Ever increasing demand for higher bandwidth wireless services such as mobile video and IPTV is turning the world’s airwaves into a precious, dwindling resource. 

“Like oil reserves, there is only so much radio spectrum to go around and it’s close to saturation with today’s level of broadband wireless applications,” says Bruce Gustafson, director, WiMAX marketing for Nortel.
“In the same way that hybrid cars are designed to get more mileage from less oil, new advanced wireless technologies are pushing past network limitations to squeeze more bandwidth out of existing spectrum,” Gustafson says. “It’s a hot commodity and it’s finite.”
The high market value of the airwaves was underlined recently when the US Federal Communications Commission (FCC) completed a $13,9-billion auction of radio spectrum no longer needed by the federal government.
More than 100 wireless service providers and cable operators bought 1087 licences in the largest offering of spectrum for wireless communications since the FCC began the auctions in 1994. Five years ago, a European auction of spectrum designated for 3G services netted $100-billion.
All spectrum is not created equal and the best spectrum for broadcast and communications is a crowded place. Each band within it is sliced and diced for countless uses ranging from commercial TV and radio programming to allotments for consumer uses such as cordless phones and garage door openers.
The recent US spectrum auctioned was in a narrow 1.710 to 1.755 GHz band, a frequency ideal for higher-bandwidth mobile communications.
“Getting the most out of the sweet spot in spectrum where bandwidth-hungry applications like video and IPTV are transmitted will be critical to a continuous mobile experience unlike anything we’ve ever experienced,” says Gustafson.
“Today’s wireless technologies just won’t get us to the hyper-connectivity of uninterrupted access from any mobile device with unlimited bandwidth at real-time speeds,” he says. “That’s where the combination of OFDM and MIMO technologies will work their magic on maximising spectral efficiencies to deliver quality mobile video and IPTV.”
Together, the transmission strengths of OFDM (orthogonal frequency division multiplexing) and advanced antenna capabilities of MIMO (multiple input, multiple output) allow more users to be packed into available spectrum at speeds more than 10 times faster than current commercially deployed UMTS networks and four to five times faster than HSDPA.
“With today’s technologies, if you are the only person for miles around sitting with your back to the antenna, you will get the great bandwidth and speed needed for quality video because the network only has to focus its resources on you,” Gustafson says.
Spectrum is a shared resource and the uncontrolled overuse of it fits the analogy “tragedy of the commons”, Gustafson adds. “For example, when a village had a shared pasture that everyone used for grazing it was fine until that one extra cow tipped the balance to the pasture being ineffective because it was overgrazed.
“It’s the same with spectrum. As more and more people show up on the network there comes a point where shared bandwidth is overgrazed and quality of communications suffers.
“When individual user demands on the network for bandwidth are multiplied thousands of times across a large area, billions of bits of data are co-ordinated at nanosecond speeds,” he says.
“And, while it’s all speeding across the airwaves, the network has to track the precise location of each device so the right information goes to the right person out of the thousands that are accessing the network at same time.
“Meeting demand for low-bandwidth services like voice and data is simple, but high-bandwidth video requires tremendous power and intelligence from the network – and OFDM-MIMO delivers that in spades.”
To support high-bandwidth content with reliable quality to every user, network transmitting power must be “cranked way up”, Gustafson says, but that can cause competition among users for resources in the band of spectrum.
Dropped calls, busy signals or jerky video viewing result because users are competing against each other for the same bandwidth and consistently, one wins and another loses in the spectrum tug of war.
With OFDM, a single channel within a spectrum band can be divided into multiple, smaller sub-signals that transmit information simultaneously without interference. Because MIMO technology is able to link together many smaller antennas to work as one, it can receive and send these OFDM’s multiple sub-signals in a way that allows the bandwidth to be substantially increased to each user as required.
Nortel has been at the leading edge of OFDM-MIMO development for the past seven years, Gustafson says, accumulating an impressive list of industry firsts in pushing the technologies to faster, more efficient use of spectrum for higher bandwidth applications. It has demonstrated the benefits and commercial feasibility of these technologies to more than 100 customers worldwide.
“OFDM and MIMO are the fundamental building blocks of all future wireless standards, and WiMAX will be the first wide-area implementation to take advantage of these advances,” says Gustafson. “Nortel’s patented OFDM-MIMO implementation has been chosen by industry as the basis for the WiMAX standard and it is at the heart of our program to deliver the world’s most flexible WiMAX solution offering both the lowest cost and the highest aggregate performance available anywhere.”
WiMAX capitalises on the efficiencies of OFDM to deliver high-quality, low-cost broadband services across large geographic areas with less equipment than current wireless networks.
“The wireless broadband revolution has already begun and the insatiable appetite for more speed and more content will continue to drive OFDM and MIMO-based technologies like WiMAX to unprecedented levels of spectral efficiency,” says Gustafson. “OFDM-MIMO will help transform the tremendous potential of unlimited mobility into reality and Nortel will be there, at the forefront of innovation, to ensure each new evolving technology lives up to the promise of a truly wireless world.”