Opportunistic Spectrum Sharing and White Space Access

The Practical Reality

Oliver Holland, Hanna Bogucka, Arturas Medeisis

• Publisher: Wiley
• Year: 2015
• Print ISBN: 9781118893746
• eBook ISBN: 9781119057307
• Edition: 1
• Topic: Technik & Maschinenbau
• Subtopic: Mobile & drahtlose Kommunikation

Details the paradigms of opportunistic spectrum sharing and white space access as effective means to satisfy increasing demand for high-speed wireless communication and for novel wireless communication applications This book addresses opportunistic spectrum sharing and white space access, being particularly mindful of practical considerations and solutions. In Part I, spectrum sharing implementation issues are considered in terms of hardware platforms and software architectures for realization of flexible and spectrally agile transceivers. Part II addresses practical mechanisms supporting spectrum sharing, including spectrum sensing for opportunistic spectrum access, machine learning and decision making capabilities, aggregation of spectrum opportunities, and spectrally-agile radio waveforms. Part III presents the ongoing work on policy and regulation for efficient and reliable spectrum sharing, including major recent steps forward in TV White Space (TVWS) regulation and associated geolocation database approaches, policy management aspects, and novel licensing schemes supporting spectrum sharing. In Part IV, business and economic aspects of spectrum sharing are considered, including spectrum value modeling, discussion of issues around disruptive innovation that are pertinent to opportunistic spectrum sharing and white space access, and business benefits assessment of the novel spectrum sharing regulatory proposal Licensed Shared Access. Part V discusses deployments of opportunistic spectrum sharing and white space access solutions in practice, including work on TVWS system implementations, standardization activities, and development and testing of systems according to the standards.

• Discusses aspects of pioneering standards such as the IEEE 802.22 "Wi-Far" standard, the IEEE 802.11af "White-Fi" standard, the IEEE Dynamic Spectrum Access Networks Standards Committee standards, and the ETSI Reconfiguration Radio Systems standards
• Investigates regulatory and regulatory-linked solutions assisting opportunistic spectrum sharing and white space access, including geo-location database approaches and licensing enhancements
• Covers the pricing and value of spectrum, the economic effects and potentials of such technologies, and provides detailed business assessments of some particularly innovative regulatory proposals

The flexible and efficient use of radio frequencies is necessary to cater for the increasing data traffic demand worldwide. This book addresses this necessity through its extensive coverage of opportunistic spectrum sharing and white space access solutions. Opportunistic Spectrum Sharing and White Space Access: The Practical Reality is a great resource for telecommunication engineers, researchers, and students.

PART I
FLEXIBLE RADIO HARDWARE AND SOFTWARE PLATFORMS SUPPORTING SPECTRUM SHARING

Opportunistic spectrum sharing and white space accessmight lead to scenarios where there is far increased spatial and temporal variation in which systems and radio access technologies are using which frequency bands.Moreover, devices with such spectrum sharing capabilities might be able to achieve significantly elevated spectrum access opportunities, and hence better performance for their end-users, if they were able to access a wider range of bands and in some cases adapt to the requirements that might exist in those bands. This might – in extreme scenarios – lead them to even adapting to the waveform or radio access technology that is necessary in a particular band in order to be able to share and access that band.

Given these observations, it is clear that radio flexibility can greatly assist what is achievable in opportunistic spectrum sharing and white space access scenarios. This part of the book therefore investigates flexible radio platforms.

1
THE UNIVERSAL SOFTWARE RADIO PERIPHERAL (USRP) FAMILY OF LOW-COST SDRs

Matt Ettus and Martin Braun

Ettus Research, USA

1.1 OVERVIEW

1.1.1 Software Defined Radio and Opportunistic Spectrum Access

With the incredible growth of devices that use the RF spectrum, the pressure to fit more users into the finite spectrum has pushed ever more efficient technologies to the fore. This growth is expected to continue at a pace faster than spectral efficiency measures are projected to grow. Despite this growth, there are still underutilized pieces of spectrum, but these pieces are often disjointed and geographically or temporally variable. At the same time, spectrum allocation is a slow and expensive process, so any technology that can lend flexibility to this process is of great value.

One piece of the puzzle may be opportunistic spectrum access (OSA), the subject of this book. A key enabling technology for OSA is software defined radio (SDR). SDR can allow one general-purpose hardware device to be used for many different types of communication systems simply by changing out the software, which implements the specific modulation, coding, and protocols. This is distinguished from previous radio systems where these functions were normally conducted by fixed-function hardware with only minimal reprogrammability. With SDR, a device that implements OSA can survey the spectrum, determine which pieces are free and which are in use, and adapt to the conditions present at that instant. It can communicate with legacy devices and bridge between different systems.

While much of the complexity in a SDR is, of course, in the software, the flexibility it allows for places additional demands on the hardware devices. In particular, the ability to operate in the presence of (and often in between) strong adjacent signals becomes paramount in crowded spectrum. Similarly, a requirement to not interfere with other users of the spectrum means that the transmitter must have exceptionally low emissions in adjacent spectrum, especially if there are incumbent and/or primary users. In order to meet these requirements, a radio must have high linearity, and this is often at odds with the need for low power consumption. The design of systems for use in OSA applications is still an area of open research.

1.1.2 Principles of SDR

While there is large variation in the design and components of SDR-based communication devices, all share certain basic features. The fundamental purpose of an SDR hardware device is to accurately capture and digitize RF signals from an antenna on the receive side and faithfully produce an analog version of the provided samples on the transmit side.

The simplest, most ideal embodiment of this concept is what we refer to here as the direct sampling radio, as shown in Figure 1.1. The basic concept is to have almost no analog components and instead to connect the data converters almost directly to the antenna. In a direct sampling radio, nearly all functions (frequency conversion, filtering, etc.) are performed in the sampled digital domain.

Figure 1.1 Direct sampling architecture.

There have been some examples of successful direct sampling radios, but widespread adoption has not happened yet. This is due to a number of factors that work against this architecture, particularly on the receiver side. Since all channel filtering is performed in the digital domain, the entire spectrum that the radio covers needs to be sampled, not just the desired portion, in order to avoid aliasing. This leads to very high sample rates. The power consumed by analog-to-digital converters (ADCs) tends to be proportional to sample rate, so it is very difficult to make a low power radio with this architecture. At the same time, having a wide open receiver means that any strong signals in the whole band can get into the ADC and cause clipping. The wider the band, the more likely there will be signals that are strong enough to cause these problems, so these types of radio are simply not yet practical for use in crowded spectrum, particularly in mobile devices.

Direct sampling radios (not to be confused with direct conversion) have seen considerable success in specialized areas like radio astronomy and high-frequency (HF, the spectrum between 3 and 30 MHz) radio. Radio astronomy observatories are often built in very remote locations to ensure that there will be very little terrestrially generated interference. That, combined with purpose-built frontend filters and generally noise-like signals, helps to limit the dynamic range of signals at the input to the radio, making direct sampling practical.

A more traditional radio architecture is the superheterodyne. While capable of high performance, these systems are harder to integrate into semiconductors due to the need for high-quality filtering at high frequencies. While there have been some superheterodyne SDR systems, they have largely fallen out of favor except in narrow band applications or in very high quality measurement receivers.

The direct conversion radio architecture has become the most popular for SDR as well as for most modern digital radio systems in general. The essential concept behind these is the concept of quadrature up- and down-conversion. In a receiver, the signals are handled at RF only to amplify and possibly apply a band filter before being converted to quadrature (or complex) baseband signals. The majority of the analog channel filtering and digitization is thus done at baseband where it can be easily integrated into semiconductor processes.

The advantage of direct conversion is in its simplicity, especially when used in a very wideband application. A superheterodyne system with more than an octave of bandwidth often entails multiple stages of frequency conversion and filtering, while a multioctave direct sampling radio would be exposed to large numbers of strong interfering signals, with corresponding dynamic range impact. A direct conversion radio, on the other hand, often only needs simple wide RF filters on the front to cover multiple octaves, with the rest of the radio handling the full range of frequencies.

The direct conversion radio is not without its disadvantages. For one, dual ADCs and digital-to-analog converters (DACs) are needed, as well as dual signal paths for the two components (I and Q) of the baseband. Direct conversion radios also suffer from a number of impairments ...

Table of contents

• COVER
• TITLE PAGE
• TABLE OF CONTENTS
• LIST OF CONTRIBUTORS
• INTRODUCTION
• ACRONYMS
• PART I: FLEXIBLE RADIO HARDWARE AND SOFTWARE PLATFORMS SUPPORTING SPECTRUM SHARING
• PART II: PRACTICAL MECHANISMS SUPPORTING SPECTRUM SHARING
• PART III: REGULATORY SOLUTIONS FOR SPECTRUM SHARING
• PART IV: SPECTRUM SHARING BUSINESS SCENARIOS AND ECONOMIC CONSIDERATIONS
• PART V: SPECTRUM SHARING DEPLOYMENT SCENARIOS IN PRACTICE
• CONCLUSIONS AND FUTURE WORK
• INDEX
• END USER LICENSE AGREEMENT