共查询到19条相似文献,搜索用时 109 毫秒
1.
2.
讨论并分析了采用数字相关器的MSK扩频系统发射和接收基本原理。在PN码元的捕获系统中使用了一种改进的附加数字相关器。分析及实验结果表明,对于MSK扩频系统,低信噪比情况下能够正确解码,处理信号的形式灵活,免除了—般扩频系统中最难解决的PN码同步,并为位同步的提取带来了极大的方便;与数字相关器相比,能够简化捕获运算,且有效改善干扰。 相似文献
3.
为了提高传统直扩通信系统的抗截获性能,本文提出了一种将混沌直接序列扩频和跳码通信相结合的通信体制,重点介绍系统的同步过程。具体实现时,利用一个通过二次扩频方式复接在业务信道上的低速隐蔽信道实现混沌序列的同步以及通信过程中扩频码的变换。由于采用了周期性长、伪随机性好的混沌序列作为扩频码,而且通信过程中可以对混沌系统的混沌映射关系及初始条件进行随机更新,因此与传统的直接序列扩频通信相比,混沌直扩跳码通信具有更好的抗截获性能。 相似文献
4.
5.
JTIDS波形采用扩频机制进行系统同步,并采用多进制扩频和MSK调制方式传输信息。针对这种特点,JTIDS波形在接收端一般采用匹配相关取相关峰位置的方法来同步和解调。一种方式是将AD(模数转换采样)下变频滤波后的IQ数据直接进行匹配相关;另一种是对AD采样数据只取符号位后进行下变频滤波再进行匹配相关。本文对两种方法的性能进行了分析比较。 相似文献
6.
根据飞行器测控技术发展特点,提出多址正交码扩频体制,分析了系统的发射、接收模型及其误码率性能;仿真了多址正交码扩频系统的噪声性能、多址性能和抗干扰性能;讨论了对正交码同步捕获与跟踪、正交扩频体制下的伪码测距等关键技术问题。 相似文献
7.
本文提出了采用MSK信号格式的 3种扩频接收机中放系统模型 ,并用计算机模拟的方法分析比较了几种典型的干扰环境下 3种系统的性能 ,文中给出的曲线可供设计MSK扩频通信系统参考。 相似文献
8.
9.
本文将无人机无线电测控系统中应用的伪码扩频技术进行扩展,提出了采用GM-SK窄带调制方式的直接序列扩频传输体制(SS/DS/GMSK)。给出了这种体制的一种实现方案,并进行了必要的性能分析。 相似文献
10.
11.
The impact of imperfect synchronization on the performance of prediction-error interference rejection filters in noncoherent direct-sequence (DS) spread-spectrum communications is considered. Bit-error-rate analysis (BER) analysis (BER) of binary DPSK (differential phase-shift keying) data modulation used in conjunction with direct-sequence spread-spectrum is used as a performance measure. A first-order noncoherent delay-lock loop is used for the pseudonoise (PN) code tracking. Conditional BER results for the DS/DPSK systems for fixed values of the code tracking error are obtained. The average BER of the system is then evaluated by averaging the conditional BER expressions over the probability density function of the code tracking error. Results include the effects of both a single fading tone and a narrowband Gaussian interferer on the overall system performance. Interferer offset frequency is considered in determining the code tracking loop noise as well as the receiver BER 相似文献
12.
13.
We report on our design and measurements that have been made for a direct-sequence spread-spectrum radio using differential phase-shift keying modulation for a wireless PBX. We describe the design and implementation of a transmitter and a receiver using a surface acoustic wave (SAW) filter matching the spread-spectrum code of a user. The receiver performance is within 1 dB of the theoretical performance of a differential phase-shift keying (DPSK) receiver in the presence of additive white Gaussian noise. We also show receiver performance in a multipath fading indoor environment with multipath fade notches of up to 50 dB depth. The indoor channel multipath fading can be overcome by using an equal gain diversity combiner which is suitable when DPSK modulation is used. We confirm that the indoor mean power level attenuation follows the inverse fourth power of the distance. Also, we investigate the multiple-access capability of the system by introducing an interfering transmitter with a different spread-spectrum code sequence. 相似文献
14.
A threshold decision for code acquisition in direct-sequence spread-spectrum packet radio systems is described. It is shown that this scheme achieves lower false alarm probability than the acquisition scheme based on the Neyman-Pearson criterion, giving comparable performance for the detection probability 相似文献
15.
Performance analysis of time-hopping spread-spectrum multiple-access systems: uncoded and coded schemes 总被引:1,自引:0,他引:1
Forouzan A.R. Nasiri-Kenari M. Salehi J.A. 《Wireless Communications, IEEE Transactions on》2002,1(4):671-681
An ultra-wide bandwidth time-hopping spread-spectrum code division multiple-access system employing a binary PPM signaling has been introduced by Scholtz (1993), and its performance was obtained based on a Gaussian distribution assumption for the multiple-access interference. In this paper, we begin first by proposing to use a practical low-rate error correcting code in the system without any further required bandwidth expansion. We then present a more precise performance analysis of the system for both coded and uncoded schemes. Our analysis shows that the Gaussian assumption is not accurate for predicting bit error rates at high data transmission rates for the uncoded scheme. Furthermore, it indicates that the proposed coded scheme outperforms the uncoded scheme significantly, or more importantly, at a given bit error rate, the coding scheme increases the number of users by a factor which is logarithmic in the number of pulses used in time-hopping spread-spectrum systems. 相似文献
16.
We propose a scheme for spread-spectrum communications using true random sequences generated by chaotic semiconductor lasers as spreading codes.These sequences can eliminate the inherent periodicity of pseudorandom sequences,enlarge the capacity of spread-spectrum codes,improve communication security,and increase the number of users of the system.When a true random sequence with an appropriate length is used as the spread-spectrum code and the information speed is maintained constant,the system acquires a greater spreadspectrum gain and a lower bit-error ratio(BER) than the traditional spread-spectrum system.The communication security is also enhanced.The BER smoothly increases with the number of users,which indicates the good multipleaccess capability of the system. 相似文献
17.
A spread-spectrum system that does not have a separate state for initial code acquisition is presented. A uniform random variate selects one of several Gold codes for transmission, thus removing the notion of pseudorandom codes from spread-spectrum systems, making the effective code length infinite, and leading to acquisitionless systems. Because coding is critical to the proposed multiaccess frequency-hopping (FH) system, more powerful codes are needed. The performance of the proposed multiaccess system using the combined modulation and coding technique (trellis) concatenated with Reed-Solomon codes in partial-band jamming is investigated. The FH multiaccess performance of noncoherent soft detection of MFSK in association with trellis coding is introduced and the performance compared to that using RS outer/RS inner concatenated codes 相似文献
18.
The performance of synchronous and asynchronous hybrid direct-sequence/slow-frequency-hopped spread-spectrum multiple-access communications over additive white Gaussian noise channels is examined. Systems employing binary or quaternary phase-shift-keying modulation with coherent demodulation are investigated. Both deterministic and random signature sequences and frequency-hopping patterns are considered and several possible assignments for them are discussed. It is shown that the multiple-access capability of hybrid spread-spectrum is superior to that of pure frequency-hopped spread-spectrum, and inferior to that of pure direct-sequence spread-spectrum for systems with identical bandwidth expansion which employ the same data modulation and demodulation scheme and random hopping patterns and signature sequences. 相似文献
19.
A parallel acquisition scheme for direct-sequence spread-spectrum systems is proposed, and its mean acquisition time performance is analyzed in both nonfading and Rayleigh-fading environments. An expression for the mean acquisition time is derived in terms of the probabilities of detection, missing, and false alarm. These parameters are first analyzed for a typical AWGN (additive white Gaussian noise) channel, then the Rayleigh-fading channel encountered in a typical UHF or microwave land mobile radio channel is studied. The channel is assumed frequency nonselective, and the effect of data modulation and code Doppler is not considered. The performance of the parallel system is compared to the corresponding serial system, and it is shown that a significant improvement can be achieved 相似文献