Fundamentals of telecommunications / by Roger L. Freeman.–2nd ed. p. cm. Includes bibliographical references and index. ISBN (cloth). 1. To present the basics concepts of telecommunication systems with focus on digital and wireless Telecommunication signals are variation over time of voltages. Fundamentals of Telecommunications Second Edition Roger L. Freeman A JOHN WILEY & SONS, INC., PUBLICATION Fundamentals of Telecommunications.
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cover the fundamentals of telephony, from its inception in Alexander Graham By telecommunications had become so important to the country that. The Second Edition of this critically-acclaimed text continues the standard of excellence set in the first edition by providing a thorough. View Table of Contents for Fundamentals of Telecommunications Demystifying the technology of telecommunications: a guided tour for the.
Modulation Mathematics: The equation of a sinusoidal voltage waveform is given by: where: v is the instantaneous voltage Vmax is the maximum voltage amplitude is the angular frequency is the phase Amplitude modulation uses variations in amplitude Vmax to convey information.
The wave whose amplitude is being varied is called the carrier wave. The signal doing the variation is called the modulating signal.
For simplicity, suppose both carrier wave and modulating signal are sinusoidal; i. The original carrier waveform, at frequency c, containing no variations and thus carrying no information. A component at frequency c - m whose amplitude is proportional to the modulation index. This is called the Lower Side Frequency.
This is called the Upper Side Frequency. It is the upper and lower side frequencies which carry the information. This is shown by the fact that only their terms include the modulation index m. Because of this, the amplitudes of the side frequencies vary in proportion to that of the modulation signal.
Sidebands: If the modulating signal is a more complex waveform, for instance an audio voltage from a speech amplifier, there will be many side frequencies present in the total waveform. This gives rise to components 2 and 3 in the last equation being bands of frequencies, known as sidebands.
Hence we have the upper sideband and the lower sideband, together with the carrier. Clearly, for a given carrier amplitude there are limits for the size of the modulating signal; the minimum must give zero carrier, the maximum gives twice the unmodulated carrier amplitude. If these limits are exceeded, the modulated signal cannot be recovered without distortion and the carrier is said to be over-modulated.
Adjust the set carrier control to extinguish the RF power monitor lamp. This reduces the transmitters carrier output to zero nominally. Set the sensitivity of this channel to 1V per division, allowing for any attenuation introduced by the probe. Set the time base to give a scale of 1s per division, and adjust the controls so that the time base is triggered from the Y1 waveform.
Set the Y2 channel to a sensitivity of 5V per division, and connect this channel to the RF monitor point on the module. Slowly rotate the set carrier control counter clockwise until a 1 MHz signal of approximately 10V peak-to-peak amplitude is present at the RF monitor point Y2 channel. Observe, and make a careful note of, the phase relationship between the two displayed waveforms.
Next, slowly rotate the set carrier control clockwise, so that the signal at the monitor point decreases, passes through a null and then increases once more. Set the voltage to about 10V peak-to-peak. Observe the phase relationship between the two waveforms in this new state, and make a note of your observation.
Readjust the set carrier control for a null output once more. Use the oscilloscope to detect the null precisely. Connect the low frequency generator to the modulation input terminals.
Set its controls to give an output of 5V peak-to-peak at 0. Rotate the set carrier control clockwise until the signal on the RF monitor point reaches a maximum peak-to-peak value of about 15V. Observe the phase of the RF output changing regularly in synchronism with the modulating input from the oscillator. The oscillator is now having the same effect as your action on the set carrier control formerly had. Raise the frequency of the oscillator to 4Hz, and you will be able to see the process speeded up.
This is the same signal as you looked at before, but on a vastly different time scale. Transfer the Y1 lead of the oscilloscope to the modulating oscillator. You should now have a display resembling fig 4. It may be necessary to readjust the trigger controls of the timebase to restore the display. The display will again resemble fig 4. Now you have a double-sideband suppressed-carrier signal or DSSC signal.
It is the result of simply multiplying the carrier oscillation and the modulating signal together. The product does not contain any carrier frequency component. Amplitude modulation is defined as the process in which is the amplitude of the carrier wave is varied about a means values linearly with the base band signal.
The envelope of the modulating wave has the same shape as the base band signal provided the following two requirements are satisfied 1.
Demodulation is the reverse process of modulation. Follow the procedure given above and attach the output of the code. Set the sampling frequency equal to and observe the output. Write your comments. For the input signal given in the procedure, perform SSB modulation and Demodulation using ssbmod and ssbdemod commands. Compare the output of the code given in the procedure with the output of the code that you have developed using ssbmod and ssbdemod commands and briefly describe the difference between the two outputs.
The main advantage of this modulation is that it can provide better discrimination against noise. Telecommunications Industry and Effects on Research. Renewing U. Telecommunications Research. Chapter 3 examines further some of the implications of curtailed research investment. The chief research and development arm of the Bell System, Bell Laboratories, was created in , following demonstration in of the feasibility of coast-to-coast long-distance service and realization of the importance of a viable research and development laboratory to effective deployment.
Successful nationwide implementation of long-distance service required, for example, a device with sufficient gain to offset the signal losses in the mile stretch of the U.
The development of the vacuum tube amplifier for use in telephone circuits, which started in the s, took many years of fundamental research and required extremely close cooperation between the research community that had originally invented the vacuum tube technology and the development community that introduced the vacuum tube amplifier into the telephone network.
Bell Laboratories relied heavily on managers who understood the benefits to the company and society of fundamental research and were able to provide a work environment that fostered world-class research in virtually every aspect of telecommunications technology. Stable funding for research was provided via a tax levied on the service revenues of most of the Bell operating companies, an approach approved by state regulators.
The revenue from the services tax was more than sufficient to fund unfettered investigations over almost 6 decades into almost every aspect of telecommunications, from basic materials and the associated physics and chemistry to large-scale computing and networking platforms and systems. Out of the Bell System research program also came many world-famous innovations, including the transistor, information theory, the laser, the solar cell, communications satellites, and fiber-optic communications.
In addition, research in basic science at Bell Labs was recognized by six Nobel prizes for strides in quantum mechanics, solid-state physics, and radio astronomy.
A number of other companies were also involved at the time in developing new telecommunications technologies and equipment. Bell Labs also served as an important nucleus for the broader telecommunications research community: in the predivestiture era, university researchers and telecommunications research leaders from around the world commonly spent summers or sabbaticals at Bell Labs, where they could conduct exploratory research that could not have been undertaken elsewhere.
For instance, until government actions forced a change, the Bell System prohibited the attachment of third-party equipment on customer premises, which many viewed as stifling innovation. Monopoly status also meant that there were few pressures on the Bell System for rapid innovation in its services, and a number of innovative technologies developed by Bell Labs either were not adopted or were adopted very slowly. Divestiture resulted in the separation of the local Bell System operating companies which provided local telephone service to large regions of the United States from the long-distance parts of the network known as long-lines communications and ended the license fee arrangement through which the regional operating companies supported Bell Labs.
That may require some culture change. The company launched in with a no-frills business model — including customer service kiosks placed in retail locations to avoid management and overhead of a large store network; primarily Internet-based marketing and customer service; and a bring-your-own-device policy designed to eliminate administrative costs for handset sales — and its flagship low-priced all-you-can-use domestic service plan has caught on with consumers.
Since its launch, Free has boosted its subscriber base to more than 12 million; it now has an 18 percent share of the mobile market in France. You should be on the vanguard of adopting digital technologies, both in services and in the back office. For example, all customer contact and sales channels online, mobile, and physical should be linked digitally so that consumer activities are maintained in a single database, making interactions with customers in all channels less costly in terms of expended time and resources and enhancing customer convenience and satisfaction.
Ideally, customer communications should be migrated toward messaging systems and well-designed mobile apps, with minimal human intervention. To reach this stage, you may need new capabilities, including data analytics expertise, to accurately segment and generate maximum value from each customer. Separate your traditional corporate IT functions from your customer-focused digital efforts, and appoint a chief digital officer who can facilitate business unit digitization efforts.
Network upgrades. The single most compelling thing you have to offer is network speed and throughput; every customer is hungry for it. Investments in telecom network improvements — fiber and 5G upgrades or other networking technologies — are critical to preparing for more dynamic, competitive environments. Every successful telecom company will be armed with a state-of-the-art infrastructure, sufficiently flexible to handle new and profitable monetization opportunities.
Network enhancements could also position your company to take back the technological advantage from OTT providers. Redefining strategic identity After developing a modernization program — and even while implementing it — work on adopting one or more new strategic identities that are relevant to customers, offering them distinctive services and experiences with real value.
You may choose your core connectivity business to be your strategic identity. This is essentially the approach Free Mobile has taken, betting everything on offering basic wireless services at the lowest possible cost. And it would obviate the investments needed to compete in the current telecom environment.
A more extreme business model makeover is another option, but tread carefully. Carriers have at various times tried to market their own devices, build portals for apps and entertainment, and provide outsourced IT services. The results, however, have been mostly disappointing, due largely to corporate cultures and capabilities gaps that put telecom companies at a disadvantage in broad, commercial markets, and to the structural challenges of selling global products in geographically bounded physical networks.
In the ecosystem of digital content, operators hold a critical card: a central position in the distribution value chain and a direct line to customers.