Relationship of Q penalty to eye-closure penalty for NRZ and RZ signals with signal-dependent noise

The relationship between Q penalty (QP) and eye-closure penalty (ECP) is examined for distorted signals in the presence of signal-dependent noise. A simple model is developed to describe the behavior of return-to-zero (RZ) modulation formats and is compared with a model for nonreturn-to-zero (NRZ) formats. The accuracy of the analysis is investigated with extensive simulations, and the numerical results from analysis and simulation are found to be in generally good agreement. Experimental measurements of distortion caused by uncompensated dispersion also show agreement with the simulation results and model predictions. The simplified models allow a means to budget QPs from distortion effects in a straightforward manner during network design for different modulation formats. The analysis predicts a smaller Q penalty as a function of ECP for RZ modulation formats in comparison with NRZ and smaller relative penalties for RZ formats with narrower pulsewidths.     

Power penalty for optical signals due to dispersion slope in WDMfilter cascades

We calculate the receiver power penalty due to the accumulated dispersion slope of optical filter cascades in wavelength-division-multiplexed optical networks. For flat-top fiber Bragg grating and thin-film filters, dispersive rather than amplitude filter effects dominate the cascade power penalty, which increases with dispersion slope and signal frequency detuning from the cascade zero-dispersion point. The dispersion slope of these filters varies as the inverse cube of their bandwidth, using increased penalties for narrow filters in systems with small channel spacing, For a 60-GHz-wide Bragg grating filter with a 1.3-ns/nm² dispersion slope, a cascade of 26 filters can be tolerated at 10 Gbit/s with ±5 GHz allowed detuning. Optically preamplified receivers have significantly larger dispersion penalties than thermal-noise-limited receivers     

Envelope detection of orthogonal signals with phase noise

The authors analyze the performance of receivers that use envelope detection at an IF to detect optical signals with orthogonal modulation formats. Exact closed-form expressions for the error probability conditioned on the normalized envelope were obtained. The only information necessary for obtaining the unconditional error probability is a small set of tilted moments of the envelope. The authors then provide an approximation to this envelope which is not only accurate to the first order in phase noise strength, but also has the same range as the actual random envelope. This approximation was used to obtain the bit error performance of the three receiver models considered. A tight lower bound in closed form is given. The analysis is extended to the case of N-ary frequency-shift-keying (FSK) to provide very tight upper and lower bounds to the bit error probability     

Feedback communication using orthogonal signals

We consider a feedback communication system in which the forward and feedback channels are disturbed by additive noise and constrained in average power. Two block coding schemes are proposed in which the signals are orthogonal waveforms. A finite number of forward and feedback transmissions per message is made. Information received over the feedback channel is used to reduce the expected value of forward signal energy on all iterations after the first. Similarly, the expected value of feedback signal energy is reduced on all iterations after the first. These schemes, which are modifications of a feedback coding scheme due to Kramer, obtain improved error performance over one-way coding at all rates up to the forward channel capacity, provided only that the feedback channel capacity is greater than the forward channel capacity. They require less feedback power than existing feedback coding schemes to achieve a given error performance.     

Gaussian orthogonal matrix transform approach for PAPR reduction of optical OFDM signals

Optical orthogonal frequency division multiplexing (O-OFDM) has been widely adopted as a high-speed data transmission technique in visible light communication systems. This technique usually suffers from high peak-to-average-power ratio (PAPR). In this paper, a new PAPR reduction technique is proposed for O-OFDM signals. At the transmitter, a matrix transformation with the Gaussian elements is applied to the time-domain O-OFDM signal and at the receiver, the inverse matrix is used to recover the original signal. We show that the Gaussian orthogonal matrices can reconstruct the original signals without degrading the bit error rate (BER) performance. Gram-Schmidt technique is used to orthogonalize the Gaussian matrices. Computer simulations are conducted for 16-QAM baseband modulated symbols and about 3 dB PAPR reduction gain is achieved by the proposed approach compared with conventional O-OFDM.     

Chirp-induced penalty in optical fibre systems

Using the output light intensity and wavelength chirp waveforms obtained with a SPICE2 equivalent circuit laser model, together with a computer model for chirp-dispersion interaction, the chirp-induced power penalty is estimated. In contrast with previously published theoretical estimates, the results obtained show good agreement with reported experiments.     

Arrangement of orthogonal polarized signals for suppressing fiber four-wave mixing in optical multichannel transmission systems

The arrangement of signal polarization states for suppressing fiber four-wave mixing (FWM) in optical multichannel transmission is described. Experiments show that light power generated through fiber FWM becomes 0 or 1/4 of the maximum value when signals are orthogonal. Based on the experimental results, power reduction of FWM light is evaluated for various arrangements of signal polarizations, and the optimum arrangements is shown to efficiently suppress fiber FWM in a multichannel system.<>     

Dispersion penalty reduction using an optical modulator with adjustable chirp

Using a unique Ti:LiNbO/sub 3/ modulator, the value of the modulation chirp parameter that minimizes the transmission power penalty caused by fiber chromatic dispersion was experimentally identified. System experiments at 5 Gb/s using nonreturn-to-zero (NRZ) amplitude-shift-keyed (ASK) transmission with direct detection reception are discussed, and the optimum values of the modulation chirp parameter versus distance for transmission at 1.5 mu m wavelength over fibre having zero dispersion at 1.3 mu m are identified. 5 Gb/s NRZ transmission was achieved through distances of 128, 192, and 256 km of conventional fiber while incurring dispersion penalties of -0.5, 0.1, and 1.1 dB respectively, by operating at the quantum chirp value.<>     

信道预测联合收发分集的正交信号误码性能

为解决采用最小均方误差(MMSE)信道预测的发射天线选择(TASP)/接收天线最大比合并(MRC)的无线通信系统设计问题,利用抛物柱面函数以及高斯Q函数的近似表达式和矩生成函数(MGF)法,分别推导了瑞利块衰落信道上采用TASP/MRC天线分集的相干检测M进制正交和双正交信号的平均误符号率(ASER)精确表达式以及正交信号ASER的近似表达式.数值计算和仿真结果验证了采用TASP/MRC和相干检测的正交/双正交ASER精确表达式的正确性以及正交信号ASER近似表达式的准确性.上述M进制正交/双正交信号ASER精确或近似表达式,可用于设计采用相干检测M进制正交和双正交信号的TASP/MRC天线分集系统,并能够快速地确定收发天线数和信道预测器级数等参数,避免耗时的计算机仿真.     

Beat interference penalty in optical duplex transmission

The near- and far-end source spectra in optical full duplex systems can heterodyne, producing a high level of beat interference noise in the receiver bandwidth. This is called coherent common-channel crosstalk, the penalty from which is found in addition to that from incoherent near-end crosstalk (NEXT) quantified in an earlier publication. We find most directly modulated high-chirp laser systems, such as those using single-mode distributed feedback lasers or multimode Fabry-Perot (FP) lasers, are relatively immune to coherent NEXT for speeds up to 100 Mb/s. In the transform limit, however, which occurs at high bit rates or low chirp, the maximum allowable NEXT must be decreased by as much as 20 dB, compared to the incoherent case. One solution is to use uncooled single-mode lasers separated by a small wavelength spacing (20 nm, for example) as popularized for the coarse wavelength division multiplexing (WDM) grid     

Randomized penalty in detection of the number of signals

For the information theoretic criterion methods of detecting the number of signals, a penalty function which is of fixed form has been utilized. A new penalty, depending on samples, is introduced. It is shown that it gives a strongly consistent estimate of the number of signals. Simulation results show that for small samples, it performs well as compared with others, such as the Hannan criterion     

Estimation of the number of orthogonal signals with unknown parameters

Algorithms for estimation of the number of signals with unknown amplitudes and several non-energy parameters are synthesized on the basis of the modified maximum likelihood method. Asymptotic values of the probabilities of the error in estimation of the signal number are determined. The effect of a reduced volume of the a priori domain of possible values and the dimensionality of the vector of unknown non-energy parameters on the quality of operation of the algorithms for estimation of the number of signals is investigated.     

OCDMA系统SAC编解码实现方案及性能研究

讨论了基于FBG的谱幅编解码spectral-amplitude-coding(SAC)系统的原理；提出了(N，w,λ)=(q^2 q l,q l，1)光正交码的SAC编解码器实现方案：给出了该系统在码分功率不均匀时，以多址干扰为主的系统信噪比和误码率。分析了谱幅编解码OCDMA系统的应用前景。     

Application of discontinuous communications in channels with random parameters to transmit narrowband signals and signals with orthogonal frequency-division multiplexing

An algorithm for increasing the interference immunity is analyzed in the case where the discontinuous communications method and its interconnecting with diversity reception in a Rayleigh channel are used for narrowband signals and signals with orthogonal frequency-division multiplexing. It is demonstrated that the probability of errors can be diminished without a significant decrease in spectral efficiency.     

Wideband optical image rejection receiver and its crosstalk penalty

Demonstrates an optical-frequency image rejection receiver with more than 18 dB suppression over the 1.5-3.0 GHz IF region. The measured crosstalk penalties were less than 1.4 dB in a 2-channel 560 Mbit/s DPSK heterodyne optical communication system.<>     

Power penalty due to the amplitude and phase response ripple of a dispersion compensating fiber Bragg grating for chirped optical signals

A concise method is presented for rigorously calculating the power penalty due to the combined implications of the amplitude and phase response ripples of a dispersion compensating fiber Bragg grating and the chirp of the transmitted optical signal. By using trigonometric series to represent the ripples, the calculated penalty can be positive or negative, as obtained in numerical simulations and measurements, depending on the signal chirp and ripple within the modulated signal bandwidth. An approximate upper bound on the power penalty is also presented as an extension of earlier results that always yield positive penalties. Calculated and measured results are compared for two 10-Gb/s return-to-zero (RZ) signals with distinct chirp properties.     

Demodulation of low-level broad-band optical signals with semiconductors

A simple approach to the problem of detection of optical signals with semiconductors leads to a general understanding of the performance. It shows that the low impedance level of broad-band circuits prevents high efficiency conversion of the incident power. Because of this, the envelope detector has a signal-to-noise ratio (SNR) which is determined by the noise of the following amplifier. As in radio communication, addition of a coherent optical signal from a local oscillator can increase SNR; however, for optical signals the limiting value of the noise figure is determined by the shot noise of the conversion current. Comparison with the limiting SNR expected from a photo-emission detector reveals no important distinction between them for frequency conversion. The unit which uses material with the higher quantum conversion efficiency will have the possibility of better SNR. For envelope detection, the photo emitter can be far superior to the photoconductive detector. The two cases of a photovoltaic and a photoelectromagnetic solid-state device are analyzed and general expressions as well as numerical examples given for the design parameters. The devices are comparable both in dimensions and performance.     

Noncoherent multistage multiuser detection of M-ary orthogonal signals

In recent years, a great deal of research has been performed on methods of alleviating the performance degradations suffered by code division multiple access (CDMA) systems due to multiple access interference. In this paper, we consider a multistage detector for noncoherent CDMA using M-ary orthogonal signals. Using a decorrelating detector as its first stage, the detector iteratively estimates the multiple access interference affecting the desired signal, subtracts the estimated interference, and forms symbol estimates for each of K users. Through numerical examples, the bit error performance of the proposed detector is demonstrated to be superior to that of previous detectors for the same signalling scheme. This revised version was published online in June 2006 with corrections to the Cover Date.     

Coherent optical orthogonal frequency division multiplexing

Coherent optical orthogonal frequency division multiplexing is proposed to combat dispersion in optical media. It is shown that optical-signal-to-noise ratio penalty at 10 Gbit/s is maintained below 2 dB for 3000 km transmission of standard-singlemode fibre without dispersion compensation.