Hi Zilliang11,
QPSK modulates information using phase shifts, requiring precise phase detection and correction mechanisms to decode data accurately. PAM4 modulates information using amplitude changes, focusing on distinguishing between four distinct amplitude levels. Simply replacing QPSK modules with PAM4 ones will not work directly, as PAM4 demands a different detection approach specific to amplitude variations.
In“commqpsktxrx_init.m”, various parameters need to be changed to work with amplitude. For example, the“TimingErrorDetectorGain”, which is currently set for both in-phase and quadrature components, should be adjusted for the single amplitude-modulated signal used in PAM4. It is important to note that QPSK has two components(in-phase and quadrature), and PAM has a single. Parameters such as “SimParams.PhaseRecoveryLoopBandwidth=0.01” and “SimParams.PhaseRecoveryDampingFactor = 1;” are not required because they are specific to QPSK modulation. Therefore, I suggest removing and adding parameters, accordingly, discarding the ones not needed to avoid confusion.
In the Simulink part, various blocks that are suggested in the model are tuned for QPSK based modelling. For example, the receiver model is tuned for detection of phase signals. The“Phase Ambiguity Correction & Demodulation”subsystem rotates the input signal by the estimated phase offset and demodulates the corrected data which is purely used for phase demodulation techniques and simply adding a PAM4 demodulator block will result in incorrect outputs.
The incorrect text information is arising because of fundamental differences between QPSK and PAM4 which should be addressed.
I hope this provides some clarifying insights!
