Sharif Digital Repository

In this paper, we consider the 3-receiver broadcast channel with one common and two confidential messages. One of the confidential messages is sent to the first and second receivers and kept secret from the third receiver (eavesdropper). The other confidential message is sent to the first receiver and kept secret from the second and third receivers (eavesdroppers). The common message is decoded by all receivers. We study some special cases of the model and determine their secrecy capacity regions  

This paper introduces a new applicable Gaussian wiretap channel with side information. In this channel, the state of the channel to the wiretapper is separated from the main channel's one. It means that the legitimate receiver and the wiretapper are listening to the transmitted signal through the different channels with different channel states which may have some correlation to each other. The state of the main channel, is assumed to be known at the transmitter, helps the sender to encrypt its messages. The achievable equivocation-rate region for this model is drived in the Gaussian case and the results are reduced to the previous works as special cases  

We propose and experimentally demonstrate a receiver structure for direct detection optical orthogonal frequency-multiplexing systems that improves the spectral efficiency by reducing the guard band between the carrier and the OFDM signal while mitigating signal-signal mixing interference  

Aims. Stars twinkle because their light propagates through the atmosphere. The same phenomenon is expected on a longer time scale when the light of remote stars crosses an interstellar turbulent molecular cloud, but it has never been observed at optical wavelengths. The aim of the study described in this paper is to fully simulate the scintillation process, starting from the molecular cloud description as a fractal object, ending with the simulations of fluctuating stellar light curves. Methods. Fast Fourier transforms are first used to simulate fractal clouds. Then, the illumination pattern resulting from the crossing of background star light through these refractive clouds is calculated... 

In noise radars, measuring the cross-correlation between transmitted and received signals is known as a common method of signal processing. However, it brings a lot of unwelcome sidelobes which can lean to masking weak echoes of far targets. There are many classical and modern methods of masking effect removal which are based on signal processing in the receiver side. A method of waveform design for decreasing this effect is presented and its efficiency is compared to purely random waveform generation method and CLEAN algorithm. Moreover, performance of collaborative using of receiver-based and transmitter-based techniques is considered  

Signal processing in noise radar is always done by calculating the cross-correlation between transmitted and received signals. Strong echoes of near targets present relatively high sidelobes in the correlation output, so they can conceal weak echoes of weak targets (masking effect). Many classical and modern methods for alleviating this effect have been offered, however, most of them are based on signal processing in the receiver side. In this paper, a new method of waveform design, able to decrease masking effect, is presented. Contrary to the other methods, this method keeps the matched filter structure in receiver unchanged and does not need performing any extra process in the receiver... 

In this paper, a chaos-based communication system in the presence of unknown transmission delay is studied. First, under master/slave configurations, two chaotic Chen systems as the slaves are synchronized with a master one via unidirectional coupling. Then at the transmitter, information of an image is embedded within a slave-one signal and the resultant signal along with another one which is used to determine the transmission delay is transmitted to the receiver. At the receiver, using the received signals and the slave-two counterpart signal, the image is recovered. The performance of the proposed method is experimentally illustrated  

In this paper, we introduce discrete memoryless Interference Channel (IFC) with two relays as two interfering transmitter-receiver pairs that are aided by two relays. We propose two different coding strategies for this channel. In the first strategy, we assume that each relay tries to mainly help one of the transmitter-receiver pairs through signal relaying and interference cancellation, while in the second strategy we assume that each relay tries to help both transmitter-receiver pairs. In our coding schemes, we employ rate-splitting, generalized block Markov coding, superposition coding and Gel'fand-Pinsker binning to cancel parts of the interference known to be experienced at the... 

A new and simple receiver structure for reducing the multipath inter-symbole interference (ISI) effect is proposed for infrared diffuse links. In this new method, bit-error rate (BER) performance of the system will be improved significantly without any essential change in the receiver structure. In our analysis, all major noise sources such as ambient light, signal shotnoise, dark current and thermal noise of the receiver are considered. © 2009 IEEE  

Radiofrequency coils provide high-resolution magnetic resonance (MR) imaging of human tissues. A small RF coil produces MR images with a higher resolution compared to the commercial volume MR coils from mass limited samples. Signal to noise ratio (SNR) plays a key role in the optimal design of receiver radiofrequency coils. In this work, we present a three-loop saddle coil suitable for MR imaging of digits of the human body. The geometry of the introduced coil is optimized to achieve the highest SNR. The coil performance is evaluated through comparing the measured SNR maps of the optimal coil derived from MR images of a saline phantom with the corresponding measured SNR maps of a commercial... 

Binary integrators are an important part of the receiver in many operating radar systems. The optimisation of a binary integrator is not a simple task, because it requires the solution of a (k×n)-dimensional nonlinear optimisation problem, where n is the number of integrated bits (or the number of sensors in a distributed radar or sensor network) and k is the number of the design parameters of the single-pulse detector. An algorithm that converts the multi-dimensional optimisation problem into a one-dimensional problem, so reducing considerably the computational complexity, is developed. This reduction in computational complexity makes the real-time optimisation possible and practical, so it... 

Due to the constraints of P2P networks (such as bandwidth limitation) multiple senders should be employed for reliable multimedia streaming. This paper introduces a mathematic approach to select a set of senders among all available senders to provide the most reliable stream for the receiver. This selection is based on upload bandwidths and availability of peers as well as bandwidth of links connecting the senders and the receiver. Our method is called IPROMISE as it is an improved version of the PROMISE algorithm. Simulation results demonstrate improved media quality delivered to the receiver, while the complexity of sender selection remains the same. © 2007 IEEE  

Unlike those on Internet, the media providers on P2P networks are ordinary nodes with limited shared resources such as bandwidth. Multi-sender methods are the best existing solutions to video streaming on P2P networks. In this paper, we propose use of a multicast method on the top of an arbitrary multi-sender method so that all requesting peers receive almost the same expected bit-rate. Experimental results, derived from implementation of the proposed algorithm on Pastry P2P network confirm our claim. Another advantage of our method over the existing methods is its scalability with the number of receivers. © 2007 Elsevier B.V. All rights reserved  

Design of a novel RF front - end structure for 2450-MHz Band IEEE 802.15.4 ZigBee standard in a 0.18-μm CMOS process is presented. Utilizing a common-gate structure instead of conventional inductive degenerated common source amplifier, Low noise figure is achieved with LNA bias current as low as 1mA. An analytical method is presented to minimize the Noise figure of proposed common-gate LNA structure. Together with the LNA, an active Gilbert Cell mixer is adopted to convert the RF signal to 2MHz IF signal. Employing an enhanced current re-use structure, simulation results show a conversion gain of 37.7dB, a Noise figure of 5.9dB and an IIP3 of -4dBm for the front -end. The RF front - end... 

The performance of OFDM-based Wireless Local Area Networks (WLANs) is investigated by employing different smart antenna techniques at the receiver. The use of multiple antennas at the Access Point (AP) receiver in IEEE802.11a standard-compliant Single Input Multiple Output (SIMO) configuration, improves the physical layer performance in different channel scenarios and interference that may arise from other stations sharing the same frequency band. For this purpose, a comparative study of smart antenna architectures for IEEE802.11a WLAN system using pre-FFT and post-FFT array processing techniques is presented. Simulations are performed on a new model for IEEE802.11a system using a... 

In this paper we propose a novel structure of a discrete-time mixed-signal linear equalizer designed for analog front end of Gigabit Ethernet receivers. The circuit is an FIR filter which involves 6 taps based on a coefficient-rotating structure. Here, a simple structure is used for merging digital to analog conversion of the filter's coefficients and multipliers needed for 6 taps. This structure results in high speed and low power dissipation as well as less A/D converter complexity. Simulated in a 0.18 um CMOS technology, this equalizer operates at 125 MHz while dissipating 10 mw from a 1.8 V power supply. © 2006 IEEE  

We propose a new multiple access technique for Ultra Wide-Band (UWB) systems based on time-hopping (TH) and direct sequence (DS) spread spectrum techniques. In this method, the duration of each bit is divided into N s frames each one consisting of Nh chips. The outputs of a super-orthogonal encoder and a PN sequence specify the frame number, in which the data is transmitted in DS spread-spectrum form using the second PN sequence. We consider hard decision with threshold and soft decision before Viterbi decoding at the receiver. We evaluate the performance of the proposed method and compare it with the conventional DS-CDMA system. The results show that the proposed method has the best... 

This article presents a very low-power clock and data recovery (CDR) circuit with 8 parallel channels achieving an aggregate data rate of 20 Gbps. A structural top-down design methodology has been applied to minimize the power dissipation while satisfying the required specifications for short-haul receivers. Implemented in a 0.18μm digital CMOS technology, total power dissipation is 70.2mW or 3.51mW/Gbps/Ch and each channel occupies 0.045 μm2 silicon area. © 2005 IEEE  

In this paper, we focus on adaptive and wavelet based systems in radar signal processing, and a new algorithm to Doppler compensation is developed. The new wavelet-based method for ambiguity surface smoothing that applies the three dimensions dual tree wavelet transform and adapt constant false alarm rate, is proposed. The model captures the dependence between a wavelet coefficient and its parent. Simulation results show that new approach is better than older algorithms. We have simulated this new method for bistatic FM-based passive coherent receiver