Sharif Digital Repository

A reduced complexity third-order digital delta-sigma modulator is presented. The modulator consists of two cascaded sections to produce proper shaping of quantization noise with minimum hardware. A new architecture for a digital third-order delta-sigma modulator based on Ritchie structure is proposed. The measurement results show 94dB SNR and 65% dynamic range  

A generalisation of Fourier transform-domain technique for narrowband interference suppression in CDMA communication systems is introduced. In this technique, first the sum of a number of sinusoids each modulated by a polynomial is chosen as a model for the narrowband interference. Then, by fitting the received signal on the proposed model, an estimate of the narrowband interference signal is obtained, and its effect is subtracted from the received signal  

In this letter, we examine the positioning in wireless networks in the presence of IRSs. We show that IRSs can be used to localize the user when there are not enough transmitters (Base Station). To this end, we consider a network of one transmitter, few IRSs, and one receiver, whose location should be determined. Our results indicate that we can achieve the accuracy required in the localization by controlling the number of elements of IRSs and properly selecting the location of IRSs for a given region. © 2012 IEEE  

In this study, an efficient handover algorithm based on the received signal strength (RSS) prediction is presented for two-tier macro-femtocell networks in which, because of the fading effects of channel and short coverage range of femtocells, ping-pong handovers may take place. In the proposed approach, first each mobile station (MS) uses the recursive least square algorithm for predicting the RSS from the candidate base stations (BSs) including both femtocell and macrocell BSs. Then, according to the predicted RSS values, several future values of signal-to-interference plus noise ratio (SINR) are calculated. Afterwards, the candidate list of BSs is pruned according to the estimated future... 

In this paper, we present a quality-of-transmission (QoT) aware dynamic routing, modulation level, and spectrum assignment scheme referred to as QoT-aware RSA. The proposed QoT-aware RSA has three stages: path computation with QoT-aware modulation level assignment, path selection, and spectrum assignment. Two schemes are presented in the path computation stage namely, modified Dijkstra and K-shortest-path algorithms. A closed-form expression is derived to model the fiber nonlinearity effects and the impairments of intermediate routers. This expression is utilized to estimate the network dependent QoT and the transmission reach of the modulation levels. We propose to select the best path in... 

Pulse compression is an active research topic in radar systems. A problem in pulse compression is masking of small targets by the range sidelobes of large nearby targets. A new filter structure is introduced here to suppress the sidelobes of radar signals that result from standard matched filtering. The proposed filter is applicable for any type of binary coding signals. Several techniques are used to calculate the filter coefficients such as Wiener filter technique, Lagrange multiplier method, and linear programming (LP) algorithm. Also, a weighting function is utilized to shape the sidelobe energy in an iterative manner that will yield more sidelobe reduction. Comparison of the proposed... 

In this paper, we consider transmission of a Gaussian source over a Gaussian channel under bandwidth compression in the presence of interference known only to the transmitter. We study hybrid digital-analog (HDA) joint source-channel coding schemes and propose two novel coding schemes that achieve the optimal mean-squared error (MSE) distortion. This can be viewed as the extension of results by Wilson et al. [1], originally proposed for sending a Gaussian source over a Gaussian channel in two cases: 1) Matched bandwidth with known interference only at the transmitter, 2) bandwidth compression where there is no interference in the channel. The proposed HDA codes can cancel the interference of... 

A low power 10 bit, 40 MS/s pipeline analog to digital converter is presented. A number of low-power techniques are proposed in various levels of abstraction. In circuit level, a low power class A/AB opamp with direct common-mode-feedback circuit (CMFB) is proposed which significantly reduces power in the opamps. In backend design, optimal series capacitors are layed out to break the deadlock between the mismatch and loading effect of the first stage capacitors. A customized software tool is developed based on the proposed opamp and architecture which provides optimum stage scaling factors, tail current and opamp transistor sizes. Simulations in 0.13um CMOS technology show that the ADC... 

Singular spectrum analysis (SSA) is a well-studied approach in signal processing. SSA has originally been designed to extract information from short noisy chaotic time series and to enhance the signal-to-noise ratio. SSA is good for offline applications; however, many applications, such as modelling, analysis, and prediction of time-varying and non-stationary time series, demand for online analysis. This study introduces a recursive algorithm called recursive SSA as a modification to regular SSA for dynamic and online applications. The proposed method is based on eigenvector matrix perturbation approach. After recursively calculating the covariance matrix of the trajectory matrix, R-SSA... 

Along with the improvement of image watermarking techniques, the necessity for effectively and comprehensively evaluating various algorithms becomes imperative. In this paper, we first propose a new categorization that fits for most of the existing watermarking algorithms that work in the wavelet domain. Then an adaptive watermarking attack for evaluating the robustness of watermarking schemes that are based on the proposed categorization is presented. This attack determines the flat regions, edges, and textures of the watermarked image and based on known features of each region the proposed attack tries to destroy the watermark information. This is done by separately manipulating the... 

A detailed 3D Monte Carlo simulation of the grid geometrical parameters in screen-film mammography (SFM) and digital mammography (DM) systems has been performed. A combination of IEC 60627:2013 international standard conditions and other more clinically relevant parameters were used for this simulation. Accuracy of our results has been benchmarked with previously published data and good agreement has been obtained. Calculations in a wide range of linear anti-scatter grid geometries have been carried out. The evaluated parameters for the SFM system were the Bucky factor (BF) and contrast improvement factor (CIF) and for the DM system it was signal differenceto- noise ratio improvement factor... 

In this paper, we use delay-amplify-and-forward relays in the uplink direction of a coordinated multi-point network based on orthogonal frequency division multiplexing. The key novelty is that we assume delay from users to different base stations (BSs), in general, may exceed cyclic prefix (CP) length as might be the case in large cells and cannot be completely compensated by traditional timing advance strategies. Consequently, interchannel interference and intersymbol interference may arise under such assumptions. We first optimize the adjustable delays added at users, relays and BS nodes in order to reduce the effective delay spread at the receive sites, then we optimize relays' weights... 

Objective: Improving signal to noise ratio (SNR) and qualified images by the various methods is very important for detecting the abnormalities at the body organs. Scatter and attenuation of photons by the organs lead to errors in radiopharmaceutical estimation as well as degradation of images. The choice of suitable energy window and the radionuclide have a key role in nuclear medicine which appearing the lowest scatter fraction as well as having a nearly constant linear attenuation coefficient as a function of phantom thickness. Methods: The energy windows of symmetrical window (SW), asymmetric window (ASW), high window (WH) and low window (WL) using Tc-99m and Sm-153 radionuclide with... 

A multiplexing technique, which is based on duty-cycle division, is proposed. The channel multiplexing and demultiplexing are performed electrically at the single user bit rate, which is very economic. In a three-user system (3×10 Gb/s), the simulation results show that the best receiver sensitivity value achieved is -30.1 dBm with an optical signal-to-noise ratio (OSNR) of 22.3 dB, while the chromatic dispersion tolerance ranges from 192 to 280 ps/nm. Migration from 30 to 120 Gb/s is achieved with the penalty of 6.4 and 5.2 dB in the receiver sensitivity and OSNR, respectively, for the worst user  

The aim of this study is to improve the performance of two-tier macro/femtocell networks using a power control approach. In wireless networks, power control plays an important role in improving a number of performance parameters such as co-channel interference and outage probability reduction, throughput increasing, and power saving. This study explores the evolution of centralised power control algorithm based on femtocell base station (FBS) clustering and predicted signal-to-interference-plus-noise ratio (SINR) of users. To reduce the computational complexity of centralised algorithm, dense deployed femtocells are considered in different clusters. In this case, femtocells inside one... 

As the increasing demands of military detection, wireless communication and remote sensing make the spectrum even more crowded, radar sequence design meeting spectral compatibility requirement is a challenging and urgent problem. This study is devoted to designing optimised phase-coded sequences which keep spectral-compatible with the overlaid electromagnetic radiators and at the same time optimise the signal-to-interference-plus-noise ratio (SINR). First, an intelligent dynamic spectrum information around the radar system is achieved by a radio environmental map. The information is introduced to form a constrained optimisation process aimed at improving the spectral compatibility and the... 

In this paper, we propose a scheme referred to as integer-forcing message recovering (IFMR) to enable receivers to recover their desirable messages in interference channels. Compared to the state-of-the-art integer-forcing linear receiver (IFLR), our proposed IFMR approach needs to decode considerably less number of messages. In our method, each receiver recovers independent linear integer combinations of the desirable messages each from two independent equations. We propose an efficient polynomial-time algorithm to sequentially find the equations and integer combinations with maximum rates and analyze its complexity. We evaluate the performance of our scheme and compare the results with the... 

Device-to-Device (D2D) communication technology, under the standardization of third generation partnership project and a component of the evolving fifth generation architecture, is mainly aimed to increase system capacity and data rate via providing direct communications between end devices without the use of routing data through the network. Apart from the attracting features, due to the resource sharing between cellular user equipment (CUE) and D2D user equipment (DUE) in such communications, an efficient algorithm for resource and power allocation to DUE, especially for mobile users is necessary to maintain the performance. The current paper introduces a joint mode algorithm for mobile... 

In this paper, we present a novel power allocation scheme for amplify and forward incremental relaying (IR) systems with the aim to minimize the overall outage probability at the destination. In our problem formulation, we take into account the outage-dependent activation of the relay when writing the power constraint. We provide a simple closed-form solution to the IR power allocation problem that is based on high signal-to-noise (SNR) approximation of the outage probability assuming maximum ratio combining (MRC) at the destination. We investigate the effectiveness of the proposed solution by comparing the achieved outage probabilities with those obtained through global numerical search. We... 

Identification of modulation and space-time block code (STBC) is an important task of receivers in applications such as military, civilian, and commercial communications. Here, we consider multiple-input multiple-output (MIMO) systems. We propose two methods for STBC identification when the modulation is known. We also introduce a method for joint identification of code and modulation. Additionally, we present an enhanced zero-forcing (ZF) equaliser to improve the separation between the features of different classes. Higher order cumulants are used as the statistical features. In the first method of STBC identification, after the proposed equalisation, received data samples are segmented,...