Joint CFO and STO Estimation for Modified Walsh-Hadamard Code Division Multiplexing

In helicopter satellite communications, the periodic blockage of the transmission channel arises due to rotor blades. Modified Walsh-Hadamard code division multiplexing (MWHCDM) overcomes the periodic blockage. In MWHCDM, estimating the symbol timing offset (STO) is necessary to perform demultiplexing. The carrier frequency offset (CFO) significantly degrades the accuracy of STO estimation. Thus, STO estimation requires estimating and removing the CFO, although CFO estimation is only possible without STO. This paper proposes a joint CFO and STO estimation method to resolve this dilemma, combining the CFO and STO estimation to complement each other. Computer simulation shows that the proposed method accurately estimates both CFO and STO.