Rate Penalty Research Articles

Performance Evaluation of Optical Cross-Connects by Improved Saddlepoint Approximation

Based on the wave theory of light and taken the random polarizations of signal and crosstalk into consideration, bit error rate (BER) and power penalties (PP) of optical cross-connects are calculated using the so-called saddlepoint approximation which is improved. The calculated results agree well with the results of experiment and Gauss approximation, shown highly calculated precision of the improved saddlepoint approximation. We also show that BER and PP for systems with random-polarizations are much smaller than that for systems with matched-polarizations when the number N of crosstalk is large, and the conclusion of near-worst-case operation is true only for N<3, so the impact of random signal and crosstalk polarizations on optical cross-connects must be considered in the design for lightwave networks.

Adaptation to high spatial inhomogeneity using wavelet methods

Many of the signals to which wavelet methods are applied, including those encountered in simulation experiments, are essentially smooth but contain a small number of high-frequency episodes such as spikes. In principle it is possible to employ a different amount of smoothing at different spatial locations, but in the context of wavelets this is so awkward to implement that it is not really practicable. Instead, it is attractive to select the primary resolution level (or smoothing param- eter) so as to give good performance for smooth parts of the signal. While this is readily accomplished using a cross-validation argument, it is unclear whether it has a deleterious impact on performance at high-frequency episodes. In this paper we show that it does not. We derive upper and lower bounds to pointwise rates of convergence for functions whose spikiness increases with sample size. (This allows us to model contexts where wavelet methods have to work hard to recover high-frequency events.) We show that, in order to achieve optimal rates of con- vergence, it is necessary for the primary resolution level of the empirical wavelet transform to vary with location, sometimes extensively. Nevertheless, the conver- gence rate penalty incurred through using a non-varying resolution level, chosen to provide good performance for coarse-scale features, equals a factor that is less than the logarithm of sample size.

Modulation-assisted unequal error protection over the fading channel

Unequal error protection (UEP) is essential when different portions of the source data do not contribute evenly to the overall duality of the decoded information. Conventional techniques achieve UEP by independent coding of the bit streams or by adopting conventional unequal error-protection codes. In this paper, we propose a practical alternative to the QPSK-based transmission systems with explicit UEP, such as GSM or IS-54 wireless transmission standards. In this scheme, the task of providing unequal protection is divided between the channel encoder and a nonuniform signal set, which discriminates in favor of the more important bits. The new approach allows for a simpler convolutional encoder and, hence, a less complex decoding procedure. Specifically, a reduction by more than half in the number of encoder states can easily be achieved using our scheme. Countering the degradation of the less important bits, we propose to adopt a high-rate punctured convolutional code to minimize the incurred transmission rate penalty. We also discuss a pilot sequence transmission scheme which realizes a coherent reception. Decentralizing the bit protection culminates in an extra degree of freedom which, in turn, introduces more flexibility into the system design.

Random sequence multisets for synchronous code-division multiple-access channels

The effect of using randomly selected sequence multisets for the uplink of a synchronous code-division multiple-access channel is considered. A tight lower bound on the expected value of the sum capacity over the ensemble of randomly selected sequence multisets is given. For large systems, the sum rate penalty for using randomly selected multisets is shown to be at most 1 nat and to vanish as the number of users becomes large, compared to the sequence length.

Wavelength tracking of a remote WDM router in a passive optical network

We propose, analyze, and demonstrate a simple, robust method which enables a laser to track uncontrolled changes in a remotely located WDM device. As opposed to locking to a wavelength standard, our method locks the wavelength comb of a tunable DBR to a waveguide grating router (200-GHz channel spacing). We have demonstrated tracking at a 1 C/min temperature slew rate without requiring sacrificial channels, a pilot tone, or analog dithering circuitry. We discuss tradeoffs between step size, slew rate, measurement accuracy, and power penalty.

Optical data synchronization using tunable transmitters and nonzero dispersion links

A new digital feedback loop for synchronizing optical data with a clock at an arbitrary point in a fiber-optic link has been experimentally demonstrated and its physical limitations have been analyzed. The feedback loop consists of a tunable transmitter, a nonzero dispersion link, and standard microwave and digital electronics. The feedback loop was able to suppress thermal fluctuations with an accuracy better than 1 ps using either a temperature tuned DFB laser diode or a current tuned DBR laser diode. No bit-error rate penalty was measured during closed loop operation compared to back-to-back transmission. The physical limitations of the loop stem from noise in the receiver and the actuator increment. Thermally induced phase fluctuations in the fiber at frequencies above the loop bandwidth were found negligible. The maximum experimental delay time for stable operation was 0.86 s, indicating the possibility of closed loop operation for very long fiber links. The feasibility of packet synchronization is discussed. Moreover, a new scheme is proposed to circumvent wavelength reset when the system approaches the operating boundaries. >

1480 nm pumped erbium doped fibre amplifier withall optical automatic gain control

A 15 dB, gain controlled, 1480 nm pumped, erbium doped silica fibre amplifier is demonstrated with &lt; 0.2 dB of gain variation for signal input levels up to –5 dBm. Gain control is effected by concomitant lasing at 1520 nm using Bragg grating reflectors. No error rate penalty is observed for a signal modulated at 2.5 Gbit/s.

Theoretical characterisation and practical implementation of optical fibre PPM self synchronisation sequences

AbstractA novel technique for estimating the optical fibre PPM frame phase and eliminating the pattern dependent jitter is proposed while practical implementations and a mathematical characterisation for the technique are reported. Use is made of naturally occurring sequences thus avoiding the sensitivity and bit rate penalties associated with the previous methods. Tracking additional sequences is demonstrated and shown to be beneficial resulting in a frame rate discrete component enhancement of 10.8 dB and timing variance reduction from 12 × 10−3 rad2 to 3.6 × 10−3 rod2. Utilising the systematic jitter rejection method proposed resulted in a measured timing variance reduction from 3.6 × 10−3 rad2 to 4.2 × 10−5 rod2. The limit is imposed by the PLL performance while good correlation is depicted with the theoretical model.

Analytical and practical evaluation of diversity penalties in multi-bit-rate coherent FSK systems

Fully analytical expressions are presented for calculating the bit-error-rate (BER) and sensitivity penalties in frequency-shift-keying (FSK) receivers with noncoherent square-law IF detection. With these results one can directly compute the sensitivity and diversity penalties as a function of the IF filter bandwidth. Postdetection filtering is included in the analysis. The BER of such receivers can be expressed in terms of a sum of generalized Laguerre polynomials, which can easily be evaluated. This yields relations between the IF bandwidth expansion factor and the sensitivity that can be applied directly for practical system analysis. This is illustrated using the results from a coherent multi-bit-rate, multichannel FSK receiver, which was used at bit rates of 140 and 560 Mb/s. The discrepancy between theory and practice is less than 0.15 dB for diversity penalties and 0.4 dB for the bit rate penalty. >

Adiabatic processes in monatomic gases

A kinetic model is used to predict the temperature evolution of a monatomic ideal gas undergoing an adiabatic expansion or compression at a constant finite rate, and it is then generalized to treat real gases. The effects of interatomic forces are considered, using as examples the gas with the square-well potential and the van der Waals gas. The model is integrated into a Carnot cycle operating at a finite rate to compare the efficiency’s rate-dependent behavior with the reversible result. Limitations of the model, rate penalties, and their importance are discussed.

Analysis of bit error rate and power penalty for a birefringent wavelength division multiplexer

Abstract The power penalty and bit error rate degradation encountered when using wavelength division multiplexing devices is analyzed. Analysis is applied to the birefringent wavelength division multiplexer (BWDM) with a sinusoidal transfer function.1 The degradation in bit error rate is attributed to laser mode partition noise and crosstalk noise.

The Jitter Tolerance of Fiber Optic Regenerators

In this paper, we will analyze the effect accumulated jitter has on the decision making process inside the N th fiber optic regenerator of a long chain of fiber optic regenerators. The criteria for a correct bit decision in the presence of receiver noise, static phase offset, and accumulated input jitter will be derived, and calculations of the bit error rate penalties caused by the presence of known distributions of accumulated input jitter will be made. We will then define the jitter tolerance of a fiber optic regenerator as an effective measure of the regenerator's capability to tolerate incoming accumulated jitter. We will show that excessive bit error rate penalties will not occur if the accumulated input jitter does not exceed the regenerator's measured jitter tolerance template. Finally, the jitter tolerance measurement technique will be used to find the optimum sampling time inside a fiber optic regenerator resulting in a regenerator that is optimized for use in long-haul systems.

Optimal control with partial preview of disturbances and rate penalties and its application to vehicle suspension

The theoretical optimal control problem posed by the concept of partial preview of disturbance inputs in the presence of generalized rate penalties and measurements is solved. The properties, computational requirements and rcalizability of the optimal controller and state estimator are discussed and the average behaviour of the optimally controlled system determined. By way of example, the theory is applied to suspension of the British tracked hovercraft high-speed ground transport vehicle. A tenfold reduction in passenger acceleration levels is demonstrated. It is shown that the stiffness parameter of the track or guideway beams can be halved to produce a saving of £18 million on track costs for a typical 800 km system.