基于自适应门限判决的TDCS基函数生成

针对变换域通信系统传统固定门限判决出现的频谱误判问题,结合能量检测法,提出了一种自适应门限判决的基函数生成方法.分析了TDCS系统电磁环境采样信号的特性,依据能量检测法建立了一种二元假设检验,使得门限能随着环境噪声不同自适应调整.仿真结果表明,采用此方法能准确判决出干扰位置,进行干扰剔除,与传统固定门限判决方法相比,误...     

高速突发通信中的自适应门限技术及其性能

本文在分析固定门限判决器性能的基础上，提出了一种自适应门限方案，并对其进行了实验和分析，结果表明，自适应门限判决器具有较宽的动态范围和较好的性能把它与其它技术如分集等结合起来，是实现高速突发通信的良好途径。     

基于S&C算法的OFDM符号同步优化设计

针对OFDM通信系统中,判决门限与时变信道不能自适应的问题,提出了一种新的基于S&C算法的符号同步设计方案,即通过对系统添加预设信息,使OFDM系统能够在不同信噪比下,进行判决门限的自适应选择,提高符号同步的精度,使得系统误同步概率降为2%以下.     

突发通信中的自适应门限信号检测方法

该文针对分组突发通信中的信号检测问题,利用信号相关前后功率之比构建判决统计量,实现自适应门限信号检测。在判决门限中加入微小偏移量,避免实际应用中存在的虚警毛刺现象。在门限判决时加入滑动比较窗口,解决了检测精度不高的问题。理论分析和仿真结果表明,改进方案可以很好地实现信号的自适应门限检测。     

基于SCA算法的OFDM符号同步优化设计

针对OFDM通信系统中,判决门限与时变信道不能自适应的问题,提出了一种新的基于S&C [1]算法的符号同步设计方案,即通过对系统添加预设信息,使OFDM系统能够在不同信噪比下,进行判决门限的自适应选择,提高符号同步的精度。     

一种PN码捕获的门限自适应估计方法

该文提出一种简单、实用的PN码捕获门限自适应设置方法.我们在对判决量统计特性分析的基础上,采用最大似然估计准则估计出等效高斯白噪声方差V.由此,我们得到了判决门限值的自适应设置方法.最后,我们进行了计算机仿真.结果表明,通过估计门限构造出的PN码捕获装置检测性能与理论值非常吻合,从而说明了其有效性.而且,判决门限的估计方法实现非常简单、快捷,很适合在工程中应用.     

GPS接收机的自适应门限设定方法

针对GPS接收机中的信号捕获问题提出了一种新颖的判决门限的自适应设定方法,它在接收信号的信噪比大幅度变化的情况下也可同时保证捕获的虚警概率和检测概率在一定范围内稳定不变.与以往自适应门限设定方法不同的是,它不是基于传统的恒虚警概率判决准则,而是基于一种新颖的恒等效信噪比准则.因为只有当输出信噪比恒定时,才有可能在虚警概率恒定的同时也保证检测概率稳定,所以这个门限监测器的目的就是要通过非相干累加来实现累加后的等效信噪比的恒定.一方面,将自适应门限设置成实时估计的噪声能量的函数,从而保证超过门限的累加输出值一定能达到指定的等效信噪比.另一方面,检测样本数也是在自适应的调整,即累加时间会不断增加直到输出的非相干累加结果超过当时的门限值.所以,一旦判决为检测到信号时,这时的输出等效信噪比都是恒定的,因此检测概率和虚警概率都可保持稳定而无论当时的输入信噪比如何变化.     

基于频域中值滤波的自适应卫星通信恶意干扰检测

卫星通信在军事领域的应用不可避免地面临人为实施的恶意干扰,针对接收信号的恶意干扰检测问题,提出了基于频域中值滤波的门限自适应调整检测方法。首先对接收的混合信号进行FFT变换,在此基础上对得到的序列进行中值平滑滤波,进而通过滤波输出序列计算判决门限,最后将序列最大值与门限对比,判断是否存在干扰。理论分析和仿真表明,该方法计算简单、易实现,对窄带和部分频带干扰具有优越的检测性能。     

基于变帧长自适应门限的端点检测方法

传统的双门限端点检测算法的门限一般通过经验值来确定。在实际应用中,这种凭经验得到的判决门限往往不能很好地适应环境变化,尤其是在噪声环境下,经验判决门限不能适应背景噪声的变化。将1种自适应门限、窗长动态变化相结合的双门限端点检测算法用于语音端点检测,实验结果表明该方法在常见的弱噪声环境下效果较好,具有一定的鲁棒性。     

一种抑制信道断续干扰的自适应门限检测算法

短波信道中存在大量突发的、断续的干扰,严重影响了通信的可靠性.对自适应多门限算法抑制窄带断续干扰的性能进行了分析,针对该算法抑制窄带断续干扰能力差的缺点,提出了一种改进算法,并进行了理论分析和性能仿真.仿真结果表明此算法可明显改善误码率性能.     

Adaptive acquisition of PN sequences for DSSS communications

Since the received signal levels in mobile communications are unknown and the location is varying, acquisition schemes for pseudonoise (PN) sequences with fixed thresholds cannot provide satisfactory performance. This fixed-threshold scheme may cause too many false alarms or result in a low detection probability for a selected threshold value. We present an adaptive acquisition scheme for PN sequences which estimate the background power level, multiply it with a threshold coefficient to keep the false alarms constant, and use it as a threshold     

Analysis of an antijam FH acquisition scheme

An easily implemented matched filter scheme for acquiring hopping code synchronization of incoming frequency-hopping (FH) signals is analyzed, and its performance is evaluated for two types of jamming: partial-band noise jamming and partial-band multitone jamming. The system is designed to reduce jammer-induced false alarms. The system's matched filter output is compared to an adaptive threshold that is derived from a measurement of the number of acquisition channels being jammed. Example performance calculations are given for the frequency coverage of the jamming either fixed over the entire acquisition period or hopped, that is, changed for each acquisition pulse. It is shown that the jammer's optimum strategy (the worst case) is to maximize the false alarm probability without regard for the effect on detection probability, for both partial-band noise and multitone jamming. It is also shown that a significantly lower probability of false acquisition results from using an adaptive matched filter threshold, demonstrating that the strategy studied here is superior to conventional nonadaptive threshold schemes     

Adaptive Integration Time and Threshold Setting Schemes for Two-Dimensional Code Acquisition

In this paper we propose and study two methods for improving two-dimensionalcode acquisition performance in scenarios with nonuniform spatialdistributions of interference. The schemes exploit the fact that integrationtimes and threshold settings are adaptively set for each angular cellaccording to the level of spatial interference prevailing in that cell. Modelsfor the schemes are first developed. Closed-form mean acquisition times arethen computed to allow performance comparisons. Acquisition performance isanalytically evaluated for different spatial distributions of interference.A system with fixed integration time and a fixed threshold is used as areference. It is found that the adaptive integration time scheme is able tofully compensate for the loss of performance caused by the nonuniformdistribution of interference. Furthermore, the mean acquisition times can bereduced by a factor of as much as two, even in environments characterized bysevere distributions of interference, e.g., a high power peak of interferenceconfined to a given angular direction. The adaptive threshold method alsoperforms better than the reference case but provides moderate performancegains.     

Adaptive threshold control scheme for packet acquisition

An adaptive threshold control scheme for packet acquisition is described. The threshold control is done adaptively by setting the threshold proportional to the maximum likelihood estimate of the noise power     

基于CDMA2000 1x移动台的一种捕获方案及其性能分析

针对CDMA2000的物理层协议．根据并行结构的快速捕获．以及自适应门限控制的方法．提出了一种移动台系统中实用的捕获方案，并对此方案在瑞利衰落信道中的性能进行理论分析。     

DS spread spectrum signal acquisition using adaptive threshold techniques

Initial synchronization (i.e. acquisition) of the spreading wave-form is a significant problem in spread spectrum system design. In this paper, adaptive threshold techniques are employed in a serial search acquisition scheme for direct sequence (DS) spread spectrum signals to improve the mean acquisition time of the system. Two approaches for adpative threshold modelling are presented, analysed and compared, namely the sample test approach and the probability-of-error approach. The results show that, using an adaptive threshold, a significant improvement may be achieved in the mean acquisition time for a certain range of interference-to-signal ratios (ISRS). The type of interference assumed is narrowband interference, from which DS spread spectrum systems suffer most, in addition to additive white Gaussian noise (AWGN). © 1998 John Wiley & Sons, Ltd.     

Adaptive delay threshold-based priority queuing scheme with opportunistic packet scheduling for integrated service in mobile broadband wireless access systems

In this letter, we propose a novel method of implementing an opportunistic priority queuing scheme that supports both latency-sensitive real-time (RT) and best-effort non-realtime (NRT) service classes in mobile broadband wireless (MBWA) systems. It employs an adaptive delay threshold as a dynamic reference of prioritizing the urgent RT service users over others, which allows for fully leveraging the multiuser diversity gain of NRT service users under the varying system conditions. It is shown that the overall system capacity can be further increased by the proposed adaptation rule, as compared with the existing opportunistic priority queuing scheme with the fixed delay threshold.     

Adaptive PN code acquisition using instantaneous power-scaled detection threshold under Rayleigh fading and pulsed Gaussian noise jamming

An adaptive serial search pseudonoise (PN) code acquisition scheme is proposed, in which the detection threshold is scaled by the instantaneous received power measured prior to PN code correlation. We observe that the proposed scheme achieves significantly improved mean acquisition times compared to the conventional nonadaptive schemes under Rayleigh fading and pulsed Gaussian noise jamming. Furthermore, the proposed scheme is shown to be optimum under pulsed Gaussian noise jamming in the sense that it forces the worst case jamming fraction to unity.     

卫星通信网中ACM技术研究

针对现有卫星通信网传输效率不高的问题,讨论了自适应编码调制(ACM)技术在卫星通信中的应用。提出了在点对点和TDM/TDMA(FDMA)组网方式下的编码调制的自适应调整策略和自适应调整门限值的计算方法,给出了中心站网管控制下的自适应调整流程;并通过重新设计2种应用方式下的调制信号帧结构,结合现有的突发解调技术,可以实现信号的自适应解调。     

自适应地波超视距雷达高频通信干扰抑制

利用高频地波超视距雷达中高频通信干扰强度大、具有一定的方向性、属于瞬态干扰和其对地波雷达所有探测距离单元均有影响的特点，提出了自适应抑制短波通信干扰的方法。该方法利用无目标(海浪)单元的样本值估计阵列的协方差矩阵，进而利用自适应波束形成的方法对待测距离单元中的短波通信干扰进行滤除。对实测数据的处理结果表明,其能够有效的抑制高频通信干扰.