共查询到20条相似文献,搜索用时 15 毫秒
1.
《Vehicular Technology, IEEE Transactions on》1978,27(4):264-275
A spread-spectrum technique for cellular high-capacity mobile communications is described and some results from an analytic study are summarized. The technique uses a very large set of frequency-hopped signals which are designed for minimal mutual interference. No synchronization of the mobile units is required, and each user is permanently assigned his own signal, which serves as an identifying signal and as a carrier for the biphase-modulated digital message. The spectral efficiency of the spread-spectrum system is analyzed and compared with the efficiencies of developmental FM/channel reuse schemes currently under construction in the U.S. and Japan. It is concluded that even with relatively simple speech digitization schemes, the efficiency of the spread-spectrum scheme may exceed those of the narrow-band schemes by a factor of almost five. More ambitious bit-rate-reducing speech digitization methods could improve still further on these figures. Additional benefits of the spread-spectrum scheme include immunity from fading and interference, more consistent speech quality, simpler system control algorithms, and more flexible blocking properties under overload conditions. 相似文献
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Soft synchronization of direct sequence spread-spectrum signals 总被引:1,自引:0,他引:1
A new technique for soft synchronization of direct-sequence spread-spectrum (DSSS) signals is presented. The technique, referred to as the dominant mode despreading (DMDS) algorithm, exploits the eigenstructure of a frequency-channelized DSSS signal to estimate the spreading code and underlying message sequence of the signal. Unlike other despreading techniques, the estimate of the code and data improves steadily with the number of code repeats. The technique is applicable to arbitrary spreading codes and message sequences and can operate in environments containing arbitrary levels of white background noise, and for signals with arbitrary unknown timing phase or carrier frequency offset. The technique requires the DSSS signal to have a constant-modulus spreading code and unrelated message and code-repeat rates. This paper introduces the basic technique, theoretically analyzes the algorithm to prove convergence under infinite time-average conditions, and demonstrates the algorithm via computer simulation for a single DSSS signal received in the presence of white Gaussian noise 相似文献
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In this paper we focus our research on the symbol timing synchronization technique in COFDM systems. A new method utilizing pilots to do coarse symbol timing is proposed. It overcomes the problem of fluctuation of the estimated symbol start position with cyclic prefix correlation method. The symbol timing error with the proposed method is within only /spl plusmn/10 samples. Different from previous algorithms in , we utilize the known pilot information to estimate the residual symbol timing offset with low system complexity. This paper also proposes a new control model for the sampling clock adjustment, different from the phase-locked loop (PLL), or delay-locked loop (DLL) method. The simulation and correspondent Field Programmable Gate Array (FPGA) circuit through test in HDTV prototype in Team of Engineering Expert Group (TEEG) proves its feasibility and availability. The proposed method is also suitable for burst mode transmission systems such as Wireless Local Area Network (WLAN) and Fixed-Broadband Wireless Access (F-BWA). 相似文献
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Typically, spectral efficiency, the throughput in bits/second/hertz, has been evaluated for fixed values of the bit error probability. We introduce a cutoff-rate-based approach to evaluation of the spectral efficiency of direct-sequence spread-spectrum schemes so that the results are independent of specific bit error rates or channel codes. Results are shown for M-ary phase-shift keyed modulation on the slow-fading Rician channel 相似文献
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Christiansen C.F. Valla M.I. Rivetta C.H. 《Industrial Electronics, IEEE Transactions on》1988,35(4):502-507
A synchronization technique for static delta-modulated PWM inverters is presented. This control strategy removes the frequency modulation inherent in the delta-modulated inverter. Furthermore, synchronization of the PWM pulses with the reference signal ensures balanced phase voltages in three-phase applications. The performance of the modulator is analyzed using digital simulations and is verified with experimental circuits 相似文献
8.
Katsis P.L. Karagiannidis G.K. Pavlidou F.-N. 《Communications, IEEE Transactions on》2008,56(12):2166-2177
Recently, Multi-User Selection Diversity (MUSDiv) for single-carrier systems has been under extensive study on account of the enhancement it provides to system performance with minimum feedback requirements. However, its application to multichannel systems is considered straightforward and thus, it has not been thoroughly examined. In this paper, the performance of MUSDiv is investigated when applied to the spread-spectrum multi-carrier multiple-access system, where the scheduling has to be performed for all the available channels and self interference must also be considered. Specifically, based on the absolute and normalized Signal-to-Noise-Ratio (SNR) scheduling algorithms, two algorithms are presented, modified and optimized, so that they can be applied on a subband instead of a single-channel basis. Moreover, we propose a new scheduling scheme which constitutes a trade-off between the previous schemes, concerning fairness and capacity performance. The new algorithms are related to the symbol Signal-to-Noise-plus-Interference-Ratio (SNIR) instead of SNR and two interference models were devised to this end. Closed-form expressions for the system capacity are extracted for each case, which are compared with simulation results. The research is also extended to the case of non-identical user power profiles among the available subcarriers. The channel state information required to utilize multi-user selection diversity is already necessary for the most common combining schemes, so no more feedback is actually needed. 相似文献
9.
Slobodan Djukanovi? Vesna Popovi?Miloš Dakovi? Ljubiša Stankovi? 《Signal processing》2011,91(6):1425-1431
The problem of non-stationary interference suppression in direct sequence spread-spectrum (DS-SS) systems is considered. The phase of interference is approximated by a polynomial within the considered interval. According to the local polynomial Fourier transform (LPFT) principle, the received signal is dechirped by using the obtained phase approximation and the interference is, in turn, suppressed by excising the corrupted low-pass frequency band. For the estimation of polynomial coefficients, we use the product high-order ambiguity function (PHAF), known for its capability to successfully resolve components of a multicomponent polynomial-phase signal (PPS). The proposed method can suppress interferences with both polynomial and non-polynomial phase. In addition, it can suppress both monocomponent and multicomponent interferences. The simulations show that the proposed method outperforms time-frequency (TF) methods, that successfully deal with multicomponent interferences, in terms of the error probability and computational complexity. 相似文献
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A new blind (non-data-aided) synchronization algorithm based on direct-sequence (DS) codes is proposed for ultra-wideband (UWB) systems. The proposed approach fully exploits prior knowledge of DS codes and bypasses channel estimation. The real-time acquisition is achieved using integrating-and-dumping (I&D) operation and DS codes matching filter. Because of pseudo randomicity and periodicity of DS codes, both the speed and the accuracy of synchronization are improved significantly. A lower bound on the acquisition probability of the proposed approach is also derived. Simulations confirm performance improvement of the proposed algorithm relative to existing alternatives in terms of acquisition probability, normalized mean square error (NMSE), and bit error rate (BER). 相似文献
11.
A method is presented for enhancing the narrow-band interference rejection capability of direct-sequence spread-spectrum systems employing an adaptive notch filter. The method, based on projection onto convex sets, restores that part of the spread-spectrum signal distorted by the filter. Simulation results are presented which show the output bit-error rate (BER) improvement gained by using the signal restoration scheme 相似文献
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适用于超宽带通信测距复合系统的同步机制 总被引:2,自引:0,他引:2
通过Simulink仿真和FPGA板级验证,为基于隧道二极管电路的脉冲超宽带(Impulse Radio Ultra -wideband,IR-UWB)接收机提出了一种同步机制.在物理层中使用了改进数据转换跟踪环的位同步方法,使之可以对单比特数据进行位同步,码速率为2 Mbit/s时误码率趋近于零;MAC层使用了经过变... 相似文献
15.
Lu Cewu Liu Xiaojun Kuang Yujun Fang Guangyou Chen Qianbin 《电子科学学刊(英文版)》2007,24(6):760-764
The paper proposes a novel approach for fine frequency synchronization of OFDM syn- chronization systems in multi-path channels. Maximum Likelihood (ML) function of frequency offsets including integral and decimal parts in frequency domain is developed according to the law of great number to eliminate the noise impact of the signal. When the timing delay close to the actual time, the proposed function produces a deep valley indicating frequency offset when large Valley-Square- Error (VSE) appears. Coarse timing offset can also be detected when function’s Valley-Square-Error (VSE) is maximized. Simulation results shows that the proposed algorithm gives very robust estimation of frequency offset, and a coarse timing offset estimation. 相似文献
16.
Vanhaverbeke F. Moeneclaey M. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2005,51(3):1136-1139
Signature sets that maximize the sum capacity of an oversaturated code-division multiple-access (CDMA) system are derived, under the constraint that the signature sets have to be quasi-scalable. It turns out that the optimal signature set is composed of orthogonal signature sets, with at most one incomplete orthogonal set. As compared to the Gaussian multiple-access channel (GMAC), the loss in spectral efficiency for this multiple-orthogonal CDMA (OCDMA) system remains very low. 相似文献
17.
Murata Y. Esmailzadeh R. Takakusaki K. Sourour E. Nakagawa M. 《Selected Areas in Communications, IEEE Journal on》1994,12(5):970-975
A fast frequency hopping (FFH) method which uses path-diversity combining is proposed. Diversity techniques are realized when a signal is received from diverse independent paths, each of which carries identical information but suffers from independent fading variations. The improvement of communication performance of FFH systems is possible as the delayed paths are used and path-diversity combination is realized. The advantages of this method, operating in Rayleigh fading channels are confirmed by theoretical analyses. The improvement is in order of 2~3 dB at bit error rate (BER) of 10-3. This method can be also effective against interferences from other users in a code division multiple access (CDMA) environment. The performance of this system in a CDMA environment is evaluated by theoretical analyses and is shown to be superior to non-combining method. At BER of 10-3 the required Eb/N0 of the proposed system is 5 dB lower. If Eb/No is fixed, a greater number of users can be accommodated using the proposed system 相似文献
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高精度双向时间同步是分布式机动无源定位系统的一项关键技术。结合机动平台的特点,对基于伪码相位测量的双向时间同步系统的误差来源和影响误差的因素进行了分析,并针对其中一些引起误差的主要因素给出了控制误差的有效方法。仿真和实测表明,最终可以在机动平台间实现0.2 ns左右的时间同步精度。 相似文献
19.
The information theoretic capacity is considered. In order to account for independent encoding and decoding and private (to the sender and receiver) hopping patterns, an interference channel model is adopted with K sender-receiver pairs with the i th receiver only interested in the message transmitted by the i th sender. Both synchronous and asynchronous hopping patterns are investigated. Although the channel exhibits memory in the latter case, it is possible to compute the capacity region. The asymptotic normalized sum capacity is also computed 相似文献
20.
Gelli G. Paura L. Tulino A.M. 《Selected Areas in Communications, IEEE Journal on》1998,16(9):1747-1755
This paper addresses the problem of narrowband interference suppression in direct-sequence spread-spectrum (DS/SS) techniques, which have been adopted to implement code division multiple access (CDMA) systems for wireless mobile communications. The theory of cyclic Wiener filtering, based on the cyclostationarity assumption for the signals involved in the reception problem, is applied to design single-channel adaptive frequency-shift filters which exploit both temporal and spectral correlation properties, i.e., the correlation between time- and frequency-shifted versions of the received signal. The numerical results show that receiving structures based on the proposed cyclostationarity-based interference suppression schemes largely outperform receivers that utilize conventional linear time-invariant suppressors, when they operate in highly contaminated interference environments 相似文献