High Spectral Efficiency (high + spectral_efficiency)

Distribution by Scientific Domains

Selected Abstracts

Scheduling and power control for MAC layer design in multihop IR-UWB networks

Reena Pilakkat
Recently, a number of researchers have proposed media access control (MAC) designs for ultra-wideband (UWB) networks. Among them, designs based on scheduling and power control seem to be of great promise, particularly for quality-of-service (QoS) traffic. We investigate the efficiencies of many different choices for scheduling and power allocation for QoS traffic in a multihop impulse radio (IR)-UWB network, with the objective of achieving both high spectral efficiency and low transmission power. Specifically, we compare different scheduling schemes employing a protocol interference-based contention graph as well as a physical interference-based contention graph. We propose a relative distance to determine adjacency in the protocol interference-based contention graph. Using our improved protocol interference model with graph-based scheduling, we obtained better performance than the physical interference-based approach employing link-by-link scheduling. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Design and comparison of turbo codes under frame-length and code-rate constraints

Franco Chiaraluce
Abstract When the performances of error-correcting codes for space communications are investigated, with the aim to translate them into practical recommendations, comparison among different schemes is usually a very difficult task. As a matter of fact, these comparisons rarely yield general conclusions. On the other hand, most practical space applications impose strong constraints on the code parameters, which have important effects on code selection. In this paper, we show a methodology and several examples of design and comparison, derived under fixed constraints imposed by the system application on the frame-length and the code-rate. CCSDS Earth observation missions requiring both large coding gains and high spectral efficiency are considered as a case study. Though referred to this specific space mission framework, the presented study is quite general and applies to many other digital communication systems; e.g. for wireless or wired applications where similar constraints exist but are often not taken in due consideration by the designer of the error-correcting schemes. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Interference evaluations and simulations for multisatellite multibeam systems

Pierpaolo Loreti
Third generation communication systems will be characterized by full integration between terrestrial and satellite components. To this aim, global coverage along with not severe requirements for user terminals are mandatory for the satellite segment and the use of constellations of satellites in low or medium Earth orbits (LEO or MEO) seems to be a viable solution. Those satellite systems will adopt multibeam antennas to achieve high spectral efficiency and low-cost terminals. Thus, interference becomes one of the most limiting factors in terms of both link availability and capacity. The paper presents a more complete interference model than previously published in literature. The identification of the interfering users set has been introduced and all the factors impacting interference generation or isolation have been considered in case of both FDMA and CDMA access. This model is suitable for instantaneous analysis of multisatellite constellations. It has been implemented and time-domain simulations have been performed to evaluate the impairments due to co-channel interference for different access techniques for LEO configuration. Simulation results on interference and users spatial distribution, on trade-offs between interference and system capacity will be presented. Finally, the main interference mitigation techniques will be listed and discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source]

8 Tb/s long haul transmission over low dispersion fibers using 100 Gb/s PDM-QPSK channels paired with coherent detection

Jérémie Renaudier
100Gb/s end-to-end broadband optical solutions are attractive to cope with the increasing demand for capacity. Polarization-division-multiplexed (PDM) quaternary-phase-shift-keying (QPSK) paired with coherent detection has been found to be promising for upgrading optical legacy systems based on 50GHz wavelength slots thanks to its high spectral efficiency (2bit/s/Hz) and its tolerance to linear effects. One of the major concerns for the deployment of such a solution is the transmission reach, mainly limited by nonlinear effects. This limitation can be exacerbated over non-zero dispersion shifted fiber (NZDSF) due to low local chromatic dispersion of the transmission fiber. The aim of this paper is first to report on the benefits brought by combining coherent detection techniques with advanced modulation formats as compared to conventional direct detection schemes for optical fiber communications. Digital signal processing paired with coherent detection is described to point out the efficiency of a coherent receiver to combat noise and to mitigate linear impairments. We then report on nonlinear tolerance of 100 Gb/s coherent PDM-QPSK through an 8 Tb/s transmission over a dispersion-managed link based on low dispersion fibers. © 2010 Alcatel-Lucent. [source]

Design and analysis of an IEEE 802.16e-based OFDMA communication system

Krishna Balachandran
IEEE 802.16e has emerged as a strong candidate standard for future wireless systems primarily because it offers the potential for high spectral efficiency, flexible spectrum options (e.g., 2,6 GHz), scalable carrier bandwidth options (e.g., from 1.25 MHz to 20 MHz), multiple duplexing options (time and frequency division duplex), various subchannelization options, and, unlike its IEEE 802.16 predecessors, mobility. Because of the recent emergence of IEEE 802.16e and the complexity it poses in system analysis, there is little published work in the literature regarding the actual system capacity/ throughput performance of IEEE 802.16e for high data rate services. In this paper, we investigate the link and system level performance on the downlink of an IEEE 802.16e-based orthogonal frequency division multiple access (OFDMA) communication system and provide recommendations on high performance IEEE 802.16e system design and deployment configurations. We also propose dynamic resource allocation methods that may be used in OFDMA systems and investigate their performance. @ 2007 Alcatel-Lucent. [source]