共查询到18条相似文献,搜索用时 921 毫秒
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2.5 Gbit/s码位重叠快跳频光码分多址实验系统 总被引:1,自引:0,他引:1
设计并实现了单用户、数据速率2.5 Gbit/s的码位重叠快跳频光码分多址(SO-FFH OCDMA)实验系统。采用波长数为7和码长为4的单重合码,在数据速率2.5 Gbit/s时设计和制作了基于光纤布拉格光栅(FBG)的光编码/解码器,并测试了光编码器和光解码器的频谱图。脉冲发生器产生2.5 Gbit/s的非归零(NRZ)脉冲信号,外调制放大自发辐射(ASE)宽带光源后,通过光环行器进入光编码器进行光信号的扩频编码。编码后的光信号经掺铒光纤放大器(EDFA)放大后,输入到光解码器进行扩频解码,并通过2.5 Gbit/s接收模块转换为电信号。从解码信号的波形看,在用户数据速率为2.5 Gbit/s时,该系统能够正确解码用户的数据信息。实验结果表明,相对于传统的快跳频光码分多址系统,码位重叠快跳频光码分多址可大大提高用户的数据速率。 相似文献
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基于光正交码,研究了WDM+OCDMA系统的性能。采用4个波长信道和3个码字的光正交码OOC(37,4,1),对12个用户的WDMA+OCDMA进行了系统仿真,用户数据速率为1Gbit/s,单模光纤长为50km,色散补偿光纤长为5km。如需增加WDMA+OCDMA的用户数,可以通过增加波长信道数或码字容量来实现。分析了色散效应对WDMA+OCDMA系统性能的影响,研究了用户之间相对延时对多址干扰和系统性能的影响。 相似文献
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异步相干扩时光码分多址系统的干扰性能分析 总被引:2,自引:0,他引:2
从码字的非周期互相关函数出发,分析异步相干扩时光码分多址(OCDMA)系统的多址干扰(MAI)和差拍噪声(BN).干扰用户不同的传输时延,非周期互相关强度均值随之变化,差拍噪声和多址干扰也随之变化.给出了差拍噪声和多址干扰与非周期互相关强度均值的关系,讨论了异步相干扩时OCDMA系统的误码率(BER)与非周期互相关强度均值的关系.最后,以码长511的Gold码为例,针对干扰用户之间不同的传输时延,得到了异步相干扩时OCDMA系统的误码率上界与平均误码率性能.在平均误码率情况下,OCDMA系统能支持12个干扰用户,而在最差情况下(误码率上界),系统容纳的干扰用户数不超过4个. 相似文献
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光码分多址(OCDMA)系统误码性能研究 总被引:8,自引:1,他引:7
对光码分多址(OCDMA)系统的误码性能进行了研究。在对OCDMA采用的光接收机及噪声讨论的基础上,综合考虑用户间的多址干扰和光接收机噪声,首次推导了计算系统误码率上限的公式,并给出了相应的曲线,得出了对实际系统设计具有指导意义的结果。分析表明:多用户光纤CDMA系统是一个具有弹性容量的系统;当用户较少时系统误码性能主要受其接收机噪声的影响,用户较多时则主要由用户间的多址干扰决定。 相似文献
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光码分多址系统所用地址码的不完全正交特性导致了多用户干扰 ,严重影响了光码分多址系统的性能 ,限制了系统中可以同时传送数据的用户数 ,因此研究如何降低多用户干扰就显得尤其重要。文中介绍了几种降低多用户干扰的方案 ,并对它们的性能进行了讨论 相似文献
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Galli S. Menendez R. Narimanov E. Prucnal P.R. 《Communications, IEEE Transactions on》2008,56(12):2133-2144
Given K simultaneously active users, an Optical CDMA (OCDMA) receiver needs to discriminate among K codes. Since the number of available codes C is always C >> K at any given time for any truly asynchronous OCDMA system that employs quasi-orthogonal codes, there is always a set of unused codes. We here propose to exploit these unused codes to increase the spectral efficiency of the system. This can be accomplished by exclusively assigning to each user a set of M codes which represent a log/sub 2/(M)-tuple of bits so that each user effectively uses a multi-dimensional modulation (multiple information bits per code are conveyed). In this paper, we analyze the performance of such a system and find in closed form an upper bound on the average probability of error. Moreover, we report for the first time that, under lightly loaded, non interference-limited conditions, the multi-dimensional OCDMA scheme here proposed allows us to obtain both higher spectral efficiency and lower biterror probability (BEP) than a conventional OCDMA system, which employs one code only per user. The analysis here presented allow us to formulate a useful system design criterion that yields truly asynchronous OCDMA systems with very high spectral efficiency. 相似文献
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We propose a wireless optical-mesh network based on optical code-division multiple-access (OCDMA)-coded free-space optical links. The performance of the proposed network under intermediate and strong turbulence channel conditions is investigated for synchronous and asynchronous OCDMA. We show that synchronous OCDMA using complementary Walsh-Hadamard codes operating at a raw bit rate of 622 Mb/s per user can achieve a bit-error rate of 10/sup -9/. This is achievable in channels with strong turbulence and high temporal correlation, or in channels with intermediate turbulence conditions; reasonable conditions based on channel characteristics inferred from the refractive index spectrum. For asynchronous OCDMA using optical orthogonal codes (OOCs), using a lower bound, we show that asynchronous OCDMA using OOCs cannot achieve acceptable performance for the same channel conditions, due to interference limitations. 相似文献
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We propose a new optical code division multiple access (OCDMA) scheme for reducing multiple access interference (MAI) and enhancing performance for optical subscriber access networks using modified pseudorandom noise (PN)‐coded fiber Bragg gratings with bipolar OCDMA decoders. Through the bipolar OCDMA decoder and the modified PN codes, MAI among users is effectively depressed. As the data are encoded either by a unipolar signature sequence of the modified PN code or its complement according to whether the data bit is 1 or 0, the bit error ratio (BER) can be more improved with the same signal to interference plus noise ratio over the conventional on‐off shift keying‐based OCDMA system. We prove by numerical analysis that the BER of the proposed bipolar OCDMA system is better than the conventional unipolar OCDMA system. We also analyze the spectral power distortion effects of the broadband light source. 相似文献
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An electric encoded/optical transmission system of code division multiple access (CDMA) is proposed. It encodes the user signal in electric domain, and transfers the different code slice signals via the different wavelengths of light. This electric domain encoder/decoder is compared with current traditional encoder/decoder. Four-user modula- tion/demodulation optical CDMA (OCDMA) system with rate of 2.5 Gbit/s is simulated, which is based on the optical orthogonal code (OCC) designed in our laboratory. The results show that the structure of electric encoding/optical transmission can encode/decode signal correctly, and can achieve the chip rate equal to the user data rate. It can over- come the rate limitation of electronic bottleneck, and bring some potential applications in the electro-optical OCDMA system. 相似文献