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Interference Reduction and Cancellation by Beamforming in Cognitive Radios
, M.Sc. Thesis Sharif University of Technology ; Nasiri Kenari, Masoumeh (Supervisor)
Abstract
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...
Probability of missed detection as a criterion for receiver placement in MIMO PCL
, Article IEEE National Radar Conference - Proceedings, 7 May 2012 through 11 May 2012, Atlanta, GA ; 2012 , Pages 0924-0927 ; 10975659 (ISSN) ; 9781467306584 (ISBN) ; Chitgarha, M. M ; Radmard, M ; Nayebi, M. M ; Sharif University of Technology
IEEE
2012
Abstract
Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar
Integer forcing-and-forward transceiver design for MIMO multipair two-way relaying
, Article IEEE Transactions on Vehicular Technology ; Volume 65, Issue 11 , 2016 , Pages 8865-8877 ; 00189545 (ISSN) ; Nasiri Kenari, M ; Maham, B ; Hejazi, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2016
Abstract
In this paper, we propose a new transmission scheme, called integer forcing-and-forward (IFF), for communications among multipair multiple-antenna users in which each pair exchanges their messages with the help of a single multiple-antenna relay in the multiple-access and broadcast phases. The proposed scheme utilizes integer forcing linear receiver (IFLR) at the relay, which uses equations, i.e., linear integer combinations of messages, to harness intrapair interference. Accordingly, we propose the design of a mean square error (MSE)-based transceiver, including precoder and projection matrices for the relay and users, assuming that perfect channel state information (CSI) is available. In...
Antenna placement and power allocation optimization in MIMO detection
, Article IEEE Transactions on Aerospace and Electronic Systems ; Vol. 50, Issue 2 , April , 2014 , pp. 1468-1478 ; Chitgarha, M. M ; Majd, M. N ; Nayebi, M. M ; Sharif University of Technology
Abstract
It is a well known fact that using multiple antennas at transmit and receive sides improves the detection performance. However, in such multiple-input multiple-output (MIMO) configuration, proper positioning of transmitters and receivers is a big challenge that can have significant influence on the performance of the overall system. In addition, determining the power of each transmitter under a total power constraint is a problem that should be solved in order to enhance the performance and coverage of such a system. In this paper, we design the Neyman-Pearson detector under the Rayleigh scatter model and use it to introduce a criterion for the antenna placement at both transmit and receive...
Spectrum Sensing in Cognitive Radio Networks
, Ph.D. Dissertation Sharif University of Technology ; Nasiri Kenari, Masoumeh (Supervisor)
Abstract
In this thesis, we consider the problem of spectrum sensing in cognitive radio networks. First, the collaborative energy detectors based spectrum sensing are investigated in the case of known noise variance for two models of primary user (PU) signal, i.e. random and unknown deterministic signals. Since the derived optimum collaborative energy detector requires the signal-to-noise ratio (SNR) of secondary users (SU) and it has complex structure, the generalized likelihood ratio (GLR) detector is proposed for both models of PU signal which leads to the same decision rules for both models. Simulation results show that the performance of the proposed GLR detector is near to that of optimal...
Ambiguity function of MIMO radar with widely separated antennas
, Article Proceedings International Radar Symposium ; 16 -18 June , 2014 ; ISSN: 21555753 ; Chitgarha, M. M ; Nazari Majd, M ; Nayebi, M. M ; Sharif University of Technology
Abstract
There has been much interest, recently, towards exploiting the Multiple-Input Multiple-Output (MIMO) technique in radar. It is shown that using multiple antennas at transmit and receive sides can improve the performance of the system. However, in order to analyze the system's performance, its ambiguity function, i.e. the ambiguity function of a MIMO radar, is needed to be defined. In this paper, beginning from the information theoretic definitions, we derive such function, specifically for a MIMO radar with widely separated antennas
Multi-antenna coded caching
, Article IEEE International Symposium on Information Theory - Proceedings, 25 June 2017 through 30 June 2017 ; 2017 , Pages 2113-2117 ; 21578095 (ISSN) ; 9781509040964 (ISBN) ; Caire, G ; Khalaj, B. H ; Sharif University of Technology
Abstract
In this paper we consider a single-cell downlink scenario where a multiple-antenna base station delivers contents to multiple cache-enabled user terminals. Based on the multicasting opportunities provided by the so-called Coded Caching technique, we investigate three delivery approaches. Our baseline scheme employs the coded caching technique on top of max-min fair multicasting. The second one consists of a joint design of Zero-Forcing (ZF) and coded caching, where the coded chunks are formed in the signal domain (complex field). The third scheme is similar to the second one with the difference that the coded chunks are formed in the data domain (finite field). We derive closed-form rate...
Linear multicast beamforming schemes for coded caching
, Article 52nd Asilomar Conference on Signals, Systems and Computers, ACSSC 2018, 28 October 2018 through 31 October 2018 ; Volume 2018-October , 2019 , Pages 172-176 ; 10586393 (ISSN); 9781538692189 (ISBN) ; Kaleva, J ; Shariatpanahi, S. P ; Khalaj, B ; Matthews M. B ; Sharif University of Technology
IEEE Computer Society
2019
Abstract
A single cell downlink scenario is considered, where a multiple-antenna base station delivers contents to cache-enabled user terminals. Depending on the available degrees of freedom, several multicast messages are transmitted in parallel to distinct subsets of users. In the multicast beamformer design, we restrict ourselves to linear receiver implementation, which does not require successive interference cancellation unlike in the more optimal baseline scheme. With a small loss in performance, the complexity of both the receiver and transmitter implementation can be significantly reduced. © 2018 IEEE
Linear decoupled and quasi-decoupled space-time codes
, Article IEEE Transactions on Communications ; Volume 55, Issue 1 , 2007 , Pages 54-59 ; 00906778 (ISSN) ; Khalaj, B. H ; Shamsi, M ; Sharif University of Technology
2007
Abstract
Space-time transmit diversity results in coupling of transmitted symbols across different antennas, which increases the complexity of maximum-likelihood decoding. Symbol coupling can be completely or partially avoided if the space-time code (STC) satisfies specific decoupling conditions; examples of such codes are orthogonal space-time block codes and quasi-orthogonal codes. In this letter, we study decoupling conditions for a linear full-diversity STC. Quasi-decoupled codes are proposed as a partially decoupled full-diversity STC of any rate for any number of transmit antennas with minimum decoding delay. By optimizing the coding gain of quasi-decoupled codes, it is shown that...
Two dimensional sensing for cognitive radio applications using antenna array
, Article APMC 2009 - Asia Pacific Microwave Conference 2009, 7 December 2009 through 10 December 2009, Singapore ; 2009 , Pages 2777-2780 ; 9781424428021 (ISBN) ; Forooragh, K ; Ahmadi, A. F ; Atlasbaf, Z ; Sharif University of Technology
Abstract
Fast, accurate and efficient sensing is of important aspects in cognitive radio technology. We propose a simple, practical design for two-dimensional sensing in spectral and spatial domain. In fact detection and localization of signal are done in a wide band elliptical array. Two sets of phase differences help to fast calculation of frequency and angle of arrival. We study the constraints, advantages and accuracy of the method. ©2009 IEEE
Sparse Channel Estimation in Multi-user OFDM Systems
, Ph.D. Dissertation Sharif University of Technology ; Hossinen Khalaj, Babak (Supervisor) ; Amini, Arash (Supervisor)
Abstract
Channel equalization is a crucial part of the OFDM communications protocols, which in turn requires channel estimation. Pilot-based methods are one the most popular channel estimation approaches in OFDM systems. The pilot signals are generally classified as orthogonal and nonorthogonal pilots. Orthogonal pilots can better estimate the channels and are widely used in communications systems. The number of orthogonal pilots is proportional to the number of transmitters. Therefore, utilizing orthogonal pilots are not amenable for the increasing number of users in communications systems and the emerging of new technologies such as Massive-MIMO employing a large number of antennas. Consequently,...
Real interference alignment: Exploiting the potential of single antenna systems
, Article IEEE Transactions on Information Theory ; Vol. 60, issue. 8 , 2014 , pp. 4799-4810 ; Oveis-Gharan, S ; Maddah-Ali, M. A ; Khandani, A. K ; Sharif University of Technology
Abstract
In this paper, we develop the machinery of real interference alignment. This machinery is extremely powerful in achieving the sum degrees of freedom (DoF) of single antenna systems. The scheme of real interference alignment is based on designing single-layer and multilayer constellations used for modulating information messages at the transmitters. We show that constellations can be aligned in a similar fashion as that of vectors in multiple antenna systems and space can be broken up into fractional dimensions. The performance analysis of the signaling scheme makes use of a recent result in the field of Diophantine approximation, which states that the convergence part of the...
Receivers' positioning in multiple-input multiple-output digital video broadcast-terrestrial-based passive coherent location
, Article IET Radar, Sonar and Navigation ; Volume 6, Issue 7 , 2012 , Pages 603-610 ; 17518784 (ISSN) ; Khalaj, B. H ; Chitgarha, M. M ; Nazari Majd, M ; Nayebi, M. M ; Sharif University of Technology
IEEE
2012
Abstract
Using multiple illuminators of opportunity at the transmit side and multiple antennas at the receiver side in a passive coherent location (PCL) scheme is expected to improve the detection performance. However, in such multiple-input multiple-output (MIMO) configuration choosing the position of the receivers is an obstacle that can have significant influence on the resulting performance. In this study, the authors consider the case of digital video broadcast (DVB)-T stations as non-cooperative transmitters and introduce a procedure based on the probability of missed detection to properly place receive antennas in a MIMO digital video broadcasting (DVB)-T based PCL configuration
Data association in multi-input single-output passive coherent location schemes
, Article IET Radar, Sonar and Navigation ; Volume 6, Issue 3 , 2012 , Pages 149-156 ; 17518784 (ISSN) ; Karbasi, S. M ; Khalaj, B. H ; Nayebi, M. M ; Sharif University of Technology
2012
Abstract
Efficient combination of multiple input multiple output (MIMO) and passive coherent location (PCL) ideas is expected to improve performance of localisation schemes. While using multiple antennas at transmit and receive sides provides spatial diversity, it is possible to obtain similar performance by using multiple transmitters, already transmitting standard signals (such as digital TV) in the environment (also known as illuminators of opportunity). However, in this case, it is not always possible to ensure that signals of different transmitters are orthogonal to each other. In such cases, resolving signals of multiple transmitters reflected from multiple objects is not a trivial problem. One...
MIMO localization by illuminators of opportunity
, Article Proceedings of 2011 IEEE CIE International Conference on Radar, RADAR 2011, 24 October 2011 through 27 October 2011 ; Volume 1 , October , 2011 , Pages 112-115 ; 9781424484416 (ISBN) ; Karbasi, S. M ; Nayebi, M. M ; Sharif University of Technology
2011
Abstract
Passive localization using MIMO techniques has attracted much attention recently. In such schemes, using multiple antennas at transmitter and receiver sides provides spatial diversity without need for identifiable transmitters. On the other hand, one of the problems facing such approach arises when transmitters of a single frequency network (SFN) are used as non-cooperative transmitters and resolving the signals of multiple transmitters reflected from multiple targets is not trivial at receiver side. Therefore, in order to obtain the diversity gain of MIMO localization schemes, it is necessary to develop a technique to assign each echo arriving at the receiver to a given transmitter. In this...
Diversity gain in MIMO passive coherent location
, Article International Radar Symposium, IRS 2011 - Proceedings, 7 September 2011 through 9 September 2011 ; September , 2011 , Pages 841-848 ; 9783927535282 (ISBN) ; Karbasi, S. M ; Nayebi, M. M ; Sharif University of Technology
2011
Abstract
MIMO (Mulitple Input Multiple Output) localization has attracted much attention recently. In such schemes, using multiple antennas at transmitter and receiver sides provides spatial diversity. On the other hand, Passive Coherent Location (PCL) by using the illuminators of opportunity (such as FM, GSM, DVB transmitters) has shown a number of advantages. In this paper, we explore the possibility of achieving diversity gain by using multiple non-cooperative transmitters. In earlier works on MIMO localization, cooperative transmitters were assumed, so that orthogonality between transmitted waveforms could be granted. However, such orthogonality condition is not assumed in the case of PCL...
Multiple antenna spectrum sensing in cognitive radios
, Article IEEE Transactions on Wireless Communications ; Volume 9, Issue 2 , 2010 , Pages 814-823 ; 15361276 (ISSN) ; Nasiri-Kenari, M ; Gazor, S ; Sharif University of Technology
2010
Abstract
In this paper, we consider the problem of spectrum sensing by using multiple antenna in cognitive radios when the noise and the primary user signal are assumed as independent complex zero-mean Gaussian random signals. The optimal multiple antenna spectrum sensing detector needs to know the channel gains, noise variance, and primary user signal variance. In practice some or all of these parameters may be unknown, so we derive the Generalized Likelihood Ratio (GLR) detectors under these circumstances. The proposed GLR detector, in which all the parameters are unknown, is a blind and invariant detector with a low computational complexity. We also analytically compute the missed detection and...
Ambiguity function based receiver placement in multi-site radar
, Article 2016 CIE International Conference on Radar, RADAR 2016, 10 October 2016 through 13 October 2016 ; 2017 ; 9781509048281 (ISBN) ; Chitgarha, M. M ; Nazari Majd, M ; Nayebi, M. M ; Sharif University of Technology
Abstract
It has been shown that using multiple antennas in a radar system improves the performance considerably, since multiple target echoes are received from different aspect angles of the target. In this way, the target detection is improved. However, when using multiple antennas, some problems, such as designing the transmit signals, synchronization, etc. emerge that should be solved. One of such problems is the receiver placement. Receiver placement deals with choosing a proper position for the receive antenna in order to optimize the whole system's performance. In this paper, a receiver placement procedure based on improving the radar ambiguity function is proposed for the case of a multisite...
Characterization of degrees of freedom versus receivers backhaul load in K-user interference channel
, Article IEEE International Symposium on Information Theory - Proceedings, 25 June 2017 through 30 June 2017 ; 2017 , Pages 1431-1435 ; 21578095 (ISSN) ; 9781509040964 (ISBN) ; Maddah Ali, M. A ; Shariatpanahi, S. P ; Khalaj, B. H ; Sharif University of Technology
Abstract
We consider a K-user Interference Channel where each transmitter is interested in conveying a message to its corresponding receiver. In addition, we assume a fully connected noiseless backhaul network through which receivers can collaborate and help each other recover their desired messages. In this paper, we fully characterize the trade-off between the rate in wireless link (per user) in terms of degrees of freedom (DoF) versus backhaul load (per user) for large values of K. In particular, we characterize the optimal trade-off for all values of K, where K is an even number. For odd values of K, we characterize the trade-off within a gap of 2(k - 1)/k(k + 1), which goes to zero as K...
Multicast beamformer design for coded caching
, Article IEEE International Symposium on Information Theory - Proceedings, 17 June 2018 through 22 June 2018 ; Volume 2018-June , 2018 , Pages 1914-1918 ; 21578095 (ISSN) ; 9781538647806 (ISBN) ; Shariatpanahi, S. P ; Kaleva, J ; Khalaj, B ; Sharif University of Technology
Abstract
A single cell downlink scenario is considered where a multiple-antenna base station delivers contents to cache-enabled user terminals. Using the ideas from multi-server coded caching (CC) scheme developed for wired networks, a joint design of CC and general multicast beamforming is considered to benefit from spatial multiplexing gain, improved interference management and the global CC gain, simultaneously. The proposed multicast beamforming strategies utilize the multiantenna multicasting opportunities provided by the CC technique and optimally balance the detrimental impact of both noise and inter-stream interference from coded messages transmitted in parallel. The proposed scheme is shown...