Radio Frequency Theory

In this blog post, we will provide you with the fundamental information and knowledge regarding broadband wireless communication, from Basics in Radio Frequency Theory all the way to understanding advanced concepts like TDD and FDD.

Outdoor, broadband wireless communication uses electromagnetic waves to pass data between two endpoints.  These electromagnetic waves are defined by two basic characteristics namely:

• Frequency – which can be described as the number of periodic cycles the wave traverses per second and is measured in Hertz (Hz)
• Wavelength – which can be described as the distance between two identical endpoints in a periodic cycle

The relationship between frequency and wavelength is described as inversely related.  This simply means that the higher your frequency, the shorter the wavelength and the lower your frequency, the longer your wavelength. What this means is that a lower frequency such as 2.4GHz, has a longer wavelength when compared to a higher frequency like 5GHz and that the 2.4GHz will propagate (travel further) than the 5GHz frequency.

Electromagnetic Spectrum and Radio Frequency Spectrum

The electromagnetic spectrum refers to the entire range of frequencies that covers electromagnetic energy, from X-rays on the higher end of the spectrum, to radio frequencies at the lower end of the spectrum. Within the RF spectrum, we need to operate within the limitations set by our regional governing body, ICASA, when using the ISM (license-exempt bands) whether 2.4GHz, 5GHz or even the 17GHz frequency.

2.4GHz Spectrum

The 2.4GHz spectrum is a worldwide, unlicensed band.  Due to its popularity in use of consumer equipment such as Bluetooth, IP Cameras, Microwave ovens and even cordless phones, wireless networks operating in the 2.4GHz spectrum faces significant challenges in densely populated areas.  In areas with less interference, the 2.4GHz is still a viable option due to its propagation properties (ability to travel further and higher penetration power when compared to 5GHz)

The 2.4GHz spectrum offers about 83MHz of spectrum for usage and this allows 3, non-overlapping channels namely 1, 6 and 11, of 20MHz in size.  Overlap in channels is undesirable as it will cause interference and ultimately a decrease in your outdoor wireless performance.

Channel Width, also known as Bandwidth, represents the entire range of frequency being used.  For example, you are using a 20MHz channel with centre frequency 2437.  The entire range of frequency that you are using is from 2427 to 2447.

5GHz Spectrum

Like the 2.4GHz spectrum, the 5GHz spectrum is also an unlicensed band (ISM Band).  This spectrum offers about 300MHz of the usable spectrum which offers about 36 non-overlapping channels of 20MHz in size. With the 5GHz spectrum, you can have larger channel sizes such as 40 and 80MHz – known as channel bonding. The IEEE standard allows channel bonding on the 2.4GHz spectrum as well, however, this is not advisable as you only have 3 non-overlapping channels and will get more interference.

With higher channel sizes, you do however have a limit in terms of distance, so larger channel sizes, limits the distance that your signal can travel.  We will touch base on this in our following blog posts when we discuss OFDM and PSD.

Follow our next blog post where we will discuss decibels in radios and antennas, EIRP, FSPL, Fresnel Zone and ultimately, using this information in a Link Power Budget.