  With the proliferation of mobile terminals and the continuous upgrading of
services, 4G LTE networks are showing signs of weakness. To enhance the
capacity of wireless networks, millimeter waves are introduced to drive the
evolution of networks towards multi-band 5G heterogeneous networks. The
distinct propagation characteristics of mmWaves and microwaves, as well as the
vastly different hardware configurations of heterogeneous base stations, make
traditional access strategies no longer effective. Therefore, to narrowing the
gap between theory and practice, we investigate the access strategy in
multi-band 5G heterogeneous networks, taking into account the characteristics
of mobile users, asynchronous switching between uplink and downlink of pico
base stations, asymmetric service requirements, and user communication
continuity. We formulate the problem as integer nonlinear programming and prove
its intractability. Thereby, we decouple it into three subproblems: user
association, switch point selection, and subchannel allocation, and design an
algorithm based on optimal matching and spectral clustering to solve it
efficiently. The simulation results show that the proposed algorithm
outperforms the comparison methods in terms of overall data rate, effective
data rate, and number of satisfied users.
