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Top1. Introduction
Due to the increasing number of users in contemporary communication systems, the demand for spectrum is growing very fast. However, the Federal Communications Commission's (FCC) technical report ((FCC), 2002) reveals that a considerable portion of spectrum remains unused over time. This suggests that the traditional fixed spectrum allocation techniques are not efficient. Thereby, the concept of cognitive networking is recognized as a promising solution to provide the chance of access to the licensed spectrum by the unlicensed users, while the spectrum is not occupied by the Primary Users (PU) (Mitola, J., & Maguire, J.G.Q., 1999).
Two general approaches to cognitive radio networks are common models and property-right models. In common models, the Primary User (PU) is oblivious to the existence of the Secondary Users (SUs). The SUs monitor the licensed band to capture the holes (idle frequency bands) in the spectrum which are not utilized by the PUs. This method is sensitive to the utilized spectrum sensing technique, since an untimely spectrum access by the secondary users may deteriorate the underlying interference management scheme and severely impact the PU operation. Therefore, this approach is not suitable for practical coexistence of networks.
On the other hand, in the property-right models, the PU willingly allocates some part of the licensed spectrum to the SUs in exchange for their relaying service (Simeone, O., Gambini, J., Bar-Ness, Y., & Spagnolini, U., 2007). This technique brings about the efficient spectrum utilization which benefits both the primary and secondary users. The cooperative packet transmission enhances the PU's throughput, especially when there is no reliable direct link between the primary transmitter and its target receiver. In return, the SUs obtain the chance to access to a part of the spectrum.
A spectrum leasing scheme is proposed in (Simeone, O., Stanojev, I., Savazzi, S., Bar-Ness, Y., Spagnolini, U., & Pickholtz, R., 2008), where a PU allocates the channel to the users of a secondary ad hoc network for a fraction of time, and the secondary network in return cooperates in forwarding the PU's packets using distributed space-time coding technique. A Stackelberg game model is used in this model, where the PU selects the fractions of time to be used for transmissions of the primary and network of the secondary users as well as the time for cooperative services, with the objective of maximizing its own transmission rate. In the next stage, the SUs that all transmit simultaneously compete with one another to set the optimal power allocation which results in a highest transmission rate.
A priced-based game model for spectrum leasing is proposed in (Wang, X., Ma, K., Han, Q., Liu, Z., & Guan, X., 2012), where time allocation parameters as well as the price of spectrum are set by the PU, while the selected SU may increase its transmission rate by optimizing its transmission power. In (Afghah, F., Costa, M., Razi, A., Abedi, A., & Ephremides, A., 2013), a cognitive radio network consisting of a single primary and a single secondary nodes is considered and a reputation-based Stackelberg game model is proposed, where the primary and secondary jointly decide about the time allocation of the spectrum. This model accounts for energy efficiency and fairness to optimally split the time into three phases: i) PU transmission, ii) cooperative relaying, and iii) SU transmission.
In the previous reported work, it is assumed that the SUs are trustable in the sense that they use the same power for transmissions of their own packets as well as cooperative packet transmission for the PU ((Simeone, O., Stanojev, I., Savazzi, S., Bar-Ness, Y., Spagnolini, U., & Pickholtz, R., 2008), (Wang, X., Ma, K., Han, Q., Liu, Z., & Guan, X., 2012), (Simeone, O., Gambini, J., Bar-Ness, Y., & Spagnolini, U., 2007), (Hao, X., Cheung, M.H., Wong, V., Leung, V.C.M., 2011)). However, this assumption may be violated in reality as cooperation is not an inherent characteristic of the cognitive users and they may prefer to save their limited available resources for their own packet transmission. In other words, although after granting the spectrum access, the SUs are supposed to treat the received packets from the primary similar to their own packets and forward them with an acceptable power, they may deviate from this rule and assign a low power to relay the PU's packet and reserve the remaining power for their individual transmission.