Simultaneous Wireless Information and Power Transfer for Decode-and-Forward Multi-Hop Relay Systems in Energy-Constrained IoT Networks

This paper studies a multi-hop decode-and-forward (DF) simultaneous wireless information and power transfer (SWIPT) system where a source sends data to a destination with the aid of multi-hop relays which do not depend on an external energy source. To this end, we apply power splitting (PS) based SWIPT relaying protocol so that the relays can harvest energy from the received signals from the previous hop to reliably forward the information of the source to the destination. We aim to solve two optimization problems relevant to our system model. First, we minimize the transmit power at the source under the individual quality-of-service (QoS) threshold constraints of the relays and the destination nodes by optimizing PS ratios at the relays. The second is to maximize the minimum system achievable rate by optimizing the PS ratio at each relay. Based on convex optimization techniques, the globally optimal PS ratio solution is obtained in closed-form for both problems. By setting the QoS threshold constraint the same for each node for the source transmit power problem, we discovered that either the minimum source transmit power or the maximum system throughput can be found using the same approach. Numerical results demonstrate the superiority of the proposed optimal SWIPT PS design over conventional fixed PS ratio schemes.Comment: 14 pages, 14 figures, Accepted for Publication in IEEE Internet of Things Journa

A Survey of Physical Layer Security Techniques for 5G Wireless Networks and Challenges Ahead

Physical layer security which safeguards data confidentiality based on the information-theoretic approaches has received significant research interest recently. The key idea behind physical layer security is to utilize the intrinsic randomness of the transmission channel to guarantee the security in physical layer. The evolution towards 5G wireless communications poses new challenges for physical layer security research. This paper provides a latest survey of the physical layer security research on various promising 5G technologies, including physical layer security coding, massive multiple-input multiple-output, millimeter wave communications, heterogeneous networks, non-orthogonal multiple access, full duplex technology, etc. Technical challenges which remain unresolved at the time of writing are summarized and the future trends of physical layer security in 5G and beyond are discussed.Comment: To appear in IEEE Journal on Selected Areas in Communication

Virtual full-duplex multiple-input multiple-output relaying in the presence of inter-relay interference

Driven by the increasing demand for wireless broadband, low latency and power-efficient networks, multiple-input multiple-output (MIMO) full-duplex relaying (FDR) schemes have gained much attention in recent years. However, the performance of FDR schemes is impaired by sophisticated self-interference suppression techniques. As such, MIMO virtual FDR (VFDR) schemes have been considered as practical alternatives to recover spectral efficiency loss in half-duplex relays (HDR) without the need for sophisticated self-interference suppression algorithms. Successive relaying (SR) scheme is one of the VFDR techniques which uses a pair of HD relays that alternate between reception and retransmission of the source information to the destination. The performance of the SR based VFDR scheme is affected by inter-relay interference (IRI) due to the concurrent transmission of the source and relay nodes. The interference in VFDR schemes is conventionally treated as a degrading factor on the information decoding receivers resulting in the design of several interference avoidance and cancellation techniques. On the contrary, this thesis developed several VFDR schemes which exploit the interference to achieve performance improvement. In this study, interference management techniques, transmit/receive beamforming matrices, power allocation and joint optimisation algorithms were developed. First, a reliable MIMO VFDR scheme in the presence of IRI was designed, where the IRI was exploited for reliability improvements. The results showed significant reliability improvement over the existing schemes. Second, a joint power allocation for MIMO VFDR schemes under network power constraint was developed. The power allocation problem in the presence of IRI was formulated based on primal-dual algorithm. The results showed that the joint optimisation algorithm can efficiently utilise the network power when compared with the conventional approach. Third, simultaneous wireless information and power transfer (SWIPT) in MIMO VFDR system was proposed, where the transmit beamforming matrices which optimise the achievable rate and harvested energy at the relays were jointly designed. The results showed that the interference energy can be harnessed to improve the SWIPT system throughput. Finally, a joint optimisation of the power split and relay position in SWIPT MIMO VFDR network were investigated. Results showed that the joint optimisation of the power split and distance factors can greatly improve the system outage performance. The analytical and numerical results in the research showed that IRI can be exploited to improve the throughput, reliability and energy harvesting of a wireless communication system. The results also showed a minimum achievable rate improvement of 80% over the HDR schemes and a reliability of 100% over the FDR schemes

Wireless Information and Energy Transfer for Two-Hop Non-Regenerative MIMO-OFDM Relay Networks

This paper investigates the simultaneous wireless information and energy transfer for the non-regenerative multipleinput multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) relaying system. By considering two practical receiver architectures, we present two protocols, time switchingbased relaying (TSR) and power splitting-based relaying (PSR). To explore the system performance limit, we formulate two optimization problems to maximize the end-to-end achievable information rate with the full channel state information (CSI) assumption. Since both problems are non-convex and have no known solution method, we firstly derive some explicit results by theoretical analysis and then design effective algorithms for them. Numerical results show that the performances of both protocols are greatly affected by the relay position. Specifically, PSR and TSR show very different behaviors to the variation of relay position. The achievable information rate of PSR monotonically decreases when the relay moves from the source towards the destination, but for TSR, the performance is relatively worse when the relay is placed in the middle of the source and the destination. This is the first time to observe such a phenomenon. In addition, it is also shown that PSR always outperforms TSR in such a MIMO-OFDM relaying system. Moreover, the effect of the number of antennas and the number of subcarriers are also discussed.Comment: 16 pages, 12 figures, to appear in IEEE Selected Areas in Communication

Analysis of Asymmetric Dual-Hop Energy Harvesting-Based Wireless Communication Systems in Mixed Fading Environments

This work investigates the performance of a dual-hop energy harvesting-based fixed-gain amplify-and-forward relaying communication system, subject to fading impairments. We consider a source node (S) communicating with a destination node (D), either directly or through a fixed distant relay (R), which harvests energy from its received signals and uses it to amplify and forward the received signals to D. We also consider maximal-ratio combining at D to combine the signals coming from S and R. Both power-splitting and time-switching energy harvesting protocols are investigated. The S-R link is modeled by Nakagami-m fading model, while the R-D and S-D links experience α-μ fading. Closed-form expressions for the statistical properties of the total signal-to-noise ratio are derived, based on which novel closed-form expressions are then derived for the average symbol error rate as well as for the average channel capacity, considering four different adaptive transmission policies. The derived expressions are validated through Monte Carlo simulations.acceptedVersionPeer reviewe

Analysis of Asymmetric Dual-Hop Energy Harvesting-Based Wireless Communication Systems in Mixed Fading Environments

This work investigates the performance of a dual-hop energy harvesting-based fixed-gain amplify-and-forward relaying communication system, subject to fading impairments. We consider a source node (S) communicating with a destination node (D), either directly or through a fixed distant relay (R), which harvests energy from its received signals and uses it to amplify and forward the received signals to D. We also consider maximal-ratio combining at D to combine the signals coming from S and R. Both power-splitting and time-switching energy harvesting protocols are investigated. The S-R link is modeled by Nakagami-m fading model, while the R-D and S-D links experience α-μ fading. Closed-form expressions for the statistical properties of the total signal-to-noise ratio are derived, based on which novel closed-form expressions are then derived for the average symbol error rate as well as for the average channel capacity, considering four different adaptive transmission policies. The derived expressions are validated through Monte Carlo simulations.Peer reviewe