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Old 01-25-2010, 01:20 AM
Nitram
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Default Doppler spread question


I have two questions about Doppler spread in a wireless channel (I a
assuming a Rician of Rayleigh channel).

Firstly, how can I compute a channel’s rate of change? Is it equal t
its Doppler frequency i.e. inverse of the time coherence of the channel? I
so, that would mean that for a system where the transmitter does not mov
relative to the receiver, the channel would never change, which is no
true. Could someone enlighten me on the topic?

Secondly, does the Doppler spectrum spread represent the power envelop o
the signal, or is the leakage present at every instant i.e. at any give
instant, is the power for the frequencies between –fd and fd alway
non-zero, or does it vary randomly between the limits? (fd being th
doppler frequency).

If I was unclear in any of the questions, let me know and I will do m
best to clarify my question.

Thank you for your help.


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Old 01-26-2010, 04:37 PM
Mark
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Default Re: Doppler spread question

On Jan 24, 8:20*pm, "Nitram" <[email protected]> wrote:
> I have two questions about Doppler spread in a wireless channel (I am
> assuming a Rician of Rayleigh channel).
>
> Firstly, how can I compute a channels rate of change? Is it equal to
> its Doppler frequency i.e. inverse of the time coherence of the channel? If
> so, that would mean that for a system where the transmitter does not move
> relative to the receiver, the channel would never change, which is not
> true. Could someone enlighten me on the topic?
>
>


Not only the Tx and Rx but also movement of some reflector or obstacle
object in the propogation path can cause the channel to change.

If really NOTHING is moving, then you are correct, the channel would
never change.

Mark


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  #3 (permalink)  
Old 02-02-2010, 04:33 PM
Nitram
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Default Re: Doppler spread question

>On Jan 24, 8:20=A0pm, "Nitram" <[email protected]> wrote:
>> I have two questions about Doppler spread in a wireless channel (I am
>> assuming a Rician of Rayleigh channel).
>>
>> Firstly, how can I compute a channel=92s rate of change? Is it equa

to
>> its Doppler frequency i.e. inverse of the time coherence of th

channel? =
>If
>> so, that would mean that for a system where the transmitter does no

move
>> relative to the receiver, the channel would never change, which is not
>> true. Could someone enlighten me on the topic?
>>
>>

>
>Not only the Tx and Rx but also movement of some reflector or obstacle
>object in the propogation path can cause the channel to change.
>
>If really NOTHING is moving, then you are correct, the channel would
>never change.
>
>Mark
>
>
>

Thank you for your reply Mark. Assuming Tx and Rx are static relative t
each other (0Hz doppler), can we assume a specific rate of change for th
channel due to moving obstacles (i.e. is there a rule of thumb or any othe
reasoning that allows us to predict the rate of change of the channel)?

Thank you!
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