Hi Johannes,
Thanks for your email. Have been reading through the link you sent me,
just trying to relate the direct UHD stuff with the equivalent in gr-uhd
code.
I am planning to implement some LDPC code that I wrote for another
application. Have you tried implementing something similar?
Regards,
David
From: Johannes D. [[email protected]]
Sent: 29 January 2014 18:53
To: David Halls
Cc: Martin B.; [email protected]
Subject: Re: [Discuss-gnuradio] Half-Duplex Relay
Hi David,
you could consider to tweak the latency [1] of your system between host
and USRP. This way your relay is less dependent on that and you can
reduce the gaps between packets if the host side signal processing can
keep up.
If you increase the packet size of your OFDM system you might also
consider to use channel coding, e.g. a convolutional code.
happy hacking
Johannes
[1] http://code.ettus.com/redmine/ettus/projects/uhd/wiki/latency
On Wed, Jan 29, 2014 at 10:11 AM, David Halls
<[email protected]mailto:[email protected]>
wrote:
Hi Martin, and all,
I am making good progress with the relay.
At the source, I transmit packets interspersed with 0’s to create a
silent period. This is achieved using vector_insert. Perhaps there are
better ways, but it works well. Currently the gap is 20ms (2e4 samples
at 1e6Ms/s) between tx’d packets from source.
At the relay I take the rx_time UHD tag, then in HPD I work out the
actual time that each trigger is received (i.e. beginning of each
packet) using nitems_read(0) with rx_time and sample_rate, I then
decode, re-encode, and then add sob, eob, and a tx_time created by
adding 10ms to the rx_time, so that it is transmitted half-way between
the packets from the source.
This works but gives large gaps - each burst is (3+3+16)*80 = 1760
samples, a lot of time is wasted.
The decoding/encoding delay in the relay seems to vary between around
3000 and 10000 samples, so I can’t reduce the timeslot length without
some packets at the relay arriving at the USRP late ‘L’.
I am not sure how to proceed. I can increase the packet length at the
transmitter to fill the gap, but not sure if this will lengthen the
relay decoding delay or not. Also with the OFDM_tx code, I get buffer
errors with a payload longer than 96Bx2. i.e. 32 symbol payload.
Any thoughts?
David
From:
discuss-gnuradio-bounces+david.halls=removed_email_address@domain.invalidmailto:discuss-gnuradio-bounces+david.halls=removed_email_address@domain.invalid
[discuss-gnuradio-bounces+david.halls=removed_email_address@domain.invalidmailto:[email protected]]
on behalf of Martin B.
[[email protected]mailto:[email protected]]
Sent: 14 January 2014 16:56
To: [email protected]mailto:[email protected]
Subject: Re: [Discuss-gnuradio] Half-Duplex Relay
On Tue, Jan 14, 2014 at 11:29:51AM +0000, David Halls wrote:
Do you feel this makes sense? I will let you know how I progress.
Sounds good. Tell us how you’re coming along, and do ask for advice
if necessary.
MB
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