Large Scale Antenna Systems Made Practical: Advanced Signal Processing for Compact Deployments [LSAS-SP]

This project investigates signal processing techniques for practical and realistic implementations of large-scale antenna systems (LSAS) for energy- and spectral- efficient wireless communication.

It is expected that the energy bill for cellular networks will double by 2015 and therefore there is a growing concern to reduce the associated operational expenditure (OPEX) along with the global CO2 emission in all fields of communications. The physical layer of wireless communication is a core building block of the telecommunication system chain and the ever-increasing Quality-of-Service demands directly reflect on the performance requirements of the relevant signal processing techniques. The physical limitations of wireless propagation form the bottleneck of physical layer transmission. Multiple Input Multiple Output (MIMO) systems have proven particularly useful in circumventing this bottleneck by providing an increased number of data streams in the physical channel. Small scale MIMO systems are currently part of communication standards and commercial designs.
LSAS are envisaged for the next generations of wireless systems, to capitalise on the utilisation of multiple antennas, and deliver the transmission rates required for future communications in a power-efficient manner. LSAS involve several critical benefits:
- The transmit power is split to many low power antennas, of the order of milliWatts.
- Hence, the design of the radio frequency (RF) front-end components is simplified as low cost power amplifiers can be deployed.
- LSAS designs can be extremely robust in that the failure of one or a few of the antenna units would not appreciably affect the system.
- In terms of signal processing, by scaling up the dimensions of MIMO low complexity user detection and precoding become close-to-optimal.
- In information theoretic terms, as the numbers of antennas grow infinitely large, the statistics of the MIMO channel tend to deterministic functions.

and associated challenges:
- The massive amount of RF chains required to feed the hundreds of antennas poses an important practical challenge in their deployment,
- With the increase of spatial dimensions the complexity of even the simplest signal processing techniques increases significantly
- The massive antenna arrays must be deployed in the limited physical space that is available in both base stations and mobile devices. This creates two main effects which become particularly relevant in LSAS: spatial correlation due to the proximity of the antennas as signal sources and mutual coupling due to the proximity of the antennas as electrical components.
- For large numbers of antennas pilot sequences for channel estimation have to be reused between adjacent cells. Channel State Information (CSI) provisioning becomes a significant burden and the performance of LSAS becomes limited by the resulting inter-cell interference (pilot contamination problem).

This project tackles the issue of large scale antenna deployment by a) information theoretical analysis with realistic modelling, b) signal processing and CSI acquisition devoted to power efficiency and c) analogue-digital beamforming designs and reduced RF-chain solutions aimed at power- and cost- effective implementations. The project aims to achieve power-efficient transmission by large scale antenna systems based on two key disruptive concepts: a) using analogue beamforming using the principles of Electrically-Steerable Parasitic Array Radiators (ESPAR) based LSAS and b) exploiting constructive interference. In addition, this project re-examines the anticipated benefits of LSAS from the viewpoint of realistic deployments of the antenna arrays in limited physical space which are prone to increased correlation and coupling between the densely deployed antennas. We aim at a thorough and pragmatic investigation of the benefits of LSAS for Green Communications, and their practical implementation solutions.

Telecommunications are transforming the global landscape, public interaction and lifestyle. At the same time, the new services and changing customer demands are reshaping the telecommunications industry. The recent energy crisis and predicted saturation of the ICT sector profits are imposing a rethink of the relevant network design and business models. Presently, the focus is turning to large-scale MIMO systems towards improving the energy-efficiency of wireless transmission, which is currently energy-inefficient.

Commercial and societal impact: This project aims at a 1000x increase in power efficiency of wireless transceivers, through a multi-fold reduction in the transmit power consumption with a simultaneous increase in data rates of wireless communication systems. The primary impact of the above will be reducing the CO2 emissions associated with the ICT industry and alleviating the relevant environmental repercussions. By pursuing energy-efficient communications, the UK will reinforce its status as a leader in promoting the ethos of Green ICT towards tackling climate change. Secondly, by reducing the power consumed by the ICT sector, the relevant operational expenditure (OPEX) and consequently the cost-per-Mbyte will be reduced, boosting the currently diminishing profits for the telecommunications industry. At the same time, by improving the data rates of wireless links, the proposed work will contribute in improving the quality of service and user experience in wireless applications. By enforcing precoding techniques in the communication standards and shifting the architectural complexity from the user devices to the base stations, the products of the research will result in cheaper mobile devices, thus enhancing the penetration of the ICT industry in current and new markets. The overall advancement of the wireless communication technology through this project will impact the associated environmental, healthcare, security and industrial applications. Overall the current proposal aligns with the EPSRC portfolio of research in the themes of ICT, Digital Economy, and Energy, as detailed in the National Importance section, and will contribute to the economic competitiveness of the UK and enhance quality of life.

Academic impact: The vast impact of the work in the broader research communities, as detailed in the Academic Beneficiaries section, will boost the profile of the Communications groups in UCL and HWU and enhance the UK research impact in these areas by citation of the proposed work and international exposure. The creation of new knowledge in the above fields within this project, and the inclusion of this in the educational curricula will further establish the UK as a world leader in technological and applied state-of-the-art knowledge transfer. Apart from the theoretical modelling that will set the benchmarks for the system performance, the practical work on implementing LSAS with parasitic antenna arrays will attract commercial interest, stimulate industrial research and encourage joint academic-industrial collaboration on the field. This will further augment the research income for UCL and HWU through follow-on research projects and industrial consultancy. The adoption of the proposed techniques by global communication standards will further establish the UK as a leader in communication standardization. The protection of the created intellectual property and the commercialization of the antenna designs and signal processing solutions will improve the penetration of the UK sector in the multibillion telecommunications industry.

New experts: The research training within the project will develop the research profile, expertise and man power of the world class research groups in UCL and HWU and establish an inter-institutional team with excellence in Green Communications, by producing new experts in the field of LSAS, energy-efficient transmission, ESPAR antennas and wireless communications in general.