In some scenarios, digital data must be transmitted over analog mediums, such as traditional telephone lines. This process involves converting digital data into an analog signal through modulation.
Here are the key concepts and components involved in this process:
Modulation
Modulation is the process of varying a carrier signal to transmit data. For transmitting digital data over an analog medium, digital modulation techniques are used.
Types of Digital Modulation:
1.) Amplitude Shift Keying (ASK):
In ASK, the amplitude of the carrier signal is varied to represent binary data. A high amplitude may represent a binary ‘1’, while a low or zero amplitude may represent a binary ‘0’.
- Applications: Used in RFID and low-frequency wireless systems.
2.) Frequency Shift Keying (FSK):
FSK modulates the frequency of the carrier signal. Different frequencies represent different binary values. For example, one frequency might represent a binary ‘1’ and another frequency a binary ‘0’.
- Applications: Common in modems, radio communication, and some telemetry systems.
3.) Phase Shift Keying (PSK):
PSK changes the phase of the carrier signal to transmit data. In Binary PSK (BPSK), one phase shift represents a binary ‘1’, and another phase shift represents a binary ‘0’. Quadrature PSK (QPSK) uses four phase shifts to represent two bits per symbol.
- Applications: Widely used in wireless communication and satellite communication.
Capacity of a Circuit
The capacity of a circuit, also known as channel capacity, is the maximum rate at which data can be transmitted over a communication channel without significant errors.
• It is often measured in bits per second (bps).
Factors Affecting Capacity:
- Bandwidth: Higher bandwidth allows more data to be transmitted.
- Signal-to-Noise Ratio (SNR): Higher SNR (less noise) increases the capacity.
- Modulation Techniques: More advanced modulation techniques can increase the capacity by efficiently utilizing the available bandwidth.
How Modems Transmit Data
A modem (modulator-demodulator) is a device that converts digital data from a computer or other digital device into an analog signal for transmission over telephone lines and then converts the incoming analog signal back into digital data.
Functioning of a Modem:
1.) Modulation:
Transmission: When a computer sends data to the modem, the modem modulates the digital data into an analog signal using one of the digital modulation techniques (ASK, FSK, PSK).
Example: For transmitting the binary sequence ‘101’, the modem might use different frequencies for ‘1’ and ‘0’ if using FSK.
2.) Demodulation:
Reception: When the modem receives an analog signal, it demodulates the signal back into digital data.
Example: The received signal with varying frequencies is interpreted back into the original binary sequence ‘101’.
3.) Error Detection and Correction:
Error Checking: Modems often include error detection and correction mechanisms, such as checksums or more advanced techniques, to ensure data integrity.
Retransmission: If errors are detected, the modem may request retransmission of the corrupted data.
Applications:
- Dial-up Internet: Modems were extensively used for dial-up internet access, converting digital data into analog signals to transmit over telephone lines.
- Point-to-Point Communication: Used in older or specialized communication systems for connecting two digital devices over an analog medium.
