Xia Lei

OFDM With Interleaved Subcarrier-Index Modulation

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is a recently developed technique which modulates part of the information bits using the indices of OFDM subcarriers. In this letter, a simple and efficient subcarrier-level interleaving scheme is introduced to improve the performance of conventional OFDM-IM through enlarging the Euclidean distances among the modulated symbols. Both theoretical analysis and simulation results are presented to show that the proposed OFDM with interleaved sucarrier-index modulation (OFDM-ISIM) can achieve better system performance than conventional OFDM-IM and OFDM with low-order modulation schemes such as binary phase shift keying, quadrature phase shift keying and 16 quadrature amplitude modulation.

A Class of Low Complexity PTS Techniques for PAPR Reduction in OFDM Systems

This letter presents a class of low complexity partial transmit sequence (LC-PTS) techniques for reducing the peak-to- average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. The basic principle is to analyze and utilize the correlation among the candidate signals generated in PTS, so as to simplify the computational complexity. Furthermore, the proposed technique focuses on simplifying the computation for each candidate signal, instead of reducing the total number of candidate signals such as in (Jayalath and Tellambura, 2000). Thus, it can be easily combined with other simplified techniques. Simulation results show that the new technique can effectively reduce the complexity compared with the conventional PTS scheme.

Clipping noise mitigation for channel estimation in OFDM systems

This letter provides a new technique to mitigate the clipping noise on pilot symbols in clipped and pilot-aided orthogonal frequency division multiplexing (OFDM) systems. The basic principle is to directly filter the clipping noise on the positions of pilots in the frequency domain before the insertion of pilots. Simulation results show that the new technique can effectively improve channel estimation and system performance

SAGE based joint timing-frequency offsets and channel estimation in distributed MIMO systems

This paper proposes a timing-frequency offset estimation algorithm joint with channel estimation in distributed multi-input multi-output (MIMO) systems, in which different timing and frequency offsets are considered for each pair of transmit and receive antennas. Different from most of the existing methods which estimate the timing or frequency offsets separately, the proposed scheme makes a joint estimation with a maximum-likelihood (ML) estimation model. Furthermore, an iterative space-alternating generalized expectation-maximization (SAGE) estimator is proposed to provide a solution to the multi-dimensional extreme-value problem. And the Cramer-Rao bound (CRB) for multiple parameter estimation is also derived. Simulations show that the estimation performance of the proposed scheme can reach the CRB effectively.

A Low-Complexity Detection Scheme for Differential Spatial Modulation

Differential spatial modulation (DSM), which does not require the channel state information at the receiver, is an attractive alternative to its coherent counterpart. The optimal maximum-likelihood (ML) detector of the DSM system employs the classic block-by-block method for jointly detecting the activated antenna matrix (AM) and the modulation symbols, resulting in high computational complexity. In this letter, a low-complexity near-ML detector, which operates on a symbol-by-symbol basis, is proposed for the DSM scheme. Specifically, in each block, the index of the activated transmit antenna and modulation symbol in each time slot are first obtained, and then, these antenna indices are utilized to simply determine the index of the activated AM. Simulation results show that the proposed algorithm is capable of offering almost the same performance as that of the ML detector with more than 90% reduction in complexity.

ML synchronization algorithm and estimation bounds for cooperative systems

In this paper, we propose a maximum-likelihood (ML) estimation method for synchronization in decode-and-forward (DF) cooperative systems. We focus on the estimation problem of the multi timing and frequency offsets in the second phase, the multiple-input-single-output (MISO) multiple access phase of cooperative communications. Different from the conventional methods which estimate the timing or frequency offsets separately, we propose a joint timing-frequency offsets and channel estimation scheme to achieve better performance. In addition, the lower bounds, the Cramér-Rao bounds (CRB) of the multiple parameter estimation are also provided. The simulation results show that the performance of our estimation scheme can reach the CRB.

Performance evaluation in PAPR and ICI for ISIM-OFDM systems

Interleaved subcarrier-index modulation for orthogonal frequency division multiplexing (ISIM-OFDM) is a recently developed technique, where the indices of OFDM subcarriers are utilized to convey information bits and subcarrier-level interleaving scheme is considered. For the conventional OFDM system, the main drawbacks lie in the high peak-to-average power ratio (PAPR) at transmitter and its sensitiveness to inter-carrier interference (ICI) in a highly mobile environment. In this paper, the performance evaluation in PAPR and ICI for ISIM-OFDM system is presented. Simulation results show that ISIM-OFDM system can efficiently reduce the PAPR and is more robust to ICI compared with traditional OFDM system.

Wiener Filter Based Channel Estimation for High-Speed Communication Environments

Wiener filter is the best channel interpolation method in terms of minimizing mean square error at the time dimension. However, Wiener filter with low order will lose its efficiency in high-speed communication environments, while Wiener filter with high order suffers from the problem of high computational complexity. In this paper, we analyze the relationships among Wiener filter with different orders and their corresponding application scenarios. Furthermore, based on the analysis, a pilot symbol design criterion for high-speed communication environments and a simplified Wiener filter based channel estimation technique are proposed, respectively.

Multiple carrier frequency offsets compensation for the uplink of interleaved OFDMA

In the uplink of interleaved orthogonal frequency division multiple access (OFDMA) systems, multiuser interference (MUI) occurs due to different carrier frequency offsets (CFOs) from different users at the receiver. In this paper, a novel scheme is presented to compensate the multiple CFOs at the interleaved OFDMA receiver. The proposed scheme is based on a calculation of optimum CFO correction value for each single user, which maximizes the average signal-to-interference ratio (SIR) so as to mitigate the MUI to each user. Both theoretical analysis and simulation results show that the proposed scheme is with enhanced and robust system performance compared to conventional schemes under various CFO conditions.

Spatial modulaiton for 5G MIMO communications

Spatial modulation (SM) is a class of novel multi-input multi-output (MIMO) techniques for wireless communications. In SM-MIMO, only part of the transmit antennas are active for transmission, which avoids the interference among multiple antennas and simplifies the structure of MIMO transceiver. In this paper, we summarize the recent researches related to SM-MIMO, to demonstrate the flexibility and effectiveness of the new technique. Furthermore, we show some potential applications of SM-MIMO in future 5G wireless communications.