| Spectral congestion has become an important issue that can not be ignored in the development of wireless communications.The main reason for this is not the lack of spectrum but the fact that most of the spectrum is not properly used.Cognitive Radio(CR)can effectively solve the problem of spectrum congestion by real-time monitoring of the spectrum,dynamic access to the spectrum,and real-time coordinated spectrum usage.Software Defined Radio(SDR)emphasizes the construction of an open,standardized and modular general-purpose hardware platform,constantly updating the software of each module to adapt to the evolving source codec,channel codec and modem system with considerable flexibility and openness.The CR-based SDR platform offers greater flexibility and provides ample room for its development in the wireless communications space.The Spectrally Modulated,Spectrally Encoded(SMSE)model provides a unified multi-carrier waveform generation framework for CR-based SDR based on it's practicality and flexibility.In this paper,the basic mathematic model of SMSE system is given.The basic multi-carrier waveforms are simulated by this model to verify the correctness and practicability of the model.Secondly,this paper expands the original SMSE model to the MIMO SMSE model,which makes it have the ability of transmitting in MIMO system,making the model more general.The transmit waveforms of Alamouti system and the V-BLAST system with 2 transmit antennas are respectively generated by the MIMO SMSE model.The correctness and practicability of the model are verified by observing the bit error rate of the waveform.In order to achieve the best throughput in the coexistence environment of primary and secondary users,a MIMO SMSE model based on soft decision is proposed.Based on the optimization of subcarrier power and bit allocation in MIMO SMSE model,a method based on intelligent soft decision is proposed to select the frequency use variable and data modulation variable to maximize system throughput. |
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