... S. Salari, M. Ahmadian, and M. Ardebilipour V. Meghdadi, and JP Cances KN Toosi University of... more ... S. Salari, M. Ahmadian, and M. Ardebilipour V. Meghdadi, and JP Cances KN Toosi University of Technology, Tehran, Iran University of Limoges, ENSIL, France E-mail:{salari,mahmoud,mehrdad}@eetd.kntu.ac.ir {meghdadi,cances}@ensil.unilim.fr Abstract ...
ABSTRACT The design of expectation-maximisation (EM)-based turbo receivers for low-density parity... more ABSTRACT The design of expectation-maximisation (EM)-based turbo receivers for low-density parity-check-coded multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems with the presence of carrier-frequency offset (CFO) is studied. First, starting from the maximum-likelihood principle, a novel EM-based CFO estimator for MIMO-OFDM systems is devised. This estimator iteratively provides the CFO estimate with the aid of pilot symbols. It is also capable of accommodating any space-time-coded-OFDM transmission. Then this CFO estimator is incorporated into the initialisation step of the turbo receiver. Simulation results show the effectiveness of the receiver design in combating CFO over unknown frequency-selective fading channels.
In this paper, we propose a multiple relay selection scheme, which allocates the global power opt... more In this paper, we propose a multiple relay selection scheme, which allocates the global power optimally to best relays which are selected to maximize signal to noise (SNR) ratio. First, all available relays are sorted from the highest priority to the lowest priority to cooperate in transmission by using the idea of relay ordering. Then, the total relay power is allocated optimally to different sets of relays to maximize received SNR. Finally, a relay set which is resulted in the highest SNR subject to total relay power constraint is selected. Simulation results show that proposed scheme provides full diversity and considerably better performance than schemes assume all relay nodes participate with same global power constraint. In addition, less relays are engaged in transmission, while the relay selection scheme has linear complexity.
In this paper, a novel approach to filter-and-forward relay beamforming in an underlay based cogn... more In this paper, a novel approach to filter-and-forward relay beamforming in an underlay based cognitive two-way relay network with frequency selective channels is proposed. In our scheme, two secondary transceivers communicate which other through multiple relays simultaneously with the primary network transmission over same spectrum. Such a network suffers from both inter-symbol interference (ISI) and bidirectional interference between networks. Our proposed approach mitigates these two types of interference by minimizing the peak interference power from the secondary network to the primary network subject to the quality of service (QoS) requirements for both secondary transceivers. Simulation results show that the proposed technique improves system performance considerably in frequency selective environments in comparison to the traditional amplify-and-forward strategy.
Cooperative diversity has been recently proposed as a technique to form virtual antenna arrays in... more Cooperative diversity has been recently proposed as a technique to form virtual antenna arrays in systems with single-antenna nodes. The Amplify-and-Forward (AF) relaying strategy is one of the most popular cooperative diversity schemes due to its low complexity. Selection AF (SAF) relaying, single or multiple relay selection, has recently been proven to achieve the same diversity order as and lower power consumption than All-Participate (AP) networks. Most SAF methods assume constant power for best relay(s), regardless of channel conditions. In these methods relay(s) with weak channels amplify received signal with considerable gain that cause reduction of performance. In this paper, we propose single and multiple relay selection strategies for two-hop relay networks. In the first part of paper, we specify factor of each relay based on MMSE criterion and relay with highest SNR is chosen for cooperation. Our simulation results show that performance of this method is better than previous works. Second part of this paper proposes selection of two, three or any number of relays and uses them. As we see in the simulation results double relay selection has better performance than single relay selection, triple than double and so on and diversity order of all is complete.
Abstract In this paper, we propose a distributed relay beam-forming design in an underlay based c... more Abstract In this paper, we propose a distributed relay beam-forming design in an underlay based cognitive relay network. In the proposed approach, beamforming coefficients of the secondary relays are obtained through minimization of the peak interference power inflicted on the primary receiver subject to the signal to noise-interference ratio (SINR) constraint at the secondary destination. We prove that the proposed scheme lead to a closed-form solution. Simulation results show that our relay beamforming improve system performance ...
In this chapter, we propose a new scheme for maximum-likelihood (ML) estimation of both carrier-f... more In this chapter, we propose a new scheme for maximum-likelihood (ML) estimation of both carrier-frequency offset (CFO) and channel coefficients in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems, assuming that a training sequence is available. Our scheme is also capable to accommodate any space–time coded (STC)-OFDM transmission. Furthermore, the Cramer–Rao bounds (CRBs) for both CFO and channel estimators are developed to evaluate the performance of the proposed scheme. The simulation results show that the proposed algorithm achieves almost ideal performance compared with the CRB for both channel and frequency offset estimations.
In this study, the problem of blind channel estimation for single-input single-output (SISO) orth... more In this study, the problem of blind channel estimation for single-input single-output (SISO) orthogonal frequency-division multiplexing (OFDM) systems, is considered. Based on auto-correlation matrix, we develop a precoding-assisted blind channel estimation algorithm which is suitable for practical SISO-OFDM applications. Compared to the popular subspace-based blind channel estimation methods, the proposed algorithm is much more computationally efficient. Simulation results show that
The problem of blind channel estimation in Multiple-Input-Multiple-Output (MIMO) Orthogonal Frequ... more The problem of blind channel estimation in Multiple-Input-Multiple-Output (MIMO) Orthogonal Frequency-Division Multiplexing (OFDM) systems is investigated in this study, assuming that the transmitted symbols are independent and identically distributed. In particular, by utilizing a generalized linear non-redundant precoder, a simple blind channel estimation technique for MIMO-OFDM systems is developed. A novel contribution is that instead of using only one column of the signal covariance matrix, as done in previous works, proposed estimator jointly considers all the information contained in the signal covariance matrix. Comparisons show that the proposed approach outperforms the existing estimators. It is also noticed that the proposed algorithm is much more computationally efficient. Consequently, the proposed method is a promising blind channel estimation candidate for MIMO-OFDM systems.
The problem of joint carrier frequency offset (CFO) and channel estimation in orthogonal frequenc... more The problem of joint carrier frequency offset (CFO) and channel estimation in orthogonal frequency division multiplexing (OFDM) systems is investigated in this study. The exact solution to this problem turns out to be too complex for practical purposes. To overcome this difficulty, we resort to the recursive least square (RLS) algorithm and propose an iterative scheme which iterates between estimating the channel parameters and the frequency offset. This results in an estimation algorithm of a reasonable complexity which is suitable for practical applications.
In this paper, we propose an Amplify-and-Forward (AF) Orthogonal Frequency Division Multiplexing ... more In this paper, we propose an Amplify-and-Forward (AF) Orthogonal Frequency Division Multiplexing (OFDM) relay scheme that each relay superimposes its own pilot symbol (PS) such that, individual relay channels can be estimated at the destination. We derive optimal PS designs including both Modification Diagonal Matrix (MDM) and superimposed PS at each relay. These designs are based on channel Mean Square-Error (MSE) minimization and Inter-Relay Interference (IRI) elimination, equivalently. It is shown that the number of relays should satisfy the condition, M <; (N/2(2L-1)), where N and L are the OFDM size and channel order, respectively, and (a) is the maximum integer part of a. Both Least-Square (LS) and linear minimum MSE channel estimators are derived. Furthermore, the estimator according to uncertain data and approximate computations is derived from an efficient convex optimization problem.
In this paper, we study the design of expectation-maximization (EM)-based iterative receivers for... more In this paper, we study the design of expectation-maximization (EM)-based iterative receivers for low-density parity check -coded multiple-input multiple-output orthogonal frequency-division multiplexing systems with the presence of carrier-frequency offset (CFO). First, starting from the maximum-likelihood principle, we devise a novel EM-based pilot-aided scheme for joint estimation of CFO and channel coefficients. Then, this estimator is incorporated into the initialization step of the iterative receiver. Simulation results show the effectiveness of our receiver design in combating CFO over unknown frequency selective fading channels.
Summary from only given. In this paper, we consider the cooperative spectrum sensing when the lin... more Summary from only given. In this paper, we consider the cooperative spectrum sensing when the links between primary user and CRs are subject to log-normal shadow fading and there is also noise uncertainty which is modeled as log-normal. The objective is to evaluate the performance of Equal Gain Combining (EGC) of local observations and propose a novel cluster-based algorithm to reduce the reporting channel bandwidth. In our proposed method, CRs in each group sense the spectrum in a distributive manner by the help of EGC method and send the hard decisions to the fusion center where final decision will be make by a simple counting rule. Lower bandwidth of reporting channel is the main advantage of the proposed method.
In this paper, two novel approaches to filter-and-forward beamforming (FF-BF) in an underlay base... more In this paper, two novel approaches to filter-and-forward beamforming (FF-BF) in an underlay based relay-assisted cognitive network with frequency-selective channels are proposed. In our scheme, secondary users are allowed to transmit through multiple relays simultaneously with primary users over the same spectrum. Such a network suffers from both inter-symbol interference (ISI) and bidirectional interference between the networks. We design FF-BF coefficients of the relays to mitigate these two types of interference. Simulation results show that the proposed approaches improve system performance considerably in frequency-selective environments in comparison to the conventional amplify-and-forward beamforming strategy.
In this paper, we propose a new scheme for joint maximum- likelihood (ML) estimation of carrier-f... more In this paper, we propose a new scheme for joint maximum- likelihood (ML) estimation of carrier-frequency offset (CFO) and channel coefficients in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. To reduce the prohibitive computational complexity of joint ML estimation problems, the expectation- maximization (EM) algorithm is employed. Moreover, the Cramer-Rao bounds (CRB) for both CFO and channel estimators
... S. Salari, M. Ahmadian, M. Ardebilipour, V. Meghdadi*, and JP Cances* KN Toosi Universit... more ... S. Salari, M. Ahmadian, M. Ardebilipour, V. Meghdadi*, and JP Cances* KN Toosi University of Technology, Tehran, Iran E-mail:{salari, mahmoud, mehrdad}@eetd.kntu.ac.ir * University of Limoges, Ensil-Geste, France E-mail:{meghdadi, cances}@ensil.unilim.fr ...
In this paper, we investigate the problem of carrier frequency-offset (CFO) synchronization and c... more In this paper, we investigate the problem of carrier frequency-offset (CFO) synchronization and channel estimation in orthogonal frequency-division multiple access (OFDMA) systems operating over unknown frequency-selective fading channels. We first devise a novel iterative method for joint CFO and channel estimation, based on the time-domain training blocks. The proposed joint estimator consists of two recursive least-square (RLS) algorithms. We then
... S. Salari, M. Ahmadian, and M. Ardebilipour V. Meghdadi, and JP Cances KN Toosi University of... more ... S. Salari, M. Ahmadian, and M. Ardebilipour V. Meghdadi, and JP Cances KN Toosi University of Technology, Tehran, Iran University of Limoges, ENSIL, France E-mail:{salari,mahmoud,mehrdad}@eetd.kntu.ac.ir {meghdadi,cances}@ensil.unilim.fr Abstract ...
ABSTRACT The design of expectation-maximisation (EM)-based turbo receivers for low-density parity... more ABSTRACT The design of expectation-maximisation (EM)-based turbo receivers for low-density parity-check-coded multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems with the presence of carrier-frequency offset (CFO) is studied. First, starting from the maximum-likelihood principle, a novel EM-based CFO estimator for MIMO-OFDM systems is devised. This estimator iteratively provides the CFO estimate with the aid of pilot symbols. It is also capable of accommodating any space-time-coded-OFDM transmission. Then this CFO estimator is incorporated into the initialisation step of the turbo receiver. Simulation results show the effectiveness of the receiver design in combating CFO over unknown frequency-selective fading channels.
In this paper, we propose a multiple relay selection scheme, which allocates the global power opt... more In this paper, we propose a multiple relay selection scheme, which allocates the global power optimally to best relays which are selected to maximize signal to noise (SNR) ratio. First, all available relays are sorted from the highest priority to the lowest priority to cooperate in transmission by using the idea of relay ordering. Then, the total relay power is allocated optimally to different sets of relays to maximize received SNR. Finally, a relay set which is resulted in the highest SNR subject to total relay power constraint is selected. Simulation results show that proposed scheme provides full diversity and considerably better performance than schemes assume all relay nodes participate with same global power constraint. In addition, less relays are engaged in transmission, while the relay selection scheme has linear complexity.
In this paper, a novel approach to filter-and-forward relay beamforming in an underlay based cogn... more In this paper, a novel approach to filter-and-forward relay beamforming in an underlay based cognitive two-way relay network with frequency selective channels is proposed. In our scheme, two secondary transceivers communicate which other through multiple relays simultaneously with the primary network transmission over same spectrum. Such a network suffers from both inter-symbol interference (ISI) and bidirectional interference between networks. Our proposed approach mitigates these two types of interference by minimizing the peak interference power from the secondary network to the primary network subject to the quality of service (QoS) requirements for both secondary transceivers. Simulation results show that the proposed technique improves system performance considerably in frequency selective environments in comparison to the traditional amplify-and-forward strategy.
Cooperative diversity has been recently proposed as a technique to form virtual antenna arrays in... more Cooperative diversity has been recently proposed as a technique to form virtual antenna arrays in systems with single-antenna nodes. The Amplify-and-Forward (AF) relaying strategy is one of the most popular cooperative diversity schemes due to its low complexity. Selection AF (SAF) relaying, single or multiple relay selection, has recently been proven to achieve the same diversity order as and lower power consumption than All-Participate (AP) networks. Most SAF methods assume constant power for best relay(s), regardless of channel conditions. In these methods relay(s) with weak channels amplify received signal with considerable gain that cause reduction of performance. In this paper, we propose single and multiple relay selection strategies for two-hop relay networks. In the first part of paper, we specify factor of each relay based on MMSE criterion and relay with highest SNR is chosen for cooperation. Our simulation results show that performance of this method is better than previous works. Second part of this paper proposes selection of two, three or any number of relays and uses them. As we see in the simulation results double relay selection has better performance than single relay selection, triple than double and so on and diversity order of all is complete.
Abstract In this paper, we propose a distributed relay beam-forming design in an underlay based c... more Abstract In this paper, we propose a distributed relay beam-forming design in an underlay based cognitive relay network. In the proposed approach, beamforming coefficients of the secondary relays are obtained through minimization of the peak interference power inflicted on the primary receiver subject to the signal to noise-interference ratio (SINR) constraint at the secondary destination. We prove that the proposed scheme lead to a closed-form solution. Simulation results show that our relay beamforming improve system performance ...
In this chapter, we propose a new scheme for maximum-likelihood (ML) estimation of both carrier-f... more In this chapter, we propose a new scheme for maximum-likelihood (ML) estimation of both carrier-frequency offset (CFO) and channel coefficients in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems, assuming that a training sequence is available. Our scheme is also capable to accommodate any space–time coded (STC)-OFDM transmission. Furthermore, the Cramer–Rao bounds (CRBs) for both CFO and channel estimators are developed to evaluate the performance of the proposed scheme. The simulation results show that the proposed algorithm achieves almost ideal performance compared with the CRB for both channel and frequency offset estimations.
In this study, the problem of blind channel estimation for single-input single-output (SISO) orth... more In this study, the problem of blind channel estimation for single-input single-output (SISO) orthogonal frequency-division multiplexing (OFDM) systems, is considered. Based on auto-correlation matrix, we develop a precoding-assisted blind channel estimation algorithm which is suitable for practical SISO-OFDM applications. Compared to the popular subspace-based blind channel estimation methods, the proposed algorithm is much more computationally efficient. Simulation results show that
The problem of blind channel estimation in Multiple-Input-Multiple-Output (MIMO) Orthogonal Frequ... more The problem of blind channel estimation in Multiple-Input-Multiple-Output (MIMO) Orthogonal Frequency-Division Multiplexing (OFDM) systems is investigated in this study, assuming that the transmitted symbols are independent and identically distributed. In particular, by utilizing a generalized linear non-redundant precoder, a simple blind channel estimation technique for MIMO-OFDM systems is developed. A novel contribution is that instead of using only one column of the signal covariance matrix, as done in previous works, proposed estimator jointly considers all the information contained in the signal covariance matrix. Comparisons show that the proposed approach outperforms the existing estimators. It is also noticed that the proposed algorithm is much more computationally efficient. Consequently, the proposed method is a promising blind channel estimation candidate for MIMO-OFDM systems.
The problem of joint carrier frequency offset (CFO) and channel estimation in orthogonal frequenc... more The problem of joint carrier frequency offset (CFO) and channel estimation in orthogonal frequency division multiplexing (OFDM) systems is investigated in this study. The exact solution to this problem turns out to be too complex for practical purposes. To overcome this difficulty, we resort to the recursive least square (RLS) algorithm and propose an iterative scheme which iterates between estimating the channel parameters and the frequency offset. This results in an estimation algorithm of a reasonable complexity which is suitable for practical applications.
In this paper, we propose an Amplify-and-Forward (AF) Orthogonal Frequency Division Multiplexing ... more In this paper, we propose an Amplify-and-Forward (AF) Orthogonal Frequency Division Multiplexing (OFDM) relay scheme that each relay superimposes its own pilot symbol (PS) such that, individual relay channels can be estimated at the destination. We derive optimal PS designs including both Modification Diagonal Matrix (MDM) and superimposed PS at each relay. These designs are based on channel Mean Square-Error (MSE) minimization and Inter-Relay Interference (IRI) elimination, equivalently. It is shown that the number of relays should satisfy the condition, M <; (N/2(2L-1)), where N and L are the OFDM size and channel order, respectively, and (a) is the maximum integer part of a. Both Least-Square (LS) and linear minimum MSE channel estimators are derived. Furthermore, the estimator according to uncertain data and approximate computations is derived from an efficient convex optimization problem.
In this paper, we study the design of expectation-maximization (EM)-based iterative receivers for... more In this paper, we study the design of expectation-maximization (EM)-based iterative receivers for low-density parity check -coded multiple-input multiple-output orthogonal frequency-division multiplexing systems with the presence of carrier-frequency offset (CFO). First, starting from the maximum-likelihood principle, we devise a novel EM-based pilot-aided scheme for joint estimation of CFO and channel coefficients. Then, this estimator is incorporated into the initialization step of the iterative receiver. Simulation results show the effectiveness of our receiver design in combating CFO over unknown frequency selective fading channels.
Summary from only given. In this paper, we consider the cooperative spectrum sensing when the lin... more Summary from only given. In this paper, we consider the cooperative spectrum sensing when the links between primary user and CRs are subject to log-normal shadow fading and there is also noise uncertainty which is modeled as log-normal. The objective is to evaluate the performance of Equal Gain Combining (EGC) of local observations and propose a novel cluster-based algorithm to reduce the reporting channel bandwidth. In our proposed method, CRs in each group sense the spectrum in a distributive manner by the help of EGC method and send the hard decisions to the fusion center where final decision will be make by a simple counting rule. Lower bandwidth of reporting channel is the main advantage of the proposed method.
In this paper, two novel approaches to filter-and-forward beamforming (FF-BF) in an underlay base... more In this paper, two novel approaches to filter-and-forward beamforming (FF-BF) in an underlay based relay-assisted cognitive network with frequency-selective channels are proposed. In our scheme, secondary users are allowed to transmit through multiple relays simultaneously with primary users over the same spectrum. Such a network suffers from both inter-symbol interference (ISI) and bidirectional interference between the networks. We design FF-BF coefficients of the relays to mitigate these two types of interference. Simulation results show that the proposed approaches improve system performance considerably in frequency-selective environments in comparison to the conventional amplify-and-forward beamforming strategy.
In this paper, we propose a new scheme for joint maximum- likelihood (ML) estimation of carrier-f... more In this paper, we propose a new scheme for joint maximum- likelihood (ML) estimation of carrier-frequency offset (CFO) and channel coefficients in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. To reduce the prohibitive computational complexity of joint ML estimation problems, the expectation- maximization (EM) algorithm is employed. Moreover, the Cramer-Rao bounds (CRB) for both CFO and channel estimators
... S. Salari, M. Ahmadian, M. Ardebilipour, V. Meghdadi*, and JP Cances* KN Toosi Universit... more ... S. Salari, M. Ahmadian, M. Ardebilipour, V. Meghdadi*, and JP Cances* KN Toosi University of Technology, Tehran, Iran E-mail:{salari, mahmoud, mehrdad}@eetd.kntu.ac.ir * University of Limoges, Ensil-Geste, France E-mail:{meghdadi, cances}@ensil.unilim.fr ...
In this paper, we investigate the problem of carrier frequency-offset (CFO) synchronization and c... more In this paper, we investigate the problem of carrier frequency-offset (CFO) synchronization and channel estimation in orthogonal frequency-division multiple access (OFDMA) systems operating over unknown frequency-selective fading channels. We first devise a novel iterative method for joint CFO and channel estimation, based on the time-domain training blocks. The proposed joint estimator consists of two recursive least-square (RLS) algorithms. We then
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