IEEE Transactions on Wireless Communications, 2015
ABSTRACT In this paper, we consider bidirectional relay networks in which two users exchange info... more ABSTRACT In this paper, we consider bidirectional relay networks in which two users exchange information only via a relay node, i.e., a direct link between both users is not present. We assume that channel state information at the transmitter is not available and/or only one coding and modulation scheme is used due to complexity constraints. Thus, the nodes transmit with a fixed predefined rate regardless of the channel state. In general, the nodes in the network can assume one of three possible states in each time slot, namely, the transmit, the receive, and the silent state. Most of the existing bidirectional relaying protocols assume a prefixed schedule for the sequence in which the states of the nodes are used. In this paper, we abandon the restriction of having a fixed and predefined schedule and consider the selection of the states of the nodes as a degree of freedom that can be exploited for performance optimization. To this end, the relay has to be equipped with two buffers for storage of the information received from the two users. In Part I of this paper, we propose a delay-unconstrained protocol that, based on the qualities of the involved links, selects the optimal states of the nodes in each time slot such that the sum throughput is maximized. In Part II, several delay-constrained protocols are proposed and analyzed. Numerical results show that the proposed protocols significantly outperform the existing bidirectional relaying protocols in the literature.
IEEE Transactions on Wireless Communications, 2015
ABSTRACT In this paper, we consider bidirectional relay networks in which two users exchange info... more ABSTRACT In this paper, we consider bidirectional relay networks in which two users exchange information only via a relay node, i.e., a direct link between both users is not present. We assume that channel state information at the transmitter is not available and/or only one coding and modulation scheme is used due to complexity constraints. Thus, the nodes transmit with a fixed predefined rate regardless of the channel state. In general, the nodes in the network can assume one of three possible states in each time slot, namely, the transmit, the receive, and the silent state. Most of the existing bidirectional relaying protocols assume a prefixed schedule for the sequence in which the states of the nodes are used. In this paper, we abandon the restriction of having a fixed and predefined schedule and consider the selection of the states of the nodes as a degree of freedom that can be exploited for performance optimization. To this end, the relay has to be equipped with two buffers for storage of the information received from the two users. In Part I of this paper, we propose a delay-unconstrained protocol that, based on the qualities of the involved links, selects the optimal states of the nodes in each time slot such that the sum throughput is maximized. In Part II, several delay-constrained protocols are proposed and analyzed. Numerical results show that the proposed protocols significantly outperform the existing bidirectional relaying protocols in the literature.
In this paper, the problem of cooperative spectrum sensing in cognitive radio networks based on l... more In this paper, the problem of cooperative spectrum sensing in cognitive radio networks based on linear combination of local observations is considered. In particular, log-normal shadow-fading is considered in both sensing and reporting channels. To reduce the effects of imperfect channel conditions, a clustering algorithm is suggested in which final decision about the primary user activity is obtained based on
AbstractIn cognitive radio systems, secondary users can be coordinated to perform cooperative sp... more AbstractIn cognitive radio systems, secondary users can be coordinated to perform cooperative spectrum sensing so as to detect the primary user more accurately. However, when the sensing observations are forwarded to a common receiver through fading channels, the sensing ...
Several Challenges like low signal-to-noise ratio (SNR), fading and inaccuracy in noise power est... more Several Challenges like low signal-to-noise ratio (SNR), fading and inaccuracy in noise power estimation make spectrum sensing techniques not reliable enough to sense the presence of primary signals accurately. These challenges substantiate the application of more robust algorithms by multiple cognitive users. Recently, Cooperative spectrum sensing is received so much attention for handling fading and low SNR problems. Therefore, in this paper, in order to overcome the above practical problems, we propose a novel ...
This paper investigates the problem of interference minimization which restricts the secondary us... more This paper investigates the problem of interference minimization which restricts the secondary users (SUs) quality of service (QoS) while coexisting the primary users (PUs), using distributed beamforming for a bidirectional cognitive relay network. We consider a network which consists of two secondary transceivers and K cognitive relay nodes and a primary network with a transmitter and receiver, all equipped with single-antenna. For effective use of spectrum we propose a two-step two-way relaying for cognitive relay ...
IEEE Transactions on Wireless Communications, 2015
ABSTRACT In this paper, we consider bidirectional relay networks in which two users exchange info... more ABSTRACT In this paper, we consider bidirectional relay networks in which two users exchange information only via a relay node, i.e., a direct link between both users is not present. We assume that channel state information at the transmitter is not available and/or only one coding and modulation scheme is used due to complexity constraints. Thus, the nodes transmit with a fixed predefined rate regardless of the channel state. In general, the nodes in the network can assume one of three possible states in each time slot, namely, the transmit, the receive, and the silent state. Most of the existing bidirectional relaying protocols assume a prefixed schedule for the sequence in which the states of the nodes are used. In this paper, we abandon the restriction of having a fixed and predefined schedule and consider the selection of the states of the nodes as a degree of freedom that can be exploited for performance optimization. To this end, the relay has to be equipped with two buffers for storage of the information received from the two users. In Part I of this paper, we propose a delay-unconstrained protocol that, based on the qualities of the involved links, selects the optimal states of the nodes in each time slot such that the sum throughput is maximized. In Part II, several delay-constrained protocols are proposed and analyzed. Numerical results show that the proposed protocols significantly outperform the existing bidirectional relaying protocols in the literature.
IEEE Transactions on Wireless Communications, 2015
ABSTRACT In this paper, we consider bidirectional relay networks in which two users exchange info... more ABSTRACT In this paper, we consider bidirectional relay networks in which two users exchange information only via a relay node, i.e., a direct link between both users is not present. We assume that channel state information at the transmitter is not available and/or only one coding and modulation scheme is used due to complexity constraints. Thus, the nodes transmit with a fixed predefined rate regardless of the channel state. In general, the nodes in the network can assume one of three possible states in each time slot, namely, the transmit, the receive, and the silent state. Most of the existing bidirectional relaying protocols assume a prefixed schedule for the sequence in which the states of the nodes are used. In this paper, we abandon the restriction of having a fixed and predefined schedule and consider the selection of the states of the nodes as a degree of freedom that can be exploited for performance optimization. To this end, the relay has to be equipped with two buffers for storage of the information received from the two users. In Part I of this paper, we propose a delay-unconstrained protocol that, based on the qualities of the involved links, selects the optimal states of the nodes in each time slot such that the sum throughput is maximized. In Part II, several delay-constrained protocols are proposed and analyzed. Numerical results show that the proposed protocols significantly outperform the existing bidirectional relaying protocols in the literature.
In this paper, the problem of cooperative spectrum sensing in cognitive radio networks based on l... more In this paper, the problem of cooperative spectrum sensing in cognitive radio networks based on linear combination of local observations is considered. In particular, log-normal shadow-fading is considered in both sensing and reporting channels. To reduce the effects of imperfect channel conditions, a clustering algorithm is suggested in which final decision about the primary user activity is obtained based on
AbstractIn cognitive radio systems, secondary users can be coordinated to perform cooperative sp... more AbstractIn cognitive radio systems, secondary users can be coordinated to perform cooperative spectrum sensing so as to detect the primary user more accurately. However, when the sensing observations are forwarded to a common receiver through fading channels, the sensing ...
Several Challenges like low signal-to-noise ratio (SNR), fading and inaccuracy in noise power est... more Several Challenges like low signal-to-noise ratio (SNR), fading and inaccuracy in noise power estimation make spectrum sensing techniques not reliable enough to sense the presence of primary signals accurately. These challenges substantiate the application of more robust algorithms by multiple cognitive users. Recently, Cooperative spectrum sensing is received so much attention for handling fading and low SNR problems. Therefore, in this paper, in order to overcome the above practical problems, we propose a novel ...
This paper investigates the problem of interference minimization which restricts the secondary us... more This paper investigates the problem of interference minimization which restricts the secondary users (SUs) quality of service (QoS) while coexisting the primary users (PUs), using distributed beamforming for a bidirectional cognitive relay network. We consider a network which consists of two secondary transceivers and K cognitive relay nodes and a primary network with a transmitter and receiver, all equipped with single-antenna. For effective use of spectrum we propose a two-step two-way relaying for cognitive relay ...
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