Ku-band satellite digital transmission systems

A nation-wide data communications service is being placed in service by a major telecommunications carrier. This service will rely on a satellite network being provided and installed by Harris Satellite Communications Corporation. The network supports information data rates from 56 kb/s to 2·048 Mb/s. This data communications network has been architectured to include a number of innovative monitor and control functions, up-link power control, modular equipment shelter design and a modular antenna/feed subsystem. This paper will detail this application.     

Expressions for the analysis of digital transmission systems

It is shown that, if the sinusoidal roll-off response commonly used in the analysis of digital transmission systmes is replaced by a trapezoidal response, it is possible to derive algebraic expressions for the signal/noise ratio and error rate in cases of practical importance.     

Flexible regenerator for digital transmission systems

The concept of a flexible regenerator employing multiple frequency timing recovery is presented. Results are given for two possible types of multiple passband timing recovery filters?narrowband-narrowband and narrowband-wideband. In both cases, results show that the regenerator can be retimed using either passband without significant degradation due to the proximity and bandwidth of the redundant passband.     

Vectored transmission for digital subscriber line systems

This paper describes the "vectored" transmission technique for digital subscriber line (DSL) systems, which utilizes user coordination at the central office or optical network unit. This method exploits the colocation of the downstream transmitters and of the upstream receivers, in order to achieve far-end crosstalk (FEXT) cancellation and perform multiuser transmission optimization. The performance improvements are particularly pronounced in environments with strong FEXT such as in very high-speed DSL. Discrete multitone is employed for each user with additional constraints on the cyclic prefix length and with the assumption of block-synchronized transmission and reception for downstream and upstream transmission correspondingly. Within each tone, upstream crosstalk is removed by multiple-input-multiple-output decision feedback at the receiving side, while downstream crosstalk is eliminated by analogous preprocessing at the transmitting side. Additionally, the issue of transmission energy allocation in frequency and among users is addressed. Assuming frequency-division duplexing, the corresponding optimization problem is formulated and solved via convex programming both for a fixed upstream-downstream band plan and for a dynamically programmable band plan. The case of power backoff as a means to reduce the impact of crosstalk on alien systems is also treated. Interestingly, the performance of the proposed methods is shown to be very close to known information theory bounds     

Performance characterization of digital transmission systems withcochannel interference

This paper presents a general methodology for performance characterization of digital transmission systems in the presence of cochannel interference, as a function of the actual number of interferers (ranging from zero to infinity). The bit error probability in time-invariant channels and outage probability in time-varying quasi-stationary channels are discussed. More precisely, a general approach to an outage probability definition based on the concept of the outage domain is introduced. This allows the discussion of the relation to the other definitions which have appeared in the literature and the proposal of some new more accurate methods for the evaluation of outage probability. A suitable comparison between exact evaluation, the well-known Gaussian approximation, and the other new approaches proposed in this paper, is carried out to evaluate performance, bit error probability is suitably obtained for linearly modulated signals by adopting a semianalytical approach, and for nonlinear (e.g., continuous phase) modulation signals, by means of simulation. Finally, as an example, the different approaches to derive performance discussed in the paper have been applied to a linear microcellular scenario     

数字图像远程监控系统的组网方式

本文阐述了数字图像远程监控系统在不同的传输介质中的组网方式,并详尽讨论了工程实现等问题.     

Synchronous digital transmission systems based on CCITT SDHstandard

The synchronous digital hierarchy (SDH) transmission systems developed by NTT are discussed. The advantages of SDH are detailed, stressing its simplified network structure and enhanced operations, administration, and maintenance functions. The layered architecture of the SDH systems is described. NTT's SDH fiber-optic transmission systems and digital radio transmission systems are presented     

Reducing parasitic BJT effects in partially depleted SOI digital logic circuits

This paper presents four new circuit techniques that reduce the parasitic bipolar junction transistor (BJT) effect in digital dynamic logic circuits in partially depleted silicon-on-insulator (PD-SOI) technology. Simulation results have shown the proposed schemes to be effective at various operating voltages. Fully functional test circuits, incorporating some of the proposed techniques, have been designed, fabricated and tested in a 130 nm IBM PD-SOI technology. The measured silicon hardware data validate the simulation predictions and have demonstrated that the new techniques can be easily incorporated to improve the robustness of PD-SOI dynamic logic circuits.     

GaAs integrated circuits for error-rate measurement in high-speed digital transmission systems

A high-speed GaAs MSI PRBS generator and an error detector have been built, tested, and applied to bit-error ratio measurements in a fiber-optic transmission link. The generator produces a 1023 bit sequence at 2 Gbit/s data rate. The detector compares, bit-by-bit, the input data with a locally regenerated sequence. With a 2 GHz clock, the direct-coupled generator/detector combination, without an optical link, exhibits less than one error in 10/SUP 14/ clock cycles. The complete fiber-optic link test system incorporates a 1 km multimode fiber, operates at 1.9 Gbits/s, and exhibits a bit-error ratio below 10/SUP -12/.     

Compensation of intrachannel effects in symmetric dispersion-managed transmission systems

This paper analyzes perturbations caused by nonlinear intrachannel effects and shows how to cancel them by symmetric configuration of transmission and dispersion-compensating fiber. From an analytical study of amplitude and timing jitter conditions are derived to reduce them effectively. Simulations are performed using different schemes of dispersion compensation and improvement and limits of regenerative symmetric links are also discussed. Finally, the paper presents a simple fiber-based configuration to reduce timing jitter in particular. The quality of existing transmission systems is improved.     

PMD-induced impairments in polarization-interleaved WDM systems

Wavelength-division-multiplexing N /spl times/ 10 Gb/s systems with 12.5-GHz channel spacing should require polarization interleaving (PI). However, fiber PMD can alter PI, giving relevant limitations. We show how impairments are affected by the filtering effect of wavelength-sensitive multiplexers/demultiplexers. For the optimum configuration, an analytical equation relates to the signal Q factor to the instantaneous differential group delay of the link. Hence, PMD-induced impairments can be significantly lower than it was previously estimated.     

Nonlinear impairments in extremely dense WDM systems

The capacity of current optical transmission systems could be greatly increased by using extremely dense wavelength-division-multiplexing. We show that this technique could suffer from enhanced interchannel interactions because of the very low frequency spacing. Considering 10-Gb/s channels with 12.5-GHz spacing, significant impairments can arise both in nonzero dispersion fiber and conventional single-mode fiber links. The effect is ascribed to cross-phase modulation, and could be partially mitigated by a proper dispersion map     

Wideband and high-gain negative-feedback AGC amplifier for high-speed lightwave digital transmission systems

A negative-feedback AGC amplifier based on a new circuit configuration concept is proposed and monolithically integrated. The amplifier exhibits characteristics 2.5 times superior to those of the conventional AGC amplifier: 410 MHz bandwidth, 16 dB maximum gain and 18 dB gain dynamic range.     

Experimental security estimation of multimedia digital data transmission systems based on SHDSL technologies

The paper presents a structure of the hardware-software complex for investigating the wiretap channels of wire segments of local communication systems. In addition, it also presents new experimental data on the estimation of hiding and noise immunity of multimedia digital data transmission systems based on SHDSL technologies.     

Impact of transmission impairments on the teletraffic performanceof wavelength-routed optical networks

In a wavelength-routed optical network, a transmitted signal remains in the optical domain over the entire route (lightpath) assigned to it between its source and destination nodes. The optical signal may have to traverse a number of crossconnect switches (XCSs), fiber segments, and optical amplifiers, e.g., erbium-doped fiber amplifiers (EDFAs). Thus, while propagating through the network, the signal may degrade in quality as it encounters crosstalk at the XCSs and also picks up amplified spontaneous emission (ASE) noise at the EDFAs. Since these impairments continue to degrade the signal quality as it progresses toward its destination, the received bit error rate (BER) at the destination node might become unacceptably high. Previous work on the lightpath routing and wavelength assignment (RWA) problem assumed an ideal physical layer and ignored these transmission impairments. The main contribution of our work is to incorporate the role of the physical layer in setting up lightpaths by employing appropriate models of multiwavelength optical devices (XCSs and EDFAs) such that the BER of a candidate lightpath can be computed, in advance, to determine if this lightpath should be used for the call. Features from existing RWA algorithms are integrated with our on-line BER calculation mechanism. Our simulation studies indicate that employing BER-based call-admission algorithms has a significant impact on the performance of realistic networks     

Multichannel 64-QAM transmission in AM/digital and all-digitalhybrid-fiber-coax based video dial-tone systems

A hybrid-fiber-coax (HFC) system is operated with a combination of 63 AM and 21 64-QAM subcarriers as well as with the 21 64-QAM subcarriers alone. The 64-QAM subcarriers are 6-MHz wide, decorrelated, and of the type intended for compressed digital video. The AM signal levels (over both the optical and coaxial links) are set to produce standard carrier-to-noise ratios (CNRs), composite second order distortion (CSO), and composite triple beat (CTB). The optical modulation depth (OMD) is independently varied and transmission tests are carried out over the optical link alone, as well as over the entire system (including two coaxial amplifiers, or actives). The relative degradation of the system due to the optical link versus the actives is investigated. For an OMD of 24% or less and with the raw bit-error ratio (BER) set to 10^-5 (as anticipated for use with forward error correction (FEC) systems), the performance is limited by the actives. There is an approximate 3.5 dB penalty in the necessary CNR for 64-QAM reception, due to the presence of the AM signals. On the other hand, when the system is operated with all-digital subcarriers, the optical modulation depth may be increased from 24% to 37% with no penalty in the required digital CNR     

PMD对平均光孤子系统传输性能影响的研究

文章采用计算机系统仿真的方法,通过数值求解简化的基本传输方程和非线性薛定谔方程,研究了采用相敏光纤参量放大器(PSA)作为在线放大器时,偏振模色散(PMD)对系统传输性能的影响.系统传输方案采用平均孤子系统.仿真结果表明:当PMD系数增大时,孤子脉冲出现分裂和展宽,幅度出现衰减,从而导致系统的传输性能下降.     

Reducing the cost of Bluetooth systems

The Bluetooth^TM industry has set itself an ambitious goal of just $5 for the implementation of a complete receiver/transmitter, including its DSP-based subsystem and associated ROM and RAM. Although this is unlikely to be realised until Bluetooth wireless technology has achieved considerable market penetration and gained economy of scale through very high volume production, some manufacturers appear to be closer to this goal than others. CSR, for example, had shipped over 1 million of its BlueCore single-chip Bluetooth radios by June this year, and 48% of all Bluetooth equipped end-user products on the market now contain this chip. This article takes a look at some of the design techniques that CSR has employed to reduce cost as much as possible, and outlines some of the issues that are likely to affect how quickly the market ramps up