29 Nov
2010
29 Nov
'10
6:25 p.m.
We have tried a half-duplex BTS with OpenBTS, only transmitting on 3
slots to avoid a duplexer, and it did not work very well. Most
handsets would not camp to it, even when it was the only signal
available. So you need to deal with the frequency duplexing problem
and the antenna switch that you find in a typical MS will not work.
There are also some small-but-important important changes in L1 and
L2 that might not be possible in a highly integrated, optimized product.
On Nov 29, 2010, at 12:29 AM, Hans Witvliet wrote:
On Sun, 2010-11-28 at 23:49 +0100, Sylvain Munaut
wrote:
David A. Burgess
Kestrel Signal Processing, Inc.
Hi,
Indeed, i am still skeptic: seeing is believing.
Got my HF-licence since 1978, so i know that it is very hard to do tx
and rx on nearby frequencies. One needs extreme good (cavity) filters.
Without those, even separate transmitters and receivers will not be
sufficient, as your receiver input stage will be completely saturated.
Eventhough "normal" bts must be capable of handling multiple
handhelds,
while these dongles needs only to communicate with just a single
one, at
extreme low power, there is not enough space inside for decent
filters.
Hans (PE1CXJ)
My first reaction was one of sceptism, but
according to the
people of
huwei it is do-able, no hardware changes needed, just some (major)
software rewrite.
With a single dongle ? Sounds weird.
The "client"/MS side of GSM have no duplexer but a TX/RX switch and a
BTS needs to be able to TX and RX at the same time.
(to be easily detectable by phones. It could 'possibly' work without
it and phone would stay camped onces they are there but it could take
several try for them to 'see' the network).