The BasicsFirst, to be clear on what we are talking about, this is all about getting more spectrum for data

communication solutions. The current Wi-Fi bandwidth is nearly fully utilized and if you look

at a spectrum allocation mask (below) you will be hard pressed to find any “free” bandwidth.

However, there is a great deal of “under-utilized” bandwidth; in fact, in many cases up to 80

percent of the allocated spectrum in not being used.

A valuable chunk of this spectrum is allocated to television broadcasting which is particu-

larly underutilized. When TV stations are allocated, the FCC intentionally spreads them out and

puts blank channels in between stations in any geographic area to prevent adjacent channel

interference between these high-powered broadcast transmitters. These blank channels are

referred to as White Space. In 2002 the FCC initiated a process to assess “…the feasibility of

allowing unlicensed devices to operate in the TV broadcast spectrum at locations and times

when spectrum is not being used…” This, in a nutshell, is the key objective of all cognitive

radio solutions in TVWS. Consequently, the discussion has clearly changed from a debate over

spectrum allocation to one of spectrum utilization.

There is a simple reason that the spectrum debates are focused on the TV broadcast spec-

trum. The relatively long wavelengths of the TV band (in particular from 5 0MHz to 400 MHz)

are able to cover a large area and penetrate buildings, vegetation and terrain with good signal

integrity. These characteristics make this technology ideal for backhaul scenarios where other

Overview

White Space is the common term used

when referring to the reuse of the guard

bands (white space) in the digital TV

spectrum for the purpose of broadband

Wi-Fi® networking. The formal standards

for this are IEEE 802.11af (White-Fi) and

IEEE 802.22 (Wi-Far™). There are sev-

eral very enticing advantages for reus-

ing this bandwidth, not the least of which

is the potential for digital broadband “hot

spots” with a range of several kilometers.

This white paper will highlight the exciting

new potential of this space, yet tempered

with a few technical realities. Key to suc-

cess in this market will be products that

have flexible, programmable and scalable

architectures which provide cost-effective

solutions to match the density, power and

throughput needs of a wide range ap-

plication scenarios. And finally, we will

discuss how new System-on-Chip (SoC)

devices can be used to meet these strin-

gent, and often conflicting, requirements.

White Space – Potentials and Realities

Peter Flynn,Product and program manager,

Multicore processors

Texas Instruments

W H I T E P A P E R

Figure 1: US radio spectrum allocation

Source: http://www.ntia.doc.gov/files/ntia/publications/spectrum_wall_chart_aug2011.pdf

White Space – Potentials and Realities January 2013

2 Texas Instruments

technologies are difficult to justify the cost per user. The VHF/UHF TV spectrum will enable Non-Line-of-Sight

(NLOS) wireless communication that can reach up to 30 km with current technology.

This year we will begin to hear a great deal more about a new wireless Internet access paradigm which will

dramatically extend wireless access to new users and expand the Internet to new applications. This may

be referenced by many names including White-Fi, Super Wi-Fi, Wi-Far, Wireless Regional Area Networks

(WRAN), IEEE 802.11af (still a draft proposal) or IEEE 802.22 (published in 2011), Television Band Devices

(TVBD) or just White Space devices, and a few others. They all fall into a general category called cognitive

radio, which defines a model for using licensed spectrum which is underutilized in a given location.

The objective is two-fold; first to expand that available spectrum for wireless data services to relieve the

overcrowding that is common in the current Wi-Fi networks; and second to expand the area of access to

broadband Internet to more users that have little or no access today.

With the development of cognitive radio TV Band Devices, which can provide a high-capacity backhaul for

Wi-Fi access points across a large geographic area, we are able reach much further beyond the predomi-

nately city-based “hot spot” access points to develop a fully linked pervasive infrastructure which can reach

far out into rural areas. This can be done with cost-effective devices without the need for large cellular tow-

ers, providing “Internet Everywhere” capabilities.

These TVBD “smart” devices will be able to sense spectrum use and negotiate with a global database for

allocation of available spectrum to ensure they do not cause interference with any licensed users in its cur-

rent location.

For example, even in a typical urban area there are significant channels available for cognitive radio use.

Consider the regional map, on the following page, showing nine TV stations, noted by channels with a boxed

“X” next to them. The channels on either side of each station are also “X” out as the protected White Space.

And other devices, such a wireless microphones are often allocated to a few channels. What remains are 18

channels for use by TVBD cognitive radio devices.

Finding creative solutions

Figure 2: Internet Everywhere via TVBD wireless infrastructure

White Space – Potentials and Realities January 2013

3Texas Instruments

Each channel will be able to provide of broadband data access through the TVBD infrastructure. In the

urban city scenario represented above, this would mean the potential for a city-wide wireless network with

significant broadband Internet capacity.

In rural areas, of course, there are far fewer TV stations, which allows for much greater TVWS capacity.

But also there are far fewer people per square kilometer so the challenge is to cover sufficient population

with each base station to warrant the cost of deployment. As noted, a key interest in TVWS is its propaga-

tion characteristics which can travel up to 30 km over various terrains. Consequently, solution providers can

cover nearly 3,000 square kilometers with a single base station and a cost-effective implementation can be

achieved even with population densities below one person per square kilometer.

The Figure 4, on the following page, showing the available TVWS channels in the US, underscores the

availability and the under utilization of this spectrum.

The list of applications for TVWS will expand with Internet applications in general but with the added benefit

that coverage will be pervasive; unlike today where we “hop” from one Wi-Fi hot spot to another and accept

the loss of Internet connectivity in between. This will open up new application scenarios which can benefit

from this universal and license free access to the Internet.

Figure 3: Most urban areas will have many channels available for cognitive radio use

Application scenarios

White Space – Potentials and Realities January 2013

4 Texas Instruments

The most common applications sited are Unified Broadband Communication services which link together

an entire office park, campus facility or public community; dedicated machine-to-machine (M2M) connec-

tions between two remote devices; remote and broad-sensing network for weather, traffic, or environmental

monitoring; wireless smart grid for utility infrastructure monitoring and rapid outage response; and mission

critical communication with fault tolerant networks for public safety.

These scenarios will commonly mean a backhaul to the Internet via a high-capacity cable link at one or

more base stations. Redundant Internet connections as well as cross connections between base stations will

be used to provide overlapping coverage, robust services and higher reliability.

Figure 5: Typical TVWS network topology

 

Available TVWS Channels in the US 

Application Scenarios 

The list of applications for TVWS will expand with internet applications in general but with the added benefit that coverage will be pervasive; unlike today where we ‘hop’ from one WiFi hot spot to another and accept the loss of internet connectivity in between. This will open up new application scenarios which can benefit from this universal and license free access to the internet. 

The most common applications sited are Unified Broadband Communication services which link together an entire office park, campus facility or public community; dedicated machine‐to‐machine (M2M) connections between two remote devices; remote and broad sensing network for weather, traffic, or environmental monitoring; wireless smart grid for utility infrastructure monitoring and rapid outage response; and mission critical communication with fault tolerant networks for public safety. 

These scenarios will commonly mean a backhaul to the Internet via a high capacity cable link at one or more base stations. Redundant Internet connections as well as cross connections between base stations will be used to provide overlapping coverage, robust services and higher reliability. 

 

Figure 4: Available TVWS channels in the US

White Space – Potentials and Realities January 2013

5Texas Instruments

Most urban areas today already have advanced cellular coverage which is designed primarily for voice ser-

vices. Data services have been added but with limited capacity. In fact, over 50 percent of all mobile “smart

phone” data is being off-loaded to the available Wi-Fi “hot spots” simply because the cellular infrastructure

cannot possibly handle the current demand. This is the situation when only 10 percent of the users out there

today are using “smart phones”. With smart phone use expected to increase to 5 fold within the next few

years, it is clear that the current macro cellular model will not be able to keep pace with this demand.

In addition, research has shown that there is a strong correlation between regional economic growth and

high-speed Internet access to global information and markets. Yet, more than 50 percent of the world popula-

tion is without such access due to the prohibitive cost of deployment for population densities below 100

people per square kilometer. This has resulted in a “Global Digital Divide” which has been identified as a key

factor of economic inequality.

Clearly, there is a need for a more cost-effective and scalable model to deliver the required broadband

capacity that will be demanded in the near future. This will require better spectrum utilization as well as more

cost effective and rapid deployment of infrastructure.

A key strategy to reconcile the data deficit is to free up the availability of underutilized licensed spectrum for

unlicensed device use (also referred to as license-exempt). Basically, the concept is that if the licensed use is

not being utilized in a given location then the spectrum should be made available for unlicensed use.

This strategy has several key advantages:

1) There is no loss of value to the licensed user, since the spectrum is not being used.

2) Unlicensed means that there are no licensing costs to pass on to the end user.

3) Cognitive radio means there is no need to involve government bureaucracies to deploy new solutions

and protect the licensed users’ priority use.

4) Much lower-cost solutions become possible, creating viable new applications and markets.

5) Multiple industries can take advantage of this spectrum to build inter-operable infrastructures that are

driven by broad market incentives.

6) Cooperative, standards-based solutions are likely to emerge and quickly expand.

The unlicensed spectrum approach, which was proposed by the FCC and reflected in the IEEE 802.22

standard, is a low-complexity cognitive radio design that will utilize available spectrum without the need for

licensing or complex negotiations between the various spectrum users.

A clear path to success for TVWS and cognitive radio is to build low-cost, yet highly adaptable equipment

which can quickly be reconfigured for applications in different spectrum ranges. Most wireless data commu-

nication equipment today is locked into a specific spectrum, communication protocol and a single application.

The unlicensed spectrum approach

The wireless data deficit

Software-Defined Radios and common

platforms

White Spaces – Potentials and Realities January 2013

These “stove pipe” solutions create roadblocks to standardization and are expensive as well as time

consuming to adapt for new applications.

A new concept is emerging call the Software Defined Radio (SDR), which can operate on many different

platforms and will offer the ability to “redefine” the protocol, spectrum and application with simply a new

software build. Several open source solutions, such as the GNU Radio (www.gnuradio.org), can provide a

rapid ramp-up for new products and significantly reduce the time to market for new applications.

A critical barrier to SDR is that much of the signal processing required in modern radios is very complex

and requires a great deal of processing power to implement in the encoding algorithms in software. Even

more intense is the Fast Fourier Transform (FFT) processing which is often required to efficiently “pack” the

data into the available spectrum. In fact, a single point-to-point connection for a high-data-rate link imple-

menting a full SDR can easily require more processing power than a modern desktop computer can provide.

Fortunately, there are processing platforms specifically designed to solve this problem by implementing

many of the most demanding algorithms in dedicated accelerators or coprocessors; leaving the main proces-

sor for the variability of application code.

TI has developed an entire new family of SoC devices providing highly integrated solutions by combining

high-performance ARM® processors, DSPs and digital radio accelerators and packet accelerators which will

make SDR solutions practical.

For example, the TMS320TCI6614 SoC includes a high-speed ARM Cortex™-A8 processor, four C66x

DSP processors, dual GigE interface and extensive I/O capabilities. In addition, this device includes the fol-

lowing radio accelerators implemented in silicon which completely off-load the SDR for these CPU-intensive

functions.

• Two FFT coprocessors (FFTC),

• Two Viterbi decoder accelerators (VCP),

• Two Turbo decoders accelerators (TCP3d),

• Wideband CDMA Receiver/Transmitter coprocessors (RAC/TAC),

• And up/down link bit-rate coprocessors (BCP).

This highly integrated approach provides the high performance, compact SoC implementation and low-

cost that is required to make SDR a reality. And the comprehensive scope of radio accelerators ensures this

device will be successful in a wide range of wireless applications scenarios.

The combination of SDR and SoC technologies will enable developers and system integrators to quickly

develop low-cost, low-power cognitive radio solutions and enable the rapid development of new applications.

The standards work developed in the IEEE 802.22 Working Group and certified in the White Space Alliance

(WSA) industry group Wi-Far specification intends to break the “glass ceiling” of wireless Internet which has

Industry initiatives for rapid standardization

6 Texas Instruments

restricted its broader distribution. Wi-Far defines an interoperable standard designed to meet the IEEE 802.22

requirements with cost-effective solutions, which defines both a full PHY and MAC layer standard.

With our participation in the WSA industry group and our work with IEEE standards for TVWS, TI is commit-

ted to making “Internet everywhere” a reality in the near future.

•WhiteSpaceAllianceIndustrygroup,www.whitespacealliance.org/

• TexasInstrumentsTMS320TCI6614SoC,www.ti.com/product/tms320tci6614

• IEEE 802.22-2011™ Standard for Cognitive Wireless Regional Area Networks (RAN) for Operation in TV

Bands, (July 2012), available at http://en.wikipedia.org/wiki/IEEE_802.22

• Unlicensed Operation in the TV Broadcast Bands, ET Docket No. 04-186, Third Memorandum Opinion and

Order, 27 FCC Rcd 3692 (2012), available at

http://transition.fcc.gov/Daily_Releases/Daily_Business/2012/db0405/FCC-12-36A1.pdf

• Protocol to Access White Spaces Data Bases, available at http://datatracker.ietf.org/wg/paws/

• Efficiency Gains and Consumer Benefits of Unlicensed Access to the Public Airwaves, Mark Cooper, at 14

(January 2012), available at http://www.markcooperresearch.com/SharedSpectrumAnalysis.pdf

• A Look Ahead to Possible Wi-Fi® Industry Trends in 2011, Andrew vonNagy, (Revolution Wi-Fi, Dec. 21

2010), available at http://revolutionwifi.blogspot.com/2010/12/look-ahead-to-possible-wi-fi-industry.html

• The Economic Significance of License-Exempt Spectrum to the Future of the Internet, Richard Thanki,

(June 2012), available at http://www.cambridgewireless.co.uk/Presentation/CWS-Richard%20Thanki.pdf

• AT&T Wi-Fi Milestones, available at http://www.att.com/Common/about_us/pdf/wi-fi_timeline.pdf

• Report to the President, Realizing the Full Potential of Government-Held Spectrum to Spur Economic

Growth (PCAST, July 2012), (“PCAST Report”), http://www.whitehouse.gov/sites/default/files/microsites/ostp/pcast-nitrd2013.pdf

7Texas Instruments

References

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