exceptionally large EVM reported by MMIMO_RECEIVER.py under simulated channels

[tingjunchen]

For some reason the EVM reported by MMIMO_RECEIVER.py with --mode=AWGN is exceptionally large. See screenshots below with --mode=REPLAY (first figure, using data collected from USRP SDRs) and with --mode=AWGN (second figure), on the same UL .bin file.

Also, please check that EVM is computed based on TX symbols (instead of the "closest" symbol on the I/Q plane which would likely to give very good EVM...)