18 research outputs found
DESIGN AND OPTIMIZATION OF SIMULTANEOUS WIRELESS INFORMATION AND POWER TRANSFER SYSTEMS
The recent trends in the domain of wireless communications indicate severe upcoming challenges, both in terms of infrastructure as well as design of novel techniques. On the other hand, the world population keeps witnessing or hearing about new generations of mobile/wireless technologies within every half to one decade. It is certain the wireless communication systems have enabled the exchange of information without any physical cable(s), however, the dependence of the mobile devices on the power cables still persist. Each passing year unveils several critical challenges related to the increasing capacity and performance needs, power optimization at complex hardware circuitries, mobility of the users, and demand for even better energy efficiency algorithms at the wireless devices. Moreover, an additional issue is raised in the form of continuous battery drainage at these limited-power devices for sufficing their assertive demands. In this regard, optimal performance at any device is heavily constrained by either wired, or an inductive based wireless recharging of the equipment on a continuous basis. This process is very inconvenient and such a problem is foreseen to persist in future, irrespective of the wireless communication method used. Recently, a promising idea for simultaneous wireless radio-frequency (RF) transmission of information and energy came into spotlight during the last decade. This technique does not only guarantee a more flexible recharging alternative, but also ensures its co-existence with any of the existing (RF-based) or alternatively proposed methods of wireless communications, such as visible light communications (VLC) (e.g., Light Fidelity (Li-Fi)), optical communications (e.g., LASER-equipped communication systems), and far-envisioned quantum-based communication systems. In addition, this scheme is expected to cater to the needs of many current and future technologies like wearable devices, sensors used in hazardous areas, 5G and beyond, etc. This Thesis presents a detailed investigation of several interesting scenarios in this direction, specifically concerning design and optimization of such RF-based power transfer systems.
The first chapter of this Thesis provides a detailed overview of the considered topic, which serves as the foundation step. The details include the highlights about its main contributions, discussion about the adopted mathematical (optimization) tools, and further refined minutiae about its organization. Following this, a detailed survey on the wireless power transmission (WPT) techniques is provided, which includes the discussion about historical developments of WPT comprising its present forms, consideration of WPT with wireless communications, and its compatibility with the existing techniques. Moreover, a review on various types of RF energy harvesting (EH) modules is incorporated, along with a brief and general overview on the system modeling, the modeling assumptions, and recent industrial considerations. Furthermore, this Thesis work has been divided into three main research topics, as follows. Firstly, the notion of simultaneous wireless information and power transmission (SWIPT) is investigated in conjunction with the cooperative systems framework consisting of single source, multiple relays and multiple users. In this context, several interesting aspects like relay selection, multi-carrier, and resource allocation are considered, along with problem formulations dealing with either maximization of throughput, maximization of harvested energy, or both. Secondly, this Thesis builds up on the idea of transmit precoder design for wireless multigroup multicasting systems in conjunction with SWIPT. Herein, the advantages of adopting separate multicasting and energy precoder designs are illustrated, where we investigate the benefits of multiple antenna transmitters by exploiting the similarities between broadcasting information and wirelessly transferring power. The proposed design does not only facilitates the SWIPT mechanism, but may also serve as a potential candidate to complement the separate waveform designing mechanism with exclusive RF signals meant for information and power transmissions, respectively. Lastly, a novel mechanism is developed to establish a relationship between the SWIPT and cache-enabled cooperative systems. In this direction, benefits of adopting the SWIPT-caching framework are illustrated, with special emphasis on an enhanced rate-energy (R-E) trade-off in contrast to the traditional SWIPT systems. The common notion in the context of SWIPT revolves around the transmission of information, and storage of power. In this vein, the proposed work investigates the system wherein both information and power can be transmitted and stored. The Thesis finally concludes with insights on the future directions and open research challenges associated with the considered framework
Efficient Globally Optimal Resource Allocation in Wireless Interference Networks
Radio resource allocation in communication networks is essential to achieve optimal performance and resource utilization. In modern interference networks the corresponding optimization problems are often nonconvex and their solution requires significant computational resources. Hence, practical systems usually use algorithms with no or only weak optimality guarantees for complexity reasons. Nevertheless, asserting the quality of these methods requires the knowledge of the globally optimal solution. State-of-the-art global optimization approaches mostly employ Tuy's monotonic optimization framework which has some major drawbacks, especially when dealing with fractional objectives or complicated feasible sets.
In this thesis, two novel global optimization frameworks are developed. The first is based on the successive incumbent transcending (SIT) scheme to avoid numerical problems with complicated feasible sets. It inherently differentiates between convex and nonconvex variables, preserving the low computational complexity in the number of convex variables without the need for cumbersome decomposition methods. It also treats fractional objectives directly without the need of Dinkelbach's algorithm. Benchmarks show that it is several orders of magnitude faster than state-of-the-art algorithms.
The second optimization framework is named mixed monotonic programming (MMP) and generalizes monotonic optimization. At its core is a novel bounding mechanism accompanied by an efficient BB implementation that helps exploit partial monotonicity without requiring a reformulation in terms of difference of increasing (DI) functions. While this often leads to better bounds and faster convergence, the main benefit is its versatility. Numerical experiments show that MMP can outperform monotonic programming by a few orders of magnitude, both in run time and memory consumption.
Both frameworks are applied to maximize throughput and energy efficiency (EE) in wireless interference networks. In the first application scenario, MMP is applied to evaluate the EE gain rate splitting might provide over point-to-point codes in Gaussian interference channels. In the second scenario, the SIT based algorithm is applied to study throughput and EE for multi-way relay channels with amplify-and-forward relaying. In both cases, rate splitting gains of up to 4.5% are observed, even though some limiting assumptions have been made
D 3. 3 Final performance results and consolidated view on the most promising multi -node/multi -antenna transmission technologies
This document provides the most recent updates on the technical contributions and research
challenges focused in WP3. Each Technology Component (TeC) has been evaluated
under possible uniform assessment framework of WP3 which is based on the simulation guidelines
of WP6. The performance assessment is supported by the simulation results which are in their
mature and stable state. An update on the Most Promising Technology Approaches (MPTAs)
and their associated TeCs is the main focus of this document. Based on the input of all the TeCs in WP3, a consolidated view of WP3 on the role of multinode/multi-antenna transmission
technologies in 5G systems has also been provided. This consolidated view is further
supported in this document by the presentation of the impact of MPTAs on METIS scenarios
and the addressed METIS goals.Aziz, D.; Baracca, P.; De Carvalho, E.; Fantini, R.; Rajatheva, N.; Popovski, P.; Sørensen, JH.... (2015). D 3. 3 Final performance results and consolidated view on the most promising multi -node/multi -antenna transmission technologies. http://hdl.handle.net/10251/7675
On the energy efficiency of spatial modulation concepts
Spatial Modulation (SM) is a Multiple-Input Multiple-Output (MIMO) transmission technique
which realizes low complexity implementations in wireless communication systems. Due the
transmission principle of SM, only one Radio Frequency (RF) chain is required in the transmitter.
Therefore, the complexity of the transmitter is lower compared to the complexity of
traditional MIMO schemes, such as Spatial MultipleXing (SMX). In addition, because of the
single RF chain configuration of SM, only one Power Amplifier (PA) is required in the transmitter.
Hence, SM has the potential to exhibit significant Energy Efficiency (EE) benefits. At
the receiver side, due to the SM transmission mechanism, detection is conducted using a low
complexity (single stream) Maximum Likelihood (ML) detector. However, despite the use of a
single stream detector, SM achieves a multiplexing gain.
A point-to-point closed-loop variant of SM is receive space modulation. In receive space modulation,
the concept of SMis extended at the receiver side, using linear precoding with Channel
State Information at the Transmitter (CSIT). Even though receive space modulation does not
preserve the single RF chain configuration of SM, due to the deployed linear precoding, it
can be efficiently incorporated in a Space Division Multiple Access (SDMA) or in a Virtual
Multiple-Input Multiple-Output (VMIMO) architecture.
Inspired by the potentials of SM, the objectives of this thesis are the evaluation of the EE of
SM and its extension in different forms of MIMO communication. In particular, a realistic
power model for the power consumption of a Base Station (BS) is deployed in order to assess
the EE of SM in terms of Mbps/J. By taking into account the whole power supply of a BS and
considering a Time Division Multiple Access (TDMA) multiple access scheme, it is shown that
SM is significantly more energy efficient compared to the traditional MIMO techniques. In
the considered system setup, it is shown that SM is up to 67% more energy efficient compared
to the benchmark systems. In addition, the concept of space modulation is researched at the
receiver side. Specifically, based on the union bound technique, a framework for the evaluation
of the Average Bit Error Probability (ABEP), diversity order, and coding gain of receive space
modulation is developed. Because receive space modulation deploys linear precoding with
CSIT, two new precoding methods which utilize imperfect CSIT are proposed. Furthermore, in
this thesis, receive space modulation is incorporated in the broadcast channel. The derivation of
the theoretical ABEP, diversity order, and coding gain of the new broadcast scheme is provided.
It is concluded that receive space modulation is able to outperform the corresponding traditional
MIMO scheme. Finally, SM, receive space modulation, and relaying are combined in order
to form a novel virtual MIMO architecture. It is shown that the new architecture practically
eliminates or reduces the problem of the inefficient relaying of the uncoordinated virtual MIMO
space modulation architectures. This is undertaken by using precoding in a novel fashion. The
evaluation of the new architecture is conducted using simulation and theoretical results
Adaptive relaying protocol multiple-input multiple-output orthogonal frequency division multiplexing systems
In wireless broadband communications, orthogonal frequency division multiplexing (OFDM) has been adopted as a promising technique to mitigate multi-path fading and provide high spectral efficiency. In addition, cooperative communication can explore spatial diversity where several users or nodes share their resources and cooperate through distributed transmission. The concatenation of the OFDM technique with relaying systems can enhance the overall performance in terms of spectral efficiency and improve robustness against the detrimental effects of fading.
Hybrid relay selection is proposed to overcome the drawbacks of conventional forwarding schemes. However, exciting hybrid relay protocols may suffer some limitations when used for transmission over frequency-selective channels. The combination of cooperative protocols with OFDM systems has been extensively utilized in current wireless networks, and have become a promising solution for future high data rate broadband communication systems including 3D video transmission. This thesis covers two areas of high data rate networks. In the first part, several techniques using cooperative OFDM systems are presented including relay selection, space time block codes, resource allocation and adaptive bit and power allocation to introduce diversity.
Four (4) selective OFDM relaying schemes are studied over wireless networks; selective OFDM; selective OFDMA; selective block OFDM and selective unequal block OFDM. The closed-form expression of these schemes is derived. By exploiting the broadcast nature, it is demonstrated that spatial diversity can be improved. The upper bound of outage probability for the protocols is derived.
A new strategy for hybrid relay selection is proposed to improve the system performance by removing the sub-carriers that experience deep fading. The per subcarrier basis selection is considered with respect to the predefined threshold signal-to-noise ratio. The closed-form expressions of the proposed protocol in terms of bit error probability and outage probability are derived and compared with conventional hybrid relay selection. Adaptive bit and power allocation is also discussed to improve the system performance.
Distributed space frequency coding applied to hybrid relay selection to obtain full spatial and full data rate transmission is explored. Two strategies, single cluster and multiple clusters, are considered for the Alamouti code at the destination by using a hybrid relay protocol. The power allocation with and without sub-carrier pairing is also investigated to mitigate the effect of multipath error propagation in frequency-selective channels.
The second part of this thesis investigates the application of cooperative OFDM systems to high data rate transmission. Recently, there has been growing attention paid to 3D video transmission over broadband wireless channels. Two strategies for relay selection hybrid relay selection and first best second best are proposed to implement unequal error protection in the physical layer over error prone channels. The closed-form expressions of bit error probability and outage probability for both strategies are examined. The peak signal-to-noise ratio is presented to show the quality of reconstruction of the left and right views
Weighted Sum Rate Maximization for Downlink OFDMA with Subcarrier-pair based Opportunistic DF Relaying
This paper addresses a weighted sum rate (WSR) maximization problem for
downlink OFDMA aided by a decode-and-forward (DF) relay under a total power
constraint. A novel subcarrier-pair based opportunistic DF relaying protocol is
proposed. Specifically, user message bits are transmitted in two time slots. A
subcarrier in the first slot can be paired with a subcarrier in the second slot
for the DF relay-aided transmission to a user. In particular, the source and
the relay can transmit simultaneously to implement beamforming at the
subcarrier in the second slot. Each unpaired subcarrier in either the first or
second slot is used for the source's direct transmission to a user. A benchmark
protocol, same as the proposed one except that the transmit beamforming is not
used for the relay-aided transmission, is also considered. For each protocol, a
polynomial-complexity algorithm is developed to find at least an approximately
optimum resource allocation (RA), by using continuous relaxation, the dual
method, and Hungarian algorithm. Instrumental to the algorithm design is an
elegant definition of optimization variables, motivated by the idea of
regarding the unpaired subcarriers as virtual subcarrier pairs in the direct
transmission mode. The effectiveness of the RA algorithm and the impact of
relay position and total power on the protocols' performance are illustrated by
numerical experiments. The proposed protocol always leads to a maximum WSR
equal to or greater than that for the benchmark one, and the performance gain
of using the proposed one is significant especially when the relay is in close
proximity to the source and the total power is low. Theoretical analysis is
presented to interpret these observations.Comment: 8 figures, accepted and to be published in IEEE Transactions on
Signal Processing. arXiv admin note: text overlap with arXiv:1301.293