Recent measurements are shown with emphasis on high and equatorial latitude observations. The long-term morphology (period 1979-1984) of intensity scintillations at 250 MHz in the polar cap shows that, in addition to the absence of diurnal variation of scintillations, and the presence of an annual variation with a pronounced minimum during local summer, there exists a marked solar control of scintillation activity such that it abruptly decreases when the solar activity falls below a threshold level.Īmplitude fluctuations produced by small irregularities in electron density in the F layer of the ionosphere can be a problem to communication and navigation systems in the very-high frequency-ultra-high frequency (VHF-UHF) range. Ively controls the structure of scintillations. The extreme variability of ionospheric motion in the auroral oval sensit. The phase rates at auroral locations are an order of magnitude smaller than in the equatorial region and attain values of 100° in 0.5 s. The power law index of phase scintillation at high latitudes is in the vicinity of -2.3, which is not a result of very strong turbulence as in the equatorial region but is considered to be a consequence of shallow irregularity spectral indexes. The corresponding values for the S 4 index of scintillation are 0.5 and 0.8 in the polar cap, which are slightly higher than those recorded in the auroral oval. In the polar cap, the 50th and 90th percentile values of rms phase deviation at 250 MHz for 82 s detrend are 3 and 12 rad, respectively, with comparable values being obtained in the auroral oval. The 90th percentile values of rms phase deviation at 244 MHz with 100 s detrend are found to be 16 rad in the early evening hours, whereas amplitude scintillation can cover the entire dynamic range of 30 dB not only in the 250 MHz band but at L -band as well. The strong scattering at VHF induces extreme phase rates of 200° in 0.1 s. The phase spectra at 244 MHz are described by power law variation of psd with frequency with typical spectral indexes of -2.4. Such structures are compatible with intensity decorrelation times of 0.1 and 0.3 s at 2 MHz, respectively. In the anomaly region, the spectra of intense amplitude scintillations at these frequencies are characterized by uniform power spectral density from the lowest frequency (10 MHz) to 4 Hz at 257 MHz and to 1 Hz at L -band (1541 MHz) and steep rolloff at higher fluctuation frequencies with power law indexes of -5 to -7. The equatorial anomaly region is identified as the most disturbed irregularity environment where the amplitude and phase structures of 250 MHz and L -band scintillations are primarily dictated by the strength of scattering rather than ionospheric motion. Ionospheric scintillation effects encountered in the equatorial anomaly crest, polar cap, and auroral regions have been contrasted to provide information for the design and evaluation of the performance of multifrequency satellite communication links in these regions. The book is attractive to both audiences through the inclusion of many practical examples and a practical flavor in the choice of topics.ĭigital Communication has a Web site at :, where the reader may find additional information from the Second Edition, other supplementary materials, useful links, a problem solutions manual, and errata. This book is ideal as a first-year graduate textbook, and is essential to many industry professionals. Three chapters from the previous edition have been moved to the book’s Web site to make room for new material. Readability is increased by relegating many of the more detailed derivations to appendices and exercise solutions, both of which are included in the book.Įxercises, problems, and solutions have been revised and expanded.
As a result, two new chapters have been added, one on the theory of MIMO channels, and the other on diversity techniques for mitigating fading.Įrror-control coding has been rewritten to reflect the current state of the art.Ĭhapters 6 through 9 from the Second Edition have been reorganized and streamlined to highlight pulse-amplitude modulation, becoming the new Chapters 5 through 7. New material on recent advances in wireless communications, error-control coding, and multi-user communications has been added. Digital Communication is relevant to the design of a variety of systems, including voice and video digital cellular telephone, digital CATV distribution, wireless LANs, digital subscriber loop, metallic Ethernet, voiceband data modems, and satellite communication systems. The general approach of this book is to extract the common principles underlying a range of media and applications and present them in a unified framework. This book is for designers and would-be designers of digital communication systems.
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