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

摘要

Since the release of the first High Speed Packet Access (HSPA) networks in2005, the demand for mobile broadband services has increased continuouslyat staggering rates, fuelled by the mass adoption of smartphones. It is forecastthat this trend will continue for at least the next decade, pushing theexisting wireless network infrastructure to the limit. Mobile network operatorsmust invest in network expansion to deal with this problem, but thepredicted 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 ratesgreater than 10 Gbps with very low latency, very low energy consumptionand provide the required scalability that will allow the network to transporta 1000 to 10000 times more mobile data traffic in 2020 than a similar networkwould do in 2010.To meet these challenging network capacity expansion requirements, thedesign of the new 5G RAT standard will make use of three main strategies:more antennas, more spectrum and more cells. All these strategies will haveimportant roles in the new system, but the deployment of a massive numberof small cells, especially indoors, is expected to provide the largest improvementin network capacity. However, the benefits of this type of ultra-densedeployment do not come for free; strong inter-cell interference, an inherentproblem of dense networks, has the potential to limit the expected gains. Dueto the fundamental role of inter-cell interference in this type of networks, theinter-cell interference problem must be addressed since the beginning of thedesign of the new standard.This Ph.D. thesis deals with the design of an interference-robust air interfacefor 5G small cell networks. The interference robustness is achievedby the clever design of the radio frame structure in such a way that interferencesuppression receivers can efficiently and effectively mitigate the effectsof inter-cell interference. A detailed receiver model is derived (including alsoreceiver imperfections, such as estimation errors and receiver front-end limitations)and applied in extensive system-level simulation campaigns. Thesesimulations show that, when the interference-robust air interface design isused, interference suppression receivers are indeed a valid alternative to traditional Inter-cell Interference Coordination (ICIC) techniques that are commonlyapplied 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 onecell cause on the neighbouring cells when interference suppression receiversare used. The concept, known as victim-aware rank adaptation, may be usedto improve the outage data rates of the network. In particular, the MaximumRank Planning (MRP) technique is shown to outperform traditional frequency reuse planning, with the advantage of lower implementation complexitydue to the simplified planning process.