Like any healthy, enterprising entity, the wireless broadband industry is comprised of various companies and associations with products to push and agendas to satisfy. The industry’s quest for a single, standardized technology is peppered with individual desires, but the final goal is all the same-to find a technology that is inexpensive and easy to deploy.
A debate is taking place between several factions, each with millions of dollars invested in a certain technology, each with an idea of which technology is best.
First tested and used by the Navy back in the 1950s, Orthogonal Frequency Division Multiplexing is at the center of wireless broadband’s current debate over standards. OFDM is a multichannel modulation technique that divides a digital message stream into parallel streams. Each stream is then carried by a different frequency. It is based on a mathematical concept called fast fourier transform, which allows channels to maintain their orthogonality and/or distance to each other.
Organizations pulling for OFDM include the OFDM Forum and the Broadband Wireless Internet Forum. The OFDM Forum is led by Calgary-based Wi-Lan Inc., which holds patents on a specific type of OFDM called wideband OFDM. Its members include Alcatel, Ericsson Inc., Motorola Inc., Nokia Corp. and Intersil.
The BWIF is led by Cisco Systems Inc., which is pushing for the proliferation of another type of OFDM called vector OFDM. Texas Instruments, Analog Devices, Andrew Corp. and several others count themselves as members.
Hovering somewhere in the middle, completely company agnostic, is the Institute of Electrical and Electronics Engineer’s 802.16.3 subcommittee. It is their job to analyze and consider proposals from all parties involved, and vote to standardize the most effective broadband wireless technologies. The 802.16 committee has the responsibility of creating a standard into three distinct layers: the physical layer, the media access layer and the higher level interface.
In addition to OFDM technologies, the IEEE is considering seriously a single carrier modulation solution. Single-carrier solution quadrature phase shifted key is robust, requires less processing power than most other modems, and is readily available. Quadrature amplitude modulation is slightly less robust than QPSK, but provides about twice the spectral efficiency. Neither are as spectrally efficient as OFDM.
In fact, the biggest drawback of single carrier modulation is its lack of spectral efficiency, which Lee Warren, business development vice president at Wi-Lan and chair of the OFDM Forum, said ” is very much the key driver for carriers going forward.”
According to Paul Struhsaker, founder, chief technology officer and senior vice president of engineering for Raze Technologies, as well as a founding and voting member of the 802.16 standards group, single carrier modulation works best on the uplink, while OFDM is best suited for the downlink connection, or the connection from the base station to the subscriber. This set-up yields the best results, however, it does not help to keep costs low.
“It’s the subscriber costs for the mass deployment of wireless that sets whether or not it’s profitable, and whether or not it will roll out,” Struhsaker said.
This need to keep costs low is key to the proliferation of a technology. Struhsaker said most companies are manufacturing equipment at around $1,000 per subscriber. That number needs to drop considerably, and if a standard is enacted soon, it could draw the industry together and help vendors realize per-subscriber costs of around $300 by 2005.
A “better” OFDM?
The OFDM Forum submitted a PHY layer proposal to the 802.16.3 subcommittee at IEEE’s 802.16 meeting last November, where the subcommittee also received single carrier modulation and hybrid system solutions. Of all the proposals submitted at that time, a few OFDM proposals and one singe carrier solution were accepted. All the CDMA solutions submitted were thrown out.
In general, the OFDM Forum, as well as the Wireless DSL Consortium, an industry group headed by Nortel Networks working with the IEEE, are collaborating well. The BWIF, however, is holding fast to its version of OFDM-VOFDM.
VOFDM’s claim-to-fame is that it utilizes spatial diversity to increase the tolerance of a wireless system to noise, interference and multipath. It can deliver multiple signals on a single antenna and receive the signals on multiple antennas.
The group released in December a white paper titled, “VOFDM Broadband Wireless Transmission and its Advantages Over Single Carrier Modulation.” Authoredby Cisco employees, the BWIF asserts that VOFDM “solves the upstream problem,” (where single carrier modulation is known to work best) because it enables robust burst-mode demodulation, even in delay spread environments.
Although the BWIF admits VOFDM has a couple flaws, including its increased sensitivity to phase noise, it aggressively stands by VOFDM’s reputed superiority over single carrier modulation. Industry experts believe the BWIF’s lack of participation in the 802.16 working group could be holding the standards process back, especially since the standard most likely to be approved will combine technologies.
Wideband OFDM, pioneered by Wi-Lan, enables independent channels to operate within the same band, allowing multipoint networks and point-to-point backbone systems to be overlaid on the same frequency band. Wi-Lan’s I.WiLL product operates in the 2.4 GHz-2.44835 GHz unlicensed frequency band.
Wi-Lan suffered a setback in its quest to make WOFDM a standard when the Federal Communications Commission denied in May the company’s request to use OFDM systems in the unlicensed frequency bands. Wi-Lan said it is continuing to seek FCC approval.
A standard for everyone
The amount of time and money pumped into the development and marketing of wireless broadband technologies warrants each company and its ideas substantial attention, but the time is soon approaching when there will only be one way to build a network.
Voting is taking place now on the standard for local multipoint distribution system technologies, while various proposals are still being considered for frequencies between 2 GHz and 11 GHz. A rough specification is expected by fall, and final approval of a standard for these frequencies is expected in Q1 of next year.
Analysts agree that OFDM’s time is coming, no matter what form it takes, but the industry must work together if it wants to progress, even if that means someone has to concede.
Struhsaker noted that carriers have slowed down their rollouts because a standard is not yet in place.
“I don’t believe any one proprietary technology will win it all. Facets of what we’re doing will fit into the standard. A number of companies are claiming they have the Holy Grail, but in fact, no one has the Holy Grail,” he said.
