... B. Zahedi†, M. Ahmadian†, K. Mohamed-pour†, M. Peyghami‡,M. Norouzi†, and S. Salari† †Faculty... more ... B. Zahedi†, M. Ahmadian†, K. Mohamed-pour†, M. Peyghami‡,M. Norouzi†, and S. Salari† †Faculty of Electrical and Computer Engineering, KNToosi University of Technology, Tehran, Iran Email: bzahedi@ee.kntu.ac.ir, {m ahmadian, kmpour}@kntu.ac.ir, majid.norouzi@ee ...
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.
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 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 consider a multiple-input multiple-output (MIMO) orthogonal frequency division ... more In this paper, we consider a multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system operating over unknown frequency selective fading channels. We propose a novel scheme to obtain frequency synchronization together with multi-antenna channel estimation. Computer simulation results are provided to demonstrate the performance of the proposed scheme.
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.
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.
... 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 ...
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.
New method for equalization and symbol detection for 8-PSK EDGE system is investigated in this st... more New method for equalization and symbol detection for 8-PSK EDGE system is investigated in this study. The exact solution to this problem, Maximum Likelihood Sequence Estimation (MLSE) turns out to be too complex for practical purposes, but this method introduce a new version of Delayed Decision Feedback Sequence Estimation (DDFSE) equalizer that has less complexity and totally comparable performance with complete DDFSE. Simulation results compare our method with DDFSE and lower complexity methods over Rayleigh multipath fading channel. For final step we show the efficiency of our method based on received packet in receiver hardware in trade off between time that each algorithm needs for process a received frame and BER.
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 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.
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, 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.
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
In this paper, we consider a multiple-input multiple-output (MIMO) orthogonal frequency division ... more In this paper, we consider a multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system operating over frequency-selective fading channels. We propose a novel scheme for joint carrier-frequency offset (CFO) and channel estimation based on the expectation–maximization (EM) algorithm. Furthermore, the Cramer-Rao bounds (CRBs) for both CFO and channel estimators are exploited to evaluate the performance of the proposed scheme. Computer simulations show that the proposed algorithm achieves almost ideal performance compared with the CRBs for both channel and frequency offset estimations.
... B. Zahedi†, M. Ahmadian†, K. Mohamed-pour†, M. Peyghami‡,M. Norouzi†, and S. Salari† †Faculty... more ... B. Zahedi†, M. Ahmadian†, K. Mohamed-pour†, M. Peyghami‡,M. Norouzi†, and S. Salari† †Faculty of Electrical and Computer Engineering, KNToosi University of Technology, Tehran, Iran Email: bzahedi@ee.kntu.ac.ir, {m ahmadian, kmpour}@kntu.ac.ir, majid.norouzi@ee ...
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.
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 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 consider a multiple-input multiple-output (MIMO) orthogonal frequency division ... more In this paper, we consider a multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system operating over unknown frequency selective fading channels. We propose a novel scheme to obtain frequency synchronization together with multi-antenna channel estimation. Computer simulation results are provided to demonstrate the performance of the proposed scheme.
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.
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.
... 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 ...
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.
New method for equalization and symbol detection for 8-PSK EDGE system is investigated in this st... more New method for equalization and symbol detection for 8-PSK EDGE system is investigated in this study. The exact solution to this problem, Maximum Likelihood Sequence Estimation (MLSE) turns out to be too complex for practical purposes, but this method introduce a new version of Delayed Decision Feedback Sequence Estimation (DDFSE) equalizer that has less complexity and totally comparable performance with complete DDFSE. Simulation results compare our method with DDFSE and lower complexity methods over Rayleigh multipath fading channel. For final step we show the efficiency of our method based on received packet in receiver hardware in trade off between time that each algorithm needs for process a received frame and BER.
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 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.
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, 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.
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
In this paper, we consider a multiple-input multiple-output (MIMO) orthogonal frequency division ... more In this paper, we consider a multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system operating over frequency-selective fading channels. We propose a novel scheme for joint carrier-frequency offset (CFO) and channel estimation based on the expectation–maximization (EM) algorithm. Furthermore, the Cramer-Rao bounds (CRBs) for both CFO and channel estimators are exploited to evaluate the performance of the proposed scheme. Computer simulations show that the proposed algorithm achieves almost ideal performance compared with the CRBs for both channel and frequency offset estimations.
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