Interference in a crowded RF spectrum: why it occurs, and what to do about it

April 07, 2014 //By Eder Eiras and Mathias Hofer
As the number of wireless services has grown in recent years, so interference, once uncommon, has become a regular headache for wireless and broadcast service providers.

‘Interference’ is in fact a catch-all term for a variety of phenomena that disrupt or even disable transmission and reception of wide-area wireless communications. It’s therefore not in itself a useful term: it does not help network engineers and wireless equipment developers to troubleshoot and repair a specific problem that is compromising a system, or to design equipment that is immune to the effects of this problem.

This article sets out to pick apart the concept of interference as it applies to cellular networks and broadcast television transmissions, and to show how the correct representation and diagnosis of the common causes of interference make it easier to fix.

Self-disturbance in cellular networks

Interference problems in European cellular networks have in part been the unwitting result of government restrictions. Environmental legislation has had the effect of limiting the availability of new base station sites. To increase network capacity, service providers have therefore had to increase the density of antennas on existing cell towers. Of course, this in itself increases the potential for one network to interfere with another.

Often, however, the interference is the result of a cellular network disturbing itself. One example is co-channel interference (CCI), which can occur in GSM and FDD-LTE networks. Normally, network operators allocate different frequency bands (250 kHz for GSM, up to 20 MHz for LTE) to neighbouring cells. The goal of the network planning process is to ensure that signals from two cells using the same frequency band do not share the same air space. In their planning, service providers take account of the geography of the cell location. For instance, transmissions from a base station at the top of a hill can radiate further than those from a base station in a valley.

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