# Channel Model **URL:** \ **Category:** GNU Radio\ **Created:** [August 5, 2015, 1:27pm UTC](https://www.ruby-forum.com/t/channel-model/242889 "2015-08-05T13:27:01Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Sadaf\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/858c86/32.png) [@Sadaf\_N](https://www.ruby-forum.com/u/Sadaf_N)\ **Post date:** [August 5, 2015, 1:27pm UTC](https://www.ruby-forum.com/t/channel-model/242889/1 "2015-08-05T13:27:01Z")
Hii I am using channels.channel\_model as channels\_channel\_model\_0 = channels.channel\_model( noise\_voltage = self.EbN0\_to\_noise\_voltage(EbN0), frequency\_offset=0.0, epsilon=1.0, taps=(1.0 + 0j, ), noise\_seed=RAND\_SEED, block\_tags=True ) in the place of Add and Noise\_Source in berawgn.py file… But the BER is not following the theory curve. I am attaching the curve i got. What does this channel model do ? Can someone please explain it. ---
**Author:** ![monika\_bansal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7c8e57/32.png) [@monika\_bansal](https://www.ruby-forum.com/u/monika_bansal)\ **Post date:** [August 5, 2015, 3:45pm UTC](https://www.ruby-forum.com/t/channel-model/242889/2 "2015-08-05T15:45:28Z")
On Wed, Aug 5, 2015 at 7:25 AM, monika bansal [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > block\_tags=True > ) > > in the place of Add and Noise\_Source in berawgn.py file.. But the BER is > not following the theory curve. I am attaching the curve i got. > > What does this channel model do ? Can someone please explain it. The channel\_model is a hierarchical block to add noise, frequency offset, timing offset, and a constant channel. In your case, you’ve turned off everything but the noise source, which is generated using a gr::analog::noise\_source\_c. > **[GNU Radio Manual and C++ API Reference: gr::channels::channel\_model Class...](https://www.gnuradio.org/doc/doxygen/classgr_1_1channels_1_1channel__model.html)** My guess is that you’re setting the noise voltage level incorrectly. Tom ---
**Author:** ![monika\_bansal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7c8e57/32.png) [@monika\_bansal](https://www.ruby-forum.com/u/monika_bansal)\ **Post date:** [August 5, 2015, 9:52pm UTC](https://www.ruby-forum.com/t/channel-model/242889/3 "2015-08-05T21:52:55Z")
On 05.08.2015 04:25, monika bansal wrote: > block\_tags=True > ) Try noise\_voltage = self.EbN0\_to\_noise\_voltage(EbN0)/sqrt(2) the original berawgn.py was already buggy, because it didn’t follow a recent change in the noise power. I’ve submitted a patch, but it probably won’t be merged before the release cycle is reset (cf [https://github.com/gnuradio/gnuradio/compare/master...mbr0wn:digital/berawgn\_fix\_noisepower?expand=1](https://github.com/gnuradio/gnuradio/compare/master...mbr0wn:digital/berawgn_fix_noisepower?expand=1)). M ---
**Author:** ![monika\_bansal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7c8e57/32.png) [@monika\_bansal](https://www.ruby-forum.com/u/monika_bansal)\ **Post date:** [August 6, 2015, 6:48am UTC](https://www.ruby-forum.com/t/channel-model/242889/4 "2015-08-06T06:48:37Z")
Hii Thanks for your responses. The problem is this channel model is eating some initial 6 bits(3 qpsk symbols) and last 10 bits(5 qpsk symbols). Because of this index of output symbol is different fron input which is resulting in error for all snr ranges. You can see the output for noise\_volage =0.0 Input = (0L, 0L, 2L, 3L, 1L, 2L, 1L, 1L, 2L, 3L, 0L, 1L, 0L, 1L, 1L, 3L, 2L, 3L, 1L, 0L, 2L, 0L, 3L, 2L, 2L, 1L, 3L, 2L, 3L, 0L, 2L, 2L, 0L, 1L, 2L, 3L, 3L, 0L, 2L, 2L, 0L, 2L, 3L, 3L, 2L, 2L, 3L, 0L, 0L, 0L, 1L, 0L, 2L, 2L, 2L, 0L, 3L, 0L, 1L, 1L, 3L, 0L, 1L, 3L, 3L, 3L, 0L, 0L, 2L, 0L, 1L, 1L, 0L, 2L, 3L, 2L, 2L, 3L, 2L, 3L) Output = (3L, 1L, 2L, 1L, 1L, 2L, 3L, 0L, 1L, 0L, 1L, 1L, 3L, 2L, 3L, 1L, 0L, 2L, 0L, 3L, 2L, 2L, 1L, 3L, 2L, 3L, 0L, 2L, 2L, 0L, 1L, 2L, 3L, 3L, 0L, 2L, 2L, 0L, 2L, 3L, 3L, 2L, 2L, 3L, 0L, 0L, 0L, 1L, 0L, 2L, 2L, 2L, 0L, 3L, 0L, 1L, 1L, 3L, 0L, 1L, 3L, 3L, 3L, 0L, 0L, 2L, 0L, 1L, 1L, 0L, 2L, 3L) Input = (0L, 1L, 0L, 2L, 0L, 1L, 1L, 3L, 2L, 3L, 3L, 1L, 0L, 2L, 2L, 0L, 0L, 1L, 1L, 1L, 0L, 0L, 3L, 2L, 3L, 1L, 1L, 2L, 1L, 0L, 3L, 0L, 0L, 0L, 3L, 0L, 3L, 2L, 1L, 0L, 3L, 1L, 3L, 1L, 1L, 3L, 1L, 2L, 0L, 1L, 0L, 3L, 1L, 0L, 3L, 2L, 1L, 2L, 3L, 3L, 2L, 1L, 3L, 0L, 1L, 2L, 3L, 3L, 0L, 0L, 0L, 2L, 3L, 3L, 1L, 3L, 3L, 1L, 0L, 3L) Output = (2L, 0L, 1L, 1L, 3L, 2L, 3L, 3L, 1L, 0L, 2L, 2L, 0L, 0L, 1L, 1L, 1L, 0L, 0L, 3L, 2L, 3L, 1L, 1L, 2L, 1L, 0L, 3L, 0L, 0L, 0L, 3L, 0L, 3L, 2L, 1L, 0L, 3L, 1L, 3L, 1L, 1L, 3L, 1L, 2L, 0L, 1L, 0L, 3L, 1L, 0L, 3L, 2L, 1L, 2L, 3L, 3L, 2L, 1L, 3L, 0L, 1L, 2L, 3L, 3L, 0L, 0L, 0L, 2L, 3L, 3L, 1L) How should i calculate the error now? Should i use Delay block? On Thu, Aug 6, 2015 at 2:34 AM, Johnathan C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![monika\_bansal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7c8e57/32.png) [@monika\_bansal](https://www.ruby-forum.com/u/monika_bansal)\ **Post date:** [August 6, 2015, 10:34am UTC](https://www.ruby-forum.com/t/channel-model/242889/5 "2015-08-06T10:34:41Z")
> How should i calculate the error now? > That pretty much depends on what /you/ want to measure – obviously, > these bits are lost, so practically, this increases your BER. > If you want to demonstrate asymptotic behaviour, however, then you could > just increase the length of your simulation until a few bits lost at > start and end just don’t matter anymore. Greetings, Marcus ---
**Author:** ![monika\_bansal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7c8e57/32.png) [@monika\_bansal](https://www.ruby-forum.com/u/monika_bansal)\ **Post date:** [August 5, 2015, 11:05pm UTC](https://www.ruby-forum.com/t/channel-model/242889/6 "2015-08-05T23:05:57Z")
On Wed, Aug 5, 2015 at 12:51 PM, Martin B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Try > > noise\_voltage = self.EbN0\_to\_noise\_voltage(EbN0)/sqrt(2) > > the original berawgn.py was already buggy, because it didn’t follow a > recent change in the noise power. I’ve submitted a patch, but it > probably won’t be merged before the release cycle is reset (cf [https://github.com/gnuradio/gnuradio/compare/master...mbr0wn:digital/berawgn\_fix\_noisepower?expand=1](https://github.com/gnuradio/gnuradio/compare/master...mbr0wn:digital/berawgn_fix_noisepower?expand=1) > ). ​This did get merged for 3.7.8 release.​ ---
**Author:** ![monika\_bansal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7c8e57/32.png) [@monika\_bansal](https://www.ruby-forum.com/u/monika_bansal)\ **Post date:** [August 6, 2015, 11:16am UTC](https://www.ruby-forum.com/t/channel-model/242889/7 "2015-08-06T11:16:45Z")
Taking a blind guess here: How many samples do you simulate for Eb/N0 = 8dB? And for 10dB? And for 12dB? Best regards, Marcus ---
**Author:** ![monika\_bansal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7c8e57/32.png) [@monika\_bansal](https://www.ruby-forum.com/u/monika_bansal)\ **Post date:** [August 6, 2015, 11:32am UTC](https://www.ruby-forum.com/t/channel-model/242889/8 "2015-08-06T11:32:32Z")
160000 bits for all snr values.,… On Thu, Aug 6, 2015 at 2:45 PM, Marcus Müller [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![monika\_bansal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7c8e57/32.png) [@monika\_bansal](https://www.ruby-forum.com/u/monika_bansal)\ **Post date:** [August 6, 2015, 10:59am UTC](https://www.ruby-forum.com/t/channel-model/242889/9 "2015-08-06T10:59:48Z")
Yes Marcus… and i used delay block at the output of the demodulator to make output bits align with input bits. Now it is tracing the theoretical curve till 9 db but after that error is not reducing. I am attaching the curve. Why is this happening ?? On Thu, Aug 6, 2015 at 2:03 PM, Marcus Müller [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![monika\_bansal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7c8e57/32.png) [@monika\_bansal](https://www.ruby-forum.com/u/monika_bansal)\ **Post date:** [August 6, 2015, 11:39am UTC](https://www.ruby-forum.com/t/channel-model/242889/10 "2015-08-06T11:39:33Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 As a rule of thumb with expected error rate BERe: num simulation bits: (1 / BERe) \* 100 that’s more like a minimum. It’s probably better to go for \* 1000. Also if you use BER block, it has a parameter ’ BER Min. Errors’. As long as it didn’t count at least this amount of errors it’ll not output anything. Depending on your code and your SNR 8-12dB I’d expect you need at least 1Gbit or in case of SNR=12dB more towards 100Gbit in order to obtain meaningful results. Hope that helps. On 06.08.2015 11:31, monika bansal wrote: > > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > > > Greetings, Marcus > > > output for noise\_volage =0.0 > > > 0L, 1L, 2L, 3L, 3L, 0L, 2L, 2L, 0L, 2L, 3L, 3L, 2L, 2L, 3L, 0L, > > > > > > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)\> wrote: > > > > > > > > didn’t follow a recent change in the noise power. I’ve > > > > > submitted a patch, but it probably won’t be merged before > > > > > the release cycle is reset (cf > > > > > > > > > > [https://github.com/gnuradio/gnuradio/compare/master...mbr0wn:digit](https://github.com/gnuradio/gnuradio/compare/master...mbr0wn:digit) > > > > > al/berawgn\_fix\_noisepower?expand=1 ). > > > > * * * > > > > > > > > Discuss-gnuradio mailing list [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > > > > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) > > > > > > * * * > > > > > > Discuss-gnuradio mailing > > > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)://lists.gnu.org/mailman/listinfo/d > > > iscuss-gnuradio * * * > mailing list [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iQIcBAEBAgAGBQJVwyrLAAoJEO7fmkDsqywMumwQAJ9YXsjZrX051rtAp61Rrbdp PqsblRAqNAy2kXNGVX+Ag1B9BUnSqsIpSZVgYCvXqiPH8Cy9qAGFv3EkPPk80BN0 O+4zzIFCovnPXHHnJB90ntyUUvHZlUd5TTDRn0RNzMSvI1ABg+ssk7pUYM424vvO wTMBA4yP41aCr7nbYDowpMd+GnzdC0nwpxpTVdEVX8yS8PlhECAv45/U2Ze/6CT2 EcK3pUIZRTgZlWezrS1mqD5afGqNYPHz1WhPQx05Hx2OjyP2wNwPx9RA6VKhIosU iywpvz4zdpbaKFEpgTwB6h0w0+CeclnqmipSP+hPIkUmFa7kbQyzNjAn5WTYfQrd Ne+v2W9ztxQlbvihswVmHdrBxwk2/gDlL6pzBWy6zf2T0NfAJxlW/zcOQlVc+fEs tL5l0ZVNha0Ppam2I6jxKzINMDOm3Gln0h3F75FD9CpcTyHRKxV9a8Sg4BCi4jei +l6rnT4mhQk6RirDBOXUwWIXLbk28RLAWYNL8Jyn0n7M50ax7WMGXBS+yDUf/G1A mmiLAFm1ATZRHBN1Aw99DXkI/LN+qp10oUYkKRcx7Ji3z6Oc+CKIqE0r9QBck0qS z0JfxOG9N1z+iEgWJ/Ui4GZx85zHJVkmyHQs72QTecoFnhO1j/GWqeRRAyyWDTJ8 zMsQVtreQnqYEPkSSQKK =rixl -----END PGP SIGNATURE----- ---
**Author:** ![monika\_bansal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/7c8e57/32.png) [@monika\_bansal](https://www.ruby-forum.com/u/monika_bansal)\ **Post date:** [August 6, 2015, 11:58am UTC](https://www.ruby-forum.com/t/channel-model/242889/11 "2015-08-06T11:58:49Z")
Yes … Thanks ! On Thu, Aug 6, 2015 at 3:07 PM, Johannes D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)