GATE Electronics and Communication (EC) Questions Paper With Answer Key Download Pdf [2025] Download Question Paper                 See Answers   Q.61 The input voltage is given by: V_I = 10 sin(100πt) Where: V I is the input voltage in volts. t is the time in seconds. The diode will be forward biased when the input voltage exceeds 5V. Therefore, we need to solve the inequality: 10 sin(100πt) > 5 Step 1: Simplify the Inequality Divide both sides by 10: sin(100πt) > 0.5 Step 2: Find when sin(100πt) = 0.5 The sine function equals 0.5 at: sin(θ) = 0.5 when θ = π/6, 5π/6, ... So, for 100πt , we have: 100πt = π/6 and 100πt = 5π/6 (first two points) Step 3: Solve for t Solving these equations for t , we get: 100πt = π/6 => t = 1/600 seconds 100πt = 5π/6 => t = 5/600 seconds Step 4: Find the Time Interval for Forward Bias ...

D Flip-Flop, S-R Flip-Flop, and J-K Flip-Flop A D flip-flop (often called a D-type flip-flop ) is a type of edge-triggered flip-flop that is commonly used in digital circuits. The primary function of a D flip-flop is to store and transfer a bit of data (either 0 or 1). It is often used for data storage, synchronization, and signal timing. How It Works Key Inputs and Outputs: D (Data) Input: This is the data input to the flip-flop. The value at this input will be transferred to the output (Q) on the clock edge. CLK (Clock) Input: The clock signal controls when the data at the D input is transferred to the output (Q). The flip-flop is edge-triggered, meaning it only responds to changes on the clock signal (either rising or falling edge, depending on the design). Q Output: This is the main output of the flip-flop, where the stored value is output. Q' (Q Not) Output: This is the inverse of the Q output. Opera...

Main Difference Between QPSK and 4-PSK Understanding how Quadrature PSK and 4-Phase PSK relate in digital modulation. Definition Term Meaning 4-PSK A general term for a phase shift keying (PSK) scheme that uses four distinct phase states to represent data. QPSK (Quadrature PSK) A specific implementation of 4-PSK where the four phases are spaced 90° apart (quadrature). In essence, QPSK = 4-PSK — both use four phase shifts (0°, 90°, 180°, 270°) to encode two bits per symbol. Bits per Symbol Modulation Number of Phases Bits per Symbol Example Phase Angles BPSK 2 1 0°, 180° ...

In real-world wireless communication, the direct line-of-sight (LOS) path between transmitter and receiver is often blocked or unavailable. As a result, the transmitted signal experiences Rayleigh fading . This phenomenon arises from multipath propagation, where the signal reaches the receiver through several different paths with varying delays and phase shifts. While constellation diagrams primarily show the effects of Additive White Gaussian Noise (AWGN) , multipath fading can heavily distort these diagrams. This distortion impacts the accuracy of symbol detection, leading to increased error rates and degraded system performance. To combat these challenges, communication systems employ techniques such as equalization and diversity methods to reduce the adverse effects of multipath fading.    MATLAB Simulation of Rayleigh Fading Impact on BPSK Constellation // MATLAB code courtesy of SalimWireless.com clc; clear; close all; % Pa...

Understanding IFFT Frequency Spacing If you gave the IFFT a list of individual ‘notes’ (subcarrier amplitudes) at specific ‘pitches’ (frequencies: 0, f, 2f, 3f). The IFFT's job is to combine them into one single ‘melody’ (the time-domain signal). Even though it's one melody, the IFFT guarantees that the individual notes are still distinctly present and perfectly spaced in frequency within that melody. We prove this because if you ‘un-mix’ the melody using the FFT, you get back exactly the original list of individual notes you started with. This means the IFFT effectively ‘defined’ and ‘placed’ them in their frequency slots within the combined signal. The entire process demonstrates that the IFFT doesn't just randomly scramble data. Instead: It takes data defined by frequency slots (X array where each element is a subcarrier). Visualizing the Concept Here's a conceptual image to help illustrate the id...

Instructions for Pulse Code Modulation (PCM) Note: Use the input fields to enter the message frequency, sampling frequency, and quantization levels. Step 1: Click on Generate Message to create the analog message signal. Sampling frequency should be higher than the message frequency. Step 2: Click on Plot Quantized Signal to view the quantized signal. Step 3: Click on Generate PCM Signal to generate the PCM signal. Message Frequency (Hz): Sampling Frequency (Hz): Quantization Levels: Generate Message Plot Quantized Signal Generate PCM Signal Quantization SNR (dB): Instructions for Pulse Code Demodulation Step 1: The decoder converts encoded binary PCM data back into quantized analog values. Step 2: Click on Demodulate PCM Signal to reconstruct the message...

MIMO (Multiple-Input Multiple-Output) systems use multiple antennas at the transmitter and receiver to improve communication performance in wireless systems. 1. Space Shift Keying (SSK) SSK is a special case of spatial modulation where only the antenna index carries the information. No modulation symbol (like QAM or PSK) is used. How it works: Only one transmit antenna is active at a time. The active antenna index represents the information bits. All other antennas remain silent. Achievable Rate: For n t transmit antennas, the rate is: log 2 (n t ) bits per channel use (bpcu) Example: For n t = 4 , we can encode log₂(4) = 2 bits: Input Bits SSK Vector Active Antenna 00 [1, 0, 0, 0]...

In practical communication systems, direct line-of-sight (LOS) paths are often unavailable, causing the signal to undergo Rayleigh fading. This type of fading occurs due to multipath propagation, where the signal arrives at the receiver through multiple paths with varying delays and phases. While constellation diagrams are typically affected by AWGN (Additive White Gaussian Noise), they are also significantly influenced by multipath fading. Multipath can distort the signal constellation, leading to errors in symbol detection and affecting overall system performance. Techniques like equalization and diversity are commonly used to mitigate the impact of multipath fading in such systems  MATLAB Code for the Effect of Rayleigh Fading on the Constellation Diagram of Binary ASK % The code is developed by SalimWireless.com clc; clear; close all; % Parameters N = 10000; % Number of symbols SNR = 20; % Signal-to-Noise Ratio in dB (for AWGN) M = 2; ...