why is GPS required in CDMA but not in WCDMA ?

[coursekec]

In ZTE based systems, GPS is mandatory for CDMA but isn't required for WCDMA based UMtS networks ...Can anyone explain in detail regarding this ?

thanks in advance..

[s52d]

In ZTE based systems, GPS is mandatory for CDMA but isn't required for WCDMA based UMtS networks ...Can anyone explain in detail regarding this ?

thanks in advance..

Hi!
It is all about timing. In CDMA (IS-95) all cells have to know exact time,
so bit 0 TS 0 frame 0 is transmitted at the same moment from every site.
As a side effect, accurate TX frequency is obtained (Remeber, T1 can not be used).

W-CDMA is designed differently, so there is no need for coordination between cells.
Thus, bit 0, TS 0, frame 0, multiframe 0 depends on last Node-B restart.
For frequency, E1 is used (or IP based methods).

GPS might be nigtmare for some indoor installation: even on macro sites, sometimes
it is not as easy as IS-95 designers felt 15 years ago.
Thus, W-CDMA managed to avoid it.

BR
s52d

[coursekec]

thanks for the reply...

But i have one query still ...
why in CDMA (IS-95) all cells have to know exact time ? Is it because of decoding or other reasons ?

[s52d]

thanks for the reply...

But i have one query still ...
why in CDMA (IS-95) all cells have to know exact time ? Is it because of decoding or other reasons ?

Quick guess (Never really looked into IS-95 details):
- ortogonality of codes.
- easy sync, remember this is 15 years old system (eh, W-CDMA is over 10...)
Maybe some IS-95 expert here could enlight us?

BR
s52d

[wolverine]

See here for a good discussion on the topic..

http://kambing.ui.ac.id/onnopurbo/library/library-ref-eng/ref-eng-2/physical/wireless/cellullar/gsm-vs-cdma/wcdma_asynch_wp_9-01.pdf