A distributed antenna system (DAS) architecture is considered to be a key enabler for further Network Virtualization where different network configurations are created as needed by a centralized decision making unit that is typically integrated into the Cloud Radio Access Networks (C-RAN) which offers a potential architecture for 5G wireless communication systems. Many schemes have been proposed for Fractional Frequency Reuse (FFR) for resource allocation in the static cellular network architecture. In this paper, we investigate the effect of different FFR resource allocation approaches on the downlink cell edge users' capacity. We use a Multiset approach to model the resource allocation and interference. Targeting maximum average capacity, a closed-form lower bound of the average capacity is derived and the optimum FFR resource allocation is obtained. This provides a guide in the evaluation of DAS performance.