketplace did not take place until 40 years later. Commercial applications became possible because of two evolutionary developments. One was the availability of very low cost, high density digital integrated circuits, which reduce the size, weight, and cost of the subscriber stations to an acceptably low level. The other was the realization that optimal multiple access communication requires that all user stations regulate their transmitter powers to the lowest that will achieve adequate signal quality.

CDMA changes the nature of the subscriber station from a predominately analog device to a predominately digital device. Old-fashioned radio receivers separate stations or channels by filtering in the frequency domain. CDMA receivers do not eliminate analog processing entirely, but they separate communication channels by means of a pseudo-random modulation that is applied and removed in the digital domain, not on the basis of frequency. Multiple users occupy the same frequency band. This universal frequency reuse is not fortuitous. On the contrary, it is crucial to the very high spectral efficiency that is the hallmark of CDMA. Other discussions in these pages show why this is true.

CDMA is altering the face of cellular and PCS communication by:

• Dramatically improving the telephone traffic capacity

• Dramatically improving the voice quality and eliminating the audible effects of multipath fading

• Reducing the incidence of dropped calls due to handoff failures

• Providing reliable transport mechanism for data communications, such as facsimile and internet traffic

• Reducing the number of sites needed to support any given amount of traffic

• Simplifying site selection

• Reducing deployment and operating costs because fewer cell sites are needed

• Reducing average transmitted power

• Reducing interference to other electronic devices

• Reducing potential health risks

Commercially introduced in 1995, CDMA quickly became one of the world's fastest-growing wireless technologies. In 1999, the International Telecommunications Union selected CDMA as the industry standard for new "third-generation" (3G) wireless systems. Many leading wireless carriers are now building or upgrading to 3G CDMA networks in order to provide more capacity for voice traffic, along with high-speed data capabilities.

CDMA is a form of Direct Sequence Spread Spectrum communications. In general, Spread Spectrum communications is distinguished by three key elements:

1. The signal occupies a bandwidth much greater than that which is necessary to send the information. This results in many benefits, such as immunity to interference and jamming and multi-user access, which we'll discuss later on.

2. The bandwidth is spread by means of a code which is independent of the data. The independence of the code distinguishes this from standard modulation schemes in which the data modulation will always spread the spectrum somewhat.

3. The receiver synchronizes to the code to recover the data. The use of an independent code and synchronous reception allows multiple users to access the same frequency band at the same time.

In order to protect the signal, the code used is pseudo-random. It appears random, but is actually deterministic, so that the receiver can reconstruct the code for synchronous detection. This pseudo-random code is also called pseudo-noise (PN).

There are three ways to spread the bandwidth of the signal:

• Frequency hopping. The signal is rapidly switched between different frequencies within the hopping bandwidth pseudo-randomly, and the receiver knows before hand where to find the signal at any given time.

• Time hopping. The signal is transmitted in short bursts pseudo-randomly, and the receiver knows beforehand when to expect the burst.

• Direct sequence. The digital data is directly coded at a much higher frequency. The code is generated pseudo-randomly, the receiver knows how to generate the same code, and correlates the received signal with that code to extract the data.

How spread spectrum works:

Spread Spectrum uses wide band, noise-like signals. Because Spread Spectrum signals are noise-like, they are hard to detect. Spread Spectrum signals are also hard to Intercept or demodulate. Further, Spread Spectrum signals are harder to jam (interfere with) than narrowband signals. These Low Probability of Intercept (LPI) and anti-jam (AJ) features are why the military has used Spread Spectrum for so many years. Spread signals are intentionally made to be much wider band than the information they are carrying to make them more noise-like.

Spread Spectrum signals use fast codes that run many times the information bandwidth or data rate. These special "Spreading" codes are called "Pseudo Random" or "Pseudo Noise" codes. They are called "Pseudo" because they are not real gaussian noise.

Spread Spectrum transmitters use similar transmit power levels to narrow band transmitters. Because Spread Spectrum signals are so wide, they transmit at a much lower spectral power density, measured in Watts per Hertz, than narrowband transmitters. This lower transmitted power density characteristic gives spread signals a big plus. Spread and narrow band signals can occupy the same band, with little or no interference. This capability is the main reason for all the interest in Spread Spectrum today.

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