检索结果-内蒙古大学图书馆

Packet access using DS-CDMA with frequency-domain equalization

IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 2006年第1期24卷 161-170页

作者： Garg, D Adachi, F Tohoku Univ Dept Elect & Commun Engn Sendai Miyagi 980 Japan Tohoku Univ Dept Elect & Commun Engn Sendai Miyagi 9808579 Japan

The next-generation mobile communications system is anticipated to support very high-speed data rates exceeding several tens megabits per second. In this paper, we consider high-speed downlink packet access for direct-sequence code-division multiple access (DS-CDMA) as in third-generation wideband code-division multiple-access systems. Adaptive modulation and coding (AMC), multicode operation and hybrid automatic repeat request (HARQ) will be the enabling technologies. With such high-speed data transmissions, however, multicode operation severely suffers from the loss of orthogonality among the spreading codes since the wireless channel becomes severely frequency-selective. In this paper, we apply frequency-domain equalization (FDE) based on minimum mean-square error (MMSE) criterion instead of conventional rake combining for receiving the packet. A new MMSE-FDE weight is derived for packet combining. The throughput in a frequency-selective Rayleigh-fading channel is evaluated by computer simulation for Chase combining and incremental redundancy (IR) packet combining. It is shown that the use of MMSE-FDE for the reception of multicode DS-CDMA packet gives an improved throughput irrespective of the channel's frequency-selectivity.

关键词： adaptive modulation coding (AMC) automatic repeat request direct-sequence code-division multiple access (DS-CDMA) equalizers error correction coding hybrid automatic repeat request (HARQ) high-speed downlink packet access (HSDPA) minimum mean-square error frequency-domain equalization (MMSE-FDE) mobile communication multicode

来源：评论

学校读者我要写书评

暂无评论

Block precoding for MUI/ISI-resilient generalized multicarrier CDMA with multirate capabilities

引用

IEEE TRANSACTIONS ON COMMUNICATIONS 2001年第11期49卷 2016-2027页

作者： Wang, ZD Giannakis, GB Univ Minnesota Dept Elect & Comp Engn Minneapolis MN 55455 USA

Potential increase in capacity along with the need to provide multimedia services and cope with multiuser interference (MUI) and intersymbol interference (ISI) arising due to wireless multipath propagation, motivate well multirate wideband code-division multiple-access (CDMA) systems. Unlike most existing continuous-time symbol-periodic and multipath-free studies, the present paper develops an all-digital block-precoded filter-bank framework capable of encompassing single- or multirate transceivers for asynchronous or quasi-synchronous CDMA transmissions through multipath channels. Thanks to symbol blocking and through appropriate design of user codes, the resulting generalized multicarrier (GMC) CDMA system not only subsumes known multicarrier CDMA variants, but also equips them with flexible multirate capabilities. It is computationally simple, and guarantees symbol recovery regardless of the (possibly unknown) FIR multipath channels in both downlink and uplink setups. Simulations corroborate that the novel GMC-CDMA system outperforms existing multirate alternatives in the presence of asynchronism and multipath, and illustrate the feasibility of recovering blindly multirate transmissions received through unknown frequency-selective channels in the uplink. Performance of GMC-CDMA system in UNITS channels is also simulated and compared with existing multirate schemes.

关键词： blind equalization multicarrier transmission multicode multipath fading channels multirate CDMA variable spreading length

来源：评论

学校读者我要写书评

暂无评论

Downlink, scheduling optimization in CDMA networks

引用

IEEE COMMUNICATIONS LETTERS 2004年第10期8卷 611-613页

作者： Kwan, R Leung, C Univ British Columbia Dept Elect & Comp Engn Vancouver BC V6T 1Z4 Canada

The problem of allocating radio resources in the downlink of a code-division multiple access (CDNU) network is studied. The modulation and coding schemes, numbers of multicodes, and transmit powers used for all mobile stations (MSs) are jointly chosen so as to maximize the total transmission bit rate, subject to certain constraints. Based on the discrete and nonlinear nature of the proposed model, a mixed-integer nonlinear programming optimization problem is formulated. It is shown that the optimal allocation generally involves simultaneous transmissions to several MSs. A scheduler which uses knowledge of MS traffic loads is also proposed and shown to yield a significant improvement in throughput.

关键词： adaptive modulation code-division multiple access (CDMA) downlink multicode optimization radio resource management

来源：评论

学校读者我要写书评

暂无评论

Optical multimedia CDMA system with novel multiplexing techniques

引用

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS 1999年第6期22卷 424-426页

作者： Lee, YH Tamkang Univ Dept Elect Engn Tamsui 25137 Taiwan

Forts novel multiplexing techniques (VSM, PSM RPM, OIM) of an optical multimedia CDMA system haw been proposed by using prime codes with different code lengths. PSM and VSM have the advantages of easily adding and controlling the inserting code system, brit with a limited successful number. RPM can dynamically add the inserting codes into the original codes at the price of a complicated algorithm and lower multiplexing speed. For example, VSM, PSM, RPM, and OIM can insert the number of inserting P3-code to be 2, 3, 4, and 15 into the simultaneous number of original P7-code being 7 with the successful number of 10 for the original P7-code system. So OIM is the best model to process the multimedia CDMA system. (C) 1999 John Wiley & Sons, Inc.

关键词： multimedia optical CDMA prime code multicode

来源：评论

学校读者我要写书评

暂无评论

On joint order statistics in correlated Nakagami fading channels

引用

IEEE COMMUNICATIONS LETTERS 2007年第9期11卷 717-719页

作者： Kwan, Raymond Ho, Paul Leung, Cyril Simon Fraser Univ Sch Engn Sci Burnaby BC V5A 1S6 Canada Univ British Columbia Dept Elect & Comp Engn Vancouver BC V6T 1Z4 Canada

In this letter, the joint probability density function (pdf) of the order statistics for a set of correlated Nakagami-m fading channels is derived. This result is useful in analyzing the performance of a variety of diversity schemes which involve branch selection. The derivation also yields a computationally efficient method for obtaining the marginal pdf of the p-th order statistic for a set of correlated Nakagami-m fading channels.

关键词： adaptive modulation and coding multicode imperfect channel estimation CDMA Nakagami fading

来源：评论

学校读者我要写书评

暂无评论

Simulation study of different code system division multiple access (DCSDMA) for optical communication

引用

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS 1999年第4期21卷 291-295页

作者： Lee, YH Tamkang Univ Dept Elect Engn Tamsui Taipei Hsien Taiwan

In this paper, we propose a novel structure using different code system division multiple access (DCSDMA) for an optical communication system and a design algorithm to increase the system capacity. This DCSDMA system can transmit two kinds of code systems (for example, the prime code of 7 and 3, respectively). This multicode architecture can improve the theoretical system capacity from P-7(2) to P-7(2) + 5 * p(3)(2). In this paper, we propose an optimal design method lo find the simultaneous capacity X% * 7(2) + Y% * 5 * 3(2). X% and Y% are the successful percentages determined by the simulation results. (C) 1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 21: 291-295, 1999.

关键词： CDMA multicode optical network

来源：评论

学校读者我要写书评

暂无评论

An enhanced DQRUMA/MC-CDMA protocol for wireless packet networks

引用

IEICE TRANSACTIONS ON COMMUNICATIONS 2000年第7期E83B卷 1567-1571页

作者： Park, JY Kim, DK Sung, DK Korea Adv Inst Sci & Technol Dept Elect Engn Yusong Gu Taejon 305701 South Korea NTT DoCoMo R&D Ctr Yokosuka Kanagawa 2398536 Japan

The original DQRUMA/MC-CDMA protocol may suffer severe code collisions due to a limited number of request codes. An enhanced DQRUMA/MC-CDMA protocol using minislots for request accesses is proposed to reduce request collisions. In the proposed protocol, request attempts are transmitted concurrently with data packets of other calls. A random scheme (Scheme I) and a designated scheme (Scheme II) are distinguished depending on the methods which select a request code and a request minislot based on a lattice pool for request accesses (LPRA). Both schemes yield low request access delays due to few or no collisions during request accesses. In Scheme I one of request minislots is selected with a randomly chosen code, while in Scheme II the minislot and the code uniquely used in request attempts can resolve a code collision problem during request accesses. The performance of the proposed protocol is evaluated by simulation and the result shows that the proposed protocol outperforms the original DQRUMA/MC-CDMA protocol in terms of average total delay.

关键词： multicode CDMA MAC LPRA

来源：评论

学校读者我要写书评

暂无评论

Application of the VLC parallel transmission technique to motion vector transmission

引用

IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES 1999年第12期E82A卷 2778-2782页

作者： Kasai, T Sanada, Y Araki, K Tokyo Inst Technol Fac Engn Meguro Ku Tokyo 1528552 Japan

Recently portable computers and mobile communications have been developed rapidly. Along with the developments of mobile computing environment, the demands of transmitting images over wireless channels are growing. However, high efficiency image coding techniques are not designed for the wireless communication channels. The use of variable length codes (VLCs) in those coding techniques makes a receiver hard to synchronize with the codewords on the noisy channel. On the other hand, a variable length code transmission technique utilizing multicode CDM (Code Division Multiplex) has been proposed. In this paper, the multicode CDM technique is applied to wireless transmission of images compressed by the H.263 algorithm. Especially, the proposed technique is employed for motion vector transmission. In consequence, the proposed transmission technique reduces the required E-b/N-o as compared with the conventional transmission technique.

关键词： multicode H.263 video image spread spectrum variable length code

来源：评论

学校读者我要写书评

暂无评论

A flexible multicarrier CDMA system with time-varying data rates and services

引用

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS 2009年第5期22卷 585-602页

作者： You, Cheolwoo Chung, Wonzoo Jeon, Taehyun Myongji Univ Dept Commun Engn Yongin 449728 Gyeonggi Do South Korea Korea Univ Div Comp & Commun Engn Seoul South Korea Seoul Natl Univ Technol Dept Elect Engn Seoul South Korea

We consider an enhanced multicarrier code-division multiple access (CDMA) system that performs the spreading in the time and frequency domains simultaneously, where time-domain spreading codes are used as a main code and frequency-domain spreading codes (FDSCs) are used as a subcode. By allocating the FDSCs to users, rates and services can be dynamically matched to users' needs. The resulting system can support different time-varying source rates and, therefore, enable multimedia applications. In addition, since the proposed scheme uses multiple carriers, it has some advantages such as the mitigated multipath fading, frequency/path diversity and narrowband interference suppression capability, in contrast to a single carrier (SC) system such as the multicode CDMA scheme. Finally, the closed-form expression for probability of bit error is derived for a frequency-selective Rayleigh fading channel. It has been also shown that the proposed system has outperformed the conventional SC RAKE system if the available bandwidth is fixed. Copyright (C) 2008 John Wiley & Sons, Ltd.

关键词： multimedia service multicarrier wideband CDMA Rayleigh fading multicode

来源：评论

学校读者我要写书评

暂无评论

On the comparisons of system performance and capacity of asynchronous STBC MC-CDMA multirate access schemes

引用

WIRELESS COMMUNICATIONS & MOBILE COMPUTING 2008年第10期8卷 1277-1295页

作者： Hu, Xiaoyu Chew, Yong Huat Stevens Inst Technol Dept Elect & Comp Engn Hoboken NJ 07030 USA Inst Infocomm Res Singapore Singapore Natl Univ Singapore Dept Elect & Comp Engn Singapore 117548 Singapore

Three multirate access schemes, multicode, variable spreading gain (VSG), and spectral overlaid multiple-symbol-rate (MSR), for asynchronous space-time block coded (STBC) multicarrier code division multiple access (MC-CDMA) systems are proposed. The three possible spectral overlaid configurations for MSR systems are also investigated. The expressions to evaluate the multiple access interferences, bit error rate (BER) performances, and system capacities of a antenna STBC MC-CDMA using the three multirate access schemes are obtained. Transmit power allocation is adjusted according to the service rates and the number of active users in each service class to maintain the link quality and to improve the system capacity. Our numerical results show that systems with multicode access scheme using orthogonal Gold spreading codes and with VSG access scheme have similar system performance and capacity, and both perform in general better than systems with MSR access scheme of any spectrum configurations. In case when non-orthogonal Gold codes are used, multicode access scheme shows degradation in the system capacity as compared to VSG, due to the presence of larger self-interference (SI) among the codes used by each user. The achievable capacities for the three spectral overlaid configurations of MSR multirate systems are also compared. Copyright (C) 2007 John Wiley & Sons, Ltd.

关键词： MC-CDMA space-time code multicode variable spreading gain (VSG) multiple-symbol-rate (MSR) BER performance system capacity

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：