16 Projects, page 1 of 4
Orthogonal Frequency Division Multiplexing (OFDM) technique has gained increasing popularity in both wired and wireless communication systems, mainly due to its immunity to multipath fading, which allows for a significant increase in the transmission rate. By inserting a cyclic prefix (CP) before each transmitted block longer than the length of the channel, OFDM effectively transforms a frequency selective channel into a parallel of flat-fading channels. This greatly simplifies both channel estimation and data recovery at receiver. However, these advantages come at the cost of a loss of 10-25% spectral efficiency due to the insertion of CP, and an increased sensitivity to frequency offset and Doppler spread as well as transmission nonlinearity accentuated by non-constant modulus of OFDM signals. Additionally, due to the time-varying nature of wireless channels, training sequence needs to be transmitted periodically for the purpose of channel estimation. The overhead imposed by training sequence and CP can be up to 50 percent for fast fading channels, causing significant loss of spectral efficiency. In this proposal we aim to tackle these problems with the filter bank based multi-carrier system employing a special pulse shaping filter called IOTA (isotropic orthogonal transform algorithm) to yield good time and frequency localization properties so that inter-symbol interference (ISI) and inter-carrier interference (ICI) are avoided without the use of CP. We also investigate a linearly precoded IOTA system which facilitates blind channel estimation, resulting in a spectrally efficient multi-carrier system without the transmission of training sequence in addition to the elimination of CP. In order to effectively combat carrier frequency offset and high PAPR problems in the current orthogonal frequency division multiple access (OFDMA) and single carrier frequency division multiple access (SC-FDMA) based uplink communications, we propose a novel multiple access scheme which combines IOTA with low density signature (LDS) technique. The focus of our work will be on the study and utilization of some special properties of IOTA which have been overlooked by others. We aim to leverage these properties in the equalization, decoding and channel estimation design in order to achieve optimal performance and maximum capacity with affordable computational complexity. Our goal is to provide theoretical references and guidelines for successful implementation of IOTA systems for future wireless communications.
There are more than five billion wirelessly connected mobile devices in service today, most of which are handheld terminals or mobile-broadband devices such as computers and tablets. By 2020, mobile communications data traffic is expected to increase 1,000-fold, by which time there will be an estimated 50 billion Internet-capable devices. This transition will present a formidable challenge. Improving the energy efficiency (EE) of existing telecommunication networks is not just a necessary contribution towards the fight against global warming, but with the inevitable increases in the price of energy, it is becoming also a financial imperative. Future technologies (e.g. 5G) on which these devices will operate will require dramatically higher data rates and will consume far more power, and as a consequence increase their environmental footprint. To mitigate this, significant network densification, that is increasing the number of antennas per unit area, seems inevitable. To this end, a novel technological paradigm, known as massive MIMO, considers the deployment of hundreds of low-power antennas on the base station (BS) site to provide enhanced performance, reduced energy consumption, and better reliability. At the same time, the spectrum scarcity in the RF bands has stimulated a lot of research effort into mm-wave frequencies (30 to 300GHz). These frequencies offer numerous advantages: massive bandwidth/data rates, reduced RF interference, narrow beamwidths. The combination of the above technologies gives rise to mm-Wave massive MIMO, which is considered by many experts as the 'next big thing in wireless'. This paradigm shift avails of the vast available bandwidth at mm-frequencies, smaller form factors than designs implemented at current frequencies, reduced RF interference, channel orthogonality, and large beamforming/multiplexing gains. Yet, the practical design of mm-Wave massive MIMO faces many fundamental challenges, in respect of total energy consumption, circuitry cost, digital signal processing among others. In the context of the project, we envision a mm-wave massive MIMO topology performing a fraction of processing in the baseband (digital) and the remaining fraction in the RF band (analogue), with a reduced number of RF chains, to effectively address most of these challenges. In addition, by deploying low-resolution (coarse) analog-to-digital converters (ADCs), we can substantially reduce the power dissipation of mm-Wave massive MIMO transceivers. This visionary project will investigate the realisable potential of hybrid processing and 1-bit ADC quantisation. The specific project goals will be to: (a) find the optimal balance between analogue and digital processing for future MIMO configurations in order to maximise the end-to-end EE and experimentally validate the proposed solution, and; (b) investigate the realisable potential of 1-bit ADC quantisation and the channel estimation/resource allocation challenges it induces. By bringing together a world leading research team with expertise in communications engineering, signal processing, microwave engineering and antenna theory, and with the technical support of the biggest telecom equipment manufacturer in the world, Huawei Technologies Ltd, we will devise scalable low-complexity, low-power solutions suitable for the new generation of BS. We will investigate the algorithms and hardware that will optimise the performance of future BS to precisely meet performance and QoS targets, allied to minimum energy consumption. The application of the project results will contribute to the reduction of the ICT sector's contribution to global warming, through reduced power consumption and improved EE of future BSs. It will also influence many dynamic economical sectors within the UK: telecom equipment manufacturing, telecom operators, positioning systems, surveillance sector, smart cities, e-health, military equipment and automotive companies.
The antenna, as an essential device for radio systems and "Internet of Things", is in high demand in a wide range of wireless products. It has traditionally been made of good conductive materials (such as copper) to minimise the ohmic loss and maximise the radiation efficiency. However conductive/metal antennas are not ideal for some applications. For example, at lower frequencies, they are normally large, heavy and expensive. They also produce relatively large radar cross sections which are not good for military applications. Furthermore, they are solid - once the antennas are made, it is hard to make them reconfigurable and flexible in terms of the electromagnetic performance and mechanical configurations. Recently, water antennas have been studied and found that they could overcome many problems facing the traditional metal antennas and offer some attractive and unique features, such as small in size, cost effective, transparent, flexible and reconfigurable. However, they cannot work at low temperatures (e.g. below 0 degree C) and may suffer from low radiation efficiency and low power handling capacity problems, which make them not suitable for practical applications. Thus, better alternatives to water and conventional metal antennas are required for a wide range of real world applications. In this project, we are going to develop a new type of antenna: liquid antennas, which will offer all the advantages but overcome the problems that water antennas have. The main challenges are 1) How to identify the most suitable liquid materials with low loss, thermal and mechanical stability which will work over the desired temperature range (from -30 to +60 degree C), frequency range (from kHz to GHz), and RF/microwave power range (up to kW). 2) How to design and make compact and efficient liquid antennas which are flexible or reconfigurable in terms of the main antenna parameters (such as the operational frequency, radiation pattern, and size) and suitable for real world applications. This is an interdisciplinary project which requires expertise from radio frequency (RF) and microwave engineering, chemical and material science. It consists of both theoretical and experimental work. A wide range of liquid materials (not limited to water and sea water) will be studied, especially ionic liquids and antifreezes. Their electromagnetic, thermal and mechanical properties will be screened against temperature, frequency and RF/microwave power levels with the ultimate goal being to make reconfigurable, small liquid antennas to work efficiently and effectively over a wide temperature, frequency and power range. In addition, the reconfigurable techniques suitable for liquid antennas will also be studied thoroughly and two reconfigurable liquid antennas will be developed, optimised to demonstrate their excellent potential features for both military and commercial applications. The work will be undertaken in collaboration with industrial leaders (BAE Systems and Huawei) and academic expert (Prof Luk from Hong Kong) to ensure that this research will bring new knowledge into material science and radio engineering, a novel type of antenna will be introduced to meet the demands from the industry and provide an alternative compact reconfigurable and/or flexible device to the wireless world. The research outcomes of this study (e.g. the liquid and reconfigurable technology) could be extended to other RF and microwave devices (such as filters, delay lines and phase shifters) where low-loss dielectric materials may be used.
The research is focused on one of our society's greatest technical challenges and economic drivers with impact on knowledge, economy, society and people as well as business and government activities. It aims to transform the development of the information and communication infrastructure. A high-capacity, flexible, cost-effective and efficient telecommunications and data infrastructure is of great national and international importance. The ability to communicate seamlessly, without delay, requires intelligent communications networks with high capacity, available when and where it is needed. To achieve this requires research advances in ultrawideband wireless and optical networks, as well as intelligent transceivers, new ultrawideband optical devices and algorithms. This is a fast-moving and internationally fiercely competitive field and to maintain international leadership requires the capability of not only making theoretical advances, but the also the ability of demonstrating these experimentally. Our vision is to create an advanced, world leading signal generation and detection test-bed for advanced communications systems research. The key feature of the proposed system are the ultra-low noise, high-resolution capture and analysis of complex broadband signals, more than quadrupling the achievable network capacity. This unique facility will allow the investigation of optical and wireless networks over a wide range of time- and length scales, including long-haul networks, data centres and enable the research into the ultra-wideband signal manipulation for the next-generation optical & wireless access networks. It will enable UCL and UK to consolidate and enhance its internationally leading position in communications systems research supporting a wide range of other areas.
The remarkable success of the internet is unquestioned, touching all aspects of our daily lives and commerce. This success is fundamentally underpinned by the tremendous capacity of unseen underground and undersea optical fibre cables and the technologies associated with them. Indeed, the initial surge in web usage in the mid 1990s coincides with the commissioning of the first optically amplified transatlantic cable network, TAT12/13 that allowed ready access to information otherwise inaccessible. Similarly, the remarkable growth of social media is supported by the introduction of optical fibres into data centres, allowing their tremendous growth. Exponential growth has been a characteristic of data communications since their first introduction in the 1970's and has been fuelled by the gradual introduction of radical technologies, such as optical amplification, wavelength-division multiplexing and coherent modulation. All of these technologies are today routinely deployed and it is widely acknowledged that fibres are becoming full. The limit to fibre capacity has its origin in the fact that the intense signals are significantly distorted by nonlinearly (a similar effect to overdriving loudspeakers). This distortion limits the maximum amount of information which may be transmitted across and optical fibre link, and unless combated, the nonlinear response will result in a capacity crunch, limiting access to the internet to today's levels. Faced with the ongoing exponential growth in demand, unless these restrictions are lifted many parallel systems will be required, resulting in exponentially increasing energy consumption, until the cost of this resource becomes prohibitive and finally curtails growth. Only one technology, optical phase conjugation (acting like a mirror for colours), has been shown to offer the prospect of supporting continued internet growth without the need for widespread use of multiple fibres and the associated growth in energy consumption. Very much like Newton's Prisms, optical phase conjugation allows the distortion of one fibre (analogous to spectral spreading in Newton's prisms) to be compensated by a second identical fibre. In PHOS, we will - Optimise the devices which perform this conjugation, both in terms of the assessment of fundamental nonlinear materials and in terms of optimised sub-system configuration. - Demonstrate orders of magnitude increase in the capabilities of optical fibres for both practical point-to-point links with non-uniform span lengths and for optical networks with a plethora of diverse routes. - Verify that the use of optical phase conjugation is cost effective, both in terms of reducing the cost of a network deployment compared to existing products and in terms of enhancing the service provided to customers through higher capacity with lower latency. Furthermore, as optical phase conjugation will transform the capabilities of the network, PHOS will work to remove bottlenecks within the network transmitters and receivers, increasing their performance by an order of magnitude, resulting in 10 times faster connections. The approach of compensating impairments in the optical domain, combined with simplified digital signal processing and enhanced exploitation of fibre bandwidth will reduce the cost, size and power consumption associated with providing 10's of Tbit/s of capacity per optical fibre. If successful, PHOS will enable massively increased data capacities from the employment of Optical Phase Conjugation, giving the UK the most advanced optical communication network and a strong position to become a leading supplier of the technology worldwide.