Technology Innovation for Wireless Broadband Access

Several years ago, Nortel’s Advanced Wireless Technology team focused its sights on achieving a target of ten times the wireless capacity, bandwidth, and performance that was available at the time. The team knew it needed to enable the network to ultimately deliver the 1-Megabit-per-second (Mbit/s) data rates necessary for real-time, truly broadband wireless services.

Today, Nortel has already shown that the ten-fold improvement is achievable and in our labs we are demonstrating the delivery of 37 Mbit/s in a 5-MHz carrier.  

By all counts, our targets and achievements are not over-reaching – the market for significant broadband wireless applications has started.  The biggest market successes to date have been in Korea and Japan, with more than 20 million intense high-speed data users (on next-generation Evolution, Data Optimized, or EV-DO, networks).  Clearly, more and more users are adopting an Internet mindset and a mobile lifestyle.  They are demanding the same capabilities in wireless that they have come to enjoy from their DSL or cable modem service at an affordable price. As a result, broadband wireless networks will first focus on data devices – notebook computers, personal music / video devices, PDA and game devices.

Laying the foundation for the future

Over the last 15 years, wireless has been focused on successfully optimizing time and code division multiplexing.  The introduction of greater EV-DO Rls A and HSUPA are the culmination of these efforts and with their introduction to the marketplace in 2007, users will get a true broadband wireless experience.  However, we are reaching the point of diminishing returns with new time division and code division techniques, to realize the goal of a scalable, high capacity, affordable broadband wireless system, spatial multiplex techniques must be used.

For an analogy, think of the highway you drive. Imagine its lanes increasingly filled by automobiles getting on at every on-ramp; at a certain point in time, there’s gridlock.  Faster, sleeker and lower cost cars will not help. Traffic and innovation potential are lost.   More lanes or more highways are the only solution.

For the past five years, Nortel has pioneered a new air interface technology for high power, macrocellular systems that combines an antenna processing technique called multiple-input multiple-output (MIMO) with a modulation scheme called orthogonal frequency division multiplexing (OFDM).

MIMO works by creating multiple parallel data streams between the multiple transmit and receive antennas. Using the multi-path phenomenon, the separate signal paths from each MIMO antenna can be differentiated. Thinking back to the highway example, MIMO effectively adds several new parallel highways.

OFDM is a modulation technique, which uses many sub-carriers, or tones, to carry a signal and has some key advantages. It is more robust, which means that it provides better performance in cluttered areas with many reflections (multipath). It also allows for simpler receivers. Perhaps most important, OFDM is more amenable to MIMO technologies.

Evolution Options for OFDM / MIMO

The first application of high power, multicellular OFDM-MIMO is in the WiMAX 802.16e standard which will be focused on the broadband wireless needs of new & alternative operators.

OFDM-MIMO is also being incorporated in the the evolution of both CDMA and UMTS networks. The 3GPP2 (Third Generation Partnership Project 2) standards bodies are discussing the incorporation of OFDM-MIMO in the evolution of 1xEV-DO networks.  As well, the 3GPP (Third Generation Partnership Project) is considering the OFDM-MIMO in the Long Term Evolution (LTE) of HSDPA/HSUPA networks – an evolution that Nortel has coined HSOPA. These OFDM – MIMO evolutions are being designed to allow wireless operators to preserve a significant portion their existing networks.

The building of large-scale, high power, multicellular OFDM-MIMO networks is only a couple of years off and it will not be without challenges. For instance, at the cell site, the use of cross-polarized antennas will prevent service providers from having to install additional large antennas which can be an installation and zoning nightmare. Technology that reduces the cabling from the antennas will be needed. Devices will also be impacted, requiring extra built-in antennas and more stringent component tolerances. Fortunately, significant work is being done to address these challenges.

In Summary 

There is considerable evidence that the appetite for wireless broadband is only just beginning and that wireless broadband will become the largest growth area within the wireless industry. The starting point for this growth is increasing consumer reliance on laptop computers. Today, more laptops are sold in the United States than desktop PCs. As this trend continues, so will users’ demand for the same type of broadband service wherever they are – at home, at the office, or on the road.  The growth of MP3 players, PDAs, portable games devices and other handheld devices will only further increase the demand for broadband wireless. All of this growth is, of course, dependent the proper regulatory environment and radio spectrum being available in a technology non-specific manner.

Going back to our earlier analogy, if the wireless industry fast-forwards the acceptance of OFDM-MIMO into the refinement of our highways, we will be able to put the latest, greatest automobiles – applications – on the new multiple parallel highways and allow people to get places faster and more efficiently than ever before. In this way, MIMO and OFDM are key technologies that allow the wireless industry to deliver on the vast potential and promise of broadband wireless.

John Hoadley
Wireless CTO
NORTEL