扩频技术及其应用

扩频技术是充分利用有限频谱资源,提高无线信息传输效率的一种新技术,文章介绍了扩频通信工作原理及其系统模型,详细阐述了扩频通信的两种主要技术:直接序列扩频和跳频扩频,解释其工作原理,并将这二者的性能进行比较。另外介绍了扩频与数字水印技术的结合,利用扩频原理的数字水印技术具有很高的健壮性和安全性。     

扩频技术及其应用

一、引言 随着1993年美国第二个数字蜂窝移动通讯系统标准IS 95的出台,CDMA技术在通讯领域掀起的热潮达到了一个新的高度,人们对CDMA技术的兴趣也越来越浓。CDMA技术基于扩频技术,而扩频技术的应用可以追溯到二次世界大战;本文从扩频技术的一般原理出发,着重介绍扩频技术的弛特之处,并主要以应用最多的直接序列扩频(DS)系统为例,最后简要介绍民用通讯方面的应用。     

高性能扩频专用集成芯片SC2001及其应用

扩频增益是在直接序列扩频技术中衡量扩频性能优劣的重要指标 ,而伪随机码的长度又直接决定了扩频处理增益。文中介绍了SIRIUS公司生产的具有高扩频处理增益的直扩芯片ASTRASC2001的结构和特点 ,同时介绍了由其构成的长码扩频系统的硬件构成和软件设计原理 ,同时给出了该系统的软件设计框图。     

一种扩频数据调制解调器

介绍了采用扩频技术,利用STEL-2000A以及相关外围芯片组成扩频调制解调器。重点介绍其硬件结构     

浅论扩频技术及其在本地接入网中的应用

本文主要介绍了扩频技术并列举了无线扩频技术在本地接入网中的主要应用方式。     

微波扩频技术在远程监控传输系统中的应用

简述了扩频技术的原理和特点,侧重介绍了扩频技术在远程监控传输系统中的应用实例,从理论和实际这两方面阐述了微波扩频技术在远程监控传输系统中所起的举足轻重的作用。     

扩频数据通信系统

本文简要介绍数据通信的基本问题。由扩频原理着手分析了扩频技术的主要优缺点。讨论了克服扩频技术缺点的方法。最后介绍一种新研制定(?)的(?)频段数话双工、收发全双工通信机。     

扩频技术及其在移动通信中的应用

扩频技术的开发已有多年的历史，并作为一种通信方式特别引人注目，得到了迅速发展和应用，本文介绍了扩频技术及其在移动通信领域中的应用，包括数字蜂窝、寻呼机、ＧＰＳ等，并重点介绍了移动通信的直序扩频技术。     

浅论扩频通信及其在本地接入网中的应用

本文主要介绍了扩频技术并列举了无线扩频技术在本地接入网中的主要应用方式.     

微波扩频无线网络在教学中的应用

阐述了微波扩频技术在无线教学网络中的应用。结合微波扩频的技术特点，侧重介绍了微波扩频的工作方式及其网络在不同条件下的接入方式和网络优势。     

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.     

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     

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.     

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     

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.     

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.     

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。     

A RAKE Receiver With an ICI/ISI Equalizer for a CCK Modem

In this paper, we first derive the theoretical performance of a complementary code keying (CCK) code on an additive white Gaussian noise (AWGN) channel and over a multipath channel. To derive the error performance, we use the weight and cross-correlation distributions of the CCK code for optimal and suboptimal decoding, respectively, based on union bound. In addition, we propose a RAKE receiver for a CCK modem, which is suitable for a multipath environment with a large delay spread. The RAKE receiver principle is acceptable for modest multipath because it can coherently combine multipath components to provide signal-to-noise ratio (SNR) enhancement. However, as the delay spread is larger and the data rate of systems goes higher, intersymbol interference (ISI) generated due to multipath environments are increased. To handle the increasing ISI, the CCK modem needs an equalization technique to remove the ISI, together with RAKE processing. Thus, our proposed system is based on a channel matched filter (CMF) with a decision feedback equalizer (DFE). The CMF is applied for RAKE processing, whereas the DFE structure is used for ISI cancellation. In our system, ISI is calculated and removed by using a decoded CCK codeword.     

CCK——高速无线局域网的关键调制技术

本文首先简要介绍了补偿码的概念,然后着重分析了补偿码序列的特性和CCK调制技术的原理,最后简述了CCK技术在Intersil HFA3863中的实现.     

Bidirectional iterative ISI canceller for high-rate DSSS/CCK communications

This paper proposes a new RAKE receiver incorporated with a bidirectional iterative intersymbol interference (ISI) canceller in order to reinforce multipath robustness of high-rate direct-sequence spread-spectrum complementary code keying (DSSS/CCK) systems. The proposed RAKE receiver first combines multipath signal components through a channel matched filter (CMF) and removes postcursor-ISI by employing a codeword decision feedback equalizer (DFE). Then, a CCK codeword detector tentatively determines the current CCK codeword symbol and reuses it to subtract precursor-ISI from the previous symbol. Therefore, the ultimate symbol decision is made using the delayed signal with both postcursor-ISI and precursor-ISI cancelled. The detection performance can be more improved through an iterative refinement processing between the postcursor and the precursor components. Simulation results exhibit a significantly improved error rate performance of the proposed receiver compared with that of the legacy RAKE receiver employing only a postcursor DFE. The additional cost for realization of the proposed receiver is one symbol decision delay and reuse complexity of the DFE and the codeword detector.