At this moment, we are work with microwave relay system.
And i tryd to find modulators/demodulators... nothing...
At this moment, we are use Altera's FPGA.
At www.altera.com you find Constallation Mapper/Demapper Megacore.
That help you to create modulator/demodulator.
QAM mod/demod chips for 155 Mb do not exist at this moment as far as I know.
This would in practice require a very high constellation like 1024 QAM, which you do not like to have.. Needs very good transmission medium and low phase noise.
I think you have more luck in the range of WLAN OFDM chipsets although 155 Mb is a lot...
Btw... you can play with those 'plug and play' IP blocks from Altera but those are not efficient with respect to hardware needs.
Furthermore.. 155Mb QAM ? Well.. good luck with your FPGA's...
Look Intersil site for Broadband wireless modems, modulation up to 128QAM, speed up to 238 Mbps:
h**p://w*w.intersil.com/data/an/an9969.pdf
h**p://w*w.intersil.com/data/an/an9934.pdf
At this time this is more integrated solution for high speed wireless modems .....