An effective tracking loop for chirp spread spectrum communication systems

Compared with pseudo-noise (PN) sequences, chirp signals have obvious advantages in acquisition time and tracking performance in the field of telemetry, track, and command (TT&C) with the large Doppler tolerance. In this paper, an effective tracking loop for chirp spread spectrum communication is proposed, which can realize chirp signals modulated by binary phase shift keying (Chirp-BPSK) coherent demodulation with particular Doppler shifts and dynamics, while the bit error rate (BER) is same with the binary phase shift keying (BPSK). First, we design an updated chirp delay locked loop (CDLL) for the chirp signal, and then analyze the performance of the tracking loop such as the pull-in range, measurement errors of CDLL and the carrier loop. Theoretical analysis and simulations demonstrate that the CDLL measurement error is close to the Cramer-Rao lower bound (CRLB) while the carrier tracking loop measurement error is close to the theoretical thermal noise jitter. Finally, BER performance of Chirp-BPSK, with exploiting the proposed loop, increases more than 3dB compared with chirp signals modulated by binary orthogonal keying (Chirp-BOK).