CPE 041 DATACOM P2 Flashcards
is the transmission, reception, and
processing of information.
Electronic communications
is defined as knowledge or intelligence that is
communicated between two or more points.
Information
include systems where relatively high
frequency analog carriers are modulated by relatively low frequency
digital information signals ( digital radio ) and systems involving the
transmission of digital pulses ( digital transmission ).
Digital communications
is the transmittal of digitally modulated analog
signals (carriers) between two or more points in a communications system.
Digital modulation
Digital modulation is sometimes called
digital radio
In the ____________ the precoder performs level conversion and then encodes the incoming data into groups of bits that modulate an analog carrier. The modulated carrier is shaped (filtered), amplified, and then transmitted through the transmission medium to the receiver.*
transmitter
can be a metallic cable , optical fiber cable , Earth’s atmosphere , or a combination of two or more types of transmission systems.
transmission medium
In the _______, the incoming signals are filtered, amplified, and
then applied to the demodulator and decoder circuits , which extracts the original source information from the modulated carrier. The clock and carrier recovery circuits recover the analog carrier and digital timing (clock)signals from the incoming modulated wave since they are necessary to perform the demodulation process.
receiver
is a highly theoretical study of the efficient use
of bandwidth to propagate information through electronic communications
systems.
Information theory
represents the number of independent symbols that
can be carried through a system in a given unit of time.
Information capacity
The most basic digital symbol used to represent information is the
binary digit , or bit
____ is simply the number of bits transmitted during one second and is expressed in ____
Bit rate, bits per second (bps)
In 1928 ,____________________ developed a useful relationship among bandwidth, transmission time, and information
capacity.
Ralph Hartley of Bell Telephone Laboratories
In 1948 , mathematician ______________ (also of Bell Telephone Laboratories ) published a paper in the Bell System Technical Journal relating the information capacity of a communications channel to
bandwidth and signal to noise ratio.
Claude E. Shannon
The relationship between information capacity, bandwidth, and the number of possible states per symbol is summarized in what is known as the ___________
Shannon Hartley theorem
________ is generally used for comparison purposes only.
ideal bandwidth
The minimum theoretical bandwidth necessary to propagate a signal is
called the ________ or sometimes the __________
minimum Nyquist bandwidth, minimum Nyquist
frequency
is a term derived from the word binary. M simply represents a
digit that corresponds to the number of conditions, levels, or combinations possible for a given number of binary variables.
M-ary
refers to the rate of change of a digital information signal, which is usually binary.
Bit rate
refers to the rate of change of a signal on the transmission
medium after encoding and modulation have occurred.
Baud
Baud is a unit of transmission rate , modulation rate , or symbol rate
and, therefore, the terms __________ and baud are often used interchangeably.
symbols per second
The simplest digital modulation technique is ____________, where a binary information signal directly modulates the
amplitude of an analog carrier.
amplitude shift keying
( ASK)
is another relatively simple, low
performance type of digital modulation.
Frequency shift keying (FSK)
Amplitude shift keying is sometimes called _____________ and ____________.
digital amplitude
modulation (DAM )
on off keying (OOK ).
FSK is sometimes called
binary FSK (BFSK)
is defined as the difference between either the mark or space frequency and the center frequency, or half the difference between the mark and space frequencies.
frequency deviation
The most common circuit used for demodulating binary FSK signals is
the phase locked loop (PLL).
is another form of angle modulated, constant amplitude digital modulation.
Phase shift keying (PSK)
The simplest form of PSK is ______________, where N = 1 and M = 2.
binary phase shift keying (BPSK)
Other names for BPSK are ______________ and biphase
modulation .
phase reversal keying (PRK)
___________ as it is sometimes called, is another form of angle modulated, constant amplitude digital modulation.
Quaternary phase shift keying (QPSK) QPSK), or quadrature PSK
is an M ary encoding scheme where three bits are encoded, forming
tribits and producing eight different output phases.
8 PSK
is an M ary encoding technique where M = 8.
8 QAM
is a form of digital modulation
similar to PSK except the digital information is contained in both the
amplitude and the phase of the transmitted carrier.
Quadrature amplitude modulation (QAM)
is an M ary system where M = 16.
16 QAM
is the transmittal of digital signals between two
or more points in a communications system.
Digital transmission
The primary advantage of digital transmission over analog transmission
is __________
noise immunity
consists essentially of sampling analog information
signals and then converting those samples into discrete pulses and
transporting the pulses from a source to a destination over a physical
transmission medium.
Pulse modulation
The four predominant methods of pulse modulation include
pulse width modulation (PWM)
pulse position modulation (PPM)
pulse amplitude modulation (PAM)
pulse code modulation (PCM)
is sometimes called pulse duration modulation (PDM) or pulse length
modulation (PLM) PLM), as the width (active portion of the duty cycle) of a constant amplitude pulse is varied proportional to the amplitude of the
analog signal at the time the signal is sampled.
PWM
, the position of a constant width pulse within a prescribed
time slot is varied according to the amplitude of the sample of the
analog signal.
PPM
, the amplitude of a constant width, constant position pulse
is varied according to the amplitude of the sample of the analog signal.
PAM
, the analog signal is sampled and then converted to a serial
n bit binary code for transmission. Each code has the same number of
bits and requires the same length of time for transmission.
PCM
is credited with inventing PCM in 1937 while working for
AT&T at its Paris laboratories .
Alex H. Reeves
Essentially, there are two basic techniques used to perform the
sampling function: ___________and _________
natural sampling and flat top sampling
is when tops
of the sample pulses retain
their natural shape during the
sample interval, making it
difficult for an ADC to convert
the sample to a PCM code.
Natural sampling
, the input voltage is sampled with a narrow pulse and then held
relatively constant until the
next sample is taken.
flat top sampling
An error called
__________ , is when the amplitude of the sampled
signal changes during the sample pulse time.
aperture error
establishes the minimum sampling rate ( f s )
that can be used for a given PCM system.
Nyquist sampling theorem
If f s is less than two times f a , an impairment called _____ or _________ occurs.
alias, foldover distortion
is the process of converting an infinite number of
possibilities to a finite number of conditions.
Quantization
is the process of rounding off the
amplitudes of flat top samples to a manageable number of levels.
quantization
A type of code is called a __________ because the codes on
the bottom half of the table are a mirror image of the codes on the top half, except for the sign bit.
folded binary code
The magnitude difference between adjacent steps is called the _________or __________.
quantization interval or quantum .
