Design and Experimental Results for a Direct-Sequence Spread-Spectrum Radio Using Differential Phase-Shift Keying Modulation for Indoor, Wireless Communications

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.     

High-Rate Direct-Sequence Spread Spectrum With Error-Control Coding

High-rate direct-sequence (DS) spread spectrum is a modulation technique in which most or all of the spreading is provided by nonbinary data modulation. For applications to mobile ad hoc wireless networks, the limited processing gain of high-rate DS spread spectrum gives only modest protection against multiple-access or multipath interference, which limits the applicability of the modulation technique to fairly benign channels. In this paper, we explore the increased interference-rejection capability that can be obtained from convolutional coding with Viterbi decoding, Reed–Solomon coding with errors-and-erasures decoding, and block product coding with iterative decoding. For channels with multiple-access or multipath interference, performance results are given for several soft-decision decoding metrics, the benefits of adaptive-rate coding are illustrated, and the accuracy and utility of the Gaussian approximation are described. We also show how to use the bit-error probability for a system without error-control coding to determine which modulation method will give the best packet-error probability in a system with error-control coding.     

Performance Criteria for Spread Spectrum Communications

The criteria for antijam (AJ) and anti-intercept (AI) systems are described, in terms of the appropriate action taken by the jammer or interceptor. Avoiding pseudonoise (PN) sequences which can be partially or totally predicted is a foremost criteria, especially for AJ, and use of nonlinear feedforward logic (NFFL) with long-period linear maximal sequences appears attractive. A frequency-hopping (FH) system must anticipate a multitone jamming signal, and an error-control code is necessary. A novel method for generating a multitone signal using repeating maximal sequences is described. PN systems must anticipate a tone jammer, and now an errorcontrol code may be needed to assure that sporadic PN sequence correlation with the tone does not reduce the processing gain. Any AI system must anticipate that the interceptor may, if advantageous, integrate his decision energy over many communicator symbols (up to the message length). Now spreading both in frequency and in time may be valuable. Finally, the use of an automatic adaptive data rate is suggested to realize flexibly either AJ or AI objectives.     

Combination Sequences for Spread Spectrum Communications

Certain communication systems which employ spread spectrum techniques as a means of supporting multiple users need very long codes to guard against the threat of intentional jamming, but cannot tolerate the lengthy acquisition time which long codes usually require. As a possible solution to this problem, the use of combination sequences has been suggested, and this paper presents some new results, both analytical and numerical, on this technique.     

扩频技术在水下声通信系统中的应用

综述了扩频技术在浅海通信环境中的应用现状,讨论了该技术在浅海通信环境中的发展前景,其中包括DS-SS直接序列扩频系统,M-family扩频系统以及RAKE接收机。在比较各系统优缺点的基础上仿真了扩频系统和RAKE接收机,并提出了进一步改进系统的方案。     

A Wireless Network for Wide-Band Indoor Communications

We propose and analyze a wide-band indoor communication system that uses radio as the transmission medium either on a stand-alone basis or to supplement a hard-wired network for those situations where complete portability is desired. One principal impairment to such a system is intersymbol interference caused by frequencyselective fading. A novel media-access scheme is proposed which permits the use of resource sharing, wherein a small pool of time slots is effectively shared among all users to provide added protection against channel impairments on an as-needed basis. Our results show that the use of resource sharing and diversity provide excellent protection against intersymbol interference caused by frequency-selective fading with negligible impact on throughput. Furthermore, resource sharing plus diversity can permit significantly higher data rates without large queueing delays. For example, a wireless network with a 10 Mbit/s data rate in a 10 MHz bandwidth using four antennas at the base station has a less than 10^-4outage probability at a 10^-4BER in buildings with less than 58 ns rms delay spread. A loading of 75 percent is permitted for a queueing delay of less than 20 packet transmission times all but 0.01 percent of the time.     

Diversity Combining and Equalization with TCM for Wireless Communications

This paper presents an equalization structure in which antennadiversity, adaptive decision feedback equalization (DFE), interleavingand trellis-coded modulation (TCM) can be effectively combined to combatboth ISI and cochannel interference in cellular mobile radioenvironments. The feedback filter of the DFE can use either tentative orfinal decision symbols of the TCM Viterbi decoding to cancel tail ISIwith the square root Kalman algorithm. A performance bound on theaverage pairwise error probability for TCM under perfect interleavingand equalization is obtained by analysis. Some simulation results whichillustrate the potential of the proposed system will also be given. Inparticular, a performance comparison between the proposed method anduncoded QPSK modulation will be undertaken.     

Utilizing Space-Time Diversity for Wireless Communications

In this paper we consider the use of multiple antennas for wireless communication over fading channels.The fading we consider is quasi-static flat Rayleigh fading. For such a scenario optimal SNR schemes are derived when the transmitter knows the channel and when the transmitter does not know the channel. But in both cases the receiver has to estimate the channel. When the SNR during channel estimation is reasonably high we derive expressions to show the impact of channel estimation errors on SNR.     

用扩频调制实现多相振荡器

LTC6902是凌特公司新推出的一款多相振荡器，该振荡器借助扩频调制和伪随机噪声技术降低了开关电源的EMI，且其多相输出可在分布式电源系统中对四个稳压器实施同步处理。本文介绍LTC6902的性能及特点，并阐述其应用电路。     

个人通信中的扩频技术

在个人通信中,必然会遇到频谱共享、通信安全、传播环境和多径干扰等复杂技术难题,而扩频通信技术是同时解决这些问题又可提供多种信息服务的良策。本文主要讨论扩频技术基础以及扩频技术在个人通信中的应用。     

扩频调制与性能分析

主要介绍了扩频调制原理,包括直接序列扩频和跳频扩频原理:对于直接序列扩频系统,利用系统发送模型和系统接收模型,详细分析了直接序列扩频调制误码性能,给出了相应的理论表达式;对于跳频扩频系统中,采用BFSK调制时,也分析了误码性能,并给出了分析结果。     

多径衰落信道中M进制直接序列扩频系统RAKE接收机性能分析

本文分析了存在码片定时误差和载波相位估计误差情况下,采用BPSK调制的M进制正交码直接序列扩频信号在多径衰落信道下的RAKE接收机性能.分别讨论了不使用分集和采用选择式合并、等增益合并和最大比合并三种分集合并策略时接收信号的误码率,并推导出相应的近似计算方法.文章最后在此基础上分析了不同的分集合并办法、码片定时误差和载波相位误差对系统性能的影响.     

RIS Assisted Dual-Function Radar and Secure Communications Based on Frequency-Shifted Chirp Spread Spectrum Index Modulation

Reconfigurable intelligent surface(RIS)assisted dual-function radar communications(DFRC)system is a promising integrated sensing and communication(ISAC) technology for future 6G.In this paper,we propose a scheme of RIS-assisted DFRC system based on frequency shifted chirp spread spectrum index modulation(RDFI) for secure communications.The proposed RDFI achieves the sensing and transmission of target location information in its radar and communication modes,respectively.In both modes,the frequen...     

Performance of Quadrature Amplitude Modulation for Indoor Radio Communications

The performance ofM-QAM for indoor radio communications is evaluated via a realistic model for indoor multipath propagation [1]. It is found that the outage (BER < 10^-4) is about 0.3 percent at 1 Mbit/s and 20 percent at 4 Mbits/s. Two-antenna predetection diversity reduces the outage from 1.2 to 0.04 percent at 2 Mbits/s. Increasing the signaling pulse rolloff factor from 0.5 to 1.0 reduces the outage by not more than 35 percent.     

自适应调制扩频技术

文中提出了在OFDM系统中结合自适应调制和自适应扩频,构成自适应调制扩频算法,该算法可适应大范围的信道变化。仿真结果表明:在OFDM系统中采用自适应调制扩频算法,信噪比在-8DB-20DB之间变化时,系统的误码率均可保持在10-3以下。     

Models for Wireless Data Communications in Indoor Train Environment

The provisioning of wireless data services in the railway environment will become increasingly important for train operators and train constructors in the upcoming years. In this paper, we present models to predict train-to-wayside wireless data communications characteristics in terms of throughput, jitter, and packet loss predictions for 2G/3G networks. To this end, an extensive measurement campaign is carried out along a Belgian Intercity railway track. Based on these measurements, we apply a multiple regression, window mean, and autoregressive model. We find that the window mean model is recommended for the prediction of throughput and jitter, while the multiple regression model is more favorable for the prediction of packet loss. The implementation of these predictions in train-to-wayside communication systems can enhance the provisioning of seamless network connection necessary for a wide variety of data services.     

Polarization Effects for Indoor Wireless Communications at 60 GHz

This letter studies the performance of indoor wireless communication systems operating at 60 GHz with different polarization schemes. Circular polarization is known to reduce multipath effects in line-of-sight (LOS) environments in the 60 GHz band. We propose a modified channel model based on the IEEE 802.15.3c channel model to incorporate the polarization effects. We then use this model to evaluate the error performance of a wireless communication system that uses circular polarization. The results are compared with linear polarization for LOS environments.     

无线扩频通信及其应用

本文介绍了无线扩频通信技术,以及将其应用于军队战术指挥自动化系统中,以实现保密通信和计算机局域网的网际互联。