基于LDPC码和PPM调制的深空光通信系统性能分析

比较了LDPC码和RS码在PPM调制下的深空光通信系统中的性能,给出了在不同阶数PPM调制下,不同码长LDPC码的性能仿真结果,以及与RS码的比较结果.结果表明,随着PPM调制阶数增加,LDPC码性能会下降.分析了调制阶数影响LDPC码性能的原因.     

定时误差对脉冲间隔调制系统的影响分析

在分析脉冲间隔调制(DPIM)的差错性能时,一般都假设时隙同步脉冲定时是理想的,忽略了定时误差的影响,然而这并不符合实际情况.在给出信道模型和解调模型的基础上,详细分析了定时误差对DPIM差错性能的影响,并推导了附加热噪声APD接收机下的误符号率.仿真结果表明,要保证正确的解调,定时误差必须只占时隙时间的一小部分,否则系统的差错性能将严重劣化.     

Spectral predictions for pulse interval and width modulation

An expression for the frequency spectrum of pulse interval and width modulation (PIWM) is presented. Experimental results obtained have shown close agreement with spectral predictions from the formula. Performance figures are also included from a practical PIWM optical-fibre transmission system intended for use with TV and video signals.<>     

Multiple-subcarrier modulation in optical wireless communications

This article overviews multiple-subcarrier modulation techniques in optical wireless communications. The basic principles and characteristics of MSM techniques in optical wireless communications are presented. MSM optical wireless systems are explained where some block codes that convert information bits to be transmitted to the symbol amplitudes of subcarriers are used to increase the minimum value of the MS electrical waveform. MSM optical communications systems using subcarrier signal point sequences (SSPS) that can improve the power efficiency of MSM systems are also explained. The performance of MSM optical communications systems is presented in the intensity modulation with direct detection (IM/DD) channel without dispersion and in atmospheric optical communications where the effects of scintillation exist.     

Noise performance of pulse interval modulation systems

Pulse interval modulation (PIM) is an asynchronous form of pulse position modulation. In this paper, the noise performance of the PIM system has been theoretically and experimentally investigated. A simple formula for the detected signal to noise ratio has been obtained which compared well with the measured data. The effect of noise shaping networks on the noise figure of the PIM detector has been predicted.     

Trellis coded polarization shift keying modulation for digital optical communications

The application of the well-known technique of trellis coded modulation to coherent optical communications using polarization shift keying (POLSK) is described and analyzed. The resulting receiver is formed by a front-end which performs the heterodyne detection and the Stokes parameter extraction, cascaded with an electronic Viterbi processor operating the maximum likelihood estimate of the transmitted sequence. Results in terms of the error event probability using optimum as well as a simpler suboptimum branch metric show power gains of the order of 3-4 dB, at the expense of a reasonable increase in complexity, only concerning the processing in the electronic domain. These coding gains are not lost even in the presence of high levels of phase noise, to which POLSK in general is highly insensitive.<>     

光纤传输光电检测脉冲间隔与宽度双重调制

文章给出了脉冲时间调制的分类方法及实现方案。推导了非同步型脉冲间隔与宽度双重调制（ Ｐ Ｉ Ｗ Ｍ） 的频谱及其特点。说明了 Ｐ Ｉ Ｗ Ｍ 是模拟信号测量的一种经济有效的调制方法,在光纤传输光电检测中有广泛应用前景     

Modulators for optical communications

This paper reviews the field of high-speed small-aperture modulators for applications in optical communications, with emphasis on electrooptic modulation. The capabilities and limitations of electrooptic modulators are discussed based on a review of the physical origin of the electrooptic effect. Thermal and photoconduction phenomena, which may severely limit the operation of practical devices, are emphasized. The modulation power and bandwidth limitations using various schemes of electrooptic interaction are derived and compared. It is shown that lumped modulators are capable of efficient modulation for bandwidths up to about 1 GHz for visible wavelengths and are also attractive for their simplicity. For broader bandwidth capability the traveling wave or zigzag types of interaction become more efficient but with added complexity. Finally, acoustooptic and magnatooptic modulators are briefly discussed and compared with electrooptic modulators.     

Photon detection for an optical pulse code modulation system (Corresp.)

A mathematical model is formulated for an optical PCM system. Using the signal-to-noise ratio at the decision circuit as the performance criterion, the optimization of a nonlinear detector is carried out. Closed-form expressions for the jointly optimum electrical filtering and biasing, and for the maximum signal-to-noise ratio are obtained.     

无线光通信中的脉冲宽度间隔调制方案

提出一种新的脉冲调制方案——脉冲宽度间隔调制(PWIM),给出了PWIM的符号结构,分析了其在平均发射功率、带宽需求和传输容量等方面的性能,并在加性高斯白噪声信道模型的基础上推导了PWIM的误包率。理论分析与仿真验证表明,PWIM不但在功率利用率和差错性能方面优于OOK和PWM,而且带宽效率和传输容量比PPM和DPIM的更高。     

无线光通信中PPM的RS级联编码调制研究

在脉冲位置调制(PPM)直接检测光通信系统中插入RS级联编码构成一种新的PPM光通信系统(RS-PPM),该方式对PPM直接检测光通信系统进行了改进,并用Matlab对编码系统和未编码系统的误比特率进行了仿真比较,仿真结果表明,基于RS级联编码的PPM系统具有较好纠错和抗干扰能力.     

Coherent optical sources for communications

The development of coherent optical sources, producing usable amounts of power, has provided a stimulus for communications research. Coherent sources in the form of lasers and parametric oscillators are available at wavelengths which span the entire optical spectrum. This paper reviews the state of the art of coherent optical sources with major emphasis on the most highly developed sources.     

Comparison of sinusoidal and pulse modulation techniques for generating optical frequency reference combs

The optical frequency combs generated by pulse and sinusoidal modulation of an LiNbO/sub 3/ Mach-Zehnder device are compared and contrasted. It is shown that the former operates with lower drive, although being restricted to narrower tooth spacings than offered by the sinusoidal technique.<>     

Trellis-coded pulse-position modulation for indoor wirelessinfrared communications

We analyze the performance of trellis-coded pulse-position modulation (PPM) on indoor, wireless infrared channels. We show that maximum-likelihood sequence detection (MLSD) of trellis-coded PPM is very effective in mitigating the multipath dispersion on such channels. We present code search results for high constraint-length, rate-2/3, 8-PPM and rate-3/4, 16-PPM codes. We provide bit-error rate curves and intersymbol interference power-penalties for MLSD of PPM with these codes, evaluated on ceiling-bounce channel models with delay spread per bit duration ratios of 0.01-0.3. Finally, we present Monte Carlo simulation results to verify our analysis     

Trellis-coded multiple-pulse-position modulation for wireless infrared communications

We present new trellis codes based on multiple-pulse-position modulation (MPPM) for wireless infrared communication. We assume that the receiver uses maximum-likelihood sequence detection to mitigate the effects of channel dispersion, which we model using a first-order lowpass filter. Compared to trellis codes based on PPM, the new codes are less sensitive to multipath dispersion and offer better power efficiency when the desired bit rate is large, compared with the channel bandwidth. For example, when the bit rate equals the bandwidth, trellis-coded (17 2)-MPPM requires 1.4 dB less optical power than trellis-coded 16-PPM having the same constraint length.     

Pulse width modulation for analog fiber-optic communications

The pulse width modulation (PWM) technique has been revisited and analyzed to evaluate its merits for application to analog signal transmission in fiber-optic links. Fourier analysis of the PWM signal reveals that it can be used as a vehicle to launch an analog signal onto optical fiber when a symmetrical natural sampling process is used. The SNR of the modulated signal depends on the timing jitter of the carrier pulses and a wide-band (45 MHz) SNR of 45 dB has been obtained with a commercially available multimode laser transmitter. A linear dynamic range of over 50 dB has been experimentally demonstrated. The full fiber bandwidth can be utilized by using a very high pulse carrier frequency, while a more popular pulse frequency modulation technique provides about a 10-MHz analog signal bandwidth when 1 km of multimode fiber is used in conjunction with a short wavelength (0.87 μm) LED transmitter. Analog transmission capability was experimentally demonstrated by constructing a simple video link using common laboratory equipment. The performance of the video link supports the PWM modulation theory developed here and elsewhere. The experimental results indicated that PWM is potentially very attractive for low-cost broad-band local area network (LAN) application, including future highly interactive offices, hospitals, and automated factory floors.     

A novel modulation for mobile satellite communications

It is a challenging problem to design a high performance modulation for mobile satellite communications due to the limited power and bandwidth resource. The paper improves Feher patented Quadrature Phase Shift Keying (FQPSK) by redefining the waveform. The novel FQPSK, with constant envelope, can be used to improve the power efficiency and frequency efficiency of mobile satellite communication. The study shows that the improved FQPSK outperforms conventional FQPSK over AWGN and is immune to the non-linearity of high power amplifier. At last, the impact of flat fading and multi-path fading of channel on the BER performance of improved modulation is analyzed.     

Deep-space optical communications

A major problem in deep-space communication systems is that of obtaining high data rates (of the order of 107 bits per second). This article proposes some design concepts that indicate the probable feasibility of achieving wide-band communications by means of the laser. The example selected here is a hypothetical mission to Venus, chosen because of its great brightness and, hence, high background-noise level. Since no earth satellite relay is assumed, the communication channel includes the atmosphere. The down-link is the one considered because of its high-information-rate requirement.