Coding and Coherent Decoding techniques for Continuous Single Slope Cyclic Shift Chirp Signal

Abstract

Chirp signals are currently widely used in broadband and spread spectrum communications due to their advantageous features, such as immunity to fading noise, low power consumption, consistent long-range transmission, and constant bandwidth. As a result, they are applied at the physical layer of the Internet-of-Things (IoT). This study proposes two techniques for encoding and decoding 4-cyclic shift chirp symbols, based on addition and subtraction operations. The proposed techniques have simple structures that can be easily implemented using analog circuits. The proposed encoding techniques reveal the relationship between cyclic-shift chirp symbols and pulse modulating signals (PWM, PPM, and PAM), which has rarely been discussed in prior research. Moreover, the circuits for encoding and decoding of the proposed techniques are implemented by discrete commercial devices at low frequency (25-35kHz) which is suitable for sonar and communication under water. However, this proposed technique is not limited to only low frequency but can also be used in high-frequency bands. Experimental and simulation results also show good agreement to theoretical analysis.