srjecsSRJECSSRJECS2788-9408https://doi.org/10.47310/srjecs.2025.v05i02.006Investigation on the BER Performance of Odd-Bit Cross M-QAM based SC-FDMA Systems in the Presence of AWGN and Phase NoiseAdaptive QAM is critical scheme that provides communication systems with the ability to adapt to the varying channel fluctuations and preserve an acceptable level of spectral efficiency. In order to further enhance the adaptive QAM performance, odd-bit cross QAM modulation schemes had long been suggested as a candidate to improve the adaptive QAM transmission efficiency of modern communication systems like SC-FDMA and OFDM systems. The superior performance of cross odd bit QAM in terms of bit error rate (BER) and peak to average power ratio (PAPR) compared to the rectangular odd-bit schemes had made it the best choice whenever an odd-bit modulation scheme implementation is intended. Though many researches and articles extensively studied and analyzed the performance of odd-bit QAM schemes for various communication systems, BER performance under the simultaneous presence of additive white Gaussian noise (AWGN) and phase noise (PhN) impairments for odd-bit cross QAM based communication systems caught almost no research interest. In this paper, the BER performance for SC-FDMA system with odd-bit cross QAM is investigated with the simultaneous presence of AWGN and phase noise for various modulation sizes. The results shows that cross odd-bit QAM schemes show better uncoded BER performance in lower modulation orders, while offering only marginal improvements at higher orders. For instance, at a phase noise standard deviation of 10°, 8-QAM achieved a substantial logarithmic BER gain of 8.7 dB over 16-QAM, whereas 128-QAM showed a modest gain of just 1.4 dB compared to 256-QAM.