Cooperative beamforming and relay selection in cognitive radio systems

This paper investigates the power allocation problem in decode-and-forward cognitive dual-hop systems over Rayleigh fading channels. In order to optimize the performance of the secondary network in terms of power consumption, an outage-constrained power allocation scheme is proposed. The secondary nodes adjust their transmit power subject to an average interference constraint at the primary receiver and an outage probability constraint for the secondary receivers while having only statistical channel knowledge with respect to the primary nodes. We compare this approach with a power allocation scheme based on instantaneous channel state information under a peak interference constraint. Analytical and numerical results show that the proposed approach, without requiring the constant interchange of channel state information, can achieve a similar performance in terms of outage probability as that of power allocation based on instantaneous channel knowledge. Moreover, the transmit power allocated by the proposed approach is considerably smaller than the power allocated by the method based on instantaneous channel knowledge in more than 50% of the time.perspective [11] but also from the economic point of view. Therefore, minimizing the energy consumption for wireless data transmission becomes one of the most important design goals in WSNs, aiming at maximizing the battery lifetime. Because the transmit power is a relevant fraction of the total consumed energy, power allocation (PA) plays an important role towards achieving the aforementioned goal. Related worksSeveral recent works investigate the outage behavior of cooperative cognitive networks under different relaying protocols, number of available relays, channel models, and interference conditions, as for instance, [12][13][14][15][16][17][18]. In [12], it is investigated the outage performance of a multi-relay network under Rayleigh fading channels in a noise-limited environment, as well as the impact of imperfect channel state information (CSI) on the system performance. The authors in [13] carry out an analysis about the capacity and outage behavior of a decode-and-forward (DF) dual-hop system in a scenario where the SUs are subject to interference imposed by the PU. Similar to [13], the presence of PU interference is also considered in [14], but the authors show that increasing the number of relays can compensate the performance degradation caused by the PU interference. The diversity order and outage performance of a single relay dual-hop system in a noise-limited scenario under Nakagamim fading are investigated in [15]. Considering the presence of multiple primary transmitters (PTs) and receivers, the outage performance of DF systems is evaluated in [16]. In all these works, the transmit power of the SUs is adjusted to its maximum allowed value such that the peak interference at the primary receiver (PR) remains below the required constraint. However, this approach requires global CSI at the secondary network, of all the related channel coefficients, but perf...

Section: Related Workmentioning

confidence: 99%

Section: Related Workmentioning

confidence: 99%

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confidence: 99%

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Energy‐efficient outage‐constrained power allocation based on statistical channel knowledge for dual‐hop cognitive relay networks

Bordon

Montejo‐Sánchez

Mafra

et al. 2015

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In this paper, we investigate a two-step cooperative cognitive radio network, which consists of two secondary links, a number of relays, and one primary link. Hence, a relay network could help by receiving the messages from the secondary source and forwarding them to the secondary destination [8][9][10].In CR networks, the beamforming (BF) strategy can be used to improve the performance [8,11,12]. During the second step, the relay network employs a proposed cooperative beamforming (CBF) scheme and transmits the received data toward both of the secondary destinations (no matter whether the primary link is idle or not).

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Optimal received SINR balancing based on cooperative beamforming in cognitive radio networks

Moghaddam

Farrokhi

Granelli

2016

In this paper, we investigate a two-step cooperative cognitive radio network, which consists of two secondary links, a number of relays, and one primary link. During the first step, the primary link is assumed to be idle; both secondary sources simultaneously broadcast their data to the relay network. During the second step, the relay network employs a proposed cooperative beamforming (CBF) scheme and transmits the received data toward both of the secondary destinations (no matter whether the primary link is idle or not). The proposed CBF scheme enables the investigated network to simultaneously maximize received signal to interference plus noise ratio at both of the secondary destinations while keeping interference plus noise power at the primary destination under a predefined threshold. Indeed, the proposed scheme represents an optimal received signal to interference plus noise ratio balancing approach based on CBF, which guarantees the required quality of service for the primary link and also both secondary links. We optimize the CBF vector by relaxing the optimization problem to a convex semidefinite programming and solving with the bisection search algorithm. Numerical results show the efficiency and robustness of our approach. A comparison of our approach with the zero-forcing beamforming method is also presented. Figure 1. Traditional two-hop cognitive radio network.The concept of cooperative communications is a new paradigm shift for wireless communications. In cooperative communications, independent paths between the source and destination are generated via a group of relays (i.e., relay network). So the relay network can represent an auxiliary path to the direct path between the source and destination [8].Cooperation among different users can improve the performance of CR networks. In a CR, because of high path loss and shadowing, the secondary source could not communicate directly with the secondary destination. Hence, a relay network could help by receiving the messages from the secondary source and forwarding them to the secondary destination [8][9][10].In CR networks, the beamforming (BF) strategy can be used to improve the performance [8,11,12]. BF is a spatial processing technique that can form the radiation pattern to meet the requirements dictated by the wireless system [13][14][15]. The BF strategy in CR networks enables both PU and SU sources to have simultaneous communications to their destinations in the same channel [9,16]. In order to exploit the BF strategy, the sources have to use multiple antennas, but they are equipped with a single antenna because of some implementation constraints [17,18].The cooperative beamforming (CBF) method would bring substantial enhancements to traditional two-hop CR networks, as shown in Figure 1. In such a network where all nodes are equipped with a single antenna, a set of SUs, which act as cooperating relays (i.e., relay network), receives the messages from the secondary source, at the first hop. At the second hop, the relays create a virtual antenna array...

Outage performance of cognitive radio networks with multiple decode‐and‐forward relays

Wang

Lin

et al. 2016

This paper considers the cognitive radio network with one primary user (PU), one secondary user (SU), and multiple decode-and-forward relays. We propose a relaying scheme to ensure the priority of primary transmission, where the relays are used to forward PU's message and sometimes also SU's message. First, SU is allowed to use the spectrum to transmit only when its transmission would not affect the decoding status of PU's message at all relays. Second, once the secondary transmission happens, the relays that successively decode SU's message are allowed to retransmit this message when it would not affect the decoding status of PU's message at primary receiver. The interference from PU to SU and the interference from SU to PU are both considered. By analyzing the decoding status of primary message and secondary message at different relays, we formulate the outage probabilities of both primary transmission and secondary transmission. When all channels follow Rayleigh distributions, we derive the analytical expressions for the general case of any number of relays, which are validated by means of Monte Carlo simulations. or improving PU's transmission by applying sophisticated signal processing and coding. In the interweave approach, SU utilizes the spectrum not currently being used by PU.A number of transmission schemes for CRN have emerged in literature. In particular, to improve the spatial diversity order, the technique of relaying has been introduced into CRN. Authors in [6-9] considered one-relay scenario, and authors in [10-13] considered multi-relay scenario, where in the latter only one appropriate relay node is selected to forward the received signals. However, in [14], multiple relays may be selected to forward SU's signals, and SU does not know which and how many secondary relays will be selected and participate in the second phase. In these papers, [7][8][9][10]12] analyzed the performance when considering the interference from PU to SU, and [12] is the first paper analyzing the outage probability in underlay cognitive networks with multiple relays when considering this interference.In the aforementioned works, that is, [6][7][8][9][10][11][12][13], the relays are only deployed for secondary transmission. Nevertheless, some other papers discussed the case when the relays may assist the primary or/and secondary transmission. In [15][16][17], the relays would forward PU's or SU's message depending on the decoding status in the first phase. In [18][19][20], a relay node could help simultaneously the primary and the secondary transmissions. Actually, primary system stands for the existing communication systems, which have been studied widely when deployed with multiple relays. All what we can do is the designs based on the existing framework; thus, it is reasonable to investigate the CRN when relays are deployed mainly for primary transmission. When the resources at the relays are redundant for primary system, the relays might also be used for secondary transmission on the premise that this operation would n...