Broadband data options for 700 MHz band overflow
Last year, public safety was uncertain about when it would be able to access 700 MHz spectrum, whether wireless broadband fit into its communications plans and how such networks could be funded. Today, public-safety officials are voicing support for proposals that call for public/private partnerships to build broadband wireless networks that first responders can use after broadcasters clear the band in February 2009.
The FCC at the end of 2006 issued a notice of proposed rulemaking to explore the possibility of a nationwide, public-safety-grade broadband network that would use 12 MHz in the band already allocated to public safety. All of the spectrum would be given to a national public-safety broadband licensee, which would lease airwaves to commercial operators to build and operate the network for public-safety use on a fee-for-service basis, and for commercial use when public safety is not fully utilizing the spectrum.
Another plan, submitted to the FCC by guardband managers Access Spectrum and Pegasus Communications, advocates the reallocation of the entire 24 MHz earmarked to public safety to consolidate the narrowband channels and establish 5.5 MHz blocks of contiguous spectrum — adjacent to commercial spectrum — that could be utilized for broadband offerings.
While markedly different in approach, both proposals have the same goal: Give public safety the ability to leverage commercial wireless broadband technologies — along with the economies of scale and swift innovation offered by commercial operators.
“All of the commercial systems coming out in the future will operate in 5 MHz-wide channels,” said Stagg Newman, chief technologist for Access Spectrum. “Now public safety can use modern technology to provide more technology and more bandwidth.”
Indeed, 3G Americas — the North American trade association that advocates the GSM family of standards, which includes wideband-CDMA (W-CDMA) and high-speed downlink packet access (HSDPA) — teamed with Cingular Wireless — now AT&T — on a demonstration aimed at convincing police, firefighters and others to use the GSM family for their technology needs.
Meanwhile, Verizon Wireless, which uses CDMA 1xEV-DO technology, reportedly has floated a solution utilizing its infrastructure that would leverage public safety’s 12 MHz in the 700 MHz band. And California-based IPWireless has extolled the benefits of UMTS TD-CDMA public-safety applications. This technology currently is being deployed in New York City in the 2.5 GHz band.
The cornucopia of proposals can be mind boggling to a public-safety community not used to being courted by commercial players.
“I think what needs to happen is public safety needs to go out and find what will meet our needs by talking to people who are using these services and finding out what applications will work,” said Steve Devine, patrol frequency coordinator with the Missouri State Highway Patrol and chair of the National Association of Regional Planning Committees. “There are some applications that work okay at 300 kilobits per second, and others that don’t. … It’s about getting feedback from the field.”
As it stands today, operators worldwide are migrating their systems to support higher data rates and voice-over-IP (VoIP) services. In the U.S., Cingular Wireless and T-Mobile have committed to HSDPA and are aggressively deploying the technology this year. HSDPA is a tremendous performance upgrade for packet data that delivers peak theoretical rates of 14 Mb/s. Peak rates in initial deployments are well over 1 Mb/s, three times faster than W-CDMA.
Meanwhile, Verizon Wireless and Sprint Nextel are busy upgrading their existing EV-DO networks to a standard called Revision A, which increases both the upstream and downstream capacities of EV-DO, making it a true two-way broadband network capable of supporting real-time multimedia applications such as VoIP.
Of the two, EV-DO is more spectrally efficient because it can operate in a separate 1.25 MHz-wide radio channel and combines three 1.25 MHz carriers to deliver its high-speed data rates. Public safety also finds EV-DO attractive because of its frequency reuse advantages. (The reuse of frequencies enables a mobile system to handle a huge number of calls with a limited number of channels.)
W-CDMA/HSDPA, on the other hand, is expected to enjoy greater economies of scale, given the fact that most of the world’s commercial operators use GSM technology. The big news in 2006 concerned how CDMA networks were losing ground to W-CDMA/HSDPA as a handful of high-profile operators, such as Vivo in Brazil, decided to give up on CDMA in favor of GSM and its broadband migration path. CDMA won’t be going away, but a question mark remains over the technology’s viability beyond 2010.
Beyond 2010 is when CDMA 1xEV-DO’s future becomes cloudy. EV-DO Rev. C will include orthogonal frequency division multiple access (OFDMA) and multiple input/multiple output (MIMO). So will the long-term evolution (LTE) standard, the next phase of the commercial 3G UMTS standard. Consequently, operators — CDMA 1xEV-DO and W-CDMA/HSDPA alike — will have to spend a significant amount of money to deploy OFDMA anyway and could more easily flip from one technology to the other.
That’s why WiMAX could become an attractive option for the 700 MHz band. The standard is considered a 4G technology because it is a mobile OFDMA system. And WiMAX has stirred significant interest for its potential to offer wireless broadband services in fixed, nomadic, portable and mobile operating scenarios. The Yankee Group predicts that between 2007 and 2010, networks will be rolled out worldwide, and devices and service delivery ecosystems will be developed and made more readily available.
However, WiMAX currently is nascent in the marketplace and therefore driven primarily by supply-side forces from silicon manufacturers, equipment vendors and telecom service providers. And WiMAX can’t have a home in the public-safety 700 MHz band unless standards-makers develop a version that operates in the frequency division duplex (FDD) access scheme, Newman said.
Current technology in the 700 MHz band can only support FDD, while WiMAX was developed to support time division duplexing (TDD). FDD and TDD are the two most prevalent duplexing schemes used in fixed broadband wireless networks. TDD is the more efficient scheme, however, because it does not waste bandwidth. Instead. it uses a single frequency to transmit signals in both the downstream and upstream directions. On the other hand, FDD — which historically has been used in voice-only applications — supports two-way radio communication by using two distinct radio channels.
“Public safety only allows FDD,” Newman said. “If you try to do TDD, you have a potential problem. Steps would need to be taken to make sure there are no inter-modulation problems.”
Perhaps the technology dark horse for the 700 MHz band is the aforementioned TD-CDMA technology championed by IPWireless. New York City is deploying the technology using 2.5 GHz spectrum leased from Sprint Nextel and the Roman Catholic Diocese of Brooklyn. Last year, city officials awarded a five-year, $500 million contract to global defense company Northrop Grumman to build the system.
TD-CDMA is a standardized next-generation network technology that originally was anticipated to be rolled out in 2008, essentially to provide overflow capacity when W-CDMA FDD channels reached capacity. But IPWireless accelerated the development and commercialization of the technology, creating a non-line-of-sight, high-capacity system designed as a replacement for DSL systems. The technology also is likely to be an important part of LTE.
The IPWireless solution utilizes TD-CDMA and MIMO to deliver data rates of 8 Mb/s to 10 Mb/s download and 1 Mb/s to 2 Mb/s upload in a typical download-intensive environment.
“Our view is that we picked the best technology for the requirements of the jurisdiction,” said Mark Adams, chief architect for Northrop Grumman. “From a performance perspective, TD-CDMA can hold its own in capacity, latency and average data rates on the street.”
|W-CDMA/HSDPA||Massive economies of scale will come as the world’s GSM operators upgrade to the technology||Not as spectrally efficient as CDMA 1xEV-DO Rev. A|
|CDMA 1xEV-DO Rev. A||Spectrally efficient, good economies of scale||Until it utilizes 5 MHz of spectrum, its data speeds might be limited.|
|WiMAX||A 4G technology coming in 2007||Isn’t designed to work in the FDD access scheme, which is required to operate in the 700 MHz band; still a nascent, commercially unproven technology for mobility|
|TD-CDMA||A commercially proven 4G technology||Lack of economies of scale compared with CDMA-based 3G technologies and little vendor support|