  We study joint spectrum allocation and user association in heterogeneous
cellular networks with multiple tiers of base stations. A stochastic geometric
approach is applied as the basis to derive the average downlink user data rate
in a closed-form expression. Then, the expression is employed as the objective
function in jointly optimizing spectrum allocation and user association, which
is of non-convex programming in nature. A computationally efficient Structured
Spectrum Allocation and User Association (SSAUA) approach is proposed, solving
the optimization problem optimally when the density of users is low, and
near-optimally with a guaranteed performance bound when the density of users is
high. A Surcharge Pricing Scheme (SPS) is also presented, such that the
designed association bias values can be achieved in Nash equilibrium.
Simulations and numerical studies are conducted to validate the accuracy and
efficiency of the proposed SSAUA approach and SPS.
