  Femtocells are recognized effective for improving network coverage and
capacity, and reducing power consumption due to the reduced range of wireless
transmissions. Although highly appealing, a plethora of challenging problems
need to be addressed for fully harvesting its potential. In this paper, we
investigate the problem of cell association and service scheduling in femtocell
networks. In addition to the general goal of offloading macro base station
(MBS) traffic, we also aim to minimize the latency of service requested by
users, while considering both open and closed access strategies. We show the
cell association problem is NP-hard, and propose several near-optimal solution
algorithms for assigning users to base stations (BS), including a sequential
fixing algorithm, a rounding approximation algorithm, a greedy approximation
algorithm, and a randomized algorithm. For the service scheduling problem, we
develop an optimal algorithm to minimize the average waiting time for the users
associated with the same BS. The proposed algorithms are analyzed with respect
to performance bounds, approximation ratios, and optimality, and are evaluated
with simulations.
