检索结果-内蒙古大学图书馆

Propagation delay estimation in asynchronous direct-sequence code-division multiple access systems

IEEE TRANSACTIONS ON COMMUNICATIONS 1996年第1期44卷 84-93页

作者： Strom, EG Parkvall, S Miller, SL Ottersten, BE UNIV FLORIDA DEPT ELECT ENGN GAINESVILLE FL 32611 USA

In an asynchronous direct-sequence code-division multiple access CDS-CDMA) communication system, the parameter estimation problem, i.e., estimating the propagation delay, attenuation and phase shift of each user's transmitted signal, may be complicated by the so-called near-far problem. The near-far problem occurs when the amplitudes of the users' received signals are very dissimilar, as the case might be in many important applications, In particular, the standard method for estimating the propagation delays will fail in a near-far situation, Several new estimators, the maximum likelihood, an approximative maximum likelihood and a subspace-based estimator, are therefore proposed and are shown to be robust against the near-far problem, No knowledge of the transmitted bits is assumed, and the proposed estimators can thus be used for both acquisition and tracking. In addition, the Cramer-Rao bound is derived for the parameter estimation problem.

关键词： Parameter estimation Estimators Propagation delay Standard Methods direct-sequence code-division multiple access Phase shift Amplitude maximum likelihood

来源：评论

学校读者我要写书评

暂无评论

Multiuser detectors for band-limited direct-sequence code-division multiple-access systems with multitone jamming and generalised-K fading

引用

IET COMMUNICATIONS 2010年第17期4卷 2021-2031页

作者： Mehdi, H. Teh, K. C. Li, K. H. Nanyang Technol Univ Sch EEE Singapore 639798 Singapore

In this study, the authors analyse the bit-error rate (BER) performance of band-limited direct-sequence code-division multiple-access (DS-CDMA) systems employing two types of multiuser detectors, namely, linear decorrelator with whitening (LDW) and linear minimum mean-squared error (MMSE) detector over frequency-selective multipath channels with multitone jamming (MTJ). The authors consider the generalised-K distribution in order to include both shadowing and small-scale fading effects. Generalised-K distribution is generic and versatile as it can incorporate various composite fading and shadowing effects observed in wireless communication channels with mathematical tractability. The authors derive analytical BER expressions that are functions of band-limited pulse shapes, MTJ parameters and shadowing and fading parameters of the wireless channel. The system incorporates either a Nyquist pulse or a cosine band-limited pulse shape. Numerical results show that the systems with cosine pulse demonstrate better BER performance than the ones with Nyquist pulse in the presence of MTJ. Furthermore, in the presence of MTJ, MMSE-based systems demonstrate improved BER performance as compared to LDW-based systems. The authors also observe that the systems employing two-dimensional scheme, that is, the combination of space and multipath diversity, outperform the ones with multipath diversity scheme.

关键词： fading color sequence coding bit error rate performance Multi-Tone Jamming direct-sequence code-division multiple access SHADOW EFFECT Multipath channels K-distribution Pulse shape Shadowing (Histology)

来源：评论

学校读者我要写书评

暂无评论

Performance comparison of chaotic spreading sequences generated by two different classes of chaotic systems in a chaos-based direct sequence-code division multiple access system

引用

IET COMMUNICATIONS 2013年第10期7卷 1024-1031页

作者： Rahnama, Nazila Talebi, Siamak Shahid Bahonar Univ Kerman Dept Elect Engn Kerman Iran

In the world of wireless communications, achieving a highly secure transmission at the lowest possible performance degradation has presented a major challenge and a number of conventional direct-sequence-code division multiple access (DS-CDMA)-based solutions have been put forward that deals with the issue. This study aims to overcome the challenge by introducing a new approach that employs a chaotic sequence in DS-CDMA system over fading channels. The proposed algorithm, which assumes a perfect sync between the transmitter and the receiver, generates a binary code by using a three-dimensional (3D) chaotic system. Simulations based on a flat-fading channel with additive white Gaussian noise and interuser interference reveal that the new approach outperforms codes generated by other classes of chaotic systems, that is, the 1D chaotic system. The results also proved the proposition's performance is comparable to conventional pseudo-noise spreading codes, the Gold code, in several key aspects including security of transmission, bit-error rate, code generation speed and the number of possible code sequences.

关键词： code division Chaotic systems direct-sequence code-division multiple access AWGN degradation of performance CDMA mobile communications flat fading channel spreading sequence transmitter receivers CARRIER SYSTEM binary code

来源：评论

学校读者我要写书评

暂无评论

Error probability analysis of multicarrier direct sequence code division multiple access system under imperfect channel estimation and jamming in a Rayleigh fading channel

引用

IET SIGNAL PROCESSING 2010年第1期4卷 89-101页

作者： El-Mahdy, A. E. German Univ Fac Informat Engn & Technol Cairo Egypt

The performance of a multicarrier direct sequence code division multiple access (MC-DS-CDMA) system in fading environment has been extensively analysed in the literatures. The analysis that is available in the literatures did not take into account the impact of jamming and channel estimation errors on the performance of the system. In this study, closed-form expressions of the average bit error probability (BEP) of the MC-DS-CDMA system with channel estimation errors in the presence of partial band, broadband and multitone jamming are derived in a Rayleigh fading channel. The analysis shows that the magnitude of the normalised correlation between the actual and the estimated complex fading channel gain, A, greatly affects the performance of the MC-DS-CDMA system. For large signal-to-noise ratio, the average BEP with A 1 and without multiple access interference (MAI) tends to zero. When A not equal 1, the BEP of the system exhibits an error floor even without MAI. This error floor increases as the number of users increases. It is also shown that increasing the number of the system subcarriers enhances the system performance against jamming.

关键词： Raleigh fading channels System performance direct-sequence code-division multiple access error floor Multi-Tone Jamming ABER channel estimation jamming MC-DS-CDMA code division CDMA mobile communications

来源：评论

学校读者我要写书评

暂无评论

Joint transmit/receive one-tap minimum mean square error frequency-domain equalisation for broadband multicode direct-sequence code division multiple access

引用

IET COMMUNICATIONS 2010年第14期4卷 1752-1764页

作者： Takeda, K. Adachi, F. Tohoku Univ Grad Sch Engn Dept Elect & Commun Engn Aoba Ku Sendai Miyagi 9808579 Japan

Multicode direct-sequence code division multiple access (DS-CDMA) can flexibly support multimedia services with various data rates simply by changing the code multiplexing order. The use of simple one-tap frequency-domain equalisation (FDE) at a receiver is known to improve the bit error rate (BER) performance of multicode DS-CDMA in a severe frequency-selective fading environment. However, the BER performance improvement is limited due to the presence of the residual inter-chip interference (ICI). The authors propose a joint transmit/receive minimum mean square error (MMSE) FDE, which carries out one-tap transmit FDE and one-tap receive FDE jointly based on the MMSE criterion. The authors theoretically derive a suboptimal set of transmit and receive FDE weights and investigate the BER performance improvement by computer simulation in a freqeuncy-selective Rayleigh fading channel. The proposed scheme improves the received signal-to-interference plus noise ratio after despreading, and consequently, the BER performance can be significantly improved compared to the conventioal receive MMSE-FDE by (a) making the variations in the equivalent channel gain shallower to reduce the residual ICI for large code multiplexing order U and (b) allocating the transmit power to the frequencies having good condition to improve the received signal-to-noise ratio for a small U. This is conformed by the computer simualtion.

关键词： TRANSMITTING Data transfer rates ICI direct-sequence code-division multiple access bit error rate performance performance boost Mini Mental State Examination Multimedia services Transmitter power Mean square error multipleXOR

来源：评论

学校读者我要写书评

暂无评论

Performance Evaluation of Minimum-Bandwidth direct-sequence code division multiple access in Multipath Fading 7

Performance Evaluation of Minimum-Bandwidth Direct-Sequence ...

引用

International Conference on Ubiquitous and Future Networks

作者： Lin, Wei-Lun Feng Chia Univ Dept Commun Engn Taichung Taiwan

ISBN: (纸本)9781479989935

The error performance of minimum-bandwidth direct-sequence code division multiple access (MB-DS-CDMA) is studied for synchronous and asynchronous scenarios in Nakagami multipath fading channels. Comparing to the bandlimited raised cosine pulsed DS-CDMA systems, MB-DS-CDMA in both synchronous and asynchronous scenarios realizes Nyquist rate transmission with zero excess bandwidth, but only synchronous MB-DS-CDMA gives equivalent error performance, whereas asynchronous MB-DS-CDMA suffers degradation in error performance, which can be deemed as a trade-off by providing the ultimate Nyquist transmission rate. This work was supported by Ministry of Science and Technology, Taiwan, under contract NSC 102-2221-E-035-005.

关键词： error performance direct-sequence code-division multiple access code division multiple access Multipath fading Performance Evaluation code division Asynchronous

来源：评论

学校读者我要写书评

暂无评论

Performance of narrowband interference suppression filters in a direct sequence code division multiple access system

Performance of narrowband interference suppression filters i...

引用

International Conference on Universal Personal Communications

作者： Youngkwon Cho Jae Hong Lee School of Electrical Engineering Seoul National University Seoul South Korea

Narrowband interference (NBI) suppression filters can substantially improve the interference suppression capability of direct sequence code division multiple access (DS/CDMA) systems under the frequency overlay situation. Analytical expressions for the performance of NBI suppression filters are derived and evaluated. A one-sided predictor with decision feedback improves the interference suppression capability much more than a linear two-sided interpolator without decision feedback and its performance is nearly independent of the number of code division multiple access (CDMA) users.

关键词： Narrowband Interference suppression Filters Multiaccess communication Feedback direct-sequence code-division multiple access Frequency conversion Performance analysis

来源：评论

学校读者我要写书评

暂无评论

Improving direct sequence code division multiple access performance in frequency selective fading channels

Improving direct sequence code division multiple access perf...

引用

Proceedings of the IEEE Circuits and Systems Symposium on Emerging Technologies

作者： C. Khirallah P. Coulton S. Mohsin J. Ruan Department of Communication Systems Lancaster University Lancaster UK

In this paper we present the results for both fixed and floating point operation of a single-input-single-output (SISO) direct spreading code-division multiple-access (DS-CDMA) communication system. Conventional Walsh codes DS-CDMA systems suffer from high levels of interference in frequency selective fading channels due to the loss of their mutual orthogonality which limits the maximum error-free data rates achieved. The CDMA system proposed uses complete complementary (CC) codes due to their robust orthogonality in frequency selective fading environment and is termed CC-CDMA, which together with Walsh-CDMA systems are simulated for an equivalent data rate equal to 3.84 Mbps. Results obtained for CC-CDMA reveal significant improvement in bit-error-rate (BER) performance and data rates when compared to a conventional SISO-CDMA system using orthogonal Walsh spreading codes. Finally to reduce complexity and power consumption of CC-CDMA system a fixed point digital signal processing (DSP) implementation is presented and a comparison with the original floating point system is shown.

关键词： direct-sequence code-division multiple access Frequency conversion Fading Multiaccess communication Interference Digital signal processing Binary phase shift keying Robustness Bit error rate Energy consumption

来源：评论

学校读者我要写书评

暂无评论

Multirate transmission in frequency-hopping multicarrier direct sequence code division multiple access systems

Multirate transmission in frequency-hopping multicarrier dir...

引用

IEEE Conference on Vehicular Technology (VTC)

作者： Lie-Liang Yang L. Hanzo Department of ECS University of Southampton UK

Against the backcloth of the explosive expansion of the Internet and the continued dramatic increase in demand for high-speed multimedia wireless services, there is an urgent demand for flexible, broadband transceivers. A versatile broadband multiple access scheme, combining frequency-hopping (FH) with multicarrier DS-CDMA (FH/MC DS-CDMA) is proposed and investigated. The FH/MC DS-CDMA scheme is capable of meeting the requirements of future mobile wireless systems, while also ensuring compatibility with the existing 2nd- and 3rd-generation systems in the context of multirate transmission.

关键词： Frequency Multiaccess communication Bandwidth Explosives Multimedia systems direct-sequence code-division multiple access Internet Transceivers Standardization Research and development

来源：评论

学校读者我要写书评

暂无评论

Integrated call admission control and packet scheduling for multimedia direct sequence code division multiple access (DS-CDMA) wireless networks

Integrated call admission control and packet scheduling for ...

引用

IEEE Conference on Vehicular Technology (VTC)

作者： Yinggan Huang A.O. Fapejuwo Department of Electrical and Computer Engineering The University of Calgary Calgary AB Canada University of Calgary Calgary AB CA Dept. of Electr. & Comput. Eng. Calgary Univ. Alta. Canada

In this paper, we propose an integrated call admission control (CAC) and packet scheduling scheme for multimedia direct sequence code division multiple access (DS-CDMA) wireless networks. The proposed scheme fully utilizes the non-real-time characteristics of packet data to achieve quality-of-service (QoS) support in DS-CDMA wireless networks. Control of traffic flow is done at both the call and packet levels. The admission control restricts the number of calls in the system such that all traffic can meet their QoS requirements. Packet scheduling balances the flows of real time calls and non-real time calls to reduce the system interference. We evaluate the performance of the proposed scheme using Markov analysis and queuing theory. The analytic results are validated by simulation results. The numerical results show that the proposed scheme provides better performance than those of previous work.

关键词： Call admission control Scheduling algorithm direct-sequence code-division multiple access Multiaccess communication Wireless networks Communication system traffic control Traffic control Quality of service Admission control Real time systems

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：