Mazari
2009-10-23, 02:18 PM
Hi Guys
I don't know if this is the right section but I didn't know where to ask this question. While reading about Flat Fading and Frequency Selective Fading I found a couple of examples (one in a book and the other one online) that confused me.
Example 1) (Book)
The example says that the Coherence Bandwidth of a channel is 250 KHz. Since a GSM channel = 200 KHz, the Bandwidth of the signal < Bandwidth of the Channel, so we got Flat Fading and there was not need for an equalizer. (All spectral components with almost equal gain and linear phase).
Example 2) (Online)
This example says that one reason for designing the CDMA IS-95 waveform with a bandwidth of approximately 1.25 MHz is because in many urban signaling environments the Coherence Bandwidth is approximately 333 KHz which is significantly less than 1.25 MHz. So, Bandwidth of the signal > Bandwidth of the Channel. Here we got Frequency Selective Fading. Therefore, the example says, when fading occurs it occurs only over a relatively small fraction of the total CDMA signal bandwidth.
The Flat Fading example is given as it was better than Frequency Selective Fading and the Frequency Selective example says the opposite.
In your experience...What's less problematic?? Flat Fading or Frequency Selective Fading??. Do you want a channel to be flat?
Best Regards
I don't know if this is the right section but I didn't know where to ask this question. While reading about Flat Fading and Frequency Selective Fading I found a couple of examples (one in a book and the other one online) that confused me.
Example 1) (Book)
The example says that the Coherence Bandwidth of a channel is 250 KHz. Since a GSM channel = 200 KHz, the Bandwidth of the signal < Bandwidth of the Channel, so we got Flat Fading and there was not need for an equalizer. (All spectral components with almost equal gain and linear phase).
Example 2) (Online)
This example says that one reason for designing the CDMA IS-95 waveform with a bandwidth of approximately 1.25 MHz is because in many urban signaling environments the Coherence Bandwidth is approximately 333 KHz which is significantly less than 1.25 MHz. So, Bandwidth of the signal > Bandwidth of the Channel. Here we got Frequency Selective Fading. Therefore, the example says, when fading occurs it occurs only over a relatively small fraction of the total CDMA signal bandwidth.
The Flat Fading example is given as it was better than Frequency Selective Fading and the Frequency Selective example says the opposite.
In your experience...What's less problematic?? Flat Fading or Frequency Selective Fading??. Do you want a channel to be flat?
Best Regards