Performance of quadratic and exponential multiuser chirp spread spectrum communication systems

A novel non-linear chirp spread spectrum modulation (CSSM) is introduced for binary data transmission in a multi-user (MU) environment. Two subclasses of non-linear signals namely quadratic (Q-CSSM) and exponential (E-CSSM) modulations are described and their properties are given. The chirp rates in these modulations are varied as a function of user in an MU environment using the orthogonal structure inherent in non-linear chirp signals. A generic MU communication system model that employs non-linear chirp signals is presented and its bit error rate (BER) performance is analyzed in additive white Gaussian noise (AWGN) channel, and Rayleigh and Nakagami-m fading environments as a function of the number of users in the system, signal-to-noise ratio (SNR), and multiple access interference (MAI). An investigation of the trade off between bandwidth and the number of users in the system is provided for both Q- and E-CSSM. Numerical results demonstrate that these proposed modulations with proper chirp rate assignment are very effective in reducing MAI.