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Ad hoc networks ascend to the airwaves

Posted: 16 May 2001 ?? ?Print Version ?Bookmark and Share

Keywords:ad hoc networks? bluetooth? ofdm? ieee 802.11b? wireless network?

That wireless networking is on the cusp of becoming a mainstream technology is irrefutable. A quick scan through this section shows that the outstanding technical issues have gone beyond getting the networks up and running into the welcome realm of how quickly, inexpensively and in what combinations they can be gotten to market.

However, while nascent technologies like the ad-hoc wireless phenomenon known as Bluetooth face relatively tractable technical issues, such is not the case for more-mature technologies such as IEEE 802.11b and HomeRF, as well as technologies based on orthogonal frequency-division multiplexing (OFDM). For them, progress will depend on more-abstract and painfully protracted political and legal issues.

The curve of wireless interest over time shows three key turning points. The first was the finalization of the IEEE-802.11b standard for 11Mbps direct-sequence radios. The rate itself was not the key, though. Standardization was. This allowed interoperability among vendors and helped bring the cost down to where it is today, with a bill of materials of less than $40 for the radio.

The second uptick in the curve of wireless interest occurred when marketing managers everywhere got fired up over the potential uses for the rising installed base of broadband connections to the home. This really caught their imagination. Their predictions of voice, audio and video streaming wirelessly throughout the home are already ringing true.

The third uptick came with Bluetooth, a cable-replacement technology that has been hyped and marketed way beyond its capabilities. By all rights, Bluetooth should not even be mentioned in the same breath as 802.11b or HomeRF, except as a complementary technology. Too many issues have yet to be resolved for the basic version at 1Mbps, before any progress can even be considered toward the proposed 10Mbps migration.

This long-anticipated ad-hoc networking technology is only now gearing up for its debut this year, as viable silicon slowly emerges and the new standard, version 1.1, gets set for release this week-provided there are no more delays. Bluetooth's ad-hoc predecessor, irda, is well-entrenched though now facing an uphill battle to maintain viability in a world warmly embracing RF's non-line-of-sight capabilities. Oddly, IrDA was not limited by any technological handicaps. It worked perfectly fine and easily meets the specified data rates of 4Mbps. Its problem was the user interface and lack of user knowledge as to what exactly to do with it.

The marketing machine behind the 2,000 or so companies in the Bluetooth working group will leave no doubt in the user's mind as to how or when to use Bluetooth.

Though emerging this year, Bluetooth faces many challenges. Testing Bluetooth radios in volume production is showing itself to be a major stumbling block. Ericsson recently assigned high-end test-equipment maker Rohde & Schwartz the task of developing a usable test suite for the radio, the most problematic part.

More-mature technologies, such as 802.11b, are facing more-serious obstacles toward advancement. As it stands now, 802.11b can reach 11Mbps. However, companies like Allantro (now part of Texas Instruments) are pushing hard for enhanced data rates at up to 22Mbps within the 2.45GHz band. While Allantro's proposal uses proprietary turbo coding to reach the higher data rates, other proposals resort to OFDM. Under the FCC's definition of spread spectrum the OFDM proposals will not fly, and the FCC has already demonstrated its intention to stand by its definition. It recently shot down an OFDM proposal for 54Mbps data rates in the 2.45GHz band from Wi-LAN Inc., though it met all the technical specifications and limits of the spread-spectrum definition in terms of interference and emissions.

But the buck would not stop there. Chris Henningsen, vice president of marketing for Intersil Corp.'s Prism Wireless LAN Products, said his company, an OFDM proponent, and a number of others, are pushing the FCC to redefine spread-spectrum to allow for OFDM-based higher data rates.

Until then the 802.11b camp is resigned to battling encroaching technologies such as HomeRF, which already is claiming victory on the home front, with 88 percent of all wireless home-networking products purchased through retail outlets in the third quarter of 2000 operating over HomeRF technology.

? Patrick Mannion

EE Times





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