aaron_do
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Hi,
You missed out one important piece of information which is the signal bandwidth. For the phase variation, you will mainly be concerned with ISI (inter-symbol interference). I believe a rule of thumb is generally you want the group delay variation of your filter to be less than 0.1 times the data period. Your filter rejection should be more than 60 dB + the required SNR for your specified BER. With those two requirements, you should be able to use filter tables or online calculators to find out what kind of filter would work (i.e. the shape of the response, and the filter order).
If your requirements turn out to be too stringent, you could consider using a digital filter. You will still need to design an anti-aliasing filter, but it will be significantly easier, especially with a high ADC sampling rate. Digital filters can be designed with excellent rejection, and zero group-delay variation.
BTW, you may have another problem to worry about, but I'm not sure how serious it is. If your channels are 500 kHz apart, and you use a 1 MHz IF, then the channel at 11 MHz or 15 MHz (is there one?) will be your image channel. Your IRR (image-rejection ratio) will need to be more than 60 dB + SNR req.. At RF, that would be a very tall order, but at IF it may be do-able. You can refer to Razavi's RF Microelectronics book to see what kind of LO IQ balance you will need to achieve that. If you down-convert to zero-IF, you can avoid the image problem and also loosen the requirements on your channel filter.
regards, Aaron
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