when a band pass filter cannot be used in a reception

[Xavipersonal]

Hi,
I would like to know in which situations is not possible the use of a Band Pass Filter in the reception of a communication.
I am implementing and alternative system and it would be nice to know when is better to use it in stead of a BPF and a demodulation signal, for example.

Thanks a lot in advance

 

[WimRFP]

Hello,

Could you be so kind to clarify your request?

 

[Xavipersonal]

yes, i ll try.

I am implementing a communication transmission in Matlab, it means, there are a transmitter and a receiver.
Modulation could be ASK. I have programmed a 'weak signal detection method' in the receiver but it doesnt work as well as 'a coherent detection system (BPF + cos(wt))' works.
The point is that my 'weak signal detection method' doesn't use Band Pass Filter, so I try to figure out in which situation could be more favorable my system. That means, in which situation in the reception, a band pass filter is not able to be used and my system would be better.
Hope this clarify

Thanks for your time!

 

[WimRFP]

Hello,

Theoretically spoken a coherent ASK/BSP detection scheme doesn’t require a BPF. With coherent I mean: signal plus noise is downconverted to DC. The mixer (downconverter) uses a phase-synchronized oscillator. An LPF after the mixer removes out of band products and the result is the base band data with in band noise.

Most non-coherent hardware schemes require BPF to remove out of band noise and require somewhat better S/N ratio for certain Bit Error Rate.

I assume that you are into wavelet and special FFT detection schemes. This is beyond my knowledge to determine whether or not a PBF is required. My feeling says that theoretically spoken a BPF is not required. But from a practical standpoint of view (limitations in dynamic range), you may require some form of BPF to reduce the total noise power.