Channel with Doppler spread

I have a channel with a determinate Coherence Time. I want transmit
information very very slow with a symbol time very very long, but then i
have the problem that symbol time is longer than coherence time.

How can i solve that (if it is possible)?


Thanks

>I have a channel with a determinate Coherence Time. I want transmit
>information very very slow with a symbol time very very long, but then i
>have the problem that symbol time is longer than coherence time.
>
>How can i solve that (if it is possible)?
>
>
>Thanks
>
>
>


What is the 'determinate coherence time' that you have? 
This is going to cause doppler shift. You just have to make sure that the
symbol time is shorter than the coherence time

JAlbertoDJ wrote:

> I have a channel with a determinate Coherence Time. I want transmit
> information very very slow with a symbol time very very long, but then i
> have the problem that symbol time is longer than coherence time.

Then you are screwed. How to distinguish a symbol from a variation of 
the channel?

> How can i solve that (if it is possible)?

That could be possible in some special cases, but I doubt you can solve 
that.


Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

http://www.abvolt.com

>
>What is the 'determinate coherence time' that you have? 
>This is going to cause doppler shift. You just have to make sure that
the
>symbol time is shorter than the coherence time
>

That is the question, that i want symbol time would be very long.

>
>Then you are screwed. How to distinguish a symbol from a variation of 
>the channel?
>
>> How can i solve that (if it is possible)?
>
>That could be possible in some special cases, but I doubt you can solve 
>that.
>
>

In thats case, i will have to add redundancy.

With 1/2 Convolutional Coding i can reduce symbol time by two, but i need
more reduction if it were possible.

I am thinking in use bi-orthogonal codes in addittion to convolutional
coding but i need to be sure gain code will be at least of 0dBs.

On Oct 12, 9:07&#4294967295;am, "JAlbertoDJ" <nietoro...@yahoo.es> wrote:
> I have a channel with a determinate Coherence Time. I want transmit
> information very very slow with a symbol time very very long, but then i
> have the problem that symbol time is longer than coherence time.
>
> How can i solve that (if it is possible)?
>
> Thanks

Your problem is ill-posed. You should "design" your transmitted signal
according to the channel condition, not simply specify what kind of
signal to use.

>Your problem is ill-posed. You should "design" your transmitted signal
>according to the channel condition, not simply specify what kind of
>signal to use.
>

For that reason i have speak about "Coherence Time of Channel". But, i
could give other parameter for undernstand better my question:  

Bit Rate requiered: As low as be possible.

>
>>Your problem is ill-posed. You should "design" your transmitted signal
>>according to the channel condition, not simply specify what kind of
>>signal to use.
>>
>
>For that reason i have speak about "Coherence Time of Channel". But, i
>could give other parameter for undernstand better my question:  
>

This is what xsong is saying. If you know what is the coherence time, then
why can not you design your signal such that your symbol time is equal to
or less than coherence time.

In case your coherence time is equal to symbol time, which means that the
channel changes every symbol, and if the fading is flat (Rayleigh or
Rician) then you can use any coding technique (Turbo, LDPC) or coded
modulation such as BICM-ID or may be diversity techniques.

I hope this helps.

Chintan

>This is what xsong is saying. If you know what is the coherence time,
then
>why can not you design your signal such that your symbol time is equal
to
>or less than coherence time.
>
>In case your coherence time is equal to symbol time, which means that
the
>channel changes every symbol, and if the fading is flat (Rayleigh or
>Rician) then you can use any coding technique (Turbo, LDPC) or coded
>modulation such as BICM-ID or may be diversity techniques.
>
>I hope this helps.
>
>Chintan
>

Because i wondered if i could select a symbol time longer than coherence
time, equalizing of any manner or so but i think that it is not possible.

Then,symbol time could not be longer than coherence time.

At the end, coding technique will be Convolutional 1/2 K=7.

Thanks

JAlbertoDJ wrote:
>> Your problem is ill-posed. You should "design" your transmitted signal
>> according to the channel condition, not simply specify what kind of
>> signal to use.
>>
> 
> For that reason i have speak about "Coherence Time of Channel". But, i
> could give other parameter for undernstand better my question:  
> 
> Bit Rate requiered: As low as be possible.

Then send one bit a week, or is that too often?

Jerry
-- 
Engineering is the art of making what you want from things you can get.
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