Carrier frequency for bandlimited channel

Hi
I would like to know can anyone explain to me is there any way to figure
out the appropriate carrier frequency(For modulation) for a given signal
frequency response and bandwidth and channel frequency response? 
I mean what criteria determine the carrier frequency ? I know it should be
higher than signal frequency but by how much ? What are the techniques to
find the best carrier frequency range?

For example assume we have signal frequency between 0-150 kHz and channel
bandwidth 0-100kHz and I would like to modulate the signal by a carrier,
what methods I can use to find the best carrier frequency ?
---------------------------------------
Posted through http://www.DSPRelated.com

On Wednesday, August 12, 2015 at 7:24:46 PM UTC+12, chess wrote:
> Hi
> I would like to know can anyone explain to me is there any way to figure
> out the appropriate carrier frequency(For modulation) for a given signal
> frequency response and bandwidth and channel frequency response? 
> I mean what criteria determine the carrier frequency ? I know it should be
> higher than signal frequency but by how much ? What are the techniques to
> find the best carrier frequency range?
> 
> For example assume we have signal frequency between 0-150 kHz and channel
> bandwidth 0-100kHz and I would like to modulate the signal by a carrier,
> what methods I can use to find the best carrier frequency ?
> ---------------------------------------
> Posted through http://www.DSPRelated.com

What method of modulation are we talking?

>On Wednesday, August 12, 2015 at 7:24:46 PM UTC+12, chess wrote:
>> Hi
>> I would like to know can anyone explain to me is there any way to
figure
>> out the appropriate carrier frequency(For modulation) for a given
signal
>> frequency response and bandwidth and channel frequency response? 
>> I mean what criteria determine the carrier frequency ? I know it
should
>be
>> higher than signal frequency but by how much ? What are the techniques
to
>> find the best carrier frequency range?
>> 
>> For example assume we have signal frequency between 0-150 kHz and
channel
>> bandwidth 0-100kHz and I would like to modulate the signal by a
carrier,
>> what methods I can use to find the best carrier frequency ?
>> ---------------------------------------
>> Posted through http://www.DSPRelated.com
>
>What method of modulation are we talking?

Assume PSK modulations like BPSK 
---------------------------------------
Posted through http://www.DSPRelated.com

On 12.8.15 17:28, chess wrote:
>> On Wednesday, August 12, 2015 at 7:24:46 PM UTC+12, chess wrote:
>>> Hi
>>> I would like to know can anyone explain to me is there any way to
> figure
>>> out the appropriate carrier frequency(For modulation) for a given
> signal
>>> frequency response and bandwidth and channel frequency response?
>>> I mean what criteria determine the carrier frequency ? I know it
> should
>> be
>>> higher than signal frequency but by how much ? What are the techniques
> to
>>> find the best carrier frequency range?
>>>
>>> For example assume we have signal frequency between 0-150 kHz and
> channel
>>> bandwidth 0-100kHz and I would like to modulate the signal by a
> carrier,
>>> what methods I can use to find the best carrier frequency ?
>>> ---------------------------------------
>>> Posted through http://www.DSPRelated.com
>>
>> What method of modulation are we talking?
>
> Assume PSK modulations like BPSK



Please do not post a separate thread into another group. I found
a post with essentially the same contents in sci.electronics.design.

If your signal is an analog real signal with a bandwidth of 150 kHz,
it will not fit into a channel of 100 kHz width.

If the signal is a bit stream, please say so.

The carrier frequency should be high enough so that no significant
sideband energy goes at or below zero frequency. The design of your
transmission channel can have a more stringent lower frequency limit.

-- 

-TV

>On 12.8.15 17:28, chess wrote:
>>> On Wednesday, August 12, 2015 at 7:24:46 PM UTC+12, chess wrote:
>>>> Hi
>>>> I would like to know can anyone explain to me is there any way to
>> figure
>>>> out the appropriate carrier frequency(For modulation) for a given
>> signal
>>>> frequency response and bandwidth and channel frequency response?
>>>> I mean what criteria determine the carrier frequency ? I know it
>> should
>>> be
>>>> higher than signal frequency but by how much ? What are the
techniques
>> to
>>>> find the best carrier frequency range?
>>>>
>>>> For example assume we have signal frequency between 0-150 kHz and
>> channel
>>>> bandwidth 0-100kHz and I would like to modulate the signal by a
>> carrier,
>>>> what methods I can use to find the best carrier frequency ?
>>>> ---------------------------------------
>>>> Posted through http://www.DSPRelated.com
>>>
>>> What method of modulation are we talking?
>>
>> Assume PSK modulations like BPSK
>
>
>
>Please do not post a separate thread into another group. I found
>a post with essentially the same contents in sci.electronics.design.
>
>If your signal is an analog real signal with a bandwidth of 150 kHz,
>it will not fit into a channel of 100 kHz width.
>
>If the signal is a bit stream, please say so.
>
>The carrier frequency should be high enough so that no significant
>sideband energy goes at or below zero frequency. The design of your
>transmission channel can have a more stringent lower frequency limit.
>
>-- 
>
>-TV

Thanks. Yes assume signal is a bit stream meaning series of rectangular
pulses therefore it has many side lobes, in this case what is the best way
to figure out the carrier frequency?

Thanks
---------------------------------------
Posted through http://www.DSPRelated.com

On Wed, 12 Aug 2015 02:24:41 -0500, "chess" <106766@DSPRelated> wrote:

>Hi
>I would like to know can anyone explain to me is there any way to figure
>out the appropriate carrier frequency(For modulation) for a given signal
>frequency response and bandwidth and channel frequency response? 
>I mean what criteria determine the carrier frequency ? I know it should be
>higher than signal frequency but by how much ? What are the techniques to
>find the best carrier frequency range?
>
>For example assume we have signal frequency between 0-150 kHz and channel
>bandwidth 0-100kHz and I would like to modulate the signal by a carrier,
>what methods I can use to find the best carrier frequency ?
>---------------------------------------
>Posted through http://www.DSPRelated.com

As has been pointed out, your signal doesn't fit in your channel
bandwidth, so that may be a problem.

In a theoretical sense the carrier frequency can be anything higher
than half the bandwidth plus a little for guardband, just enough that
energy wrapping back across DC doesn't interfere too much.   Really,
you can put it anywhere in the spectrum theoretically.

Practically, there are a lot of things that will determine what
frequency or frequency band your signal should be in, with a Big One
being regulations.   You can't just broadcast on any frequency if it's
wireless.   If you're sending a signal down a cable, then you need to
know if there are any other signals on that cable so that you don't
interfere with them.

If you have a channel frequency response, that will only be valid for
the frequency at which it was measured or estimated.   Put it
somewhere else and you may get a different response.

Cost will have a impact as well, as some radio architectures,
amplifiers, and antennas cost more or less and take up more or less
room and weigh more or less than others.  

Most of the things that determine that carrier frequency have pretty
much zero to do with the signal or its bandwidth.


Eric Jacobsen
Anchor Hill Communications
http://www.anchorhill.com

>On Wed, 12 Aug 2015 02:24:41 -0500, "chess" <106766@DSPRelated> wrote:
>
>>Hi
>>I would like to know can anyone explain to me is there any way to
figure
>>out the appropriate carrier frequency(For modulation) for a given
signal
>>frequency response and bandwidth and channel frequency response? 
>>I mean what criteria determine the carrier frequency ? I know it should
be
>>higher than signal frequency but by how much ? What are the techniques
to
>>find the best carrier frequency range?
>>
>>For example assume we have signal frequency between 0-150 kHz and
channel
>>bandwidth 0-100kHz and I would like to modulate the signal by a
carrier,
>>what methods I can use to find the best carrier frequency ?
>>---------------------------------------
>>Posted through http://www.DSPRelated.com
>
>As has been pointed out, your signal doesn't fit in your channel
>bandwidth, so that may be a problem.
>
>In a theoretical sense the carrier frequency can be anything higher
>than half the bandwidth plus a little for guardband, just enough that
>energy wrapping back across DC doesn't interfere too much.   Really,
>you can put it anywhere in the spectrum theoretically.
>
>Practically, there are a lot of things that will determine what
>frequency or frequency band your signal should be in, with a Big One
>being regulations.   You can't just broadcast on any frequency if it's
>wireless.   If you're sending a signal down a cable, then you need to
>know if there are any other signals on that cable so that you don't
>interfere with them.
>
>If you have a channel frequency response, that will only be valid for
>the frequency at which it was measured or estimated.   Put it
>somewhere else and you may get a different response.
>
>Cost will have a impact as well, as some radio architectures,
>amplifiers, and antennas cost more or less and take up more or less
>room and weigh more or less than others.  
>
>Most of the things that determine that carrier frequency have pretty
>much zero to do with the signal or its bandwidth.
>
>
>Eric Jacobsen
>Anchor Hill Communications
>http://www.anchorhill.com

But as I said my signal is bit streams therefore its side lobes stays
forever therefore with your reasoning it does not fit in any channel.
Therefore there is no good carrier frequency for that. 
---------------------------------------
Posted through http://www.DSPRelated.com

On Wed, 12 Aug 2015 12:26:23 -0500, "chess" <106766@DSPRelated> wrote:

>>On Wed, 12 Aug 2015 02:24:41 -0500, "chess" <106766@DSPRelated> wrote:
>>
>>>Hi
>>>I would like to know can anyone explain to me is there any way to
>figure
>>>out the appropriate carrier frequency(For modulation) for a given
>signal
>>>frequency response and bandwidth and channel frequency response? 
>>>I mean what criteria determine the carrier frequency ? I know it should
>be
>>>higher than signal frequency but by how much ? What are the techniques
>to
>>>find the best carrier frequency range?
>>>
>>>For example assume we have signal frequency between 0-150 kHz and
>channel
>>>bandwidth 0-100kHz and I would like to modulate the signal by a
>carrier,
>>>what methods I can use to find the best carrier frequency ?
>>>---------------------------------------
>>>Posted through http://www.DSPRelated.com
>>
>>As has been pointed out, your signal doesn't fit in your channel
>>bandwidth, so that may be a problem.
>>
>>In a theoretical sense the carrier frequency can be anything higher
>>than half the bandwidth plus a little for guardband, just enough that
>>energy wrapping back across DC doesn't interfere too much.   Really,
>>you can put it anywhere in the spectrum theoretically.
>>
>>Practically, there are a lot of things that will determine what
>>frequency or frequency band your signal should be in, with a Big One
>>being regulations.   You can't just broadcast on any frequency if it's
>>wireless.   If you're sending a signal down a cable, then you need to
>>know if there are any other signals on that cable so that you don't
>>interfere with them.
>>
>>If you have a channel frequency response, that will only be valid for
>>the frequency at which it was measured or estimated.   Put it
>>somewhere else and you may get a different response.
>>
>>Cost will have a impact as well, as some radio architectures,
>>amplifiers, and antennas cost more or less and take up more or less
>>room and weigh more or less than others.  
>>
>>Most of the things that determine that carrier frequency have pretty
>>much zero to do with the signal or its bandwidth.
>>
>>
>>Eric Jacobsen
>>Anchor Hill Communications
>>http://www.anchorhill.com
>
>But as I said my signal is bit streams therefore its side lobes stays
>forever therefore with your reasoning it does not fit in any channel.

Explain what you meant by your signal having a bandwidth of 0-150kHz
and the channel being 100kHz wide?

>Therefore there is no good carrier frequency for that. 

Did you just answer your own question?




Eric Jacobsen
Anchor Hill Communications
http://www.anchorhill.com

Eric Jacobsen <eric.jacobsen@ieee.org> wrote:
> On Wed, 12 Aug 2015 12:26:23 -0500, "chess" <106766@DSPRelated> wrote:

(snip)
>>But as I said my signal is bit streams therefore its side lobes stays
>>forever therefore with your reasoning it does not fit in any channel.
 
> Explain what you meant by your signal having a bandwidth of 0-150kHz
> and the channel being 100kHz wide?
 
>>Therefore there is no good carrier frequency for that. 
 
> Did you just answer your own question?

If the signal is a bit stream, such that you have 0's and 1's
at 150kHz, there are many ways to encode that in a 100kHz channel.

You have to recode it such that more than one bit goes into each
sample (usually symbol when describing such modulation methods)
and the symbol rate is low enough.

Consider that gigabit ethernet gets 1Gb/s down 100MHz channels?

When you do this, you trade S/N for bandwidth.

It is a little less obvious for analog signals. Quadrature modulation
lets you get two signals in the bandwidth for one, with just a tiny
but of extra information. 

-- glen

On Wed, 12 Aug 2015 12:26:23 -0500, chess wrote:

<< snip >>
> But as I said my signal is bit streams therefore its side lobes stays
> forever therefore with your reasoning it does not fit in any channel.
> Therefore there is no good carrier frequency for that.

Are you trolling, or do you really need an answer?

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com