The Study Of Adaptive Modulation And Demodulation In Cognitive Anti-interfere

Future mobile communications have to support the transmission of high rate data and multimedia applications in the radio spectrum, which is already extremely scarce. As one of the key techniques of new generation mobile communication systems and broadband wireless communications systems, "Adaptive transmission" technique can exploit potential channel transmission ability sufficiently so that it enables the systems to reach the maximum transmission capacity and reliability by dynamically adjusting transmission parameters according to channel estimation and traffic QoS requirement.In the adaptive transmission, the way of combining signal signaling and detection technology to receive and detect transmission parameter, to complete information sharing between sender and receiver, can save the spend of signal, while reducing the estimation error, simplify transceiver. It has important significance to enhance receiver intelligent level and overall performance.The most important character of the next generation mobile system will be smart transmission whose function module will be implemented by smart processing unit. This paper deals with the blind detection techniques in adaptive transmission. The main research works and results are listed as follows:1. On the basis of existing Adaptive modulation system, it has constructed on the combining signal signaling and detection technology, variable baud rate and variable rate adaptive modulation system.2. The two properties of QAM constellation map have been analyzed and compared, and receive satellite signals in the best-QAM constellation map.3. Because of the modulation system based on variable baud rate, the estimation to signal's baud rate is one of its key technologies. The article has estimated the signal's baud rate in both time domain and frequency domain. To the estimation of the baud rate for the known sequence, it can be used in the estimation in the time domain, simple and efficient.4. Modulation system cheese the mode of modulation based on the signal to noise ratio of the signals. So, the estimation of signal to noise ratio is also one of its key technologies. The algorithm of the SNR estimation has been improved in this article. In the case of known modulation mode, reducing the estimated range, abandoning samples of large deviation, in order to raise the accuracy of the estimation.5. The spectrum efficiency has been compared between adaptive modulation and the general MQAM modulation. It shows that the adaptive modulation has the higher spectral efficiency by computer simulation.