Sharif Digital Repository

In this letter we introduce an effective tool to demonstrate signal power behavior of a typical spectrally encoded spread-time (SE/ST) CDMA system using probabilistic approach. By defining power level profile (PLP), as the probability of stretching instantaneous power from a pre-specified threshold, we can find novel upper bounds on the signal power profile. We discuss various properties owing to PLP and elaborate on the main parameters affecting the PLP value. We present three theorems, propose some simple upper bounds on the PLP, and give an insight on the main contributions of the results. We introduce a fundamental parameter, namely ß, as a key design parameter which relates the most... 

In this study the authors present an in-depth study, analysis and discussion on maximum likelihood (ML)-based receiver for a typical spectrally encoded spread-time CDMA in the presence of multiple narrowband interference (NBI) signals in an additive white Gaussian noise channel. Furthermore, the authors demonstrate that by combining useful properties of ML-based receiver and three-level codes, that is, codes with values of -1, 0, +1, the authors can introduce a new strategy in which superior performance with respect to previous receiver structure based on two-level codes, that is, codes with values of -1, +1, can be attained. With the help of an example, the authors drive, first, the... 

In this letter we consider optimum code structure for positive optical code division multiple-access (optical CDMA) systems. Positive systems are a class of systems that operate with positive real numbers only. We consider the effect of multipleaccess interference in our model and show that code design for both On-Off Keying (OOK) and Binary PPM optical CDMA systems results in the same solutions. Furthermore, we show that a class of codes known as optical orthogonal codes (OOCs) are the best possible positive codes. In obtaining the results we define normalized divergence based on signal-to-multipleaccess interference ratio (SIR) for a multiple-access system in a useful manner and use it as... 

In this paper we study and analyze the performance of the RAKE receiver for a typical Ultrawideband (UWB) Spectrally-Encoded Spread-Time (ST) CDMA in the presence of multiple Gaussian Interference (GI) signals. We demonstrate that by combining useful properties of three-level codes, i.e., codes with values of - 1, 0, +1, and RAKE receiver, we can introduce a new strategy in which it can result in superior performance when compared to previous results. In particular, following a discussion on three-level codes we can show that RAKE receiver with optimum multiplicative weights achieves a better performance when compared with simple two-level codes. With the help of an example we show various... 

In this paper, we present a deep insight into the behavior of optical code-division multiple-access (OCDMA) systems based on an incoherent, intensity encoding/decoding technique using a well-known class of codes, namely, optical orthogonal codes (OOCs). As opposed to parts I and II of this paper, where OOCs with cross-correlation lambda=1 were considered, we consider generalized OOCs with 1leslambdalesw, where w is the weight of the corresponding codes. To enhance the performance of such systems, we propose the use of an optical and logic gate receiver, which, in an ideal case, e.g., in the absence of any noise source, except the optical multiple-access interference, is optimum. Using some... 

Background: in this paper, fuzzy pole placement control approach is proposed to control the speed of D.C motor. In this method, state feedback gain is tuned by fuzzy logic. Methods: In conventional pole placement control, constant gain is considered to insert the poles of system in the desired place. Therefore, unnecessary effort is appliedto the system, and the system implementation becomes costly. In contrast, in fuzzy pole placement control, poles of system alter gradually based on the performance of system and are settled in desired point causing the system to display apposite performance. In other words, in conventional pole placement, a determined pair of poles exists, whereas in fuzzy... 

In this letter we introduce an effective tool to demonstrate signal power behavior of a typical spectrallyencoded spread-time (SE/ST) CDMA system using probabilistic approach. By denning power level profile (PLP), as the probability of stretching instantaneous power from a pre-specified threshold, we can find novel upper bounds on the signal power profile. We discuss various properties owing to PLP and elaborate on the main parameters affecting the PLP value. We present three theorems, propose some simple upper bounds on the PLP, and give an insight on the main contributions of the results. We introduce a fundamental parameter, namely β, as a key design parameter which relates the most... 

A novel UWB MIMO antenna with band-notched characteristic operating in the frequency range between 3.1 GHz and 10.6 GHz is presented. The designed MIMO antenna has two ports and the size of 32×14 mm2 which is fabricated on an FR-4 printed-circuit-board. The feeding system of the proposed antenna is a microstrip line. The two antennas are positioned face to face but laid reversely upon the substrate in order to have a good isolation, less cross polarization, high gain and good envelope correlation coefficient. S-parameters describe the input-output relationship between ports (or terminals) in a MIMO antenna. The effects of the strip feed line width on the variations in reflection coefficient... 

In this study the authors present an in-depth study, analysis and discussion on maximum likelihood (ML)-based receiver for a typical spectrally encoded spread-time CDMA in the presence of multiple narrowband interference (NBI) signals in an additive white Gaussian noise channel. Furthermore, the authors demonstrate that by combining useful properties of ML-based receiver and three-level codes, that is, codes with values of -1, 0, +1, the authors can introduce a new strategy in which superior performance with respect to previous receiver structure based on two-level codes, that is, codes with values of -1, +1, can be attained. With the help of an example, the authors drive, first, the... 

The common voice channels existing in cellular communication networks provide reliable, ubiquitously available and top priority communication mediums. These properties make voice dedicated channels an ideal choice for high priority, real time communication. However, such channels include voice codecs that hamper the data flow by compressing the waveforms prior to transmission. This study designs codebooks of speech-like symbols for reliable data transfer through the voice channel of cellular networks. An efficient algorithm is proposed to select proper codebook symbols from a database of natural speech to optimise a desired objective. Two variants of this codebook optimisation algorithm are... 

In this letter we consider optimum code structure for positive optical code division multiple-access (optical CDMA) systems. Positive systems are a class of systems that operate with positive real numbers only. We consider the effect of multipleaccess interference in our model and show that code design for both On-Off Keying (OOK) and Binary PPM optical CDMA systems results in the same solutions. Furthermore, we show that a class of codes known as optical orthogonal codes (OOCs) are the best possible positive codes. In obtaining the results we define normalized divergence based on signal-to-multipleaccess interference ratio (SIR) for a multiple-access system in a useful manner and use it as...