SUMMARYThis paper studies the impact of a femto-cell underlay deployment that shares radio frequency resources with urban macro-cells. Due to their random and uncoordinated deployment, femto-cells potentially cause destructive interference to macro-cells and vice versa. On the other hand, femto-cells promise to substantially enhance the spectral efficiency due to an increased reuse of radio resources. The performance of networks with indoor Home Evolved NodeB (HeNB) deployment is compared to a system where all users, including indoor users, are served by the outdoor macro Evolved NodeB (eNB). In addition, the impact of closedaccess and open-access femto-cell operation is examined. It is demonstrated that significant capacity gains can be achieved through such HeNB deployment, regardless of whether closed-access or open-access is considered. Results clearly indicate that the capacity gains through femto-cell deployment outweigh the additional interference they introduce.