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Message started by srikanthvajjala on Jan 10th, 2011 at 8:07am

Title: Nyquist filter bandwidth
Post by srikanthvajjala on Jan 10th, 2011 at 8:07am
I have a data rate of 2.048 Mbps data rate. I need to modulate at 70 MHz by using QPSK modulation.
I selected a filter bandwidth of 1.3312 MHz which is 1.3 times of symbol rate. My question is incase if i have a nyquist bandwidth filter(datarate/2=1.024MHz) is available at 70 MHz can i use that kind of filter ? In this case 1 time of the symbol rate. Please clarify.

Title: Re: Nyquist filter bandwidth
Post by Eric Johnston on Jan 10th, 2011 at 4:09pm
An important consideration for you should be the specification that you are trying to meet in terms of the spectrum of your transmiied signal to avoid unacceptable interference to adjacent carriers.

These links may help you:
http://en.wikipedia.org/wiki/Raised-cosine_filter
http://www.nonstopsystems.com/radio/article-raised-cosine.pdf
http://en.allexperts.com/q/Satellite-Communications-2436/2009/9/Roll-Factor.htm
http://www.freqdev.com/guide/DgtlFltrDsgnGd.pdf

If your information rate is 2048 kbit/s don't forget to add the FEC overhead, if applicable, to get the higher transmission rate.

Best regards, Eric.

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