Spectrum Efficiency Metrics

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Executive Summary

The FCC established a non-partisan Technological Advisory Council (TAC) of private sector, public sector, and academic specialists to help address some of the most strategic policy and technical issues that the Commission faces.

The TAC is comprised of a number of work groups, including one designated as the Sharing Work Group. This TAC has the responsibility to formulate recommendations to promote near term private investment and job creation. To accomplish this objective, the Sharing Work Group has focused on techniques such as spectrum sharing, facilities sharing, acceleration of small cell technology to improve localized coverage for cell phones using smaller, lower power transmission technology, and elimination of current friction points in the application of improved communication technology.
All communication systems that send or receive signals wirelessly, including telephone, television, radio, satellite, radio telescopes, and consumer electronics, consume a scarce resource known as radio spectrum. This spectrum comprises a range of radio frequencies that are allocated for licensed or unlicensed use to operators and/or users of each wireless communication system. Spectrum must be allocated and managed to prevent intentional or unintentional interference between wireless communication systems and devices as well as to guarantee acceptable levels of service for the users of all wireless communication systems.
This white paper is the result of extensive work by the Sharing Work Group to help improve the methods by which this scarce radio spectrum is evaluated, allocated, and utilized. Even though this is a highly technical subject, the Sharing Work Group believes that any interested reader should be able to understand and respond to the critical issues that are described.
The radio spectrum is a finite resource on which demands for access continue to grow. The ability to better share the radio spectrum is an important enabler of increasing access to it by the ever growing universe of radio-based services. The current cell phone systems provide an excellent example of how the widespread sharing of spectrum among cell phone uses provides this continually expanding availability and breadth of application services. In the future, the further expansion of these kinds of services to ever wider portions of the spectrum and both heterogeneous and homogeneous application classes is highly desirable.
To accomplish this goal, it is important to develop a uniform set of metrics that can be used to measure and describe the efficiency of how various segments of the radio spectrum are being utilized. Without a coherent and unbiased measurement system, there is no way to judge whether particular frequencies in the spectrum can be further optimized, better shared, or in some cases allocated for a different use to broaden their value to a wider range, or in some cases more valuable range (e.g. public safety), of users.
Just as counting the number of cars on a highway is not the only measure of a road’s value, efficiency is not the only consideration when it comes to re-evaluating the use of spectrum. Overall cost, quality of service, reliability, security and operational considerations are issues that must also be carefully weighed. The primary objective of this paper is to characterize spectrum efficiency metrics that can establish a foundation for creating jobs to “design, manufacture, deploy and maintain more spectrally efficient technologies”.
A key report, published in October of 2008 by the National Telecommunications and Information Administration’s Commerce Spectrum Management Advisory Committee (CSMAC) highlights how difficult it is to establish a uniform metric for spectrum efficiency. No single set of metrics captures the full range of issues because the underlying technologies are so varied and the services provided are so broad. Consequently, a taxonomy was developed of different classes of systems (e.g. broadcast, personal communications, radar, satellite, passive listeners such as radio telescopes, short-range systems, etc.) that share enough common characteristics that individual efficiency metrics are useful.
The Sharing Work Group has expanded on the original taxonomy, creating a refined taxonomy that is described in detail in this paper. The updated taxonomy is split into six classes. There are two classes of satellite systems (broadcast and point-to-point) and four classes of terrestrial systems (broadcast, personal communications, point-to-point, and hybrid). Potential measures of efficiency are described in detail for each class. Radar is also considered as a separate class since it occupies “a significant portion of the most desirable regions of the radio spectrum resource.”
One of the revolutions in wireless technology has been the development of devices and systems using technologies like Bluetooth and Wi-Fi that communicate over a short range using frequencies that are currently part of radio spectrum that is not licensed by the FCC. The Sharing Work Group is continuing to assess potential efficiency metrics for these unlicensed technologies but has not included any conclusions on this topic in the paper.
To better characterize metrics for satellite systems, the paper distinguishes between communication services and non-communication services. For each of these, the report explains in detail how efficiency can be measured. For satellites, factors such as antenna size, field of view, orbital arc, and responsiveness are also described as part of the overall evaluation of relevant metrics.
There is also complexity in assessing the different efficiency characteristics of the four classes of terrestrial systems. In addition to engineering factors, there are a number of critical policy and public-good related considerations that must be considered. These include unfettered and appropriately prioritized access for public safety and provision for service to rural areas, even though investment return for service providers is often lower in these less densely populated communities.
The Sharing Work Group took an integrated systems approach to this entire evaluation because every component of a radio based communication system involved with either the transmission and/or reception of a signal has to be considered as part of efficiency. The good news is that there is already precedent for sharing these systems to increase efficiency. For instance, sharing can be enhanced by mitigating interference through the introduction of filters and separating users by different technical characteristics (e.g. transmission techniques).
The efficiency metrics described in this paper can form the basis for an even more robust use of existing technologies which can drive capital investment, job creation, and a wealth of advanced services to support the needs and desires of the people of this great country.
Establishing metrics for measuring the efficiency of spectrum utilization provides a foundation for optimizing the use of this finite resource through cooperative actions between the FCC and all other stakeholders. Once spectrum efficiency metrics have been established to provide a technical basis for evaluation and comparison, in the opinion of the Sharing Work Group, a combination of market-based incentives and appropriate regulatory mechanisms is required to stimulate progress towards increasing spectrum utilization efficiency, allocation efficiency, and sharing based on the spectrum efficiency metrics and other relevant criteria. Fortunately, there are established precedents for work between government and the private sector to improve the allocation and utilization of other scarce resources. Markets for tradable wetland credits, pollution credits, and CAFE standards for improving automotive fuel consumption are some examples that the Sharing Work Group recommends as models for the FCC to consider as it continues to make progress towards more efficient use of this vital national resource. Additional work is required on the metrics proposed in this document before they can be used to support market incentives or regulatory mechanisms. In the coming year, the Sharing Work Group intends to further develop the metrics and prepare case studies of how they are to be applied.

  1. Introduction

The radio spectrum is a national and international resource of increasing economic and social value. It is critical to the safety of life and property and to national defense and homeland security. Wireless systems of all types depend on this congested resource. The efficiency of spectrum usage must improve at an accelerating rate if the Nation is to accommodate rapidly increasing demand for wireless systems and applications and to stimulate related job growth. Metrics are necessary to support the national effort to improve spectrum efficiency. Unfortunately, as discussed herein, the various services that rely on spectrum differ so fundamentally that there is no single universal measure of spectrum efficiency.

While it does not appear possible to develop a single measure of spectrum efficiency, metrics have been developed that allow efficiency comparisons to be made among similar spectrum uses. Such metrics can be a useful tool. For example, they can help assess historical gains in efficiency, evaluate the gains that might be achieved with new or improved technologies, and identify opportunities for evolving to more efficient systems or for implementing replacement technologies.
It is important to distinguish the efficiency of spectrum allocations from the efficiency of wireless systems. Although the two concepts are closely related, they differ because spectrum allocations are increasingly shared by multiple systems. Spectrum managers are primarily concerned with the efficiency of spectrum allocations. Spectrum allocation efficiency can be improved through increased efficiency of the systems using that allocation, increased sharing with other systems, or some combination of those approaches.
It should be emphasized at the outset that spectrum efficiency is not the only factor to be considered in spectrum management decisions. Other factors including the overall cost, the quality of service (QoS), the availability of equipment, compatibility with existing equipment and techniques, the reliability of the system, the security afforded by the system, and operational factors all affect the choice of the best system in a given circumstance.
With that caveat, the purpose of the Working Group’s effort and of this White Paper is to identify, analyze, and describe spectrum efficiency metrics for a taxonomy of different services with the hope that jobs will be created immediately to design, manufacture, deploy, and maintain more spectrally efficient technologies that are “fit for purpose” and, over the longer term, to create expanded opportunities for the growth of the wireless industry and, hence, for the Nation’s economy more generally.
The balance of this report is divided into six sections. Section II summarizes prior work in the area of spectrum efficiency metrics while Section III identifies and describes the six classes of systems upon which the Working Group concentrated its initial effort and also identifies additional classes that may be analyzed in its future efforts. Section IV then addresses spectrum efficiency metrics for satellite systems while Section V addresses terrestrial systems. Section VI offers further thoughts on spectrum efficiency metrics and in particular the importance of viewing these metrics from a systems perspective, while Section VII offers the summary and conclusions associated with the Working Group’s efforts on spectrum efficiency metrics to date. Appendix A provides a table (still largely unpopulated at this point) illustrating the use of spectrum efficiency metrics. Appendix B provides a table illustrating representative examples of spectrum sharing experience in US FCC history. Appendix C provides an initial set of case studies of instances where receiver performance played a significant role in spectrum allocation decisions and often the related inefficiencies in the current use of the spectrum.

  1. Summary of Prior Work

The Working Group began its work on Spectrum Efficiency Metrics by identifying and reviewing prior work in the area. An important item in that regard was a report entitled “Definitions of Efficiency in Spectrum Use” which was prepared by Working Group 1 of the Commerce Spectrum Management Advisory Committee (CSMAC) and dated October 1, 2008.A As touched upon above, the CSMAC report recognized that it was impossible “to establish a uniform metric for spectrum use efficiency that encompasses the wide range of services and uses for which spectrum is needed.”1 Therefore it first developed a taxonomy of spectrum use (i.e., classes of systems that had enough characteristics in common to indeed be comparable) and, second, identified and discussed possible spectrum efficiency measures for each such class. The classes addressed in the CSMAC report included the following:

Broadcast Systems

Personal Communications Systems

Point-to-Point Systems

Radar Systems

Satellite Systems

Passive Listeners (e.g., radio astronomy)

Short Range Systems2
The CSMAC report on definitions of spectrum efficiency drew upon an earlier report/recommendation by the International Telecommunications Union entitled “Recommendation ITU-R SM.1046-2, Definition of Spectrum Use and Efficiency of a Radio System.”B,3 In developing this report, the Working Group also took note of a presentation entitled “Frequency Use Status Investigation and Spectrum Utilization Metric” by Sang Yun Lee at the International Symposium on Advanced Radio Technology (ISART) in 2008C, NTIA Report 94-311 by R.J. Matheson entitled “A Survey of Relative Spectrum Efficiency of Mobile Voice Communication Systems” and dated July 1994D, and a presentation entitled “What is Spectral Efficiency” by Dag Åkerberg of the DECT Forum in 2005E.
Importantly for the study conducted by the Working Group, ITU-R SM.1046-2 “Definition of Spectrum Use and Efficiency of a Radio System”B provides a definition of Spectrum Efficiency. ITU-R SM.1046-2 defines the Spectrum Utilization Efficiency, SUE, (or Spectrum Efficiency as a shortened term) of a radiocommunication system by the complex parameter:
SUE={M,U}4 (1)


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