1,380 research outputs found
Modeling and Analysis of Energy Efficiency in Wireless Handset Transceiver Systems
As wireless communication devices are taking a significant part in our daily life, research steps toward making these devices even faster and smarter are accelerating rapidly. The main limiting factors are energy and power consumption. Many techniques are utilized to increase the battery’s capacity (Ampere per Hour), but that comes with a cost of raising the safety concerns. The other way to increase the battery’s life is to decrease the energy consumption of the devices. In this work, we analyze energy-efficient communications for wireless devices based on an advanced energy consumption model that takes into account a broad range of parameters. The developed model captures relationships between transmission power, transceiver distance, modulation order, channel fading, power amplifier (PA) effects, power control, multiple antennas, as well as other circuit components in the radio frequency (RF) transceiver. Based on the developed model, we are able to identify the optimal modulation order in terms of energy efficiency under different situations (e.g., different transceiver distance, different PA classes and efficiencies, different pulse shape, etc). Furthermore, we capture the impact of system level and network level parameters on the PA energy via peak to average ratio (PAR) and power control. We are also able to identify the impact of multiple antennas at the handset on the energy consumption and the transmitted bit rate for few and many antennas (conventional multiple-input-multiple-output (MIMO) and massive MIMO) at the base station. This work provides an important framework for analyzing energy-efficient communications for different wireless systems ranging from cellular networks to wireless internet of things
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
Grant-Free Massive MTC-Enabled Massive MIMO: A Compressive Sensing Approach
A key challenge of massive MTC (mMTC), is the joint detection of device
activity and decoding of data. The sparse characteristics of mMTC makes
compressed sensing (CS) approaches a promising solution to the device detection
problem. However, utilizing CS-based approaches for device detection along with
channel estimation, and using the acquired estimates for coherent data
transmission is suboptimal, especially when the goal is to convey only a few
bits of data.
First, we focus on the coherent transmission and demonstrate that it is
possible to obtain more accurate channel state information by combining
conventional estimators with CS-based techniques. Moreover, we illustrate that
even simple power control techniques can enhance the device detection
performance in mMTC setups.
Second, we devise a new non-coherent transmission scheme for mMTC and
specifically for grant-free random access. We design an algorithm that jointly
detects device activity along with embedded information bits. The approach
leverages elements from the approximate message passing (AMP) algorithm, and
exploits the structured sparsity introduced by the non-coherent transmission
scheme. Our analysis reveals that the proposed approach has superior
performance compared to application of the original AMP approach.Comment: Submitted to IEEE Transactions on Communication
Performance Enhancement Using NOMA-MIMO for 5G Networks
The integration of MIMO and NOMA technologies addresses key challenges in 5G and beyond, such as connectivity, latency, and dependability. However, resolving these issues, especially in MIMO-enabled 5G networks, required additional research. This involved optimizing parameters like bit error rate, downlink spectrum efficiency, average capacity rate, and uplink transmission outage probability. The model employed Quadrature Phase Shift Keying modulation on selected frequency channels, accommodating diverse user characteristics. Evaluation showed that MIMO-NOMA significantly improved bit error rate and transmitting power for the best user in download transmission. For uplink transmission, there was an increase in the average capacity rate and a decrease in outage probability for the best user. Closed-form formulas for various parameters in both downlink and uplink NOMA, with and without MIMO, were derived. Overall, adopting MIMO-NOMA led to a remarkable performance improvement for all users, even in challenging conditions like interference or fading channels
Cross-Layer Optimization for Power-Efficient and Robust Digital Circuits and Systems
With the increasing digital services demand, performance and power-efficiency
become vital requirements for digital circuits and systems. However, the
enabling CMOS technology scaling has been facing significant challenges of
device uncertainties, such as process, voltage, and temperature variations. To
ensure system reliability, worst-case corner assumptions are usually made in
each design level. However, the over-pessimistic worst-case margin leads to
unnecessary power waste and performance loss as high as 2.2x. Since
optimizations are traditionally confined to each specific level, those safe
margins can hardly be properly exploited.
To tackle the challenge, it is therefore advised in this Ph.D. thesis to
perform a cross-layer optimization for digital signal processing circuits and
systems, to achieve a global balance of power consumption and output quality.
To conclude, the traditional over-pessimistic worst-case approach leads to
huge power waste. In contrast, the adaptive voltage scaling approach saves
power (25% for the CORDIC application) by providing a just-needed supply
voltage. The power saving is maximized (46% for CORDIC) when a more aggressive
voltage over-scaling scheme is applied. These sparsely occurred circuit errors
produced by aggressive voltage over-scaling are mitigated by higher level error
resilient designs. For functions like FFT and CORDIC, smart error mitigation
schemes were proposed to enhance reliability (soft-errors and timing-errors,
respectively). Applications like Massive MIMO systems are robust against lower
level errors, thanks to the intrinsically redundant antennas. This property
makes it applicable to embrace digital hardware that trades quality for power
savings.Comment: 190 page
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