Forums

Need of Eqaulization ?

Started by mite_learner September 27, 2013
On Sat, 28 Sep 2013 02:35:49 -0500, "mite_learner" <94814@dsprelated>
wrote:

>>On Fri, 27 Sep 2013 07:39:48 -0500, "mite_learner" <94814@dsprelated> >>wrote: >> >>>Dear Members, >>> >>>I am experimenting on digital 4-FSK (orthogonal) communication system. >On >>>the demodulation side, I am using AGC and then 4 filters to detect tones >>>and then using symbol timing. My question is how can I know that I need >>>equalization looking at the signal if I transmit and receive the signal >>>over the air? How can I verify that my signal is being affected by >>>multipaths ? >> >>Do you have any means of sounding the channel, e.g., via a preamble or >>known signal transmission? >> > >Yes Eric. > >>Other than the easy steps of looking at the demodulator outputs and >>general performance, you kind of need some way to measure the channel >>to know whether there is multipath present and how much. A preamble >>or test signal that transmits all four tones in a usable fashion >>(e.g., stepped, random, etc.) and then analyzes the output can be used >>to do that. Look at the output in the frequency domain to look for >>channel frequency selectivity and correlate the received signal >>against the transmitted signal to estimate the channel impulse >>response. >> >>Estimating the channel impulse response with a data sequence is best >>done with a PN or similar sequence that allows easy correlation >>analysis. >> > >Yes, I can send the tones in controlled fashion (i.e I can send whatever >data I want to). So, I need to send data sequence, lets say DATA1 and then >I receive this and demodulate. If the data after demodulation is DATA2, >then I have to correlate DATA1 and DATA2. What kind of correlation output >indicates the affect and severity of multipaths? > >Mite
You want to correlate the received waveform against the transmitted waveform. The demodulated data usually won't preserve the details of the multipath profile. Is the ADC before the filters? If so, then you can cross correlate the output of the ADC against the original transmitted waveform. If the transmitted waveform has good autocorrelation properties (e.g., a PN sequence), then the output of the cross correlation will provide an estimate of the multipath channel impulse response. The multipath delays should be reasonably clear if they are significant.
>>> >>>-- >>>Mite >>> >>>_____________________________ >>>Posted through www.DSPRelated.com >> >>Eric Jacobsen >>Anchor Hill Communications >>http://www.anchorhill.com >> > >_____________________________ >Posted through www.DSPRelated.com
Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
On Sat, 28 Sep 2013 09:56:14 -0500, Vladimir Vassilevsky wrote:

> On 9/28/2013 1:47 AM, gyansorova@gmail.com wrote: >> On Saturday, September 28, 2013 7:01:56 AM UTC+12, Vladimir Vassilevsky >> wrote: >>> On 9/27/2013 1:24 PM, Randy Yates wrote: >>> >>>> "mite_learner" <94814@dsprelated> writes: >>> >>> >>>> >>>>> Dear Members, >>> >>> >>>>> >>>>> I am experimenting on digital 4-FSK (orthogonal) communication >>>>> system. On >>> >>>>> the demodulation side, I am using AGC and then 4 filters to detect >>>>> tones >>> >>>>> and then using symbol timing. My question is how can I know that I >>>>> need >>> >>>>> equalization looking at the signal if I transmit and receive the >>>>> signal >>> >>>>> over the air? How can I verify that my signal is being affected by >>> >>>>> multipaths ? >>> >>> >>>> >>>> Did you mean AGC in front of your ADC? >>> >>> >>>> >>>> By the way, ignore Vlad. He's made a career out of calling people >>>> idiots >>> >>>> - doesn't mean they are. >>> >>> >>> >>> No matter how to call it, idiots are idiots. Let them make careers. >>> >>> I design DSP systems which work. And I do it very well. >>> >>> >>> >>> >>> >> Maybe you do, maybe you don't, I have never purchased your products so >> I don't know. However. I cannot see the point in you being in this - a >> tutorial style ng if you are not prepared to help others. So either >> help people or fuck off! >>
Oh come come. If you're going to be a troll, do it with style. At least go buy a dictionary of creative insults. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
On Sunday, September 29, 2013 12:44:36 PM UTC+13, Tim Wescott wrote:
> On Sat, 28 Sep 2013 09:56:14 -0500, Vladimir Vassilevsky wrote: > > > > > On 9/28/2013 1:47 AM, gyansorova@gmail.com wrote: > > >> On Saturday, September 28, 2013 7:01:56 AM UTC+12, Vladimir Vassilevsky > > >> wrote: > > >>> On 9/27/2013 1:24 PM, Randy Yates wrote: > > >>> > > >>>> "mite_learner" <94814@dsprelated> writes: > > >>> > > >>> > > >>>> > > >>>>> Dear Members, > > >>> > > >>> > > >>>>> > > >>>>> I am experimenting on digital 4-FSK (orthogonal) communication > > >>>>> system. On > > >>> > > >>>>> the demodulation side, I am using AGC and then 4 filters to detect > > >>>>> tones > > >>> > > >>>>> and then using symbol timing. My question is how can I know that I > > >>>>> need > > >>> > > >>>>> equalization looking at the signal if I transmit and receive the > > >>>>> signal > > >>> > > >>>>> over the air? How can I verify that my signal is being affected by > > >>> > > >>>>> multipaths ? > > >>> > > >>> > > >>>> > > >>>> Did you mean AGC in front of your ADC? > > >>> > > >>> > > >>>> > > >>>> By the way, ignore Vlad. He's made a career out of calling people > > >>>> idiots > > >>> > > >>>> - doesn't mean they are. > > >>> > > >>> > > >>> > > >>> No matter how to call it, idiots are idiots. Let them make careers. > > >>> > > >>> I design DSP systems which work. And I do it very well. > > >>> > > >>> > > >>> > > >>> > > >>> > > >> Maybe you do, maybe you don't, I have never purchased your products so > > >> I don't know. However. I cannot see the point in you being in this - a > > >> tutorial style ng if you are not prepared to help others. So either > > >> help people or fuck off! > > >> > > > > Oh come come. If you're going to be a troll, do it with style. > > > > At least go buy a dictionary of creative insults. > >
That is because you have identified a normal ng user - he is the Troll and why you cannot see that escapes me.
>>"mite_learner" <94814@dsprelated> writes: >> >>> Dear Members, >>> >>> I am experimenting on digital 4-FSK (orthogonal) communication system.
>On >>> the demodulation side, I am using AGC and then 4 filters to detect >tones >>> and then using symbol timing. My question is how can I know that I >need >>> equalization looking at the signal if I transmit and receive the
signal
>>> over the air? How can I verify that my signal is being affected by >>> multipaths ? >> >>Did you mean AGC in front of your ADC? >> >>By the way, ignore Vlad. He's made a career out of calling people idiots >>- doesn't mean they are. >>-- > >Currently I don't have AGC in front of ADC, but I am keeping my signal
low
>so that ADC doesn't start clipping. I applied AGC on my baseband signal, >after digitization, before doing matched filtering for individual tones.
I
>am using this AGC to keep signal level in a range for symbol timing >synchronization. > >But Vlad says AGC is harmful in this setup, why? I would have asked him
but
>searching on the group, I found that he never gave an answer that could
be
>*useful* for anybody in the world . > >--
Randy or any body, please comment on this. Mite
>Mite > >>Randy Yates >>Digital Signal Labs >>http://www.digitalsignallabs.com >> > >_____________________________ >Posted through www.DSPRelated.com >
_____________________________ Posted through www.DSPRelated.com
On Mon, 30 Sep 2013 07:21:06 -0500, "mite_learner" <94814@dsprelated>
wrote:

>>>"mite_learner" <94814@dsprelated> writes: >>> >>>> Dear Members, >>>> >>>> I am experimenting on digital 4-FSK (orthogonal) communication system. > >>On >>>> the demodulation side, I am using AGC and then 4 filters to detect >>tones >>>> and then using symbol timing. My question is how can I know that I >>need >>>> equalization looking at the signal if I transmit and receive the >signal >>>> over the air? How can I verify that my signal is being affected by >>>> multipaths ? >>> >>>Did you mean AGC in front of your ADC? >>> >>>By the way, ignore Vlad. He's made a career out of calling people idiots >>>- doesn't mean they are. >>>-- >> >>Currently I don't have AGC in front of ADC, but I am keeping my signal >low >>so that ADC doesn't start clipping. I applied AGC on my baseband signal, >>after digitization, before doing matched filtering for individual tones. >I >>am using this AGC to keep signal level in a range for symbol timing >>synchronization. >> >>But Vlad says AGC is harmful in this setup, why? I would have asked him >but >>searching on the group, I found that he never gave an answer that could >be >>*useful* for anybody in the world . >> >>-- > >Randy or any body, please comment on this. > >Mite
I think most people are unwilling to speculate why Vladimir thinks a lot of things that he thinks. AGC can be a complicated topic, especially for FM/FSK. AGC can be useful, especially to manage composite power, etc. Much depends on the system architecture and the requirements.
>>Mite >> >>>Randy Yates >>>Digital Signal Labs >>>http://www.digitalsignallabs.com >>> >> >>_____________________________ >>Posted through www.DSPRelated.com >> > >_____________________________ >Posted through www.DSPRelated.com
Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com
"mite_learner" <94814@dsprelated> writes:

>>"mite_learner" <94814@dsprelated> writes: >> >>> Dear Members, >>> >>> I am experimenting on digital 4-FSK (orthogonal) communication system. > On >>> the demodulation side, I am using AGC and then 4 filters to detect > tones >>> and then using symbol timing. My question is how can I know that I > need >>> equalization looking at the signal if I transmit and receive the signal >>> over the air? How can I verify that my signal is being affected by >>> multipaths ? >> >>Did you mean AGC in front of your ADC? >> >>By the way, ignore Vlad. He's made a career out of calling people idiots >>- doesn't mean they are. >>-- > > Currently I don't have AGC in front of ADC, but I am keeping my signal low > so that ADC doesn't start clipping. I applied AGC on my baseband signal, > after digitization, before doing matched filtering for individual tones. I > am using this AGC to keep signal level in a range for symbol timing > synchronization.
I guess the basic reasons not to use a post-ADC AGC would be a) you degrade the SNR if the AGC attentuates, and b) you don't gain any improvement in SNR if the AGC amplifies, and you could saturate as well. Additionally, timing synchronization should not be that sensitive to signal level. How are you doing synchronization? -- Randy Yates Digital Signal Labs http://www.digitalsignallabs.com
>On Mon, 30 Sep 2013 07:21:06 -0500, "mite_learner" <94814@dsprelated> >wrote: > >>>>"mite_learner" <94814@dsprelated> writes: >>>> >>>>> Dear Members, >>>>> >>>>> I am experimenting on digital 4-FSK (orthogonal) communication
system.
>> >>>On >>>>> the demodulation side, I am using AGC and then 4 filters to detect >>>tones >>>>> and then using symbol timing. My question is how can I know that I >>>need >>>>> equalization looking at the signal if I transmit and receive the >>signal >>>>> over the air? How can I verify that my signal is being affected by >>>>> multipaths ? >>>> >>>>Did you mean AGC in front of your ADC? >>>> >>>>By the way, ignore Vlad. He's made a career out of calling people
idiots
>>>>- doesn't mean they are. >>>>-- >>> >>>Currently I don't have AGC in front of ADC, but I am keeping my signal >>low >>>so that ADC doesn't start clipping. I applied AGC on my baseband
signal,
>>>after digitization, before doing matched filtering for individual
tones.
>>I >>>am using this AGC to keep signal level in a range for symbol timing >>>synchronization. >>> >>>But Vlad says AGC is harmful in this setup, why? I would have asked him >>but >>>searching on the group, I found that he never gave an answer that could >>be >>>*useful* for anybody in the world . >>> >>>-- >> >>Randy or any body, please comment on this. >> >>Mite > >I think most people are unwilling to speculate why Vladimir thinks a >lot of things that he thinks. >
True that.
>AGC can be a complicated topic, especially for FM/FSK. AGC can be >useful, especially to manage composite power, etc. Much depends on >the system architecture and the requirements. > >
That means I need to study more :) Thanks! Mite
>>>Mite >>> >>>>Randy Yates >>>>Digital Signal Labs >>>>http://www.digitalsignallabs.com >>>> >>> >>>_____________________________ >>>Posted through www.DSPRelated.com >>> >> >>_____________________________ >>Posted through www.DSPRelated.com > >Eric Jacobsen >Anchor Hill Communications >http://www.anchorhill.com >
_____________________________ Posted through www.DSPRelated.com
>"mite_learner" <94814@dsprelated> writes: > >>>"mite_learner" <94814@dsprelated> writes: >>> >>>> Dear Members, >>>> >>>> I am experimenting on digital 4-FSK (orthogonal) communication system.
>> On >>>> the demodulation side, I am using AGC and then 4 filters to detect >> tones >>>> and then using symbol timing. My question is how can I know that I >> need >>>> equalization looking at the signal if I transmit and receive the
signal
>>>> over the air? How can I verify that my signal is being affected by >>>> multipaths ? >>> >>>Did you mean AGC in front of your ADC? >>> >>>By the way, ignore Vlad. He's made a career out of calling people
idiots
>>>- doesn't mean they are. >>>-- >> >> Currently I don't have AGC in front of ADC, but I am keeping my signal
low
>> so that ADC doesn't start clipping. I applied AGC on my baseband
signal,
>> after digitization, before doing matched filtering for individual tones.
I
>> am using this AGC to keep signal level in a range for symbol timing >> synchronization. > >I guess the basic reasons not to use a post-ADC AGC would be a) you >degrade the SNR if the AGC attentuates, and b) you don't gain any >improvement in SNR if the AGC amplifies, and you could saturate as well. >
Yes, that is right. I put AGC there for symbol timing.
>Additionally, timing synchronization should not be that sensitive to >signal level. How are you doing synchronization? >--
I am using Timing Synchronization using poly phase filter banks. Each filter consisting of 32 parallel filters to get a good enough resolution in phase. Setting up two filter-banks; one filter-bank contains the signal's pulse shaping matched filter (such as a root raised cosine filter). The second filter-bank contains the derivatives of the filters in the first filter-bank. If the signal out of the derivative filters is d_i[n] for the ith filter, and the output of the matched filter is x_i[n], we calculate the error as: er[n] = (Re{x_i[n]} * Re{d_i[n]} + Im{x_i[n]} * Im{d_i[n]}) / 2.0. This equation averages the error in the real and imaginary parts. The error signal, er[n], gives us a value proportional to how far away from the zero point we are in the derivative signal. We want to drive this value to zero, so we set up a second order loop. What do you say ? Thanks, Mite
>Randy Yates >Digital Signal Labs >http://www.digitalsignallabs.com >
_____________________________ Posted through www.DSPRelated.com
On Tuesday, October 1, 2013 6:10:32 PM UTC+13, mite_learner wrote:
> >On Mon, 30 Sep 2013 07:21:06 -0500, "mite_learner" <94814@dsprelated> > > >wrote: > > > > > >>>>"mite_learner" <94814@dsprelated> writes: > > >>>> > > >>>>> Dear Members, > > >>>>> > > >>>>> I am experimenting on digital 4-FSK (orthogonal) communication > > system. > > >> > > >>>On > > >>>>> the demodulation side, I am using AGC and then 4 filters to detect > > >>>tones > > >>>>> and then using symbol timing. My question is how can I know that I > > >>>need > > >>>>> equalization looking at the signal if I transmit and receive the > > >>signal > > >>>>> over the air? How can I verify that my signal is being affected by > > >>>>> multipaths ? > > >>>> > > >>>>Did you mean AGC in front of your ADC? > > >>>> > > >>>>By the way, ignore Vlad. He's made a career out of calling people > > idiots > > >>>>- doesn't mean they are. > > >>>>-- > > >>> > > >>>Currently I don't have AGC in front of ADC, but I am keeping my signal > > >>low > > >>>so that ADC doesn't start clipping. I applied AGC on my baseband > > signal, > > >>>after digitization, before doing matched filtering for individual > > tones. > > >>I > > >>>am using this AGC to keep signal level in a range for symbol timing > > >>>synchronization. > > >>> > > >>>But Vlad says AGC is harmful in this setup, why? I would have asked him > > >>but > > >>>searching on the group, I found that he never gave an answer that could > > >>be > > >>>*useful* for anybody in the world . > > >>> > > >>>-- > > >> > > >>Randy or any body, please comment on this. > > >> > > >>Mite > > > > > >I think most people are unwilling to speculate why Vladimir thinks a > > >lot of things that he thinks. > > > > > True that. > > >AGC can be a complicated topic, especially for FM/FSK. AGC can be > > >useful, especially to manage composite power, etc. Much depends on > > >the system architecture and the requirements. > > > > > > > > That means I need to study more :) Thanks! > > > > Mite > > > > >>>Mite > > >>> > > >>>>Randy Yates > > >>>>Digital Signal Labs > > >>>>http://www.digitalsignallabs.com > > >>>> > > >>> > > >>>_____________________________ > > >>>Posted through www.DSPRelated.com > > >>> > > >> > > >>_____________________________ > > >>Posted through www.DSPRelated.com > > > > > >Eric Jacobsen > > >Anchor Hill Communications > > >http://www.anchorhill.com > > > > > > > _____________________________ > > Posted through www.DSPRelated.com
AGC is not a complicated topic at all. It is pretty easy. All you need is a way of finding the size of your signal - say by rectification or squaring or a non-linear device. Then you filter (or integrate) and feed back to a voltage-controlled amplifier (which can also be a multiplier). What's difficult in that? It requires a large amount of gain (maybe 120dB split in three) so layout is tricky.
On Tue, 1 Oct 2013 17:47:06 -0700 (PDT), gyansorova@gmail.com wrote:

>On Tuesday, October 1, 2013 6:10:32 PM UTC+13, mite_learner wrote: >> >On Mon, 30 Sep 2013 07:21:06 -0500, "mite_learner" <94814@dsprelated> >>=20 >> >wrote: >>=20 >> > >>=20 >> >>>>"mite_learner" <94814@dsprelated> writes: >>=20 >> >>>> >>=20 >> >>>>> Dear Members, >>=20 >> >>>>> >>=20 >> >>>>> I am experimenting on digital 4-FSK (orthogonal) communication >>=20 >> system.=20 >>=20 >> >> >>=20 >> >>>On >>=20 >> >>>>> the demodulation side, I am using AGC and then 4 filters to detect >>=20 >> >>>tones >>=20 >> >>>>> and then using symbol timing. My question is how can I know that I >>=20 >> >>>need >>=20 >> >>>>> equalization looking at the signal if I transmit and receive the >>=20 >> >>signal >>=20 >> >>>>> over the air? How can I verify that my signal is being affected by >>=20 >> >>>>> multipaths ? >>=20 >> >>>> >>=20 >> >>>>Did you mean AGC in front of your ADC? >>=20 >> >>>> >>=20 >> >>>>By the way, ignore Vlad. He's made a career out of calling people >>=20 >> idiots >>=20 >> >>>>- doesn't mean they are. >>=20 >> >>>>--=20 >>=20 >> >>> >>=20 >> >>>Currently I don't have AGC in front of ADC, but I am keeping my signal >>=20 >> >>low >>=20 >> >>>so that ADC doesn't start clipping. I applied AGC on my baseband >>=20 >> signal, >>=20 >> >>>after digitization, before doing matched filtering for individual >>=20 >> tones. >>=20 >> >>I >>=20 >> >>>am using this AGC to keep signal level in a range for symbol timing >>=20 >> >>>synchronization.=20 >>=20 >> >>> >>=20 >> >>>But Vlad says AGC is harmful in this setup, why? I would have asked hi= >m >>=20 >> >>but >>=20 >> >>>searching on the group, I found that he never gave an answer that coul= >d >>=20 >> >>be >>=20 >> >>>*useful* for anybody in the world .=20 >>=20 >> >>> >>=20 >> >>>-- >>=20 >> >> >>=20 >> >>Randy or any body, please comment on this. >>=20 >> >> >>=20 >> >>Mite >>=20 >> > >>=20 >> >I think most people are unwilling to speculate why Vladimir thinks a >>=20 >> >lot of things that he thinks. >>=20 >> > >>=20 >> True that. >>=20 >> >AGC can be a complicated topic, especially for FM/FSK. AGC can be >>=20 >> >useful, especially to manage composite power, etc. Much depends on >>=20 >> >the system architecture and the requirements. >>=20 >> > >>=20 >> > >>=20 >> That means I need to study more :) Thanks! >>=20 >>=20 >>=20 >> Mite >>=20 >>=20 >>=20 >> >>>Mite >>=20 >> >>> >>=20 >> >>>>Randy Yates >>=20 >> >>>>Digital Signal Labs >>=20 >> >>>>http://www.digitalsignallabs.com >>=20 >> >>>> =20 >>=20 >> >>> >>=20 >> >>>_____________________________ =09 >>=20 >> >>>Posted through www.DSPRelated.com >>=20 >> >>> =20 >>=20 >> >> >>=20 >> >>_____________________________ =09 >>=20 >> >>Posted through www.DSPRelated.com >>=20 >> > >>=20 >> >Eric Jacobsen >>=20 >> >Anchor Hill Communications >>=20 >> >http://www.anchorhill.com >>=20 >> > =20 >>=20 >>=20 >>=20 >> _____________________________ =09 >>=20 >> Posted through www.DSPRelated.com > >AGC is not a complicated topic at all. It is pretty easy. All you need is a= > way of finding the size of your signal - say by rectification or squaring = >or a non-linear device. Then you filter (or integrate) and feed back to a v= >oltage-controlled amplifier (which can also be a multiplier). What's diffic= >ult in that? It requires a large amount of gain (maybe 120dB split in three= >) so layout is tricky.
When a simple architecture like that works, it's not hard, and many systems have been implemented like that. But many systems aren't that simple, like if you're trying to demodulate multiple, independently faded signals through the same AFE, have a wide IF filter that can potentially let in a lot of adjacent energy that comes and goes, or want to use something dirt simple like a limiter to detect your signal but not get swamped by interferers or adjacents. It's all simple until you sort out something cool that gives you a big edge on your competition. ;) Eric Jacobsen Anchor Hill Communications http://www.anchorhill.com