Modified quadratic congruence codes for fiber Bragg-grating-basedspectral-amplitude-coding optical CDMA systems

We have constructed a series of new code families for the spectral-amplitude-coding optical code-division multiple-access (CDMA) system, and proposed new transmitter and receiver structures based on tunable chirped fiber Bragg gratings (FBGs). The proposed system has been analyzed by taking into account the effects of phase-induced intensity noise, shot noise, and thermal noise. We have also compared the performance of this system with that of a former system where a Hadamard code is used. It has been shown that the new code families can suppress the intensity noise effectively and improve the system performance significantly. When the effective power is large (i.e., >-10 dBm), the intensity noise is the main factor that limits the system performance. When the effective power is not sufficiently large, thermal and shot noise sources become the main limiting factors and the effect of thermal noise is much larger than that of shot noise     

一种PON系统光缆监测新方案

无源光网络(PON)是一种点到多点的光接入技术,采用传统的光时域反射仪(OTDR)技术对PON的各分支光路进行监测出现了技术瓶颈.针对这一问题,文章分析了现有几种解决方案的不足之处,在此基础上,提出了一种以光供能方式驱动光开关测试的新方案,并详细描述了该方案的实现过程.     

A novel 1:N protection scheme for WDM passive optical networks

This paper presents a 1:N protection scheme based on the cyclic property of an array waveguide grating and a specific connection pattern among the optical network units (ONUs). The proposed scheme requires half the number of wavelengths of existing schemes presented in the literature. Although the current scheme requires more fiber links among the ONUs than previous schemes, the network resource demands are greatly reduced and the protection performance is improved.     

Wavelength reused upstream transmission scheme for WDM passive optical networks

A novel technique facilitating wavelength reused upstream transmission in a WDM passive optical network, eliminating wavelength source at ONUs, is proposed and experimentally demonstrated. A subcarrier frequency is used for downstream transmission and the pure optical carrier is filtered and reused for upstream transmission. The scheme requires only simple baseband receivers at both ONU and OLT terminals.     

OSLG: A new granting scheme in WDM Ethernet passive optical networks

Several granting schemes have been proposed to grant transmission window and dynamic bandwidth allocation (DBA) in passive optical networks (PON). Generally, granting schemes suffer from bandwidth wastage of granted windows. Here, we propose a new granting scheme for WDM Ethernet PONs, called optical network unit (ONU) Side Limited Granting (OSLG) that conserves upstream bandwidth, thus resulting in decreasing queuing delay and packet drop ratio. In OSLG instead of optical line terminal (OLT), each ONU determines its transmission window. Two OSLG algorithms are proposed in this paper: the OSLG_GA algorithm that determines the size of its transmission window in such a way that the bandwidth wastage problem is relieved, and the OSLG_SC algorithm that saves unused bandwidth for more bandwidth utilization later on. The OSLG can be used as granting scheme of any DBA to provide better performance in the terms of packet drop ratio and queuing delay. Our performance evaluations show the effectiveness of OSLG in reducing packet drop ratio and queuing delay under different DBA techniques.     

A new modulation scheme using asymmetric erorr-correcting codesembedded in optical orthogonal codes for optical CDMA

An embedded-modulation scheme is proposed for optical code division multiple access (CDMA). In this scheme, codewords in an asymmetric error-correcting (AEC) code is embedded in a signature sequence in an optical orthogonal code (OOC) used for identification. We classify the codewords of the AEC code according to the number of "1"s in each codeword, and then derive the bit error rate (BER) of the embedded-modulation scheme. Numerical results show that although the performance has the error floor, for achieving the floor value, the embedded-modulation scheme requires less optical energy per bit than the traditional modulation scheme with the correlation and chip-level receivers. The error floor is primarily due to multiaccess interference (MAI), we furthermore apply Reed-Solomon (RS) coding to the embedded-modulation scheme. Consequently, RS coding reduces the floor value to be negligibly small     

An ultraviolet laser communication system using frequency-shift keying modulation scheme

A communication system based on an ultraviolet(UV) laser at 266 nm is presented to improve the communication distance. The pulse frequency-shift keying(FSK) modulation scheme is studied and improved in order to reduce the bit error rate(BER), and is put into practice on a field programmable gate array(FPGA). The mathematical models of the modulation and demodulation are established. A test platform is set up to measure the energy density and pulse response under different distances and receiver elevation angles. It is shown that the omnibearing communication can be realized, and the bit rate is limited to 12.5 Mbit/s. The BER is estimated to be less than 10-7 at distance of 300 m in line-of-sight(LOS) communication model and to be less than 10-6 at distance of 80 m in non-line-of-sight(NLOS) communication model.     

Repeater using two wavelengths for passive optical star networks connection

A repeater for the 32 Mbit/s star-configured optical local area network (SOLARnet) has been developed. This repeater permits a tree-type interconnection of SOLARnets at layer 1 and enlarges the network scale. Wavelength-division multiplexing (WDM) is used to overcome self-collision (collision of the packet header with its packet).     

Energy-saving scheme based on downstream packet scheduling in ethernet passive optical networks

With increasing network sizes, the energy consumption of Passive Optical Networks (PONs) has grown significantly. Therefore, it is important to design effective energy-saving schemes in PONs. Generally, energy-saving schemes have focused on sleeping the low-loaded Optical Network Units (ONUs), which tends to bring large packet delays. Further, the traditional ONU sleep modes are not capable of sleeping the transmitter and receiver independently, though they are not required to transmit or receive packets. Clearly, this approach contributes to wasted energy. Thus, in this paper, we propose an Energy-Saving scheme that is based on downstream Packet Scheduling (ESPS) in Ethernet PON (EPON). First, we design both an algorithm and a rule for downstream packet scheduling at the inter- and intra-ONU levels, respectively, to reduce the downstream packet delay. After that, we propose a hybrid sleep mode that contains not only ONU deep sleep mode but also independent sleep modes for the transmitter and the receiver. This ensures that the energy consumed by the ONUs is minimal. To realize the hybrid sleep mode, a modified GATE control message is designed that involves 10 time points for sleep processes. In ESPS, the 10 time points are calculated according to the allocated bandwidths in both the upstream and the downstream. The simulation results show that ESPS outperforms traditional Upstream Centric Scheduling (UCS) scheme in terms of energy consumption and the average delay for both real-time and non-real-time packets downstream. The simulation results also show that the average energy consumption of each ONU in larger-sized networks is less than that in smaller-sized networks; hence, our ESPS is better suited for larger-sized networks.     

A hybrid cycle bandwidth allocation scheme with differentiated services support in Ethernet passive optical networks

The Ethernet passive optical network (EPON) has emerged as one of the most promising solutions for next generation broadband access networks. Designing an efficient upstream bandwidth allocation scheme with differentiated services (DiffServ) support is a crucial issue for the successful deployment of EPON, carrying heterogeneous traffic with diverse quality of service (QoS) requirements. In this article, we propose a new hybrid cycle scheme (HCS) for bandwidth allocation with DiffServ support. In this scheme, the high-priority traffic is transmitted in fixed timeslots at fixed positions in a cycle while the medium- and low-priority traffic are transmitted in variable timeslots in an adaptive dynamic cycle. A suitable local buffer management scheme is also proposed to facilitate QoS implementation. We develop a novel feature providing potentially multiple transmission opportunities (M-opportunities) per-cycle for high-priority traffic. This feature is significant in improving delay and delay-variation performance. The HCS provides guaranteed services in a short-cycle scale for delay and jitter sensitive traffic while offering guaranteed throughput in a moderately long-time scale for bandwidth sensitive traffic and at the same time maximizing throughput for non-QoS demanding best-effort traffic. We develop analytical performance analysis on the deterministic delay bound for high-priority traffic and minimum throughput guarantees for both high- and medium-priority traffic. On the other hand, we also conduct detailed simulation experiments. The results show a close agreement between analytical approach and simulation. In addition, the simulation results show that the HCS scheme is able to provide excellent performance in terms of average delay, delay-variation, and throughput as compared with previous approaches.

A novel reliable and secure communication scheme for cognitive radio networks using concatenated kernel codes

Cognitive radio networks have emerged as a possible solution for the spectrum scarcity problem. Cognitive radio networks involve heterogeneous entities as part of it for facilitating spectrum sharing. Ensuring reliability and security in such scenario is inevitable for the licensed users (primary users) as well as for the unlicensed users (secondary users). To address the challenges of reliable and secure communication for the secondary users, in this paper, a novel reliable and secure communication framework is proposed. A class of group codes called concatenated kernel codes is used to achieve reliability and techniques of fundamental cutset and fundamental circuit to achieve security in terms of authentication of sender. It is shown that the proposed communication framework provides reliability mitigating the continuous interference of primary users and security by defending against the cryptanalytic attacks such as replay attack, related key attack, and man‐in‐the‐middle attacks. The theoretical basis of the proposed framework is validated, and its performance is evaluated through simulations.     

Multiclass optical orthogonal codes for multiservice optical CDMA networks

Optical code division multiple access (CDMA)-based networks are an interesting alternative to support various traffic types of multimedia applications with highly variable performance targets. Generally, multilength codes are designed to support multirate services, while the multiweight codes are designed to support differentiated quality of service (QoS) for multimedia applications. However, existing optical orthogonal codes (OOCs) are limited to single class or multiclass with restricted weight and length properties. Therefore, there exists a lack of flexibility in the existing OOCs to support arbitrary rate and QoS. This paper presents a proposal of generation procedure and performance analysis of joint multiweight multilength strict OOCs. The approach used in this paper is to apply a methodology strongly relying on developed analytical theory that is supported by computer optimization, because it has turned out that it is mathematically intractable to construct unconstraint joint multilength multiweight OOCs using pure algebraic techniques. The generated code set fulfills the conditions of strictly OOCs, namely, the maximum nonzero shift autocorrelation and the maximum cross correlation constraints of one. The mark position difference (MPD) approach is used to generate in a flexible way the multiclass code set. The MPD results in the simple evaluation of multiclass code set cardinality. Furthermore, the multiple-access interference (MAI) in a multiclass OOC system is evaluated by modeling the interference per class as a Poisson distribution to simplify performance evaluation with acceptable accuracy.     

运用卷积码降低峰均比的一种新方法

正交频分复用(OFDM)是一种高效的传输技术,它有着很高的比特速率,并能抵抗符号间干扰(ISI).然而,过高的峰均比(PAPR)一直是影响OFDM系统性能的重要因素.本文将卷积码与传统的选择性映射(SLM)方法结合起来,通过插入比特标签,提出了降低峰均比的一种新方法.仿真结果表明,新方法可以大大降低峰均比.     

A new family of Grassmann space-time codes for non-coherent MIMO systems

A family of space-time codes suited for noncoherent multi-input multi-output (MIMO) systems is presented. These codes use all the complex degrees of freedom of the system, i.e. M/spl times/(1-(M/T)) symbols per channel use. They are constructed as codes on the Grassmann manifold G/sub T,M/(/spl Copf/) where T is the temporal codelength and M is the number of transmit antennas.     

Two-dimensional optical orthogonal codes for fiber-optic CDMA networks

Several constructions of two-dimensional (2-D) codes have been proposed to overcome the drawbacks of nonlinear effects in large spread sequences of one-dimensional (1-D) unipolar codes in fiber-optic code-division multiple-access (FO-CDMA) networks. Wavelength-time (W/T) encoding of the 2-D codes is practical in FO-CDMA networks. W/T codes reported so far can be classified mainly into two types: 1) hybrid codes, where one type of sequence is crossed with another to improve the cardinality and correlation properties and 2) conversion of 1-D sequences to 2-D codes to reduce the "timelike" property. This paper describes the basic principles of a new family of wavelength/time multiple-pulses-per-row (W/T MPR) codes, for incoherent FO-CDMA networks, which have good cardinality, spectral efficiency, and minimal cross correlation values. In addition, an expression for the upper bound on the cardinality of W/T MPR codes is derived. Another feature of the W/T MPR codes is that the aspect ratio can be varied by a tradeoff between wavelength and temporal lengths. The correlation properties of W/T MPR codes are verified by simulation using Matlab. For given wavelength /spl times/ time dimensions, various W/T codes, whose cardinalities are known, are compared, and it is shown that the W/T MPR family of codes have better cardinality and spectral efficiency than the other W/T codes. Performance analysis of the W/T MPR codes and their limiting cases is carried out for various parameter variations such as the dimensions of wavelength, time, and weight of the code.     

Network coding based joint signaling and dynamic bandwidth allocation scheme for inter optical network unit communication in passive optical networks

As an innovative and promising technology, network coding has been introduced to passive optical networks (PON) in recent years to support inter optical network unit (ONU) communication, yet the signaling process and dynamic bandwidth allocation (DBA) in PON with network coding (NC-PON) still need further study. Thus, we propose a joint signaling and DBA scheme for efficiently supporting differentiated services of inter ONU communication in NC-PON. In the proposed joint scheme, the signaling process lays the foundation to fulfill network coding in PON, and it can not only avoid the potential threat to downstream security in previous schemes but also be suitable for the proposed hybrid dynamic bandwidth allocation (HDBA) scheme. In HDBA, a DBA cycle is divided into two sub-cycles for applying different coding, scheduling and bandwidth allocation strategies to differentiated classes of services. Besides, as network traffic load varies, the entire upstream transmission window for all REPORT messages slides accordingly, leaving the transmission time of one or two sub-cycles to overlap with the bandwidth allocation calculation time at the optical line terminal (the OLT), so that the upstream idle time can be efficiently eliminated. Performance evaluation results validate that compared with the existing two DBA algorithms deployed in NC-PON, HDBA demonstrates the best quality of service (QoS) support in terms of delay for all classes of services, especially guarantees the end-to-end delay bound of high class services. Specifically, HDBA can eliminate queuing delay and scheduling delay of high class services, reduce those of lower class services by at least 20%, and reduce the average end-to-end delay of all services over 50%. Moreover, HDBA also achieves the maximum delay fairness between coded and uncoded lower class services, and medium delay fairness for high class services.     

Narrow-FSK optical packet labeling scheme for optical ethernet networks

In this work, an intensity modulation/frequency-shift keying (IM/FSK) orthogonal modulation scheme is achieved by direct modulation of a distributed feedback laser source using its adiabatic chirp characteristics. Optical frequencies for "1" and "0" bits are separated only 0.7 GHz, obtaining a narrow-FSK modulation and, accordingly, a low residual intensity modulation. Ethernet frames at 1.25 Gb/s (GbE) are transmitted with a label inserted using coded mark inversion codification at a 155-Mb/s rate. Error rates for the Ethernet payload and for the label have been measured for different payload extinction ratios, showing the viability of this scheme for distances up to 25 km.     

An embedded transmission scheme using PPM signaling with symmetric error-correcting codes for optical CDMA

An embedded transmission (ET) scheme is proposed to easily apply error-correcting codes into optical code-division multiple-access (CDMA) systems for immunity from multiple-access interference (MAI). The ET scheme offers high transmission capability over the traditional scheme using pulse position modulation (PPM) signaling, because a 2/sup J/-ary symbol of each user is embedded in the signature sequence with 2/sup J/ weighted positions. Furthermore, the ET scheme with 2/sup J/-ary PPM signaling makes the optical CDMA system J parallel transmission systems, because J bits consisting of 2/sup J/-ary symbol are separately decided. Since such a separate decision is a comparison decision, the effect of MAI added in the optical channel is converted to symmetric errors in the individual parallel transmission systems. Using the symmetric error-correcting (SEC) code immunizes the individual parallel transmission systems against MAI more easily than the embedded-modulation scheme described in because the ET scheme avoids using the asymmetric error correcting code, which is difficult to implement. We analyze the bit error rate under Poisson photon counting channel and show that the ET scheme has an advantage of good energy efficiency over the traditional scheme in applying SEC codes.     

A wavelength-buffering scheme for dynamic traffic in optical wavelength-division multiplexing networks

In optical wavelength-division multiplexing (WDM) networks, traffic can be very “bursty” at a fine time scale, even though it may seem to be smooth at coarser scales (e.g., Poisson or Poisson-related traffic). This paper analyzes the instantaneous characterization of Poisson traffic at a fine time scale. The analysis shows that the irregular oscillation of the instantaneous traffic load and the occurrence of blockings in a light-loaded network are highly correlated. Specifically, most blockings occur concentratively at the peaks of the instantaneous load. In some other time, network resources may not be sufficiently utilized. To make better utilization of network resources, a novel wavelength-buffering (WB) scheme is proposed for the first time in this paper. By reserving a portion of resources in a “wavelength buffer” under light loading and releasing them when the load goes up, a number of blockings brought by the oscillation of the traffic load can be avoided. Simulation results show that compared with other schemes such as adaptive routing, wavelength conversion (WC), and rerouting, the novel wavelength-buffering scheme achieves significantly better performance with respect to the network utilization and overall blocking probability.

A novel approach for physical layer security in future-generation passive optical networks

The ever increasing growth of users and network capacity makes the security of passive optical networks (PON) an issue of great concern. In this paper, we present a novel work to enhance the physical layer security for wavelength division multiplexing orthogonal frequency division multiplexing PON. Elliptic curve with Diffie–Helman key exchange protocol is employed to derive a session key for Advanced Encryption Standard algorithm at optical line terminal and optical network units to provide secure communication. Encryption is applied on partial data of I/Q channel in order to reduce the computational time. Successful transmission of 16-Quadrature Amplitude Modulation encrypted OFDM signals at a distance of 100 km is demonstrated within the limits of peak to average power ratio value.