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Optimal Energy-Efficient Relay Selection and Power Allocation for Cognitive Two-Way Relay Network Using Physical-Layer Network Coding
Abstract
This paper addresses relay selection(RS) and power allocation(PA) issues for a physical-layer network coding (PNC) relay based secondary user (SU) communication in cognitive radio networks, in which two secondary transceiver nodes exchange their information with the assistance of a relay under interference power threshold (IPT) constraints. We propose an optimal energy-efficient RS and PA (OE-RS-PA) scheme to minimize total energy consumption per bit with the sum rate constraint and IPT constraints. A closed-form solution for optimal allocation of transmit power among the SU nodes and relay node are then derived analytically and confirmed by numerical results. Furthermore, numerical simulations and comparisons are presented to illustrate the performance of the proposed scheme.
... 9 On the basis of this method, 2 transmitter nodes to exchange information via a relay send their data (X A , X B ) to the relay, simultaneously, and the relay extracts a network coded signal (in the simplest way, the modulo-sum mapping of data, X R = X A ⊕ X B ) from the received superimposed signals and sends this code to the source nodes in the second time slot. Receiving the network code, each node with the knowledge of its own information can extract the information of the other node (for example, X B = X R ⊕ X A ). Performance of PLNC in CRN has been studied in previous studies 10, [16][17][18][19][20] 22 However, in these recent works, 2 different PUs coverage areas with 2 separate orthogonal frequency sets are considered, where SUs in each area operate on the frequency range of the opposite area. ...
In this paper, the power allocation problem in a relay-assisted Cognitive Radio Network (CRN) is considered where the secondary users (SUs) exchange information in an interweave mode based on Physical Layer Network Coding (PLNC). In order to enhance the capacity of CRN, using multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM) has become very popular in the literature. This paper goes one step further to improve the throughput of SUs using PLNC by drawing off the transmission time. The main goal is to maximize the capacity of CRN, while keeping the total interference imposed on the primary users under a certain threshold. An optimal solution to this power allocation problem with limited relay power constraint, due to the limited budget, is derived; however, due to the high complexity of this method, an efficient sub-optimal solution is also proposed.
Cognitive radio combined with bidirectional relay could greatly improve spectrum utilization. In this paper, we consider a multi-relay cognitive radio network with imperfect channel state information (CSI). Interference to primary users and secondary users’ quality of service (QoS) are the main factors considered and optimized. Using semidefinite relaxation (SDR), the optimization problem could be transferred into a convex form and solved. Simulation results validate the effectiveness of our proposed scheme compared to nonrobust one, particularly in ensuring the stability of the system.
In this paper, we present an optimal scheme for power allocation and relay selection in a cognitive radio network where a pair of cognitive (or secondary) transceiver nodes communicate with each other assisted by a set of cognitive two-way relays. The secondary nodes share the spectrum with a licensed primary user (PU), and each node is assumed to be equipped with a single transmit/receive antenna. The interference to the PU resulting from the transmission from the cognitive nodes is kept below a specified limit. We propose joint relay selection and optimal power allocation among the secondary user (SU) nodes achieving maximum throughput under transmit power and PU interference constraints. A closed-form solution for optimal allocation of transmit power among the SU transceivers and the SU relay is presented. Furthermore, numerical simulations and comparisons are presented to illustrate the performance of the proposed scheme.
We propose a two-phase protocol based on cooperative decode-and-forward relaying for a secondary system to achieve spectrum access along with a primary system. The primary and secondary systems comprise of a transmitter-receiver pair, PT-PR and ST-SR, respectively. In the first transmission phase, PT transmits the primary signal to PR, which is also received by ST and SR, where it is decoded. At ST, the primary signal is regenerated and linearly combined with the secondary signal by assigning fractions alpha and (1 - alpha) of the available power to the primary and secondary signals respectively. This combined signal is then broadcasted by ST in the second transmission phase. We show that as long as ST is located within a critical radius from PT, there exists a threshold value for alpha above which the outage probability of the primary system will be equal to or lower than the case without spectrum sharing. We also determine the outage probability achieved by the secondary system. Theoretical and simulation results confirm the efficiency of the proposed spectrum sharing scheme.
Cognitive radios hold tremendous promise for increasing spectral efficiency in wireless systems. This paper surveys the fundamental capacity limits and associated transmission techniques for different wireless network design paradigms based on this promising technology. These paradigms are unified by the definition of a cognitive radio as an intelligent wireless communication device that exploits side information about its environment to improve spectrum utilization. This side information typically comprises knowledge about the activity, channels, codebooks, and/or messages of other nodes with which the cognitive node shares the spectrum. Based on the nature of the available side information as well as a priori rules about spectrum usage, cognitive radio systems seek to underlay, overlay, or interweave the cognitive radios' signals with the transmissions of noncognitive nodes. We provide a comprehensive summary of the known capacity characterizations in terms of upper and lower bounds for each of these three approaches. The increase in system degrees of freedom obtained through cognitive radios is also illuminated. This information-theoretic survey provides guidelines for the spectral efficiency gains possible through cognitive radios, as well as practical design ideas to mitigate the coexistence challenges in today's crowded spectrum.
Spectrum sensing is a fundamental and critical issue for opportunistic spectrum access in cognitive radio networks. Among the many spectrum-sensing methods, the information theoretic criteria (ITC)-based method is a promising blind method that can reliably detect the primary users while requiring little prior information. In this paper, we provide an intensive treatment on the ITC sensing method. To this end, we first introduce a new overdetermined channel model constructed by applying multiple antennas or oversampling at the secondary user to make ITC applicable. Then, a simplified ITC sensing algorithm is introduced, which needs to compute and compare only two decision values. Compared with the original ITC sensing algorithm, the simplified algorithm significantly reduces the computational complexity with no loss in performance. Applying the recent advances in random matrix theory, we then derive closed-form expressions to tightly approximate both the probability of false alarm and the probability of detection. Based on the insight derived from the analytical study, we further present a generalized ITC sensing algorithm that can provide a flexible tradeoff between the probability of detection and the probability of false alarm. Finally, comprehensive simulations are carried out to evaluate the performance of the proposed ITC sensing algorithms. Results show that they considerably outperform other blind spectrum-sensing methods in certain cases.
Wireless systems where the nodes operate on batteries so that energy consumption must be minimized while satisfying given throughput and delay requirements are considered. In this context, the best modulation strategy to minimize the total energy consumption required to send a given number of bits is analyzed. The total energy consumption includes both the transmission energy and the circuit energy consumption. For uncoded systems, by optimizing the transmission time and the modulation parameters, it is shown that up to 80% energy savings is achievable over nonoptimized systems. For coded systems, it is shown that the benefit of coding varies with the transmission distance and the underlying modulation schemes.
We study two-hop communication protocols where one or several relay terminals assist in the communication between two or more terminals. All terminals operate in half-duplex mode, hence the transmission of one information symbol from the source terminal to the destination terminal occupies two channel uses. This leads to a loss in spectral efficiency due to the pre-log factor one-half in corresponding capacity expressions. We propose two new half-duplex relaying protocols that avoid the pre-log factor one-half. Firstly, we consider a relaying protocol where a bidirectional connection between two terminals is established via one amplify-and-forward (AF) or decode-and-forward (DF) relay (two-way relaying). We also extend this protocol to a multi-user scenario, where multiple terminals communicate with multiple partner terminals via several orthogonalize-and-forward (OF) relay terminals, i.e., the relays orthogonalize the different two-way transmissions by a distributed zero-forcing algorithm. Secondly, we propose a relaying protocol where two relays, either AF or DF, alternately forward messages from a source terminal to a destination terminal (two-path relaying). It is shown that both protocols recover a significant portion of the half-duplex loss
The LambertW function is defined to be the multivalued inverse of the functionw we
w
. It has many applications in pure and applied mathematics, some of which are briefly described here. We present a new discussion of the complex branches ofW, an asymptotic expansion valid for all branches, an efficient numerical procedure for evaluating the function to arbitrary precision, and a method for the symbolic integration of expressions containingW.
Cognitive radio and cooperative communication can greatly improve the spectrum efficiency in wireless communications. We study a cognitive radio network where two secondary source terminals exchange their information with the assistance of a relay node under interference power constraints. In order to enhance the transmit rate and maintain fairness between two source terminals, a practical 2-phase analog network coding protocol is adopted and its optimal power allocation algorithm is proposed. Numerical results verify the superiority of the proposed algorithm over the conventional direct transmission protocol and 4-phase amplify-and-forward relay protocol.
In this paper, we investigate joint relay selection and power allocation to maximize system throughput with limited interference to licensed (primary) users in cognitive radio (CR) systems. As these two problems are coupled together, we first develop an optimal approach based on the dual method and then propose a suboptimal approach to reduce complexity while maintaining reasonable performance. From our simulation results, the proposed approaches can increase the system throughput by over 50%.
In this paper new architectural approaches that improve the energy efficiency of a cellular radio access network (RAN) are investigated. The aim of the paper is to characterize both the energy consumption ratio (ECR) and the energy consumption gain (ECG) of a cellular RAN when the cell size is reduced for a given user density and service area. The paper affirms that reducing the cell size reduces the cell ECR as desired while increasing the capacity density but the overall RAN energy consumption remains unchanged. In order to trade the increase in capacity density with RAN energy consumption, without degrading the cell capacity provision, a sleep mode is introduced. In sleep mode, cells without active users are powered-off, thereby saving energy. By combining a sleep mode with a small-cell deployment architecture, the paper shows that the ECG can be increased by the factor n = (R<sub>large</sub>/R<sub>small</sub>)<sup>2</sup> while the cell ECR continues to decrease with decreasing cell size.
In this paper, we consider an optimal power allo- cation scheme for a physical layer network coding relay based secondary user (SU) communication in cognitive radio networks. SUs are located on two different primary user (PU) coverage areas and we introduce an energy and spectrally efficient SU communication scheme. The sum rate of relay based two way communications for SUs is maximized under a total power constraint and interference power threshold (IPT) constraints to PUs. The optimal power allocation schemes are illustrated for different cases of SUs and relay powers. Numerical results confirm that the power allocation scheme provides the optimal solution for the achievable sum rate and the IPT constraints have an effect on the sum rate variation with the total available power.
This paper investigates delay constrained performance of a cognitive radio relay network when the cognitive (secondary) user transmission is subject to satisfying spectrum-sharing restrictions imposed by a primary user. The primary user allows a secondary user to gain access to its allocated spectrum band as long as certain thresholds on the interference power, on the peak or average values, inflicted on the primary receiver are not exceeded by the transmission of the secondary users. In addition, we assume that the secondary transmitter benefits from an intermediate node, chosen from K terminals, to relay its signal to the destination. Considering that the transmission of the secondary user is subject to satisfying a statistical delay quality-of-service (QoS) constraint, we study the maximum arrival rate of the secondary user's relay link while the interference limitations required by the primary user are satisfied. Particularly, we obtain the effective capacity of the secondary network and determine the power allocation policies that maximize the effective capacity of the secondary user's relaying channel. In addition, we derive closed-form expressions for the effective capacity of the channel in Rayleigh block-fading environment under peak or average interference-power constraints. Numerical simulations are provided to endorse our theoretical results.
In this paper, we propose a two-phase protocol based on cooperative relaying for a secondary system to achieve spectrum access along with a primary system. The primary system comprises of a transmitter-receiver pair PT-PR, and the secondary system comprises of M transmitters STi, i ∈ {1, 2,..., M} and a common receiver SR. The secondary transmitter STp which achieves the request target rate for the primary system is selected to serve as a decode-and-forward (DF) relay for the primary system. With the cooperation of STp, the primary system is able to tolerate interference lower than a certain threshold in the relaying phase, without degrading its outage performance. The secondary transmitter STs, which satisfies this interference constraint and provides the optimal outage performance for the secondary system, is then selected to access the spectrum band simultaneously when STp is relaying the primary signal. Theoretical and simulation results confirm the efficiency of the proposed spectrum sharing protocol, and we show that both primary and secondary systems are able to achieve better outage performance with increasing M.