OFDM, Narrowband noise and Frequency selective fad

[khmaies]

Dear Admin,

First of all thank you very much for setting up such a helpful site.

I am actually working on OFDM and different type of noises. narrowband interference, frequency selective fading channel and AWGN.

I would like to understand more the OFDM and the OFDM symbols transmitted to the channel, how they look like. And how the noise effect the transmitted data.

My questions are:


1-Adding Narrowband noise. How the narrow band noise look like. Do you have a model for the narrow band noise. And how it will effect the transmitted data. Can I suppose that the Narrowband noise is just saturating the data at the receiver which is the demodulator.

Is it correct to say that at the receiver, instead to receive 1 0 0 1 for example I will receive 1 1 1 1. Is it correct to say that.

2- Frequency selective fading channel.
Can predict, at which is frequency I will have fading( like in Narrowband interference we can know which is the frequency will be affected). Is there a type of frequency selective fading channel where I can predict such noise.
Is the fading for a certain period of time like the case for the Narrow band interference. In the case of frequency selective fading channel, how my received data will look like. Like in Narrowband, the output is saturated, what will be the case in the frequency selective channel.


Thank you very much for your help.
Kind regards
Khmaies

[bavithi]

Hi Everybody,
I'm trynig to calculate the IBO & OBO of a Saleh HPA in a OFDM system. I need to know if to calculate IBO, do I need to have just the amplitude of the OFDM signal or a complex OFDM signal(The output of the IFFT Operation)?

Thank you.

Regds,
Bavithi.

[charan langton]

The IBO is the power of the input signal normalized to the maximum input power. So 0 dB IBO means you are at maximum input power of the amplifier.

Lets say that your amplifier can handle a maximum of 1 watt input power, and can produce 10 watt output power. The IBO at this point is 0 dB, and so is the OBO, which is normalized to 10 watts. Since these are normalized to their maximum values, you can not determine the absolute gain of the amplifier from the IBO, OBO values.

Now as you reduce the power, the IBO will decrease. 3 dB IBO means you have input half a watt. The OBO will also go down, depending on your IBO/OBO relationship, which is different for every amplifier. Before any kind of analysis of an amplifier, you need to know this relationship, which is sometimes given in IBO/OBO and sometimes in actual power out such as dBms. To get IBO/OBO from dBms. read my tutorial.

IBI/OBO are usually referred to as positive numbers because they are backoffs from the maximum number.

There is no such thing as a Saleh amplifier. This is a way of characterizing the IBO/OBO relationship by way of curve fitting.

So to measure your IBO, just measure the power out of the modulator and divide by maximum power. For an OFDM signal this is just the amplitude squared.

Charan Langton

[kader]

Hi everybody,
I am learning how to simulate OFDM on matlab. I need your help for an simple program for simulation.
Thanks

[kader]

Please!
Let me precise that i have trouble with multiple path and how to arrange the data .