445 research outputs found
Spectral-energy efficiency trade-off for next-generation wireless communication systems
The data traffic in cellular networks has had and will experience a rapid exponential
rise. Therefore, it is essential to innovate a new cellular architecture with
advanced wireless technologies that can offer more capacity and enhanced spectral
efficiency to manage the exponential data traffic growth. Managing such mass
data traffic, however, brings up another challenge of increasing energy consumption.
This is because it contributes into a growing fraction of the carbon dioxide
(CO2) emission which is a global concern today due to its negative impact on
the environment. This has resulted in creating a new paradigm shift towards both
spectral and energy efficient orientated design for the next-generation wireless access
networks. Acquiring both improved energy efficiency and spectral efficiency
has, nonetheless, shown to be a difficult goal to achieve as it seems improving one
is at the detriment to the other. Therefore, the trade-off between the spectral and
energy efficiency is of paramount importance to assess the energy consumption in
a wireless communication system required to attain a specific spectral efficiency.
This thesis looks into this problem. It studies the spectral-energy efficiency tradeoff
for some of the emerging wireless communication technologies which are seen
as potential candidates for the fifth generation (5G) mobile cellular system. The
focus is on the orthogonal frequency division multiple access (OFDMA), mobile
femtocell (MFemtocell), cognitive radio (CR), and the spatial modulation (SM).
Firstly, the energy-efficient resource allocation scheme for multi-user OFDMA
(MU-OFDMA) system is studied. The spectral-energy efficiency trade-off is
analysed under the constraint of maintaining the fairness among users. The
energy-efficient optimisation problem has been formulated as integer fractional
programming. We then apply an iterative method to simplify the problem to an
integer linear programming (ILP) problem.
Secondly, the spectral and energy efficiency for a cellular system with MFemtocell
deployment is investigated using different resource partitioning schemes.
Femtocells are low range, low power base stations (BSs) that improve the coverage
inside a home or office building. MFemtocell adopts the femtocell solution to be deployed in public transport and emergency vehicles. Closed-form expressions
for the relationships between the spectral and energy efficiency are derived for
a single-user (SU) MFemtocell network. We also study the spectral efficiency
for MU-MFemtocells with two opportunistic scheduling schemes.
Thirdly, the spectral-energy efficiency trade-off for CR networks is analysed at
both SU and MU CR systems against varying signal-to-noise ratio (SNR) values.
CR is an innovative radio device that aims to utilise the spectrum more efficiently
by opportunistically exploiting underutilised licensed spectrum. For the SU system,
we study the required energy to achieve a specific spectral efficiency for a
CR channel under two different types of power constraints in different fading environments.
In this scenario, interference constraint at the primary receiver (PR)
is also considered to protect the PR from harmful interference. At the system
level, we study the spectral and energy efficiency for a CR network that shares
the spectrum with an indoor network. Adopting the extreme-value theory, we
are able to derive the average spectral efficiency of the CR network.
Finally, we propose two innovative schemes to enhance the capability of (SM). SM
is a recently developed technique that is employed for a low complexity multipleinput
multiple-output (MIMO) transmission. The first scheme can be applied for
SU MIMO (SU-MIMO) to offer more degrees of freedom than SM. Whereas the
second scheme introduces a transmission structure by which the SM is adopted
into a downlink MU-MIMO system. Unlike SM, both proposed schemes do not
involve any restriction into the number of transmit antennas when transmitting
signals. The spectral-energy efficiency trade-off for the MU-SM in the massive
MIMO system is studied. In this context, we develop an iterative energy-efficient
water-filling algorithm to optimises the transmit power and achieve the maximum
energy efficiency for a given spectral efficiency.
In summary, the research presented in this thesis reveals mathematical tools to
analysis the spectral and energy efficiency for wireless communications technologies.
It also offers insight to solve optimisation problems that belong to a class
of problems with objectives of enhancing the energy efficiency
Design guidelines for spatial modulation
A new class of low-complexity, yet energyefficient Multiple-Input Multiple-Output (MIMO) transmission techniques, namely the family of Spatial Modulation (SM) aided MIMOs (SM-MIMO) has emerged. These systems are capable of exploiting the spatial dimensions (i.e. the antenna indices) as an additional dimension invoked for transmitting information, apart from the traditional Amplitude and Phase Modulation (APM). SM is capable of efficiently operating in diverse MIMO configurations in the context of future communication systems. It constitutes a promising transmission candidate for large-scale MIMO design and for the indoor optical wireless communication whilst relying on a single-Radio Frequency (RF) chain. Moreover, SM may also be viewed as an entirely new hybrid modulation scheme, which is still in its infancy. This paper aims for providing a general survey of the SM design framework as well as of its intrinsic limits. In particular, we focus our attention on the associated transceiver design, on spatial constellation optimization, on link adaptation techniques, on distributed/ cooperative protocol design issues, and on their meritorious variants
Optical MIMO communication systems under illumination constraints
Technology for wireless information access has enabled innovation of 'smart' portable consumer devices. These have been widely adopted and have become an integral part of our daily lives. They need ubiquitous connectivity to the internet to provide value added services, maximize their functionality and create a smarter world to live in. Cisco's visual networking index currently predicts wireless data consumption to increase by 61% per year. This will put additional stress on the already stressed wireless access network infrastructure creating a phenomenon called 'spectrum crunch'.
At the same time, the solid state devices industry has made remarkable advances in energy efficient light-emitting-diodes (LED). The lighting industry is rapidly adopting LEDs to provide illumination in indoor spaces. Lighting fixtures are positioned to support human activities and thus are well located to act as wireless access points. The visible spectrum (380 nm - 780 nm) is yet unregulated and untapped for wireless access. This provides unique opportunity to upgrade existing lighting infrastructure and create a dense grid of small cells by using this additional 'optical' wireless bandwidth. Under the above model, lighting fixtures will service dual missions of illumination and access points for optical wireless communication (OWC).
This dissertation investigates multiple-input multiple-output (MIMO) optical wireless broadcast system under unique constraints imposed by the optical channel and illumination requirements. Sample indexed spatial orthogonal frequency division multiplexing (SIS-OFDM) and metameric modulation (MM) are proposed to achieve higher spectral efficiency by exploiting dimensions of space and color respectively in addition to time and frequency. SIS-OFDM can provide significant additional spectral efficiency of up to (Nsc/2 - 1) x k bits/sym where Nsc is total number of subcarriers and k is number of bits per underlying spatial modulation symbol. MM always generates the true requested illumination color and has the potential to provide better color rendering by incorporating multiple LEDs. A normalization framework is then developed to analyze performance of optical MIMO imaging systems. Performance improvements of up to 45 dB for optical systems have been achieved by decorrelating spatially separate links by incorporating an imaging receiver. The dissertation also studies the impact of visual perception on performance of color shift keying as specified in IEEE 802.15.7 standard. It shows that non-linearity for a practical system can have a performance penalty of up to 15 dB when compared to the simplified linear system abstraction as proposed in the standard. Luminous-signal-to-noise ratio, a novel metric is introduced to compare performance of optical modulation techniques operating at same illumination intensity. The dissertation then introduces singular value decomposition based OWC system architecture to incorporate illumination constraints independent of communication constraints in a MIMO system. It then studies design paradigm for a multi-colored wavelength division multiplexed indoor OWC system
Optical Wireless Communications Using Intelligent Walls
This chapter is devoted to discussing the integration of intelligent
reflecting surfaces (IRSs), or intelligent walls, in optical wireless
communication (OWC) systems. IRS technology is a revolutionary concept that
enables communication systems to harness the surrounding environment to control
the propagation of light signals. Based on this, specific key performance
indicators could be achieved by altering the electromagnetic response of the
IRSs. In the following, we discuss the background theory and applications of
IRSs and present a case study for an IRS-assisted indoor light-fidelity (LiFi)
system. We then highlight some of the challenges related to this emerging
concept and elaborate on future research directions
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