Experiment-07

7.1 Title: Design and Implementation of Time Division Multiplexing (TDM) with Four Channels

7.2 Aim of the experiment:  To design and implement a Time Division Multiplexing (TDM) system with a minimum of four input channels and analyze the multiplexed and demultiplexed signals.

7.3 Theoretical background for the experiment:  Time Division Multiplexing (TDM) is a technique where multiple signals share the same transmission medium by allocating a distinct time slot to each signal in a cyclic manner. This ensures that multiple input channels can be transmitted simultaneously over a single communication line without interference.

Key Components:

• Multiplexer (MUX): Combines multiple input signals into a single output stream by interleaving time slots.

• Demultiplexer (DEMUX): Separates the multiplexed signal into individual channel signals using time slot allocation.

7.4  Design:

1.  Input Signals: Four distinct signals (e.g., sine wave, square wave, random noise, and triangular wave).

2.  Multiplexing: Assign fixed time slots for each channel and combine the signals sequentially.

3.  Demultiplexing: Use time slot identification to recover individual channel signals.

4.  System Parameters:

o    Sampling frequency: Sufficient to sample all input signals.

o    Time slot duration: Equal for all channels.

Step by step procedure to carry out the experiment:

1.      Generate four input signals.

2.      Define a time slot duration for each channel.

3.      Combine the signals in time-domain using interleaving.

4.      Transmit the multiplexed signal.

5.      At the receiver, demultiplex the signal by extracting data from corresponding time slots.

6.      Compare the recovered signals with the original input signals.

7.5  Code:

Time Division Multiplexer (TDM)

% Define the input signals

t = 0:0.01:1;              % Time vector (0 to 1 second, step 0.01)

signal1 = sin(2*pi*5*t);   % Signal 1: 5 Hz sine wave

signal2 = cos(2*pi*15*t);  % Signal 2: 15 Hz cosine wave

signal3 = sin(2*pi*25*t);  % Signal 3: 25 Hz sine wave

signal4 = cos(2*pi*35*t);  % Signal 4: 35 Hz cosine wave

% Combine the signals using TDM (4 channels)

mux_signal = [signal1; signal2; signal3; signal4];  % Stack the signals vertically

mux_signal = mux_signal(:)';                        % Convert to a row vector by reshaping

% Plot the input signals

figure;

subplot(5,1,1);

plot(t, signal1);

title('Input Signal 1');

xlabel('Time (s)'); ylabel('Amplitude');

subplot(5,1,2);

plot(t, signal2);

title('Input Signal 2');

xlabel('Time (s)'); ylabel('Amplitude');

subplot(5,1,3);

plot(t, signal3);

title('Input Signal 3');

xlabel('Time (s)'); ylabel('Amplitude');

subplot(5,1,4);

plot(t, signal4);

title('Input Signal 4');

xlabel('Time (s)'); ylabel('Amplitude');

% Plot the multiplexed signal

subplot(5,1,5);

plot(1:length(mux_signal), mux_signal);

title('Multiplexed Signal');

xlabel('Sample Index'); ylabel('Amplitude');

% Demultiplex the signals (extracting each original signal from the multiplexed signal)

demux_signal1 = mux_signal(1:4:end);  % Every 4th sample starting from 1st

demux_signal2 = mux_signal(2:4:end);  % Every 4th sample starting from 2nd

demux_signal3 = mux_signal(3:4:end);  % Every 4th sample starting from 3rd

demux_signal4 = mux_signal(4:4:end);  % Every 4th sample starting from 4th

% Plot the demultiplexed signals

figure;

subplot(4,1,1);

plot(t, demux_signal1);

title('Demultiplexed Signal 1');

xlabel('Time (s)'); ylabel('Amplitude');

subplot(4,1,2);

plot(t, demux_signal2);

title('Demultiplexed Signal 2');

xlabel('Time (s)'); ylabel('Amplitude');

subplot(4,1,3);

plot(t, demux_signal3);

title('Demultiplexed Signal 3');

xlabel('Time (s)'); ylabel('Amplitude');

subplot(4,1,4);

plot(t, demux_signal4);

title('Demultiplexed Signal 4');

xlabel('Time (s)'); ylabel('Amplitude');

7.6  Observations and results:

1.  The multiplexed signal shows the interleaved input signals, each occupying their assigned time slot.

2.  The demultiplexed signals successfully reconstruct the original input signals.

3.  Minimal distortion is observed due to proper sampling and synchronization.

7.8 Plotting of the graph:

Observations and results:

1. Time Division Multiplexing (TDM):

7.9 Conclusion of the experiment:

The TDM system was successfully designed and implemented for four input channels. The experiment demonstrated the effective use of time slots for multiplexing and demultiplexing, enabling simultaneous transmission of multiple signals over a single medium. This validates the principles of Time Division Multiplexing.