Using hypergraph theory to model coexistence management and coordinated spectrum allocation for heterogeneous wireless networks operating in shared spectrum

Electromagnetic waves in the Radio Frequency (RF) spectrum are used to convey wireless transmissions from one radio antenna to another. Spectrum utilisation factor, which refers to how readily a given spectrum can be reused across space and time while maintaining an acceptable level of transmission errors, is used to measure how efficiently a unit of frequency spectrum can be allocated to a specified number of users. The demand for wireless applications is increasing exponentially, hence there is a need for efficient management of the RF spectrum. However, spectrum usage studies have shown that the spectrum is under-utilised in space and time. A regulatory shift from static spectrum assignment to DSA is one way of addressing this. Licence exemption policy has also been advanced in Dynamic Spectrum Access (DSA) systems to spur wireless innovation and universal access to the internet. Furthermore, there is a shift from homogeneous to heterogeneous radio access and usage of the same spectrum band. These three shifts from traditional spectrum management have led to the challenge of coexistence among heterogeneous wireless networks which access the spectrum using DSA techniques. Cognitive radios have the ability for spectrum agility based on spectrum conditions. However, in the presence of multiple heterogeneous networks and without spectrum coordination, there is a challenge related to switching between available channels to minimise interference and maximise spectrum allocation. This thesis therefore focuses on the design of a framework for coexistence management and spectrum coordination, with the objective of maximising spectrum utilisation across geographical space and across time. The amount of geographical coverage in which a frequency can be used is optimised through frequency reuse while ensuring that harmful interference is minimised. The time during which spectrum is occupied is increased through time-sharing of the same spectrum by two or more networks, while ensuring that spectrum is shared by networks that can coexist in the same spectrum and that the total channel load is not excessive to prevent spectrum starvation. Conventionally, a graph is used to model relationships between entities such as interference relationships among networks. However, the concept of an edge in a graph is not sufficient to model relationships that involve more than two entities, such as more than two networks that are able to share the same channel in the time domain, because an edge can only connect two entities. On the other hand, a hypergraph is a generalisation of an undirected graph in which a hyperedge can connect more than two entities. Therefore, this thesis investigates the use of hypergraph theory to model the RF environment and the spectrum allocation scheme. The hypergraph model was applied to an algorithm for spectrum sharing among 100 heterogeneous wireless networks, whose geo-locations were randomly and independently generated in a 50 km by 50 km area. Simulation results for spectrum utilisation performance have shown that the hypergraph-based model allocated channels, on average, to 8% more networks than the graph-based model. The results also show that, for the same RF environment, the hypergraph model requires up to 36% fewer channels to achieve, on average, 100% operational networks, than the graph model. The rate of growth of the running time of the hypergraph-based algorithm with respect to the input size is equal to the square of the input size, like the graph-based algorithm. Thus, the model achieved better performance at no additional time complexity.Electromagnetic waves in the Radio Frequency (RF) spectrum are used to convey wireless transmissions from one radio antenna to another. Spectrum utilisation factor, which refers to how readily a given spectrum can be reused across space and time while maintaining an acceptable level of transmission errors, is used to measure how efficiently a unit of frequency spectrum can be allocated to a specified number of users. The demand for wireless applications is increasing exponentially, hence there is a need for efficient management of the RF spectrum. However, spectrum usage studies have shown that the spectrum is under-utilised in space and time. A regulatory shift from static spectrum assignment to DSA is one way of addressing this. Licence exemption policy has also been advanced in Dynamic Spectrum Access (DSA) systems to spur wireless innovation and universal access to the internet. Furthermore, there is a shift from homogeneous to heterogeneous radio access and usage of the same spectrum band. These three shifts from traditional spectrum management have led to the challenge of coexistence among heterogeneous wireless networks which access the spectrum using DSA techniques. Cognitive radios have the ability for spectrum agility based on spectrum conditions. However, in the presence of multiple heterogeneous networks and without spectrum coordination, there is a challenge related to switching between available channels to minimise interference and maximise spectrum allocation. This thesis therefore focuses on the design of a framework for coexistence management and spectrum coordination, with the objective of maximising spectrum utilisation across geographical space and across time. The amount of geographical coverage in which a frequency can be used is optimised through frequency reuse while ensuring that harmful interference is minimised. The time during which spectrum is occupied is increased through time-sharing of the same spectrum by two or more networks, while ensuring that spectrum is shared by networks that can coexist in the same spectrum and that the total channel load is not excessive to prevent spectrum starvation. Conventionally, a graph is used to model relationships between entities such as interference relationships among networks. However, the concept of an edge in a graph is not sufficient to model relationships that involve more than two entities, such as more than two networks that are able to share the same channel in the time domain, because an edge can only connect two entities. On the other hand, a hypergraph is a generalisation of an undirected graph in which a hyperedge can connect more than two entities. Therefore, this thesis investigates the use of hypergraph theory to model the RF environment and the spectrum allocation scheme. The hypergraph model was applied to an algorithm for spectrum sharing among 100 heterogeneous wireless networks, whose geo-locations were randomly and independently generated in a 50 km by 50 km area. Simulation results for spectrum utilisation performance have shown that the hypergraph-based model allocated channels, on average, to 8% more networks than the graph-based model. The results also show that, for the same RF environment, the hypergraph model requires up to 36% fewer channels to achieve, on average, 100% operational networks, than the graph model. The rate of growth of the running time of the hypergraph-based algorithm with respect to the input size is equal to the square of the input size, like the graph-based algorithm. Thus, the model achieved better performance at no additional time complexity

Malawi's TV white space regulations : a review and comparison with FCC and Ofcom regulations

Regulators are in the process of framing regulations to allow secondary use of vacant TV channels while protecting TV broadcast services from harmful interference. While the US and UK regulators have already passed such regulations in 2008 and 2015 respectively, other countries are still in drafting stages and the underlying circumstances in these countries could be different from those of the US and UK. Malawi released its final draft regulations in 2016. While the US and UK legislate for dynamic spectrum access and licence-exemption for secondary users, Malawi’s draft regulations require such users to apply for a licence for assigned TV white space spectrum. This paper provides an analytical review of Malawi’s regulations and a comparison with FCC and Ofcom regulations, which new regulations can build on. This analysis will also inform future work on network management tools that can enable practical deployment and coexistence of large-scale TV white space networks in a dynamic spectrum access environment in Africa

Comparison of graph-based and hypergraph-based models for wireless network coexistence

Dynamic Spectrum Access (DSA) is regarded as a promising solution for efficient spectrum management. Regulators have also approved licence-exemption or general authorisation access (GAA) to further improve spectrum accessibility for DSA systems in the Television (TV) and 3.5 GHz bands. However, heterogeneous DSA radio standards have been developed and the gains in spectrum efficiency could be undermined by coexistence challenges. Hence, the IEEE 802.19.1 standard for wireless network coexistence methods was published, but it leaves algorithmic implementation of the methods to the industry. When the spectrum is not sufficient for exclusive channel allocation, the standard includes a method for co-channel sharing among coexistent neighbour networks. In previous work, channel sharing was introduced on top of the exclusive channel allocation. However, channel sharing options could be significantly limited by the outcome of the exclusive channel allocation. Alternatively, this paper proposes use of hypergraph theory to model the co-sharing strategy for coexistence management of heterogeneous radio systems. Results demonstrate that the hypergraph method achieves higher average spectrum utilisation by up to 8% and requires up to 5 fewer channels to achieve, on average, 100% operational networks than the previous method

Hypergaph-based model for coexistence management of heterogeneous wireless networks

raditional graph theory is typically used to model interference relations among networks to realise channel assignment that enables improvement in spectrum utilisation through spatial re-use of the channels. Studies have shown that spectrum utilisation could be further improved through co-sharing among networks that are capable of spectral coexistence as long as the channel load is not excessive. The co-sharing networks use their inherent media access control (MAC) techniques to coordinate access to a shared channel. However, the concept of an edge in a traditional graph, which is a two-element subset, is not sufficient to model subsets of potential co-sharing networks because such subsets may have cardinality of greater than 2. Instead, this paper proposes use of hypergraph theory to model the co-sharing strategy in an environment that comprises heterogeneous radio systems. The model could be applied in centralised coexistence management frameworks such as IEEE 802.19.1-based systems. Results demonstrate that spectrum sharing using the hypergraph model achieves higher average spectrum utilisation by up to 17.5% when there are 3 available channels, and requires up to 7 fewer channels to achieve, on average, 100% operational networks than spatial re-use alone

TV white space for Internet access in the developing world

In 2013, the University of Strathclyde began working with Microsoft’s 4Afrika programme to create a data communications network in Kenya, providing connectivity and Internet access to a number of rural locations, including schools and health clinics in remote villages. This project has led to the development of Mawingu Networks, a fully licensed internet service provider using “White Space” radio frequencies to enable low cost internet access via renewable powered base stations. Since going live in 2016, the network now has more than 27,000 unique users across a wide geographical area. Despite the fact that universal Internet access is part of the UN’s sustainable development goals, and has been shown to spur social and economic development, a large percentage of people in developing countries do not yet have access. This is often due to a lack of infrastructure, large distances and dispersed populations. This poster presents an overview of TV White Space technologies, with emphasis on our 4Afrika collaboration with Microsoft and Mawingu Networks. In addition, an insight into some recent developments in other African countries (Malawi, Zambia, and Ghana) is presented

Software Defined Radio with Zynq Ultrascale+ RFSoC

This book introduces Zynq Ultrascale+ RFSoC, a technology that brings real, single-chip Software Defined Radio (SDR) to the marketplace. RFSoC devices are the first adaptive SoCs (Systems-on-Chip) to monolithically integrate multiple RF signal chains along with Arm application and real-time, multicore processors and programmable logic. RFSoC is not so much a radio on a chip, but almost an entire base station on a chip! We anticipate that the book will be of interest and use across a number of technical areas. It serves as an introduction to the family of RFSoC devices and its key features and programmability. The book explores SDR concepts and architecture and key DSP algorithms. A selection of hands-on exercises via Jupyter Lab notebooks accompany the book and are available from the companion GitHub repositor