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Capacity Claims are Hype!
casual_observer_1
Jun 20 1998
4:30PM EDT
nnovick,
I am not pro or anti CDMA. I just wanted to put some perspective on the CAPACITY claims
of CDMA (i.e. 20 to 1 vs. AMPS) - Its just not true for dense metropolitan areas. Its HYPE!
Note that for the IS-95 system, because the bandwidth is so small, many of CDMA's
potential benefits (e.g. flat fading mitigation) aren't fully utilized.
However, as for the other more tangible claims, I believe that CDMA was chosen by Nokia
and Ericy for 3G because it DOES have some other GREAT benefits over TDMA for HIGH
data rate (e.g. WIDEBAND multimedia) systems, which outweighs some of its
disadvantages.
But FORGET the 20 to 1 vs. AMPS claims, its smoke and mirrors!
Here's a simple list of CDMA & TDMA's main advantages and disadvantages.
CDMA Benefits:
1) Multipaths can be resolved and combined at the mobile rx.
2) More resistant to delay spread & Raleigh (flat) fading.
3) The larger the channel bandwidth, the better the potential gains.
4) Robust to other users interference, (but not random noise).
5) Secure.
CDMA Disadvantage:
1)Accurate and very fast power control required to combat fading.
2)Any near-far jamming problem affects all users on the cell.
3)Very accurate synchronization required.
4)Long mobile synchronization time, based on length of PN Code.
TDMA Advantages:
1)Simpler and faster synchronization.
2)Reduced intermoduation products, easier PA design.
3)Jammers only affect limited users, timeslots, frequencies.
TDMA Disadvantages:
1) Cannot resolve multipath or combine intersymbol interference.
2) Peak PA power is higher for mobiles.
3) Narrower signal is more affected by flat fading, short delay spread.
4) Overhead due to guard time and equalizer synch bits required.
The key CDMA technology advantages for 3G are its ability to mitigate fading and
resolve/combine multipath
As for comparing 3G CDMA proposals, the system with the (much!) larger bandwidth will
be able to better resolve/combine the multipath and mitigate the effects of Rayleigh
fading. When the bandwidths are similar there is no practically no difference in
performance.
Note that the error rate requirements for 3G high speed data will be around 10E-7, so all
systems will require heavy coding overhead, reducing system efficiency.
Although 3G systems will support very useful wireless data services, don't be fooled again
by the wild capacity claims of the manufacturers. Let's get rid of the technology hype. Note
to manufacturers - Less BS please, Under Promise and Over Deliver!
QCOM: Quote | Profile | Research
This Is a Reply to: Msg 5613 by nnovick
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