无线局域网采用的补偿码键控调制方式

采用补偿码健控（CCK）可以使IEEE802．11b无线局域网系统实现多速率通信，这是补偿码第一次用于调制。介绍了无线局域网的直接序列扩频（DSSS）的各种模式，着重介绍了无线局域网所采用的CCK调制方式，并对CCK调制的性能进行了理论上的分析。     

一种扩展CCK调制速率的新方法

针对IEEE802.11提出的CCK调制技术,分析了CCK调制所采用的补偿码自相关和互相关性能,给出一种CCK调制速率扩展的新方法,并对其进行了性能分析.仿真结果证明了该方法的可行性.     

WLAN基带处理中CCK方式的实现技术

文章全面介绍了用于IEEE-802.11b无线局域网的CCK方式.我们首先讨论了CCK码字的由来和特征,接下来重点介绍了在基带处理中CCK方式的调制和解调电路的设计,最后提了一下上述设计在实现中的考虑.     

不同调制码型的偏振模色散补偿研究

在40Gb/s的光纤通信系统中,用三段模拟器模拟光纤传输中的一阶与二阶偏振模色散(PMD),采用单偏振态的偏振度(DOP)作为多级PMD补偿器的反馈信号,对归零(RZ)码、非归零(NRZ)码、载波抑制归零(CSRZ)码和啁啾归零(CRZ)码分别进行四个自由度的一级、六个自由度的二级和十个自由度的三级PMD补偿器的补偿.仿真得到了四种码型的DOP与误码率(BER)的关系,同时补偿后的BER、DOP和PMD的变化关系表明,对RZ和NRZ码采用二级补偿器的效果比一级和三级补偿器要好得多,对CSRZ码和CRZ码采用单偏振态的DOP作为反馈信号进行PMD补偿的效果并不理想.     

基于DOP反馈的10 Gb/s系统PMD自适应补偿实验

报道了基于DOP反馈的10 Gb/s NRZ码和RZ码光通信系统的PMD自适应补偿实验,自适应补偿器的搜索时间低于1 s,受到突然扰动后的恢复时间少于20 ms.     

一种减少频率槽的同步码捕获方法

针对大动态下同步码实时捕获中频率槽过多、硬件资源消耗大的问题，提出了一种减少频率槽数量的同步码捕获方法。新方法将频率槽数量减小一半后，利用频率槽中的同步码相关值进行多普勒的估计和多普勒补偿，将补偿后的数据进行同步码捕获。理论分析和仿真验证表明，新算法在完成相同的同步码捕获性能下，基本将硬件资源降低到了原有系统的一半。     

近地应用CCSDS标准LDPC码动态补偿译码算法研究

针对CCSDS推荐的(8176,7154)有限几何准循环LDPC码,研究了LDPC码的修正最小和译码算法,提出了一种新的动态补偿最小和译码算法,并将本算法和修正最小和译码算法进行了性能比较。仿真结果显示,动态补偿最小和译码虽然算法迭代的收敛速度有所减慢,但具有比修正最小和算法更好的误码性能。     

RZ码和NRZ码的偏振模色散自适应补偿特性比较

建立了自适应偏振模色散补偿系统,利用偏振度作为反馈信号,对40 Gb/s的RZ和NRZ码分别进行了PMD补偿的数值模拟,结果显示,采用DOP作反馈信号、用二段补偿器和三段补偿器对二种码型的PMD补偿均是有效的.但由于高阶PMD的影响对NRZ码的补偿效果要优于RZ码,特别是存在偏振相关色散的影响时,对RZ码的补偿的影响在明显大于NRZ码,这说明,对于RZ码补偿偏振相关色散是必要的.     

大动态下扩频码捕获的一种改进方法

针对现有扩频码捕获方法在大动态下捕获时间长、硬件资源消耗大、动态适应性差的问题,提出了一种改进的扩频码捕获方法。新方法把码钟多普勒的补偿放在本地扩频码上进行,先对接收信号进行降采样和存储再进行频率分槽和补偿,一次采样实现了所有频率槽的搜索。计算结果表明,完成同样的捕获过程新方法所需时间和存储器容量不到原方法的1/5,且具备更强的动态适应能力。     

全相位单通道混合LDPC码识别安全跟踪算法

LDPC码识别和安全跟踪是自适应调制编码技术研究的核心。在此提出一种基于全相位单通道混合的LDPC码识别安全跟踪算法,构建LDPC码识别模型,设计全相位单通道混合编码技术。采用相空间重构技术对LDPC码进行多维空间向量重组,通过信宿译码降低加密信息的带宽占用率,同时减小了对编码向量分配的限制,通过全相位单通道混合补偿,降低码间干扰,提高LDPC码识别能力。仿真实验表明,该算法具有较好的LDPC码输出空间增益响应,提高了LDPC码的识别安全跟踪性能,输出误差较小,误码率较低,在自适应调制编码通信等领域具有较高的应用价值。     

高速无线数据传输中的补码键控扩频调制

补码键控扩频调制在克服多径效应、抗频率选择性衰落及抗窄带干扰方面有着优异的性能.IEEE802.11b标准规定采用补码键控技术以达到11Mbps,5.5Mbps的数据传输速率.介绍了该技术中采用的码字及其结构,并详细地给出了其调制与解调的具体实现.     

新型高效编码调制方式

在无线局域网中有很多调制方式,每个方式有它自己的特点。补码键控被采用可支持5.5Mbps,11Mbps,22Mbps,33Mbps的数据速率。超过了以前无线局域网标准2Mbps的速率。但是CCK在室内多径环境下性能相当不好。文中一个新的调制方案是把网格编码和CCK调制结合起来提出来的。通过仿真,这种方式在中到大的时延扩展信道环境下表现比较好的误码性能。     

Properties and performance of the IEEE 802.11b complementary-code-key signal sets

We describe similarities and differences between complementary-code-key (CCK) modulation and modulation that is derived from biorthogonal signals, and we present performance results and other information that may be useful to those who have applications for CCK modulation that do not require IEEE 802.11b compliance. The properties and performance of the highrate IEEE CCK 802.11b modulation formats are investigated and compared with the properties and performance of alternative modulation formats that are based on biorthogonal signals. Several complementary properties are derived for the full-rate (11 Mb/s) CCK signal set, the half-rate (5.5 Mb/s) CCK signal set, a full-rate signal set obtained from biorthogonal signals, and a half-rate biorthogonal signal set. Each signal set is a complementary set, but each also has stronger complementary properties. We evaluate the performance of IEEE 802.11b standard CCK modulation, CCK with certain modifications that depart from the IEEE standard, and modulation that is derived from biorthogonal signals. Performance comparisons are presented for additive white Gaussian noise (AWGN) channels and for channels with specular multipath. In particular, for AWGN channels, we provide an accurate analytical approximation for the frame error probability for full-rate CCK modulation.     

补码键控技术及其在无线局域网中的应用

补码键控技术是一种多进制编码扩频技术。本文介绍了该技术的相关函数特征及序列结构,并以无线局域网基带处理器HFA3861A为例,介绍了CCK扩频调制方式的典型应用。     

Trellis-coded complementary code keying for high-rate wireless LANsystems

In high-rate wireless LAN, complementary code keying (CCK) is adopted in the IEEE 802.11b standard to support data rates up to 11 Mbps, much higher than the 2-Mbps data rate in the previous wireless LAN standard. Due to less-than-ideal characteristics of the CCK codewords, the CCK performs quite poorly in large-delay-spread multipath channels. In this paper, a new modulation scheme that combines the trellis coding with the CCK modulation is proposed. This scheme is shown, through simulation, to achieve much better error rate performance in medium-to-large channel delay spread environments     

Bit and symbol error rates for complementary code key modulation with alternative bit mappings

Full-rate modulation in the IEEE 802.11b standard employs complementary code keying (CCK) with a set of 256 signals that provides 11Mb/s in favorable indoor propagation environments. The bit-to-symbol mapping of IEEE 802.11b is suboptimal for applications in which the bit error probability is important. We present analytical and simulation results on the bit and symbol error probabilities for IEEE 802.11b CCK and alternative bit mappings that improve CCK systems that need not adhere to the standard.     

Transmission and Reception Concepts for WLAN IEEE 802.11b

State-of-the-art wireless local area network (WLAN) IEEE 802.11b terminals employ complementary code keying (CCK) as modulation format. In this paper, receiver concepts tailored for CCK transmission over frequency-selective fading channels are presented in a unified and systematic framework. First, optimum maximum-likelihood (ML) detection for CCK signaling is considered. Second, for complexity reduction, minimum mean-squared error block decision-feedback equalization (MMSE-DFE) is investigated and reduced-state sequence estimation (RSSE) is considered on the basis of an Ungerbock-like set partitioning of the multidimensional CCK code wordset. In order to improve the reliability of CCK transmission over fading channels, time-reversal space-time block codes (TR-STBCs) combined with receive diversity are applied. Simulation results of the considered suboptimum receivers are compared with a performance approximation for optimum detection. Our results demonstrate the excellent performance of the advocated equalization schemes and the significant gains that can be achieved with TR-STBCs and receive diversity in typical WLAN environments     

卫星导航系统中数字调制技术研究

介绍了卫星导航系统中使用的各种调制技术及其优缺点,从调制信号的各种特性以及仿真结果出发,说明在频谱资源相当紧张的情况下,可利用各种调制技术的优势互补,来提高频谱资源的利用率和系统的整体性能,指出了未来卫星导航系统中调制技术的发展方向.