Juquan Mao

A low complexity 256QAM soft demapper for 5G mobile system

The future wireless network demands higher-level modulation to enhance spectral efficiency, which means a symbol-to-bit soft demapper with much higher complexity is required if using conventional demapping algorithm. In this paper, we proposed a low-complexity soft demapper for 256 QAM. Simulations show that it achieves much lower complexity with the negligible performance degradation in comparison with max-log-MAP demapper.

Output SNR Analysis and Detection Criteria for Optimum DCT-Based Multicarrier System

The discrete cosine transform (DCT) based multicarrier system is regarded as one of the complementary multicarrier transmission techniques for 5th Generation (5G) applications in near future. By employing cosine basis as orthogonal functions for multiplexing each real-valued symbol with symbol period of T, it is able to reduce the minimum orthogonal frequency spacing to 1/(2T) Hz, which is only half of that compared to discrete Fourier transform (DFT) based multicarrier systems. Critical to the optimal DCT-based system design that achieves interference-free single-tap equalization, not only both prefix and suffix are needed as symmetric extension of information block, but also a so-called front-end pre-filter is necessarily introduced at the receiver side. Since the pre-filtering process is essentially a time reversed convolution for continuous inputs, the output signal-to-noise ratio (SNR) for each subcarrier after filtering is enhanced. In this paper, the impact of pre-filtering on the system performance is analyzed in terms of ergodic output SNR per subcarrier. This is followed by reformulated detection criterion where such filtering process is taken into consideration. Numerical results show that under modified detection criteria, the proposed detection algorithms improve the overall bit error rate (BER) performance effectively.