Analog versus Digital Communications

Analog versus Digital Communications

Analog signal is a continuous signal and takes infinite number of amplitude values. Note that ‘Majority of signals in the world around us are in analog form’. Voice is best example of analog signal. Other examples are: heart beat signal, temperature, atmospheric pressure etc. Digital signal is discrete in nature. Discrete means countable (finite). Digital signal has only two levels (bit 1 and bit 0). In electrical engineering bit 1 is represented with 5 V and bit 0 is represented with 0 V.

Communication systems can be: (i) Analog. (ii) Digital.

Analog transmission

The analog signal attenuates (losses power) over distance of the transmission. To overcome the attenuation, amplifiers are used to strengthen the signals. However, noises are also amplified.

Advantages of Analog communications:

• Transmitters and Receivers are simple
• Low bandwidth requirement
• FDM can be used

Disadvantages of analog communication

• Noise affects the signal quality
• It is not possible to separate noise and signal
• Repeaters can‘t be used between transmitters and receivers
• Coding is not possible
• It is not suitable for the transmission of secret information
• Noise affects the signal quality. It is not possible to separate noise and signal

Digital transmission

Digital transmission is the transmission of digital pulses between two or more points/places. The signals can be binary (1010101111) or any other form of discrete-level digital pulses. Digital signals can be transmitted over a limited distance due to the attenuation and noises. Repeater can overcome the attenuation and are used to reconstruct the transmitted bits without amplifying noise signals.

Advantages of Digital communications

Note that today’s tendency is to change an analog signal to digital data.

• It has a better noise immunity. The effect of distortion, noise and interference is less in a digital communication system. i.e., Digital circuits are less subject to distortion and interference than analog circuits
• Low cost, VLSI technologies have made the cost of circuits for digital signals cheaper than that for analog signals
  Better capacity utilization, the high bandwidth digital links are cheaper than their analog
  counterparts and it is easier to have high degree multiplexing (a technique which allows
  multiple users sharing a common link) on digital links
• Combining digital signals using TDM (Time Division Multiplexing) is simpler than combining analog signals using FDM (Frequency Division Multiplexing).
• Better security and privacy, it is easier to encrypt (converting to secret messages) digital signals
• In digital systems transmission errors can be corrected and detected more accurately. So probability of occurring errors is less

Disadvantages of Digital Communication

• Digital communication system requires a larger channel bandwidth. The transmission of digitally encoded analog signals requires significantly more bandwidth. This is due to modulation and other changes made for ease of transmission. Remember that bandwidth is costliest parameter in any communication system.
• Additional encoding (Analog to Digital) and decoding (Digital to analog) circuitry required
  Digital transmission requires precise time synchronization between transmitter and receiver. But the analog signals generally do not support such requirement.