Electronics Communication Flashcards
Is the transmission, reception, and processing of information with the use of electronic circuits.
Electronic Communication
System involving the transmission of digital pulses.
Digital Transmission
Is the transmittal of digitally modulated analog signals(carriers) between two or more points in a communication system.
Digital Modulation
The information signal is digital and the frequency (f) of the carrier is varied proportional to the information signal.
Frequency Shift Keying ( FSK )
The information signal is digital and the amplitude (V) of the carrier is varied proportional to the information signal.
Amplitude Shift Keying ( ASK )
The information signal is digital and the phase (θ) of the carrier is varied proportional to the information signal.
Phase Shift Keying ( PSK )
Is defined as knowledge or intelligence that is communicated between two or more points.
Information
A modulation where both the amplitude and the phase are varied proportional to the information signal.
Quadrature Amplitude Modulation (QAM)
Performs level conversion and then codes the incoming data into groups of bits that modulate an analog carrier.
Pre-coder
Is a highly theoretical study of the efficient use of bandwidth to propagate information through electronic communications systems.
Information Theory
Is a measure of how much information can be propagated through a communications system and is a function of bandwidth and transmission time.
Information Capacity
The most basic digital symbol used to represent information.
Binary Digit / Bit
Refers to the rate of change of a signal on a transmission medium after encoding and modulation have occurred.
Baud
In 1928, _________ of Bell Telephone Laboratories developed a useful relationship among bandwidth, transmission time, and information capacity.
R. Hartley
Simply represents a digit that corresponds to the number of conditions, levels, or combinations possible for a given number of binary variables.
M
Refers to the rate of change of a digital information signal, which is usually binary.
Bit Rate
Sometimes called a symbol and could be encoded as a change in the amplitude, frequency, or phase
Signaling Element
The minimum theoretical bandwidth necessary to propagate a signal.
Nyquist Bandwidth
The carrier is either “on” or “off” which is why amplitude-shift keying is sometimes referred to as ________.
On-Off Keying
A logic 1 frequency (fm) for FSK.
Mark
A logic 0 frequency (fs) for FSK.
Space
The mark and space frequencies are separated from the carrier frequency by the _________and from each of by 2 Δf.
Peak Frequency Deviation (Δf)
_______ is the peak frequency deviation of the carrier and is equal to the difference between the carrier rest frequency and either the mark or space frequency.
Δf
Is binary FSK except the mark and space frequencies are synchronized with the input binary bit rate.
Continuous-Phase FSK ( CP-FSK )
A signal state-space diagram, is similar to a phasor diagram except that the entire phasor is not drawn. Only the relative positions of the peaks of the phasors are shown.
Constellation Diagram
Is a product modulator; the output signal is the product of the two input signals.
Balanced Modulator
Also known as quadrature PSK that is another form of angle-modulated, constant-amplitude digital modulation.
Quaternary PSK (QPSK)
A group of two bits.
Dibit
It modulates the carrier that is in phase with the reference oscillator.
I bit
It modulates the carrier that is 90 out of phase or in quadrature with reference carrier.
Q bit
Is two BPSK modulators combined in parallel
QPSK Modulator
The highest fundamental frequency present at the data input to the I or the Q balanced modulator is equal to _______ of the input data rate.
1/4
The fastest output rate of change (baud) is also equal to________ of the input bit rate.
1/2
The outputs of the product detectors are fed to the ________, here they are converted from parallel I and Q data channels to a single binary output data stream.
Bit Combining Circuit
Is a modified for of QPSK where the bit waveforms on the I and Q channels are offset or shifted in phase from each other by one-half of a bit time.
Offset QPSK( OQPSK )
The advantage of OQPSK is the _________ that must be imparted during modulation.
Limited Phase Shift
With ________, three bits are encoded, forming tribits and producing eight different output phases.
8 PSK
Group of 3 bits
Tribit
Also known as maximum distance code used to reduce the number of transmission errors.
Gray Code
Converts the I/C and Q/C bit pairs to serial, Q, and C output data streams.
Parallel-to-SerialLogic Circuit
Group of 4 bits.
Quadbit
Is an M-ary encoding technique where M = 8. The output signal from this modulator is not a constant-amplitude signal.
8 - QAM
The process of introducing transitions (pulses) into the binary signal using a prescribed algorithm
Scrambling
It uses the same algorithm for scrambling to remove the transitions
Descrambler
Is an alternative form of digital modulation where the binary input is contained in the difference between two successive signaling elements rather than the absolute phase
Differential Phase-Shift Keying ( DPSK )
Is the ratio of the average carrier power (the combined power of the carrier and its associated sidebands) to the thermal noise power.
Carrier-To-Noise Power Ratio
Is the process of extracting a phase-coherent reference carrier from a receiver signal. Sometimes called phase referencing.
Carrier Recovery
Three methods of carrier recovery.
Squaring Loop, Costas Loop, & Remodulator
Can be used to determine the approximate bandwidth for an FSK wave.
Bessel Functions
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)
A theoretical (mathematical) expectation of the bit error performance.
Probability of error P(e)
An empirical (historical) record of a system’s actual bit error performance.
Bit Error Rate (BER)
A function of the carrier-to-noise power ratio (or, more specifically, the average energy per bit-to-noise power density ratio) and the number of possible encoding conditions used (M-ary)
probability of error
A common method of achieving carrier recovery for BPSK.
Squaring loop
A second method of carrier recovery. Produces the same results as a squaring circuit followed by an ordinary PLL in place of the BPF.
Costas Loop
A third method of achieving recovery of a phase and frequency coherent carrier. Produces a loop error that is proportional to twice the phase error between the incoming signal and the VCO signal.
Remodulator
Is the transmittal of digital signals between two or more points in a communications system.
Digital Transmission
Circuit for digitizing voice at a low data rate by using knowledge of the way in which voice sounds are produced
Vocoder
_________ developed the first digital transmission system forthe purpose of carrying digitally encoded analog signals, such as humanvoice, over metallic wire cables between telephone offices.
AT&T
The primary advantage of digital transmission over analog transmission.
Noise Immunity
Digital signals are also better suited than analog signals for processing and combining using a technique called _____.
Multiplexing
Is the processing of analog signals using digital methods and includes band limiting the signal with filters, amplitude equalization, and phase shifting.
Digital Signal Processing ( DSP )
Digital transmission systems are more resistant to analog systems to additive noise because they use ________ rather than signal amplification.
Signal Regeneration
Consist 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.
PWM, PPM, PAM and PCM
Sometimes called pulse duration modulation (PDM) or pulse length modulation (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.
Pulse Width Modulation ( 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.
Pulse Position Modulation ( PPM )
The amplitude of a constant-width, constant-position pulse is varied according to the amplitude of the sample of the analog signal.
Pulse Amplitude Modulation
The analog signal is sampled and then converted to a serial ln-bit binary code for transmission.
Pulse Code Modulation ( PCM )
A circuit that periodically samples the analog input signal and converts those samples to a multilevel PAM signal.
Sample-and-Hold Circuit
The transmission line ________ are placed at prescribed distances to regenerate the digital pulses.
Repeaters
An integrated circuit that performs the PCM encoding and decoding functions.
Codec ( Coder / Decoder )
The function of a _________ in a PCM transmitter is to periodically sample the continually changing analog input voltage and convert those samples to a series of constant-amplitude pulses that can more easily be converted to binary PCM code.
Sampling Circuit
The sampling process alters the frequency spectrum and introduces an error called _________.
Aperture Error
The ________ of the capacitor is called the A/D conversion time because it is during this time that the ADC converts the sample voltage to a PCM code.
Storage Time
If the input to the ADC is changing while it is performing the conversion, _______ results.
Aperture Distortion
_________ theorem establishes the minimum sampling rate (fs)that can be used for a given PCM system.
Nyquist Sampling
The binary codes used for PCM are _________, where n may be any positive integer greater than 1.
N-Bit Codes
The sign bit in a sign-magnitude code.
Most Significant Bit ( MSB )
Is the process of converting an infinite number of possibilities to a finite number of conditions. Is the process of rounding off the amplitudes of flat-top samples to a manageable number of levels.
Quantization
A type of code where 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.
Quantization Interval or Quantum
If the magnitude of the sample exceeds the highest quantization interval, ________ (also called peak limiting) occurs.
Overload Distortion
Any round-off errors in the transmitted signal are reproduced when the code is converted back to analog in the receiver.
Quantization Error (Qe ) QuantizationNoise (Qn)
Is the ratio of the largest possible magnitude to the smallest possible magnitude (other than 0V) that can be decoded by the digital-to-analog converter in the receiver.
Dynamic Ratio
During times when there is no analog input signal, the only input to the PAM sampler is random, thermal noise also called as __________, that is converted to a PAM sample just as if it were a signal.
Idle Channel Noise
A way to reduce idle channel noise wherein the first quantization interval is made larger in amplitude than the rest of the steps.
Midtread Quantization
Is the process of compressing and then expanding.
Companding
Two methods of companding:
μ-Law and A-law Companding
Involves compression in the transmitter after the input sample has been converted to a linear PCM code and then expansion in the receiver prior to PCM decoding.
Digital Companding
When digitizing speech signals only, special voice encoders/decoders called _______ are often used
Vacoders
A _________ coder extracts the most significant portions of speech information directly from the time waveform rather than from the frequency spectrum as with the channel and formant vocoders.
Linear Predictive
_________ modulation uses a single-bit PCM code to achieve digital transmission of analog signals.
Delta
Two problems associated with delta modulation that do not occur with conventional PCM.
Slope Overload and Granular Subdivision
With ________, the difference in the amplitude of two successive samples is transmitted rather than the actual sample.
Differential PCM ( DPCM )
A ________ is simply the superposition of a series of harmonically related sine waves with specific amplitude and phase relationships.
Pulse Modulation
Multiple sources that originally occupied the same frequency spectrum are each converted to a different frequency.
Frequency Division Multiplexing
Used for the transmission of PCM-encoded time-division multiplexed digital signals.
T Carriers
Forms of delay-modulated codes where a logic 1 condition produces a transition in the middle of the clock pulse, and a logic 0 produces no transition at the end of the clock intervals unless followed by another logic 0.
Miller Codes
Commonly called the Manchester Code and specified in IEEE standard 802.3 for Ethernet local area networks.
Biphase L
Used for encoding SMPTE(Society of Motion Picture and Television Engineers) time-code data for recording on videotapes.
Biphase M
Uses one cycle of a square wave at 0◦ phase to represent a logic 1 and one cycle of a square wave at 180◦ phase to represent a logic 0.
Biphase
Popular type of line encoding that produces a strong timing component for clock recovery and does not cause dc wandering.
Digital Biphase
Produces a condition in which a receive may lose its amplitude reference for optimum discrimination between received 1’s & 0’s.
DC Wandering
Less than 100% of the bit time.
Return to Zero
Categorize the type of transmission.
Duty Cycle
Two nonzero voltages are involved ( a positive voltage for a logic 1 and an equal-magnitude negative voltage for a logic 0 or vice versa).
Bipolar
Involves the transmission of only a single nonzero voltage level.
Unipolar
Converting standard logic levels.
Digital Line Encoding
First bit of the code.
Address Bit
Identify when transitions occur in the data and whether that transition is from a 1 to a 0 or vice versa.
Three-Bit Code
Provides frequency shifting for the master group signals.
Signal Processor
Transmission of information from one or more source To one or more destination over the same transmission medium (facility).
Multiplexing
Unsophisticated form of multiplexing that simply constitutes propagating signals from different sources of different cables that are contained within the same trench.
Space-Division Multiplexing
Considered as transmission medium.
Trench
Form of phase-division multiplexing (PDM) where to date channels (the I and Q) modulate the same carrier frequency that has been shifted 90◦ in phase.
QPSK
Modulates a sine wave carrier.
I - Channel Bits
Modulates a cosine wave carrier.
Q - Channel Bits
Three most predominant methods of multiplexing signals.
Time-Division Multiplexing; Frequency-DivisionMultiplexing; Wavelength-Division Multiplexing
Transmissions from multiple sources occur on the same but not on the same time.
Time-Division Multiplexing
Most prevalent encoding technique used for TDM digital signals.
PCM
Simply an electronically controlled digital switch with two inputs and one outputs.
Multiplexer
A communications system that uses digital pulses rather than analog signals to encode information.
Digital Carrier System
Voice band channel bandwidth.
300 Hz to 3000 Hz
Circuit for digitizing voice at a low data rate by using knowledge of the way in which voice sounds are produced
Vocoder
A coding scheme that records the change in the signal level since the previous sample
Delta Modulation
Distortion created by using too low a sampling rate when coding an analog signal for digital transmission
Either aliasing or foldover distortion
Inaccuracies caused by the representation of a continuously varying quantity as one of a number of discrete values
Quantizing Errors
A device that encodes and recodes a digital signal as well as amplifying it.
Regenerative Repeater
The ratio of the largest possible magnitude to the smallest possible magnitude (other than 0 V) that can be decoded by the digital-to-analog converter in the receiver.
Dynamic Range (DR)
What is the control system that generates a signal with a fixed relation to the phase of a
reference signal and responds to both the frequency and the phase of the input signals?
Phase Locked Loop (PLL)
Simplest form of PSK, where N=1 and M=2. A form of square-wave modulation of a continuous wave (CW) signal.
Binary Phase Shift Keying (BPSK)
other form of angle-modulated, constant-amplitude digital modulation. An M-ary encoding scheme where N=2 and M=4
Quaternary phase shift keying (QPSK) /or quadrature PSK
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
It is popular type of line encoding that produces a strong timing component for
clock recovery and does not cause DC wandering.
Digital Biphase
