High efficiency spreading spectrum modulation using double orthogonal complex sequences

This paper presents a novel scheme of high efficiency spreading spectrum modulation using double orthogonal complex sequences （DoCS）. In this scheme, input data bit-stream is split into many groups with length M. Each group is then mapped into a word of width M and then utihzed to select one sequence from 2u-2 DoCS sequences each with length L. After that, the selected sequence is modulated on carrier in quadrature phase shift keying （QPSK） mode. In addition, a new method named forward phase correction （FPC） is put forward for carrier recovery. Theoretical analysis and bit-error-ratio（BER） experiment results indicate that the proposed scheme has better performance than the conventional direct sequence spread spectrum（DSSS） scheme both in bandwidth efficiency and processing gain of the receiver.

Improved BLAST for wireless communications

Bell layered space-time architecture （BLAST） is a multi-antenna communication structure with high spectrum efficiency, and it has found wide applications in LANs and WLANs. However, its performance is much poorer than those of other space-time coding approaches. In order to improve its performance, an improved BLAST based on RAKE receiving is investigated. The new system introduces orthogonal spreading sequences （OSS） into the transmitter while retains the basic structure of BLAST. The proposed receiver suppresses interferences from other antennas by the orthogonality contained in the received signals, and extracts information from each receiving antenna by using RAKE receiving principle to construct efficient statistic decision. Simulation results show that the improved system performs well over both frequency-fiat and frequency-selective fading channels.

Channel estimation for MIMO-OFDM systems in wireless mobile channels

New training sequences and frame structure are proposed to estimate time-varying channel for multi-pie-input multiple-output and orthogonal frequency division multiplexing (MIMO-OFDM) systems.Thetraining sequences are modulatable orthogonal polyphase sequences,which have both good autocorrela-tions and cross-correlations.The channel impulse response (CIR) can be obtained by measuring the cor-relation between the received training sequence and the locally generated training sequence.The trainingsequences are used as guard interval instead of cyclic prefix,which not only improve the transmission ef-ficiency but also enable the channel estimator to track time-varying channel.The simulation results showthat the proposed method has about 2dB SNR gain over conventional methods in fast time-varying chan-nel.

Finding Non-liner Register on Binary M-Sequence Generating Binary Multiplication Sequence

In the current time there is an important problem that is for a received linear or nonlinear binary sequence{z_(n)}how we can find the nonlinear feedback shift register and its linear equivalent which generate this sequence.The linear orthogonal sequences,special M-Sequences,play a big role in these methods for solving this problem.In the current research trying give illuminations about the methods which are very useful for solving this problem under short sequences,and study these methods for finding the nonlinear feedback shift register of a multiplication sequence and its linear equivalent feedback shift register of a received multiplication binary sequence{z_(n)}where the multiplication on h degrees of a binary linear sequence{a_(n)},or finding the equivalent linear feedback shift register of{z_(n)},where the sequence{z_(n)}of the form M-sequence,and these methods are very effectively.We can extend these methods for the large sequences using programming and modern computers with large memory.