and linear XT. For this block, FDE is preferable over TDE for accumulated dispersion higher than 2000 ps/nm in 100 Gbit/s systems . The second digital filtering block compensates for polarization rotation, PMD, linear XT, and DMD, since the four im- pairments are interdependent. In the second block, FDE is also the preferable option since it has been shown that, for long-haul MDM transmission, TDE is unfeasible with present technology even for low DMD values, on the order of ∼10 ps/km . In order to mitigate the polarization rotation, PMD, linear XT, and DMD, the 2M × 2M fiber matrix H has to be estimated (for a FMF guiding M modes, each with two polar- izations), inverted and applied to the received signal through a matrix multiplication operation. In contrast to the chromatic dispersion, which may be considered constant, H may evolve in time due to effects such as rapid variations in the polarization state or linear XT, and thus the compensation scheme must be adaptive. The problem of the estimation of H is addressed using the formalism of MIMO systems, as in PDM- SSMFs systems, where each H matrix element is an adaptive FIR filter. The optimum number of taps of FIR filters depends on the CIR length, determined by the combined effect of DMD and linear XT. The methods for H estimation can be divided in two types: algorithms based on TS, or blind algorithms based on the characteristics of the signal . In , it has been shown that TS-based equalization provides several orders of lower complexity, compared to blind equalization, for long-haul transmis- sion systems. However, the reach is limited by the maximum TS overhead allowed, since the TS length has to be at least the CIR length. Limiting these additional overheads to 10 %, a fiber with a DMD as low as 12 ps/km is required for 2000 km of FMF transmission at 100 Gb/s . Considering the use of TS, H is estimated in the time domain by correlating the received and transmitted training symbols, and is subsequently inverted. There are three main equalization and detection schemes:
Submarine cables must meet extremely tough requirements. Their transmissioncapacity should be as high as possible, because the cables are costly to make, lay, and operate. The cable, and any optical amplifiers or repeaters, must withstand harsh conditions on the bottom of the ocean for a design life of 25 years . Components must be extremely reliable, because it is very expensive to recover the cable from the sea floor and haul it to the surface for repairs. The cable should transmit digital signals cleanly to be compatible with modern equipment. These specifications veritably call out "fiber optics," and since the 1980s fibers have been standard for submarine cables . Submarine optical fiber cables are being used in a number of countries to realize long length high bit-rate optical fiber transmissionsystems utilizing the 1.3 m wavelength region. For these systems, optimum fiber parameter design, low-loss optical fiber and cable manufacturing techniques, low-loss splicing technique, and system and repeater circuit design have been examined .
O ptical interconnections on silicon have been extensively investigated in recent years as interconnections become the bottleneck for the next- generation computing systems . The goal of these investigations is to provide a compact, low power consumption, high bandwidth and low-latency optical interconnection system with full CMOS compatibility. Silicon basedoptical components such as low-loss silicon-on-insulator (SOI) optical waveguides , high speed silicon modulators, and Germanium on SOI detectors enabling large-scale optical integration on a silicon chip. While most attention is focused on single channel systems at this stage, wavelength divisionmultiplexing (WDM) technology is necessary to fully utilize the ultra wide bandwidth of the optical interconnection medium, given that the transmission bandwidths of both silicon waveguides and optical fibers are on the order of 10 to 100 THz. As the key components of such a system, we show high speed and multi-channel modulation using cascaded silicon micro ring modulators .
to achieve different constellations, as shown in Fig.7 (i.e., a cubic or spherical lattice, which are described later; Fig.8). All the carriers are combined and transmitted by a single- modeoptical fiber. Finally, at the receiver end, an optical splitter divides the optical carriers to recover the information. Fig.3(a) shows the general block diagram of the H-SAPDP transmitter which accepts m-bit inputs from the information sources, passes them through a set of identical LDPC encoders with a code rate of R = k/n, where k represents the number of information bits that the encoder accepts and n the length of the resulting codeword. The encoded data from these branches is forwarded to an [m × n] block interleaver where it is written row-wise and read column-wise. In addition, the interleaver process performed by a dual-lattice multidimen- sional [D N × D N ] building matrix that is defined based on
Optical CDMA principles can be translated to the optical domain, where the enormous bandwidth offered by single modeoptical fiber is ideal for this spectrum spreading transmission technique. Implementation of the encoding decoding function directly onto the optical carrier through optoelectronic means results in all optical equivalents of the classical electrical systems. There are a number of approaches to realizing an all optical CDMA system, the most general division being into incoherent  and coherent systems. The simplest implementation, subject to the most rigorous development utilizing readily available componentry and direct detection, operates in the incoherent regime (with coherent schemes, the phase information of the carrier is crucial in the despreading, and consequently due to the nature of optical fiber transmission and its phase noise limitations, the complexity of the receiver makes the approach more difficult to realize). Optical CDMA systems can be further divided into systems employing encoding into the time position of the pulses (time spreading); systems using pulse position modulation; systems with encoding into the temporal frequencies spectrum (pulse shaping); systems with encoding into the spatial frequencies spectrum and systemsbased on two dimensional time/space or time/wavelength encoding .
Future wireless services including internet and real-time video will continue to increase the required data rates for wireless communication systems. This paper investigates modulation formats for high data rate applications in wireless environments. In particular, we consider situations where the delay spread of the channel is long compared to the bit duration. Highly dispersive channels cause significant inter-symbol interference (ISI), but they also offer a substantial potential for performance improvement through diversity. Traditional single carrier modulation formats such as phase shift keying (PSK), frequency shift keying (FSK), and quadrature amplitude modulation (QAM) require significant equalization to perform adequately in a highly dispersive
Following the increase in the networks size, the power consumption of network equipment, such as servers, ampli ﬁ ers, routers, storage devices and communication links, has rapidly increased . Given the ecological and economic impact, signi ﬁ cant research efforts are focused on reducing the energy consumption of information and communication technology networks. Energy-ef ﬁ cient and cost-effective solutions are needed to meet the increasing demand for highcapacity networking infrastructures. In the last decade, wavelength divisionmultiplexing (WDM) has emerged as the technology of choice to increase the bandwidth of networks. Recent technological advances in optical networks have enabled data rates per wavelength of 40 and 100 Gb/s with extended transmission distance. In our previous work, we studied different energy-ef ﬁ cient approaches for Internet protocol (IP) over WDM [2 – 4]. The authors in  have shown that dynamic optical path switching is capable of reducing energy consumption by four orders of magnitude. However, the rigid nature and coarse granularity of WDM networks result in inef ﬁ cient capacity utilisation because of the bandwidth mismatch between the application layer with bandwidth requirements varying from several to hundreds of Gb/s, and the wavelength channels with data rates of 10 Gb/s and beyond. Current WDM networks address this mismatch by allowing sub-wavelength granularity connections to be groomed onto
When multichannel DBP has been applied in experiments, the reported benefits have proved relatively low, typically less than 1 dB in Q 2 factor for long-haul systems [21–23]. The factors which contribute to the discrepancy between the theoretically achievable DBP benefit and the gains experimentally realized have not yet been well identified or explained. In our previous work , it has been shown that limitations to the sampling rate and number of steps can reduce the effectiveness of multichannel DBP to below that of single channel DBP. In this paper, we focus on investigating the DSP and system parameters that can have an impact on multichannel DBP effectiveness and explore the discrepancy between the theoretically and experimentally achieved results. We first focus on the impact on the DBP algorithm performance with variation of operation parameters, such as nonlinear phase rotation per step, number of steps per span and sampling rate. Second, the impact of polarization mode dispersion (PMD) was studied as an additional limitation to the performance improvement enabled by multichannel DBP.
In RoF systems, system designers have to deal with the inherent linear distortions that exist in the fibre link (in the form of chromatic dispersion and PMD) as well as in the wireless link (in the form of multipath fading). Despite optical fibre being historically thought to be a virtually inexhaustible resource and with transmission rates being low enough to render linear distortion effects negligible , this is not the norm in the context of next-generation optical access. This is because as stated in section 2.2, there has been an explosion of demand of subscribers for bandwidth-intensive applications that require multi-Gbit/s data rates to support them. As data rates increase, both chromatic dispersion increases quadratically with the data rate while PMD increases linearly with the data rate . In addition, recent research has shown that the optical fibre channel itself imposes some fundamental capacity limits .
In telecommunication networks the challenge is to increase the information capacity at a minimal cost or in a cost-effective way. An optical fibre allows for high bit rates and there- fore higher capacity communication solutions. Wavelength DivisionMultiplexing (WDM) is a technique of Frequency DivisionMultiplexing (FDM) applied at optical frequencies i.e. terahertz, usually referred to by wavelength; for example 193.3 THz converts to 1550nm. WDM allows an optical fibre to have multiple channels propagating simultaneously. A channel is a collection of wavelengths about a centre wavelength, or a small bandwidth about a centre frequency. In a basic point-to-point link multiplexing occurs when multiple inputs, each operating at a different wavelength, are transformed into a single output with the multiple wavelengths being superimposed. Demultiplexing reverses the multiplexing transformation such that the multiple wavelengths are separated into independent outputs. There are limits to how much information can be sent down an optical fibre. The pa- rameters to be considered in an optical network are the laser sources or wavelength band, wavelength separation, bit rate, type of fibre/s in the network and the associated attenu- ation and dispersion characteristics, link length, amplification requirements, and detector characteristics. The parameters affect the quality of service such as crosstalk and signal- to-noise ratio. The telecommunication problem has been investigated to the extent that standards have been established for WDM systems. A characteristic for all WDM systems is transparency to protocol, this gives the WDM systems the ability to be impartial to transmitted protocols such as SONET/SDH [Synchronous Optical Network/Synchronous Digital Hierarchy], Gigabit Ethernet, fibre channel, and ATM [Asynchronous TransmissionMode].
Abstract.Mode divisionmultiplexing (MDM) technique has been introduced as a promising solution to the rapid increase of data traffic. However, although MDM has the potential to increase transmissioncapacity and significantly reduce the cost and complexity of parallel systems, it also has its challenges. Along the optical fibre link, the deficient characteristics always exist. These characteristics, damage the orthogonality of the modes and lead to mode coupling, causing Inter-symbol interference (SI) which limit the capacity of MDM system. In order to mitigate the effects of mode coupling, an adaptive equalization scheme based on particle swarm optimization (PSO) algorithm has been proposed. Compared to other traditional algorithms that have been used in the equalization process on the MDM system such as least mean square (LMS) and recursive least squares (RLS) algorithms, simulation results demonstrate that the PSO algorithm has flexibility and higher convergence speed for mitigating the effects of nonlinear mode coupling.
compatible with number of parallel lanes in data buses required in high performance computers as well as on-chip integrated photonic systems comparing to MCF with popular hexagonal or ring structure [3, 4]. Furthermore, achieving efficient coupling of MCF to standard single core fibers (SCFs) is a significant challenge which limits the application of MCF as OI. To solve this problem, various types of fan-in fan-out (FIFO) schemes have been recently proposed, such as fiber bundled type , physical contact method , grating coupler array based FIFO , and coupling with lens optics . However, it has also been reported that the least squares boundary residual (LSBR) method  would be more efficient and accurate to use to analyze the coupling losses due to misalignments between MCF and SCF.
below 6.7db within the 36nm L-band range (1570-1605nm) is obtained . The L-band erbium-doped fiber amplifier (EDFA) is one of the key devices for dense wavelength divisionmultiplexing (DWDM) transmissionsystems, because it significantly increases the amplification wavelength range by combining with a conventional band (C-band) EDFA in a parallel configuration . The demand for high speed data transmission has increased tremendously. With the new development of the internet applications, the demand for more and more bandwidth continues to grow. Although EDFA (Erbium-doped fiber amplifier) is a mature technology and is workhorse for dense wavelength divisionmultiplexing (DWDM) and all optical networks, yet its relatively large size requires further research and development efforts to achieve the ever-wanted small , compact, and efficient fiber amplifiers. In this paper, initial investigations on a high-gain, short-length Phosphate glass Erbium- Ytterbium-doped fiber amplifier are presented .
Code division multiple access technique was originally investigated in radio frequency communication systems [1- 3]. This multiplexing technique consists to allow to each subscriber a specific codeword. This codeword permits to the transmitter to modulate its data sequences. In order to satisfy faster and more reliable optical communication system requirements and optimize the huge optical bandwidth sharing, Optical CDMA presents an attractive solution. The advantages of this technique are principally the asynchronous users emission and the possibility to emit at any time and on any wavelength without generating more interference. In Optical CDMA technique, each bit is divided up into L time periods, called chips. By sending a short optical pulse during some chips intervals, and leaving the others to “0”, an optical signature sequence can be created. For this particular case, specific optical codes have to be conceived because of the scrambling phase of the optical channel, which not permit to use bipolar optical signals. An optical code is defined by its length L (number of chips), its weight w (number of "1" chips), and its multiplexingcapacity N (number of users). In addition, for a useful optical code, the intercorrelation and asynchronous autocorrelation levels have to be limited. Two important families of optical codes were previously developed: optical orthogonal codes (OOC)  and Prime Sequences (PS) . CDMA principles can be translated to the optical domain, where the enormous bandwidth offered by single modeoptical fiber is ideal for this spectrum spreading transmission technique. Implementation of the encoding decoding function directly onto the optical carrier through
An investigation done in many research studies such as in (Amirshahi & Kavehrad, 2007) for performance of OFDM modulation for high data rate transmission over PLC channels indicates that for better performance in data transmission of PLC systems, the OFDM is a well suited modulation technique for power line networks. In this modulation data are transmitted on a number of sub-carriers within the usable spectrum thereby increasing the data rate of transmission in a multi-path environment. Another advantage of OFDM is that frequencies/sub-carriers susceptible to interference can be turned off to avoid any interference. The obtained results from simulations show the single carrier schemes require complex non-linear equalizers to mitigate the effects of multipathing. It also shows that adding a linear equalizer to the system results in increasing the noise level rather than eliminating an intersymbol interference (ISI). As in other communication systems, coding increases the overall performance in terms of Bit Error Rate (BER). Block codes, and convolution codes such as hamming code and turbo coding repeatedly can be incorporated to improve the PLC performance.
In present day scenario there has been a vast demand for high data rate wireless communication system and that demand is increasing continuously. On similar lines, the research is also progressing. One of the key technologies which started its birth in 3G communication and continuing its existence with modifications to till latest 5G wireless standards is orthogonal frequency divisionmultiplexing (OFDM). The principal advantage OFDM is that it provides high resistance to inter symbol interference (ISI) caused by the high data rate systems over a non-linear frequency selective channel [1-3]. OFDM uses the basic PSK, QAM constellations, the modelling and simulation of QAM is presented in . Vast applications of OFDM includes wireless LAN, Wi-Fi and WiMAX standards with a provision of high speed multimedia transmission.
As per any new technology, it is still facing a lot of problems preventing it from being commercially standardized and used. One of the main MDM issues is the mode coupling, which is an inventible phenomena occurs when the energy of one mode transfers to another mode during their propagation throughout the optical fibre causes inter-symbol interference (ISI), increasing the bit error rate (BER) and reducing the overall system performance. Different equalization schemes have been proposed so far attempting to mitigate the effect of mode coupling on the MDM optical signal. However, they suffer from high computational complexity and rely on training signals in estimating the optical channel which increases the overhead payload. These technique mainly rely on Least Mean Squared (LMS) and Recursive Least Squared (RLS) algorithms. The purpose of this study is to introduce a Zero Forcing LU-based equalization scheme for MDM. Previous research in the radio domain on multiple-input multiple output (MIMO) and orthogonal frequency divisionmultiplexing (OFDM) demonstrated that zero forcing schemes have low computational complexity compared to current schemes as they equalize the signal without training signals, thus reducing the overhead payload. All of the previous points motivate the work of this study to adapt this approach in optical communications.
Recent studies show that the capacity limitation of a single modeoptical fiber (SMF) is rapidly approaching the fundamental Shanon limit [1, 2]. Space divisionmultiplexing (SDM) is considered to be an important approach to overcome the capacity limitation of single core basedtransmissionsystems. A multi-core fiber (MCF) or multimode fiber (MMF) has the advantage of boosting the transmissioncapacity without increasing the fiber count . A few-mode fiber (FMF) has core radius slightly larger than a conventional SMF, which not only enables more guided modes but also results in a larger effective area. This larger effective area of MMF or FMF enhances the power transmission capabilities that may result in longer distance communication and also less sensitive to area reduction due to the external perturbation like bending in fiber [4–6]. However, an important issue arises in FMF transmission system that is the crosstalk or mode coupling between the modes of propagation [7, 8]. The modedivisionmultiplexing in a three-mode fiber using multiple-input multiple-output (MIMO) processing have shown significant transmissioncapacity improvements over the long distance communication . MIMO based processing techniques are considered necessary to reduce the cross-talk and to reproduce the input signal. However, MIMO introduces latency in the system that further increases with the increased number of modes and also increases the overall complexity of the networks significantly [10,11]. The cross-coupling between the modes is inversely proportional to the effective index difference between these modes and it is more severe between the neighboring modes. A low effective index difference ∆n e f f between the modes may result in energy transfer
This paper introduces hierarchic al modulated OFDM system for local service insertion in single frequency network. This paper includes the analysis of the system in various channels. The performance in AWGN channel is better compared to fading channel. This system is strongly recommended for multiplexing different types of data and for transmitting both local and global contents in single constellation for a single frequency network. It outperforms the MFN for local service transmission in DVB by spectral efficiency. Higher order system like 64HQAM system is also discussed. The selection of decision rules plays an important role in detection process. The BER of low priority stream is comparatively more than high priority stream. This technique is also comply with LTE systems. The performance of the system can be improved by selection of proper channel estimation technique and block coders for encoding as the future work.
In this paper we are trying to reduce the congestion and fault problem in the Dense Wavelength DivisionMultiplexing (DWDM). DWDM is one of the widely used optical networks used for the Metropolitan Area Network (MAN).With the tremendous growth in traffic in Ethernet and internet, there is the congestion that takes place in the network. This traffic arrives randomly, so it is very necessary to tolerate otherwise the throughput of the network is reduced. So any intellectual approach is needed to apply on the network which can overcome the problem of traffic grooming. Samy Ghoniemy et. al.  presented modeling and design, simulation, characterization and performance evaluation of high data rate and highcapacity long-haul DWMD light wave systems as well, a methodology for finding the optimum modulation format that can effectively enhance the system performance without major changes in the existing infrastructure. The performance of the exemplary system is examined using four different modulation formats: NRZ-OOK, optical duo binary, differential binary phase shift keying (NRZDBPSK), and differential quadrature phase shift keying (RZDQPSK).Simulation results show that the overall system’s performance using a combination RZ- DQPSK with the LEAF based on reduced channel spacing provides a remarkable improvement over implementations based on other fiber and modulation format combinations.