What is CDMA
(Code Division Multiple Access)
CDMA
is a "spread spectrum" technology, which means that it spreads the
information contained in a particular signal of interest over a much greater
bandwidth than the original signal.
When
implemented in a cellular telephone system, CDMA technology offers numerous
benefits to the cellular operators and their subscribers. The following is an
overview of the benefits of CDMA.
|
1. |
Capacity
increases of 8 to 10 times that of an AMPS analog system |
|
2.
|
Improved
call quality, with better and more consistent sound as compared to AMPS
system |
|
3. |
Simplified
system planning through the use of the same frequency in every sector of
every cell |
|
4. |
Enhanced
privacy |
|
5. |
Improved
coverage characteristics, allowing for the possibility of fewer cell sites |
|
6. |
Increased
talk time for portables |
|
7. |
Bandwidth
on demand |
There
are now different variations, but the original CDMA is now known as cdmaOne.
We
now have cdma2000 and its variants like 1X EV, 1XEV-DO, and MC 3X. The refer to
variants of usage of a 1.25Mhz channel. 3X uses a 5 Mhz channel.
Wideband
CDMA that forms the basis of UMTS 3G networks, Developed originally by
Qualcomm, CDMA is characterized by high capacity and small cell radius,
employing spread-spectrum technology and a special coding scheme.
CDMA was adopted by the Telecommunications Industry Association (TIA) in 1993.
May 2001 there were 35 million subscribers on cdmaOne systems
worldwide.
Over
35 countries have either commercial or trial activity ongoing. There are
already 43 Wireless Local Loop (WLL) systems in 22 countries using cdmaOne
technology.
Enhancing today's data capabilities is the 1XRTT CDMA standard - this next
evolutionary step for cdmaOne operators will provide data rates up to
300 kbps, significant capacity increases as well as extended battery life for
handsets.
Worldwide
resources are being devoted to roll out third-generation CDMA technology,
including Multi-Carrier (cdma2000 1xMC and HDR in 1.25 MHz bandwidth), and 3xMC
in 5 MHz bandwidth) and Direct Spread (WCDMA in 5 MHz bandwidth).
This
first phase of cdma2000 - variously called 1XRTT, 3G1X, or just plain 1X - is
designed to double current voice capacity and support always-on data
transmission speeds 10 times faster than typically available today, some 153.6
kbps on both the forward and reverse links.
the
packet data design that is standardized in the network and handsets of the
cdmaOne standards technology facilitates easier and therefore less expensive
packet data implementation than GPRS from a network operator, handset,
application developer and corporation's point of view. All cdmaOne handsets are
packet data capable and work on all implementations of cdmaOne networks. Phones
do however remain a significant barrier to the widespread uptake of higher
speed data services on both GSM and CDMA networks.
Any
network operator who is facing the decision of which network to buy should
consider the upgrade paths of each network. GSM networks were not designed for
packet data-- a GPRS upgrade adds this capability but at a higher cost than
cdmaOne. Also, the GPRS network is not based on standard IP network elements,
which will result in a more complicated integration than the cdmaOne packet
data solution that was designed with standard IP in the handsets and with
standard IP elements in the network. These standard elements will follow the
cost curves of the Internet network elements. Additionally, GPRS and EDGE
dedicate network resources to data taking capacity away from the GSM voice
network which could cause network congestion. CDMA is a voice and data solution
where voice and data share the same resources. 1x also increases data speeds to
144 kbps and doubles the voice capacity of current cdmaOne systems
By
incorporating standard IP protocols and network IP routing, cdmaOne sensibly
maximizes the leverage it gains from the considerable economies of scale
conferred by the Internet. This will allow cdmaOne carriers to offer the
equivalent Internet services as GPRS and EDGE operators with a lower overall
investment in equipment and human resources and without decreasing voice
capacity. Network operators will more readily find the skills to integrate
equipment and develop services because the same IP elements are used on the
landline Internet.
ABOUT
CDMA in China.
By
the end of September, there are 4 million CDMA users in China. And in China,
China mobile manage the GPRS, and China Unicom manage the CDMA. CDMA and GPRS
will be the next emphasis of their competition. CDMA and GPRS both belong the
2.5G. From GSM develop to GPRS is easy, just need small investment to change
some equipment and develop some equipment. But from GPRS develop to 3G, need
big investment to change so different equipments. From GSM develop to CDMA,
need a big investment to change the different equipment, but from CDMA develop
to 3G, just need small investment to develop the equipments and change some.
Just
last week, China Unicom gave a big order to 6 companies especially US companies
to buy the equipment of CDMA 1x. And plan when they finish CDMA 1x, they can
support 30 million CDMA users in China.