Expanding the potential of wireless broadband services in the US using the 3.65GHz band

For wireless broadband operators, the availability of affordable, clean spectrum in which they can deploy the most advanced technologies is critical to their success.

Monica Paolini
Senza Fili Consulting

Until recently, operators in the US have faced spectrum restrictions that have limited the market growth of wireless broadband services.  License-exempt bands in the 2.4GHz and 5.8GHz frequencies have been successfully used by many operators, but interference has increasingly become an issue, especially for Point to Multipoint (PMP) networks.  In these bands, operators face interference not only from other operators, but also from consumer devices (microwaves, phones, residential Wireless Local Area Network [WLAN] hardware, etc.) that make it difficult to manage interference successfully. 

The other two bands that are available in many markets are 2.5GHz and 3.5GHz.  The 2.5GHz band is available in the US, but it is largely controlled by large operators-mostly by Clearwire, Sprint, and AT&T.  In most countries, wireless broadband operators have access to licensed spectrum in the 3.5-3.7GHz band-along with a large choice of commercial equipment, because this is the licensed band most widely used for fixed broadband services.  In the US, wireless operators were not able to use this band until the end of 2007.

The Federal Communications Commission (FCC) recognized the spectrum limitations that US operators faced, and introduced an innovative licensing scheme in the 3.65GHz band.  It is designed to unlock the market potential for wireless services and widen the availability of broadband to underserved areas in the country.  The newly available spectrum is subject to light licensing: licenses are not exclusive, and they are easy and inexpensive to obtain.  In many ways, the 3.65GHz band promises to combine most of the advantages of unlicensed bands with substantially lower, manageable levels of interference. 
 

While the light-licensing scheme used for the 3.65GHz band is still largely untested because of its recent introduction, the results so far are very encouraging.  Commercial equipment based on Worldwide Interoperability for Microwave Access (WiMAX) with the necessary FCC approval is now available from multiple vendors.  In some cases where vendors have invested in Interoperability Testing (IOT), operators can use interoperable gear from different vendors within the same network.  As of September 2008, 420 operators nationwide have applied for or received a license, and some of them have launched commercial services using WiMAX-based equipment.

Wireless operators have welcomed the availability of the spectrum in the 3.65GHz band because it allows them to better serve their existing and prospective clients, to extend coverage, or to start new deployments in a cost-effective way.  This is possible because, in addition to the low levels of interference, the 3.65GHz band has good propagation characteristics that enable Non-Line-Of-Sight (NLOS) operations.  This results in lower deployment costs and better coverage. 

The additional benefit of the 3.65GHz band is that it brings wireless operators access to WiMAX-based technology, which before now was available only for licensed spectrum.  WiMAX supports improved spectral efficiency, lower per-bit costs, and Quality of Service (QoS) for carrier-grade voice services and enterprise Service Level Agreements (SLAs).  As WiMAX equipment is deployed worldwide, operators can expect to reap the advantages of economies of scale-lower equipment prices and wider choice of vendors and products-even though equipment for the US market has to be slightly modified to meet the domestic regulatory requirements. 

The FCC regulatory framework for the 3.65GHz band

Licensing in the 3.65GHz band and FCC product certification both started in 2007, with the first commercial deployments announced in 2008.
 

The FCC's goal was to create a band with low entry costs and minimal regulatory delays to enable multiple wireless operators to roll out services, while keeping interference at a minimum.  In trying to find a compromise between expensive, difficult-to-obtain licensed spectrum and interference-prone unlicensed spectrum, the FCC decided to adopt a nonexclusive licensing scheme with a contention protocol requirement.

Under the nonexclusive licensing scheme, there is no limit to the number of operators that can obtain a nationwide license.  The implicit expectation is that each operator will focus on selected geographical areas and that this will prevent spectrum overcrowding.  Obtaining a license in the 3.65GHz spectrum is a fast and straightforward process that can be completed at any time with minimal cost (210 USD).

To manage interference, the FCC uses two tools: a requirement that operators "make any effort" necessary to minimize harmful interference, and the adoption of a contention protocol.  All operators with a license are required to register their base station locations with the ULS (Universal Licensing System) prior to deployment, and to appropriately coordinate operations to minimize interference.  Operators that deploy first in a given area do not enjoy any first-to-market advantage over operators coming on later.  They are all required to collaborate to find a solution that enables multiple operators to coexist. 

Furthermore, base station registration allows new entrants in a market to evaluate spectrum availability-as well as market potential-based on the base stations already installed.  This may turn out to be the most effective tool in preventing spectrum (and market) overcrowding.  In most markets, there is effectively room for only one or two operators to roll out services profitably in the band.  In this sense, early operators enjoy a substantial advantage and may effectively stop others from entering the market, unless they are not successful at attracting or retaining customers.
The adoption of a contention protocol to manage interference has attracted a lot of criticism from operators and vendors alike, especially as the FCC initially had not defined what the contention protocol was.  In 2007, the FCC issued a clarification that opened the door to equipment certification, but there is still considerable uncertainty about which contention protocols will be allowed by the FCC.

The FCC has defined two types.  A restricted contention protocol manages interference among devices using the same wireless interface.  WiMAX qualifies as implementing a restricted contention protocol, as multiple subscriber devices can coexist within the same network, and multiple networks can coordinate operations to minimize interference.  All products certified by the FCC to date support restricted contention protocols.

Unrestricted contention protocols work across multiple wireless air interfaces.  The FCC defines such a protocol as one that "can avoid co-frequency interference with devices using all other types of contention-based protocols."

The "listen-before-you-talk" protocol used by Wi-Fi is the most commonly cited example of an unrestricted contention protocol.  While a listen-before-you-talk protocol can limit the impact of interference, it carries significant overhead requirements that can dramatically affect the spectral efficiency of the technology.  For the end user, the difference in performance between interference and network congestion may be difficult to see.  As of September 2008, the FCC had not yet certified any equipment that supports an unrestricted contention protocol, but the IEEE 802.11y Amendment was defined to develop equipment that meets the FCC requirements using Wi-Fi technology.

The FCC has reserved the upper half of the spectrum (3.675-3.700 GHz) for equipment using only unrestricted contention protocols, to encourage their development.  The lower half of the band (3.650-3.675 GHz) is available to equipment that implements both types of contention protocols.

The FCC has also taken into account the fact that the band was already allocated to FSS licensees and to radiolocation services.  As a result, wireless operators are not allowed to operate in areas surrounding grandfathered satellite earth stations and radiolocation stations. 

The market impact

The availability of the 3.65GHz band on a nonexclusive licensed basis greatly expands the market opportunity for wireless broadband services in the US.  It will widen the availability of broadband in digital-divide, underserved areas, and it will provide more choice to broadband subscribers in competitive markets.

It is still unclear whether the contention protocol and frequency coordination mandated by the FCC will be effective in controlling the impact of interference.  The new licensing scheme adopted for the 3.65GHz band may prove effective and usher in further innovation in licensing frameworks in the US and abroad.  If its effectiveness is limited, operators will still benefit from affordable access to the 3.65GHz band and from the ability to finally deploy WiMAX-based solutions in the US, even if they do not have access to the much more expensive and difficult-to-obtain 2.5GHz spectrum.

All types of fixed wireless operators in the US can benefit from the availability of the 3.65GHz spectrum-although, realistically, in each market the number of operators that will be able to successfully operate side by side within the band will be limited.  This may have the positive effect of containing interference within manageable levels. 
Established wireless broadband operators have already started to deploy 3.65GHz equipment to expand their reach to new market segments, to offer new services, or to improve the performance or capacity of their network. 

The availability of WiMAX technology for the 3.65GHz band will give both new and established operators the ability to roll out carrier-grade networks with improved performance, NLOS capabilities, and QoS support, which can support voice and data services on the basis of a compelling business case.

Monica Paolini is the founder and president of Senza Fili Consulting and can be contacted at monica.paolini@senzafiliconsulting.com.   Senza Fili Consulting provides expert advisory services on wireless data technologies and services.
 

Wednesday, November 12, 2008 in Applications  | Permalink |  Comments (0)