USRP Implementation of Transmission Timing Control Function for Synchronized SS-CDMA Using Wireless Two-Way Interferometry (Wi-Wi)

Synchronized spread spectrum code division multiple access (SS-CDMA) is very effective for increasing the capacity and reducing the interference with a rapid spread of Internet of things (IoT) devices. Since the synchronized SS-CDMA requires to receive timing synchronization, it is essential to realize transmission timing control of each node using spacetime synchronization. In this paper, we investigate precise time synchronization between nodes using Wireless Two-Way Interferometry (Wi-Wi). The measurement results show that the precision of initial timing synchronization of the Wi-Wi module is nearly equal to 400 ns. Furthermore, we implement transmission timing control function on Universal Software Radio Peripheral (USRP) synchronized by reference signals of Wi-Wi module. As a result of the measurement evaluation of the implemented system, it is realized that the transmission timing is controlled at the accuracy of the sampling rate of USRP.