Performance evaluation of a network synchronization technique for CDMA cellular communications

Abstract

For code-division multiple-access (CDMA) cellular communications synchronous operation offers significant advantages over asynchronous operation. This feature has been already included in second-generation systems, such as the CdmaOne based on the IS-95 standard. Nonetheless, synchronous operation does not seem to be assessed as a basic system option for third-generation systems. This is mainly due to the contrasted choice of having global positioning system (GPS) receivers located at any of the base transceiver stations (BTSs) to perform station synchronization. However, the existing CdmaOne interface permits time transfer between the various BTSs and a simple time difference measurement technique can provide an internal, network-based means for time synchronization of base stations clocks. This paper considers a previously proposed approach based on the pilot strength measurements message delivered by every mobile station (MS), combined with round trip delay measurements that BTSs perform on the MS transmissions. We consider some possible algorithms to reduce time misalignments, and continuously phase-lock the clocks at different BTSs. Having developed an appropriate analytical/simulation approach, in the environment of a CDMA network, the paper evaluates and compares the performance of two suitable centralized architecture configurations, i.e., master-slave synchronization (MSS) and mutual synchronization (MUS). Both network architectures turn out to be applicable and provide suitable timing performance. Finally, the paper provides a preliminary discussion on some related issues, such as GPS avoidance, synchronization of BTSs inside buildings, tunnels, and subways and hybrid MSS/MUS synchronization network architectures.