This is the summary notes of the important terms and concepts in Chapter 9 of the book "Electronic Communications System" by Wayne Tomasi. The notes are properly synchronized and concise for much better understanding of the book. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.
CHAPTER 9 |
DIGITAL MODULATION |
Items |
Definitions |
Terms |
1 |
Is the transmission, reception, and processing of information with the use of electronic circuits. |
Electronic Communication |
2 |
Is defined as knowledge or intelligence that is communicated between two or more points. |
Information |
3 |
Is the transmittal of digitally modulated analog signals (carriers) between two or more points in a communication system. |
Digital Modulation |
4 |
System involving the transmission of digital pulses. |
Digital Transmission |
5 |
The information signal is digital and the amplitude (V) of the carrier is varied proportional to the information signal. |
Amplitude Shift Keying ( ASK ) |
6 |
The information signal is digital and the frequency (f) of the carrier is varied proportional to the information signal. |
Frequency Shift Keying ( FSK ) |
7 |
The information signal is digital and the phase (θ) of the carrier is varied proportional to the information signal. |
Phase Shift Keying ( PSK ) |
8 |
A modulation where both the amplitude and the phase are varied proportional to the information signal. |
Quadrature Amplitude Modulation ( QAM ) |
9 |
Performs level conversion and then codes the incoming data into groups of bits that modulate an analog carrier. |
Pre-coder |
10 |
Is a highly theoretical study of the efficient use of bandwidth to propagate information through electronic communications systems. |
Information Theory |
11 |
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 |
12 |
The most basic digital symbol used to represent information. |
Binary Digit / Bit |
13 |
In 1928, _________ of Bell Telephone Laboratories developed a useful relationship among bandwidth, transmission time, and information capacity. |
R. Hartley |
14 |
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 |
15 |
Simply represents a digit that corresponds to the number of conditions, levels, or combinations possible for a given number of binary variables. |
M |
16 |
Refers to the rate of change of a digital information signal, which is usually binary. |
Bit Rate |
17 |
Refers to the rate of change of a signal on a transmission medium after encoding and modulation have occurred. |
Baud |
18 |
Sometimes called a symbol and could be encoded as a change in the amplitude, frequency, or phase. |
Signaling Element |
19 |
The minimum theoretical bandwidth necessary to propagate a signal. |
Nyquist Bandwidth |
20 |
According to ________, binary digital signals can be propagated through an ideal noiseless transmission medium at a rate equal to two time the bandwidth of the medium. |
H. Nyquist |
21 |
The carrier is either “on” or “off” which is why amplitude- shift keying is sometimes referred to as ________. |
On-Off Keying |
22 |
A logic 1 frequency (fm) for FSK. |
Mark |
23 |
A logic 0 frequency (fs) for FSK. |
Space |
24 |
The mark and space frequencies are separated from the mark and space frequencies are separated from the carrier frequency by the _________ and from each of by 2 Δf. |
Peak Frequency Deviation (Δf) |
25 |
_______ 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 |
26 |
A type of FSK detection wherein there is no frequency involved in the demodulation process that is synchronized either in phase, frequency, or both with the incoming FSK signal. |
Noncoherent Detection |
27 |
A type of FSK detection wherein the incoming FSK signal is multiplied by a recovered carrier signal that has exact same frequency and phase as the transmitter reference. |
Coherent Detection |
28 |
Is binary FSK except the mark and space frequencies are synchronized with the input binary bit rate. |
Continuous-Phase FSK ( CP-FSK ) |
29 |
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 |
30 |
Is a product modulator; the output signal is the product of the two input signals. |
Balanced Modulator |
31 |
Detect and regenerates a carrier signal that is both frequency and phase coherent with the original transmit carrier. |
Coherent Carrier Recovery Circuit |
32 |
Also known as quadrature PSK that is another form of angle-modulated, constant-amplitude digital modulation. |
Quaternary PSK ( QPSK ) |
33 |
A group of two bits. |
Dibit |
34 |
It modulates the carrier that is in phase with the reference oscillator. |
I Bit |
35 |
It modulates the carrier that is 90 out of phase or in quadrature with reference carrier. |
Q Bit |
36 |
Is two BPSK modulators combined in parallel. |
QPSK Modulator |
37 |
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 |
38 |
The fastest output rate of change (baud) is also equal to ________ of the input bit rate. |
1/2 |
39 |
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 |
40 |
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 ) |
41 |
The advantage of OQPSK is the _________ that must be imparted during modulation. |
Limited Phase Shift |
42 |
With ________, three bits are encoded, forming tribits and producing eight different output phases. |
8 PSK |
43 |
Group of 3 bits. |
Tribit |
44 |
Also known as maximum distance code used to reduce the number of transmission errors. |
Gray Code |
45 |
Converts the I/C and Q/C bit pairs to serial, Q, and C output data streams. |
Parallel-to-Serial Logic Circuit |
46 |
Group of 4 bits. |
Quadbits |
47 |
16-PSK can undergo only a _______ phase shift during transmission and still retain its integrity. |
11.25° |
48 |
Is an M-ary encoding technique where M = 8. The output signal from this modulator is not a constant-amplitude signal. |
8 – QAM |
49 |
The process of introducing transitions (pulses) into the binary signal using a prescribed algorithm. |
Scrambling |
50 |
It uses the same algorithm for scrambling to remove the transitions. |
Descrambler |
51 |
Is an alternative form of digital modulation where the binary input is contained in the difference between two successive signalling elements rather than the absolute phase. |
Differential Phase-Shift Keying ( DPSK ) |
52 |
Data transmission rates in excess of 56 kbps can be achieved, over standard telephone circuits using an encoding technique called ________. |
Trellis Code Modulation ( TCM ) |
53 |
__________ at IBM Zuerich Research Laboratory developed TCM, which involves using convolutional (tree codes, which combines encoding and modulation to reduce the probability of error, thus improving the bit error performance. |
Dr. Ungerboeck |
54 |
Defines the manner in which signal-state transitions are allowed to occur, and transitions that do not follow this pattern are interpreted in the receiver as transmission errors. |
Trellis Coding |
55 |
The distance between symbols on the constellation of the TCM coding scheme on standard QAM. |
Euclidean Distance |
56 |
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 |
57 |
Is simply the energy of a single bit of information. |
Energy Per Bit |
58 |
The phase relationship between signalling elements for BPSK (i.e., 180° out of phase) is the optimum signalling format, referred to as ________. |
Antipodal Signaling |
59 |
Two types of FSK systems. |
Noncoherent ( Asynchronous ) And Coherant ( Synchonous ) |
60 |
The transmitter and receiver are not frequency or phase synchronized. |
Noncoherent FSK |
61 |
Local receiver reference signals are in frequency and phase lock with the transmitted signals. |
Coherent FSK |
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