Design and performance analysis in multiuser optical CDMA systems

The article presents comparative performance analysis of the proposed Optical CDMA system for 32 and 16 users with two dimensional codes. Numerical simulations have been done under interference significant environment, considering noise and dark current at data rates 2.5, 5, 7.5 and 10 Gbps over single mode fiber for transmission distance of more than 270 km. Results illustrate overall good performance, degraded with augment in bit rate and transmission distance, impervious with raise in number of simultaneous active users. Depicts significant performance improvement with inclusion of forward error correction RS (255,239), for low attenuation and chirp factor. It perceived, this is one of the efficient functional techniques for next generation broadband optical networks together with higher security owing to encoding and decoding, as it allow multiple users in the network to access the same fiber channel asynchronously.     

2.50 Gbit/s optical CDMA over FSO communication system

Optical CDMA over FSO communication system is very effective to provide high data rate transmission with very low bit error rate and low amount of multiple access interference. In this paper, we have presented optical CDMA over FSO communication system to the range of 8000 m. The simulative results reveal that the transmission distance is limited mainly by the multi-access interference (MAI) which arises when there are number of users in the system because of the fact that one user data becomes noisy for all other users in the channel.     

Enhanced performance analysis of optical CDMA communication system

Optical CDMA technique is required to meet the increased demand for high speed, large capacity communications in optical networks. OCDMA assures data access security and supports asynchronous burst data transmission. In this paper, improvement in optical CDMA has been done by implementing forward error correction technique and a distance of 100 km was achieved BER 10⁻¹⁹ at bit rate 3.75 Gbps with forward error correction in optical CDMA.     

Spectrally Efficient 3D Optical CDMA Using Coherent Spatial Phase–Time Coding/Decoding

We demonstrate a WDM compatible optical CDMA system incorporating 3D spectral phase–time encoding/decoding. We provide coding and decoding using binary [0, π] phase chips for six users at 6 Gb/s, with a single coded signal separated with an acceptable bit-error rate ≤10 ^?9. The coding and decoding method is based on 3D coding of tightly spaced phase-locked laser lines that is compatible with conventional WDM networking. In optical CDMA systems, we propose to provide encoding and decoding done by converting Hadamard codes (used for conventional CDMA system) to the phase codes. We report that duo-binary modulation format is the best with adequate bandwidth compression. We confirm that better simulation results are reached in terms of the Q factor and bit error rate.     

基于频分信道双极性光码分多址实现研究

提出了采用光纤法-玻滤波器与电吸收调制器实现频域幅度编解码的频分信道双极性OCDMA系统方案.推导了系统模型理论公式,分析了系统信噪比对接收端探测误差、不同编解码系统和传输信道对系统性能的影响.仿真结果表明：比较高的信噪比有利提高接收端探测效果;系统容纳用户能力增强;系统有良好的相关特性;20 km的SMF搭配300 m的DCF传输系统明显优于20 Km的DSF传输系统.     

Performance analysis and improvement of spectrally amplitude encoded/decoded OCDMA system

This paper describes a performance analysis of an incoherent optical code-division multiple-access scheme based on wavelength/time (W/T) codes. The system supports 16 users operating at 2.5Gb/s/user while maintaining bit-error rate (BER) < 10⁻¹¹ for the correctly decoded signal. It has been observed that there are two major problems giving rise to performance degradation of the system in terms of number of users and type of code.In this paper we have studied the optical simulator Encoding/Decoding for different lengths & gain in terms of Quality factor (Q) and Bit Error Rate (BER) performance. The system supports 16 users while maintaining bit-error rate (BER) < 10⁻¹¹ for the correctly decoded signal. Our aim is to design and simulate a Tree Network Topology Optical Code Division Multiple Access System for large number of users using wavelength–time code and to analyze the performance of the system based on BER and Eye Diagram under the influence of number of simultaneous users with different received powers.     

On spectrum sensing in cognitive radio CDMA networks with beamforming

In this paper, the performance of cognitive radio (CR) code division multiple access (CDMA) networks is analyzed in the presence of receive beamforming at the base stations (BSs). More precisely, we analyze, through simulations, the performance achievable by a CR user, with and without spectrum sensing, in a three-cell scenario. Uplink communications are considered. Three different schemes for spectrum sensing with beamforming are presented, together with a scheme without spectrum sensing. CR users belong to a cognitive radio network (CRN) which is coexisting with a primary radio network (PRN). Both the CRN and the PRN are CDMA based. The CRN is assumed to utilize beamforming for its CR users. Soft hand-off (HO) and power control are considered in both the CRN and the PRN. The impact of beamforming on the system performance is analyzed, considering various metrics. In particular, we evaluate the performance of the proposed systems in terms of outage probability, blocking probability, and average data rate of CR users. The results obtained clearly indicate that significant performance improvements can be obtained by CR users with the help of beamforming. The impact of several system parameters on the performance of the three considered spectrum sensing schemes with beamforming is analyzed. Our results, in terms of probability of outage, show that the relative improvement brought by the use of beamforming is higher in the absence of spectrum sensing (reduction of 80%) than in the presence of spectrum sensing (reduction of 42%).     

Performance of Indoor Infrared Wireless CDMA Systems with Angle Diversity

Indoor infrared communication systems is one of the possible ways of offering data rates in excess of 100 Mbit/s without the need for wiring. Multiple users can share an infrared channel by code division-multiple access (CDMA) techniques. However, the CDMA system performance is limited by both background noise and co-channel interference. In this paper we study the use of angle diversity for mitigating the effects of the noise and interference. The system considered uses on-off shift keying modulation with multibeam transmitters and imaging receivers. The overall system performance for different diversity combining techniques is evaluated and compared to a system without diversity. Numerical results for a 2-user CDMA system indicate that signal to noise and interference ratio (SNIR) improvement (over systems with no diversity) of 5 dB is obtained for at least 50% of an ensemble of 10000 sample evaluations. The generalized selection combining (GSC)--a new diversity technique yet to be implemented for infrared systems--offers the best performance even with its reduced complexity.     

Analysis of electrically configurable spectral phase encoding techniques for optical CDMA

We present the theoretical analysis and simulation of an encoder/decoder pair with applications in Optical Code Division Multiple Access (OCDMA) systems. The theory and simulations presented are valid for any technique that relies on the combination of dispersion/phase modulation/dispersion for spectral phase encoding. We perform a theoretical study of the system, characterizing its main limiting factors, and a comparative study of the Multi-Access Interference (MAI) and Bit Error Rate (BER) for a simple multi-user system at high-bit rate in a Passive Optical Network (PON) environment. The capacity of the system to carry out error-free operation for codes of different length and with different numbers of users is also demonstrated through simulation.     

Simulation of Fiber to the Home at 10 Gbit/s using GE-PON architecture

In this paper, a fiber communication system is employed using Giga Ethernet Passive Optical Network (GE-PON) architecture. In this architecture an optical fiber is employed directly from a Central Office to the home. A 1:8 splitter is used as a PON element which establishes communication between a Central Office to different users. The architecture has been investigated for different lengths from a Central Office to the PON in terms of BER. For 10 Gbit/s system the plots between the BER and transmission distance are plotted and it are seen that as the distance increases beyond the 15 km the BER is increased very sharply. The results in the form of voice and data spectrum for different users of FTTH with GE-PON architecture are shown.     

利用布拉格光栅阵列实现二维光码分多址的研究

利用布拉格光栅阵列,实现了在波长和时问上的素数跳频码的编解码。利用该编解码器,完成了在两个发送用户和一个接收用户的条件下,传输速率从20Mb／s到1．4Gb／s的光码分多址通信系统。研究了当系统传输速率超过相邻布拉格光栅间距限制条件时,系统的性能变化情况。结果表明当用户数不超过(3／2)Ps(素数跳频码的扩展因子)时,速率超限对系统性能基本无影响。在同样误码率要求条件下,地址码较长的系统,传输速率可以达到限制速率的2～3倍而不会造成明显的系统性能下降。这表明相邻布拉格光栅间距条件所限制的系统速率并非不可逾越的。     

Simulation of fiber to the home triple play services at 2 Gbit/s using GE-PON architecture for 56 ONUs

This paper evaluates and compares FTTH (Fiber To The Home) GEPON (Gigabit Ethernet Passive Optical Network) link design for 56 subscribers at 20 km reach at 2 Gbps bit rate. A 1:56 splitter is used as a PON (Passive Optical Network) element which creates communication between a Central Office to different users and. A boosting amplifier is employed before fiber length which tends to decrease BER and allows more users to accommodate. This architecture is investigated for different values of data rate from a CO (Central Office) to the PON in terms of BER (Bit Error Rate). The simulation work reports BER of 4.5246e−009 at 2 Gbit/s systems for the case of 56 users and if we further increase data rate of system say 5 Gbps, then we observe a sharp increase in BER. Similarly in the variation of BER with respect to transmission distance, we observe that BER shows an increase in its value as transmission distance increases.     

基于2D-OOC的OCDMA系统的地址码结构研究

提出了二维光正交码 (2D OOC)设计方案 ,围绕光码分多址 (OCDMA)技术实用化的两个主要指标—最大并发用户数和系统误码率的改进和提高 ,系统地研究了基于 2D OOC的OCDMA的性能 ,分析了 2D OOC码字的相关性 ,导出了系统的最大用户容量 ,详细研究了 2D OOC系统以多址干扰为主的系统误码率 .研究表明 :较之一维时域扩频码或一维谱域扩频码 ,2D OOC系统性能大大提高 ,在大信息量传输时 ,适当选择码长和码重 ,系统总容量可高达Tbits/s量级 ,性能优于基于 1D OOC的OWDM和OCDMA混合系统 .     

基于2D-OOC的OCDMA系统的地址码结构研究

提出了二维光正交码(2D-OOC)设计方案,围绕光码分多址(OCDMA)技术实用化的两个主要指标-最大并发用户数和系统误码率的改进和提高,系统地研究了基于2D-OOC的OCDMA的性能,分析了2D-OOC码字的相关性,导出了系统的最大用户容量,详细研究了2D-OOC系统以多址干扰为主的系统误码率.研究表明:较之一维时域扩频码或一维谱域扩频码,2D-OOC系统性能大大提高,在大信息量传输时,适当选择码长和码重,系统总容量可高达Tbits/s量级,性能优于基于1D-OOC的OWDM和OCDMA混合系统.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Two-Dimensional Optical Data Transmission with Space-Time Conversion Combined with Code Division Multiple Access

A new scheme for two-dimensional parallel data transmission with a femtosecond laser pulse through a single-mode fiber, which is based upon one-dimensional space-time conversion technique in conjunction with code division multiple access (CDMA), is implemented and numerically demonstrated. Since many one-dimensional spatial data, which are encoded with their own M-sequence code, must be embedded in a single pulse, the bit-error rate performance degrades compared with conventional CDMA driven by many unsynchronized pulses. Still, two-dimensional digital images in a 16 bits × 16 bits plane (256-bits parallel data) are successfully transmitted by a single femtosecond laser pulse at an equivalent transmission rate of 1.6 Tbit/s and recovered by spectral holography.     

An adaptive reservation scheme for optical network

In this paper, the various Optical Burst Switching (OBS) reservation schemes have been examined in order to reduce data loss caused by either channel scheduling or resources. A novel multi-service OBS edge node with synchronized bandwidth reservation mechanism (SRM) has been proposed, which enables high-speed network transport nodes to dynamically reserve bandwidth needed for active data burst flows. The performance of the proposed mechanism is evaluated by means of NS-2 simulation. The results show that the packet delay is kept within the constraint for each traffic flow and the performance metrics such as burst loss rate, throughput and fairness are remarkably improved.     

Contention reduction and service differentiation in OBS networks

Optical burst switching (OBS) has been proposed to be a competitive switching technology for wavelength division networks (WDM) networks. In this switching technique, single burst loss due to contention influences loss of multiple data. Thus, burst loss ratio (BLR) is the main deciding factor for determining the performance of an OBS network. Also, inefficient data channel scheduling algorithm causes burst loss in OBS. In addition to this, the same service to all model of the current Internet is inadequate for the diverse quality of service expectations of Internet applications and users. In this paper, an efficient technique is proposed in which data burst is assembled from several Internet protocol (IP) packets in such a manner that the number of IP packets is changed according to the traffic load. In the proposed scheme, the burst is segmented because the segment located at the end of the contended burst has a greater chance of surviving contention (as the dropped segments are those at the beginning of the contending burst). Thus, the most important (or higher priority) information is enveloped in the last segmented. Further to prevent resource wastage due to over admitting of bursts, the proposed scheme is extended by admission control test for an output link without a fiber delay line (FDL) buffer. Also, modified latest available unscheduled channel with void filling (LAUC-VF) scheduling algorithm utilizing MPLS has been used to provide a scalable and manageable architecture for service differentiation (DiffServ) in IP networks. Simulation results demonstrate that the proposed technique has reduced burst loss rate and better quality of service (QoS) performance in comparison to existing techniques.     

Design and performance analysis of various one dimensional codes using different data formats for OCDMA system

In this paper, the design, implementation and performance analysis of various one dimensional codes in an OCDMA system for different data formats is presented. A number of different codes are used with optical CDMA to improve its error performance. Here, three such codes, optical orthogonal codes (OOC), Walsh Hadamard codes and zero cross-correlation (ZCC) codes have been compared using different data formats, NRZ raised cosine, NRZ rectangular, RZ raised cosine and RZ rectangular. It is found that NRZ raised cosine has the best system performance for all the codes used. After that, the three codes have been compared in terms of the BER, eye diagrams and received optical power using NRZ raised cosine modulation format. It is analyzed that ZCC codes have zero cross-correlation property. The simulation results revealed that ZCC codes can provide a better BER compared to the OOC and Walsh Hadamard codes and it is most suitable to be employed in the OCDMA systems.     

Performance enhancement using the bipolar capacity of bipolar coded fiber Bragg gratings and balanced detection in the spectral encoded code-division-multiple-access systems

This paper proposes a performance-enhanced code-division-multiple-access (CDMA) system using modified pseudorandom noise (PN) coded fiber Bragg gratings (FBGs) with a bipolar optical CDMA encoder/decoder. The data were encoded either by a unipolar signature sequence of modified PN code or by its complement, depending on whether the data bit was ‘1’ or ‘0’. Numerical simulation confirmed that bit error rate (BER) performance largely improved due to the increased decision margin at the receiver. Furthermore, at the BER of 10⁻⁹, the tolerance of spectral power distortion in the optical source appeared to be nearly twice that of conventional optical CDMA systems.