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View all threadsframe synchronization and pulse shaping in matlab-simulink
Hi, everyone:
I am working on the transceiver system design in the simulink+UHD testbed
recently. I try to add several practical modules, such as frame
synchronization, to build up a complete transceiver system. But still there
are several problems, especially on frame synchronization. Does anyone have
the experience on how to design a frame synchronization module?
Secondly, after modulated the signals in baseband, do we need pulse shaping
(RRC filter) the modulated signal before sending it to USRP_tx module?
Also, how about carrier frequency, phase, timing recovery modules, are they
already implemented in the USRP2_rx module or need to be added by ourselves?
Thanks a lot for your help.
Best wishes,
--
Yuanqian Luo
On Wed, 2011-02-09 at 01:48 -0800, yqluo wrote:
Hi, everyone:
I am working on the transceiver system design in the simulink+UHD
testbed recently. I try to add several practical modules, such as
frame synchronization, to build up a complete transceiver system. But
still there are several problems, especially on frame synchronization.
Does anyone have the experience on how to design a frame
synchronization module?
Any communications textbook should have at least an overview of the
approach to framing packets. Sorry I can't be more specific than that.
If you're using a standard framing like HDLC there are a number of code
examples available from a Google search to work from.
Secondly, after modulated the signals in baseband, do we need pulse
shaping (RRC filter) the modulated signal before sending it to USRP_tx
module?
Only if your modulation requires it. GMSK, for instance, uses pulse
shaping via a RRC filter, although typically the filtering is done to
the data before phase modulation in that case.
Also, how about carrier frequency, phase, timing recovery modules, are
they already implemented in the USRP2_rx module or need to be added by
ourselves?
You'll need to add all this in order to create a complete real-world
communication system. They are not implemented in the USRP RX block
because different modulation schemes require very different approaches
to accomplish those standard tasks. I'm pretty sure Simulink's
Communications Blockset includes blocks to do all of these things, but
I'm not familiar with their operation.
--n
Thanks a lot for your help.
Best wishes,
--
Yuanqian Luo
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Hi Yuanqian,
For frame sync, you can use the Barker Code blocks in the Comms Blockset to prepend a frame marker to your payload data. Then cross-correlate your received waveform with the Barker code to find the start of your frame.
Most practical comms systems use pulse shaping prior to transmission, so you should try to use an RRC filter before the USRP Tx.
The Comms Blockset has blocks that perform carrier phase and timing phase recovery. Since you need carrier and timing frequency recovery, you should look at the MIL-STD-188-110a Receiver demo in the Comms Blockset. Just type 'commmilstd188110a' at the MATLAB command prompt to bring it up.
Hth,
Mike
From: usrp-users-bounces@lists.ettus.com [mailto:usrp-users-bounces@lists.ettus.com] On Behalf Of yqluo
Sent: Wednesday, February 09, 2011 4:48 AM
To: usrp-users@lists.ettus.com
Subject: [USRP-users] frame synchronization and pulse shaping in matlab-simulink
Hi, everyone:
I am working on the transceiver system design in the simulink+UHD testbed recently. I try to add several practical modules, such as frame synchronization, to build up a complete transceiver system. But still there are several problems, especially on frame synchronization. Does anyone have the experience on how to design a frame synchronization module?
Secondly, after modulated the signals in baseband, do we need pulse shaping (RRC filter) the modulated signal before sending it to USRP_tx module?
Also, how about carrier frequency, phase, timing recovery modules, are they already implemented in the USRP2_rx module or need to be added by ourselves?
Thanks a lot for your help.
Best wishes,
--
Yuanqian Luo
On Wed, Feb 9, 2011 at 10:36 AM, Nick Foster nick@ettus.com wrote:
On Wed, 2011-02-09 at 01:48 -0800, yqluo wrote:
Hi, everyone:
I am working on the transceiver system design in the simulink+UHD
testbed recently. I try to add several practical modules, such as
frame synchronization, to build up a complete transceiver system. But
still there are several problems, especially on frame synchronization.
Does anyone have the experience on how to design a frame
synchronization module?
Any communications textbook should have at least an overview of the
approach to framing packets. Sorry I can't be more specific than that.
If you're using a standard framing like HDLC there are a number of code
examples available from a Google search to work from.
Secondly, after modulated the signals in baseband, do we need pulse
shaping (RRC filter) the modulated signal before sending it to USRP_tx
module?
Only if your modulation requires it. GMSK, for instance, uses pulse
shaping via a RRC filter, although typically the filtering is done to
the data before phase modulation in that case.
Quick correction, GMSK uses a Gaussian shaped pulse, not an RRC
filter. Otherwise, Nick is right, you generally want to shape your
signal before transmitting it.
The reason we use RRC filters is because we want to both limit the
signal's spectrum on transmit as well as filter it in the receiver.
When you convolve two RRC filters like this (one from the Tx and one
from the Rx), you get an RC filter, which is a Nyquist filter (at
least, theoretically it is) that reduces ISI.
Tom
Thanks, guys. The answers help a lot.
Although it is a tough job to add all these components for different
modulation, it seems we don't have any choice. I really hope someone could
post a complete transceiver example with USRP2 modules in maltlab-simulink
testbed. That would be greatly helpful to develop our own system.
Best wishes,
yuanqian
On Thu, Feb 10, 2011 at 6:48 AM, Tom Rondeau trondeau1122@gmail.com wrote:
On Wed, Feb 9, 2011 at 10:36 AM, Nick Foster nick@ettus.com wrote:
On Wed, 2011-02-09 at 01:48 -0800, yqluo wrote:
Hi, everyone:
I am working on the transceiver system design in the simulink+UHD
testbed recently. I try to add several practical modules, such as
frame synchronization, to build up a complete transceiver system. But
still there are several problems, especially on frame synchronization.
Does anyone have the experience on how to design a frame
synchronization module?
Any communications textbook should have at least an overview of the
approach to framing packets. Sorry I can't be more specific than that.
If you're using a standard framing like HDLC there are a number of code
examples available from a Google search to work from.
Secondly, after modulated the signals in baseband, do we need pulse
shaping (RRC filter) the modulated signal before sending it to USRP_tx
module?
Only if your modulation requires it. GMSK, for instance, uses pulse
shaping via a RRC filter, although typically the filtering is done to
the data before phase modulation in that case.
Quick correction, GMSK uses a Gaussian shaped pulse, not an RRC
filter. Otherwise, Nick is right, you generally want to shape your
signal before transmitting it.
The reason we use RRC filters is because we want to both limit the
signal's spectrum on transmit as well as filter it in the receiver.
When you convolve two RRC filters like this (one from the Tx and one
from the Rx), you get an RC filter, which is a Nyquist filter (at
least, theoretically it is) that reduces ISI.
Tom
--