Home > Broadband, Whitespaces > Whitespaces for HSPA+/LTE offload

Whitespaces for HSPA+/LTE offload

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.

FCC by establishing unlicensed use of the Whitespaces has taken a major step towards universal broadband access similar to the UNII bands that are used today for Wi-Fi access. Wi-Fi today is being used to offload the macro network for traffic congestion due to smartphones and dongles, whitespaces which has better propagation properties which will allow users to have indoor penetration as well as indoor femtocell deployment. But the way FCC has carved out chunks of spectrum in different markets due to changes to legislation as well as due to incumbent TV channels, whitespaces will require both a database for spectrum availability as well cognitive devices to sense and operate in different channels. Hence, it would make perfect sense to use it as a complementary technology rather than a standalone technology, serving as a mechanism to offload the congested macro networks.

What are Whitespaces?
“Whitespaces” are unused television channels created by the allocation of spectrum in the broadcasters’ digital TV band. These channels are used to protect a broadcast in one channel from interference caused by signals transmitted in an adjacent channel. To solve this problem, the FCC left some channels vacant on either side of a licensed channel, called “adjacent channel” guard bands. To further prevent interference, the FCC did not assign the same channel for use in an adjacent geographic market — these are called “co-channel” guard bands. Here is a detailed study that I had done earlier.


  • 600 MHz band has better propagation than AWS and PCS bands.
  • Frequency reuse possible using multiple TV channels
  • Greater than 10 channels available in most markets, reducing Femto-Femto interference as penetration increases (>5%)
  • Eliminates Macro coverage holes (Donut problem)
  • Co-locating Fixed TVBD at Node B adds sector capacity without requiring additional licensed spectrum
  • Better propagation in WS band and isolation of channels compensates for lower transmit power
  • Offloaded users reduce load on macro, improving user experience for remaining mobiles
  • Existing towers can be leveraged for deployment
  • Fixed TVBD can be added to licensed base station tower at lower cost than acquiring a new tower

Whitespaces & 4G deployments
Whitespaces is a complimentary technology to 4G spectrum because of its similarity in superior propagation characteristics – longer transmission ranges and higher rates of penetration at the same power level as devices currently operating in higher bands (namely 2.4 GHz).

The location of whitespace spectrum is complimentary to 4G launch schedules which include a mix of urban and suburban. Estimates vary, but most of the population (between 73% and 97%) lives in areas with access to 24 MHz or more of whitespace. Rural areas in particular, have a great deal of whitespace as they generally have fewer TV stations.

Whitespace spectrum, on its own, cannot achieve a national footprint because past FCC actions to license the broadcast TV spectrum have resulted in a distribution of whitespaces that, to use the common analogy, resembles Swiss cheese. In other words, the whitespaces are:

  • not contiguous
  • not distributed uniformly across the country
  • not in large blocks like licensed TV channels are

Therefore, a secondary market regime with a whitespace bent might help 4G carriers to fill in small holes of coverage or gain extra capacity on a short term limited geographic basis. Also 4G can used to retrieve the information from the whitespaces databases for what frequencies for offloading.

Whitespaces for Wi-Fi
Using the whitespaces for wireless broadband could effectively serve as a complement and competitor to the 802.11g Wi-Fi standard, meaning in-home/in-office local area networks would become faster and stronger, with fewer or no dead spots within one’s house or office.

Whitespaces for Mesh Networks
Whitespaces 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 Whitespace 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.

The broadcasters view whitespaces as a potential threat, as it could cause interference with their TV signals. There was some suggestion (from prior FCC filings) that the broadcasters want to utilize the white spaces themselves for interactive video applications. They are particularly concerned with portable unlicensed devices. Among other things, they argued that such devices could negatively affect the converter boxes that were distributed when the digital TV transition ends. The commission suggested two-sided auction where broadcasters on a voluntary basis could put spectrum into the auction. Therefore they could keep on transmitting and get some of the proceeds out of the auction.

Whitespace coalition & ecosystem
Improved spectrum sensing, has caused a coalition of leading consumer electronics and technologies companies — including Dell (DELL), Google, Hewlett-Packard (HPQ), Intel, Microsoft (MSFT), Philips Electronics (PHG), and Samsung (“the Coalition”) — to view the end of the DTV transition as an opportunity to use the whitespaces for a variety of unlicensed applications.

Google suggested adding more safeguards for broadcasters and others threatened by white spaces use by requiring new devices to get an “all clear” signal before they start using the whitespaces. Others in the Coalition regard Google’s suggestions as overkill that will add costs without commensurate benefits, but the additional requirements are not seen as a deal killer. Both the Coalition and broadcasters are likely to offer such compromises to move commissioners to their side but a compromise between the sides is unlikely, in our view.

Whitespaces Technical Requirements
UHF Frequency Operation
o 500-700 MHz
Frequency Agile RF
o Re-tune to any channel for operation and sensing
o FDD – provide frequency agile TX/RX isolation
Full 6 MHz Bandwidth to support Sensing
o Even if the operating bandwidth is less than 6 MHz, the system must be able to adjust the bandwidth to the full 6 MHz during sensing
Receive Diversity for Sensing (Desired)
o Though not strictly required spatial diversity is very useful in sensing of narrowband
o signals (wireless mics)
Dynamic Frequency Selection (DFS) Protocol
o Protocol messages to select a new channel and a list of backup channel
Quiet Periods
o Quiet the network every 60 seconds to allow for spectrum sensing
o Typically a sequence of approximately ten 5ms quiet periods
Synchronization of Quiet Periods
o Need to either synchronize quiet periods between nearby cells or to know schedule of
o their quiet period
Spectrum Sensing Techniques
o Each node senses for ATSC, NTSC and wireless microphones using data collected
o during quiet periods
Spectrum Sensing Reporting
o Nodes report sensing results to base station
o Final decisions made at base station
Stringent Spectral Mask
o Improved spectral shaping
o Increased PA back-off or improved PA linearity
o Fixed and Portable Mode II devices must provide geo-location capability
o Accuracy to ±50 meters
Internet/Database Access
o Fixed and Portable Mode II devices must have Internet access
o Must access Incumbent Database daily
Spectrum Sharing Techniques (Desired)
o Methods of selecting optimum frequency using DFS
o Multichannel DFS
o Multi-antenna techniques at Base Station

Whitespaces disadvantages
Unlicensed integration might not be feasible for 4G operators who plan to deploy on top of legacy networks using multi-spectrum bands. These are the absolute limit on how many bits of data you can shovel into a given chunk of radio spectrum, and how many radios and antennas you can shoe-horn into a mobile device. Then there is the battery power required to bring all that kit to life. High-end phones already have 11 or 12 antennas, which is a challenge for space and battery engineers. There is also disharmony about what frequencies to use. “Right now there appear to be 21 different LTE bands around the world, because countries are allocating spectrum from whatever spectrum has not yet been allocated,” but LTE [Long Term Evolution, or 4G mobile) which will require cohesion amongst multiple spectrum bands including unlicensed which will renew the challenge.

While there are a series of policy issues affecting the whitespaces debate, the question is whether technology will produce devices that can operate in the whitespaces without causing interference with TV signals and other signals operating near the spectrum bands. The essential characteristics of the radio frequencies available, database-driven cognitive radio and the protection of incumbent services all align to create, an exciting and productive new application opportunities. The only major concern is the requirement for spectrum sensing, which, adds complexity but no real benefits. That is why whitespaces can only be a complimentary technology to either HSPA+ or LTE devices are capable of doing similar applications like either a video broadcast, broadband or VOIP.

But on a more positive note, the possibility of a database-driven approach to cognitive radio is an  an entirely new – and we, believe, far more valuable and productive – approach to spectrum allocation than has previously existed. The optimizations inherent in this technology effectively address any notions of the scarcity of spectrum that still remain. This model, in fact, could work for essentially all spectrum, enabling dynamic, priority-driven, lease-based access that maximizes spectral efficiency and application availability. In short:  it will be a truly cognitive network that adapts automatically to meet applications requirements – both current and emerging – creating a new, and potentially global, opportunity for economic growth.

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