Understanding Communication Systems: Definitions, History, and Models

Posted on Mar 11, 2025 in Communication

Understanding Communication Systems

  1. Definition of a System

A combination of interacting elements organized to achieve one or more stated purposes.

  1. What is System Engineering?

Systems engineering is an iterative process of top-down synthesis, development, and operation of a real-world system that satisfies, in a near-optimal manner, the full range of requirements for the system.

  1. Chronology of Communication Systems

The Visual Era: Smoke signals → Pigeon Post → Printing Press (1450)

The Wired Era: Telegraph → Telephone (1876) → First Videophone → Fax machine (1964)

The Wireless Era: Mobile phone (1973) → Cellular → SMTP email → First text message (1992)

IP Cloud Era: Skype (2003) → iPhone (2007) → Social media platforms (2010)

  1. Claude Shannon: The Father of Information Theory

Claude Elwood Shannon was an American mathematician, electrical engineer, and cryptographer known as “the father of information theory”. Shannon is noted for having founded information theory with a landmark paper, “A Mathematical Theory of Communication”, that he published in 1948.

  1. Analog vs. Digital Signals: Key Differences

Analog Signal

  1. Must have a continuous value.
  2. Must feature a time-varying flow of information. Each fluctuation in the signal has important meaning, unlike digital, which deals with numeric representation.
  3. The most common context of analog is in electronics.

Digital Signal

  1. Represents data as a sequence of discrete values.
  2. Can only take on one value from a finite set of possible values at a given time.
  3. The physical quantity representing information can be many things.
  1. Quantization of an Analog Signal

Is the second step for A/D conversion. Is the process of mapping the sampled analog voltage values to discrete voltage levels, which are then represented by binary numbers (bits).


  1. The Shannon Communication System Model

Information Source: Refers to anything generating any content for communication.

Transmitter: The objective of the transmitter block is to collect the incoming message signal and transform it, such that, it can be reliably (controllable errors) transmitted via the chosen channel to the receiving point. (encoding)

Physical Channel: The channel is the physical medium which connects the transmitter block with the receiver block. The type of encoding of the transmitter block is decided by the type or nature of the channel chosen for communication.

Receiver: Receives the incoming modified version of the message digital signal from the channel. Upon reception, it decodes such modified version of the message signal. The goal of the receiver is to recover the original digital form of the message signal with some guaranteed negligible small errors.

Destination: Is the final block in the communication system. It receives the recovered message signal. Usually, humans have been the usual destination block.

  1. Binary Source of Information

Assume a transmitter sending the signal X taking values “0” and “1” with probability p(x):

  • The probability to send “0” is p(x=0) = 1/2
  • The probability to send “1” is p(x=1) = ½

H(X)= -p(X=0) log2p(x=0)-p(X=1) log2p(x=1)

= -(1/2) log2 (1/2) – (1/2) log2 (1/2) = 1 bit

  1. Entropy and Mutual Information Explained

Entropy is a key measure in information theory. Entropy quantifies the amount of uncertainty involved in the value of a random variable or the outcome of a random process.

wX+A1v5RtUDPgAAAABJRU5ErkJggg==

When X and Y are NOT independent random variables, then we define the mutual information as:

It tells us what happens to information transmitted across the channel, or it “characterises” channel. It seems a bit too mathematical (too abstract).

In engineering, it is better to characterise such thing with physical quantities, such as bandwidth, signal power and noise power.


  1. Codification of Information at the Transmitter

Encoding: The objective of the transmitter block is to collect the incoming message signal and transform it, such that, it can be reliably (controllable errors) transmitted via the chosen channel to the receiving point.

Encoding the digital signal message roughly means to include extra zeroes and ones such that the noise of the channel does not affect the information.

  1. The Gaussian Channel: A Model for Noise

A first advantage of Gaussian noise is that the distribution itself behaves nicely. It’s called the normal distribution for a reason: it has convenient properties and is very widely used in natural and social sciences. People often use it to model random variables whose actual distribution is unknown.

  1. Objective of Communication System Standards

The goal of any form of communication is to promote complete understanding of a message. Control and monitor each action in the city due reduce the human intervention.

Communication standards allow to design any communication system according to agreed rules.

  1. Three Types of Standardization

Proprietary standards are developed by an individual firm or firms through the market process.

Standards institutions set up institutional standards through their consensus decisions.

Governments intervene and establish governmental standards when they are deemed necessary.

  1. Standardization in the US vs. Europe

The European standardization policy strongly favored a single European standard:

  • By means of institutional coordination in the telecommunications industry.
  • Political intervention of the European Union and national governments.

Service providers do not have many incentives to switch to a non-European standard since they might be isolated in the market.


Single national standard / Sponsored by national champions / Endorsed by regulators

  • US: multiple standards / Market competition
  • Europe: Single regional standard/ Government intervened institutional coordination
  1. Over-the-Top (OTT) Applications

An over-the-top (OTT) application is any app or service that provides a product over the Internet and bypasses traditional distribution. Services that come over the top are most typically related to media and communication and are generally, if not always, lower in cost than the traditional method of delivery.

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  1. Design Methodologies: Advantages and Disadvantages

Waterfall Model

Advantages

  • Easy to allocate resources and budget because requirements are very clear in advance.
  • Every member of the team knows what happens, when, and why.
  • Progress is easily measured.
  • Customers do not need to be involved in the development.

Disadvantages

  • Hard requirements gathering phase.
  • The customer does not see the project until the end.
  • Customer satisfaction is not guaranteed. Misunderstanding exists.
  • Hard, costly, or even impossible to fix problems found in the testing phase.


Lean Model

Advantages

  • Tasks are evaluated for their benefit for the customer and their financial opportunities.
  • The big picture overshadows individual needs; effectiveness is vital.
  • Cutting off the possibility for obstacles smooths out the project process.

Disadvantages

  • Value is only defined by the end customer. Things get complicated fast in projects where there are multiple end customers.
  • It is hard to find a Flow in projects.

Agile Model

Advantages

  • Short planning cycles allow changes.
  • Customers provide constant feedback, so meeting their expectations is more feasible.
  • Faster discovery of problems due to team interactions.
  • Project fast evolution.

Disadvantages

  • Difficult to estimate cost upfront.
  • Customer involvement is tiring for both parts.
  • The plan changes constantly, so stress is higher and there is a little bit of chaos.
  • Additional requirements add up predicted costs and make the project last longer. Difficult to set a stop point.