5 research outputs found
Robust Active and Passive Beamforming for RIS-Assisted Full-Duplex Systems under Imperfect CSI
The sixth-generation (6G) wireless technology recognizes the potential of
reconfigurable intelligent surfaces (RIS) as an effective technique for
intelligently manipulating channel paths through reflection to serve desired
users. Full-duplex (FD) systems, enabling simultaneous transmission and
reception from a base station (BS), offer the theoretical advantage of doubled
spectrum efficiency. However, the presence of strong self-interference (SI) in
FD systems significantly degrades performance, which can be mitigated by
leveraging the capabilities of RIS. Moreover, accurately obtaining channel
state information (CSI) from RIS poses a critical challenge. Our objective is
to maximize downlink (DL) user data rates while ensuring quality-of-service
(QoS) for uplink (UL) users under imperfect CSI from reflected channels. To
address this, we introduce the robust active BS and passive RIS beamforming
(RAPB) scheme for RIS-FD, accounting for both SI and imperfect CSI. RAPB
incorporates distributionally robust design, conditional value-at-risk (CVaR),
and penalty convex-concave programming (PCCP) techniques. Additionally, RAPB
extends to active and passive beamforming (APB) with perfect channel
estimation. Simulation results demonstrate the UL/DL rate improvements achieved
considering various levels of imperfect CSI. The proposed RAPB/APB schemes
validate their effectiveness across different RIS deployment and RIS/BS
configurations. Benefited from robust beamforming, RAPB outperforms existing
methods in terms of non-robustness, deployment without RIS, conventional
successive convex approximation, and half-duplex systems
Energy Efficient Robust Beamforming and Cooperative Jamming Design for IRS-Assisted MISO Networks
Energy-efficient design and secure communications are of crucial importance
in wireless communication networks. However, the energy efficiency achieved by
using physical layer security can be limited by the channel conditions. In
order to tackle this problem, an intelligent reflecting surface (IRS) assisted
multiple input single output (MISO) network with independent cooperative
jamming is studied. The energy efficiency is maximized by jointly designing the
transmit and jamming beamforming and IRS phase-shift matrix under both the
perfect channel state information (CSI) and the imperfect CSI.
In order to tackle the challenging non-convex fractional problems, an
algorithm based on semidefinite programming (SDP) relaxation is proposed for
solving energy efficiency maximization problem under the perfect CSI case while
an alternate optimization algorithm based on -procedure is used
for solving the problem under the imperfect CSI case.
Simulation results demonstrate that the proposed design outperforms the
benchmark schemes in term of energy efficiency. Moreover, the tradeoff between
energy efficiency and the secrecy rate is found in the IRS-assisted MISO
network. Furthermore, it is shown that IRS can help improve energy efficiency
even with the uncertainty of the CSI.Comment: arXiv admin note: text overlap with arXiv:1911.0513
Efficient and Secure Resource Allocation in Mobile Edge Computing Enabled Wireless Networks
To support emerging applications such as autonomous vehicles and smart homes and to build an intelligent society, the next-generation internet of things (IoT) is calling for up to 50 billion devices connected world wide. Massive devices connection, explosive data circulation, and colossal data processing demand are driving both the industry and academia to explore new solutions.
Uploading this vast amount of data to the cloud center for processing will significantly increase the load on backbone networks and cause relatively long latency to time-sensitive applications. A practical solution is to deploy the computing resource closer to end-users to process the distributed data. Hence, Mobile Edge Computing (MEC) emerged as a promising solution to providing high-speed data processing service with low latency.
However, the implementation of MEC networks is handicapped by various challenges. For one thing, to serve massive IoT devices, dense deployment of edge servers will consume much more energy. For another, uploading sensitive user data through a wireless link intro-duces potential risks, especially for those size-limited IoT devices that cannot implement complicated encryption techniques. This dissertation investigates problems related to Energy Efficiency (EE) and Physical Layer Security (PLS) in MEC-enabled IoT networks and how Non-Orthogonal Multiple Access (NOMA), prediction-based server coordination, and Intelligent Reflecting Surface (IRS) can be used to mitigate them.
Employing a new spectrum access method can help achieve greater speed with less power consumption, therefore increasing system EE. We first investigated NOMA-assisted MEC networks and verified that the EE performance could be significantly improved. Idle servers can consume unnecessary power. Proactive server coordination can help relieve the tension of increased energy consumption in MEC systems. Our next step was to employ advanced machine learning algorithms to predict data workload at the server end and adaptively adjust the system configuration over time, thus reducing the accumulated system cost. We then introduced the PLS to our system and investigated the long-term secure EE performance of the MEC-enabled IoT network with NOMA assistance. It has shown that NOMA can improve both EE and PLS for the network. Finally, we switch from the single antenna scenario to a multiple-input single-output (MISO) system to exploit space diversity and beam forming techniques in mmWave communication. IRS can be used simultaneously to help relieve the pathloss and reconfigure multi-path links. In the final part, we first investigated the secure EE performance of IRS-assisted MISO networks and introduced a friendly jammer to block the eavesdroppers and improve the PLS rate. We then combined the IRS with the NOMA in the MEC network and showed that the IRS can further enhance the system EE
Holographic MIMO Communications: Theoretical Foundations, Enabling Technologies, and Future Directions
Future wireless systems are envisioned to create an endogenously
holography-capable, intelligent, and programmable radio propagation
environment, that will offer unprecedented capabilities for high spectral and
energy efficiency, low latency, and massive connectivity. A potential and
promising technology for supporting the expected extreme requirements of the
sixth-generation (6G) communication systems is the concept of the holographic
multiple-input multiple-output (HMIMO), which will actualize holographic radios
with reasonable power consumption and fabrication cost. The HMIMO is
facilitated by ultra-thin, extremely large, and nearly continuous surfaces that
incorporate reconfigurable and sub-wavelength-spaced antennas and/or
metamaterials. Such surfaces comprising dense electromagnetic (EM) excited
elements are capable of recording and manipulating impinging fields with utmost
flexibility and precision, as well as with reduced cost and power consumption,
thereby shaping arbitrary-intended EM waves with high energy efficiency. The
powerful EM processing capability of HMIMO opens up the possibility of wireless
communications of holographic imaging level, paving the way for signal
processing techniques realized in the EM-domain, possibly in conjunction with
their digital-domain counterparts. However, in spite of the significant
potential, the studies on HMIMO communications are still at an initial stage,
its fundamental limits remain to be unveiled, and a certain number of critical
technical challenges need to be addressed. In this survey, we present a
comprehensive overview of the latest advances in the HMIMO communications
paradigm, with a special focus on their physical aspects, their theoretical
foundations, as well as the enabling technologies for HMIMO systems. We also
compare the HMIMO with existing multi-antenna technologies, especially the
massive MIMO, present various...Comment: double column, 58 page