A NEW DECODER OF SYNCHRONOUS OPTICAL CODE DIVISION MULTIPLE ACCESS SYSTEMS USING SEGMENTED CORRELATION

A new segmented correlating decoder of synchronous optical CDMA using modified prime sequence codes is proposed. The performance of the proposed system is analyzed under the assumption of Poisson shot noise model for the receiver photodetector. The decoder technique is shown to be more effective to improve the bit error probability performance than the method using an optical hard-limiter.

A passive optical network based on optical code division multiplexing and time division multiple access technology

A passive optical network （PON） scheme based on optical code division multiplexing （OCDM） for the downstream traffics is proposed and analyzed in detail. In the PON, the downstream traffics are broadcasted by OCDM technology to guarantee the security, while the upstream traffics pass through the same optical fiber by the common time division multiple access （TDMA） technology to decrease the cost. This schemes are denoted as OCDM/TDMA-PON, which can be applied to an optical access network （OAN） with full services on demand, such as Internet protocol, video on demand, tele-presence and high quality audio. The proposed OCDM/TDMA-PON scheme combines advantages of PON, TDMA, and OCDM technology. Simulation results indicate that the designed scheme improves the OAN performance, and enhances flexibility and scalability of the system.

Performance Analysis of Multiple User Optical Code Division Multiple Access

In this paper, we discuss and analyze an optical code division multiple access for multiple user system. Media access control implementation has been considered. For fulfilling the huge need of bandwidth services, technology tends to move to optical networks and three major optical systems come into existence. Code division of the optical network is most used and real concept interacted with users up to this time. Optical code division multiple access provides complete spectrum to each and every user for the time of accessing the channel. In the paper, we have proposed network architecture with optical encoder and decoder along with optical code translator which is supporting multiple user systems. We integrate the code translator with encoding and decoding of optical code to use the optical network at full extent and present the simulation validation results of 6 Gb/s 3-hop transmission by use of proposed architecture. Further, we have implemented experimentation with 6 users 3 Gb/s optical code division multiple access network. Through simulation structure, it is shown that the combination of encoding with EDFA in multiple user environment system provides improvement in bit error rate and also improves the multiple access interference. With increase of users in the network, MAI value increases and our proposed scheme controls interference in the network.

A New Family of Optical Codes Based on Complementary Theory for OCDMA System

A new family of optical codes for Optical Code-division Multiple Access (OCDMA) systems, named as Optical Complementary Codes (OCCs), is proposed in this paper. The constructions of these codes consist of multiple sub-codes, and the codes have an auto-correlation interference constraint as 0 and a cross-correlation interference constraint as 1. Compared with conventional optical codes such as OPCs, OOCs and 2-D OOCs, the OCC has a shorter code length and higher code efficiency with better correlation property.

Mathematical demonstration of correlation of optical prime code

Starting from the configuration of the optical prime code, a kind of key signature code for the optical code-division multiple access （OCDMA） system, based on the linear congruence theory in the finite Galois field, the correlation properties of the basic prime code, the extended prime code and the modified prime code are mathematically analyzed, the distribution of cross-correlation values is given and the overlap area of ＂1＂s in the case of periodically circularly shifting is indicated. It is mathematically demonstrated that the maximum cross-correlation of the basic prime code is 2, and that of the extended prime code and the modified prime code is 1. The integrated correlation analysis process is proposed. The signal-interfere ratio （SIR） and the BER performance of the systems employing different signature codes are calculated, respectively, and the performances of OCDMA systems employing different signature codes mode are compared.

A Novel Optical Code Division Multiple Access Ring Network System for LAN

In this paper the impact factors on the optical fiber LAN network with ring topology are considered. The couple ratio, the self-ring effect, the Multiple-Access Interference (MAI), and the channel noises are the main factors degrading the system performance. We develop a systematic method that employs the smallest p multiplication method to analyze the optimization of the ring network. The results show that choosing an optimal couple ratio and power control will enhance the system performance dramatically. In addition, the “self-ring” interference and MAI can be suppressed by power control to some extent.

Microwave Oscillator Phase Noise Requirement for TD-SCDMA Wireless Communication Systems

In time division synchronous code division multiple access （TD-SCDMA） wireless communication systems, QPSK or 8PSK has been employed to support high data rate services and high efficiency in available bandwidth. The performance of such systems is affected by the phase noise of the microwave local oscillator. The phase noise model of synthesizer and the RF transceiver model for the phase noise effect are proposed for applications of TD-SCDMA systems. The relationship between the power spectral density （PSD） and root mean square （RMS） phase error is given. Then, the error vector magnitude （EVM） performance is analytically evaluated by using the single side band （SSB） phase noise. Theoretical results show agreement with those obtained by measurement data and therefore can be used to derive the TD-SCDMA system performance.

A New Performance Analysis Method of Optical Code Division Multiple Access Systems with An Optical Hard-Limiter

A new performance analysis method of Optical Code Division Multiple Access ( OCDMA ) systems with an optical hard limiter is studied. The bit error probability of the OCDMA system is derived, and the numerical results of the system with and without an ideal optical hard limiter are analyzed respectively. The results show that although the derived expression is different from the one derived by J A Salehi , the numerical results are the same as those analyzed by J A Salehi, and the numerical result can be easily achieved in this expression.

A Random Multi-Access Method for Data Services in CDMA Cellular System

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WAVELET-BASED OFDM-CDMA HIGH SPEED POWER LINE COMMUNICATION SYSTEMS

This letter derives the Equivalent M-band Discrete Wavelet(EMDW) transmission mode of Orthogonal Frequency Division Multiplexing(OFDM) transmission systems, and presents a new Quadrature M-band Discrete Wavelet(QMDW) based OFDM-CDMA(Code Division Multiple Access) communication systems for high speed Power Line Communication (PLC) channels.This system gives much better robustness to Inter-Channel Interference (ICI), Multi-User Interference (MUI) and noise interference, which is verified by simulation.

PERFORMANCE ANALYSIS AND SIMULATION OF OCDMA SYSTEM BASED ON FBGs ENCODER/DECODER

The encoding/decoding scheme based on Fiber Bragg Grating (FBG) for Optical Code Division Multiple Access (OCDMA) system is analyzed and the whole process from transmitting end to receiving end is researched in detail. The mathematical mode including signal transmission, summing, receiving and recovering are established respectively. One of the main sources of Bit Error Rate (BER) of OCDMA system based on FBGs is the unevenness of signal power spectrum, which leads to the chip powers unequal with each other. The Signal to Interfere Ratio (SIR) and BER performance of the system are studied and simulated at the case with uneven distribution of chips' powers.

基于OptiSystem软件的OCDMA系统仿真

分析了采用光素数地址码的异步OCDMA系统设计原理,阐述了OptiSystem软件针对光系统的强大仿真功能。在设计原理的基础上,采用光纤延时线编码技术给出了基于OptiSystem的异步OCDMA系统仿真模型,得出仿真结果并进行了分析,验证了系统设计的正确性和设计方案的可行性。

Hybrid WDMA/OCDM system with the capability of encoding multiple wavelength channels by employing one encoder and one corresponding optical code

A hybrid wavelength division multiple access （WDMA）/optical code division multiplexing （OCDM） system is proposed, where the optical code is not the same as the address of every optical network unit （ONU）; rather, the code is a virtual fiber of hybrid passive optical network （PON）. To our knowledge, this is the first report analyzing a single encoder/decoder with a single corresponding optical code being exploited to encode/decode multiple wavelength signals simultaneously. This system enables OCDM to become transparent to ONU so that the existing wavelength division multiplexing （WDM） PON can be upgraded. Thus, redesigning the optical line terminal and ONU can be easily accomplished, and greatly decreasing the number of encoder/decoder becomes possible. In experiment, we only employ two encoder/decoder pairs to combine two WDM-PONs in one fiber. Simulation results confirm the feasibility of the proposed system.

BLIND ADAPTIVE MULTIUSER DETECTOR FOR NONLINEARLY MODULATED SATELLITE MOBILE CDMA SYSTEMS

This paper presents a novel blind adaptive noncoherent decorrelative multiuser detector for nonlinearly modulated satellite mobile Code Division Multiple Access (CDMA) systems. By using the known signature waveforms of the counterpart earth station in the blind adaptive multiuser detector, the system performance has been improved obviously. The computation results about the convergence properties of the new detector and the previous detectors demonstrate that the proposed multiuser detector has better performance than previous multiuser detectors for nonlinearly modulated CDMA systems.

ANALYSIS OF SPECTRAL PHASE ENCODING OCDMA SYSTEM WITH PSEUDORANDOM CODING

Multiple access interference (MAI) is the most serious interference in spectral phase encoding optical code division multiple access (SPE OCDMA) systems. This paper focuses on the behavior of MAI in SPE OCDMA systems with pseudorandom coding. The statistical expectation of multi access interference (MAI) is derived and plotted. The results confirm that MAI can be suppressed effectively by pseudorandom coding with m sequences.

The Application of Optical CDMA-Based Fiber Radio Networks in Wireless Sensor Networks

One fiber radio scheme using shifted prime codes for interference elimination is proposed for optical code-division multiple-access (OCDMA) network. By taking advantage of the cyclic property of the shifted prime codes in the same code groups, the proposed compact decoder is low cost and suitable to be used in the task manager node in the applications of wireless sensor networks. The performance comparison for sev-eral OCDMA-based fiber radio networks is also given to clarify the advantage of the proposed one.

Performance Analysis of 32-User Spectral Phase Encoding Time Domain System for Fiber-Optic CDMA Networks

Multiple access techniques are required to meet the demand for high-speed and large-capacity commtmications in optical networks, which allow multiple users to share the fiber bandwidth. O-CDMA （optical code-division multiple-access） is receiving increased attention due to its potential apphcations for LAN optical networks. O-CDMA is attractive for next generation broadband access networks due to its features of allowing fully asynchronous transmission with low latency access, soft capacity on demand, protocol transparency, simplified network management as well as increased flexibility of QoS （Quality of Service） control and enhanced confidentiahty in the network. Hence, the authors experimentally investigate an ultra short pulse O-CDMA scheme based on spectral phase encoding and decoding of coherent mode-locked laser pulses, they proposed a technique using spectral phase encoding time domain system for 32 users. This technique is proved to be much effective to handle 32 users at 4 Gb/s bit rate and 60 km SMF （single mode fiber） transmission used for SPE O-CDMA system. Results indicate significant improvement in term low BER （beat error rate） and very high quality factor in the form of QoS. The authors have used PSO （pseudo orthogonal） codes and random phase code. The simulations are carried out using OptSim （RSOFT）.

不相关多子集零相关区序列集的构造

在多小区环境下的准同步码分多址(quasi-synchronous code-division multiple-access,QS-CDMA)系统中,不相关多子集零相关区(zero correlation zone,ZCZ)序列集不仅可以消除一定时延内来自相同小区的信号干扰,而且可以完全消除来自相邻小区的信号干扰。针对如何基于仿酉矩阵构造多子集ZCZ序列集的问题,设计了两种构造方法。具体地,通过构造具有一定特性的多个初始矩阵,再结合仿酉矩阵,进而利用不同的初始矩阵产生不同的ZCZ序列集,且序列集间互不相关。所提方法的核心是多个初始矩阵的设计,方法1通过对离散傅里叶变换(discrete Fourier transform,DFT)矩阵进行分块与叠加实现,方法2利用已有的不相关多子集ZCZ序列集实现。由两种方法得到的构造结果,其参数趋近于最优,为解决多小区环境下的干扰抑制问题提供了新的序列设计方法。

Optical PPM-CDMA Communication System with Optical Hard Limiter

An optical PPM CDMA communication system with an optical hard limiter in front of the correlator of a receiver is proposed in order to reduce multi user interference. The performance of the system is evaluated when the effects of both multi user interference and photo detector shot noise are considered. An upper bound on the bit error rate is derived. The comparison of the performance of the above receiver with that of the optical PPM CDMA system without an optical hard limiter is made. Simulation results show that the performance of the system with an optical hard limiter is superior to that of the conventional one.

An underwater acoustic direct sequence spread spectrum communication system using dual spread spectrum code

With the goal of achieving high stability and reliability to support underwater point-to-point communications and code division multiple access(CDMA) based underwater networks, a direct sequence spread spectrum based underwater acoustic communication system using dual spread spectrum code is proposed. To solve the contradictions between the information data rate and the accuracy of Doppler estimation, channel estimation, and frame synchronization, a data frame structure based on dual spread spectrum code is designed. A long spread spectrum code is used as the training sequence, which can be used for data frame detection and synchronization, Doppler estimation, and channel estimation. A short spread spectrum code is used to modulate the effective information data. A delay cross-correlation algorithm is used for Doppler estimation, and a correlation algorithm is used for channel estimation. For underwater networking, each user is assigned a different pair of spread spectrum codes. Simulation results show that the system has a good anti-multipath, anti-interference, and anti-Doppler performance, the bit error rate can be smaller than 10^(-6) when the signal-to-noise ratio is larger than-10 dB, the data rate can be as high as 355 bits/s, and the system can be used in the downlink of CDMA based networks.