Lecture 9: Digital Modulation Techniques

Comprehensive flashcards covering digital modulation techniques (ASK, FSK, PSK, QAM), their receiver architectures, mathematical models, applications, and performance comparisons based on Dr. Waleed El Nahal's Lecture 9.

Amplitude Shift Keying (ASK)

A digital-to-analog conversion technique where different bits are represented by different amplitudes (real values) while maintaining the same phase and frequency.

Phase Shift Keying (PSK)

A digital modulation technique where bits are represented by different phases while the amplitude and frequency remain constant.

Frequency Shift Keying (FSK)

A modulation method where different frequencies are used to represent digital data, while the amplitude and phase remain fixed.

Quadrature Amplitude Modulation (QAM)

A modulation technique that varies both the amplitude and the phase of the carrier signal while keeping the frequency constant.

Coherent Receiver

A receiver where the transmitter and receiver oscillators are locked, meaning the phase difference $\phi = 0$. It requires phase estimation but offers better performance than non-coherent receivers.

Non-coherent Receiver

A receiver where the transmitter and receiver oscillators are not locked, and the phase difference $\phi$ is random between $0$ and $2\pi$. They are simpler and less complex as phase knowledge is not required.

Bit Error Rate (BER)

The key performance metric in digital band-pass signals, representing the probability of error during bit stream transmission.

Amplitude Shift Keying Signal Equation

The transmitter sends signal $s(t) = A\cos(2\pi f_c t)$ for bit 1 and $s(t) = 0$ for bit 0.

Asynchronous Demodulation

Also known as Non-coherent Detection, it is a process where the carrier signal used at the receiver is not in the same phase as the carrier signal used at the transmitter.

On-Off Keying (OOK)

A specific case of ASK where the carrier is turned off when transmitting a '0' to save power.

Binary Frequency Shift Keying (BFSK) Signal

The transmitter sends a carrier with frequency $f_0$ for bit 0 ($s_0(t) = A\cos(2\pi f_0 t)$) and frequency $f_1$ for bit 1 ($s_1(t) = A\cos(2\pi f_1 t)$).

BFSK Orthogonality Condition

The two frequencies $f_0$ and $f_1$ are separated such that $(f_1 - f_0)T$ is an integer, where $T$ is the bit duration.

Binary Phase Shift Keying (BPSK)

A modulation scheme using Non-Return-to-Zero (NRZ) signaling where logic 1 is represented by $A\cos(2\pi f_c t)$ and logic 0 is represented by $-A\cos(2\pi f_c t)$, resulting in a $180^{\circ}$ phase shift.

Binary Differential Phase Shift Keying (BDPSK)

A non-coherent PSK method where source bits $b_n$ generate a shifted stream $s_n = b_n \oplus s_{n-1}$. If $b_n = 0$, the value does not change; if $b_n = 1$, the value changes.

BDPSK Bit Error Rate Formula

The probability of error is defined as $P_e = \frac{1}{2} \exp(-\text{SNR})$.

Non-coherent BFSK Bit Error Rate Formula

The probability of error is defined as $P_e = \frac{1}{2} \exp\left( -\frac{\text{SNR}}{2} \right)$, requiring twice the SNR of BDPSK for the same BER.

BPSK Bit Error Rate Formula

The probability of error is defined as $P_e = Q(\sqrt{2\text{SNR}})$, typically providing the best performance (lowest BER).

Constellation Diagram

A graphical representation used in digital modulation, such as BPSK, where symbols are plotted as points in a complex plane (e.g., $+A$ and $-A$ on the real axis for BPSK).

Quadrature Amplitude Modulation (QAM) Signal Equation

The modulated signal is given by $S_{QAM}(t) = m_1(t) \cos(2\pi f_c t) + m_2(t) \sin(2\pi f_c t)$, where it encodes messages into both the in-phase and quadrature-phase components.

Bandwidth Efficiency

A comparison metric for modulation schemes; ASK and FSK have low efficiency, while PSK is high and QAM is very high.