Load pull compensation in multi user massive MIMO

The purpose of this research is to determine an algorithm and/or process that lends itself to a practical solution for load pull (mutual coupling), an issue that manifests itself in 'multi user massive multiple in multiple out' (MIMO) systems.

Antenna arrays used for beam forming or MIMO require the antenna elements to be physically close to each other. With this arrangement, active antenna elements affect their neighbours and visa versa; modifying the antenna impedance (at a given frequency) and electromagnetic field(s). This causes unwanted shifts in radiated power, RF beam direction and intensity.

Digital pre-distortion used to compensate for the non linear nature of power amplifiers has been used extensively and can also be employed to compensate for load pull. With a uniform linear phase difference across antenna elements, such as in conventional beam steering, the digital pre-distortion coefficients can be calculated relatively easily. However, with MIMO, the antenna elements phase and amplitude configuration is irregular and hence the effects of antenna elements on one another cannot be predicted. The dynamic MIMO channel matrix, in conjunction with the power amplifier transfer function and the antenna array characteristics are thus processed by said novel algorithm that calculates the digital pre-distortion coefficients for each element, actively compensating for load pull at each element.

This research details the MIMO load pull compensation algorithm and a practical real-time hardware/firmware solution. The resulting algorithm/implementation works within a large frequency range and for any PA/antenna combination. It is also inexpensive, low power and scale-able to ultra massive MIMO.

'Future Communications 2: Training Tomorrow's Internet Innovators' will deliver advanced training for the communications community nationally. Building on the existing Bristol CDT in Communications, our training will be extended to address High Performance Distributed and Embedded Systems (co-design in hardware and software domains) and Integrative Technologies (cross discipline focus in electronics and photonics devices, wireless and wired networks, software and hardware engineering), while providing a strong footing in New Digital Ventures (delivering highly skilled, professionally equipped, entrepreneurial engineers). The new Centre will become a major training hub for UK industry, addressing its skills shortage and contributing to its prosperity.

The impact of the new Centre can be summarised under 4 main headings:

1. Developing the engineers and leaders of the future

We will continue to train the future leaders of industry. However, despite its major contribution to UK GDP and its track-record of innovation, the Electronics sector is still not recognised as an attractive career option by strong UK graduates. We will address this by delivering innovative, interdisciplinary and rigorous training, informed by ongoing engagement with our industrial partners. Key features will be Creative Researcher training, and an Entrepreneurship programme that provides the motivation and competencies required to commercialise research outcomes.
Graeme Hobbs, Chairman, Motorola Solutions UK has remarked, "I recently took part in one of your CDT student business plan panels. This initiative provides students with an insight into the real world, combining pure business skills with both engineering and technology-driven aspects. It is of huge value and ultimately good, both for our business and for the future of UK plc".

2. Building the UK research base

In order to conduct world-leading research which is focused on both skills and technology demands, we recognise that a strong partnership with industry is essential. We have therefore shaped our programme to address specific sector needs and hence maximise its contribution to enhancing the UK's economic performance. Our success in this is evidenced by the significant and firm financial contributions from industry in the letters of support (£1.9M in cash, £1.9M in kind). Through the CDT Advisory Board, the academic team will have continuous guidance from industry to ensure alignment of the taught programme content, specialist training activities and research topics with the foreseen needs of the sector.

Our approach enables industry to undertake medium to long term research which would otherwise be extremely difficult in today's economic climate. Placing fundamental research in an application driven framework will yield academic excellence as well as commercial pull-through of our best results. Significant industrial involvement with both the group and solo research projects is common practise in our current CDT and we plan to continue this mode.

3. Impact on the wider public

Our research will develop solutions which will provide efficient communications, motivated by environmental (energy) and demand (increasing volumes of data constraints). This will have a significant impact on consumers and business through the development of new technologies and applications, and through our contributions to international standards processes.

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All students will be trained to deliver outreach activity and to disseminate their work effectively through our publicity materials, our annual conference and other international research conferences. We will take a student-led approach to this dissemination activity, making the cohort stakeholders in order to promote their career development.