Advanced Modulation Techniques Research Articles

Architectural tradeoffs for reconfigurable dense wavelength-division multiplexing systems

Advances in optical technology now allow practical reconfigurable wavelength networks to be constructed. These networks use wavelength-switching components to dynamically route wavelengths, and provide a level of flexibility and scalability previously not possible. Other components such as low-noise optical amplifiers, electronic dispersion compensators, and advanced modulation techniques simplify system operation, increase capacity, and extend reach. From an application perspective, the architecture of optical transport networks is evolving based on the requirement to support a higher bandwidth access infrastructure. The network architecture also needs to provide the flexibility to incrementally expand on the basis of customer demand and to provide key features such as optical broadcast to lower the cost of video services. The development of new architectures for optical transport networks and how these networks are influenced by critical system parameters and emerging component technologies is reviewed

High-rate–long-distance fiber-optic communication based on advanced modulation techniques

The presence of fiber attenuation and chromatic dispersion is one of the major design aspects of fiber-optic communication systems when one addresses high-rate and long-distance digital data transmission. Conventional digital communication systems implement a modulation technique that generates light pulses at the fiber input end and tries to detect them at the fiber output end. Here an advanced modulation transmission system is developed based on knowledge of the exact dispersion parameters of the fiber and the principles of space-time mathematical analogy. The information encodes the phase of the input light beam (a continuous laser beam). This phase is designed such that, when the signal is transmitted through a fiber with a given chromatic dispersion, high peak pulses emerge at the output, which follows a desired bit pattern. Thus the continuous input energy is concentrated into short time intervals in which the information needs to be represented at the output. The proposed method provides a high rate-distance product even for fibers with high dispersion parameters, high power at the output, and also unique protection properties. Theoretical analysis of the proposed method, computer simulations, and some design aspects are given.

Adaptive array sensor processing applications for mobile telephone communications

The mobile telephone cellular communication system is rapidly being saturated with an increase in subscribers. Although advanced coding and modulation techniques as well as different cell cluster architectures have been implemented, a great increase in the channel capacity is needed, especially in large markets. Adaptive sensor processing has been introduced as a possible remedy to increase the channel capacity by using the directional sensitivity, which leads to a reduction of the interference. Some high-resolution algorithms are evaluated for the direction of arrival (DOA) estimation for a cellular mobile radio environment whose cluster size is varied from K=7, K=4, and K=3; more signals and scattering scenarios that typically arise in urban areas are taken into account. This information is used to beamform toward the signal of interest, resulting in a decrease of the interference. Several signal estimation procedures are evaluated and compared, and it is observed that the DOAs, among other benefits, leads to even higher performance compared with the reference signal method. The computational aspects for the different signal processing, detection and estimation schemes are also discussed.

A High-Performance Microprocessor-Controlled PWM Inverter for AC Motor Drives

Abstract The paper describes a digitally-controlled voltage-source three-phase inverter for ac motor drive applications. High inverter performances, with regards to output spectral quality, power conversion efficiency and switching losses, are obtained throughout the overall operating range by dynamically exploiting different advanced pulse width modulation (PWM) techniques. A multiprocessor architecture has been devised for the control system, which handles both the drive high-level control tasks and the on-line synthesis process of the inverter three-phase switching pattern without the need of specialized hardware. Extensive simulation studies as well as preliminary experimental tests have emphasized the validity and wide applicability of the fully digital solution conceived for drive control.

Advanced modulation and channel coding tecniques for digital HDTV via satellite in the 20 GHz range

Three advanced modulation and channel coding techniques, making use of soft-decision Viterbi decoding, are evaluated over a simulated satellite channel affected by noise and interference to assess the feasibility of Wide RF-band digital HDTV emission systems (W-HDTV) in the 20 GHz range, capable of providing near studio quality. These techniques are evaluated, for different bit-rates (i.e. 140, 105 and 70 MBit/s), in the context of a possible ‘common frequency allocation’ by the WARC 1992 of the frequency range 21.4-22 GHz. This would allow a very efficient use of the spectrum by assigning the overall bandwidth (on one or both polarisations) to all service areas. The systems are compared in terms of required C/ N for high quality pictures and for service continuity, protection ratios and number of channels available in 600 MHz, using both polarisations (i.e. frequency reuse).

Passage of electric current through rolling bearings: Ballbearing Journal, No 153 (June 1968) pp 6–12

The demand for more reliable and efficient electric machines and drives is constantly growing in the renewable energy and transport electrification sectors. Such drive systems are usually fed by semiconductor switch-based inverters, which, unlike balanced pure sine-wave AC sources, produce large-amplitude, high-frequency common-mode voltage (CMV) waveforms, as a result of the application of pulse-width modulation (PWM). This can lead to a number of issues, such as high electromagnetic interference, deterioration of stator winding insulation, and leakage current flow through motor bearings, which dramatically reduce the life-cycle of machines and drives. Thus, this topic has been extensively investigated in the scientific literature, where either corrective or preventive mitigation approaches have been proposed. The former attempt to relieve the damage produced, whereas the latter tackle the problem at its root, by minimizing or eliminating the CMV produced by the inverter. This work provides a comprehensive review of the major CMV mitigation/elimination solutions, with emphasis on preventive actions, in the form of inverter topology variants and/or advanced modulation techniques. A wide picture of this subject is provided to researchers and field engineers, with valuable information and practical hints for the design and development of high-performance electric drive systems. Indeed, an in-depth analysis of the most recent literature clearly shows that best results are obtained by conveniently combining alternative topologies and modulation techniques, which, in some cases, make it possible to completely suppress the CMV component.