In the unlicensed wireless environment, interference can be defined as unwanted, competing radio signals in the same frequency band. These interfering signals can disrupt, delay and reduce the reliability and quality of your network traffic and performance. In licensed frequency bands where no outside signals are competing, the issue is self-interference, i.e., your own network’s signals competing with each other. In either case, the results go beyond lower quality transmission; they extend to customer dissatisfaction, loss of competitive advantage and decreased return on investment.
Exclusivity and free use of spectrum
There are two types of frequency bands in which wireless networks operate: the licensed and unlicensed bands. Characteristics of each include:
Licensed frequencies
Licensed frequencies are bands reserved for the exclusive use of a public/private entity. Since the spectrum is clean and clear with no RF emitters (controlled by other entities) operating in the same frequency, wireless system reliability is greatly improved. Interference issues are largely confined to self-interference problems.
Unlicensed frequencies
Frequently described as a “Free Use” environment, unlicensed frequencies provide spectrum that is available to virtually anyone that wants to use it. Signals from different transmitting organizations and entities may compete with one another for space, creating an environment in which interference and ambient noise — as well as self-interference — can be significant impairments to reliable communications. The sheer number of the competing signals in unlicensed spectrum places a premium on ensuring that the equipment you use is of exceptionally high quality and design.
Sources of interference
In general, there are three basic categories of interference:
Self-interference
Emanating from an organization’s own operating environment, self-interference is a factor in both licensed and unlicensed frequencies. In either band, self-interference occurs when distinct signals come from a network under your control, whether from the same tower location or from several miles away. Furthermore, the larger and denser the network grows, the more it will be exposed to self-interference and the reliability and performance issues it may cause.
In most cases, it is best dealt with self-interference the network planning stage. In building or extending a wireless network, proper product design, ad- vanced technology (such as Cambium’s industry leading use of GPS synchronization) and the ability to reuse a frequency band within the spectrum can in most cases combine to reduce self-interference to a point at which it does not have a significant impact on network performance and reliability.
External interference
In unlicensed frequencies, interference is more difficult to manage, since the interference comes from networks and technology not under your control. Because a single access point can support hundreds of subscribers or end users, interference can have a substantial impact.
Other networks aren’t the only culprits; more and more network interference is coming from a wide range of consumer devices — such as surveillance cameras, Wi-Fi hotspots, and microwave ovens — that may operate in or near the same frequency. Furthermore, a network must be designed to not only deal with present interference sources, but must also be pre- pared to deal with potential future sources as the wireless environment evolves and usage of the spectrum expands.
Ambient Noise
Also called the noise floor, ambient noise is simply background noise that is always present in a frequency band. It is caused by the growing numbers of wireless devices — from garage door openers to other wireless networks — operating in the same unlicensed frequency. These all crowd the spectrum and can be a significant factor in degrading signal and bandwidth. Ambient noise levels increase as more devices and networks are deployed in the spectrum.