More than mere talk
computeruser.com
Article on 3G.
Excerpt:
The CDMA buzz
Currently, the various flavors of CDMA appear to be the rising stars of the available protocols,
thanks in part to its spread-spectrum quality. One reason is that as a user roams between
cells, signal hand-off is somewhat smoother with CDMA than it was with older technologies,
meaning fewer dropped calls as you travel. Additionally, CDMA exhibits more flexibility when
handling data.
The CDMA2000 push
Although it currently has some speed limitations, CDMA2000 is getting the most attention
within the wireless industry. CDMA2000, which is actually an upgrade of CDMAOne (the
original specification), provides high data transmission speeds, flexibility, and a relatively
low-cost of deployment. At present, the peak speed of CDMA2000 is 144Kbps. A planned
software upgrade will take this peak speed to more than 300Kbps, and that's only the start.
According to Brodsky, Qualcomm has demonstrated what it calls High Data Rate (HDR),
which is planned to be folded into the CDMA2000 specification. Known as CDMA2000-DO
(the DO stands for data only), it will bring the peak speed of CDMA2000 to 2Mbps.
"Because of its flexibility, CDMA2000 systems will reach 25 million subscribers by the end of
2002," Brodsky notes. "We [DataComm] predicted years ago that CDMA would drive TDMA,
which was the industry standard, out of business, and that's exactly what has happened."
WCDMA, which is used mainly in the 2,100MHz band, seems to have it all: high transfer rate
(up to 2Mbps), increased system capacity, and communication quality by statistical
multiplexing. Unfortunately, it also has a couple of big disadvantages: high cost of deployment
and some serious spectrum worries. An April 2001 report from the Federal Communications
Commission, titled "The Potential for Accommodating Third Generation Mobile Systems,"
says that some of the airwaves initially identified as usable for WCDMA are already in use by
the U.S. Defense Department, fixed wireless cable and video services at schools, and health
care centers. According to the report, it could take anywhere between nine and 29 years to
reallocate the airwaves to accommodate the deployment of 3G wireless. An even bigger
concern, notes Brodsky, is bandwidth. "WCDMA was defined to require a minimum channel
of 5MHz, which is almost as wide as that of a TV channel," notes Brodsky. "In most cases,
that means a new frequency spectrum." |
