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 <[email protected]> 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:* [email protected] > [mailto:[email protected]] *On > Behalf Of *Marcus Müller > *Sent:* Tuesday, June 23, 2015 11:59 AM > *To:* [email protected] > > *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 < > [email protected]> 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:[email protected]] > *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 <[email protected]> > 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:* [email protected] > [mailto:[email protected]] *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 > > > > > _______________________________________________ > > Discuss-gnuradio mailing list > > [email protected] > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > -- Sincerely, Surya Agam University Al Azhar of Indonesia, Jakarta
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