The combination of macrocells and microcells in a two-tier cellular system is attractive because it provides a balance between maximizing the number of users per unit area and minimizing the network control associated with handoff. In this paper we study system capacity of a two-tier cellular architecture employing 3 TDMA/CDMA strategies. Both the uplink and downlink are evaluated via mathematical analysis. It shows that system performance degrades for larger macrocells or microcells and the capacities are poor for users near the macrocells' boundary. It also shows a huge discrepancy between the results obtained for the center cell versus those obtained for the boundary cell.