Reduction of bit error rate performance deterioration caused bystimulated Brillouin scattering in high-power CPFSK coherent opticaltransmission systems

The characteristic phenomena of demodulated waveform distortion and bit error rate (BER) performance deterioration caused by stimulated Brillouin scattering (SBS) in CPFSK coherent optical transmission systems with erbium doped optical fibre booster amplifiers are investigated for the first time, experimentally. The effectiveness of reducing the BER deterioration by adjusting the threshold voltage bias of the decision circuit in a 2.5 Gbit/s heterodyne receiver is clarified     

Performance of smart lightwave receivers with linear equalization

Signal processing techniques can be used to reduce linear and nonlinear distortion in high-speed lightwave systems caused by fiber dispersion and nonideal responses of optoelectronic and electronic components. The improvement in the performance of 2.5 and 10 Gb/s intensity modulation, direct detection systems is assessed for receivers which utilize an analog taped delay line equalizer to compensate for signal distortion. Synchronous and fractionally spaced equalizers are evaluated. Smart receivers that jointly optimize the decision time, decision threshold, and equalizer tap weights under a minimum bit error ration criterion are considered. This yields the optimum system performance and allows consideration of both reduced distortion and enhanced noise arising from the signal processing. The effectiveness of the equalization is determined as a function of several important system parameters. Three-tap and five-tap synchronous equalizers yield virtually the same improvement in receiver sensitivity. Depending on the system, a five-tap fractionally spaced equalizer with half-bit-period tap spacing may or may not be significantly more effective than a three-tap synchronous equalizer     

The effect of laser chirping on lightwave system performance

Directly modulated semiconductor lasers exhibit a dynamic wavelength shift (chirping) arising from gain-induced variations of the laser refractive index. The effect of laser chirping on the performance of multi-Gb/s lightwave systems operating at a wavelength of 1550 nm is investigated. Models suitable for computer-aided analysis are used to describe the dynamic response of the laser and the propagation of chirped optical pulses through a step-index single-mode optical fibre. A truncated pulse train, Gauss quadrature rule method is used to evaluate the average bit error rate of the receiver. This permits pattern effects in the transmitted optical waveform due to the laser dynamics and nonlinear optical power transmission properties of optical fibers to be included in the system model. The influence that modulation and device parameters have on the receiver sensitivity is assessed     

Probability of Error Analyses of a BFSK Frequency-Hopping System with Diversity Under Partial-Band Jamming Interference--Part I: Performance of Square-Law Linear Combining Soft Decision Receiver

In this paper, error probability analyses are performed for a binary frequency-shift-keying (BFSK) system employingLhop/bit frequency-hopping (FH) spread-spectrum waveforms transmitted over a partial-band Gaussian noise jamming channel. The error probabilities for theLhop/bit BFSK/FH systems are obtained as the performance measure of the square-law linear combining soft decision receiver under the assumption of the worst-case partial-band jamming. The receiver in our analysis assumes no knowledge of jamming state (side information). Both exact and approximate (multiple bound-parameter Chernoff bound) solutions are obtained under two separate assumptions: with and without the system's thermal noise in the analyses. Numerical results of the error rates are graphically displayed as a function of signal-to-jamming power ratio withLand signal-to-noise ratio as parameters. All of our results, exact and approximate, indicated that the higher number of hops per bit produced higher error probabilities as a result of increased combining losses when the square-law linear combining soft decision receiver is employed in demodulating the multihop-per-bit waveform.     

Multigigabit-per-second avalanche photodiode lightwave receivers

High-speed avalanche photodiodes and high-sensitivity receivers are vital components for future multigigabit-per-second lightwave transmission systems. We review theoretical and experimental performance of high-speed III-V avalanche photodiodes, and also that of multigigabit-per-second lightwave receivers using FET and bi-polar amplifiers. Particular attention is given to APD gain-bandwidth product, and to its effect on high-speed receiver sensitivity. Comparisons between measured receiver sensitivities and calculated performance are presented for bit rates up to 8 Gbit/s.     

EDFA-based DWDM lightwave transmission systems with end-to-end power and SNR equalization

An approximate analysis is presented which can be used to predict the performance of power and signal-to-noise ratio (SNR) equalization schemes when applied to dense wavelength-division multiplexing (DWDM) lightwave systems employing erbium-doped fiber amplifier (EDFA) cascades. Expressions are provided which relate the maximum number of amplifiers, EDFA gain imbalance, bit rate (R/sub b/), transmitter power, receiver dynamic range and number of channels. The relative advantages of these two equalization strategies are quantified by comparing the maximum number of amplifiers allowed by each scheme. It is shown that, while SNR equalization represents, on balance, the more desirable equalization strategy for future EDFA-based DWDM lightwave transmission systems, under certain conditions power equalization may be a better choice. When employing an APD receiver, for instance, power equalization can support 1.9 times more amplifiers than SNR equalization. However, when employing the more conventional preamplified PIN/FET receiver, SNR equalization can support 1.7 times more amplifiers than power equalization.     

A 10 Gb/s high sensitivity, monolithically integrated p-i-n-HEMToptical receiver

A high-sensitivity, monolithically integrated optical receiver, composed of a p-i-n-PD and high electron mobility transistors (p-i-n-HEMTs) is described. The receiver sensitivity is -17.3 dBm at a bit error rate of 1×10^-9 for a 10-Gb/s non-return-to-zero (NRZ) lightwave signal. This value is the best result yet reported for 10-Gb/s monolithically integrated receivers. The sensitivity is -30.6 dBm if an erbium-doped fiber amplifier (EDFA) is placed ahead of the p-i-n-NEMT receiver. A transmission experiment using a 150-km dispersion-shifted fiber (DSF) indicates no degradation in the bit error rate characteristics or the eye pattern. This verifies the practicality of the p-i-n-HEMT optical receiver for high-speed transmission systems     

Effect of chirping-induced waveform distortion on the performanceof direct detection receivers using traveling-wave semiconductor opticalpreamplifiers

The influence of chirping-induced waveform distortion on the performance of multigigabit-per-second traveling-wave semiconductor optical amplifier (TWSOA)/p-i-n direct detection receivers is evaluated. The results are based on a novel method of evaluating the probability of error in the presence of the signal-spontaneous and spontaneous-spontaneous beat noise components. Laser chirping causes the dependence of the receiver sensitivity on the fiber dispersion coefficient×length product DL to be different for TWSOA/p-i-n and avalanche photodiode (APD) receivers. Compared to the APD receiver, the sensitivity of the TWSOA/p-i-n receiver degrades less quickly. So for cases of practical interest, the TWSOA/p-i-n receiver is more tolerant of chirping-induced waveform distortion     

On improving the computational efficiency of digital lightwave linksimulation

Monte Carlo simulation can be used to estimate the bit error rate (BER) in digital lightwave communication links. However, when the link includes an avalanche photodetector (APD) receiver and is operating at a low BER, Monte Carlo simulation requires excessive execution time unless assumptions are made about the APD statistics. Techniques are presented that reduce the computational resources required to estimate the BER for these systems by two orders of magnitude. The speed-up is achieved by developing anew, more efficient random number generation algorithm for APD shot noise and by applying a tail extrapolation technique to the conditional distributions at the sample-and-decide input in the receiver. Receiver thermal noise is handled analytically. Accurate BER estimates for an NRZ direct-detection system are obtained in approximately 1.5 CPU hours on a VAXstation II using a combination of these techniques     

On the use of a suppression filter for CDMA overlay

This paper is concerned with a direct-sequence code-division multiple-access (DS-CDMA) system operating over a Rayleigh fading channel and sharing a common spectrum with a narrow-band waveform. A suppression filter at the receiver is employed to reduce the narrow-band interference. We evaluate the average up-link bit error rate (BER) performance and investigate how the performance is influenced by various parameters, such as the number of taps of the suppression filter, the number of multiple-access users, the ratio of narrow-band interference bandwidth to the spread-spectrum bandwidth, the interference power to signal power ratio, the ratio of the offset of the interference carrier frequency from the spread-spectrum carrier frequency to the half spread-spectrum signal bandwidth, and so on     

广义UWB-ATR接收机

提出了一种广义UWB-ATR接收机,该接收机的本地模板信号为非限定的M个接收的参考脉冲波形的平均.通过对该接收机输出噪声进行高斯近似,获得了该接收机的误码性能,表明该接收机性能表达式可对PAM调制情况下的TR信号的相关接收机、STR和ATR接收机的误码性能进行了统一的表达.     

Theory and design of coherent digital systems which track Doppler frequency

A unified theory from which the design of a large class of coherent digital communication systems can be optimally carried out is presented. In the design of digital communication systems, the error rate is the criterion which is invariably emphasized. In many digital systems, however, there is relative motion between transmitter and receiver which must be estimated by making use of Doppler frequency information. A new analysis of a general class of coherent digital systems is herein developed, in which the tradeoffs that exist between Doppler measurement capability and bit demodulation error rate are quantitatively presented. The theoretically unrecoverable power loss which exists when employing frequency division multiplexing subcarriers as compared to time division multiplexing is described. The results point out that there is significant parametric dependence of the optimal choice of system parameters on the carrier loop signal-to-noise ratio and the data rate.     

Gain equalization of EDFA cascades

Investigates the impact of wavelength-dependent erbium-doped fiber amplifier (EDFA) gain spectrum on multichannel direct-detection lightwave transmission systems employing multiple amplifiers. An analysis is presented which quantifies the constraints imposed by received power imbalance, signal-to-noise ratio (SNR), and receiver sensitivity on an EDFA cascade. Expressions are derived which relate the system constraints to the EDFA gain imbalance, bit rate, number of channels, and receiver dynamic range. Results demonstrate that when four-wave mixing (FWM) is compensated in an 11-channel system, received power imbalance can impose a significant constraint on transmission distance when the EDFA gain imbalance is greater than 1 dB or when bit rate is less than 1.8 Gb/s. In addition, performance of the preemphasis gain equalization technique is studied for multichannel systems employing APD or p-i-n/FET direct-detection optical receivers. Simple expressions are derived which can be used to quantify the increase in transmission distance obtained when employing preemphasis equalization. Results indicate that equalization of the received power spectrum can provide a two- to four-fold increase in the transmission distance when using APD receivers, compared to a one- to two-fold improvement with p-i-n/FET receivers. Analytic results are compared with results obtained by proven simulation methods and found to be in good agreement     

On the Decision-Feedback Equalizer in Optically Amplified Direct-Detection Systems

This paper investigates the combined feed-forward and decision-feedback equalizer (DFE) in a lightwave system with optical amplifiers and a direct-detection receiver. Based on a nonlinear channel model, the paper provides a modification of the classical minimum mean square error theory of the DFE. Furthermore, an analytical method that is capable of accurate bit error rate (BER) evaluation is used to optimize the DFE for minimum BER. The paper evaluates the DFE performance for both optical ON-OFF keying and duobinary modulation formats in the presence of chromatic dispersion as well as the DFE performance for the mitigation of higher order polarization mode dispersion in first-order compensated systems. The paper shows that the DFE can compensate for the BER degradation due to narrow-band receiver-side optical filtering and can significantly improve the spectral efficiency of dense wavelength-division multiplexed systems.     

An analytical framework for CDMA systems with a nonlinear amplifier and AWGN

The design of code-division multiple-access (CDMA) transmission systems for satellite communications requires an appropriate consideration of the distortion effects due to on-board nonlinear amplification. The aim of this paper is to provide an analytical framework for the evaluation of the in-band nonlinear distortion effects on the performance of CDMA systems. Both synchronous systems with orthogonal codes and asynchronous systems are considered. It is first shown that, when the users accessing the channel have the same power and their number is sufficiently large, the nonlinear distortion in the decision variables at the receiver can be simply described by a complex scale factor, which depends on the high-power-amplifier (HPA) characteristics only, and an additive noise, which is uncorrelated to the useful signal. Moreover, an analytical formulation of the bit error probability and the total degradation as a function of the output back-off and number of users is given. In the results, which are obtained for three classes of HPA models (i.e., the traveling wave tube amplifier, the solid-state power amplifier, and the amplifier with ideal predistortion), the performance and the capacity of power-limited systems is also discussed.     

Joint detection with coherent receiver antenna diversity in CDMAmobile radio systems

In code division multiple access (CDMA) mobile radio systems, both intersymbol interference and multiple access interference arise which can be combated by using either elaborate optimum or favorable suboptimum joint detection (JD) techniques. Furthermore, the time variation of the radio channels leads to degradations of the receiver performance. These degradations can be reduced by applying diversity techniques. Using coherent receiver antenna diversity (CRAD) is especially attractive because only the signal processing at the receiver must be modified. In the present paper, the application of CRAD to the more critical uplink of CDMA mobile radio systems with suboptimum JD techniques is investigated for maximal-ratio combining. The authors study six different suboptimum JD techniques based on decorrelating matched filtering, Gauss-Markov estimation, and minimum mean square error estimation with and without decision feedback. These six suboptimum JD techniques which are well-known for single antenna receivers are extended for the application to CRAD. A main concern of the paper is the determining of the SNR performance of the presented JD techniques for CRAD and the achievable average uncoded bit error probabilities for the transmission over rural area, typical urban and bad urban mobile radio channels are determined     

Impact of an Additional All-Optical Decision Element in Band-Limited Receivers for RZ Systems

We investigate both theoretically and experimentally how the use of an all-optical decision element (ODE) in front of a conventional receiver improves, in return-to-zero (RZ) systems, the receiver performance when the signal bandwidth exceeds the bandwidth of the available optoelectronic components. A theoretical analysis of the ODE behavior shows the field of applicability of the investigated solution. The experimental evaluation of the performance improvement in an RZ system is realized using an ODE based on two cascaded nonlinear optical loop mirrors. Benefits in terms of bit error rate for different signal bandwidths and for a different received optical signal-to-noise ratio are presented. Substantial agreement of the experimental results with the theoretical analysis is obtained. The impact of the ODE in the presence of relevant thermal noise at the receiver is also considered. The ODE can extend the use of common band-limited receivers to wide-bandwidth signals and can be an alternative solution to the development of wideband receivers.     

Optimum pulse amplitude modulation--I: Transmitter-receiver design and bounds from information theory

Intersymbol interference and additive noise are two common sources of distortion in data transmission systems. For pulse amplitude modulation (PAM) communication links, the combination of transmitter waveform and linear receiver that minimizes the mean-squared error arising from these sources is determined. An extension to include the effects of timing jitter is performed in a companion paper. Performance characteristics of the optimal PAM systems, showing the mean-squared error versus the signal-to-noise ratio, are determined explicitly for several examples. These characteristics are compared both with those of certain suboptimal systems and with the optimal performance theoretically attainable (OPTA), derived by combining Shannon's concepts of the capacity of a channel and the rate distortion function of a source. The optimal PAM systems are seen to perform very close to the OPTA for low signal-to-noise ratios. For high signal-to-noise ratios, however, the mean-squared error of optimal PAM systems decreases as the reciprocal of the signal-to-noise ratio, but the OPTA decreases more rapidly, except for band-limited channels. The performance of PAM systems can be improved at high signal-to-noise ratios by coding techniques. One such technique, called Shannon-Cantor coding, is discussed briefly.     

Performance of coherent ASK lightwave systems with finiteintermediate frequency

The impact of finite intermediate frequency (IF) on the performance of heterodyne ASK lightwave systems is examined and quantified in the presence of laser phase noise and shot noise. For negligible linewidths, it is shown that certain finite choices of IF (R _b,3R_b/2,2R_b,5R_b/2, etc.) lead to the same ideal bit-error-rate (BER) performance as infinite choices of IF. Results indicate that for negligible linewidths the worst case sensitivity penalty is 0.9 dB for proper heterodyne detection and occurs when f_IF=1.25 R_b. For nonnegligible linewidths (e.g., when ΔνT⩾0.04) the sensitivity penalty is always less than 0.9 dB for finite choices of IF. The analysis presented does lead to a closed-form signal-to-noise ratio (SNR) expression at the decision gate of the receiver which can readily be used for BER and sensitivity penalty computations. The SNR expression provided includes all the key system parameters of interest such as system bit rate (R_b), the peak IF SNR (ξ), laser linewidth (Δν), and the IF filter expansion factor (α). The findings of this work suggest that the number of channels in a multichannel heterodyne ASK lightwave system can be increased substantially by properly choosing a small value for the IF at the expense of a small penalty <1 dB. On the negative side, IF frequency stabilization becomes a more critical requirement in multichannel systems employing small values of IF     

Fast simulation of diversity Nakagami fading channels using finite-state Markov models

We designed a multi-channel Nakagami fading simulator by modeling the received combined signal-to-noise ratio as a finite-state Markov chain, following a previously proposed approach. Our model generates directly the error process at the output of a diversity receiver and can emulate selection, maximal-ratio, and equal-gain combining. As the order of diversity increases, the savings in computational complexity improve linearly with respect to a traditional waveform simulator. The level crossing rates of the simulated envelope are shown to be very close to their theoretical values. The simulator's performance is also evaluated in terms of the accuracy of the obtained bit error rates, for both uncoded and coded systems. The simulator speeds up the performance evaluation of high-rate communication links where a high number of samples is needed.