  In this paper, we consider a novel cache-enabled heterogeneous network
(HetNet), where macro base stations (BSs) with traditional sub-6 GHz are
overlaid by dense millimeter wave (mmWave) pico BSs. These two-tier BSs, which
are modeled as two independent homogeneous Poisson Point Processes, cache
multimedia contents following the popularity rank. High-capacity backhauls are
utilized between macro BSs and the core server. A maximum received power
strategy is introduced for deducing novel algorithms of the success probability
and area spectral efficiency (ASE). Moreover, Monte Carlo simulations are
presented to verify the analytical conclusions and numerical results
demonstrate that: 1) the proposed HetNet is an interference-limited system and
it outperforms the traditional HetNets; 2) there exists an optimal pre-decided
rate threshold that contributes to the maximum ASE; and 3) 73 GHz is the best
mmWave carrier frequency regarding ASE due to the large antenna scale.
