133 research outputs found
Millimetre wave frequency band as a candidate spectrum for 5G network architecture : a survey
In order to meet the huge growth in global mobile data traffic in 2020 and beyond, the development of the 5th Generation (5G) system is required as the current 4G system is expected to fall short of the provision needed for such growth. 5G is anticipated to use a higher carrier frequency in the millimetre wave (mm-wave) band, within the 20 to 90 GHz, due to the availability of a vast amount of unexploited bandwidth. It is a revolutionary step to use these bands because of their different propagation characteristics, severe atmospheric attenuation, and hardware constraints. In this paper, we carry out a survey of 5G research contributions and proposed design architectures based on mm-wave communications. We present and discuss the use of mm-wave as indoor and outdoor mobile access, as a wireless backhaul solution, and as a key enabler for higher order sectorisation. Wireless standards such as IEE802.11ad, which are operating in mm-wave band have been presented. These standards have been designed for short range, ultra high data throughput systems in the 60 GHz band. Furthermore, this survey provides new insights regarding relevant and open issues in adopting mm-wave for 5G networks. This includes increased handoff rate and interference in Ultra-Dense Network (UDN), waveform consideration with higher spectral efficiency, and supporting spatial multiplexing in mm-wave line of sight. This survey also introduces a distributed base station architecture in mm-wave as an approach to address increased handoff rate in UDN, and to provide an alternative way for network densification in a time and cost effective manner
Recent Advances in RF Propagation Modeling for 5G Systems
Stefanovic, M.; Panic, SR.; De Souza, RAA.; Reig, J. (2017). Recent Advances in RF Propagation Modeling for 5G Systems. International Journal of Antennas and Propagation (Online). 2017(4701208):1-5. doi:10.1155/2017/4701208S152017470120
Millimeter Wave Hybrid Beamforming Systems
The motivation for this thesis is the design of millimetre wave (mmWave) hybrid beamforming systems for supporting high user density. mmWave systems with hybrid digital-to-analogue beamforming (D-A BF) have the potential to fulfil 5G traffic demands. However, the capacity of mmWave systems is severely limited as each radio frequency (RF) transceiver chain in current sub-array mmWave base station (BS) architectures support only a particular user. Therefore, two new algorithms have been proposed for broadband mmWave systems. The algorithms operate on the principles of selection combining (SC) and principal component (PC). SC is a spatio-temporal hybrid D-A BF which has been designed to exploit multipath diversity, which is a characteristic feature of broadband propagation at mmWave. A novel low-complexity variant of SC, called low-complexity selection combining (LC-SC) has also been proposed for supporting high user density for such sub-array mm-Wave BS.
mmWave lens-antenna systems are an emergent beamforming technology. They are novel because they eliminate the requirement of traditional analog beamformers. In this context, a low-complexity beam allocation (LBA) algorithm, proposed in an earlier research, has been applied to solve the challenging problem of maximizing sum data-rates in switched-beam mmWave systems. However, there are practical limitations, such as restrictions in the number of available RF chains at the BS, sensitivity to sidelobe interference and the beam generation techniques. Using generalized beam-patterns, the maximum sum data-rates achievable in switched-beam mmWave systems is compared to fixed-beam systems by applying LBA. Then, the impact on maximum sum data-rates of actual beam-patterns, obtained from a practical mmWave lens-antenna, which have higher and non-uniform sidelobes compared to the theoretical beams, is assessed.
Non-orthogonal multiple access (NOMA) relay with hybrid digital-to-analog precoding (D-A P) as a promising solution for supporting high user densities in overloaded millimeter wave (mmWave) systems is investigated. To support high user densities in current mmWave hybrid D-A P systems, an idea based on exploiting the concept of NOMA relay to support 2K users per RF chain is proposed, where 2K M. To design the hybrid D-A P systems, the SC and PC algorithms are combined with NOMA relay to support significantly higher user densities. In future research, performance impairments in beamforming assistedmmWaveNOMA systems due to far-user's angle-of-departure (AoD) divergence with respect to the near-user is being investigated. This investigation is novel since most literature in NOMA considers both the near-user and far-user pairs static with respect to one another
Radio Channel Characterization for Future Wireless Networks and Applications
The new frontier of Above-6GHz bands is revolutionizing the field of
wireless telecommunications, requiring new radio channel models to support
the development of future Giga-bit-per-second systems. Recently, deterministic
ray-based models as Ray Tracing are catching on worldwide thanks to their
frequency-agility and reliable predictions. A modern 3D Ray Tracing developed
at University of Bologna has been indeed calibrated and used to investigate the
Above-6GHz radio channel properties. As starting point, an item-level electromagnetic
characterization of common items and materials has been achieved successfully
to obtain information about the complex permittivity, scattering diagrams and
even de-polarization effects, both utilizing Vector Spectrum Analyzer (at 7-15GHz)
and custom Channel Sounder (at 70GHz). Thus, a complete tuning of the Ray Tracing
has been completed for Above-6GHz frequencies. Then, 70GHz indoor doubledirectional
channel measurements have been performed in collaboration with TU
Ilmenau, in order to attain a multidimensional analysis of propagation mechanisms
in time and space, outlining the differences between Below- and Above-6GHz propagation.
Furthermore, multi-antenna systems, as Multiple-Input-Multiple-
Output (MIMO) and Beamforming have been taken into considerations, as strategic
technologies for Above-6GHz systems, focusing on their implementation, limits
and differences. Finally, complex system simulations of Space-Division-Multiple-
Access (SDMA) networks in indoor scenarios have been tested, to assess the capabilities
of Beamforming. In particular, efficient Beam Search and Tracking algorithms
have been proposed to assess the impact of interference on Multi-User Beamforming
at 70GHz and, also, novel Multi-Beam Beamforming schemes have been tested
at 60GHz to investigate diversity strategies to cope with NLOS link and Human
Blockage events. Moreover, the novel concept of Ray-Tracing-assisted Beamforming
has been outlined, showing that ray-based models represent today the promising
key tools to evaluate, design and enhance the future Above-6GHz multi-antenna
systems
Millimetre-wave radio-over-fibre supported multi-antenna and multi-user transmission
In this thesis, various features of the RoF supported mmW communication for
future wireless systems have been analysed including photonic generation of mmW
for MIMO operation, performance analysis of mmW MIMO to achieve spatial
diversity and spatial multiplexing with analog RoF fronthaul, and multi-user
transmission in the 60 GHz-band using multiplexing-over-fibre transport and
frequency-selective antenna.
A low cost mmW generation system for two independent MIMO signals has been
presented, consisting of a single optical Phase Modulator (PM). The different
aspects of experimental analysis on RoF-supported mmW MIMO in this thesis,
which were not considered before, include use of specific MIMO algorithm to
understand the amount of improvement in coverage and data rate for a particular
MIMO technique, performance comparison with SISO at several user locations, and
verification of optimum RAU physical spacing for a particular transmission
distance with the theoretical results. The results show that flexible and wider RAU
spacings, required to obtain optimum performance in a mmW MIMO system, can
be achieved using the proposed analog RoF fronthaul. The investigation was
extended to verification of a method to individual measurement of mmW channel
coefficients and performing MIMO processing, which shows that mmW channels
are relatively static and analysis can be extended to much longer distances and
making projections for NĂ—N MIMO.
For mmW multi-user transmission, a novel low cost, low complexity system using
single RoF link and single RF chain with single transmitting antenna has been
presented and characterized, which was based on large number of RF chains and
multiple antenna units previously. The setup involves generation and RoF transport
of a composite SCM signal, upconversion at the RAU and transmission of different
frequency channels towards spatially distributed users using a frequency-selective
Leaky-Wave-Antenna (LWA), to convert Frequency Division Multiplexing (FDM)
in to Spatial Division Multiple Access (SDMA). Analysis on low user-signal
spacing for the SCM shows the feasibility to serve a large number of users within a
specific transmission bandwidth and experimental demonstration to achieve sum
rate of 10Gb/s is shown by serving 20 users simultaneously. Furthermore, investigation on SNR degradation of high bandwidth signals due to beamsteering
effect of the LWA and theoretical calculations of the sum data rate for different
number of users is performed, which shows that the proposed system can provide
much higher sum rates with high available SNR. It was also experimentally
demonstrated that improvement in coverage and spectral efficiency is obtained by
operating multiple LWAs using single RF chain. Finally, an experimental
demonstration of a DWDM-RoF based 60 GHz multi-user transmission using
single LWA is presented to show the feasibility to extend the setup for a multiple
RAU based system, serving each at distinct optical wavelength and performing
direct photonic upconversion at the RAU for low cost mmW generation
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