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Re: [Discuss-gnuradio] Very low packet loss rate for the discontinuous B

From: Jawad Seddar
Subject: Re: [Discuss-gnuradio] Very low packet loss rate for the discontinuous BPSK communications- the analysis and looking for solution
Date: Wed, 6 Mar 2013 11:09:55 +0100

Ok, well thank you for the fast answer.
I'll keep looking around but this is a serious issue for me, it means I can't use my two USRP to send and receive any useful traffic.

2013/3/6 Alex Zhang <address@hidden>
I don't believe this problem can be solved by adjusting the loop bandwidth.
Applying faster tracking algorithm may solve this problem, but I think it takes long time to develop for a new guy.

On Wed, Mar 6, 2013 at 3:44 AM, Jawad Seddar <address@hidden> wrote:

I am getting the same problem you described here i.e very high packet loss in discontinuous mode (first and last packet received with ok=False).

Could you please elaborate on how to adjust the synchronisation loops bandwidth?
I have tried adjusting the --timing-bw and --phase-bw parameters on the benchmark-rx example, but I don't know if that is what you were talking about.

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


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) 


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:

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:

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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