Xiaolong Zhu

Novel Space-Time Coding and Mapping Scheme in Single-Carrier FDMA Systems

In this paper, for the frequency domain generation of SC-FDMA, i.e., DFT-SOFDMA, with the localized subcarrier mapping, we proposed novel Space-Time Coding and Mapping scheme and Space-Frequency Coding and Mapping scheme, which provides better PAPR property compared with other schemes. The new schemes also provide the capability of low-complexity frequency domain equalization and full space diversity. The low PAPR of the new schemes can be used to improve the power amplifier efficiency and/or enhance the cellular coverage, especially for the uplink of the future broadband wireless communication systems.

On the Correlation of Subcarriers in Grouped Linear Constellation Precoding OFDM Systems Over Frequency Selective Fading

This paper addresses the correlation of subcarriers in orthogonal frequency division multiplexing (OFDM) systems over frequency selective fading, and derives the optimum grouping scheme for grouped linear constellation precoding (GLCP-) OFDM systems. Since the subcarriers are generally correlated over practical propagation channel, a larger group size in GLCP-OFDM using the optimum grouping scheme always achieves a better diversity benefit, regardless of the channels path length. This result differs from the existing one, and it is verified by computer simulations

2-D Switching Diversity Aided Collaborative Spatial Multiplexing for Uplink Wireless Access

This paper proposes a two-dimensional switching diversity (2DSD) technique to enhance the collaborative spatial multiplexing (CSM) scheme for uplink wireless access. By the 2DSD, a single data stream is transmitted over multiple antennas and the mobile station (MS) alternates the transmit antennas from one time-frequency resource unit (RU) to another or from one group of RUs to another. That is, the RU-to-Antenna mapping pattern can change in both time and frequency domains. The new scheme has several advantages. First, by sharing one pilot pattern among multiple transmit antennas belonging to one MS, it is backward compatible with the legacy CSM specified in the WiMAX Forum mobile system profile Release 1.0 where two users each with one transmit antenna are scheduled in the same RUs to communicate with a common base station. Second, it saves the pilot overhead and allows as many MSs as possible to be involved in the CSM. Third, it can work in an open-loop manner and does not require additional signaling overhead. Finally, it achieves the power gain and diversity gain to improve the performance, as verified by computer simulations.

Enhanced Phase-Shifted Pilots Based Channel Estimation for MIMO-OFDM Systems with Virtual Subcarriers

Generalizing a conventional phase-shifted pilot (PSP) sequences and discrete Fourier transform (DFT) based channel estimator to MIMO-OFDM systems with virtual subcarriers, this paper presents two enhanced channel estimators applying Wiener interpolation and smoothing. Simulation results show that the proposed schemes can almost eliminate the mean square error floor of the conventional PSP/DFT-based channel estimator and improve the channel estimation accuracy further in some cases. Additionally, the application of a robust channel correlation matrix estimator avoids the complicated measurement of channel statistical properties and thus makes the proposed schemes more feasible in practical systems

A Cross-Designed V-Blast Code Robust to Channel Correlation

The vertical Bell laboratory layered space-time (V-BLAST) code transmits independent data streams from each transmit antenna, and it may perform poorly over spatially correlated channels. To overcome this drawback, we present in this paper a cross-designed V-BLAST code, each component of which is, like a linear dispersion code, a combination of several transmitted symbols. Since the new code incorporates the advantages of V-BLAST and linear dispersion codes, it achieves robust performance to spatial correlation with low complexity, full transmission rate, and short decoding delay. Computer simulations demonstrate the efficiency of the proposed code by comparison with the V-BLAST and two typical full-diversity full-rate codes.