And let's not forget the third form of 3G,
Time Division-Synchronous Code Division
Multiple Access (TD-SCDMA). This technology, a more spectrum-efficient version
developed by the Chinese, is an official
3GPP/ITU-blessed option. According to
Doug Grant of Analog Devices, the Chinese are moving rapidly ahead with this
unique form of CDMA.
Fully operational systems should be
online by 2008, when China will host the
Summer Olympics. The Chinese most likely
will be the primary user of this unique system, but the volume could be very high.
Only about 25% of the total Chinese market has been tapped for cell phones, with
nearly 400 million current subscribers—the
largest subscriber group in the world.
The Fourth Generation
Some
people call 3G LTE (long-term evolution)
Super 3G, but others call it 4G. As the
carriers and manufacturers invent the
next generation of cell phones, they're
looking at ways to cut basestation costs
by reducing the number of required
basestations, boost reliability and quality
of service (QoS), reduce latency, boost
data speeds beyond even the advanced
3G rates, and increase subscriber capacity per basestation.
3G LTE promises these benefits. It uses
orthogonal frequency-division multiplexing (OFDM) instead of CDMA with multicarrier adaptive modulation options of quadrature phase-shift keying (QPSK), 16QAM,
and 64QAM for the downlink and singlecarrier frequency-division multiple access
(SC-FDMA) for the uplink.
Combined with adaptive bandwidth
capabilities of 1.25, 2.5, 5, 10, 15, and 20
MHz, the maximum data rate goal is 100
Mbits/s downlink and 50 Mbits/s uplink in
mobile environments within a 20-MHz
band. 3G LTE also supports multiple-input
multiple-output (MIMO) antenna techniques with up to four antennas on the
handset and basestation tower. 3G LTE is
still a long way off, but some expect it to
begin showing up by 2012 in some places.
Some sources also say the WiMAX
broadband wireless access technology
could be a huge competitor for 4G. By
using OFDM and SIP (session initiation
protocol) VoIP, WiMAX will be very similar
to 3G LTE. In fact, some say that since
WiMAX is here now, it will become the 4G
system, leaving 3G LTE undeveloped. That remains to be seen, but it's certainly an option to watch. High capital
expenditures will continue to slow 3G rollout and 4G development, leaving the
opportunity for WiMAX to potentially snag
the 4G gold.