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Blind estimation of multipath delays in OFDM systems

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Science china(Information Sciences) 2012年第6期55卷 1397-1401页

作者： SHENG Bin & YOU XiaoHu national mobile communications research Laboratory,Southeast university,nanjing 210096,china national mobile communications research Laboratory Southeast University Nanjing China

In order to coherently detect the transmitted data symbols,an orthogonal frequency division multi-plexing (OFDM) receiver requires reliable identification and equalization of the experienced wireless multipath fading *** information of path delays plays an important role in the procedure of identification and *** need for high data rates motivated the search for blind identification and equalization methods because they save bandwidth by avoiding the use of training *** OFDM systems,multipath fading channels introduce interference between adjacent symbols which can be prevented by inserting a cyclic prefix (CP) before each *** this paper,we find that the power of the interference in the CP interval can be estimated by using the circular convolution and based on the variations of the interference power,the time delay of each path can be estimated blindly.

关键词： multipath delay cyclic prefix OFDM

Multi-user MIMO downlink eigen-mode transmission over jointly correlated MIMO channels

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Science china(Information Sciences) 2011年第10期54卷 2124-2137页

作者： LI Xiao ,JIN Shi & GAO XiQi national mobile communications research Laboratory,Southeast university,nanjing 210096,china national mobile communications research Laboratory Southeast University Nanjing China

The study of multi-user multiple-input multiple-output (MU-MIMO) systems has emerged recently as an important research topic because such systems have the potential to combine the high capacity that can be achieved through MIMO processing with the benefits of spatial-division ***,receiver and transmitter channel state information (CSI) is generally required,especially for the downlink *** this paper,MU-MIMO downlink transmission systems with statistical CSI at the transmitter are studied for jointly correlated MIMO ***-mode space division multiple access transmission is derived based on the maximization of the ergodic sum rate,and two eigen-mode power allocation algorithms are proposed using matrix permanent and convex optimization *** new algorithms can overcome the limitations of the existing multi-user downlink transmission algorithm in practical applications.

关键词： MIMO eigen-mode multi-user downlink

Performance analysis of variable-power adaptive modulation in space-time block coded MIMO diversity systems

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Science china(Information Sciences) 2010年第10期53卷 2106-2115页

作者： YU XiangBin 1,2 & SHI HuiBin 1 1 College of Information Science and Technology, nanjing university of Aeronautics and Astronautics, nanjing 210016, china 2 national mobile communications research Laboratory, Southeast university, nanjing 210096, china College of Information Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing China national mobile communications research Laboratory Southeast University Nanjing China

In this paper, the performance analysis of multi-antenna MIMO systems with variable-power (VP) adaptive modulation and space-time coding is presented. The fading gain value is partitioned into a number of regions by which we decide the transmission power according to the region the fading gain falls in. The optimum fading gain region boundaries (switching thresholds) for maximizing spectrum efficiency (SE) under a target BER and average power constraint are derived. It is shown that the Lagrange multiplier in the constrained SE optimization will be unique if the existence condition for multi-antenna systems is satisfied, and is unique for single antenna systems. A practical iterative calculation method based on Steepest Descent Algorithm for finding the Lagrange multiplier is proposed. With the switching thresholds, the closed-form expressions of the SE and average BER, respectively for VP system and constant-power (CP) system are achieved. Simulation results for SE and average BER are in good agreement with the theory analysis. The results show that VP adaptive modulation with space-time coding provides better SE than the counterpart with CP under a target BER and average power constraint.

关键词： adaptive modulation variable power space-time block code constant power multiple input multiple output (MIMO)

Joint subcarrier and power allocation in uplink OFDMA systems based on stochastic game

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Science china(Information Sciences) 2010年第12期53卷 2557-2566页

作者： WU Dan 1,CAI YueMing 1,2 & SHENG YanMing 1 1 Institute of communications Engineering,PLA university of Science and Technology,nanjing 210007,china 2 national mobile communications research Laboratory,Southeast university,nanjing 210096,china Institute of communications Engineering PLA University of Science and Technology Nanjing China national mobile communications research Laboratory Southeast University Nanjing China

In uplink orthogonal frequency division multiplexing access(OFDMA) systems,efficient resource allocation can greatly improve system ***,in this paper,we present a game-theoretical approach to achieve a joint subcarrier and power allocation in a distributed ***,the subcarrier allocation problem is modeled as a multi-player discrete,stochastic and finite strategy game,where each of the subcarriers is viewed as a player to choose the most satisfying *** subcarriers of each user are allocated with equal *** the proposed game model,on the one hand,we exploit the support and programming methods to obtain the Nash equilibriums,and analyze their theoretical *** the other hand,we propose a lowcomplexity algorithm based on the linear reward-inaction(L R-I) algorithm to search for the Nash *** the relationship between the convergence results of this algorithm and the Nash equilibriums is *** simulation results demonstrate the effectiveness of the resource allocation game model and algorithm.

关键词： stochastic game OFDMA subcarrier allocation power allocation learning automata linear reward-inaction

Spectral Estimation based on Filter Bank and Cepstrum Thresholding for Cognitive Radios

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china communications 2009年第1期6卷 92-98页

作者： Cao Zhiping, Bi Guangguo, Zhang Zaichen national mobile Communication research Laboratory, School of Information Science and Engineering, Southeast university, nanjing 210096, china national mobile Communication research Laboratory School of Information Science and Engineering Southeast University Nanjing 210096 China

Spectrum sensing plays an important role in cognitive radio (CR). Nonparametric spectrum estimation is considered as a feasible candidate for CR. Some filter bank based periodogram algorithms, such as Thomson’s multitaper spectral estimator, can achieve fine spectral dynamic range1 but have large estimation variance. On the other hand, recently, Cepstrum Thresholding is proposed to reduce the variance of periodogram estimation. In this paper, we combine these two methods to achieve spectral dynamic range and variance request at the same time.

关键词： spectrum analysisfifilter bank cepstrum thresholding.

Negacyclic codes over Galois rings of characteristic 2a

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Science china Mathematics 2012年第4期55卷 869-879页

作者： ZHU ShiXin 1,2,& KAI XiaoShan 1,2 1 School of Mathematics,Hefei university of Technology,Hefei 230009,china 2 national mobile communications research Laboratory,Southeast university,nanjing 210096,china School of Mathematics Hefei University of Technology Hefei China national mobile communications research Laboratory Southeast University Nanjing China

Abstract We investigate negacyclic codes over the Galois ring GR（2a,m） of length N = 2kn, where n is odd and k≥0. We first determine the structure of u-constacyclic codes of length n over the finite chain ring GR（2a, m）[u]/〈u2k ＋ 1〉. Then using a ring isomorphism we obtain the structure of negacyclic codes over GR（2a, m） of length N = 2kn （n odd） and explore the existence of self-dual negacyclic codes over GR（2a, m）. A bound for the homogeneous distance of such negacvclic codes is also given.

关键词： negacyclic codes constacyclic codes Galois rings self-dual codes homogeneous distance

Performance analysis of uplink MIMO MC-CDMA systems based on linear zero-forcing V-BLAST algorithm

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Science in china(Series F) 2008年第9期51卷 1305-1318页

作者： YANG Wei1,2 & YANG Wei1 1 State Key Laboratory of Rail Traffic Control and Safety,Beijing Jiaotong university,Beijing 100044,china 2 national mobile communications research Laboratory,Southeast university,nanjing 210096,china State Key Laboratory of Rail Traffic Control and Safety Beijing Jiaotong University Beijing China national mobile communications research Laboratory Southeast University Nanjing China

A structure was proposed for multiple-input-multiple-output multicarrier code divi- sion multiple access （MIMO MC-CDMA） uplink transmission system. Linear zero- forcing V-BLAST （ZF V-BLAST） algorithm and maximum ratio combining （MRC） scheme was applied to the receivers. The average bit error rate （BER） expression was derived on condition that the number of receive antennas was larger than that of transmit antennas and it was verified by simulations. Numerical results show that the number of transmit and receive antennas, as well as the number of sub- carriers, all exert significant effects on the BER performance. The space diversity and frequency diversity show different abilities to improve the BER performance. The MIMO MC-CDMA system based on linear ZF V-BLAST algorithm is capable of achieving better BER performance than that of the conventional MC-CDMA system by reducing the number of transmit antennas or increasing the number of receive antennas.

关键词： bit error rate(BER) multiple-input-multiple-output(MIMO) multicarrier code division multiple access(MC-CDMA) zero-forcing(ZF)

Low-complexity distributed differential spacetime coding scheme for amplify-and-forward cooperative networks

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Science in china(Series F) 2009年第8期52卷 1418-1427页

作者： YU XiangBin1,2, BI GuangGuo3 & XU WeiYe4 1 College of Information Science and Technology, nanjing university of Aeronautics and Astronautics, nanjing 210016, china 2 Department of Electronic Engineering, City university of Hong Kong, Hong Kong, china 3 national mobile communications research Laboratory, Southeast university, nanjing 210096, china 4 Department of Communication Engineering, nanjing Institute of Technology, nanjing 211167, china College of Information Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing China Department of Electronic Engineering City University of Hong Kong Hong Kong China national mobile communications research Laboratory Southeast University Nanjing China Department of Communication Engineering Nanjing Institute of Technology Nanjing China

By introducing a space-time coding scheme based on amicable orthogonality, we develop a distributed differential space-time coding scheme with the amplify-and-forward （AF） method for wireless cooperative networks. The scheme requires no knowledge of the channel state information at both transmitters and receivers, and effectively decreases the realization complexity due to no channel estimation. Moreover, it has lower decoding complexity and higher coding advantage than the existing scheme, thus avoiding the shortcoming of exponential decoding complexity of some existing schemes. According to the pairwise error probability （PEP） analysis of the system, the power allocations of source and relay terminals are jointly optimized, and as a result, the PEP is minimized, which will provide a helpful guideline for system design. Numerical calculation and simulation results show that the developed scheme is superior to the existing scheme. Moreover, the scheme with optimal power allocation yields obvious performance improvement over that with equal power allocation.

关键词： differential space-time coding cooperative communication amplify-and-forward method power allocation

On the number of rotation symmetric Boolean functions

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Science china(Information Sciences) 2010年第3期53卷 537-545页

作者： FU ShaoJing1, LI Chao1,2 & QU LongJiang1,3 1Science College of national university of Defense Technology, Changsha 410073, china 2State Key Laboratory of Information Security, Beijing 100039, china 3national mobile communications research Laboratory, Southeast university, nanjing 210096, china Science College of national university of Defense Technology Changsha China State Key Laboratory of Information Security Beijing China national mobile communications research Laboratory Southeast University Nanjing China

Rotation symmetric Boolean functions (RSBFs) have been used as components of different cryptosystems. This class of functions are invariant under circular translation of indices. In this paper, we investigated balanced RSBFs and 1st order correlation immune RSBFs. Based on constructive techniques, we give an accurate enumeration formula for n-variable balanced RSBFs when n is a power of a prime. Furthermore, an original and efficient method to enumerate all n-variable (n prime) 1st order correlationimmune functions is presented. The exact number of 1st order correlation immune RSBFs with 11 variables is 6925047156550478825225250374129764511077684773805520800 and the number of 13 variables has 189 digits. Then for more variables, we also provide a significant lower bound on the number of 1st order correlation immune RSBFs.

关键词： cryptography rotation symmetry correlation immunity balancedness