Modulated Lapped Biorthogonal Transform for Non-orthogonal Narrowband Interference Excision in Spread Spectrum Communications

Traditional lapped transform domain excision techniques obtain good performance at the expense of increased processing delay. Extension of transform domain filtering techniques to the lapped biorthogonal transform domain can help solve the problem. By incorporating biorthogonality into the lapped transforms, more flexibility is obtained in the design of windows. Thus transform bases with better stopband attenuation can be generated by designing windows, but not by increasing the overlapping factor. In this paper, a new modulated lapped biorthogonal transform (MLBT) with optimized windows is introduced for efficient compression of multi-tone interfering signal energy. The bit error rate (BER) performance of the receiver employing the proposed MLBT excision technique is analyzed and compared with that of the lapped transform domain excision-based receivers. Simulation results demonstrate the improved performance and increased robustness of the proposed technique.

THE SCHEME STUDY OF THE APPLICATION OF W-CDMA SPREAD SPECTRUM COMMUNICATION IN MINE MOBILE COMMUNICATION

For the purpose of making the best use of the mine frequency resource and realizing the instruction idea “to exchange bandwidth for distance" a W-CDMA mine spread spectrum mobile communication scheme based on spread spectrum communication technique and the propagation characteristic of electromagnetic wave along laneways is proposed.The structure and make up of the system are studied and the working frequency and channels are assigned.Analysis indicates the scheme is a simple one that can fulfill the mine saying requirement.

Despreader for Direct Sequence Spread Spectrum System and Its Performance Analysis

A new type of despreader for direct sequence spread spectrum signal is proposed. Compared with traditional despreaders, the new despreader does not contain hard decision ware or handle binary sequence any more, and the locally stored spread spectrum signals are pre-modulated baseband signals (such as Gaussian minimum shift keying (GMSK) signals), which are much more similar to the received spread spectrum signals. Moreover, the missed detection probability of the despreader is about one order of magnitude lower than that of traditional ones. Based on the maximum likelihood criterion and phase probability density function of demodulated signal, a new method of ana- lyzing the despreaders’ performance is put forward, which is proved to be more accurate than traditional methods according to the numerical results. Finally, an adaptive despreader under different signal-to-noise ratios is given.

A Fine Synchronization Method for Coherent Fast Frequency Hopping

Coherent fast frequency hopping(CFFH)is attracting growing attention owing to its good antijamming performance and the coherent combining ability.However,compared with the conventional non-coherent fast frequency hopping,CFFH requires a more precise system synchronization.In this paper,we propose a new fine synchronization algorithm for CFFH.This algorithm consists two stages,namely,open-loop stage and closed-loop stage.In the openloop stage,a grid-based search parameter estimation method is proposed.In the closed-loop stage,we construct a fully coherent phase-locked loop(PLL)and a delay-locked loop(DLL)with decoding feedback structure to perform further fine estimation of the system clock skew and time delay,respectively.Moreover,we analyze the effect of the search parameter settings on the estimation error and derive the root mean squared error(RMSE)of estimates in the steady state of the closed-loop stage.Finally,through simulation,the RMSE performance are compared with the corresponding Cramer-Rao low bound(CRLB)and conventional code loop estimation to show the effectiveness of proposed algorithm.

A method of multichannel chaotic phase modulation spread spectrum and its application in underwater acoustic communication

Direct-sequence spread spectrum （DSSS） communication possesses low probability of detection and has been widely used in confidential communications. However, pseudo-noise （PN） sequences, used as spreading code in conventional DSSS communications, possess peri- odic character and binary value. In hostile environments, these distinct characters may lead to some important parameters of signals being estimated accurately, and then lead to the leakage of transmitted information. To solve the problem, we propose the chaotic phase modulation （CPM） sequence alternating the PN sequences. CPM sequence has complex values and constant envelope, and also possesses large quantity and good correlation characteristics. Moreover, it has more hidden features than conventional sequences by modulating its phases using chaotic sequence. To improve the data rate, we apply it into the technique of multichannel communica-tion. Simulation results show this scheme＇s superior bit error ratio （BER） performance, which demonstrates its feasibility in underwater acoustic communications.

Chaotic Spread- Spectrum Communication using Discrete-Time Synchronization

The statistic characteristics of chaotic sequences generated by improved logistic map are analyzed and it is found that improved logistic map chaotic sequences have good correlation and they can be used as address sequences in spread spectrum communication. The discrete time synchronization of Henon map is immediate. We apply the discrete time synchronization to chaotic spread spectrum communication and propose an original communication scheme. The simulation shows that the application is successful.

BLIND ADAPTIVE MULTIUSER DETECTION BASED ON A CONSTRAINED MMSE CRITERION

The proposed blind adaptive multiuser detector utilizes the signature waveform and time information of the desired user. With each received sample vector, the proposed algorithm updates the detector and gives the symbol estimate in the current time slot. Such property facilitates it to track time-varying channels.

Using Feedforward Net for Direct Sequence Parallel Search Acquisition

A feedforward net that quickly determines the maximum of a set of real values and its application in direct sequence parallel search acquisition (DSPSA) are described. The net is very suitable for a VLSI implementation due to its primary feedforward structure.

Frequency hopping sequences based on d-form functions

By using d-form function, a new construction of frequency hopping sequence with optimal Hamming correlation is presented in this article, which generalizes the results presented by Ding （2007）. Furthermore, a new class of non-power function style d-form function is proposed and an upper bound of the Hamming autocorrelation of the corresponding sequence is also derived.