共查询到20条相似文献,搜索用时 15 毫秒
1.
On Next Generation CDMA Technologies: The REAL Approach for Perfect Orthogonal Code Generation 总被引:1,自引:0,他引:1
《Vehicular Technology, IEEE Transactions on》2008,57(5):2822-2833
2.
Hsiao‐Hwa Chen Shin‐Wei Chu N. Kuroyanagi A. J. Han Vinck 《Wireless Communications and Mobile Computing》2007,7(5):605-622
This paper introduces an algebraic approach to generate the super‐set of perfect complementary (PC) codes suitable for new generation CDMA applications, characterized by isotropic multiple access interference (MAI) free and multipath interference (MI) free properties. The code design methodology proposed in this paper takes into account major impairing factors existing in real applications, such as MAI, MI, asynchronous transmissions, and random signs in consecutive symbols, such that a CDMA system using the generated codes can insure a truly interference‐free operation. Two important facts will be revealed by the analysis given in this paper. First, implementation of an interference‐free CDMA will never be possible unless using complementary code sets, such as the PC code sets generated in this paper. In other words, all traditional spreading codes working on an one‐code‐per‐user basis are not useful for implementation of an MAI‐free and MI‐free CDMA system. Second, to enable the interference‐free CDMA operation, the flock size of the PC codes should be made equal to the set size of the codes, implying that a PC code set can support as many users as the flock size of the code set. A systematic search has been carried out to generate the super‐set of various PC codes with the help of carefully selected seed codes belonging to distinct sub‐sets. This paper will also propose an implementation scheme based on multi‐carrier CDMA architecture and its performance is compared by simulations with the ones using traditional spreading codes. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
3.
Codes for spectral-amplitude-coding optical CDMA systems 总被引:4,自引:0,他引:4
Codes with ideal in-phase cross correlation (CC) are required in spectral-amplitude-coding optical code-division multiple-access (CDMA) systems since these codes eliminate multiuser interference and also suppress the effect of phase-induced intensity noise. However, little research work has been done on such codes although codes with ideal CC have been studied for many years. In a paper by Zhou et al. (2000), such a code has been introduced, but no clear construction method has been presented. In this paper, we first review the construction method of this old code and then construct two new codes with ideal in-phase CC in algebraic ways. Both of the proposed new codes are obtained by modifying former codes with ideal CC. It has been shown that the system performance can be improved significantly by using codes with ideal in-phase CC instead of the Hadamard code. These codes can also be used in the synchronous optical CDMA systems for multiuser interference cancellation. 相似文献
4.
Synchronous fiber-optic CDMA using hard-limiter and BCH codes 总被引:3,自引:0,他引:3
Jyh-Horng Wu Jingshown Wu 《Lightwave Technology, Journal of》1995,13(6):1169-1176
In this paper, synchronons code division multiple access (S/CDMA) for fiber-optic local area networks is considered. The performance of the fiber-optic S/CDMA network with negligible thermal and shot noises is interference limited. Here we derive the bit error rate of the S/CDMA system as a function of code length and number of active users, and the performance characteristics are also discussed. Furthermore, we analyze the performance of the fiber-optic S/CDMA system with an ideal optical hard-limiter, and the error probability with error control coding is also derived. In addition, the optimization between the S/CDMA and BCH codes of a constant bandwidth system is presented. The results show that by using an ideal hard-limiter in conjunction with BCH codes in this system, the influence of interference arising from other users can be greatly reduced, and the number of active users can also be increased significantly 相似文献
5.
Inter-Group Complementary Codes for Interference-Resistant CDMA Wireless Communications 总被引:2,自引:0,他引:2
Jing Li Aiping Huang Guizani M. Hsiao-Hwa Chen 《Wireless Communications, IEEE Transactions on》2008,7(1):166-174
Spreading code plays an extremely important role on the overall performance of a CDMA system. The correlation properties and available number of spreading codes determine the interference-resist capability as well as system capacity. In this paper, we analyze the characteristics and limitations of traditional and recently reported spreading codes. Based on the analysis, we propose a new code design approach which will be used to generate inter-group complementary (IGC) codes. The correlation functions of the IGC codes possess definite and bi-valued interference-free windows. In addition, a corresponding code assignment algorithm and spreading scheme will be introduced to take advantage of the desirable properties of the IGC codes for their applications in CDMA systems. Both theoretical analysis and simulation results show that an IGC-CDMA system is interference-resistant and capable to offer a high spectral efficiency if compared with the ones based on other spreading codes. 相似文献
6.
Unipolar codes with ideal in phase cross-correlation are important in spectral amplitude-coding optical code-division multiple-access (CDMA) systems since these codes eliminate multiuser interference and also suppress the effect of phase-induced intensity noise. However, very little research work has been done on such codes although codes with ideal cross-correlation have been studied for many years. In the paper by Zhou et al.(see Electron. Lett., vol.36, p.728-29, 2000), such a code has been introduced without a clear construction method. In this paper, we firstly review this old code, and then construct two new codes with ideal in-phase cross-correlation in algebraic ways. Both of the proposed new codes are obtained by modifying former codes with ideal cross-correlation. It has been shown that the system performance can be improved significantly by using codes with ideal in-phase cross-correlation instead of the Hadamard code. These codes can also be used in synchronous optical CDMA systems for multiuser interference cancellation. 相似文献
7.
Hsiao‐Hwa Chen 《International Journal of Communication Systems》1999,12(1):49-64
Most CDMA systems serve only finite number of active users. Therefore, using Gaussian approximation to evaluate its performance is inappropriate. In such finite CDMA systems, the selection of spreading codes is of great importance because its performance is very much spreading‐code‐dependent. In this paper, a new algorithm based on multiple variable Bernoulli process is introduced to evaluate bit error rate due to co‐channel interference and thus the capacity of a CDMA system. The algorithm can also be used for large‐sized CDMA systems. The results show that small Kasami and Gold‐like codes offer higher capacity than the others do. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
8.
Debolina Chakraborty Milan Kumar Tarafder Abhijit Chandra 《Wireless Personal Communications》2016,88(4):711-729
Present generation mobile communication system employs one of the most popular wireless access technologies called code division multiple access (CDMA). Design of CDMA spreading codes has drawn significant attention amongst the researchers over the last few decades. CDMA code family is generally categorized into purely orthogonal and non-orthogonal (near-orthogonal) members which have established their application in synchronous (downlink) and asynchronous (uplink) CDMA system respectively. Walsh code has been regarded as the most useful spreading code to be used in synchronous link because of its orthogonality property. However, the performance of Walsh code is significantly inferior in asynchronous surroundings. A number of codes have consequently been proposed with an aim to mitigate the shortcomings of Walsh code. This paper makes an innovative attempt to enhance the correlation properties of existing Walsh code through one simple yet powerful algorithm. Proposed code of length ‘N’ has been generated from code sets of length ‘N/4’ and thus makes the code generation algorithm recursive in nature. Performance of the proposed code has subsequently been compared with some existing orthogonal and semi orthogonal codes in terms of various performance metrics and finally the supremacy of our proposition has been established. 相似文献
9.
Interference-free broadband single- and multicarrier DS-CDMA 总被引:2,自引:0,他引:2
The choice of the direct sequence spreading code in DS-CDMA predetermines the properties of the system. This contribution demonstrates that the family of codes exhibiting an interference-free window (IFW) outperforms classic spreading codes, provided that the interfering multi-user and multipath components arrive within this IFW, which may be ensured with the aid of quasi-synchronous adaptive timing advance control. It is demonstrated that the IFW duration may be extended with the advent of multicarrier DS-CDMA proportionately to the number of subcarriers. Hence, the resultant MC DS-CDMA system is capable of exhibiting near-single-user performance without employing a multi-user detector. A limitation of the system is that the number of spreading codes exhibiting a certain IFW is limited, although this problem may be mitigated with the aid of novel code design principles 相似文献
10.
Jincheng Huang Shinya Matsufuji Takahiro Matsumoto Noriyoshi Kuroyanagi 《International Journal of Communication Systems》2012,25(12):1620-1638
A quasi‐timing synchronous code division multiple access (CDMA) system called ZCZ‐CDMA, which uses a set of sequences with a zero‐correlation zone called ZCZ code as a spreading code, is useful for short‐range wireless communications because of its excellent properties such as co‐channel interference‐free performance, simplified hardware design, and low transmit power as well as fast frame synchronization capability. In this paper, a ZCZ‐CDMA system with binary frequency‐shift keying (BFSK) modulation called BFSK‐ZCZ‐CDMA is proposed. This system is characterized by using a pair of balanced ZCZ codes for spreading and transmitting the two spread components over the respective keying carrier frequencies. Its bit error rate performance, compared with those of existing BPSK‐ZCZ‐CDMA, ASK‐ZCZ‐CDMA, and CDMA systems using the other spreading codes, is evaluated in theory and simulation. The bit error rate performance of the three ZCZ‐CDMA systems over additive white Gaussian noise and Rayleigh fading channels are formulated. It is proved that BFSK‐ZCZ‐CDMA is much more robust in anti‐fading performance and low transmit power in such an environment that fading distributions on the keying frequencies are independent mutually. Fading versus frequency characteristics are also investigated. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
11.
Direct sequence spread spectrum code-division multiple-access (DS/CDMA) is receiving increasing attention for cellular communications systems. When the users are synchronized and special symbol-length sequences, such as Gold codes, are used, the mutual interference can be substantially reduced relative to a system with very long or purely random spreading sequences. It is shown that this approach degrades the performance of the code phase acquisition and tracking, however. This effect prevents the system from acquiring and tracking long before the data detection is affected by the multiuser interference 相似文献
12.
Walsh–Hadamard transform, a discrete unitary transform is widely used in many applications such as signature codes in the current wireless standards IS-95 CDMA, WCDMA, CDMA2000 and image transform applications. It is simple to implement this transform since they can be generated by a single Kronecker product recursion formula. In this paper, a new set of binary code families similar to Walsh codes are obtained based on the concept of code concatenation and permutation. It is shown that these codes can be generated by reconfiguring the Walsh–Hadamard code generator. Hence it can be utilized in reconfigurable radios such as underlay cognitive radio (UCR). Theoretical results showing the BER performance due to MAI between primary users and secondary users in an UCR is also obtained. Simulation results showing the BER performance of these codes in a direct sequence spread spectrum system and UCR system with quadrature multiplexing operating in the individual decoding mode under AWGN plus flat fading Rayleigh channel conditions is also obtained. 相似文献
13.
《Vehicular Technology, IEEE Transactions on》2008,57(6):3563-3577
14.
Optimum code structures for positive optical CDMA using normalized divergence maximization criterion
In this letter we consider optimum code structure for positive optical code division multiple-access (optical CDMA) systems. Positive systems are a class of systems that operate with positive real numbers only. We consider the effect of multipleaccess interference in our model and show that code design for both On-Off Keying (OOK) and Binary PPM optical CDMA systems results in the same solutions. Furthermore, we show that a class of codes known as optical orthogonal codes (OOCs) are the best possible positive codes. In obtaining the results we define normalized divergence based on signal-to-multipleaccess interference ratio (SIR) for a multiple-access system in a useful manner and use it as our criterion to maximize the multiple-access capability of the codes. Finally, we demonstrate that BPPM/OOC can be considered as the closest counterpart of ±1 pseudorandom sequence in radio CDMA communication systems. 相似文献
15.
CDMA蜂窝移动通信系统是一种采用多址技术的通信系统,即采用不同的地址码来区分用户、基站和信道。然而由于其在多径衰落信道中的自相关和互相关特性的不理想造成了多址干扰。在扩频通信系统的下行链路中,有效地抵消多址干扰是进一步改善系统性能和提高系统容量的重要途径。本文提出一种应用于CDMA下行链路的干扰抵消算法,分析了下行链路接收机的实现原理及过程,并对其中的关键算法进行了详细地分析,仿真结果表明,所选取的下行接收算法能改善系统的性能。 相似文献
16.
17.
综述了光码分多址(CDMA)多用户干扰的问题及其抑制方法,指出目前光CDMA系统中多用户干扰主要影响发送比特为"0"时的误码率.提出了一种基于最大值判决的并行干扰抑制方法,进行误码性能仿真.仿真结果表明采用上述多用户干扰抑制方法的新型系统比常规系统的误码性能改善10个数量级以上. 相似文献
18.
The recently proposed loosely synchronized (LS) spreading code can in principle realize an intracell-interference-free quasi-synchronous code-division multiple-access (QS-CDMA) system by creating a wide enough interference-free window (IFW). However, the problem of minimizing intercell interference (ICI) in a cellular QS-CDMA system remains an open issue. Addressing the problem from a sequence design viewpoint, the key challenge is how to generalize the known construction of a single LS code to the design of many families of generalized LS (GLS) codes so that a desirable code family can be selected for the realization of a low-ICI cellular QS-CDMA system. Our main contribution is a systematic construction of new families of GLS codes with favorable intercode cross-correlation properties within a certain window, while maintaining the desirable IFW property. Many such code families can be obtained from our construction by choosing different Hadamard matrices and different uncorrelated complementary pairs. Their effectiveness with respect to some meaningful evaluation criteria are compared. In particular, by a simplified system bit-error rate analysis, it is demonstrated that a new GLS code family significantly outperforms the conventional scrambled LS codes. 相似文献
19.
Xhi-Shun Weng Jingshown Wu 《Lightwave Technology, Journal of》2001,19(2):186-194
In this paper, we introduce the perfect difference sets and propose a synchronous fiber-optic code-division multiple-access system (CDMA) using these sets to generate the signature codes. Two interesting properties of these codes are discussed: (1) any two different codes are cyclic-shifted with each other; and (2) the cross correlation between any two different codes is exactly one. Thus, we may treat these codes as quasi-orthogonal codes. Using the first property of these codes, we can simplify design of the transmitter. In the receiver, we can use the second property to effectively eliminate the multiple-user interference (MUI) without reducing the number of usable codes. Based on the proposed transmitter and receiver, the system performance is derived. The numerical examples reveal that the proposed system can provide reliable communication even under heavy load. We believe that the proposed system using perfect difference codes outperforms any other synchronous fiber-optic CDMA systems 相似文献