Cellular CDMA capacity improvement using ad hoc relaying with a dynamic relay selection protocol

In this paper we consider the capacity of a cellular CDMA system when there is out-of-band ad hoc traffic relaying. In the system studied, the mobile stations (MSs) are dual-mode, having both ad hoc and cellular CDMA radios. An active MS is free to choose any available relay station (RS) within its ad hoc radio coverage area for communication with the CDMA base station (BS). A number of relay station selection criteria are considered, namely ad hoc relaying with least interference ratio (ARIR), ad hoc relaying with best link gain (ARLG), and ad hoc relaying with shortest distance (ARSD). The results show that very significant capacity improvements are possible by using these criteria, compared with conventional CDMA with hard or soft handoff. Ad hoc relaying which can dynamically track the CDMA link quality when choosing an RS (including ARIR and ARLG) can achieve even higher capacity improvement than that with a static relay station selection criterion (ARSD). Furthermore, the capacity improvement achieved using ARIR and ARSD is almost independent of the transmission quality of the ad hoc air interface.