Electronic Communications System Flashcards

VOCABULARY flashcards based on the Chapter 9 notes of Electronic Communications System by Wayne Tomasi, covering digital modulation terms and definitions.

Electronic Communication

Is the transmission, reception, and processing of information with the use of electronic circuits.

Information

Is defined as knowledge or intelligence that is communicated between two or more points.

Digital Modulation

Is the transmittal of digitally modulated analog signals (carriers) between two or more points in a communication system.

Digital Transmission

System involving the transmission of digital pulses.

Amplitude Shift Keying (ASK)

The information signal is digital and the amplitude ($V$) of the carrier is varied proportional to the information signal.

Frequency Shift Keying (FSK)

The information signal is digital and the frequency ($f$) of the carrier is varied proportional to the information signal.

Phase Shift Keying (PSK)

The information signal is digital and the phase ($\theta$) of the carrier is varied proportional to the information signal.

Quadrature Amplitude Modulation (QAM)

A modulation where both the amplitude and the phase are varied proportional to the information signal.

Pre-coder

Performs level conversion and then codes the incoming data into groups of bits that modulate an analog carrier.

Information Theory

Is a highly theoretical study of the efficient use of bandwidth to propagate information through electronic communications systems.

Information Capacity

Is a measure of how much information can be propagated through a communications system and is a function of bandwidth and transmission time.

Binary Digit / Bit

The most basic digital symbol used to represent information.

R. Hartley

In 1928, of Bell Telephone Laboratories developed a useful relationship among bandwidth, transmission time, and information capacity.

Claude E. Shannon

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.

M

Simply represents a digit that corresponds to the number of conditions, levels, or combinations possible for a given number of binary variables.

Bit Rate

Refers to the rate of change of a digital information signal, which is usually binary.

Baud

Refers to the rate of change of a signal on a transmission medium after encoding and modulation have occurred.

Signaling Element

Sometimes called a symbol and could be encoded as a change in the amplitude, frequency, or phase.

Nyquist Bandwidth

The minimum theoretical bandwidth necessary to propagate a signal.

H. Nyquist

According to this researcher, binary digital signals can be propagated through an ideal noiseless transmission medium at a rate equal to two time the bandwidth of the medium.

On-Off Keying

A form of amplitude-shift keying where the carrier is either "on" or "off".

Mark

A logic 1 frequency ($f_m$) for FSK.

Space

A logic 0 frequency ($f_s$) for FSK.

Peak Frequency Deviation ($\Delta f$)

Is the difference between the carrier rest frequency and either the mark or space frequency; mark and space are separated from each other by $2\Delta f$.

Noncoherent Detection

A type of FSK detection wherein there is no frequency involved in the demodulation process that is synchronized in phase, frequency, or both with the incoming signal.

Coherent Detection

A type of FSK detection wherein the incoming FSK signal is multiplied by a recovered carrier signal that has the exact same frequency and phase as the transmitter reference.

Continuous-Phase FSK (CP-FSK)

Binary FSK where the mark and space frequencies are synchronized with the input binary bit rate.

Constellation Diagram

A signal state-space diagram that shows the relative positions of the peaks of the phasors rather than the entire phasor.

Balanced Modulator

A product modulator where the output signal is the product of the two input signals.

Coherent Carrier Recovery Circuit

Detects and regenerates a carrier signal that is both frequency and phase coherent with the original transmit carrier.

Quaternary PSK (QPSK)

Also known as quadrature PSK, it is a form of angle-modulated, constant-amplitude digital modulation.

Dibit

A group of two bits.

I Bit

The bit that modulates the carrier that is in phase with the reference oscillator.

Q Bit

The bit that modulates the carrier that is $90^\circ$ out of phase or in quadrature with the reference carrier.

QPSK Modulator

Consists of two BPSK modulators combined in parallel.

Fundamental Frequency (QPSK)

The highest fundamental frequency present at the data input to the I or the Q balanced modulator is equal to $\frac{1}{4}$ of the input data rate.

Baud Rate (QPSK)

The fastest output rate of change (baud) is equal to $\frac{1}{2}$ of the input bit rate.

Bit Combining Circuit

Converts the outputs of product detectors from parallel I and Q data channels to a single binary output data stream.

Offset QPSK (OQPSK)

A modified form of QPSK where the bit waveforms on the I and Q channels are offset or shifted in phase by one-half of a bit time.

Limited Phase Shift

The specific advantage provided by OQPSK during modulation.

8 PSK

An encoding technique where three bits are encoded, forming tribits and producing eight different output phases.

Tribit

A group of 3 bits.

Gray Code

Also known as maximum distance code, used to reduce the number of transmission errors.

Parallel-to-Serial Logic Circuit

Converts the I/C and Q/C bit pairs to serial, Q, and C output data streams.

Quadbits

A group of 4 bits.

16-PSK Integrity

To retain integrity, 16-PSK can undergo a maximum phase shift of only $11.25^\circ$ during transmission.

8-QAM

An M-ary encoding technique where $M=8$ and the output signal is not constant-amplitude.

Scrambling

The process of introducing transitions (pulses) into the binary signal using a prescribed algorithm.

Descrambler

Removes transitions using the same algorithm used for scrambling.

Differential Phase-Shift Keying (DPSK)

Digital modulation where the binary input is contained in the difference between two successive signalling elements rather than absolute phase.

Trellis Code Modulation (TCM)

An encoding technique used to achieve data rates in excess of $56\,kbps$ over standard telephone circuits.

Dr. Ungerboeck

Developed TCM at IBM Zuerich Research Laboratory using convolutional (tree) codes to reduce the probability of error.

Trellis Coding

Defines allowed signal-state transitions; non-following patterns are interpreted as transmission errors.

Euclidean Distance

The distance between symbols on the constellation of the TCM coding scheme on standard QAM.

Carrier-To-Noise Power Ratio

The ratio of the average carrier power (carrier plus sidebands) to the thermal noise power.

Energy Per Bit

The energy of a single bit of information.

Antipodal Signaling

The optimum signalling format where elements are $180^\circ$ out of phase, as seen in BPSK.

FSK System Types

The two varieties are Noncoherent (Asynchronous) and Coherent (Synchronous).

Noncoherent FSK

System where the transmitter and receiver are not frequency or phase synchronized.

Coherent FSK

System where local receiver reference signals are in frequency and phase lock with the transmitted signals.