Performances of trigonometric chirp spread spectrum modulation in AWGN & rayleigh channels

A linear CSS (Chirp Spread Spectrum) system generally requires its time-bandwidth product to be 60 or more in order to achieve satisfactory orthogonality between different chirp signals. Thus, a linear CSS system occupies very wide bandwidth (e.g. 60MHz or higher) for 1μs chirp duration. To improve the orthogonality and to reduce the bandwidth requirements, this paper explores two kinds of non-linear chirps: power function chirp and trigonometric chirp. It is concluded that a pair of trigonometric chirp can be made orthogonal under some mild conditions, and the orthogonality shows periodic characteristic. In other words, the CSS system based on trigonometric chirp could result in significant reduction in required bandwidth as compared to that of linear chirps for the same channel performance. Further, extensive simulations have been carried out to illustrate the BER vs. Eb/No performance in Gaussian and Rayleigh channels. The results show that the performance of the CSS system based on trigonometric chirp outperforms that of linear chirp based systems, especially when the time-bandwidth product of chirp is small (e.g. 30sHz or less).

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