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what is the signal carrier frequency?
what is the signal bandwidth?
what is the transport medium?
EDIT: are you sure you have to implement 16 qam, for beginner QPSK would be much more suitable .. then you can try to upgrade to 8PSK and when you master that, only then I'd suggest you try yourself with qam .. but .
16qam is cool, give you more data tp on same bw compared to 8psk or qpsk .. problem is that it requires 2 level bigger dish for example in sat comm then 8psk (or 3-4 level bigger dish then qpsk) meaning that if your sat channel is qpsk modulated and you can catch it with 60cm dish (prime focus) that means that you need 2.4m dish to be able to receive 16qam with the same power output on transponder to achieve same error rate... you can reduce FEC to gain some virtual power but all in all 16qam modulation can be only used with very strong signal...
If OP want to make modem implementing modulation himself - that is absolutely out of his abilities 1/1 but if he want to use some of the available chips (like the ad one) for modulation it is theoretically possible but still unlikely ..