Noise and its effect in Mobile Communication
In any communication system, during the transmission of the signal, or while receiving the signal, some unwanted signal gets introduced into the communication, making it unpleasant for the receiver, questioning the quality of the communication. Such a disturbance is called as Noise.
What is Noise?
In terms of wireless communication, noise refers to any energy interference that affects the quality of a wireless signal. Noise is an unwanted signal which interferes with the original message signal and corrupts the parameters of the message signal. This alteration in the communication process, leads to the message getting altered.
Thus, it is important for wireless network engineers to understand how noise is caused and the ways to mitigate it.
Causes for Noise ?
There are various causes for noise that can interfere with wireless networks. Noise can have natural (e.g. atmospheric interference) or man-made causes (e.g. electrical transformers).
Generally, however, noise can be classified as either external or internal.
External noise is any noise that comes from a source outside of the wireless network. For instance, suppose you are trying to reach someone via radio, but the communication is distorted because another radio in the vicinity is generating noise that interferes with the signal. Other causes of external noise can include severe weather and electrical appliances.
Internal noise, on the other hand, refers to any noise that is generated within the wireless network. This would be akin to you shouting while your friend is trying to talk to you.
Types of Noise
The classification of noise is done depending on the type of the source, the effect it shows or the relation it has with the receiver, etc.
- Thermal noise
- Inter-modulation noise
- Crosstalk noise
- Impulse noise
Let’s look all noise in detail:
- Thermal Noise
- Thermal noise occurs in all transmission media and communication equipment, including passive devices.
- It arises from random electron motion and is characterized by a uniform distribution of energy over the frequency spectrum with a Gaussian distribution of levels.
- Every equipment element and the transmission medium itself contribute thermal noise to a communication system if the temperature of that element or medium is above absolute zero.
- Whenever molecules heat above absolute zero, thermal noise will be present. The more heat generated or applied, the greater the level of thermal noise.
- Inter-Modulation Noise
- Inter-modulation noise is the result of the presence of inter-modulation products.
- If two signals of frequencies F1 and F2 are passed through a nonlinear device or medium, the result will contain IM products that are spurious frequency energy components.
- These components may be inside or outside the frequency band of interest for a particular device.
- IM products result when two (or more) signals beat together or “mix.”
- Crosstalk Noise
- Crosstalk refers to unwanted coupling between signal paths.
- There are essentially three causes of crosstalk:
- Electrical coupling between transmission media, such as between wire pairs on a voice- frequency (VF) cable,
- Poor control of frequency response (i.e., defective filters or poor filter design) and
- Nonlinear performance in analog (FDM) multiplex systems.
- Impulse Noise
- Impulse noise is a discontinuous series of irregular pulses or noise “spikes” of short duration, broad spectral density and of relatively high amplitude.
- In the language of the trade, these spikes are often called “hits.“
- Impulse noise degrades telephony only marginally, if at all. However, it may seriously corrupt error performance of a data circuit.