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...