DESIGN AND PERFORMANCE OF SYMBOL/SEQUENCE TCM FOR DS/SSMA SYSTEM OVER MOBILE RADIO CHANNEL

A novel kind of multidimension symbol/sequence trellis coded modulation (TCM) based on TCM of lower coding rate has been constructed. The redundancy of this new kind of TCM is provided not only by the modulated symbol sequence but also by the PN sequences for spreading spectrum as well. The performance of direct sequence spread spectrum multiple access (DS/SSMA) system with this symbol/sequence TCM over flat Rayleigh fading channel has been investigated by theoretical analysis and numerical simulation. The results obtained in this research demonstrate the performance improvements of this system in comparison with that of the DS/SSMA system with conventional TCM under the same conditions.

Ac/Ds Transposition Activity in Transgenic Rice Population and DNA Flanking Sequence of Ds Insertion Sites

The Agrobacterium mediated transgenic rice ( Oryza saliva L.) population with inserts of maize transposon Activator/Dissociation (Ac/Ds) was investigated. DNA sequences flanking the T-DNA were analyzed with inverse PCR. Results showed that 65.4% of the T-DNA was integrated in different locations of rice genome, and some T-DNA flanking sequences were located on certain chromosomes. A number of T-DNA was found to have inserted into protein coding regions. In order to induce transposition of the inserted Ds elements, 354 crosses of Ac x Ds and Ds x Ac were constructed. The excision frequency of Ds element trans-activated by Ac transposase was 22.7% in the F-2 populations, and the transposition was confirmed with analyses of DNA sequences flanking the Ds elements. In addition to the transposition due to 'cut-paste' mechanism, Ds can replicate itself and integrate into a new locus, and inaccurate excisions were also found. A proportion of DNA segments flanking the Ds elements showed no homologies to sequences published in GenBank, of which two were registered under the accession numbers AF355153 and AF355770. The strategy of using transposon tagging for rice genomics study was discussed.

Neural network approach to blindestimation of PN spreading sequence in lower SNR DS/SS signals

An approach based on discrete Karhunen-Loeve transformation of the DS/SS signals is proposed to estimate PN sequence in lower S/N ratio DS/SS signals. Characteristics of self-organization and principle components extraction of unsupervised neural networks are exploited adequately. Theoretical analysis and experimental results are provided to show that this approach can work well on the lower S/N ratio input signals.

Approach to blind estimation of the PN sequence in DS-SS signals with residual carrier

This paper presents an approach of singular value de- composition plus digital phase lock loop to solve the difficult problem of blind pseudo-noise （PN） sequence estimation in low signal to noise ratios （SNR） direct sequence spread spectrum （DS-SS） signals with residual carrier. This approach needs some given parameters, such as the period and code rate of PN sequence. The received signal is firstly sampled and divided into non-overlapping signal vectors according to a temporal window, whose duration is two periods of PN sequence. An autocorrelation matrix is then computed and accumulated by those signal vectors one by one. The PN sequence with residual carrier can be estimated by the principal eigenvector of the autocorrelation matrix. Further more, a digital phase lock loop is used to process the estimated PN sequence, it estimates and tracks the residual carrier and removes the residual carrier in the end. Theory analysis and computer simulation results show that this approach can effectively realize the PN sequence blind estimation from the input DS-SS signals with residual carrier in lower SNR.

Low complexity method for spreading sequence estimation of DSSS signal in non-cooperative communication systems

It is a necessary step to estimate the spreading sequence of direct sequence spread spectrum （DSSS） signal for blind despreading and demodulation in non-cooperative communications. Two innovative and effective detection statistics are proposed to implement the synchronization and spreading sequence estimation procedure. The proposed algorithm also has a low computational complexity with only linear additions and modifications. Theoretical analysis and simulation results show that the algorithm performs quite well in low SNR environment, and is much better than all the existing typical algorithms with a comprehensive consideration both in performance and computational complexity.

Ultra-wideband direct-sequence design approach for multiple narrowb and interference suppression

A novel direct sequence （DS） design method for suppressing the narrowband interference in DS spread spectrum ultra-wideband receivers is proposed. The method has low computational complexity and can be easily implemented in practical systems. Simulation results prove that the proposed method is effective to suppress the narrowband interference. Therefore, the integrity of both the ultra-wide bandwidth and the narrowband systems can be highly enhanced.

Fast method for spreading sequence estimation of DSSS signal based on maximum likelihood function

To estimate the spreading sequence of the direct sequence spread spectrum (DSSS) signal, a fast algorithm based on maximum likelihood function is proposed, and the theoretical derivation of the algorithm is provided. By simplifying the objective function of maximum likelihood estimation, the algorithm can realize sequence synchronization and sequence estimation via adaptive iteration and sliding window. Since it avoids the correlation matrix computation, the algorithm significantly reduces the storage requirement and the computation complexity. Simulations show that it is a fast convergent algorithm, and can perform well in low signal to noise ratio (SNR).

Research on Estimator and Testing Acquisition Schemes in Direct Sequence Spectrum Spreading Systems

Serveral methods for the pararrel acquisition of a PN sequence in a baseband direct sequence spread spectrum system are investigated. Four different kinds of schemes are considered: the optimal estimation scheme, the locally optimal estimation scheme, the optimal testing searches and the locally optimal testing scheme. In the four kinds of parallel acquisition schemes, the expressions for the probability of error are given and compared with the actual error probabilities obtained via Monte Carlo simulation. We also outline a technique that can be suboptimal because of a large amount of hardware and computation when using the parallel acquisition schemes.

High-Sensitivity Acquisition of Ultrahigh Dynamic Direct Sequence Spread Spectrum Signals in Space Communications

According to the requirements of the high-sensitivity acquisition of Direct Sequence Spread Spectrum(DSSS) signals under ultrahigh dynamic environments in space communications, a three-dimensional joint search of the phase of Pseudo-Noise-code(PN-code),Doppler frequency and its rate-of-change is presented to achieve high sensitivity in sensing high-frequency dynamics. By eliminating the correlation peak loss caused by ultrahigh Doppler frequency and its rate-of-change offset,the proposed method improves the acquisition sensitivity by increasing the non-coherent accumulation time. The validity of the algorithm is proved by theoretical analysis and simulation results. It is shown that signals with a carrier- to-noise ratio as low as 39 dBHz can be captured with high performance when the Doppler frequency is up to ±1 MHz and its rate-of-change is up to ±200 kHz/s.

New Acquisition Algorithm for Direct Sequence Spread Spectrum Signals

Aiming at improving acquisition performance for direct sequence spread spectrum （DSSS） signals, a new acquisition algorithm based on fast Fourier transform （FFT） is proposed. The code phases are parallel searched throughout the Doppler frequency domain. Since the influence of Doppler frequency errors on peak-to- average ratios of correlation power shows a pattern similar to the sinc function, it is our belief that by judging on peak-to-average ratios for different Doppler frequency errors false alarm probabilities should be lowered. Analyses have supported the underlying principle of this new algorithm. Simulation results have also indicated that the new algorithm can effectively improve the acquisition performance for DSSS signals.

A Neural Network Approach to Blind Estimation of PN Spreading Sequence in DS/SS Signals

In this paper, a new approach is proposed to estimate pseudo noise(PN) sequence in the lower SNR DS/SS signals blindly. This method utilizes the characteristics of self-organization, principal components analysis and extraction of unsupervised neural networks adequately, in addition to its higher-speed operation ability, successfully solve the difficult problem about PN sequence blind estimation. The theoretic analysis and experimental results show that this approach can work very well on lower SNR input signals.

Several Modulation in Direct-Sequence Spectrum-Spread Systems

Performances of BPSK, balanced quaternary modulation, dual quaternary modulation and complex quaternary modulation in direct sequence spectrum spread (DS SS) system are discussed in this paper. Based on the criterion the power of original signal is the same, it is shown that complex quaternary modulation has the best performance, and dual quaternary modulation degrades 2dB. Moreover, the frequency efficient of the two modulations is 2bit/Hz. Balanced quaternary has the same performance as BPSK with frequency efficient 1bit/Hz.

Ternary Zero Correlation Zone Sequence Sets for Asynchronous DS-CDMA

In this paper we propose a new class of ternary Zero Correlation Zone (ZCZ) sequence sets based on binary ZCZ sequence sets construction. It is shown that the proposed ternary ZCZ sequence sets can reach the upper bound on the ZCZ sequences. The performance of the proposed sequences set in asynchronous Direct Sequence-Code Division Multiple Access (DS-CDMA) system is evaluated. In the simulation we used two types of channels: Additive White Gaussian Noise (AWGN) and frequency non-selective fading with AWGN noise. The proposed ternary ZCZ sequence sets show better results, in term of Bit Error Rate (BER), than Hayashi’s ternary ZCZ sequence sets.

用Direct3D结合3DSMAX实现动画技术

系统介绍了Direct3D ,3DSMAX在动画技术方面的功能和作用 ,并为它们结合实现动画技术提供了一个基本框架。

Influence of Single Base Change in Shine-Dalgarno Sequence on the Stability of B.Subtilis Plasmid PSM604

B.Subtilis expression plasmids generally require a stringent Shine Dalgarno Sequence(SDS). Site directed mutagenesis was explored to change the Shine Dalgarno Sequence from AAAAATGGGG (mutant type) to AAAAAGGGGG (wild type) in recombinant plasmid PSM604. The single base substitution made the plasmid with wild SDS unstable in structure and segregation. The interaction of SDS with subtilisin leader sequence of PSM604 might be responsible for the instability of plasmid.

Solidification sequence and as-cast microstructure of a model Pb-Bi-Sn alloy with quasi-peritectic reaction

The Pb39 Bi25 Sn36 alloy was directionally solidified at varied withdrawal rates followed by quenching.From metallographic observation,composition analysis and differential scanning calorimetry(DSC)analysis,the solidification sequence of Pb39 Bi25 Sn36 alloy was characterized.The Sn-dendrite is observed as the primary phase during solidification,followed by theβ(Pb7 Bi3)/Sn divorced eutectic.At lower temperatures,theβ(Pb7 Bi3)/Sn binary eutectic is formed in the interdendritic region.However,the quasi-peritectic reaction[L+α-Pb→β(Pb7 Bi3)+Sn]does not occur as the prediction based on ternary phase diagram analysis,which can be attributed to the unequilibrium solidfication condition.Moreover,the as-cast microstructure is significantly refined with the increasing withdrawal rates.The quenched sample only exhibits the lamellar structure of Sn,β(Pb7 Bi3)and Bi phases.The results can provide instructions to optimize the as-cast microstructure of ternary alloys with quasi-peritectic reaction.

Non-Supervised Learning for Spread Spectrum Signal Pseudo-Noise Sequence Acquisition

An idea of estimating the direct sequence spread spectrum（DSSS） signal pseudo-noise（PN） sequence is presented. Without the apriority knowledge about the DSSS signal in the non-cooperation condition, we propose a self-organizing feature map（SOFM） neural network algorithm to detect and identify the PN sequence. A non-supervised learning algorithm is proposed according the Kohonen rule in SOFM. The blind algorithm can also estimate the PN sequence in a low signal-to-noise（SNR） and computer simulation demonstrates that the algorithm is effective. Compared with the traditional correlation algorithm based on slip-correlation, the proposed algorithm＇s bit error rate（BER） and complexity are lower.

经ERCP联合SpyGlass DS治疗的74例不明原因胆管狭窄患者的临床特征分析

目的 分析经内镜逆行胰胆道造影(endoscopic retrograde cholangiopancreatography, ERCP)联合SpyGlass DS治疗的不明原因胆管狭窄(indeterminate biliary stricture, IBS)患者的临床资料,为IBS的诊疗提供更多临床数据参考。方法 回顾性分析2020年1月至2023年4月北京中医药大学东方医院消化内镜中心经ERCP联合SpyGlass DS治疗的74例IBS患者的临床资料,归纳采用SpyGlass DS直视下视觉印象评估良恶性狭窄的情况,总结SpyGlass DS引导下视觉印象和SpyGlass DS引导下活检(SpyBite活检)在诊断IBS的性能特点。结果 共纳入74例IBS患者,男49例,女25例,年龄(67±12)岁(26~94岁)。74例患者中,61例(82.4%)直视下考虑为恶性狭窄,其中40例(65.6%)病理诊断提示恶性,5例(8.2%)病理诊断未提示恶性,16例(26.2%)未取活检。随访过程中,有1例患者经影像学检查被诊断为恶性肿瘤,而其余患者未发现进展;13例(17.6%)SpyGlass DS直视下考虑为良性狭窄,其中3例(23.0%)病理诊断恶性,5例(38.5%)病理诊断未提示恶性,5例(38.5%)未取活检并在随访过程中均未发现狭窄处进展。SpyGlass DS直视下视觉印象为肿瘤血管、增生物、黏膜不规则/结节性/增生性改变、黏膜损伤、胆管内渗出物的表现而病理诊断提示恶性的占比分别为24.4%、20.0%、62.2%、2.2%、8.9%。SpyGlass DS直视下视觉印象的敏感度为88.9%,特异度为37.5%,准确度为81.1%,SpyBite活检的诊断敏感度为95.7%,特异度为66.7%,准确度为92.3%。结论 对IBS可采用ERCP联合SpyGlass DS进行诊断,可大大提高疾病确诊率。

DS/FH信号跟踪的频率相位修正技术

直序/跳频(direct sequence/frequency hopping,DS/FH)扩频信号的跟踪受到多普勒效应和电离层效应的严重影响,使其难以应用于卫星导航的抗干扰领域。为了解决该问题,提出将递归最小二乘滤波修正的方法应用在DS/FH信号跟踪上。将处于不同通道中心频率的多普勒频率估计转化到DS/FH信号的整体中心频率进行并滤波,在频率捷变时对载波数控振荡器进行修正。根据对频率跳变前后载波相位和码相位突变的观察,实时估计电离层的电子密度,在频率捷变时修正载波相位和码相位。仿真实验证明,所提方法能够有效地消除DS/FH信号跟踪中的频率相位不连续问题,其跟踪精度与直序扩频信号度基本是相同量级。

Rapid Coherent Acquisition for PN Sequence UsingOptimum Search Algorithm

An optimun search algorithm for the coherent acquisition in direct-sequence spread-spectrum （DSSS） receivers is proposed and analyzed in this paper. The system consists of two major parts： a phase region estimator and a phase alignment detector. We use an auxiliary sequence to correlate the incoming signal in the phase region estimator. Since the cross-correlation value between the auxiliary sequence and the incoming PN signal has linear magnitude, and can provide the direction for the phase updating, an optimum search algorithm, try and error method, can be adopted to obtain the phase region information of the incoming signal. The mean acquisition time is derived through the signal flow graph theory. The time is compared with that of the conventional serial search scheme, and the results show that the proposed scheme can achieve coarse acquisition significantly faster than the conventional scheme.