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Wireless sensor networks are being geared up for applications that range from consumer markets to military industries. While the wireless sensors perform the same sensing task within the region of interest, there may be a lot of topological asymmetry with respect to their roles in other operational activities. Double tiered wireless sensor network (DWSN) is such kind of heterogeneous sensor network where lower tier is responsible to detect each and every event and upper tier conveys that data to base-station. A real challenge for this architecture is to deploy a minimum set of relay nodes in such a fashion that each sensor node must have at least one relay node within its one hop distance and all deployed relay nodes eventually form a connected network among themselves including one or more base-stations. This is an NP-hard problem. Thus, an approximation algorithm is necessary to find a feasible solution, which is bounded by a polynomial time complexity. Unfortunately, we have very few such algorithms. This paper reveals an approximation algorithm that runs in O(n2) time complexity, to find a feasible solution for above challenge. This paper also describes a framework to solve the above problem in nonconvex shaped deployment region.