Quadrature-Amplitude Modulation (QAM) Transmitter and Diagrams Quiz

18 Questions

What is the key feature of Offset-QPSK (OQPSK) modulation compared to standard QPSK?

I and Q channel bit waveforms are phase-shifted by half a bit time

What is the number of possible conditions in a QPSK modulation scheme?

In a QPSK modulator, how many possible output phases can be generated for each dibit code?

How many bits are encoded to form tribits in an 8-PSK modulation scheme?

What is the number of different output phases produced in an 8-PSK modulation scheme?

In Quadrature-Amplitude Modulation (QAM), what combination does each symbol carry information about?

Both Phase and Amplitude

What is the minimum double-sided Nyquist bandwidth (fN) for an 8-PSK modulator with an input data rate of 10 Mbps?

30 MHz

In a 16-PSK modulation, how many different output phases are possible?

In Quadrature-Amplitude Modulation (QAM), where is the digital information contained?

In both the amplitude and the phase

What is the relationship between bandwidth and baud for 16-PSK modulation?

$f_b = 4B$, $B = 4f_b$

Which type of modulation combines amplitude and phase shifts to optimize signaling elements' positions on constellation diagrams?

OQPSK

For an 8-PSK modulator with a carrier frequency of 70 MHz, what would be the baud if the input data rate is 20 Mbps?

$\frac{1}{4}$ MHz

What is the bandwidth efficiency defined as?

Ratio of the transmission bit rate to the minimum bandwidth required for a particular modulation scheme

In Quadrature-Amplitude Modulation (QAM), what does the 'Q' stand for?

Quadrant

What is the minimum double-sided Nyquist frequency, and baud for a 16-QAM modulator with an input data rate of 10 Mbps and a carrier frequency of 70 MHz?

fN = 35 MHz, Baud = 5 Msps

What is the purpose of using Quadrature Phase-Shift Keying (QPSK) modulation in communication systems?

To double the transmission rate without increasing the bandwidth

How many distinct phases are typically used in 8-PSK modulation?

What does the 'O' in Offset Quadrature Phase-Shift Keying (OQPSK) refer to?

Original

Study Notes

Phase-Shift Keying (PSK)

BPSK (Binary PSK): N = 2, M = 2
QPSK (Quaternary PSK): N = 2, M = 4
QPSK combines binary input data into groups of two bits (dibits) and generates one of four possible output phases (45°, 135°, 45°, and 135°)

QPSK

QPSK transmitter: generates four possible output phases based on dibits
QPSK truth table: shows the relationship between dibits and output phases
QPSK phasor diagram: represents the output phases
QPSK constellation diagram: represents the possible states of the signal
QPSK bandwidth and baud: 𝑓𝑏 𝐵= 2 𝑓𝑏 𝑏𝑎𝑢𝑑 = 2

QPSK Sample Problem

For a QPSK modulator with an input data rate (fb) of 10 Mbps and a carrier frequency of 70 MHz, determine the minimum double-sided Nyquist bandwidth (fN) and the baud

Offset-QPSK (OQPSK)

Modified form 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
OQPSK transmitter: generates four possible output phases based on dibits
OQPSK constellation diagram: represents the possible states of the signal

8-PSK

8-PSK: three bits are encoded, forming tribits and producing eight different output phases
8-PSK transmitter: generates eight possible output phases based on tribits
8-PSK truth table: shows the relationship between tribits and output phases
8-PSK phasor diagram: represents the output phases
8-PSK constellation diagram: represents the possible states of the signal
8-PSK bandwidth and baud: 𝑓𝑏 𝐵= 3 𝑓𝑏 𝑏𝑎𝑢𝑑 = 3

8-PSK Sample Problem

For an 8-PSK modulator with an input data rate (fb) of 10 Mbps and a carrier frequency of 70 MHz, determine the minimum double-sided Nyquist bandwidth (fN) and the baud

16-PSK

16-PSK: an M-ary encoding technique where M=16; four bits (called quadbits) are combined, producing 16 different output phases
16-PSK bandwidth and baud: 𝑓𝑏 𝐵= 4 𝑓𝑏 𝑏𝑎𝑢𝑑 = 4
16-PSK truth table: shows the relationship between quadbits and output phases
16-PSK constellation diagram: represents the possible states of the signal

Quadrature-Amplitude Modulation (QAM)

Form of digital modulation similar to PSK except the digital information is contained in both the amplitude and the phase of the transmitted carrier
Amplitude and phase-shift keying are combined to optimize the distance between elements on the constellation diagram

8-QAM

8-QAM transmitter: generates eight possible output phases based on input data
8-QAM output wave: represents the modulated signal
8-QAM truth table: shows the relationship between input data and output phases
8-QAM phasor diagram: represents the output phases
8-QAM constellation diagram: represents the possible states of the signal
8-QAM bandwidth and baud: 𝑓𝑏 𝐵= 3 𝑓𝑏 𝑏𝑎𝑢𝑑 = 3

16-QAM

16-QAM transmitter: generates 16 possible output phases based on input data
16-QAM truth table: shows the relationship between input data and output phases
16-QAM phasor diagram: represents the output phases
16-QAM constellation diagram: represents the possible states of the signal
16-QAM bandwidth and baud: 𝑓𝑏 𝐵= 4 𝑓𝑏 𝑏𝑎𝑢𝑑 = 4

Bandwidth Efficiency

Bandwidth efficiency: ratio of the transmission bit rate to the minimum bandwidth required for a particular modulation scheme
Bandwidth efficiency formula: 𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑠𝑠𝑖𝑜𝑛 𝑟𝑎𝑡𝑒 (𝑏𝑝𝑠) 𝐵𝜂 = 𝑚𝑖𝑛𝑖𝑚𝑢𝑚 𝑏𝑎𝑛𝑑𝑤𝑖𝑑𝑡ℎ (𝐻𝑧)

Bandwidth Efficiency Sample Problem

For an 8-PSK system, operating with an information bit rate of 24 kbps, determine (a) baud, (b) minimum bandwidth, and (c) bandwidth efficiency

Test your knowledge on Quadrature-Amplitude Modulation (QAM) with questions about 8-QAM and 16-QAM transmitters, truth tables, phasor diagrams, constellation diagrams, bandwidth, and baud rates.

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