Fast polarization controllers and scramblers for high-speed lightwave systems

PMD mitigation through interleaving LDPC codes with polarization scramblers

By using adiabatic perturbation theory, we calculate the timing jitter generated by fluctuations in soliton amplitude, frequency, and position that are induced by the amplifiers noise in high-speed soliton communication systems. The analysis is applied to dispersion-tailored fibers which, in contrast with conventional constant-dispersion fibers, allow ultrashort solitons (width <10 ps) to propagate over long distances with minimum production of dispersive waves. We show that a transition from a regime in which amplifier noise-induced frequency fluctuations dominate the timing jitter (Gordon–Haus jitter) to a regime in which amplitude fluctuations dominate the timing jitter occurs when solitons become shorter than 2–7 ps, depending on the total distance of transmission. The latter source of jitter arises because fluctuations in the soliton amplitude are converted to frequency fluctuations by the Raman effect, which in turn are converted to position fluctuations by the group-velocity dispersion. The contribution of third-order dispersion to the timing jitter is evaluated and discussed. We provide an estimate of the distance at which soliton-control elements (such as synchronous modulators) should be inserted to reduce the timing jitter and extend the transmission distance.

In recent years, the OFDM (Orthogonal Frequency Division Multiplexing) modulation method is widely used in high-speed communication systems such as terrestrial digital broadcasting systems and high-speed wireless communication systems. However, the amplitude of the OFDM signal shows large fluctuation. Then an OFDM system requires high linearity, especially in its high power amplifier (HPA). As a result of HPA back-off operation, its efficiency deteriorates, and then its power consumption increases. In this paper, we propose a spatially superposed OFDM transmission system with multiple amplifiers and a spatial power combining technology. We carried out the simulation of the total power consumption and transmission characteristics. From this investigation, it is expected that the proposed system can reduce the power consumption by about 44%, compared with a conventional system with one HPA.

An equalizer using cascode MESFET's in a distributed structure has been designed for pulse-shaping data in high-speed lightwave systems. Pulse-shaping is accomplished by controlling the gain of each individual cascode stage separately in the distributed circuit. The circuit was fabricated in a microwave monolithic integrated circuit (MMIC) implementation using Nortel's 0.8-/spl mu/m GaAs MESFET technology. Frequency response measurements demonstrate that the bandwidth can be controlled up to 8 GHz. Eye pattern measurements demonstrate the ability to control the pulse shape at 5 Gb/s.

The two-section gain-coupled DFB laser can be designed to exhibit self pulsing. The self-pulsing dynamics have been exploited to demonstrate a variety of application in high-speed optical communication systems, including wavelength and polarization-independent all-optical clock recovery up to 100 Gb/s and conversion from the NRZ or RZ format to CSRZ format.

Wide-band digital indoor and future mobile communication systems are being developed in the quasi-millimeter and millimeter wave frequency bands. In such high-speed systems, the degradation of transmission quality by multipath fading constitutes a limiting barrier. Multipath fading, which results from reflection, refraction and scattering of radio waves by buildings and other structures, gives rise to more than one path reaching the receiver and produces a distorted version of the transmitted signal. In mobile and indoor communication systems it cannot be eliminated, therefore the multipath channel must be well characterized in order to reduce its effect in the design of such systems. The objective of this research is to study the multipath fading and delay spread effects due to buildings in an urban propagation channel. In particular, the effects of the building materials, shapes and number of buildings on multipath fading are being studied.

"The clock generator is a critical component in high-speed wireline communication systems. The clocks in these systems mark time at precise regular intervals. Any deviation of the clock edges from these ideal time points is called jitter and it degrades the overall integrity of the communication system. This thesis looks at both phase locked loops (PLLs) and delay locked loops (DLLs) and their ability to provide these precise clocks. Expressions for the thermal noise-induced jitter in both the PLL and DLL are compared. From this, the DLL is shown to possess the potential for better jitter performance. However, to realise the potential of the DLL, another source of jitter peculiar to the DLL has to be reduced. This jitter in DLLs is caused by Static Phase Offset (SPO). The thesis details the causes of SPO and describes a number of good design practices for reducing it. It then describes an input and feedback clock phase interpolation technique which reduces SPO by half. Finally a novel chopping technique is used to essentially eliminate SPO resulting in a DLL which is ideal for high-speed wireline communication systems. Some of this work was published at the lEE Irish Signals and Systems Conference, which took place at Queens University Belfast, in June 2004."

In this paper, the problem of fast time-varying channel prediction is investigated in high-speed railway communication systems. A channel prediction algorithm is proposed based on a support vector machine (SVM) model. In order to further improve the prediction accuracy, the penalty coefficient and Gaussian kernel width of the SVM model are optimized by a genetic algorithm (GA). Simulation results show that the proposed prediction model based on both the SVM and the GA (SVM-GA) has lower prediction error than traditional auto-regressive (AR) and single SVM prediction models. In addition, when the effect of the noise on prediction performance is considered, the SVM-GA prediction model is superior to the AR and the SVM models in terms of normalized mean squared error.

A new scheme to realize terahertz (THz) radiation generation, as well as high-speed THz modulation, for future high-speed THz communication systems, is proposed and discussed. The proposed experimental scheme includes two elemental parts: dual-wavelength mode-locking oscillating cavity and photomixing elements. The conditions for double-wavelength operation using the proposed experimental setup have been theoretically discussed and obtained. The mode-locked output optical short pulses with two highstability wavelengths are obtained and demonstrated. These can be used to produce THz radiation, as well as high-speed signal modulation, through the photomixing effects in an ultrafast oxygen-ion-implanted and epitaxial InGaAs:O for the future high-speed THz communication systems.

In this paper, an input-decimation technique for the recursive discrete Fourier transform (RDFT)/inverse DFT (RIDFT) algorithm is proposed for the high-speed broadband communication systems. It is worth noting that the input-decimation approach is presented to decrease the number of input sequences for the recursive filter so that the computation cycle of RDFT/RIDFT can be shortened to meet the commuting time requirement (3.6 μs) for the high-speed broadband communication systems. Therefore, the input-decimation RDFT/RIDFT algorithm is able to carry out at least 55.5% reduction of the total computation cycles compared with the considered algorithms. Furthermore, holding the advantages of input-decimation technique, the computational complexities of the real-multiplication and −addition are reduced to 41.3% and 22.2%, respectively. The area and the power consumption can be minimized by employing the cost-efficient constant multiplier with the refined signed-digit expression of twiddle factors. Finally, the physical implementation results show that the core area is 0.37×0.37 mm2 with 0.18 μm CMOS process. The power consumption is 5.16 mW with the supply voltage of 1.8 V and the operating clock of 40 MHz. The proposed design can achieve 258 million of computational efficiency per unit area (CEUA) and really outperform the previous works.

FH(frequency hopping) is widely concerned in the field of communication because of its outstanding ability of noise suppression. The suppression ability of FH communication can be improved by increasing the bandwidth and hopping rate. MSK is chosen as a modulation of high-speed broadband FH communication system to research the suppression ability of FH to different noise signals. The diagram between ratio peak and ISR (interference-signal power) can be given in different bandwidths and different hopping rates. It is verified that the broadband high-speed FH communication system with MSK as the modulation mode has not only a smaller BER (bit error rate) but also a higher noise suppression.

In this paper, optimized transmit schemes for multiple-input multiple-output (MIMO) systems with simplified receivers are proposed for the downlink of high-speed wireless communication systems. In these systems, MIMO signal preprocessing is performed at the transmitter or base station with the receiver at the mobile station having a simplified structure that requires only limited signal processing. An important potential application for our transmit MIMO techniques is in the downlink of high-speed wireless communication systems with Vertical Bell Laboratories Layered Space-Time (V-BLAST) or a similar technique utilized in the uplink, creating a high-speed duplex system with a simplified mobile station transceiver structure. Two approaches are introduced and these depend on whether or not receive diversity is employed at the receiver. Both methods require that channel state information be available at the transmitter. In addition, some important associated issues such as peak-to-average power ratio requirements at the transmitter and robustness to downlink channel errors are also investigated and various solutions are proposed. Simulation results are provided and these show that performance improvement can be achieved when compared with other MIMO transmit schemes.

In this paper we propose novel modulation technique based of quaternion signals aimed at incrising the capacity of Radio-over-fiber (RoF) systems based on OFDM technology. The application of hypercomplex quaternion signals processing has already demonstrated many advantages over the conventional analytical signals. The mathematical and simulation models of the quaternion QPSK modulator and demodulator are presented. Next, the improved scheme for OFDM RoF system is provided taking into account the quaternion signal processing. Simulation and evaluation of the proposed models were carried out by transmitting the QQPSK signal over the RoF system with AWGN wireless channel. The obtained BER vs SNR results for proposed modulation technique were compared to conventional QPSK providing double channel capacity with a little degradation of the noise immunity for QQPSK technique.

Combining a channel memory-shortening filter with maximum likelihood sequence estimation (MLSE) effectively reduces MLSE complexity in low-bandwidth optical fiber communication systems. In this paper, we propose an enhanced decision feedback equalizer (DFE)-MLSE for high-speed fiber optic communication systems. This enhanced algorithm builds on our previous work by introducing a dispersion filter that adjusts channel memory length and by directly applying feedback filter coefficients in MLSE branch metric calculations. These advancements improve channel equalization performance, which we experimentally validate in a pulse-amplitude modulation level-4 (PAM-4) system. At a transmission rate of 112 GBd and a distance of 2 km, the enhanced DFE-MLSE achieves an approximate 0.5 dB improvement over the previous DFE-MLSE at a bit error rate of 3.8·10-3, demonstrating its potential for 200 Gbps transmission in short-reach optical networks.

Linear Motors forms an integral part of propulsion systems used in linear motor propelled high-speed transport systems. Generally, motors such as linear induction and linear synchronous are preferred worldwide for these applications. In spite of showing the immense capabilities, linear switched reluctance motor (LSRM) is still under research for applications in high-speed systems. This paper focuses on a LSRM with enhanced propulsion force for the application in high-speed transportation systems. It has a linear structure with moving translator for direct force transmission and two-teeth in each stator pole to attain better force performance. In the proposed motor, translator teeth count is more as compared to the stator teeth count. A 6/16 LSRM with three- phase split-teeth stator has been proposed. The performance of the proposed 6/16 LSRM has been compared with 6/4 and 6/8 three-phase conventional motors to highlight the improvements in the proposed motor. The paper also modifies the proposed 6/16 LSRM into 12/32 configuration to analyse its force ripple reduction capability. The performance of the 6/16 is compared with the 12/32 LSRM. All the motors are modelled and analysed in 3D with the help of finite-element analysis (FEA). The paper optimizes the 6/16 LSRM using parameter based cumulative deterministic optimization algorithm (PBCDOA) to maximize its propulsion force. The FEA based analysis shows better force performance for the proposed motor.