Interference-robust Air Interface for 5G Small Cells: Managing inter-cell interference with advanced receivers and rank adaption

Since the release of the first High Speed Packet Access (HSPA) networks in
2005, the demand for mobile broadband services has increased continuously
at staggering rates, fuelled by the mass adoption of smartphones. It is forecast
that this trend will continue for at least the next decade, pushing the
existing wireless network infrastructure to the limit. Mobile network operators
must invest in network expansion to deal with this problem, but the
predicted network requirements show that a new Radio Access Technology
(RAT) standard will be fundamental to reach the future target performance.
This new 5th Generation (5G) RAT standard is expected to support data rates
greater than 10 Gbps with very low latency, very low energy consumption
and provide the required scalability that will allow the network to transport
a 1000 to 10000 times more mobile data traffic in 2020 than a similar network
would do in 2010.
To meet these challenging network capacity expansion requirements, the
design of the new 5G RAT standard will make use of three main strategies:
more antennas, more spectrum and more cells. All these strategies will have
important roles in the new system, but the deployment of a massive number
of small cells, especially indoors, is expected to provide the largest improvement
in network capacity. However, the benefits of this type of ultra-dense
deployment do not come for free; strong inter-cell interference, an inherent
problem of dense networks, has the potential to limit the expected gains. Due
to the fundamental role of inter-cell interference in this type of networks, the
inter-cell interference problem must be addressed since the beginning of the
design of the new standard.
This Ph.D. thesis deals with the design of an interference-robust air interface
for 5G small cell networks. The interference robustness is achieved
by the clever design of the radio frame structure in such a way that interference
suppression receivers can efficiently and effectively mitigate the effects
of inter-cell interference. A detailed receiver model is derived (including also
receiver imperfections, such as estimation errors and receiver front-end limitations)
and applied in extensive system-level simulation campaigns. These
simulations show that, when the interference-robust air interface design is
used, interference suppression receivers are indeed a valid alternative to traditional
Inter-cell Interference Coordination (ICIC) techniques that are commonly
applied to improve the outage performance of these networks.
Moreover, a novel inter-cell interference management concept is proposed.
This concept is based on the effect that the rank adaptation decisions in one
cell cause on the neighbouring cells when interference suppression receivers
are used. The concept, known as victim-aware rank adaptation, may be used
to improve the outage data rates of the network. In particular, the Maximum
Rank Planning (MRP) technique is shown to outperform traditional frequency reuse planning, with the advantage of lower implementation complexity
due to the simplified planning process.