Re: [Discuss-gnuradio] PSK Mod Block

[Surya Agam]

So,

"it appears that PSK Mod expects packed bytes" = from Packet Encoder direct to PSK Mod

"the Demod block outputs a stream of bits with 1 meaningful bit in the LSB position" = Repack Bits 1 to 8 (packet alignment = input)

the result, without delay the output is similar but not same. I don't know if need a long delay (the input and output from attachment not from the same packet) or I use a wrong Repack Bits block setting.

On Tue, Jun 23, 2015 at 11:51 PM, Nowlan, Sean <address@hidden> wrote:

Looking quickly at the documentation, for PSK Mod and Demod blocks, it appears that PSK Mod expects packed bytes (8 bits of meaningful data in each byte) and that the Demod block outputs a stream of bits with 1 meaningful bit in the LSB position. Use a Repack Bits block. However, you may need to play with the delay (insert a Delay Block) to make sure that the Repack Bits block is aligning bits into bytes properly.

 

Mod: “The input is a byte stream (unsigned char), treated as a series of packed symbols. Symbols are grouped from MSB to LSB.”

 

Demod: “The output is a stream of bytes, each representing a recovered bit. The most significant bit is reported first.”

 

From: discuss-gnuradio-bounces+sean.nowlan=address@hidden [mailto:discuss-gnuradio-bounces+sean.nowlan=address@hidden] On Behalf Of Marcus Müller
Sent: Tuesday, June 23, 2015 11:59 AM
To: address@hidden

Subject: Re: [Discuss-gnuradio] PSK Mod Block

 

Then you really want some pulse shaping filter, like the RRC that is used by default.

On 06/23/2015 05:39 PM, Surya Agam wrote:

My target is using USRP, but still simulate using a noise channel. The output of PSK Demod is bit "0" a with some "1" and no input data in the output.

 

I attach the input and the output screenshot.

 

On Tue, Jun 23, 2015 at 10:12 PM, Nowlan, Sean <address@hidden> wrote:

This depends on your setup. If you’re just simulating with PSK Mod --> PSK Demod and then comparing the input with the output, then you may be seeing some initial output from the filters due to the convolution operations. Try searching through your output after some delay.

 

If you disabled differential encoding, you may be seeing a bitstream that is not correct due to phase locking with a fixed phase offset at the receiver.

 

If you’re going over hardware or through a noise channel, you might not have enough SNR to decode properly.

 

If you’re using USRPs, have you experimented with the benchmark_tx/rx scripts? These implement various types of single carrier modulation, including many variants of PSK.

 

Sean

 

From: Surya Agam [mailto:address@hidden]
Sent: Tuesday, June 23, 2015 10:53 AM
To: Nowlan, Sean
Cc: GNURadio Discussion List
Subject: Re: [Discuss-gnuradio] PSK Mod Block

 

Thank you for the fast respond,

 

But, when I use PSK Mod then PSK Demod the output different from the input so no output from the Packet Decoder. Any suggestion?

 

On Tue, Jun 23, 2015 at 9:17 PM, Nowlan, Sean <address@hidden> wrote:

Introducing ISI to a PSK signal with a root-raised cosine (RRC) filter is a standard communications technique. At the receiver, use a matched RRC filter to eliminate the intentional ISI introduced at the transmitter. This works because the combined filter response of the two filters is a raised cosine pulse, which satisfies the Nyquist criterion for zero ISI.

 

In the PSK Mod block, the filter construction is not exposed to the user except through the excess bandwidth or roll-off parameter. You could adjust that bandwidth factor to be close to zero, but this will create a very long filter. If you really want to do what you are saying, it would be worth looking at the source code for the PSK Mod block, and taking the filter out. However, it is likely that you don’t really want to do this.

 

Sean

 

From: discuss-gnuradio-bounces+sean.nowlan=address@hidden [mailto:discuss-gnuradio-bounces+sean.nowlan=address@hidden] On Behalf Of Surya Agam
Sent: Tuesday, June 23, 2015 9:47 AM
To: GNURadio Discussion List
Subject: [Discuss-gnuradio] PSK Mod Block

 

Hello,

 

I wanna use PSK Mod Block, but the ISI is annoying. Why PSK Mod Block have a it's own ISI?

And also is there anyway to disable the ISI from the block?

 

--

Sincerely,

 

Surya Agam

University Al Azhar of Indonesia, Jakarta

 

--

Sincerely,

 

Surya Agam

University Al Azhar of Indonesia, Jakarta

 

--

Sincerely,

 

Surya Agam

University Al Azhar of Indonesia, Jakarta

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--

Sincerely,

Surya Agam

University Al Azhar of Indonesia, Jakarta

PSK 2.png
Description: PNG image