The current explosion of information and demand for high speed data communication call for novel solutions to utilize the radio resources more efficiently. The cognitive communication paradigm aims to mitigate this spectrum crunch by exploiting unused resources that are allocated to the primary communications systems. The aim of this research is to employ the concept of cognition in wireless devices and combine it with three recently introduced wireless communication techniques namely, K-user multi-input multi-output (MIMO) interference networks, spatial modulation scheme and molecular communications. Firstly, the feasibility of cognitive radio (CR) is studied in the presence of a K-user MIMO interference channel as the primary network. Assuming that the primary interference network has unused spatial degrees of freedom, the sufficient condition on the number of antennas is investigated at the secondary transmitter under which the secondary system can communicate and then the secondary precoding and decoding matrices are derived to have zero interference leakage into the primary network. A fast sensing method based on the eigenvalue analysis of the received signal covariance matrix is proposed to determine the availability of spatial holes. Also, a fine sensing method is provided based on the generalized likelihood ratio test to decide the absence of individual primary streams. The second part of this research is relevant to the application of spatial modulation (SM) in overlay CR networks, in which the primary and secondary networks work concurrently over the same spectrum band. The CR transmitter assists the primary network as a relay to amplify-and-forward (AF) the transmitted symbols of the primary. The secondary transmitter retransmits the primary symbols in amplitude-phase modulation domain, while its own information is transmitted by the index of transmitting antenna. The performance of the optimal detectors in terms of the average symbol error rate (ASER) and the asymptotic behavior of the ASER at both the primary and secondary at high signal-to-noise ratios (SNRs) are then provided. In the last part, a novel nanonetwork with cognitive capabilities is proposed, which is able to intelligently sense a primary molecular channel and use the channel opportunistically for its own transmission. In the proposed method, the secondary nanonetwork measures the concentration of molecules as a criterion to decide the presence or absence of the primary communication using a molecular energy detection scheme. When the molecular channel is available, the secondary transmitter sends its information using the same carrier molecules. Depending on the availability of timing information at the sensing nanodevice, two synchronous and asynchronous sensing mechanisms are provided based on the likelihood ratio test as the optimal detection method.