Search for: beamforming
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    Two layers beamforming robust against direction-of-arrival mismatch

    , Article IET Signal Processing ; Volume 8, Issue 1 , 2014 , Pages 49-58 ; ISSN: 17519675 Rahmani, M ; Bastani, M. H ; Shahraini, S ; Sharif University of Technology
    The presence of the desired signal (DS) in the training snapshots makes the adaptive beamformer sensitive to any steering vector mismatch and dramatically reduces the convergence rate. The objective of the present study is to propose a new adaptive beamformer which is robust against direction-of-arrival (DOA) mismatch and its convergence rate is not sensitive to the presence of the DS. This method is applicable to the arrays with specific structure such as the linear array. Our approach is based on the DS elimination from the training snapshots and the sub-array beamforming technique. To accomplish this goal, a blocking matrix which converts the primary data to the DS-free data is... 

    Robust and rapid converging adaptive beamforming via a subspace method for the signal-plusinterferences covariance matrix estimation

    , Article IET Signal Processing ; Vol. 8, Issue. 5 , July , 2014 , pp. 507-520 ; ISSN: 17519675 Rahmani, M ; Bastani, M. H ; Sharif University of Technology
    The presence of the desired signal (DS) in the training snapshots makes the adaptive beamformer sensitive to any steering vector mismatch and dramatically reduces the convergence rate. Even the performance of the most of the existing robust adaptive beamformers is degraded when the signal-to-noise ratio (SNR) is increased. In this study, a high converging rate robust adaptive beamformer is proposed. This method is a promoted eigenspace-based beamformer. In this paper, a new signal-plus-interferences (SPI) covariance matrix estimator is proposed. The subspace of the ideal SPI covariance matrices is exploited and the estimated covariance matrix is projected into this subspace. This projection... 

    Phased array radar beamforming method based on MIMO radar covariance

    , Article IET Conference Publications ; Volume 2013, Issue 617 CP , 2013 ; 9781849196031 (ISBN) Roshanzamir, A. S ; Bastani, M. H ; Sharif University of Technology
    A multiple input multiple output (MIMO) radar is an emerging field which has attracted many researchers recently. In this type of radar, unlike an standard phased array radar, one can choose transmitted probing signals freely to maximize the power around the locations of the targets of interest, or more generally to approximate a given transmit beam-pattern, or to minimize the cross-correlation of the signals reflected back to the radar by the targets of interest. These signals can be correlated to each other or noncorrelated. Many papers have investigated beampattern design and waveforming in MIMO radars. One of the most famous approaches for beampattern design is named covariance based... 

    Analysing of 3D beamforming in MIMO radars

    , Article Proceedings of the 2012 World Congress on Information and Communication Technologies, WICT 2012 ; 2012 , Pages 745-749 ; 9781467348041 (ISBN) Roshanzamir, A ; Bastani, M. H ; Roshanzamir, M ; Machine Intelligence Research Labs (MIR Labs) ; Sharif University of Technology
    A multiple input multiple output (MIMO) radar system is an emerging research field which has attracted many studies in recent years. This type of radar, unlike conventional phased array radar, can transmit different probing signals via its antennas, that may be correlated or uncorrelated with each other. This waveform diversity offered by MIMO radar systems enable superior capabilities compared to conventional phased array radar. Many papers have introduced different ways for beamforming of MIMO radar. In this paper it is desirable to analysis some methods for beamforming of MIMO radars with planar arrays constellation and examine their 3D result beam-pattern of such constellations for... 

    Rate adaptation and power allocation for time-correlated MISO Rayleigh fading channel with delay-limited HARQ

    , Article IEEE International Conference on Communications, 10 June 2012 through 15 June 2012 ; 2012 , Pages 3915-3919 ; 15503607 (ISSN) ; 9781457720512 (E-ISBN) Rastegar, S. H ; Vakilinia, S ; Khalaj, B. H ; Sharif University of Technology
    In this paper, we consider the problem of optimum rate adaptation and power allocation to maximize the delay-limited throughput (DLT) in a time-correlated 2×1 MISO Rayleigh fading channel with Hybrid ARQ in Chase-Combining mode (HARQ-CC). To this aim, we have first formulated the DLT equation based on the outage probability for 2×1 MISO-HARQ channel. We show that exact analytical calculation of the outage probability is not tractable. Therefore, we approximate the outage probability using a log-normal approximation approach. Based on such approximation, optimal rate and power allocations are derived. Finally, using Monte-Carlo simulation, we show that the approximation method provides... 

    Precoding in relay networks with frequency selective channels

    , Article Conference Record - Asilomar Conference on Signals, Systems and Computers ; 2012 , Pages 537-541 ; 10586393 (ISSN) ; 9781467350518 (ISBN) Schad, A ; Khalaj, B ; Pesavento, M ; Sharif University of Technology
    We consider a wireless network with one source, multiple relays and multiple destinations. The source and the relays are assumed to utilize multiple antennas. To reduce the effects of the frequency selective source-to-relay and relay-to-destination channels, and to compensate for the different delays of the various signal paths in the network and for multi-user interference and noise, the source, the relays and the destinations apply linear filtering to their signals. The proposed scheme generalizes the recently proposed filter-and-forward relaying scheme. We propose an iterative algorithm to solve the problem of maximizing the quality-of-service at the destinations. Simulation results... 

    Design of Digital Block of Receiver Section of Smart Antenna System

    , M.Sc. Thesis Sharif University of Technology Naderi Shahi, Sina (Author) ; Haj Sadeghi, Khosro (Supervisor)
    In recent years with the increase of cellular phone subscribers, demand for high capacity networks is inevitable. For this reason, different methods have been proposed to increase the channel capacity. One method which has become popular in recent years is utilizing of Smart Antenna Systems. Smart antennas basically attempt to enhance the desired signal power and suppress the interferers by beamforming toward the DOA (direction-of-arrival) of the desired signal and nullsteering in the interferences’ DOAs. Smart Antennas first find the direction of signal sources, and then put the main gain toward the desired signal and put the nulls toward unwanted signals. As a result, we can obtain the... 

    Diversity and Error Probability Analysis and Determining the Effect of Non-Ideal Phase Estimation in Amplify-and-Forward and Beamforming Techniques

    , M.Sc. Thesis Sharif University of Technology Safavi, Ebrahim (Author) ; Hossein Khalaj, Babak (Supervisor)
    In this study we investigate the performance of amplify-and-forward (AF) and beamforming schemes in wireless networks. In our study we consider a general cooperative network consisting one transmit-receive pair and an arbitrary number of relays in which each relay has a separate power constraint. A two-step master-slave protocol is deployed in which at the first stage, relays listen to the transmitter and at the second stage, relays forward the recently received signal coherently. Main contributions of this dissertation are providing the exact closed-form of bit error rate analysis in the case of general AF networks, providing an integral-form upper bound of error probability of network... 

    Interference Reduction and Cancellation by Beamforming in Cognitive Radios

    , M.Sc. Thesis Sharif University of Technology Gavili Gilan, Adnan (Author) ; Nasiri Kenari, Masoumeh (Supervisor)
    Cognitive Radio (CR), as a new concept to efficiently utilize a licensed spectrum, and this has received intensive attension in recent years. By applying the cognitive technique, an unlicensed user (the secondary user (SU)) is allowed to transmit at the Primary User’s (PU) spectrum band under some conditions. Different approaches have been introduced to be utilized by the SU in order to be able to efficiently transmit at the PR’s spectrum without any sustainsial destructive effects on PR transmission and reception, which one of them is using multiple antenna in the cognitive transmitter. Hereby, CR is able to increase its throughput without substansial harmfull effect on PR’ transmission by... 

    MIMO Radars Waveform Design

    , M.Sc. Thesis Sharif University of Technology Shadi, Kamal (Author) ; Behnia, F (Supervisor)
    MIMO radar is a next generation radar which transmits arbitrary waveforms at each one of its apertures. It has been shown that design of waveforms for MIMO radars in order to synthesize a desired spatial beampattern, is mapped into a waveform correlation matrix (R) design in the narrowband case. Therefore, waveform design in MIMO radar for beamforming could be broken into two steps, namely correlation matrix design and waveform synthesis for achieving given R. As of now, given a desired beampattern or estimated location information of targets, calculating R has been modeled as an optimization problem like SDP. Also, in some special cases like rectangular beampattern, close form solutions for... 

    Direction of Arrival Estimation and Digital Beamforming in the Presence of Mutual Coupling Effects and Implementation

    , Ph.D. Dissertation Sharif University of Technology Emadi, Mohammad (Author) ; Haj Sadeghi, Khosrow (Supervisor)
    Different beamforming methods are prevalent in wireless and mobile communication systems. However, a lot of practical issues, such as the quality of these methods in compact arrays and the huge computational burden are the major defects of the proposed methods. These problems restrict most of the algorithms to the theoretical domain and render them anappropriate for commercial applications. Therefore, the major focus of this thesis is on the practical issues in the implementation of the digital beam steering and direction of arrival estimation systems for linear, circular and random array configurations. To do so, compact arrays with super directivity are presented and considered. Different... 

    Designi an Adaptive Beamforming Algorithm, Robust Against Direction-of-Arrival Mismatch

    , M.Sc. Thesis Sharif University of Technology Rahmani, Mostafa (Author) ; Bastani, Mohammad Hasan (Supervisor)
    Adaptive beamforming performance is very sensitive to any mismatch between actual and presumed steering vectors of desired signal. In addition to this sensitivity, presence of desired signal in training snapshots dramatically reduces the convergence rate, as compared to the case that signal-free training snapshots are available.
    The present work is aimed at proposing a new adaptive beamformer that is robust against direction-of-arrival (DOA) mismatch and has high convergence rate. This method is based on desired signal elimination from training snapshots and sub-array beamforming technique. To this end, a Blocking matrix that converts primary data to desired signal free data is... 

    Interference Avoidance Algorithms in Cognitive Radio Networks and Performance Analysis

    , M.Sc. Thesis Sharif University of Technology Mohammadbeiki, Akram (Author) ; Nasiri Kenari, Masoumeh (Supervisor)
    Cognitive radio faces specific challenges due to its special spectrum access scheme. Providing required QoS and preventing irrecoverable interference on the primary users is among the crucial requirements. Beam forming is one of the interference avoidance schemes utilized in MIMO networks. Most of the studies on this scheme assume that each symbol is transmitted via vectors in order to grant desired beam forming and specific combinations in the receiver. Since transmitting multiple symbols at every transmission can provide higher data rates, it seems necessary to exploit beam forming through matrixes instead of vectors. In this thesis, by neglecting the interference of the secondary user,... 

    Beamforming Through Array Thinning

    , M.Sc. Thesis Sharif University of Technology Tohidi, Ehsan (Author) ; Nayebi, Mohammad Mahdi (Supervisor)
    Modern communication and space systems such as satellite communication devices, radars, SAR and radio astronomy interferometers are realized with large antenna arrays since this kind of radiating systems are able to generate radiation patterns with high directivity and resolution. In such a framework, conventional arrays with uniform inter-element spacing could be not satisfactory in terms of costs and dimensions. An interesting alternative is to reduce the array elements obtaining the so called ‘ thinned arrays’. Large thinned arrays have been exploited because of their advantages in terms of weight,consumption, hardware complexity, and cost over the... 

    Design and Simulation of Smart Patch Antenna Array in 2.4 GHz band

    , M.Sc. Thesis Sharif University of Technology Hosseini, Mahdi (Author) ; Farzaneh, Forouhar (Supervisor)
    Over the past few years , demand for wireless communication services have grown at a formidable rate. As such we need to find new ways to support more and more wireless users in a confined space. this means that the capacity of networks should be significantly increased to overcome formidable rate of subscribers growth. That is why the smart antennas have become very popular in communication systems. Smart antennas are a kind of adaptive antenna arrays with smart signal processing algorithms used to find direction of arrival(DOA) of the signal, and use it to calculate suitable weights to direct the antenna beam on the desired user and nulling interferences. In this thesis, DOA estimation... 

    Analysis and Design of a Multi-Beam Millimeter-Wave Antenna

    , M.Sc. Thesis Sharif University of Technology Kazemi, Hamid Reza (Author) ; Borji, Amir (Supervisor)
    So far, Investigations have shown that microstrip antennas (MSA) offer a lot of advantages at microwave and millimeter wave frequencies. These advantages include small size, large impedance bandwidth, high radiation efficiency, ease of fabrication, low price, and simple and easy excitation (such as probe coupling,aperture coupling or proximity coupling).Microstrip antennas are fabricated in many different shapes such as square,rectangle, circle, etc. The proposed antenna in this dissertation is a multi-beam millimeter wave antenna with annular ring strip. This antenna is a multi-beam antenna with the ability to switch between different beams. Beam direction switches by changing the position... 

    Distributed synchronization and beamforming in uplink relay asynchronous OFDMA CoMP networks

    , Article IEEE Transactions on Wireless Communications ; Volume 14, Issue 6 , 2015 , Pages 3471-3480 ; 15361276 (ISSN) Pilaram, H ; Kiamari, M ; Khalaj, B. H ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    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... 

    Performance evaluation of asynchronous multi-carrier code division multiple access for next-generation long-reach fibre optic access networks

    , Article IET Optoelectronics ; Volume 9, Issue 6 , 2015 , Pages 325-332 ; 17518768 (ISSN) Shoreh, M. H ; Beyranvand, H ; Salehi, J. A ; Sharif University of Technology
    Institution of Engineering and Technology  2015
    In this study, the authors evaluate the performance of asynchronous optical multi-carrier code division multiple access (MC-CDMA) for intensity modulated/direct detection systems to be used in next-generation optical access networks. The proposed system employs Gold sequence in frequency-domain to provide asynchronous resource sharing. In long-reach passive optical networks, fibre impairments degradation to the performance of ordinary optical CDMA can be avoided by frequency-domain digital compensation methods in the proposed MC-CDMA. In comparison with orthogonal frequency division multiple access, peak-to-average power ratio in the proposed MC-CDMA is reduced and asynchronous resource... 

    Secure Communication via Cooperation and Cooperative Jamming

    , M.Sc. Thesis Sharif University of Technology Hatami, Mohammad (Author) ; Behroozi, Hamid (Supervisor)
    The broadcast nature of wireless communications makes the propagation medium vulnerable to security attacks such as eavesdropping and jamming from adversarial or unauthorized users. Applying physical layer secrecy approaches will enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers, without using any secret keys. However, physical layer security approaches are typically feasible only when the source-eavesdropper channel is weaker than the source-destination channel. Cooperative jamming can be used to overcome this challenge and increase the secrecy rate. In this thesis, the security of two-phase relaying system with multiple... 

    Cooperative transmission for wireless relay networks using limited feedback

    , Article IEEE Transactions on Signal Processing ; Volume 58, Issue 7 , Jun , 2010 , Pages 3828-3841 ; 1053587X (ISSN) Paredes, J. M ; Khalaj, B. H ; Gershman, A. B ; Sharif University of Technology
    To achieve the available performance gains in half-duplex wireless relay networks, several cooperative schemes have been earlier proposed using either distributed space-time coding or distributed beamforming for the transmitter without and with channel state information (CSI), respectively. However, these schemes typically have rather high implementation and/or decoding complexities, especially when the number of relays is high. In this paper, we propose a simple low-rate feedback-based approach to achieve maximum diversity with a low decoding and implementation complexity. To further improve the performance of the proposed scheme, the knowledge of the second-order channel statistics is...