Aijun Cao

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.

Frequency offset estimation based on PRACH preambles in LTE

This paper presents a novel method to estimate the frequency offset between a mobile phone and the infrastructure when the mobile phone initially attaches to the LTE network. The proposed scheme is based on PRACH (Physical Random Access Channel) preambles and can significantly reduce the complexity of preamble detection at the eNodeB side.

Performance analysis of an ultra dense network with and without cell cooperation

This paper presents an analysis on performance of an ultra dense network (UDN) with and without cell cooperation from the perspective of network information theory. We propose a UDN performance metric called Total Average Geometry Throughput which is independent from the user distribution or scheduler etc. This performance metric is analyzed in detail for UDN with and without cooperation. The numerical results from the analysis show that under the studied system model, the total average geometry throughput reaches its maximum when the inter-cell distance is around 6 ~ 8 meters, both without and with cell cooperation. Cell cooperation can significantly reduce inter-cell interference but not remove it completely. With cell cooperation and an optimum number of the cooperating cells the maximum performance gain can be achieved. Furthermore, the results also imply that there is an optimum aggregate transmission power if considering the energy cost per bit.

Performance evaluation and comparison of different multicarrier modulation schemes

Several techniques such as carrier aggregation (CA) and cognitive radio (CR) have been proposed to achieve high data rates to meet the demand of future wireless communication systems. Those techniques pose a strict adjacent channel interference (ACI) requirement. However, currently employed orthogonal frequency division multiplexing (OFDM) systems suffer from significant spectrum leakage and require large guard bands to avoid ACI. To tackle this problem, there is a need to explore new suitable multicarrier modulation (MCM) schemes that can exhibit lower ACI. In this paper, we compare the conventional OFDM with the OFDM with transmit windowing (WOFDM) and Filter Bank based Multicarrier (FBMC) system to explore potential candidates to fulfil the ACI requirement. Those MCM schemes are compared in terms of better spectral containment, throughput, bit error rate (BER) performance and complexity.

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.

Frequency domain pilot-based carrier frequency offset estimation in SC-FDMA system

Carrier frequency offset estimation in Single Carrier Frequency Division Multiple Access (SC-FDMA) system is a challenging task. In this paper, a novel estimation method based on the pilot signal in frequency domain is proposed. This algorithm does not require the knowledge of the channel, and only one pilot symbol is needed for frequency offset estimation. These promising features will facilitate its deployment in the current systems without changing the air-interface. A performance evaluation is conducted over Demodulation Reference Signal in Evolved Universal Terrestrial Radio Access uplink SC-FDMA system. In frequency selective channels, it has the least estimation error among three benchmark methods in large CFO scenarios.