WIRELESS NETWORKS AND MOBILE COMMUNICATIONS

Fundamentals of Wireless Networks

Unlike wired connections that utilize guided media, wireless communication uses the

air as its channel, which is relatively unpredictable. This module will discuss the fundamental concepts that control signal transmission using air as the medium. It covers the electromagnetic spectrum, the physical features of radio frequencies, and the different impairments that reduce signal quality, such as path loss, interference, and fading. And at the end of it, it discusses Shannon's Theorem, which specifies the theoretical limits of wireless data transmission.

The Electro-Magnetic Spectrum

Wireless communication relies on radio waves, which are a form of electromagnetic (EM) radiation. The entire range of this radiation, from radio waves to gamma rays, is called the electromagnetic spectrum. Wireless technologies like Wi-Fi, Bluetooth, and cellular networks operate in specific, regulated parts of this spectrum to avoid interference.

The Electromagnetic (EM) spectrum is the complete range of all types of radiation that have both electric and magnetic fields and travel in waves.  A wave's frequency is the number of cycles it completes in one second and is measured in Hertz (Hz). Different frequencies have different properties, and the different frequencies are divided into different frequency bands.

Figure 1: The Electromagnetic Spectrum - [https://en.wikipedia.org/wiki/Electromagnetic_spectrum - accessed 26 August 2025]

Radio Frequency (RF)

Radio frequency (RF) is the electromagnetic spectrum that is most commonly used for wireless communication. This range is the band from about 3 kilohertz (kHz) to 300 gigahertz (GHz), and the different wireless technologies operate at the different RF bands as follows:

• Bluetooth and Wi-Fi typically operate in the 2.4 GHz and 5 GHz bands.
• Cellular networks use a variety of bands, including 700 MHz, 1.9 GHz, and 2.1 GHz.
• Understanding the specific frequency is critical because it dictates how a signal propagates, its range, and its resistance to obstacles.

The Wireless Channel
In wired networks, the channel is a physical medium like a fiber optic, twisted pair, coaxial cable or Ethernet cable. In wireless communication, the wireless channel is the air or space between the transmitter and the receiver. Unlike a cable, the wireless channel is unpredictable and introduces significant challenges as follows;

•          Path Loss: Path loss is the natural decrease in signal's power as it travels from source to destination. The farther a signal travels, the weaker it gets.
•          Interference: Interference refers to the disturbances of data as it is transmitted from source to destination.
•          Fading: This is caused by multipath propagation, where signals bounce off objects and arrive at the receiver at different times, causing rapid fluctuations in signal strength. 

Shannon's Theorem and Data Transmission
 Shannon's Theorem, (Shannon-Hartley theorem), is a fundamental principle that defines the theoretical maximum data rate of a channel with a given amount of noise. It provides an absolute limit on how fast we can send data over a wireless link.

It is expressed by the following formula:

C=Blog2​(1+S/N)

•      C is the channel capacity, the maximum achievable data rate in bits per second (bps). 
•      B is the bandwidth of the channel in Hertz (Hz). This is the width of the frequency band being used. 
•      S/N is the Signal-to-Noise Ratio (SNR), a measure of the signal's strength relative to the background noise. A higher SNR means a clearer signal.

The theorem shows that to increase the data rate (C), you must either increase the bandwidth (B) or improve the signal quality by increasing the SNR. It explains techniques to improve SNR, to achieve higher speeds.