In this paper, we propose a robust synchronization technique for an asynchronous spread spectrum communication system based on chaotic symbolic dynamics modulation. A back-ward iteration of the chaotic map is used to avoid the problem of sensitivity to initial conditions of the chaotic generator. The proposed system integrates a spread spectrum unit, which is used to increase transmission security and to achieve the transmission in a multi-user case. The synchronization technique is assessed in terms of probability of detection and of probability of false alarm. Simulation results prove that the proposed system can achieve phase synchronization with a low signal-to-noise ratio.