In traditional cellular systems, the call requests initiated by mobile stations (MSs) must be carried through a base station (BS) via the cellular interface, but when MSs are located in the dead spots, their call requests will be blocked because the MSs cannot communicate with the BS. It is considered to relay these blocked communication traffic by using ad hoc relaying, which will improve the performance of the system as a whole. This paper firstly introduces a novel architecture of two-hop-relay cellular system, and analyzes the communication traffic characteristics of the traditional cellular system and two-hop-relay cellular system respectively in the dead spots environment. Numerical results show that the two-hop-relay cellular system outperforms the traditional cellular system in terms of the call blocking rate when considering the impact of dead spots.