Localization is one of the fundamental tasks in underwater acoustic sensor network (UASN) which is a challenging issue due to inhomogeneity and bandwidth limitation of underwater medium. Time of flight (TOF) and received signal strength (RSS) measurements are two major techniques used for localization. The TOF based localization achieves high resolution when available bandwidth is high enough and also transmitter and receiver can be synchronized well. However, in the RSS, sensors do not need to be synchronized. In this paper we propose a new RSS based localization method for inhomogeneous underwater medium with an isogradient sound speed profile in which acoustic waves propagate along curvature path. To develop the localization algorithm, at the first step, we obtain the relation of transmission loss for acoustic wave propagation in inhomogeneous medium. Then, an oversampled matched filter based method for RSS measurement (OSMF-RSS) is proposed in asynchronous transmitter–receiver scenario. After that, an iterative localization algorithm is derived based on the RSS measurements. Moreover, we examine how the performance of our proposed algorithm affects by flat fading phenomenon which is a challenge of RSS based algorithms. We evaluate the performance of the proposed OSMF-RSS method by computer simulations under different conditions. The results show that the OSMF-RSS method outperforms the TOF based method in accuracy sense when the bandwidth of received signal is less than specific level. Note that, this achievement of the OSMF-RSS method is attained in asynchronous scenario, while in the TOF method transmitter–receiver should be synchronized

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