  Small cells are a cost-effective way to reliably expand network coverage and
provide significantly increased capacity for end users. The ultra-high
bandwidth available at millimeter (mmWave) and Terahertz (THz) frequencies can
effectively realize short-range wireless access links in small cells enabling
potential uses cases such as driver-less cars, data backhauling and
ultra-high-definition infotainment services. This paper describes a new
software defined network (SDN) framework for vehicles equipped with
transceivers capable of dynamically switching between THz and mmWave bands. We
present a novel SDN controlled admission policy that preferentially handoffs
between the mmWave and THz small cells, accommodates asymmetric uplink/downlink
traffic, performs error recovery and handles distinct link states that arise
due to motion along practical vehicular paths. We then analytically derive the
resulting capacity of such a small cell network by accounting for the channel
characteristics unique to both these spectrum bands, relative distance and the
contact times between a given transceiver pair. We then formulate the optimal
procedure for scheduling multiple vehicles at a given infrastructure tower,
with regards to practical road congestion scenarios. The search for the optimal
schedule is shown to be a NP-hard problem. Hence, we design a
computationally-feasible polynomial-time scheduling algorithm that runs at the
SDN controller and compare its performance against the optimal procedure and
random access. Additionally, we present a simulation-based case study for the
use case of data center backhauling in Boston city to showcase the benefits of
our approach.
