Fast adaptive interference cancellation in chirp spread spectrum systems

For a fast reliable data transmission in a heavily distorted indoor environment, a SAW based chirp spread spectrum system operating in the 2.45 GHz ISM band is presented. Due to the implementation of SAW matched chirp filters for impulse compression there is no necessity of synchronization for coherent detection in the receiver. This system design remains low cost. Using a bandwidth as wide as allowed makes it possible to mitigate Rayleigh fading with large coherence bandwidths. A chirp matched filter system allows jammers to pass though corresponding to its transfer loss at the jammers frequency. Dividing the SAW chirp interdigital transducer (IDT) in time (equivalent to frequency) intervals, a jammer can be suppressed by switching off the corresponding frequency interval. The switchable chirp filter is implemented by interrupting one bus bar of the dispersive IDT and adaptive summation of intervals by external summation. Gating away one or more taps means switching off a part of the chirp in the frequency and time domain, respectively. The method can be applied to a wide range of applications, such as interference reduction, control of the transmitted spectrum and enhancing the data rate. Due to its simplicity it is suitable even for low cost systems. Theoretical and experimental results prove the capability of the method.