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In this paper, a novel synchronization method is proposed for a heterogeneous cognitive radio that combines public safety mobile communication systems (PMCSs) with commercial mobile wireless communication systems (CMWCSs). The proposed method enables selfsynchronization of the PMCSs as well as co-synchronization of PMCSs and CMWCSs. In this paper, the self-synchronization indicates that each system obtains own timing synchronization. The co-synchronization indicates that a system recognizes data transmitted from other systems correctly. In our research, we especially focus on PMCS self-synchronization because it is one of the most difficult parts of our proposed cognitive radio that improves PMCS's communication quality. The proposed method is utilized for systems employing differentially encoded π/4 shift QPSK modulation. The synchronization can be achieved by correlating envelopes calculated from a PMCS's received signals with subsidiary information (SI) sent via a CMWCS. In this paper, the performance of the proposed synchronization method is evaluated by computer simulation. Moreover, because this SI can also be used to improve the bit error rate (BER) of PMCSs, BER improvement and efficient SI sending methods are derived, after which their performance is evaluated.

A novel synchronization technique is proposed for a heterogeneous cognitive radio combining a public safety mobile communication system (PMCS) with a commercial mobile wireless communication system (CMWCS). Since the PMCS is crucial in public safety activities such as search-and-rescue operations, we have implemented a heterogeneous cognitive technique to improve the communication quality of the PMCS. To combine the PMCS with the CMWCS properly, the proposed synchronization technique enables not only the co-synchronization between the PMCS and the CMWCS but also the self-synchronization of the PMCS. In this paper, we especially focus on the PMCS's self-synchronization that is one of the most difficult parts of our proposed cognitive radio system. The proposed technique is utilized for systems employing differentially encoded π/4-shift QPSK modulation. The synchronization can be achieved by correlating the envelopes calculated from the PMCS's received signals with subsidiary information (SI) sent via the CMWCS. In this study, the performance of the proposed synchronization technique is evaluated by computer simulation.