Re: [Discuss-gnuradio] Very low packet loss rate for the discontinuous BPSK communications- the analysis and looking for solution

[Alex Zhang]

Hi Sreeraj and Tom,

For the discontinuous mode, by cutting the freq_bw to below half of the default value, I found that for differential_bpsk, the packet loss rate can be improved(from 30% to 70%), but for non-differential bpsk, the improvement is hard to see. Especially, for non-differential bpsk, I found that often the whole burst (5 packets) could lost. Maybe, it is due to the Phase rotation. I am still trying to investigate.

On Thu, Mar 7, 2013 at 11:08 AM, Sreeraj Rajendran <address@hidden> wrote:

Alex,

That one is non data aided(no preamble) frequency syncronization. As Tom mentioned FLL must be the slowest one in the three.

Did you try adjusting loop bandwidth?. There is an example_fll example in gr-digial. Just try that one and check how many symbols/samples it takes to settle.

Just go through the papers I mentioned and that idea is easy to implement to do coarse synchronization during fast burst transmissions.

 

---
Regards
Sreeraj Rajendran
http://home.iitb.ac.in/~rsreeraj

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From: Alex Zhang <address@hidden>
To: Sreeraj Rajendran <address@hidden>
Sent: Thursday, 7 March 2013 10:24 PM

Subject: Re: [Discuss-gnuradio] Very low packet loss rate for the discontinuous BPSK communications- the analysis and looking for solution

Dear Sreeraj,

You mentioned the openloop synch algorithms. Are they refered to the preamble based carrier recovery? 

Thanks

On Mon, Mar 4, 2013 at 8:03 AM, Sreeraj Rajendran <address@hidden> wrote:

Alex,

If Adeel's solution is not meeting your burst transmission specs, you can try implementing some fast openloop synchro algorithms given in [1],[2]. You could look into some data aided schemes too, though I haven't tried those yet.

[1] Digital Communication Receivers, Heinrich Meyr, Section 8.2.2 

[2] Two Frequency Estimation Schemes Operating Independently of Timing Information, Ferdinand Classen and Heinrich Meyr

 

---
Regards
Sreeraj Rajendran
http://home.iitb.ac.in/~rsreeraj

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From: Adeel Anwar <address@hidden>
To: Alex Zhang <address@hidden>
Cc: address@hidden
Sent: Monday, 4 March 2013 5:51 PM
Subject: Re: [Discuss-gnuradio] Very low packet loss rate for the discontinuous BPSK communications- the analysis and looking for solution

Alex,

1: U can try adjusting the synchronization loops bandwidth (Phase/Timing etc) see PFB_Timing documentation

2: Try reducing the receiver gain (for a constant tx-amplitude/gain) or reduce transmission amplitude/gain (for constant rx gain) 

-Adeel

On Sat, Mar 2, 2013 at 10:21 AM, Alex Zhang <address@hidden> wrote:

I think you may rarely get the correct packet with pktno = 0, in continuous mode, as my guess. Your received correct packet starts from pktno = 1.

Could you also try the discontinuous mode for the BPSK communications?

My question is actually a problem that how to implement a more reliable BPSK mod/demod in burst mode. The current bpsk example in GNURadio does not work well in burst mode.

On Fri, Mar 1, 2013 at 11:12 PM, Manu T S <address@hidden> wrote:

Alex,

If it was about loosing sync, we would mostly loose the first packet even if we are sending in continuous mode. I personally face no such issues.

On Sat, Mar 2, 2013 at 3:25 AM, Alex Zhang <address@hidden> wrote:

Seems no one can shed a light on this topic?

On Thu, Feb 28, 2013 at 10:25 PM, Alex Zhang <address@hidden> wrote:

Hello,

In the current gr-digital/narrowband, I am using the benchmark_tx.py and rx.py to test the bpsk communications.

It is found that the packet loss rate is very high (70% loss) in discontinuous mode where every 5 packets are in a burst. But in continuous mode, the paket loss rate is less than 10% for the same point to point link.

I captured the waveform data. From the observed result, it seems that for each burst (5 packet), the bpsk receiver needs to re-do the frequency/time sync. This will directly causes that the first packet of each burst will definitely be crashed. Also, some burst can not be demodulated correctly at all. For the same reason, even in the continuous mode, the very first packet is also crashed at the receiver.

I have tried  to add very long preamble for each packet to ensure the data part of the packet can be received in well sync status. But the result is not very good.

Before I get further investigation on the solutions, just wondering if any ideas or existing work within this community.

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Alex,

Dreams can come true – just believe.

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Alex,

Dreams can come true – just believe.

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Manu T S

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Alex,

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Alex,

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Alex,

Dreams can come true – just believe.