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Grasping the realities of spectrum

Posted: 25 Oct 2012     Print Version  Bookmark and Share

Keywords:Network testing  engineering test tools  field spectrum analysers  drive test measurement equipment 

Consumer demand for faster-performing advanced services is fuelling a battle not only between the broadcast and broadband industries, but also between commercial providers and government users for space on the airwaves. The roll out of 4G LTE services is adding fuel to the fire, creating a nearly insatiable desire for scarcer spectrum. In response to these challenges, providers are looking for options such as moving to new bands, which is opening up a whole new can of worms.

Spectrum: Limited natural resource
Wireless devices, now ubiquitous in consumer, business, and military applications, all have one thing in common: a need for radio frequency (RF) spectrum. And, while spectrum is a renewable resource, that is no matter how it's used today will still be available tomorrow, it is not unlimited. Only so many transmitted signals can fit within this available spectrum "real estate." As demands for wireless devices and services continue to increase, how more of this real estate be made available to these new systems without causing disruption to existing users and systems is a worldwide problem since the first AM radio station was licensed in 1920.

To solve such problems as real estate limitations, and in an attempt to promote sharing of this limited natural resource, the spectrum has historically been subdivided into "bands," where each band has been assigned to one or more specific uses such as television broadcasting, satellite uplinks and downlinks, air traffic control radar, and maritime communications to name a few. In some nations, these band assignments have been made and updated over several decades. Because of that, some of the older users were some of the first to get spectrum—they were often given large sections of the best spectrum—the ocean-front property of the RF spectrum so to speak.

Once spectrum was assigned, wireless equipment manufacturers invested huge amount of money in building their systems to work in the bands allocated to these specific uses. Simply evicting the squatters to move legacy users who may not really need all the spectrum they have to different parts of the spectrum (known as spectrum relocation) can require a very real, very large financial outlay—it is usually not just a matter of turning a knob to tune to a different frequency.

Challenges to increasing spectrum availability
As an example, in the United States spectrum band allocation has grown in complexity over the years to the point where it has become a patchwork designed to try to keep up with a changing wireless environment. To further complicate cohesiveness, spectrum in the said country is regulated by two separate agencies that often have competing demands: the Federal Communications Commission (FCC), which presides over commercial and private users, and the National Telecommunications and Information Administration (NTIA) for military and civilian government users.

In addition, it is important to note that radio waves do not stop at political borders, so coordination among and between countries must also be considered when national frequency allocations are made. The International Telecommunications Union (ITU), an agency of the United Nations, is responsible for coordinating international use of the radio spectrum. It has its own table of frequency allocations (actually, one for each of three regions) from which individual national tables are to be derived. Every few years, national representatives meet at the World Radio Communication Conference to discuss changes to the ITU allocation tables and to negotiate specific exceptions for their countries.

This is all to say that spectrum relocation can be a very complex activity, fraught with both regulatory, financial and practical implications. This means that just taking spectrum from legacy government users and re-purposing it for new services like LTE can be difficult, expensive, and time-consuming, sometimes taking as many as 10 to 20 years. There is another very important factor. Some governments have realised that the spectrum resources had real monetary value.

When these governments understood that they could generate significant revenue, spectrum auctions were born. Since its beginning in 1994, the U.S. auctions have generated over $60 billion and have become a model for the rest of the world. However, in the said country, the "easy" bands that could be auctioned have now all been completed. This created complications that can create problems, or at least increased expenses, for commercial providers.

Network testing and measurement
As discussed, spectrum is a very valuable resource to acquire. Once you have it, the challenges are in making the best possible use of it to maximise the return on investment. By regulation, the types of modulation that can be used in a given spectrum are often tightly controlled and specified. Within the constraints of their licence, renters of the bandwidth need to be able to monitor their spectrum and identify problems introduced by other emitters that may be present (both intentional and unintentional) as well as make sure their equipment isn't operating outside of the regulated performance thereby impacting other adjacent spectrum owners. Network testing and teasurement is a key component of the practical optimisation of a network's performance.

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