Design And Performance Evaluation Of Noise-Like Carrier Modulation Digital Communication System

In conventional digital communication modulation schemes, the transmitted information is always mapped to a fixed analog carrier. Such modulation schemes have not any protective measures against eavesdropping. However, if broadband noise-like signal is used as a carrier to transmit the digital signal, since the transmitted signal is similar to the ambient noise, it is difficult to detect. Thus, the purpose of secure communication is achieved.In many communication channels, such as MIMO-OFDM Fading Channels, acoustic channels and the multiple access interference in a multi-user network, the observed noise exhibits non-Gaussian impulsive characteristics, e.g., the received signal is corrupted by heavy-tail distributions noise. Such kind of ambient noise can be modeled with α-stable distribution based on the generalized central limit theorem. As a consequence, a noise-like carrier modulation digital communication system is proposed based on α-stable distribution. The main work and achievements are as follows:1. Based on the communication scheme proposed by Cek, this paper makes several improvements to the parameter estimation module. Logarithmic Moments method is adopted to take the place of Fractional Lower Order Moment method, which greatly reduces the numerical computing. Besides, Bit Error Rates under different parameters are simulated to get the appropriate parameters, thus solving the problem unsettled in the original paper.2. A novel structure of noise-like carrier modulation digital communication system is proposed. The α-stable noise sequence, which is used for random carrier, is modulated by the binary message sequence to achieve the purpose of secure communication. The proposed communication system significantly simplifies the structure of the transceiver because only one α-stable noise source in the transmitter and a simple non-coherent demodulation in the receiver are required.3. On the basis of the noise-like carrier modulation digital communication system above, a multi-user concurrent transmission system is proposed based on Walsh function. The binary message sequence modulates SaS distributed noise-like carrier with the corresponding Walsh function. The receiver demodulates the transmitted signal according to the orthogonality of the Walsh function. The system retains the advantage of the system described above that each carrier corresponding to the transmitted bit is different. Thus, the transmitted signals are non-periodic. It is beneficial to secure transmission.