Sharif Digital Repository

The exact symbol and bit error probabilities of linearly modulated signals in frequency non-selective Rician fading channels with Lth diversity branches are derived, where coherent detection with maximum ratio combining (MRC) is used at the receiver. For performance evaluation, the multiplicative distortion is combined with the additive Gaussian noise and form an additive noise is formed. This method allows computing the exact symbol and bit error probabilities of M-ary phase shift keying (M-PSK), M-ary quadrature amplitude modulation (M-QAM), M-ary amplitude modulation (M-AM) and M-ary amplitude modulation phase modulation (M-AMPM) for any arbitrary bit mappings. The results contain several... 

We consider a combined time-hopping (TH) and spread-time (ST) multiple-access technique that uses an internal code. In this method, the duration of each bit is divided into Ns frames. The outputs of the encoder and a pseudorandom (PN) sequence specify the number of the frame in which the data bit is transmitted in ST code-division multiple-access (ST-CDMA) form using the second PN sequence. We consider the correlator receiver, followed by the channel decoder. We obtain the performance of the combined method in additive white Gaussian noise (AWGN) and fading channels in the presence of multiple-access interference (MAI) and narrowband interference (NBI). We also consider the conventional... 

Celery residue modified with H2SO4 was utilized as a low-cost adsorbent for elimination of methylene blue cationic dye from aqueous solution in batch adsorption process. The adsorbent was characterized by Fourier transform infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). The efficacy of dye removal of the modified celery residue (MCR) was verifying by changing adsorbent dose, contact time, pH, initial dye concentration, and temperature. The isotherm models analysis shows that the experimental data can be better demonstrated by Freundlich isotherm model. In order to evaluate the best fit isotherm, three error analysis methods (χ2, ARE and MPSD) as well as correlation... 

This study introduces a new and bio-friendly adsorbent based on natural and cetyltrimethylammonium bromide (CTAB) modified adsorbent, celery (Apium graveolens) residue for removal of organic pollutants. The adsorbent was characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and pHpzc techniques. Removal applicability and efficiency of this biosorbent were studied using Congo red (CR) as a sample organic pollutant. To reach the best results, main parameters such as pH, adsorbent mass, contact time, initial dye concentration and temperature were optimized through the adsorption experiments in a batch system. The kinetic and isotherm of CR removal... 

We consider an internally coded multiple access technique for Ultra Wide-Band systems which combines time-hopping (TH) and spread-time (ST) techniques using a super-orthogonal encoder. In this method, the duration of each bit is divided into Ns frames. The outputs of a superorthogonal encoder and a PN sequence specify the frame number, in which the data is transmitted in spread-time CDMA form using the second PN sequence. We consider soft decision before Viterbi decoding at the receiver. We obtain the performance of the proposed method. We also consider the uncoded ST-CDMA system and compare its performance with our method. The results indicate that our method has much more better... 

A new internally coded scheme that combines frequency hopping (FH) and multicarrier (MC) code division multiple access (CDMA) techniques using a super-orthogonal encoder is proposed. In this method, the total bandwidth is partitioned into Ns1 disjoint bands and each band is also segmented into Ns2 subbands. On the basis of a super-orthogonal encoder output and a pseudorandom sequence, one of the Ns1 bands is selected. The data bit is then transmitted in the band in the form of the multicarrier FH (MC-FH) CDMA scheme, that is, Ns2 carriers are transmitted in the Ns2 subbands of the selected band. At the receiver, both hard and soft detectors are used. The performance of the proposed method in... 

We consider an internally coded scheme for multicarrier frequency-hopping CDMA (MC-FH-CDMA) communication systems. In this method, the total bandwidth is partitioned into Ns1 disjoint bands and each band is also segmented into Ns2 subbands. Based on the super-orthogonal encoder output and a pseudorandom (PN) sequence, one of the Ns1 bands is selected. Then, the data is transmitted in that band in the form of multicarrier frequency-hopping technique using BPSK modulation. At the receiver front end, we use soft detector, then we apply Viterbi decoding algorithm. We evaluate the performance of the proposed method. The results indicate that our method outperforms the previously presented uncoded... 

In this paper, we consider the internally coded time-hopping spread-time multiple access scheme introduced in [1]. We evaluate the performance of the correlator receiver followed by the Viterbi algorithm in fading channel. We analyze the effect of multiple access interference (MAI) and narrowband interference (NBI). We also provide simulation results and further evaluate the performance of the system for the ultra wide band (UWB) application with the UWB channel model specified by the IEEE 802.15.4a group. For comparison, we consider the conventional ST-CDMA system. The results indicate that our method has much better performance while it has the same bandwidth and spectral efficiency as the... 

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... 

We consider multirate time-hopping ultra-wideband (TH-UWB) communication systems where each user can have several multirate services. We investigate both constant spreading factor scheme, which uses multicode, and variable spreading factor scheme, which uses constant chip time and variable frame number. For multicode structure, we consider two methods. In the first, one kind of signature (PN) code is used to distinguish users and their diverse services alike. Whereas in the second one different users and different services of the same user are distinguished through two kinds of signature codes, namely PN code and Walsh code, respectively. For variable spreading factor scheme, one signature... 

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... 

This study presents an efficient fractional frequency reuse scheme for macrocell network which uses six directional antennas to cover the outer region and analyses the performance. Cross-tier interference between macrocell and femtocell networks leading to throughput and outage probability degradation is a major issue in two-tier networks when femtocells are deployed in co-channel with macrocells. In this study, the received interference from the macrocell network to femtocell network is analysed. Then, based on the degree of received interference, an algorithm for orthogonal resource allocation to femtocells with low cross-tier interference is presented. According to the introduced scheme,... 

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,... 

Schizophrenia is a severe brain disease that influences the behaviour and thought of person. These effects may fail in achieving the expected levels of interpersonal, academic, or occupational functioning. Although the underlying mechanism is not yet clear, the early detection of schizophrenia is an attractive and challenging research area. There are differences in brain connections of patients and healthy people. This study presents a new computer-aided diagnosis (CAD) method to diagnose schizophrenia (SZ) patients from normal control (NC) people by using the rest-state functional magnetic resonance imaging (R-fMRI) data. fMRI data has a huge dimension, and extracting efficient features is... 

Device-to-device (D2D) communication improves spectrum efficiency (SE) and increases system capacity. Heterogeneous networks comprise macrocell and several small cells, such as picocells and femtocells, where femtocells are more efficient. In cooperative communications, one or several additional nodes help to send data from source to destination to improve the quality of service (QoS). Network coding (NC) in cooperative networks can extend data rate and coverage area of D2D communication. The purpose of this article is to minimize power consumption of transmitting nodes during network-coded cooperative D2D transmission to reduce the interference on co-channel transmissions. In this study, we... 

Exceptional mechanical properties of carbon nanotubes (CNTs) such as high elastic modulus, stiffness and tensile strength have made them as promising reinforcement in polymer nanocomposite systems. The characteristics of CNTs/polymer interphase region directly affect the efficiency of nanotubes for improving the nanocomposite mechanical properties. In this work, the influence of chains alignment within the interphase region on elastic response of the nanocomposite is assessed using a novel ordered-inordered approach. The applicability of the presented approach is examined by implementing the approach on a series of reported data available in the literature. The effects of CNT content,... 

In this paper, the problem of coarse timing synchronization in orthogonal frequency-division multiplexing (OFDM) systems is investigated, and two new timing metrics with better performance are presented. The new metrics take advantage of two novel differential normalization functions that are based on the fourth-order statistics and are designed depending on the value of carrier frequency offset (CFO). The proposed timing metrics are theoretically evaluated using two different class separability criteria. It is shown that the new schemes considerably increase the difference between the correct and wrong timing points in comparison with previous methods. The computational complexity of the... 

A new time-hopping ultrawideband (TH-UWB) CDMA scheme for indoor wireless communications is presented. In the proposed method, the duration of each bit is divided into Ns1 frames, each one containing Ns2 subframes. Two pseudorandom sequences are assigned to each user. During each bit interval, based on the output of a super-orthogonal encoder and the user's first dedicated pseudorandom sequence, the transmitter selects one of the Ns1 frames and then transmits Ns2 narrow pulses in that frame, one in each of the Ns2 subframes. The location of the pulse in each subframe is determined by the user's second dedicated PN sequence. Four different detection techniques are considered at the receiver...