communication systems

Published on ~polarhive/wiki

input -> input transducer Tx <== channel ==> Rx -> output transducer -> output

Communication systems involve the conversion of information from one form to another. In the context of electrical signals, this process involves several key components:

  1. Input Transducer (Tx): This is the first step in the communication process. It converts the input signal into an electrical signal that can be transmitted over the channel.
  2. Channel: This is the medium through which the electrical signal is transmitted. It can be a wire, air, or any other medium that allows the signal to travel from the transmitter to the receiver.
  3. Output Transducer (Rx): Upon receiving the signal from the channel, the output transducer converts the electrical signal back into the original form of the information.
  4. Output: This is the final step where the information is presented in its original form to the user.


Transducers play a crucial role in communication systems by converting signals between different forms. There are two main types of transducers:

Transducers operate on the principle of energy conversion, transforming the signal from one form to another.


Modulation is a technique used in communication systems to encode information onto a carrier signal. This process allows for the efficient transmission of information over a channel. There are several types of modulation:

Continuous Modulation

Digital Modulation

Information will be in binary form i.e. 1s and 0s where as carrier will be continuous. The amplitude or phase of the carrier will be varied according to binary data.


The process of recovering the message from the modulated signal is called demodulation.

Types of demodulation

Need for Modulation

| Application  | Frequency Band |
| ------------ | -------------- |
| AM Radio     | 0.54-1.6 MHz   |
| TV           | 54-8 MHz       |
| FM Radio     | 8-108 MHz      |
| Mobile Radio | 806-901 MHz    |

The Objectives of a Cellular System Include

However, for achieving a large coverage area, a single transmission necessitates high power and the use of tall towers. This approach limits the service to a small number of users and results in efficient spectrum utilization.

Cellular Concept and Frequency Reuse Pattern

Use of Cellular Concept


Handoff Strategies


  1. Prioritising Handoffs:

    • Issue: Perceived Grade of Service (GOS) – the quality of service as viewed by users.
    • Quality Consideration: "Quality" in terms of dropped or blocked calls (not voice quality).
    • Prioritization: Handoffs are assigned higher priority over new call requests.
    • Impact of Dropped Calls: A dropped call is more aggravating than an occasional blocked call.
  2. Guard Channels:

    • Percentage of total available cell channels exclusively set aside for hand off requests
    • Makes fewer channels available for new call requests
    • A good strategy is dynamic channel allocation (not fixed)
    • adjust number of guard channels as needed by demand
  3. Queuing Handoff Requests

    • Use time delay between handoff threshold and minimum usable signal level to place a blocked handoff request in queue.
    • A handoff request can "keep trying" during that time period, instead of having a single block/no block decision.
    • Prioritise requests (based on mobile speed) and handoff as needed.
    • Calls will still be dropped if time period expires.

Practical Handoff Considerations

Problems occur because of a large range of mobile velocities

Umbrella Cells

Example areas: interstate highway passing through urban centre, office park, or nearby shopping mall.

Typical handoff parameters

Benefits of small handoff time

Co-Channel Interference

During Frequency reuse there are several cells that use the same set of frequencies which leads to co-channel interference.

co-channel interference is a function of:

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