| dc.description.abstract | The fifth generation (5G) mobile networks expect significantly higher transmission rate
and energy efficiency than existing networks. Heterogeneous networks (HetNets), where
various low power base stations (BSs) are underlaid in a macro-cellular network, are
likely to become the dominate theme during the wireless evolution towards 5G. However
the complex HetNets scenario poses substantial challenges to the user association design.
This thesis focuses on the user association optimisation for different HetNets scenarios.
First, user association policy is designed for conventional grid-powered HetNets via game
theory. An optimal user association algorithm is proposed to improve the downlink (DL)
system performance. In order to address the uplink-downlink (UL-DL) asymmetry issue
in HetNets, a joint UL and DL user association algorithm is further developed to enhance
both UL and DL energy efficiencies. In addition, an opportunistic user association
algorithm in multi-service HetNets is proposed for quality of service (QoS) provision of
delay constraint traffic while providing fair resource allocation for best effort traffic.
Second, driven by increasing environmental concerns, user association policy is designed
for green HetNets with renewable energy powered BSs. In such a scenario, the proposed
adaptive user association algorithm is able to adapt the user association decision to the
amount of renewable energy harvested by BSs.
Third, HetNets with hybrid energy sources are investigated, as BSs powered by both
power grid and renewable energy sources have the superiority in supporting uninterrupted
service as well as achieving green communications. In this context, an optimal
user association algorithm is developed to achieve the tradeoffs between average traffic
delay and on-grid energy consumption. Additionally, a two-dimensional optimisation on
user association and green energy allocation is proposed to minimise both total and peak
on-grid energy consumptions, as well as enhance the QoS provision.
Thorough theoretical analysis is conducted in the development of all proposed algorithms,
and performance of proposed algorithms is evaluated via comprehensive simulations. | en_US |
