Design and Verification of High-Order QAM Transceiver Systems for mmWave SDRs under Large Delay Multipath and High Frequency Offset Effects

Future communication technologies offer the benefits of wide coverage, low latency, and high speeds. In particular, low-Earth orbit (LEO) satellite transmission will play an important role in 5G and 6G systems. However, with high-speed mobile and high-frequency transmission, the Doppler effect can seriously affect the demodulation performance of the receiver. This paper addresses the problem of deriving factors such as large-delay multi-path interference and high-frequency offset effects when using high-order QAM modulation signals for long-distance communication, e.g., 256 QAM for LEO satellite communication. To overcome the high Doppler effect, we adopt a phase locked loop (PLL) with preprocessing high-order power operation and cross-correlation scheme. Next, an adaptive decision feedback equalizer is employed to eliminate the multipath factor. Furthermore, a hybrid LDPC channel decoder is utilized to improve packet error rate performance. Finally, we complete simulation and verification of the high-order QAM transceiver algorithms. Moreover, the actual measurements of the mmWave phase array software defined radio (SDR) platform confirm the proposed transceiver algorithms being useful in the high Doppler and large delay spread environments.