In recent years, the cognitive radio technology has attracted the attention of all the players in the telecommunication field (i.e., researchers, industry, service providers, and regulatory agencies) as a way of facing the spectrum scarcity. In this regard, and after having reviewed the vast activity linked to this concept it is quite easy to realize that the spectrum sensing task turns out to be the keystone of this technology. However, nowadays it is still unclear which is (are) going to be the globally recommended technique(s) for carrying out this procedure. So, and aiming at finding an alternative to the technical impediments behind the spectrum sensing task, this research work proposes that the advanced knowledge that is already being collected at the modern primary networks be used in benefit of the cognitive radios. Here, the 3GPP LTE network has been adopted as the primary system providing the information that the cognitive radio transceiver will be using for co-transmitting opportunistically (i.e., at specific moments) through the licensed radio resources, being the secondary access based on a novel model which proposes to overlay the secondary transmission whenever extreme channel conditions be found in the radio link of a particular primary user.
The spatiotemporal robustness of the MIMO transmissions is exploited aiming at inducing opportunistic secondary communications on the primary radio resources. The proposed model makes use of the smallest singular values and the Extreme Value Theory for characterizing the robustness of the MIMO systems, having always the premise of preventing significant degradations in the performance of the primary communications, while at the same time an attractive number of potential opportunities for secondary are intended to be offered. So, the idea behind the suggested scheme consists in reusing the information that is already available within the primary MIMO networks aiming at cotransmitting opportunistically in a clever manner, which at the end will allow us to make a much more efficient use of both the natural and technical resources.
We propose a methodology based on the prioritization and opportunistic reuse of the optimization algorithm known as Hungarian method for the feasible implementation of a channel-dependent scheduler in the long-term evolution uplink (single carrier frequency division multiple access system). This proposal aims to offer a solution to the third generation system’s constraint of allocating only adjacent subcarriers, by providing an optimal resource
allotment under a fairness scheme. A multiuser mobile environment following the third generation partnership project TS 45.005v9.3.0/25.943v9.0.0 was also implemented for evaluating the scheduler’s performance. From the results, it was possible to examine the channel frequency response for all users (four user equipments) along the whole bandwidth, to visualize the dynamic resource allocation for each of the 10,000 channel realizations
considered, to generate the statistical distribution and cumulative distribution functions of the obtained global costs, as well as to evaluate the system’s performance once the proposed algorithm was embedded. Comparing and emphasizing the benefits of utilizing the proposed dynamic allotment instead of the classic static-scheduling
and other existent methods.
The sensing function is one of the most important features of cognitive radios since a reliable detection of available spectrum ensuring non-interference to licensed users is necessary to initiate a lower priority communication. In this paper, the proposal of a physical layer sensing method using the
multiple-level wavelet decomposition analysis for the detection of primary users is presented. The proposed scheme consists of
four stages (sampling, multiple-level decomposition analysis, coefficients analysis and evaluation criterion), where the energy percentage through the decomposed levels is proposed as a metric to determine if there is a high priority user present on the channel or not. For simulation purposes different input signals involving the presence/absence of a primary user as well as variations in the SNR were considered in order to evaluate the model.
In this article, the proposal to establish a simultaneous cognitive radio communication based on a subdistribution of power made over discovered unselected subchannels
identified by an initially optimal power allotment for a primary user is shown. The aim of this work is to show the possibility of introducing a low priority (secondary)
communication into a single user (licensed) transmission where the total power constraint is shared. The analysis of the
proposed transmission scheme was performed by considering eight independent subchannels affected by Rayleigh fading, over 2000 channel realizations, and three different signal-to-noise ratios (4dB, 8dB, and 15dB). From the system evaluation it was possible to find the optimal power allotment for the primary user, the subdistribution of power for the secondary user, as well as the attenuation and the capacity per subchannel for every channel realization. Moreover, the PDF of the total capacities and their averages were obtained as a complementary result.