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Whitespaces – Spectrum, Database & Ecosystem

Whitespaces are frequencies allocated to a broadcasting service but remain unused. In the United States, it has gained prominence after the Federal Communications Commission (FCC) ruled that unlicensed devices that can guarantee that they will not interfere with assigned broadcasts can use the empty white spaces in the frequency spectrum. The TV broadcast band in the United States has evolved through a number of changes over time, primarily due to the FCC’s desire to make more VHF and UHF bandwidth available for wireless usage for communications. TV White Spaces are unused TV broadcast channels, made more available through the transition from analog to digital TV. The FCC has not dictated specific modulation or protocol requirements for TV Band Devices (TVBDs), allowing TV White Space to employ a wide range of devices and applications on an unlicensed basis, similar to Wi-Fi.

Each TV channel is 6MHz wide

Spectrum Efficiencies & Applications

Increasing spectrum supply is good for all wireless carriers, handset vendors, and providers of wireless apps, wireless backhaul, and towers.  Wireless demand is still likely to outpace supply, creating incentive and pressure on those without deep spectrum holdings.  Emphasis on unlicensed could create opportunities for equipment makers and carriers to build out networks and devices that meet wireless data demands. TV White Spaces are located in the VHF and UHF bands and have several important properties that make them highly desirable for wireless communications:

  • Excellent propagation
  • Ability to penetrate buildings and foliage
  • Non-line of sight connectivity
  • Broadband payload capacity

The application potential for TV White Spaces is essentially limitless, but limited due to past FCC actions to license the broadcast TV spectrum which has resulted in a distribution of white spaces that, to use the common analogy, resembles Swiss cheese. In other words, the white spaces are (1) not contiguous, (2) not distributed uniformly across the country, and (3) not in large blocks like licensed TV channels are. Whitespaces can be used as a complementary technology just as other unlicensed wireless frequencies are used for a wide variety of services and technologies, TV White Spaces can also be applied to an extensive range of applications including:

Rural Area Wireless Internet: The United States is experiencing a fundamental transformation driven by broadband connectivity. However, un-served and underserved areas of the country remain, particularly in rural communities. The current administration has allocated $4.7B to broadband stimulus programs that seek to address this. TV White Space can enable cost-effective and rapidly deployable solutions to bring wireless broadband to these communities.

Video: The broadband capacity and robust signal characteristics of TV White Space spectrum make it ideal for video applications. TV White Space can provide one-way and two-way video communications for security, monitoring, entertainment and other video applications in locations where other frequencies, cable or fiber are not cost-effective.

Home & Enterprise Wireless Networking: TV White Spaces provide significantly better coverage and wall penetration inside buildings and other structures than the 2.4GHz and 5GHz Wi-Fi frequencies currently in use. In addition to wireless computer networking applications, TV White Spaces are being discussed as a solution for whole house media distribution and networking between home entertainment, as well as computer–based media storage and distribution.

Muni Networks: A comprehensive term for giving a city government and citizens the digital tools to measure, monitor and alter the way they use valuable resources and services. The wireless applications extend over most services including healthcare, industry, education, buildings, infrastructure, environment, public safety, retail business, water, electricity (notably, expanding the country’s Smart Grid, which has received $3.4 billion in stimulus funding from the US government, traffic and more. TV White Spaces can be a valuable contributor to the wireless ecosystem supporting these applications.

White space to Mesh Networks: White spaces could even provide the necessary spectrum for a mesh network approach that could be a solution for delivering broadband. The FCC has authorized use of the white spaces with fixed devices but the White Space Coalition believe the lion’s share of the innovations and uses would be generated by devices that are portable and, therefore, wants permission to tap the spectrum for portable uses. It also believes that without the economies of scale created by portable devices, fixed-use devices will be too expensive ever to be widely used.

Whitespaces database, Google & CogNeA

Google came up with a proposal to FCC earlier this year to fund an end-to-end TVWS database funding it for five years which provides a list of channels available for operation at a registered WSD’s (whitespace Device) location. The database, which could have several providers, is needed to ensure devices do not cause interference with nearby signals used for TV broadcasts. In November 2008, the FCC approved the use of devices at powers of up to 100 milliwatts on the white space spectrum or up to 40 milliwatts on spectrum adjacent to operating TV stations.

FCC made clear in its ruling, a working white spaces database must be deployed in order for consumer devices to be available in the market. Before sending or receiving data, devices will be required to access this database to determine available channels in the vicinity. Combined with spectrum sensing technologies, use of a geo-location database will offer complete protection to licensed signals from harmful interference. A conglomeration of companies including Google, Comsearch, Dell, HP, Microsoft, Motorola, and Neustar to launched the White Spaces Database Group last year. The above architecture proposed by Google is a clearinghouse approach that contemplates a clearinghouse which  would serve as a single or aggregated point of entry for protected entity information, and disseminate protected information to multiple TVWS database service providers who would provide the core database functions and device interface (enroll devices, take registration information, and respond to queries).

COGNEA

The Cognitive Networking Alliance (CogNeA), since its formation in late 2006 and subsequent public announcement in December 2008, is helping drive the definition and adoption of an industry-wide standard for low power personal and portable devices to operate over Television White Spaces (TVWS) in the Ultra High Frequency (UHF) TV bands. In March 2009 the alliance members transferred their specification (version 0.8) to Ecma International for further development, which was later published by the standards development organization as Ecma-392.

The Ecma-392 standard serves a broad range of applications, including in-home high-definition multimedia networking and distribution, and internet access for communities. Simply put, the new standard will deliver more robust wireless connectivity, and result in cost effective networking solutions, both indoors and outdoors. Since the standard leverages frequencies allocated for television services in the UHF bands, it inherits superior propagation characteristics of UHF to penetrate walls to deliver improved coverage and extended range.

Spectrum regulators, such as the FCC in the US, require (or regulators in other regions worldwide will require) the protection of incumbent users in order to operate in TVWS. These incumbent protection regulations may vary from one region to another. Ecma-392 takes a toolbox approach and specifies a number of incumbent protection mechanisms including

  • Dynamic Frequency selection (DFS), Transmit Power Control (TPC), and spectrum sensing, that may be adapted based on the regulatory requirements of a particular region.
  • Geo-location/database access is out of the scope of this standard but the standard facilitates the use of information so obtained (e.g. available channel list) by the devices to protect incumbent users.

Frequency Agile RF and Cognitive Radio

Cognitive Radio Networks (CRNs) are a perfect fit to realize the goals of whitespaces. Broadly speaking, CRNs are networks that can sense their operating environment and adapt their implementation to achieve the best performance. “Operating environment” should be interpreted very broadly, and includes the signal propagation environment, node density, traffic load, mobility, and, in the case of DSA networks, available spectrum. While today’s wireless networks (e.g., Wi-Fi) already use very restricted forms of cognitive optimization (e.g., rate adaptation) and spectrum agility (e.g., channel selection), much more aggressive adaptation, such as across wider spectrum bands and more radical runtime protocol optimizations, are needed to dramatically improve spectrum efficiency and wireless network capacity. In the last decade, there has been a significant amount of research in CRNs, looking at adaptation at the physical (modulation and coding), link (adaptive MAC protocols) and network (collaborative network formation, routing) layer.

Much of this research can be leveraged in Whitespace networks.CRNs require a radio device that is very flexible, so it can radically change various protocol functions at runtime. Software-defined radios (SDRs) are an ideal platform for CRNs. Most radios today implement virtually all physical layer processing and some MAC protocol functions in hardware, limiting the degree of runtime adaptability to a small predefined set of changes, e.g., choosing between a handful of transmission rates. SDRs, on the other hand, attempt to do as much processing as possible in the digital domain. However, due to the limitations of analog/digital converters, digital processing capacity and power constraints, a combination of analog and digital processing is still used. An analog circuit (frontend) converts the signal between the radio carrier frequencies and an intermediate frequency. The signal at the intermediate frequency is digitized so all other processing can be done digitally in software, making it easy to change at runtime. Even the analog circuits are designed to be flexible. For example, oscillator frequencies, receiver attenuation, transmit power, filter center frequencies, and receiver gain may all be under the control of SDR software. While cognitive networks do not strictly require SDRs, the flexibility offered by SDRs is very attractive, especially when prototyping and evaluating cognitive networking technology. Some features of cognitive radio networks include:

Sensing the current RF spectrum environment: This includes measuring which frequencies are being used, when they are used, estimating the location of transmitters and receivers, and determining signal modulation. Results from sensing the environment can be used to determine radio settings.

Policy and configuration databases: Policies specifying how the radio can operate and physical limitations of radio operation can be stored in the radio or made available over the network. Policies might specify which frequencies can be used in which locations. Configuration databases would describe the operating characteristics of the physical radio. These databases would normally be used to constrain the operation of the radio to stay within regulatory or physical limits.

Self-configuration: Radios may be assembled from several modules. For example, a radio frequency front-end, a digital signal processor and a control processor. Each module should be self-describing and the radio should automatically configure itself for operation from the available modules. Some might call this “plug-and-play.”

Adaptive algorithms: During radio operation, the cognitive radio is sensing its environment, adhering to policy and configuration constraints, and negotiating with peers to best utilize the radio spectrum and meet user demands.

Distributed collaboration: Cognitive radios will exchange current information on their local environment, user demand, and radio performance between themselves on a regular basis. Radios will use their local information and peer information to determine their operating settings.

Security: Radios will join and leave wireless networks. Radio networks require mechanisms to authenticate, authorize and protect information flows of participants.

CRNs operate in a rich environment. The agility of underlying SDR platforms provides a level of flexibility well beyond conventional radio and networking platforms.

Ecosystem – Trials, Deployments & Players

Microsoft has done some serious trials, and deployed ‘White-Fi’ networks in their campus and shuttle buses, which are used by their employees.

Microsoft Reasearch which is based in Redmond, WA is driving this project since 2008, as they launched the first trial network and call it KNOWS (Networking Over White Spaces). Here is an excerpt from their site – http://research.microsoft.com/en-us/projects/KNOWS/default.aspx

Under the umbrella of the KNOWS project we are revisiting “classical” wireless networking problems and designing new solutions that incorporate and build upon recent advances in software and hardware technologies for networking over the recently opened white spaces spectrum.

We have deployed base stations on two different buildings within the Microsoft campus in Redmond, WA. These base stations operate over the white spaces, and provide coverage to nearly all of campus. We have also deployed a mobile client on a Microsoft shuttle, which bridges packets from white spaces to Wi-Fi within the shuttle, thereby providing Internet connectivity to existing laptops. As part of the deployment, we have also built a research prototype of a white space database, which is hosted at: http://whitespaces.msresearch.us

Deployment History

August 14, 2010. Demonstrated shuttle network and techniques on avoiding MIC interference to FCC Chairman Genachowski and Managing Director Steven VanRoekel.

October 22, 2009. Demonstrated network to a delegation from the Telecom Regulatory Authority of India (TRAI) including Chairperson Dr. J. S. Sarma.

October 16, 2009.  Reached a significant and historic milestone! Successfully deployed WSN between buildings on Microsoft’s Redmond Campus.  To the best of our knowledge this is the first urban WSN. (Click here for deployment pictures)

Technologies tested include:

  • An opportunistic data network in the UHF and VHF bands
  • Channel occupancy database service with real-time Longley-Rice RF propagation modeling over NASA Terrain Data
  • Coexistence with wireless microphones
  • Handling mobile clients
  • Varying channel widths to accommodate varying needs of the application

July 15, 2009  Outdoor tests succeeded. Achieved communications with 1% BER between white spaces devices transmitting at 100 mW and separated by more than 0.5 Km.  Tests proved that enterprise wireless network coverage can be significantly enhanced with a combination of Wi-Fi & White-Fi.

July 6, 2009 Received FCC experimental license to test a deployment of a white space network.

January 15, 2009 Demonstrated a fast channel discovery algorithm (a.k.a SIFT) and an efficient channel assignment algorithm (a.k.a. MCHAM) to achieve high throughput in a WSN

October 23, 2008 The first white space network (WSN) is alive and kicking!  Successfully demonstrated a network of five nodes communicating over the UHF white spaces.

Spectrum Bridge, Inc., together with the Hocking Valley Community Hospital announced recently, the deployment of the first TV White Spaces broadband trial network for healthcare providers in Logan, Ohio. With its excellent propagation and building penetration characteristics, this TV White Spaces solution enables the community and supporting healthcare providers to utilize affordable broadband while providing data transmission for telemedicine applications.

Wilmington, N.C., is also one of a handful of U.S. communities testing the technology, is using white-spaces connections to send live video feeds from traffic and surveillance cameras. Spectrum Bridge, which helped build the Wilmington network, also helped build a test system in rural Claudeville, Va., a community that had only dial-up Internet and costly satellite-based broadband service before.

Conclusion

On Sept. 23, the FCC plans to vote on rules meant to resolve those issues. FCC Chairman Julius Genachowski predicts electronics makers will jump at this “super Wi-Fi” technology, as the agency calls it, and make it just as popular as conventional Wi-Fi.

“We’re hoping history will repeat itself,” Genachowski said. “White spaces are a big deal for consumers and for investment and innovation.” The commission’s plan would make white spaces available for free, without specific permission, just as it already does for Wi-Fi and Bluetooth.

Thus, while there are a series of policy issues affecting the white spaces debate, the threshold question is whether technology will produce devices that can operate in the white spaces without causing interference with TV signals and other signals operating near the spectrum bands.

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