MATLAB: How to set the passband gain to be 0 dB when using the raised cosine transmit / receive filter blocks in Communications Blockset 3.0 (R14) and later versions

Question

I want to be able to set my passband gain to 0 dB when using the Raised Cosine Transmit/Receive Filter blocks.

I tried to put "1" as the "Linear Amplitude Filter Gain" parameter, but when I looked at the filter's frequency response (for instance, by using FVTool), I see that its passband gain is not 0dB.

Answer 1

This change has been incorporated into the documentation in Release 14 Service Pack 3 (R14SP3). For previous releases, read below for any additional information:

In order to set your passband gain to 0dB, adjust the parameters as follows:

In the Raised Cosine Receive Filter block:

1. Choose "Filter gain" parameter to be "User Specified".

2. Choose "input samples per symbols (N)" parameter to be the inverse of the "Linear amplitude filter gain" parameter.

The Filter's gain (dB) in the passband will be:

20*log(T*Gain) in the case of a normal filter, and

20*log(sqrt(T)*Gain) in the case of a Square root filter.

Where 'T' is the 'input samples per symbols (N)' parameter in the Receive filter or the 'Unsampling factor (N)' parameter in the Transmit filter, and 'Gain' is the 'Linear amplitude filter gain' parameter.

You should match T = 1/Gain (or T=1/((Gain)^2) for square root filter) to get a gain of 0dB.