Spread spectrum synchronizing loop for spreading code modulated by code shift keying
Tadayoshi Yoshida, Masao Nakagawa · Electronics and Communications in Japan (Part I Communications) · 1984
Abstract Sequence Inversion Keying (SIK) which inverts the signs of the spreading codes, has been used mainly for conventional Spread Spectrum (SS) modulation. Since SIK modulation is essentially not suited to multilevel transmission which enables us to decrease inter‐channel interference, the inter‐channel interference begins increasing significantly if we try to improve the interference characteristic or the multiplexing capability. to improve the performance of the SS, code shift keying (CSK), which is a kind of multilevel modulation, of the spreading code has been proposed recently. However, there have been no reports of a synchronous technique for CSK at the receiver. This paper proposes two types of new synchronizing loops for CSK of SS and their performances are evaluated through experiments. the loops for a 2‐phase and 4‐phase CSKs are treated in the experiments. Both show good synchronizing characteristics and the synchronizing loops which show little performance deterioration despite the increase in the number of phases, are obtained. the proposed schemes compare favorably with the conventional SIK synchronizing loops and give practically sufficient results.