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Analysis of time and frequency synchronization error for wireless systems using OFDM

Science in China(Series F) 2005年第3期48卷 379-396页

作者： SHUFeng CHENGShixin JamesLee CHENMing YOUXiaohu nationalmobilecommunicationsresearchlaboratory SoutheastUniversityNanjing210096China

Due to frequency-selective and time-variant property of wireless channel together with additive noise and mismatch of oscillators between transmitter and receiver, there are always time and frequency synchronization errors in a practical OFDM system. To investigate the effect of the two kinds of errors on system performance, the average normalized interference power (NIP) is defined. A simple supper bound for NIP caused by time synchronization error (TSE) and the tighter upper bound for NIP resulting from frequency synchronization error (FSE) are derived independently. Simulations in typical short wave (SW) and medium wave (MW) channels further verify the correctness and tightness of these upper bounds. They actually provide good approximations to NIPs. Moreover, the upper bound for NIP resulting from FSE is tighter than traditional upper bound. Additionally, a new solution is proposed to relax the precision requirement for time synchronization algorithm, which can achieve a better tradeoff between time synchronization precision and bandwidth efficiency. These upper bounds will be useful in developing and choosing time and frequency synchronization algorithms in OFDM system to achieve a specific NIP value for a given channel condition.

关键词： OFDM time synchronization error frequency synchronization error normalized interference power upper bound.

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Discrete-Rate Adaptive Modulation with Variable Threshold for Distributed Antenna System in the Presence of Imperfect CSI

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China Communications 2014年第A1期11卷 31-39页

作者： YU Xiangbin TAN Wenting WU Binbin LI Yang KeyLaboratoryofRadarImagingandMicrowavePhotonics MinistryofEducationCollegeofElectronicandInformationEngineeringNanjingUniversityofAeronauticsandAstronauticsNanjing210016China nationalmobilecommunicationsresearchlaboratory SoutheastUniversityNanjing210096China

Discrete-rate adaptive modulation （AM） scheme for distributed antenna system （DAS） with imperfect channel state information （CSI） is developed, and the corresponding performance is investigated in composite Rayleigh channel. Subject to target bit error rate （BER） constraint, an improved fixed switching threshold （FST） for the AM scheme is presented by means of tightly-approximate BER expression, and it can avoid the performance loss fxom conventional FST. Based on the imperfect CSI, the variable switching threshold （VST） is derived by utilizing the maximum a posteriori method. This VST includes the improved FST as a special case, and may lower the impact of estimation error on the performance. By the switching thresholds, the spectrum efficiency （SE） and average BER of the system are respectively derived, and resulting closed- form expressions are attained. With these expressions, the system performance can be effectively evaluated. Simulation results show that the derived theoretical SE and BER can match the simulations well. Moreover, the AM with the presented FST has higher SE than that with the conventional one, and the AM with VST can tolerate the large estimation error while maintaining the target BER.

关键词： distributed antenna system adaptive modulation imperfect estimation variable thresholds

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INTERLEAVING SCHEME FOR MULTICARRIER CDMA SYSTEM

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Journal of Electronics(China) 2004年第1期21卷 16-22页

作者： ShiFeng ChengShixin nationalmobilecommunicationsresearchlaboratory SoutheastUniversityNanjing210096

In MultiCarrier Code-Division Multiple-Access (MC-CDMA) system, the received signals scattered in the frequency domain are combined to get frequency diversity gain. However, the frequency diversity gain is limited because of correlation between aubcarriers. A novel interleaving scheme for MC-CDMA system is proposed in this paper. A circular shifting register is introduced into each subcarrier branch to decrease the correlation between subcarriers. By using interleaving, frequency diversity gain of system is increased. System structure and model with interleaver are discussed. In the case of multiple users, Parallel Interference Cancellation (PIC) technique is also introduced. Computer simulations demonstrate the performance of proposed scheme, and the performance comparison of MC-CDMA with interleaver and conventional MC-CDMA system is shown as well.

关键词： Multicarrier Interleaving PIC

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Improved DOA Estimation Algorithm with Sensor Array Perturbations for CDMA System

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Transactions of Tianjin University 2003年第1期9卷 11-15页

作者：杨维程时昕 SchoolofElectronicsandInformationEngineering NorthernJiaotongUniversity nationalmobilecommunicationsresearchlaboratory SoutheastUniversity

An improved direction of arrival (DOA) estimation algorithm with sensor gain and phase uncertainties for synchronous code division multiple access(CDMA) system with decorrelator is presented. Through decorrelating processing DOAs of the desired users can be estimated independently and all other resolved signal interferences are eliminated. Emphasis is directed to applications in which sensor gain and phase are perturbed that often happen actually. It is shown that improved DOA estimation can be achieved for decoupled signals by gain and phase pre estimation procedures.

关键词： antenna array CDMA DOA estimation perturbations

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