What is a modem, Electrical Engineering

Assignment Help:

Q. What is a Modem?

Modems are generally used to interface digital circuits to transmit information on analogue channels such as telephone systems. Modem (from modulator-demodulator) is a device which modulates an analogue carrier signal to encode digital information and also demodulates such a carrier signal to decode transmitted information. The goal is to produce a signal which can be transmitted easily and decoded to reproduce original signal data. Modems can be used over any means of transmitting analog signals. Two main modulation schemes are currently being used to implement ADSL: carrier less amplitude/ phase (CAP) a single carrier modulation scheme which is based on quadrature amplitude modulation (OAM); and discrete multi-tone (DMT), a multichannel modulation scheme. Choice between them naturally relies on how well they perform in the presence of impairments on existing copper twisted -pair access cabling (see side bar), as these can limit the transmission capacity. Furthermore high bit rate services carried by ADSL mustn't interfere with other services. Essentially multicarrier modulation superimposes a number of carrier modulated waveforms to represent input bit stream. Transmitted signal is the sum of these sub-channels(or tones)that have same band width and equally spaced centre frequencies. The number of tones should be large enough to make sure good performance. Practically a value of 256 provides near optimum performance while ensuring manageable implementation complexity.


Related Discussions:- What is a modem

The value of resistance in the regulator circuit, A zener regulator consume...

A zener regulator consumes a zener diode with an internal zener resistance of 5 ohm and the value of resistance in the regulator circuit is 82 ohm. If the supply voltage alters by

Guarding Against Loss in Transformers, Guarding Against Loss in Transformer...

Guarding Against Loss in Transformers Distribution transformers are expected to convert up to 95-98% of the input power into usable output power. A distribution transformers i

Illustrate the working of full wave rectifier, Illustrate the working of fu...

Illustrate the working of full wave rectifier using bridge rectifier. How is it different from centre tapped Rectifier ? Illustrate Avalanche and Zener breakdown. Draw & explain

Discuss endp assembler directive, Discuss the ENDP assembler directive ...

Discuss the ENDP assembler directive with example ENDP: It is stands for End Procedure, which informs assembler the end of a procedure. Within assembly language programm

Prepaid metering, Prepaid Metering Prepaid metering is the state of ar...

Prepaid Metering Prepaid metering is the state of art for single and three-phase although current metering, and should be implemented through utilities desirous of protecting

Electronic monitor and alarm system for an oil separator, This assignment i...

This assignment is to develop a User Requirements Specification for an electronic monitor and alarm system for an Oil Separator in Surface Water Drainage Systems. These separato

Illustrates power dissipation management in embedded system, Illustrates ab...

Illustrates about the power dissipation management in embedded system? Power Dissipation Management a. Clever real-time programming through Wait and Stop instructions b.

Determine the signal to noise ratio, Your manager has requested you to revi...

Your manager has requested you to review current techniques for reducing, or eliminating, the effects of external interference upon electronic circuits. He requires a short report

Digital signal processing, A DT LTI system has the following impulse respon...

A DT LTI system has the following impulse response: h(n)=[cos(pi/+delta(n)] u(n-3)u(n-2) (a) Find the system’s frequency response h(e^jw ). (b) Sketch the magnitude and phase respo

Op-amp amplifier, A voltage signal generated by a sensor conditioning circu...

A voltage signal generated by a sensor conditioning circuit varies from -0.5V to +0.5V . The signal from the sensor is to be connected to the analog to digital  converter which onl

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd