Introduction to Spectrum
Spectrum is something everyone needs to know. You basically find spectrum around you and these are waves that allow us to send signals to our various devices such as our cellphones. Actually, you really don’t need to be a scientist to know more about the spectrum. Literally, you can consider it as radio waves with some with lower frequencies and some with higher frequencies.
In today’s world, we use different techniques to send signals through them. Meanwhile, all of these possible frequencies in combination make up the spectrum. It’s fascinating to know that, everything that communicates wirelessly, especially what you have in your home, like your cellphones, television, monitors, and many more, uses a small slice of this spectrum.
You can literally picture these different spectrum slices as a road path with different signals or data moving back and front through it. Meanwhile, each type of signal travels at its own frequency. So, now you have seen that signals from your wireless communication devices move in this spectrum. This could result in some form of signal traffic, just like vehicles moving around different roads but there’s always a point where these roads meet each other. So, how do we cater for this signal traffic?
This is handled by regulatory bodies. They decide which part of the spectrum is used for which type of service. Also, how this spectrum can be used to deliver a better benefit for society. However, the world today has gone far in the advancement of spectrum technology. Like the first SMS, it was sent back then in 1992, and up till now, there are more SMS sent each day and this is actually more than the number of persons we have on the planet. This technology has been made faster and more efficient in applications. Meanwhile, at every second, millions of persons are purchasing a smart device to connect to the internet wirelessly.
The thing is that people want to connect with each other. Considering all kinds of smart devices we have today, in the health segment, Transportation, Education, utilities, and even more. Well, the spectrum, on the other hand, is a limited resource, the reason why mobile operators are investing in this technology. To be able to handle more signal traffic with the same about of spectrum. But because users demand increases each day, then we still need more signal paths. So, let’s get a more in-depth understanding of the spectrum.
Factors that govern Spectrum
Think about the operation of an FM radio tower. Let’s say, you have two radio stations around your town on the same frequency or channel. What will happen is that, you won’t be able to clearly hear any station, because both signals will interfere with each other. Meanwhile, this problem is solved through what we know as isolation. This involves geographic separation or by assigning a different frequency to different transmitters which we will look into later on.
Spectrum: Application on Cellphones
The use of the internet or making phone calls is achieved with the help of electromagnetic waves that these devices emit or receive wirelessly. Whenever you use your cellphone to access the internet or to make phone calls. What actually occurs is that your cellphone is either sending or receiving information through what is known as invisible electromagnetic waves. Meanwhile, these invisible electromagnetic waves are picked up by your cell tower. Then from your cell tower around you, these signal is then transmitted to the destination tower. From the destination tower, the signal is there transmitted to the end-user.
Cellular Communication: Spectrum
In cellular communication, geographical areas are divided into different cells. Although, in cellular communication, part of the difficulty experienced is that. When there are let’s say ten(10) users within that cell area, then ten different frequencies will be used to transmit their individual signals. However, to avoid each of these individual signals from mixing up. Then each of these signals is made unique and this way, your cellphone will only accept the signal which has your frequency assigned to it. While, all other signals that don’t have your assigned cellphone frequency, will be rejected with the help of your cellphone filter circuit. This is the reason why when you try to make a phone call, you don’t end up hearing the call conversation of your neighbor.
However, to be more precise, instead of using the word “unique frequency”, we use the word “frequency range” that’s sound better. Antennas are capable of transmitting signals in a frequency range or band. Moreover, for any signal to transmit, we will require a modulation technique. Although there are different types of modulation if we are using frequency modulation, then we will require two frequencies to transmit signals. That is, the high frequency can be represented by 1. While the low frequency can be represented by 0.
Although, this could result in the question of privacy. What happens when a hacker set his cellphone to our own frequency so that he can receive our information. Despite this though, however, this isn’t simple because the signal sent over each frequency is protected using encryption. This implies that only your device can be able to decrypt it. Again, the entire frequency range of the electromagnetic spectrum is not actually useful for cellular communication for various reasons. Then assigning a specific unique frequency range to each user, becomes is a difficult task.
Reasons why the Frequency band is limited
The Electromagnetic Spectrum ranges from radio waves to gamma rays. Meanwhile, the higher frequency of electromagnetic radiation has the worst penetration capability. For this reason, we don’t use those frequencies for cellular communication. Again, the lower frequency of the electromagnetic spectrum has low energy. Meanwhile, with lower energy, implies that it will require larger antennas for operation. Well, this is practically impossible to design.
In the next segment of the electromagnetic spectrum, coming from radio waves, the propagation is dependent on the property of the ionosphere layer. So, due to all this restriction, only a small segment of the electromagnetic spectrum is left. Moreover, these frequencies slots are also used for several other purposes. This further reduces cellular technology shared among them.
The government earns from the spectrum, by distributing various portions of the spectrum between companies. Meanwhile, in the united state, both the regulatory bodies, the Federal Communications Commission (FCC), and the National Telecommunications and Information Administration(NTIA) govern the radio spectrum. Whereas in Europe, the Centre for Environmental Planning and Technology(CEPT) does the job. While the International Telecommunication Union manages all technical things related to spectrum.
QUADRATURE AMPLITUDE MODULATION(QAM)
The frequency modulation which we earlier explained, is already obsolete. The frequency modulation was adopted in the 1G application and in analog form. Meanwhile, in 4G, the QUADRATURE AMPLITUDE MODULATION(QAM) was used. In this type of modulation, you can send more bits at a time.
In QAM, variations are made on both the amplitude and phase. While the page generates different digital signals. Hence, for cellular communication, there are limited frequency rangers. So, it becomes necessary to effectively make use of these frequencies. Meanwhile, to achieve this effective usage, the cellular system then divides the available ranges into a number of frequency slots. Then, this divided slots is then shared among nearby cell towers.
There’s actually an advantage with this form of distribution. In that, the same frequency slot can be utilized for different cell towers. Although, the same frequency slot can’t be allocated to neighboring cell towers. The reason for this is to avoid your cellphone from receiving signals might for a neighbor cell tower.
FREQUENCY SLOT DISTRIBUTION
However, the process of assigning different frequency slots to different cell areas is known as FREQUENCY SLOT DISTRIBUTION. The process helps a user to obtain a different frequency slot when the user is within any cell area, with experiencing any obstructing in calls.
MULTIPLE ACCESS TECHNIQUE
Again, the way in which the tower’s allocated frequency slot is being shared among different users in that area is something to manage. Meanwhile, this management is done with what is known as MULTIPLE ACCESS TECHNIQUE. Well, this can be best explained and picture in a way, whereby different musicians want to record a song. They can either do it in different rooms at the same time or in the room but at different times. Similarly, in cellular communication, both the cell towers and the users can share information over a different frequency slot or in a different time slot or using different encoding techniques.
In cellular communication, every cellphone device has different multiple access techniques. Example of these techniques is the WCDMA, FDMA, OFDMA, TDMA/CDMA, including others. All these techniques are designed to utilize the available spectrum more efficiently.
That of 4G makes use of OFDMA, which is the ORTHOGONAL FREQUENCY DIVISION MULTIPLE ACCESS TECHNIQUE. Here, the available range is split into a larger number of smaller ranges known as subcarriers. These subcarriers are mathematically orthogonal to each other and each of them is modulated individually.
We have seen that spectrum is limited, but what will happen when 5G is being introduced. Knowing that 5G demands more spectrum for its application, to carry a whole new level of data.
Well, this could be achieved with the technological advancement on frequency hopping, time modulation, and waveform modulation.
Types of Spectra
- Continuous Spectrum
- Emission Line Spectrum
- Dark Line Absorption Spectrum
Well, in physics, there is a principle that actually governs how each of this spectral is produced. One of which states that: when the excited atoms within a hot dense object give off light of all colors and produce a continuous spectrum. Then a complete rainbow of colors without any spectral line.
Continuous Spectrum: This spectrum is actually produced from a hot and dense energy source.
Emission Line Spectrum: This is produced when atoms with a hot or cloud of gas give off only a particular color of light and produce an emission line spectrum. This type of spectrum is actually a series of bright spectral lines against a dark background.
Dark Line Absorption Spectrum: When the light produced from a continuous source, is passed through a lower density and cooler temperature cloud of gas, the light that result fro this is what is known as the Absorption spectrum.
Thanks for coming around, and don’t forget to check out our telecommunication category under academic, to learn more about telecommunication.