Thursday, August 03, 2006

Wireless Enterprise--Part II

Blog #5 by Martin Cooper, Executive Chairman
and Co-Founder of ArrayComm LLC

Wireless Enterprise
Part II

Revolutionary Technology
The wireless broadband technology revolution is well underway. Multi Antenna Signal-processing (MAS), the modern version of what was once called “smart antennas,” will pervade every existing and future wireless system. MAS systems already in operation today have dramatically changed the economics of wireless communications. OFDM (Orthogonal Frequency Division Multiplex) will reduce multi-path interference and increase speed. Software defined radios will bring down the compatibility barriers, and cognitive radio using all of the previous technologies will, ultimately, eradicate the myth of spectrum scarcity.

All of this will take time. There are precursor wireless systems in operation now, like iBurst and Ripwave, that use MAS as do many WiFI access points. The WiMAX standard is now real and mobile; WiMAX will be in the market by next year. Led by industry giants like Intel, Samsung, Motorola, Alcatel, and others, WiMAX has the potential to be the next generation of broadband wireless connectivity. Inherent in WiMAX is the use of MAS and OFDM. MAS has already provided orders of magnitude improvement in spectral efficiency in iBurst systems that are deployed in more than a half dozen countries. This high spectral efficiency allows many more people to be served in a given amount of radio spectrum with many fewer base stations. The result – far lower costs to serve each user! Furthermore, because MAS is still in its infancy and because the power of MAS is achieved by upgradeable software, there is the potential to continue improving the economics and the spectral efficiency indefinitely.

And WiMAX will not be the only new wireless system. Qualcomm and Kyocera are standardizing their versions of broadband wireless in a separate process from WiMAX and their systems will offer unique advantages in addition to incorporating MAS and other modern technologies.

The vision is clear. There is no reason why broadband wireless cannot be totally ubiquitous, as speedy as an RJ45 connection, and lower in cost than wired broadband. It will take some time for this to happen, but our natural mobility, and the competitive marketplace, will make it happen.

The need for, and availability of, low-cost untethered communications will force spectrum regulators to recognize the evolution of technology. Among their challenges:

Most two-way radio systems today, including cellular radio communications, use frequency division duplex (FDD). A separate radio channel is used to communicate in each direction, i.e., from the mobile user to a base station and from the base station to the mobile user. This allows both people in a conversation to talk and listen at the same time, to “duplex.” At the time these radio systems were conceived, FDD was the only way to provide duplex communications. It is now possible to achieve the same duplex communications on a single radio channel; this is called TDD or time division duplex.

There is no inherent difference in the spectral efficiency and economics of FDD and TDD; they each require guard-bands and the same laws of physics apply, except for one very important distinction. When MAS, smart antennas, are deployed, they are far more effective in a TDD system than in FDD. The reason is pretty simple. In an MAS system the user initiates a call and a base station receives the user’s signal. Through the use of arrays of antennas and complex signal-processing, the base station computes an electronic image of the user’s position. The base station now transmits the return signal to that same location. The assumption is that the return path is exactly the same as the path from the user to the base station. In FDD systems, this is much less true than with TDD. Because the two transmissions are on different paths, the multi-path is very different and the MAS technology is less effective. Even TDD is not perfect since the return transmission occurs milliseconds or microseconds later than the forward transmission, but it is still far better than the FDD case. Regulators will first have to recognize this great potential improvement introduced by FDD systems and they will have to manage the difficult problem of intermixing FDD and TDD systems.

Ultimately, the regulators are going to get out of the business of spectrum allocation. That’s the promise of cognitive radio.

Cognitive Radio
As a young engineer fighting the spectral efficiency battle, I envisioned a wireless world populated with intelligent radios. How wonderful would it be if a person requiring spectrum for a particular purpose would reach out and use only the amount of spectrum that person needs for only the time that need is required and only over the geography required to reach all of the people involved in this communication. Cognitive radio technology promises to do that. Unfortunately, cognitive radio is still very much in the laboratory. Some of the tools that will be an essential part of cognitive radio, like software-defined radios, are achieving practicality today but it will be a long time before cognitive radio technology is commercially practical.

Implementation of cognitive radio faces an even more difficult problem. Regulators have conditioned spectrum licensees to exclusively own their spectrum. Existing owners will not take the intrusion of others onto their God-given (or at least FCC-given) spectrum.

Software-defined radios, on the other hand, are here today. Because a software-defined radio can be programmed to recognize multiple air-interfaces, the technical barriers to standards compatibility are destined to fall – but the carriers will make the decisions that will deliver that wonderful world of universal access.


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