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Otaru M.U.,MTN Nigeria Communications Ltd | Zerguine A.,King Fahd University of Petroleum and Minerals | Cheded L.,King Fahd University of Petroleum and Minerals
Digital Signal Processing: A Review Journal | Year: 2011

The steady flow of new research results and developments in the field of adaptive equalization that was witnessed for at least the last four decades is clearly evidenced by the many footprints of success it left behind and shows no sign of ending. The thrust of research and implementation in this field is mainly powered by the use of the well-known mean-square cost function upon which relies the ubiquitous least-mean square (LMS) algorithm. However, such an algorithm is well-known to lead to sub-optimal solutions in the real world that is largely dominated by non-Gaussian interference signals. The use of a non-mean-square cost function would successfully tackle these types of interference signals but would invariably involve a higher computational cost. To address these important practical issues, this paper proposes a new adaptive equalization technique that combines both the least-mean-fourth (LMF) algorithm, which is governed by a non-mean-square cost function, with a power-of-two quantizer (PTQ) in the coefficient update process, which greatly reduces the computational cost involved and which therefore makes the proposed technique applicable to time-varying environments. This paper not only elaborates on the basic idea behind the proposed technique but also defines the necessary assumptions and provides a thorough statistical performance analysis (including a study of the convergence behavior) of the combined algorithm LMF-PTQ that is at the core of the proposed technique. An extensive simulation work was carried out and showed that the theoretical predictions are very well substantiated. © 2010 Elsevier Inc.

Adebesin B.O.,Landmark University | Adekoya B.J.,Olabisi Onabanjo University | Ikubanni S.O.,Landmark University | Adebiyi S.J.,Landmark University | And 2 more authors.
Journal of Earth System Science | Year: 2014

Diurnal, seasonal and annual foF2 variability and the response of the F2-layer height over Jicamarca (11.9°S, 76.8°W, 1°N dip) during periods of low (LSA), moderate (MSA) and high (HSA) solar activities was investigated. The relative standard deviation (VR) was used for the analysis. The F2-layer critical frequency pre-noon peak increases by a factor of 2 more than the post-noon peak as the solar activity increases. The variability coefficient (VR) is lowest during the day (7-16%) for the three solar epochs; increases during nighttime (20-26%, 14-26%, and 10-20%, respectively for the LSA, MSA and HSA years); and attained highest magnitude during sunrise (21-27%, 24-27%, and 19-30%, respectively in similar order). Two major peaks were observed in VR - the pre-sunrise peak, which is higher, and the post-sunset peak. Generally, the variability increases as the solar activity decreases. Annually, VR peaks within 23-24%, 19-24% and 15-24% for the LSA, MSA, and HSA periods, respectively. The ionospheric F2-layer height rises to the higher level with increasing solar activity. The foF2 comparison results revealed that Jicamarca is well represented on the IRI-2012 model, with an improvement on the URSI option. The importance of vertical plasma drift and photochemistry in the F2-layer was emphasized. © Indian Academy of Sciences.

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