In orthogonal frequency-division multiplexing (OFDM) amplify-and-forward (AF) relay networks,in order to exploit diversity gains over frequency-selective fading channels,the receiver needs to acquire the knowledge of channel state information (CSI).In this article,based on the recent methodology of distributed compressed sensing (DCS),a novel channel estimation scheme is proposed.The joint sparsity model 2 (JSM-2) in DCS theory and simultaneous orthogonal matching pursuit (SOMP) are both introduced to improve the estimation performance and increase the spectral efficiency.Simulation results show that compared with current compressed sensing (CS) methods,the estimation error of our scheme is reduced dramatically in high SNR region while the pilot number is still kept small.
Based on the assumption of large number of constellation points and high signal-to-noise ratio (SNR),phase noise sensitivity of lattice constellation is analyzed. The upper bound of symbol error rate (SER) in additive white Gaussian noise (AWGN) channel is derived from pairwise error probability. For small phase noise,phase noise channel is transformed to AWGN channel. With the aid of Wiener model,the obtained upper bound can be extended to phase noise channel. The proposed upper bound can be used as performance criterion to analyze the sensitivity of phase noise in multi-dimensional lattice constellation. Simulation results show that with the same normalized spectral efficiency,higher dimensional lattice constellations are more sensitive than lower ones in phase noise channel. It is also shown that with the same dimension of constellation,larger normalized spectral efficiency means more performance loss in phase noise channel.
YU Guang-wei NIU Kai HE Zhi-qiang WANG Xu-zhen LIN Jia-ru
The channel state information at transmitter (CSIT) acquisition plays a key role in the multi-input multi-output (MIMO) system,especially for the precoding schemes. However it is unrealizable to acquire perfect CSIT in practice. In this article,an effective and practical dynamic CSIT model is introduced to acquire imperfect channel state information. For practicability,the channel temporal and spatial correlations are considered and the channel estimate and its error covariance are obtained by utilizing the outdated channel state information. Based on the dynamic CSIT mode,closed-form solution of robust Tomlinsion-Harashima precoding (THP) is derived by a Lagrangian approach. Numerical simulations are presented to demonstrate the performance.
WANG Xu-zhen ,NIU Kai,HE Zhi-qiang,YU Guang-wei,WU Wei-ling Key Laboratory of Universal Wireless Communications,Ministry of Education,Beijing University of Posts and Telecommunications,Beijing 100876,China
In this paper, a robust THP is proposed for broadcast channel in multi-user multi-input multi-output (MU-MIMO) system, in which the channel uncertainty caused by feedback delay and mobile speed is taken into account. In order to acquire the imperfect channel state information at transmitter (CSIT), a dynamic CSIT model is introduced where the channel temporal and spatial correlations are considered. By utilizing the unchanged channel statistics and accurate outdated feedback channel information jointly, the imperfect CSIT is obtained as the channel estimate and error covariance. Based on the obtained imperfect CSIT, a Minimum Mean-Square Error (MMSE) Tomlinsion-Harashima precoding (THP) is designed and the closed-form solution is derived by the Lagrangian multiplier approach under total power constraint. Simulation results are provided to indicate the preferable performances of the robust THP. Performance analysis with respect to feedback delay and mobile speed is also given.
This article investigates the performance of hybrid automatic repeat request (HARQ) with code combining over the ideally interleaved Nakagami-m fading channel. Two retransmission protocols with coherent equal gain code combining are adopted, where the entire frame and several selected portions of the frame are repeated in protocols I and II, respectively. Protocol II could be viewed as a generalization of the recently proposed reliability-based HARQ. To facilitate performance analysis, an approximation of the product of two independent Nakagami-m distributed random variables is first developed. Then the approximate analysis is utilized to obtain exact frame error probability (FEP) for protocol I, and the upper bound of the FEP for protocol II. Furthermore, the throughput performance of both two protocols is presented. Simulation results show the reliability of the theoretical analysis, where protocol II outperforms protocol I in the throughput performance due to the reduced amount of transmitted information.
This article investigates resource allocation in multi-hop orthogonal frequency division multiplexing (OFDM) system with amplifying-and-forwarding relaying to maximize the end-to-end capacity. Most existing methods for multi-hop system focus on power allocation or subcarrier selection separately, but joint resource allocation is rarely considered due to the absence of effective interaction schemes. In this work, a novel joint resource allocation methodology is proposed based on Partheno genetic algorithm (PGA), which produces excellent subcarrier allocation set (referred to as individual in PGA) with higher capacity by evolution operator generation by generation. In addition, an adaptive power allocation is also designed to evaluate the fitness of PGA and further enhance the system capacity. Both theoretical analysis and simulated results show the effectiveness of the proposed joint strategy. It outperforms the traditional method by as much as 40% capacity improvement for 3-hop relaying system when system power is high, and obtains much more capacity enhancement percent under conditions of low system power.
SHI Jie , XU Wen-jun, HE Zhi-qiang, NIU Kai, WU Wei-ling School of Information and Telecommunication Engineering, Beijing University of Posts and Telecommunications, Beijing 100876, China
This article addresses the multicast resource allocation problem with min-rate requirement constraints in orthogonal frequency division multiplexing (OFDM) systems. Due to the prohibitively high complexity for nonlinear and combinatorial optimization, the original problem is relaxed and reformulated to form a standard optimization problem. By theoretical derivation according to the Karush-Kuhn-Tucker (KKT) conditions, two propositions are presented as the necessary criteria for optimality. Furthermore, a two-step resource allocation scheme, including subcarrier assignment and power allocation, is proposed on a basis of the propositions for practical implementation. With the min-rate based multicast group order, subcarriers are assigned in a greedy fashion to maximize the capacity. When subcarrier assignment is determined, the proposed power allocation can achieve the optimal performance for the min-rate constrained capacity maximization with an acceptable complexity. Simulation results indicate that the proposed scheme approximates to optimal resource allocation obtained by exhaustive search with a negligible capacity gap, and considerably outperforms equal power distribution. Meanwhile, multicast is remarkably beneficial to resource utilization in OFDM systems.
XU Wen-jun HE Zhi-qiang NIU Kai LIN Jia-ru WU Wei-ling
