Research on Code Division Multiple Access Based on Chirp Multi-Carrier

Underwater acoustic (UWA) channels are characterized by narrow-band, time-varying, and strong multipath interference. At the same time, Doppler effect also has a significant impact in UWA communications due to low sound speed in water. Therefore, traditional wireless multiple access technology cannot be used directly underwater. However, by combining some existing technologies in underwater communications, the traditional multiple access method can be improved to enable underwater multiple access. In this paper, we introduced chirp signals as carriers, which is widely used in UWA communications. Combined with code division multiple access (CDMA) and orthogonal frequency division multiple access (OFDMA) techniques, a multi-carrier chirp signal based CDMA method is proposed, which improves the reliability and spectrum efficiency of underwater multiple access. The simulation results show that the proposed method has good Bit error rate (BER) performance. Further, the method is also able to achieve good BER performance under the influence of Doppler effect because chirp signals is capable of resisting Doppler effects.