Resume of Understanding Spectrum - ICT #6

Invisible electromagnetic waves makes phone calls and internet usage possible. Spectrum is electromagnetic frequency range which is a precious resources.

          Each time we use our mobile phones to share or receive information, the mobile phones emits electromagnetic waves. These waves are picked up by cell tower and transmitted to the destination tower near the receiver to be sent to the end user. This technique iis called cellular communication.

In cellular communication, geographical areas are divided into different cells. The cells need to transmit different signals based on the users. Each user's frequency is unique. This way a certain device is built to accept certain signal with filter circuit. By using frequency modulation, two  frequencies (high and low) are needed to transmit signals. 

However assigning a different signals fora approximately 5 billion users is impossible. 

ELECTROMAGNETIC SPECTRUM

> Ranges from radio waves to gamma rays

> The higher frequencies have the worst penetration capabilities (not suitable for cellular communication)

> The lower frequency have lower energy that would require a larger antenna

> Only a small portion of the electromagnetic spectrum that could be used for cellular technology

Spectrum is one of the resources which is managed by the government. In most countries, government earns by distributing various portions of the spectrum between companies using an auction system.

These days, we use a technique called Quadrature Amplitude Modulation which we can send more bits at a time. Variations are made to the amplitude and phasing to generate different digital signals.

The cellular system divides the available range into a number of frequency slots. Then they are distributed to some towers. This technique helps to use the same frequency range for different cell towers. The technique of allocating the frequency slots for different cell areas is called frequency slot distribution.

            Another challenge is to manage all the users within a cell area at the same time. This challenge is solved by using the multiple access technique. A cell tower with multiple users can share informations over a different frequency slot in a different time windows using different encoding. Each generation of cellular use different multiple access technique, trying to utilize the available spectrum efficiently

Source :

Learn Engineeting. 2019. Understanding Spectrum! _ ICT #6

https://www.youtube.com/watch?v=DXt-rXDu9M8