High-sensitivity semiconductor optically preamplified Q-PPM receiver

An optically preamplified receiver for 980-nm laser intersatellite communications is reported. A record sensitivity of 330 photons/bit for a semiconductor optically preamplified receiver is obtained at 50 Mb/s with quaternary pulse-position-modulation (Q-PPM). The experimental results are shown to be in excellent agreement with a novel exact calculation of the optically preamplified receiver Q-PPM bit-error rate (BER). Calculated performance based on these results shows that with an improved optical transmitter the receiver attains 1.5 dB higher sensitivity than previously achieved at this wavelength.     

Error performance of preamplified optical PPM systems with finite extinction ratios

In this paper, we present an analytical study of the error performance in optically preamplified, M-ary pulse position modulation, in free-space optical communication systems with finite extinction ratios. We derive a theoretical expression for the probability of bit error and compute it numerically for different symbol sizes and extinction ratios. We also provide the power penalty due to a finite extinction ratio for both coded and uncoded systems. The study shows that, in certain cases and for a given extinction ratio, lower symbol sizes may yield an error performance similar to that achieved by higher symbol sizes.     

Performance of preamplified direct detection systems underinfluence of receiver noise

We present new results for optically preamplified direct detection systems where the receiver thermal noise is significant. The results obtained with this model is in good agreement with measured results from a system experiment at 10 Gbit/s. It is found that an optical gain of 30 dB is sufficient to keep the penalty due to thermal noise below 0.1 dB for a simple receiver consisting of a photodiode loaded with a broadband amplifier with 50-Ω input impedance     

Q-factor estimation and impact of spontaneous-spontaneous beat noise on the performance of optically preamplified systems with arbitrary optical filtering

Simple explicit expressions to estimate the Q-factor and the sensitivity of optically preamplified receivers with arbitrary optical filtering, which only require the eye-diagram analysis and the knowledge of the optical and electrical filters transfer functions, are proposed. The physical insight and fast computation time are its main advantages. The noise-equivalent bandwidths associated with the nonuniformity of the amplified spontaneous emission (ASE) noise spectrum at the photodetector input are fully characterized and taken into account in the expressions derivation. By using the noise-equivalent bandwidths, a simple way of designing the optical receiver filters to bound the impact of the ASE-ASE beat noise on the receiver performance is provided. Results show that this impact can be neglected for extinction ratio below 25 dB, as long as the optical-filter -3 dB bandwidth does not exceed 8/spl times/ the bit rate. Numerical results reveal that our Q-factor expression provides acceptable estimates. Only for systems where the impact of the ASE-ASE beat noise is significant (high extinction ratio) or in case of low Q (below 4) and high intersymbol interference (ISI), less accurate estimates have been found. In case of high ISI and low Q, the accuracy is improved by taking the probability of occurrence of the nearest rails to the decision threshold in the eye-diagram into account.     

3 Gbit/s optically preamplified direct detection DPSK receiver with 116 photon/bit sensitivity

For the first time experimental bit error rate curves are presented for an optically preamplified direct detection differential phase and shift keying (DPSK) communication link. DPSK offers approximately 6 dB peak power sensitivity improvement over more traditionally optically preamplified on/off keying (OOK). Using an erbium doped fibre preamplifier, a fibre Fabry-Perot filter, an optical DPSK demodulator consisting of a fibre-optic Mach-Zehnder interferometer with a 1 bit differential delay, and a balanced receiver, a sensitivity of 116 photon/bit was obtained. To the authors' knowledge these results represent the first demonstration of optically preamplified DPSK with better sensitivity than previously reported multigigabit per second heterodyne DPSK and approximately 3 dB more sensitivity on a peak power basis than previously reported preamplified OOK systems.<>     

Performance of optically preamplified receivers with Fabry-Perotoptical filters

A technique is presented for evaluating the probability of error for an optically preamplified receiver with a fiber Fabry-Perot optical filter of arbitrary bandwidth between the preamplifier and photodiode. The technique permits simultaneous consideration of the distortion due to modulator chirp and fiber dispersion, the optical filter and the baseband electrical filter. The optical filter is characterized by a Lorentzian passband response, and the quadrature noise processes due to the amplified spontaneous emission are represented by Karhunen-Loeve expansions. For an arbitrary optical filter bandwidth, the evaluation of the probability of error depends explicitly on the details of the Karhunen-Loeve expansion. The solution procedure is general and consequently can, in principle, be applied to other filter passband responses. The influence of the bandwidths of the optical and electrical filters on the performance of a 10 Gb/s system is assessed     

Sensitivity of optically preamplified receivers with optical filtering

The noise spectral densities resulting from detection of preamplified signals using an optical filter are discussed. The authors also carried out a simplified analysis of preamplified receiver sensitivities with ASK and FSK signals. The analysis shows that total optical bandwidths of less than 50 times the data rate result in (10/sup -9/ BER) sensitivities close to the limit set by the amplifier noise figure. The development of low-noise high-gain amplifiers in conjunction with narrowband tunable optical filters enable high-sensitivity FDM systems to be constructed, without the complication of a local oscillator or polarization control/diversity networks which are required for heterodyne coherent detection systems.<>     

收发异源FMCW太赫兹系统误差分析

近年来,随着太赫兹器件研究不断取得进展,对太赫兹收发前端的研究逐渐增多。随着工作频率的增加,以及带宽的增大,由器件非理想性能带来的误差成为影响太赫兹系统性能的重要因素。基于一个采用二级混频设计的收发异源调频连续波太赫兹系统,研究分析了时钟同步误差、调频非线性误差以及IQ不平衡问题所带来的误差。通过对3种误差的建模分析,为后续对误差进行消除和补偿提供了良好的理论基础。     

Capacity of multiple-antenna systems with both receiver and transmitter channel state information

The capacity of multiple-antenna systems operating in Rayleigh flat fading is considered under the assumptions that channel state information (CSI) is available at both transmitter and receiver, and that the transmitter is subjected to an average power constraint. First, the capacity of such systems is derived for the special case of multiple transmit antennas and a single receive antenna. The optimal power-allocation scheme for such a system is shown to be a water-filling algorithm, and the corresponding capacity is seen to be the same as that of a system having multiple receive antennas (with a single transmitter antenna) whose outputs are combined via maximal ratio combining. A suboptimal adaptive transmission technique that transmits only over the antenna having the best channel is also proposed for this special case. It is shown that the capacity of such a system under the proposed suboptimal adaptive transmission scheme is the same as the capacity of a system having multiple receiver antennas (with a single transmitter antenna) combined via selection combining. Next, the capacity of a general system of multiple transmitter and receiver antennas is derived together with an equation that determines the cutoff value for such a system. The optimal power allocation scheme for such a multiple-antenna system is given by a matrix water-filling algorithm. In order to eliminate the need for cumbersome numerical techniques in solving the cutoff equation, approximate expressions for the cutoff transmission value are also provided. It is shown that, compared to the case in which there is only receiver CSI, large capacity gains are available with optimal power and rate adaptation schemes. The increased capacity is shown to come at the price of channel outage, and bounds are derived for this outage probability.     

Sensitivity of optically preamplified DPSK receivers withFabry-Perot filters

The error-rate performance of a DPSK lightwave receiver having an optical amplifier followed by a Fabry-Perot filter and delay-line demodulator is analyzed. Receivers with sampling and with integrate-and-dump threshold comparison are compared to the well-known result for a matched optical filter. The Fabry-Perot filter decreases the sensitivity at 10^-9 error-rate from 20 to 24.5 photons/b with optimum optical filter bandwidth and postdetection integration time     

Capacity of QAM SCM systems utilising optically linearisedMach-Zehnder modulator as transmitter

The limitation imposed by nonlinear distortion and Gaussian noise on the capacity of a subcarrier multiplexed system with quadrature amplitude modulated channels and an optically linearised Mach-Zehnder externally modulated laser transmitter is calculated. A typical system can support 140 6 MHz quadrature phaseshift keying channels (an aggregate bit rate of 1.4 Gbit/s) at 10^-9 bit error rate with a received power of -25 dBm or 300 64-QAM channels (8.9 Gbit/s) with a received power of -15 dBm     

Joint optimization of transmitter and receiver filters in digital PAM systems with a Viterbi detector

Joint optimization of transmitter and receiver filters in a pulse-amplitude modulation (PALM) system with an arbitrary but fixed Viterbi detector is considered. Optimization is performed under an average transmitted power constraint with respect to a new criterion called the effective mean-square error (EMSE). It is shown that the optimization problem is convex. A necessary and sufficient condition for optimality is derived, and a method for optimization is proposed. Numerical results are obtained for a channel with coaxial cable characteristics.     

Optically preamplified receiver performance due to VSB filtering for 40-Gb/s optical signals modulated with various formats

Optically preamplified receiver performance according to the vestigial sideband (VSB) filtering has been numerically investigated for 40-Gb/s optical signals modulated with nonreturn-to-zero, duobinary nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed RZ, and duobinary carrier-suppressed RZ formats. The VSB filtering enables the spectral widths of NRZ, duobinary NRZ, and RZ signals to be reduced without severe power penalties at the receiver. On the other hand, carrier-suppressed RZ and duobinary carrier-suppressed RZ signals have no large advantages over VSB filtering because of the characteristics of their signals. Our results suggest that RZ signals are the most suitable modulation format for VSB filtering, without considering the filter loss, because of the tolerance of the intersymbol interference and a large spectral width. However, duobinary NRZ signals are the most suitable modulation format for VSB filtering, considering the filter loss, because of their narrow spectral width.     

On joint transmitter and receiver optimization formultiple-input-multiple-output (MIMO) transmission systems

The problem of joint transmitter and receiver optimization for MIMO systems under the mean-squared error (MSE) criterion is revisited. We address the general problem of N (number of users) ≠M (number of channel inputs) ≠P (number of channel outputs) when the system is Nyquist bandlimited and obtain analytical solutions for the optimal transmit-receive pair. Next, we demonstrate how the above result is directly applicable to the problem where the system has excess bandwidth, thereby generalizing the results of Salz (1985). In conclusion, several numerical examples are included to demonstrate the performance gains obtainable with jointly optimized MIMO systems vis-a-vis systems based only on receiver optimization     

分层空时码的模型、泽码接收及其性能仿真

本文讨论分层空时编码技术,给出了种基于分层空时编码技术的发送和接收模型,分析了分层空时编码方案,译码与接收技术,分层空时编码的译码与接收技术是分层空时编码应用的关键,对此,我们讨论了具有线性复杂度的迫零判决反馈均衡器结合分层空时译码方法,仿真结果显示了良好的性能和更高的频谱利用率。     

Joint linear transmitter and receiver design for the downlink of multiuser MIMO systems

In this letter, we address the problem of designing jointly the linear transmitter and receiver for the downlink of Multiuser MIMO system, using minimum total mean square error criterion (T-MMSE), subject to a total transmit power constraint. We show that transmitter and receiver under such criterion could be realized through a joint iterative algorithm. The convergence of the proposed algorithm is proved. Simulation results have also been provided to demonstrate the feasibility of this new method.     

高速多带NGI-OOFDM传输系统中的非对称发射机与接收机设计

在高速多带无保护间隔(NGI)光正交频分复用(OOFD M)传输系 统中,采用非对称发射机/接收机结构,对接收信号通过多个通用光相干接收机进行部分探 测,可一次完整 接收整个多带NGI-OOFDM信号。发射端采用单个激光源,通过差分马赫曾德尔外调制器产生 8根等频率 间隔为28GHz的光频梳作为光子载波,经112 Gbit/s PDM-QPSK信号调制,波分复用后形成8路宽带的全 光NGI-OOFDM信号。接收端采用非对称发射机/接收机结构,即采用4个接收带宽为 18GHz的通用光相 干接收机,每个接收机接收2路子载波,可以完整接收整个多带NGI-OOFDM信号。采用本文 结构的高速多 带NGI-OOFDM传输系统,误码率(BER)为10－3时, 光信噪比(OSNR)代价较单载波112Gbit/s PDM-QPSK系 统多约9dB。 经16,0ps/nm光纤色散及偏振扰动,在系统接收端通过电色散补偿 后,约有 0.2dB OSNR代价。最后 对传输13×80km的光纤链路进行了仿真,仿真结果表明,与背靠背 情况相比,在进行电色散补偿后,OSNR代价约1.5dB。     

Optimization of transmitter and receiver filters for digitalcommunication systems using mean field annealing

A technique for finding transmitter and receiver filters for a wide class of digital communication systems which minimize the bit-error rate (BER) is presented. The technique uses Monte Carlo simulation to estimate the BER and mean field annealing (MFA) to optimize the pulse shapes. Modeling of the link can be as complex as simulation will allow, while MFA is resistant to the statistical variation in the BER estimate from the simulation. Initially, the MFA technique was applied to a binary symmetric channel in a nonsimulation environment, and an approximate analysis of the behavior of MFA for this problem was performed. In a more complex example, MFA was coupled with Monte Carlo simulation techniques to find near-optimal transmit and receive filters for a satellite communications link, taking 6 CPU hours on a DECstation 3100. The BER of the link was found to be as much as three orders of magnitude lower when using the MFA-constructed optimal filters than when using filters from other comparison results. For this example, the pulse shapes obtained using MFA exhibit a low BER even as the parameter controlling the nonlinearity of the satellite-link model is varied over a wide range, thus showing the solution is robust     

EVM estimation by analyzing transmitter imperfections mathematically and graphically

This letter analyzes the effects of transmitter imperfections, including carrier leakage, unwanted sideband, nonlinearity, local oscillator (LO) phase noise and frequency error, on error vector magnitude (EVM) performance. Predictor equations of transmitter EVM are given for radio designers to estimate the level of EVM or set appropriate design specifications to obtain desired EVM performance. These predictor equations are validated by measurement results of other reported works.     

Error probability of interleaved MC-CDMA systems with MRC receiver and correlated Nakagami-m fading channels

The performance of an interleaved multicarrier code-division multiple access system with a maximal-ratio combining receiver is studied with the help of the characteristic function of correlated Nakagami-m random variables. Computer simulations are used to demonstrate the accuracy of the analysis. Based on the analytical results, with an exhaustive search of different subcarrier interleaving schemes, the optimal subcarrier interleaver which provides the minimum bit-error rate (BER) can be achieved. Compared to a random interleaver, the optimal subcarrier interleaver offers significant performance improvement.