基于施密特正交化的降噪多载波相关延迟键控混沌通信系统

为解决传统相关延迟键控(CDSK)混沌通信系统存在的误码(BER)性能差的问题,该文提出一种基于施密特正交化的降噪多载波相关延迟键控(NR-MC-CDSK)混沌通信系统。在发送端,利用施密特正交化算法产生N组完全正交的混沌载波,并复制P次作为参考信号,与N个信息信号叠加进行传输,并利用多载波技术,复用每帧信号传输MN个用户信息。在接收端,将信号经匹配滤波器解调,然后通过滑动平均滤波器降噪,并进行相关解调。推导了系统在加性高斯白噪声(AWGN)信道和多径Rayleigh衰落信道中的BER公式并进行了仿真分析,结果表明系统的BER性能优于众多多载波混沌通信系统,数据传输速率也相较CDSK系统有明显提升,为该系统在实际通信系统中的应用提供了理论依据,并显示了较强的应用价值。     

Generalized correlation-delay-shift-keying scheme for noncoherent chaos-based communication systems

In this paper, we propose a generalized correlation-delay-shift-keying (GCDSK) scheme for noncoherent chaos-based communications. In the proposed scheme, several delayed versions of a chaotic signal are first produced. Some of them will be modulated by the binary data to be transmitted. The delayed signals will then be added to the original chaotic signal and transmitted. At the receiver, a simple correlator-type detector is employed to decode the binary symbols. The approximate bit error rate (BER) of the GCDSK scheme is derived analytically based on Gaussian approximation. Simulations are performed and compared with the noncoherent correlation-delay-shift-keying (CDSK) and differential chaos-shift-keying (DCSK) modulation schemes. The effects of the spreading factor, length of delay, and the number of delay units on the BER are fully studied. It is found that GCDSK can achieve better BER performance than DCSK under reasonable bit-energy-to-noise-power-spectral-density ratios.     

正交多用户CD-DCSK方案的设计及性能分析

为了进一步提升现有多用户混沌键控系统的信息传输速率和误码率(BER) 性能,该文提出一种正交多用户CD-DCSK(OMU-CD-DCSK)系统。该系统在差分混沌移位键控(DCSK)的基础上结合了相关延迟移位键控(CDSK),每个时隙中利用正交的Walsh码序列可以传输N bit的多用户信息,然后通过正交调制技术进一步提升传输速率。在接收端,采用滑动平均滤波器降低噪声方差,改善误码性能,之后进行相关解调即可恢复多用户信息比特。推导了多径瑞利衰落信道下系统的理论BER,并通过蒙特卡罗仿真实验进行了验证。此外,还定义了系统的综合效用,用于评估混沌系统的综合性能。与其他混沌键控系统相比,OMU-CD-DCSK的综合性能有明显优势,因此具有较好的实用价值。     

Effects of baseband predistortion at the transmitter on the performance of a DEQPSK satellite modem

The paper presents the results of an extensive series of computer-simulation tests to determine the effects of bandlimiting, nonlinear distortion with and without predistortion, and adjacent channel interference (ACI), on the tolerance to additive white Gaussian noise of a digital satellite modem. The modem transmits a differentially encoded quaternary phase-shift keyed (DEQPSK) signal over a satellite link, where the high-power amplifier (HPA) at the earth-station transmitter may introduce AM—AM and AM—PM conversion effects into the DEQPSK signal, but the satellite transponder is linear. Four different bandwidths of the transmitted signal are tested, together with three different levels of output back-off in the HPA at the transmitter. The predistorter operates on the baseband signal at the input to the modulator in the transmitter and assumes a prior knowledge of the HPA characteristics. ACI can be introduced into the transmitted DEQPSK signal by the corresponding DEQPSK signals, which occupy the two immediately adjacent frequency bands. The latter signals are assumed to have the same transmission rate and bandwidths as the first signal. Various combinations of the different distortion and interference effects are studied, using an equivalent baseband model of the transmission system, and the arrangements selected are those achieving the most efficient use of bandwidth together with the best tolerance to additive white Gaussian noise. A surprisingly good performance is achieved.     

An adaptive correlator receiver for direct-sequence spread-spectrumcommunication

This paper presents a novel receiver for direct sequence spread-spectrum signals over channels containing interference and multipath. The receiver employs an adaptive correlator that jointly detects the transmitted data, removes interference, and compensates for multipath. The optimum correlation vector is derived by determining the Wiener vector that minimizes the mean squared error (MSE) between the transmitted data bit and the correlator output. For an additive white Gaussian noise (AWGN) channel, the optimal correlation vector is the spreading sequence used by the transmitter. For interference and multipath channels, the optimal correlation vector will suppress the interference and combine the multipath while optimizing the detection of the transmitted data bit. The paper presents analytical and simulation results which illustrate the bit-error rate (BER) performance of the receiver in multipath and narrowband interference. Additionally, simulation results are presented illustrating the convergence performance of the receiver when the tap weights are adjusted using either the least mean square (LMS) or recursive least squares (RLS) adaptive algorithms     

无信号内干扰的相关延迟键控混沌通信方案

该文提出一种名为无信号内干扰相关延迟键控(Correlation-Delay-Shift-Keying with No Intrasignal Interference, CDSK-NII)的新型混沌通信方案。采用重复混沌序列为参考信号,同时利用零和序列确保参考信号与信息信号严格正交,CDSK-NII能够在解调过程中消除信号内干扰。在高斯白噪声信道和Rayleigh衰落信道中分析CDSK-NII的比特误码率。实验结果表明：由于无信号内干扰,CDSK-NII的比特误码率低于CDSK和通用相关延迟键控(GCDSK);随着复帧长度的增加,CDSK-NII的性能将进一步提升,比特误码率低于参考自适应相关延迟键控(RA-CDSK)。     

Performance analysis of an adaptive receiver structure for digital mobile communications

In this paper we investigate the performance of a combined estimation/equalization technique for the mobile radio channel, assuming a GSM-recommended transmission format (narrowband TDMA with midamble, recommendation 5.04) and MSK modulation scheme. Channel estimation is performed via correlation of the received signal with a suitably modulated replica of the transmitted midamble. Equalization is then obtained by means of a maximum likelihood sequence estimation (MLSE) scheme in the form of a so-called Viterbi equalizer. Our analysis provides theoretical results concerning the bit error rate (BER) attained by the receiver for a given stationary multipath channel model. Simulation results are also presented in order to integrate and validate the theory.     

Power domain cyclic spread multiple access: An interference‐resistant mixed NOMA strategy

The next generation wireless access technology highly relies on nonorthogonal multiple access (NOMA) technique. This paper proposes a novel power domain cyclic spread multiple access (PDCSMA) scheme for the design of NOMA system with power domain superposition coding (SC) and cyclic spreading at the transmitter concurrent with symbol level successive interference cancellation (SL‐SIC) at the receiver. Based on acceptable difference in channel gain, the users are grouped together to form PDCSMA clusters, and the unique power is allotted to each user in a cluster. The user with good channel condition is allotted less power, and the user with poor channel condition is allotted more power. Each PDCSMA cluster has its own spreading code, and the data of every user in a cluster are cyclic spread with the same code. Each cluster supports the number of multipath components equivalent to the length of the spreading code. The use of cyclic spreading makes the signal suffered by multipath fading less prone to intra cluster interference. The user signal is decoded by minimum mean square error‐frequency domain equalization (MMSE‐FDE) or maximal ratio combining (MRC)–based receiver in which weak user is detected with hard decision, and strong user is detected with SIC. Compared with conventional power domain NOMA (PDNOMA) and interleaved NOMA, the proposed PDCSMA achieves better bit error rate (BER) performance and assures guaranteed detection.     

Interference mitigation in uplink STBC MC-CDMA system based on PIC receiver

Multi Carrier Code Division Multiple Access (MC-CDMA) is attractive technique for high speed data transmission in multipath fading channel. MC-CDMA system cannot handle the sudden time variations of the channel which cause the subcarriers to lose their orthogonality. The loss of orthogonality between the subcarriers of a user or unwanted correlation between the spreading codes of different user can lead to increase in Multiple Access Interference (MAI). Space Time Block Code (STBC) based MC-CDMA system is chosen to achieve full diversity and transmission rate without the knowledge of Channel State Information (CSI) at the transmitter. Thus, in the paper STBC is introduced at the transmitter to improve the quality of the receiver. Space Time Block Code-Parallel Interference Cancellation (STBC-PIC) receiver has been proposed for MC-CDMA system. In the proposed STBC-PIC receiver, at each interference cancellation stage, weighted signal of the other user is subtracted from signal of the desired user, thereby reducing the MAI and improving the BER performance. From the simulation results, it is observed that the proposed receiver outperforms STBC-Orthogonal Complete Complementary Code (STBC-OCCC), STBC-Minimum Mean Square Error (STBC-MMSE) and STBC-Zero Forcing (STBC-ZF) receivers for MAI reduction.     

Non-coherent UWB Radio for Low-rate WPAN Applications: A Chaotic Approach

The requirements of low cost, low power and longer operation range for low-rate wireless personal area network (LR-WPAN) applications has driven the utilization of non linear communication approach. In this paper, a combined ultra-wideband (UWB) and chaotic communication technologies is proposed to meet these challenging demands. Among the candidates, the differential chaos shift keying (DCSK) modulation appears to be a very promising solution. The DCSK is a family of transmit reference (TR) system where a correlator based receiver is used to demodulate the received signal. However, this is not very well understood in the literature and therefore we will exemplify this issue in terms of noise performance. Furthermore, the feasibility study of the proposed DCSK is presented through the scalability and link budget analysis in two different operation modes. The system performance in both additive white Gaussian noise (AWGN) channel and standardized IEEE 802.15.4a UWB multipath channels are provided in order to further demonstrate the capability of the proposed system.     

Hybrid Access Network Integrated With Wireless Multilevel Vector and Wired Baseband Signals Using Frequency Doubling and No Optical Filtering

This letter experimentally demonstrated a hybrid access network which supports both radio-over-fiber and fiber-to-the-x systems. A 20-GHz radio-frequency (RF) 312.5-MSymbol/s M-ary phase-shift keying (PSK) signal and a baseband (BB) 1.25-Gb/s on–off keying signal are simultaneously generated and transmitted over an identical distributed infrastructure. The wired BB signal is compatible with the existing passive optical network (PON) system, and the wireless RF PSK signal can also share the same distributed infrastructure. The proposed system has no RF fading issue, no narrowband optical filter at remote node to separate the RF and BB signals, and can carry vector signals. Moreover, a frequency doubling for optical RF signal generation is achieved to reduce the bandwidth requirement of the transmitter. After transmission over 25-km standard signal-mode fiber, the receiver sensitivity penalties are less than 0.5 dB for both the RF and BB channels.      

异步垂直空时结构中的功率扩展技术

在平坦衰落信道中,针对异步垂直贝尔实验室空时结构(V-BLAST)信号模型下,现有线性最佳检测算法误码率性能随信噪比提高改善缓慢的问题,提出一种基于功率扩展的迭代检测方法:发射端用功率扩展将发射信号扩展到整个空时信号块上,接收端进行基于功率扩展的迭代检测。同时,分析了所提方法在每次迭代检测后的误码率性能。分析和仿真验证了误码率性能的改进。在4发4收场景下,误码率为10^-5时,相比于线性最优最小均方误差(MMSE)方法,获得了约6dB信噪比增益。     

Space diversity in presence of discrete multipath fading channel

Most analytical studies of the performance of space diversity systems on fading channels assume a very rich multipath environment. In certain wireless applications, however, the number of significant multipath components can be small. In this letter, we consider a multipath channel in which the signal propagates from the transmitter to the receiver via L discrete paths which are uniformly distributed about the transmitter and receiver. For this channel, we study the effects of the number of multipath components and antenna array size on the error probability and outage capacity of space diversity systems. We observe that performance is significantly influenced by the presence of a channel with few multipath components.     

多用户降噪差分混沌键控通信方案

传统多用户差分混沌键控主要缺点是误码率差,该文提出一种多用户降噪差分混沌键控(MU-NRDCSK)通信方案。在发射端,发送M/P长度混沌序列,复制P次后作为参考信号,所有用户共用同一参考信号,信息信号延迟不同的时间来区分用户。在接收端,将接收到的信号通过滑动平均滤波器平均,再与其不同时间延迟后的信号进行相关。该方案通过降低噪声项的方差来提高系统误码性能。文中推导了该方案在加性高斯白噪声(AWGN)信道和Rayleigh信道下的理论误码率公式并进行了蒙特卡洛仿真。理论分析和仿真结果表明,理论公式与仿真结果能较好地吻合,MU-NRDCSK方案能较好地提高系统误码性能,在混沌通信领域具有很好的发展前景与研究价值。

     

Theoretical studies of a simulcast digital radio paging system using a carrier frequency offset strategy

In a multistation simulcast digital radio paging system, each base station transmits the same RF signal simultaneously with the resulting efficient frequency utilization and simplified receiver design. In this system a paging receiver in the overlapping area receives several RF signals transmitted from different base stations. When frequency-shift keying (FSK) is used as a modulation method, experimental test results have already shown that the timing of each RF signal should be synchronized as closely as possible, but that the carrier frequency of each transmitter should be set following a certain offset assignment. The signal transmission performance in a multipath fading environment can then be markedly improved. The cause of this improvement effect is theoretically analyzed. It is clarified that the improvement effect is caused by transforming the probability distribution of time-averaged signal power.     

Multipath combining scheme in single-carrier transmission systems

In this letter, we introduce and investigate the RAKE combining receiver which is widely used in the code-division multiple access (CDMA) systems to the non-spectrum-spreading single-carrier transmission system. The initial estimate of the transmitted data is obtained by linear single-carrier equalizers, and then all the multipath signals are constructed from this initial solution and channel impulse response. By interference cancellation (IC) technique, we can acquire every multipath component in the received signal after cancelling the sum of all the other multipath signals constructed. Finally, all the components are combined together using selection combining (SC), equal gain combining (EGC) or maximal ratio combining (MRC), so that temporal diversity gain from the combined output can be obtained. Simulation results show that bit error rate (BER) performance of the new combining receiver based on zero forcing (ZF) and minimum mean square error (MMSE) equalizers can achieve the SNR gain dramatically in the SUI-5 wireless communication link.     

Multidimensional Adaptive Power Management for Low-Power Operation of Wireless Devices

Currently, wireless circuits are designed to meet minimum quality-of-service requirements under worst case wireless link conditions (interference, noise, multipath effects), leading to high power consumption when the channel is not worst case. In this work, we develop a multidimensional adaptive power management approach that optimally trades-off power versus performance across temporally changing operating conditions by concurrently tuning control parameters in the RF and digital baseband components of the wireless receiver. Simulation and hardware results indicate significant power savings in the receiver using the proposed approach while maintaining the system bit error rate specification.      

Verification of Digital RF Processors: RF, Analog, Baseband, and Software

Single-chip RF SoCs are seeing widespread acceptance in wireless applications. In this paper we address the issue of design verification of single-chip RF SOCs in a framework that accepts RF input and analyzes receiver BER performance and transmitter output distortion and phase noise by processing several thousand packets of baseband information while compensation algorithms are simultaneously executed. No comprehensive methodology exists to date for designing such complex systems. This paper present a novel approach that allows building complex RF SoC systems based on VHDL modeling and simulation and opens up major avenues of model development for RF and analog circuits. This approach has been successfully applied to verify two generations of digital RF processors (DRP) in deep-submicron technologies     

Transmitter-based multiuser interference rejection for thedown-link of a wireless CDMA system in a multipath environment

In wireless code division multiple access (CDMA) communications systems, there has been interest in processing the transmitted down-link signal in order to shift signal processing to the transmitter where power and computational resources are plentiful, thus simplifying receiver operation and reducing the power it requires. Multiuser interference (MUI) and multipath effects observed by the receiver are anticipated and suppressed at the transmitter; channel equalization and multiuser detection are therefore not required. This paper introduces two methods that are able to combat both degradations, yet allow the receiver to remain as simple as a single user receiver for a perfect channel. For mild multipath channels, the performance of the algorithms is excellent, within a few decibels of the single user ideal channel case, at the cost of additional computation at the base station at which complete knowledge of the channels and the receiver codewords is required. One method, the decorrelating prefilter, is most flexible and applicable to existing systems yet less powerful than other previously published methods. The second, the jointly optimized sequences algorithm, has a performance on average superior to published methods. In addition to theoretical analysis and simulation of the algorithms' potential, these algorithms have also been implemented and tested on a software radio testbed and experimental data are shown. The jointly optimized sequences performed particularly well even in severe multipath and multiuser interference environments     

Improved auxiliary particle filter‐based synchronization of chaotic Colpitts circuit and its application to secure communication

In this paper, we propose a synchronization scheme based on an improved auxiliary particle filter (IAPF) for chaotic Colpitts circuit and conduct an experimental study on the synchronization performance with application to secure communications. Specifically, with the synchronization scheme, when the chaotic signals generated by an analog Colpitts circuit are transmitted through a nonideal channel, the distorted signals are processed digitally by the novelly designed IAPF at the receiver, in order to obtain the synchronized signals of the transmitter circuit. Experimental results indicate that synchronization can be achieved over both the additive white Gaussian noise channel and the multipath fading channel with low signal‐to‐noise ratio, even if there exist severe circuit parameter mismatches between the transmitter and the receiver. Furthermore, a chaos‐masking secure communication system is constructed and verified over both the additive white Gaussian noise channel and the multipath fading channel, and the bit error rate is evaluated versus different signal‐to‐noise ratios and symbol periods. It is shown that the achievable bit error rate can reach the order of magnitude of 10 ^{− 4} without error correction coding techniques. In addition, security analysis demonstrates that the proposed chaotic secure communication system is resistant to the brute‐force attack. Copyright © 2013 John Wiley & Sons, Ltd.