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۱Approximation of Spherical Wave Reflection Coefficient from Rough Sea Surface
اطلاعات انتشار: بیستمین کنفرانس مهندسی برق ایران، سال
تعداد صفحات: ۶
In underwater applications, acoustic scattering from the sea surface must be considered in any system that utilizes surface–reflected acoustic energy. In this paper, we obtainspherical wave reflection coefficient approximately by expansion of a spherical wave into plane waves and using the method ofstationary phase. The obtained spherical wave reflection coefficient depends on various parameters such as frequency and incidence angle of the spherical wave, the length of the path thatconnects the source to the receiver, and the root–mean–square (RMS) displacement of the rough sea surface. We verify that thespherical wave reflection coefficient approaches to the plane wave reflection coefficient in far field approximation. Finally, the statistical distribution of the spherical wave reflection coefficient is obtained considering statistical characteristics of the source and receiver positions.<\div>

۲Hybrid Decoding for LT Codes
نویسنده(ها): ،
اطلاعات انتشار: اولین کنفرانس ملی مهندسی برق اصفهان، سال
تعداد صفحات: ۴
Fountain codes provide a highly reliable and efficient transmission over Bit Erasure Channels (BEC) and LubyTransformation (LT) codes are the first realization of these codes. LT codes, like other sparse codes, use BeliefPropagation (BP) decoding. The most disadvantage of this decoding is that it fails if no degree–1 encoding packetsappear in some iteration. In this paper, after the failure of BP decoding, in order to recover remained source packets,we use another method of decoding. We also show that the computation complexity of our method is less thanGaussian elimination and its overhead is as less as Gaussian elimination.<\div>

۳Investigation of a Simple Symbol Combining Scheme at DF Relays for BICM–OFDM Cooperative Systems
نویسنده(ها): ،
اطلاعات انتشار: اولین کنفرانس سراسری توسعه محوری مهندسی عمران، معماری، برق و مکانیک ایران، سال
تعداد صفحات: ۷
In this paper, performance analysis of a new scheme for linear symbol combination at relays for cooperative communication systems is considered. We employ Bit Interleaved Coded Modulation (BICM) and Orthogonal Frequency Division Multiplexing (OFDM), performing over frequency selective channels. Relays operate in DF mode and the effect of their errouneous detection will be considered. We present a closed form of the asymptotic worst–case pairwise error probability (PEP) at the destination for the proposed system. It will shown that this system exploits the full spacial and frequency diversity. Finally, the simulation results reveal the analytical derivations and confirm the diversity gain of the system, and provide a comparison between two competing method<\div>

۴On the Practical Aspects of Joint Passive Phase Conjugation and Equalization in Underwater Communication Systems
نویسنده(ها): ،
اطلاعات انتشار: Majlesi Journal of Telecommunication Devices، چهارم،شماره۲، Jun ۲۰۱۵، سال
تعداد صفحات: ۷
Underwater acoustic communication is suffered from the channel effects which results in time spreading of the transmitted signal. In underwater environment multiple replicas of the transmitted signal are received at the receiver through different paths, which causes significant Inter–Symbol Interference (ISI). Decision Feedback Equalizers (DFE) was utilized to overcome this type of interference in digital communications so many years ago. However, because of the complexity of adaptive equalizers Passive Phase Conjugation (PPC) was widely exploited in underwater communications in the recent years. Because of the poor performance of the PPC method, adaptive equalizers are jointed to improve the PPC performance. In this paper, experimental results conducted in Shiraz Electronic Industrials’ pool are reported. Three different approaches are compared in terms of Symbol Error Rate (SER) versus the number of used channels at the pool: 1) the PPC method; 2) DFE equalizer for only a single channel; 3) the PPC method combined with adaptive DFE. The experimental results showed that the third approach outperforms the others while a simpler receiver is obtained.
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