Two-path succesive relaying schemes in the presence of inter-relay interference

Relaying is a promising technique to improve wireless network performance. A conventional relay transmits and receives signals in two orthogonal channels due to half duplex constraint of wireless network. This results in inefficient use of spectral resources. Two-Path Successive Relaying (TPSR) has been proposed to recover loss in spectral efficiency. However, the performance of TPSR is degraded by Inter-Relay Interference (IRI). This thesis investigates the performance of TPSR affected by IRI and proposes several schemes to improve relaying reliability, throughput and secrecy. Simulations revealed that the existing TPSR could perform worse than the conventional Half Duplex Relaying (HDR) scheme. Opportunistic TPSR schemes are proposed to improve the capacity performance. Several relay pair selection criteria are developed to ensure the selection of the best performing relay pair. Adaptive schemes which dynamically switch between TPSR and conventional HDR are proposed to further improve the performance. Simulation and analytical results show that the proposed schemes can achieve up to 45% ergodic capacity improvement and lower outage probability compared to baseline schemes, while achieving the maximum diversity and multiplexing tradeoff of the multi-input single-output channel. In addition, this thesis proposes secrecy TPSR schemes to protect secrecy of wireless transmission from eavesdropper. The use of two relays in the proposed schemes deliver more robust secrecy transmission while the use of scheduled jamming signals improves secrecy rate. Simulation and analytical results reveal that the proposed schemes can achieve up to 62% ergodic secrecy capacity improvement and quadratically lower intercept and secrecy outage probabilities if compared to existing schemes. Overall, this thesis demonstrates that the proposed TPSR schemes are able to deliver performance improvement in terms of throughput, reliability and secrecy in the presence of IRI

Cooperative NOMA system with virtual full duplex user relaying

Cooperative non-orthogonal multiple access (NOMA) system employs user relaying to enhance performance. Although full-duplex (FD) user relaying scheme does not incur additional bandwidth for relaying, the imperfect self-interference cancellation degrades the performance significantly. Alternatively, a virtual full-duplex (VFD) user relaying scheme can be used. In this paper, we study a cooperative NOMA system in cognitive radio scenario using VFD relaying scheme, where two half-duplex (HD) secondary users take turn to relay message of a primary user with decode-and-forward (DF) strategy. First, we derive the closed-form and asymptotic expressions of the outage probability and ergodic rate of the users. Then, we demonstrate the outage probability, ergodic rate, and ergodic sum rate performance of the proposed scheme using Monte Carlo simulations. We also provide a comprehensive comparison between the proposed VFD user relaying and existing FD and HD user relaying in orthogonal multiple access and NOMA systems. The simulation results verify the analytical results and demonstrate the advantages of the proposed VFD user relaying over existing schemes

Study of relay position in two-path successive relaying with interference cancellation

Two-path successive relaying scheme is designed to recover the loss of spectral efficiency due to half-duplex constraint When not operating in orthogonal channels, the relay pair used in the successive relaying scheme interferes each other. This inter-relay interference degrades the capacity performance of the successive relaying scheme significantly. Successive interference cancellation has been proposed to tackle the inter-relay interference in two-path successive relaying. The effectiveness of such interference cancellation technique relies heavily on the instantaneous channel conditions, which is not only depending on the small scale fading but also the large scale path loss. However, in the existing literature of two-path successive relaying, the effect of path loss and the position of relays have not been considered. Therefore, in this paper, we study the effect of path loss and relay position to the ergodic capacity of the two-path successive relaying with and without interference cancellation. We also compare the performance of successive relaying with the conventional half-duplex relaying. Simulation results show that the ergodic capacity of the two-path successive relaying not only depends on the relative position of the relays from source and destination nodes, but it is also affected by the inter-relay distance. When the relays are relatively closer to the destination and the inter-relay distance is short, the ergodic capacity of the two-path successive relaying with interference cancellation outperforms the conventional half-duplex relaying

Physical layer security using two-path successive relaying

Relaying is one of the useful techniques to enhance wireless physical-layer security. Existing literature shows that employing full-duplex relay instead of conventional half-duplex relay improves secrecy capacity and secrecy outage probability, but this is at the price of sophisticated implementation. As an alternative, two-path successive relaying has been proposed to emulate operation of full-duplex relay by scheduling a pair of half-duplex relays to assist the source transmission alternately. However, the performance of two-path successive relaying in secrecy communication remains unexplored. This paper proposes a secrecy two-path successive relaying protocol for a scenario with one source, one destination and two half-duplex relays. The relays operate alternately in a time division mode to forward messages continuously from source to destination in the presence of an eavesdropper. Analytical results reveal that the use of two half-duplex relays in the proposed scheme contributes towards a quadratically lower probability of interception compared to full-duplex relaying. Numerical simulations show that the proposed protocol achieves the ergodic achievable secrecy rate of full-duplex relaying while delivering the lowest probability of interception and secrecy outage probability compared to the existing half duplex relaying, full duplex relaying and full duplex jamming schemes

Amplify-and-forward virtual full-duplex relaying-based cooperative NOMA

This letter studies the performance of a virtual full-duplex relaying technique in cooperative non-orthogonal multiple access (NOMA)-based systems. In particular, two half-duplex amplify-and-forward relays imitate the operation of full-duplex relaying in cooperative NOMA systems using the successive relaying (SR) technique, in order to recover the loss of spectral efficiency due to the half-duplex constraint at the relays. The closed-form outage probability of the proposed scheme is derived. The simulation results show that the proposed SR-based cooperative NOMA system with an opportunistic power split factor achieves a lower outage probability and a higher ergodic rate than the existing SR-based orthogonal multiple access system and ideal full duplex relaying-based NOMA systems

Application of packaging technique in fiber bragg grating temperature sensor for measuring localized and nonuniform temperature distribution

The development of Fiber Bragg Grating (FBG) sensing technique has improved significantly especially in the sensor head design and real-time data acquisition technique. This paper presents the development of a simple and cost effective packaging technique that further enhances the performances of the FBG sensor. The packaged FBG sensor overcomes the nonuniform heat distribution of a bare FBG that causes eccentric response of FBG spectrum. Therefore, the packaged FBG sensor could be operated for a localized area with high temperature differential. The packaging also compensates the unwanted strain effect from the surrounding which makes temperature measurement become more accurate. The experimental works have been successfully carried out to demonstrate the system operation and the packaging functionalities. The temperature sensitivity coefficient of the bare FBG sensor measured in experiment is 10.05 pm/°C, while the packaged fiber sensor is 10.09 pm/°C, which are expected from the desig

Distinct effects of human glioblastoma immunoregulatory molecules programmed cell death ligand-1 (PDL-1) and indoleamine 2,3-dioxygenase (IDO) on tumour-specific T cell functions.

International audienceImmunotherapy is a promising new treatment for patients suffering from glioma, in particular glioblastoma multiforme (GBM). However, tumour cells use different mechanisms to escape the immune responses induced by the treatment. As many other tumours, gliomas express or secrete several immunosuppressive molecules that regulate immune cell functions. In this study, we first analysed FasL, HLA-G, IDO, PDL-1 and TGF-beta1, -beta2 and -beta3 expression by transcriptomic microarray analysis in a series of 20 GBM samples and found respectively 15%, 60%, 85%, 30%, 70%, 80% and 35% of positive specimens. mRNA expression was then confirmed in 10 GBM primary cell lines and 2 immortalised cell lines U251 and U87MG. Furthermore, the protein expression of PDL-1, IDO activity and TGF-beta2 secretion were found on most of the untreated GBM primary cell lines. Remarkably, treatment with IFN-gamma increased the PDL-1 cell surface expression and the IDO activity, but reduced the TGF-beta2 secretion of GBM cell lines. We finally analysed the immunosuppressive effects of IDO, PDL-1 and TGF-beta1-3 by measuring IFN-gamma production and cell cytotoxicity activity of tumour antigen-specific T cells. PDL-1 partially affected the IFN-gamma production of antigen-specific T cells in response to GBM primary cell lines, and IDO inhibited lymphocyte proliferation induced by lectins. None of these molecules directly affected the T cell cytotoxicity function. Due to the functional role of PDL-1 and IDO molecules expressed by GBM cells, one could expect that blocking these molecules in the immunotherapy strategies would reinforce the efficiency of these treatments of GBM patients