  Heterogeneous network (HetNet) is a promising concept for increasing capacity
and alleviating spectrum scarcity. In HetNets, however, channel assignment and
transmit power control affect the distribution of users among base stations. We
present a novel scheme to maximize the uplink sum rate in two-tier HetNets with
one macrocell and several femtocells, where the transmit power of each user is
bounded and at least one channel is assigned to each user. We divide the
problem into two sub-problems: one for channel assignment and one for transmit
power control and solve them by iteratively alternating between the two. Our
scheme is convergent and yields a transmission rate above 6 bps/Hz for almost
50% of users as compared to the same for 10% of users in SINR-based schemes.
When users are in cell boundaries, the average transmission rate for fractional
frequency reuse is up to 20% more compared to the conventional full frequency
reuse. This is due to reduced transmit power resulting in less interference.
