Dear all,
Most BTS code I have, generate only one or two 200 kHz channels, but I need to test a receiver using several (multiplexed) 200 kHz channels, composing approximately 5 MHz of total bandwidth. This should be a "valid" multiplex signal (correct and "decodable" control channel). Can anyone pointout where should I start to put together the software to generate a binary file with such signal? I guess I can inspect the code of a BTS that supports two TRX (two 200 kHz channels) but I would like to double check whether there is a more direct approach.
Thanks beforehand, Marcus Dias UFPA - Lasse - LaPS
Hi Marcus,
On Tue, May 9, 2017 at 9:53 AM, Marcus Dias vmarcusv@gmail.com wrote:
Most BTS code I have, generate only one or two 200 kHz channels, but I need to test a receiver using several (multiplexed) 200 kHz channels, composing approximately 5 MHz of total bandwidth. This should be a "valid" multiplex signal (correct and "decodable" control channel). Can anyone pointout where should I start to put together the software to generate a binary file with such signal? I guess I can inspect the code of a BTS that supports two TRX (two 200 kHz channels) but I would like to double check whether there is a more direct approach.
It sounds like you need a raw IQ sampled binary file at about 5 Msps. Is that correct?
There are a variety of methods to achieve this depending on your requirements. You could generate the multiplexed signal live with up to 3 adjacent ARFCN channels (800 kHz separation) with a B200 and osmo-trx with multi-ARFCN enabled.
But, it sounds like you just need a test file, so you could post-process an existing single ARFCN signal file in Octave or Matlab to carry multiple versions of the same GSM signal. That may or may not be sufficient depending on your needs.
-TT
It sounds like you need a raw IQ sampled binary file at about 5 Msps. Is that correct?
Thanks a lot for your hints!
If my math (sampling theorem) is not wrong, because I need a bandwidth of 5 MHz (assuming only downstream transmission, given I will not use upstream), it would require 5 Msps in case each sample is a complex number or 10 Msps in case the samples are real-valued.
There are a variety of methods to achieve this depending on your requirements. You could generate the multiplexed signal live with up to 3 adjacent ARFCN channels (800 kHz separation) with a B200 and osmo-trx with multi-ARFCN enabled.
That is a good starting point. But I would need to increase the number of 200 kHz to reach a total of 5 MHz.
But, it sounds like you just need a test file, so you could post-process an existing single ARFCN signal file in Octave or Matlab to carry multiple versions of the same GSM signal. That may or may not be sufficient depending on your needs.
Yes, exactly: just a test file. I am still studying the GSM PHY and I suspect if I simply position the ARFCNs in different frequencies I will end up with an invalid GSM signal (that is, it will not be properly decoded by the Keysight VSA equipment that I have to interface to).
Marcus Dias UFPA - Lasse - LaPS
2017-05-09 15:41 GMT-03:00 Tom Tsou tom@tsou.cc:
Hi Marcus,
On Tue, May 9, 2017 at 9:53 AM, Marcus Dias vmarcusv@gmail.com wrote:
Most BTS code I have, generate only one or two 200 kHz channels, but I
need
to test a receiver using several (multiplexed) 200 kHz channels,
composing
approximately 5 MHz of total bandwidth. This should be a "valid"
multiplex
signal (correct and "decodable" control channel). Can anyone pointout
where
should I start to put together the software to generate a binary file
with
such signal? I guess I can inspect the code of a BTS that supports two
TRX
(two 200 kHz channels) but I would like to double check whether there is
a
more direct approach.
It sounds like you need a raw IQ sampled binary file at about 5 Msps. Is that correct?
There are a variety of methods to achieve this depending on your requirements. You could generate the multiplexed signal live with up to 3 adjacent ARFCN channels (800 kHz separation) with a B200 and osmo-trx with multi-ARFCN enabled.
But, it sounds like you just need a test file, so you could post-process an existing single ARFCN signal file in Octave or Matlab to carry multiple versions of the same GSM signal. That may or may not be sufficient depending on your needs.
-TT
Hi,
Yes, exactly: just a test file. I am still studying the GSM PHY and I suspect if I simply position the ARFCNs in different frequencies I will end up with an invalid GSM signal (that is, it will not be properly decoded by the Keysight VSA equipment that I have to interface to).
It should work fine. A GSM broadcast channel doesn't include its own frequency, so you can just take it and position it anywhere (as long as it's on an actual possible frequency).
In gr-osmosdr the siggen application even has a small hardcoded burst sequence that's "good enough" for the E4406 VSA to lock onto.
Cheers,
Sylvain
-
Marcus Dias -
Sylvain Munaut -
Tom Tsou