LDPC编码FFH/MFSK系统的性能分析

信道编码与跳频技术结合是提高系统抗干扰能力的一种有效方法。将LDPC码应用于多进制调制快跳频系统,研究其在瑞利衰落信道中对抗部分频带干扰的能力。仿真结果表明,当分集级数固定时,调制阶数越高性能越好,但增加调制阶数带来的增益差会逐渐降低并且增大系统复杂度。另外,由于分集增益和非相干合并损失的同时存在,增大分集级数在干扰因子较小时能够提高系统性能,较大时则降低系统性能。     

FFH/BFSK选择分集合并接收机在部分频带干扰Nakagami-m信道下的性能分析

快速跳频通信系统选择分集合并接收机可以有效减轻干扰及衰落对系统带来的性能损伤。该文给出了快速跳频BFSK系统在部分频带干扰下的选择分集合并接收机模型,并对该接收机在同时存在部分频带干扰以及加性高斯白噪声的非频率选择性Nakagami-m衰落信道下的性能进行了推导,给出了误码率的闭合表达式。最后进行了仿真验证,仿真结果与理论分析结果完全一致。分析表明：具有高分集度的选择分集合并接收机受干扰影响较小;在干扰功率较大时,其性能要好于其它几种分集合并接收机;在一定的信道条件下,存在一个最佳分集度。最后针对选择分集合并接收机在弱干扰信号下的性能不足,提出相应的改进措施。     

LDPC编码慢跳频系统中的一种信道状态估计算法

采用信道编码技术能提高跳频系统的抗干扰能力,而精确的信道状态信息有利于提高系统误码率性能。基于和积译码过程,提出一种新的迭代信道估计译码算法,把译码后验信息反馈给信道节点并重新计算信道状态概率,生成新的对数似然比作为下一次迭代的先验消息,而且信道估计与编码信息在迭代中交替更新。仿真结果表明在部分频带干扰的LDPC编码慢跳频系统中,该算法性能优于传统的门限检测法,而且每个跳频时隙只需要较少符号就能够接近有精确信道状态信息的情况。     

强干扰环境下LDPC编码慢跳频系统的传输方法设计

为进一步提升跳频通信系统抗干扰能力,基于低密度奇偶校验(Low-density Parity-check,LDPC)编码慢跳频抗干扰通信系统模型,提出了一种"比特预存储"的码字传输方法,将编码后各分段中的部分比特以"列重大小"的选择方式进行复制,并随机预存储在其他分段前端,在接收端对被干扰比特置零处理后,进行比特的合并...     

低密度奇偶校验码差分跳频系统的抗干扰性能

基于对无编码差分跳频系统抗干扰性能的研究,将低密度奇偶校验（LDPC）码引入差分跳频系统,研究了其对差分跳频系统抗部分频带干扰性能的改善。当系统有精确干扰状态信息时,针对不同的干扰因子对非规则LDPC码进行了优化,给出了码长趋于无穷大时的抗干扰渐近集合平均比特误码率,并对优化后的LDPC码与规则LDPC码的抗干扰性能进行了仿真。结果表明：当系统有精确干扰状态信息时,优化后的LDPC码差分跳频系统,相对于规则LDPC码差分跳频系统以及无编码差分跳频系统,在抗干扰性能上有明显改善。当系统无干扰状态信息时,提出一种迭代干扰状态估计及译码算法,其仿真结果表明：采用该算法可使编码系统在无精确干扰状态信息的情况下,仍具有极强的抗干扰能力。     

采用空间分集的LDPC编码协作系统性能研究

为了提高无线通信系统的可靠性,将协作通信技术和空间分集技术都引入到传统的信道编码系统中,提出了更高质量的无线传输方法。采用全盲瑞利信道来模拟实际的无线通信环境,用自适应算法LMS和RLS分别对信道进行估计,并比较2种算法的收敛特性。理论分析和仿真均表明,在原有的仅采用信道编码技术的基础上,提出的新传输方法能使无线通信系统获得更高的可靠性。     

MFSK/FFH系统多用户能力分析与仿真

MFSK/FFH系统特指采用快速跳频（FFH）技术和多进制频移键控（MFSK）非相干解调技术的系统,主要研究MFSK/FFH通信系统的多用户能力,并把它与差分跳频技术DFH的组网能力进行对比分析。通过分析MFSK/FFH通信系统的性能,给出了MFSK/FFH通信系统和差分跳频系统的比特差错率公式,为了公平对比MFSK/FFH网络和差分跳频网的组网能力,采用多用户频带利用率这个参数,理论和仿真表明,采用特定的检测方法,MFSK/FFH系统的多用户能力比差分跳频系统的好。     

LDPC码在非相干BFSK系统中的性能分析

通过理论分析和计算机仿真研究了LDPC码在非相干BFSK系统中的性能.首先证明单输入双输出的非相干BFSK系统满足信道对称条件,然后分别利用离散密度进化(DDE)和高斯近似(GA)算法给出了LDPC码的性能下界,后者与前者相比性能非常接近而且计算量要小很多.通过仿真得到几种常用LDPC码的性能并与译码门限以及香农极限进...     

乘积合并接收的差分跳频通信系统在瑞利衰落信道上抗部分频带干扰的性能分析

该文介绍了一种新型短波跳频通信技术差分跳频,频率转移函数设计和信号的检测方法是差分跳频中的关键技术。在瑞利衰落信道上,在有部分频带干扰和加性高斯白噪声共存的条件下,采用乘积合并接收的方法,对差分跳频通信系统的误符号性能进行了理论分析,同时做出相应的计算机仿真。结果证实了,在瑞利衰落信道上差分跳频通信系统采用乘积合并接收的方法要比采用线性合并接收的方法具备更好的抗部分频带干扰的性能。     

采用高阶QAM的LDPC编码OFDM系统

正交频分复用(orthogonal frequency division multiplexing,OFDM)已成为多径环境下实现高速数据传输的主流技术之一,包括LDPC码在内的各种纠错编码技术被运用到其中以提高误码性能。文中提出了采用高阶QAM的LDPC编码OFDM(LDPC-COFDM)系统,在提高传输效率的同时取得了较好的编码增益。AWGN信道及频率选择性衰落信道下的仿真显示了该方案的良好性能。     

Performance analysis of an FFH/BFSK product-combining receiverunder multitone jamming

The performance of a fast frequency-hopped binary frequency-shift keying (FFH/BFSK) spread-spectrum (SS) communication system is studied in this paper. The FFH system employs a product-combining receiver against the worst case multitone jamming (MTJ) and additive white Gaussian noise (AWGN). The compact characteristic functions of the natural logarithm of the product-combiner outputs are obtained based on the Taylor series expansion. The characteristic functions are then used to derive the bit error rate (BER) expressions that are applicable to higher diversity levels. Our analysis, validated by the simulation results, shows that the band MTJ is generally more harmful than the corresponding independent MTJ. The BER performance of the product-combining receiver is shown to possess good MTJ rejection capability compared to that of the soft-decision linear-combining receiver, especially under both moderate and strong MTJ power conditions     

Performance analysis of an FFH/BFSK linear-combining receiveragainst multitone jamming

A computationally efficient bit-error rate (BER) expression for a fast frequency-hopping binary frequency-shift-keying (FFH/BFSK) spread-spectrum system is derived based on Taylor-series expansion of the central differences. The FFH system employs a soft-decision linear-combining receiver against the worst-case band multitone jamming (MTJ) and additive white Gaussian noise. The analytical results are shown to match closely with the BER results based on simulation. This approach allows us to efficiently analyze the performance of the linear-combining receiver with higher diversity levels, which is otherwise mathematically intractable     

Performance analysis of FFH/BFSK product-combining receiver with partial-band jamming over independent Rician fading channels

This study investigates how independent Rician fading channels affect both the fast frequency-hopped binary frequency shift keying (FFH/BFSK) product-combining receiver (PCR) and partial-band jammer (PBJ). We demonstrate that the average bit-error-rate (BER) expressions of FFH/BFSK PCR can be derived with the aid of an approximation by quantizing the product-combiner's output. Numerical results show that system performance of the FFH/BFSK PCR over fading channels and PBJ is lower than that in nonfaded PBJ at a low signal-to-jammer density ratio E/sub b//N/sub J/.     

FFH/BFSK AGC接收机在部分带干扰Nakagami衰落信道下的性能分析

该文对基于自适应增益控制(AGC)的非相干快速跳频二进制正交移频键控(FFH/BFSK)扩频(SS)接收机在同时存在部分带干扰(PBJ)和加性高斯白噪声(AWGN)的频率非选择性慢衰落Nakagami信道下的比特误码率(BER)性能进行了分析,推导出一重积分形式的BER准确表达式,分析了衰落参数和分集数目取任意值时对系统性能的影响,数值分析结果比较了AGC接收机与乘积合并(PC)接收机在最坏情况下的BER性能。与以往误码率分析方法相比,本文所用方法的优点在于用统一的分析模式可以分析系统在不同衰落信道下的性能,简化了分析步骤。     

Maximum-likelihood receiver of FFH/BFSK systems with multitonejamming and AWGN over Rayleigh-fading channels

A maximum-likelihood receiver for fast frequency-hopped binary frequency-shift-keying (FFH/BFSK) systems which operates in an additive white Gaussian noise (AWGN) environment and is subjected to multitone jamming over Rayleigh-fading channels is derived. Simulation results show that the proposed maximum-likelihood receiver outperforms existing receivers with the same channel and jamming conditions     

Performance Study of an FFH/BFSK Self-Normalizing Receiver with Multitone Jamming's Frequency Offsets

This study investigates how frequency offsets of multitone jamming affect the fast frequency-hopped binary frequency shift keying (FFH/BFSK)self-normalizing (SNZ) receiver under additive white Gaussian noise (AWGN). The average bit-error-rate (BER) expressions of the FFH/BFSK SNZ receiver and the average BER expressions of an FFH/BFSK spread-spectrum (SS) communication system with frequency offsets of multitone jamming for the sake of understanding the simulation results better. Simulation results show that BER performance of the FFH/BFSK SNZ receiver with diversity under the worst casemultitone jamming (MTJ) and AWGN suffers from multitone jamming's frequency offsets when the jamming power is moderate, which is validated by several simulations with different frequency offsets configured in multitone jamming. Therefore, an FFH/BFSK SNZ receiver under multitone jamming can be combated with the help of frequency offsets of multitone jamming.     

Performance analysis of an FFH/BFSK receiver with ratio-statistic combining in a fading channel with multitone interference

The bit-error probability (BEP) is evaluated for a fast frequency-hopping/binary frequency-shift keying spread-spectrum communication system over a frequency-nonselective, slowly fading channel with worst-case band multitone jamming and additive white Gaussian noise. A diversity reception technique with ratio-statistic combining is applied at the receiver. Both square-law and envelope detectors are utilized and analyzed. Based on circularly symmetric signal theory, the paper obtains the closed-form expressions of probability density function and cumulative distribution function of the ratio-statistic output. It is shown from the analytical results, and verified by simulation, that the BEP performance of the ratio-statistic receiver is sensitive to the fading effect on the desired signal, but is insensitive to that on the jamming tones. It is also shown that the envelope detector provides better performance than the square-law detector.     

Performance analysis of an FFH/BFSK receiver with product-combining in a fading channel under multitone interference

The bit-error probability (BEP) is evaluated for a fast frequency-hopping binary frequency-shift-keying (FFH/BFSK) spread-spectrum communication system over Rician fading channels in the presence of worst-case multitone jamming (MTJ) and additive white Gaussian noise (AWGN). A diversity reception scheme of product-combining is applied at the receiver. Two types of MTJ models, namely n=1-band MTJ and independent MTJ, are considered in this letter. To obtain the final decision statistics, the closed-form or a single finite integral expressions of cumulative distribution functions (CDFs) of the ratio of two square-law detectors' outputs per hop are derived. According to the numerical results, it is shown, unlike the known knowledge for the AWGN channel, that independent MTJ is more harmful than n=1-band MTJ for the product-combining receivers (L/spl ges/2) in fading channels.     

Performance of FFH/BFSK product combining receiver over aRician-fading channel with partial-band jamming

A theoretical performance evaluation for an FFH/BFSK spread spectrum product combining receiver over a Rician-fading channel in the presence of partial-band jamming and AWGN is presented. The BER of this receiver is better than that of a linear combining receiver for a strong direct signal, and improvement is significant when diversity is increased     

Performance of LDPC coded FMT systems over frequency selective fading channel

This paper proposes the Low Density Parity Check （LDPC） coded Filtered MultiTone （FMT） systems with high-order modulation for the high data rate reliable transmission over frequency selective fading channel. For the purpose of accomplishing soft input soft output iterative decoding of LDPC codes, a new soft decision metric generation method is proposed, which obviates the need of the noise variance estimation, for M-PSK/M-QAM-type high-order modulation over frequency selective fading channel. Computer simulation indicates that, there is no performance loss with our new metric, but the complexity of implementation is reduced, and that the LDPC codes are effective to improve the Bit Error Rate （BER） of FMT in frequency selective fading channel.