Receiver : acoustic modem

GNU Radio
1

hello ,

  I have implemented receiver for detecting and decoding data frame
based FHSS. At the moment, I am feeding Rx with recorded wav file and it
works fine.
The problem is when i want to do online decoding by replacing wav source
with alsa source, I see nothing happening beyond frame sync.

if anyone has implemented modem based on acoustic , please guide me.

thanks in advance
Ram

2

On 16 July 2010 00:51, Raman O [email protected] wrote:

hello ,

I have implemented receiver for detecting and decoding data frame based FHSS. At the moment, I am feeding Rx with recorded wav file and it works fine.
The problem is when i want to do online decoding by replacing wav source with alsa source, I see nothing happening beyond frame sync.

if anyone has implemented modem based on acoustic , please guide me.

Could it be that your wav file has integer samples with range 0…32768
(or signed)? The samples from the audio input are float between -1.0
and +1.0

Alex

3

Alexandru C. wrote:

On 16 July 2010 00:51, Raman O [email protected] wrote:

hello ,

�� I have implemented receiver for detecting and decoding data frame based FHSS. At the moment, I am feeding Rx with recorded wav file and it works fine.
The problem is when i want to do online decoding by replacing wav source with alsa source, I see nothing happening beyond frame sync.

if anyone has implemented modem based on acoustic , please guide me.

Could it be that your wav file has integer samples with range 0…32768
(or signed)? The samples from the audio input are float between -1.0
and +1.0

Alex

Hi Alex,

Thanks for your response. wav file contains correct values within the
range -1:1.

My question is when i replace wav source block with Alsa source,Receiver
does not function.
I am not sure if it is timing issue because for frame synchronization
i use auto-correlation of two repeated preamble parts. Rx flowgraph
looks like:

   ALSA Source --> TIME SYNC --> DEMODULATION --> DEINTERLEAVER

–>VITERBI DECODE → CRC CHECK

any suggestions please

Thanks
Ram

4

Hello Raman,

Did you resolve your problem?
I’ve a similar problem: I need to implement an acoustic modem and I must
first deal with the problem of synchronization.

Can you help me?

Thanks
Luigi