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Evolution and accessibility of smart-phones have led to a huge demand in network bandwidth. The ubiquitous use of smart-phones in high-speed trains poses a unique challenge in delivering high-speed internet service on board. This challenge can be overcome by employing free-space optics, an alternative to radio-frequency technology. Previous coverage models for ground-train communications employed single laser systems with a larger divergence angle to cover a larger distance. Larger divergence angles lead to larger geometric losses, which may result in a non-reliable communication link. This study proposes a sectorised multi-beam coverage model with a smaller divergence angle to reduce the impact of geometric losses in the system. This study also proposes two receiver (Rx) architectures for Rxs deployed on the train. Along with geometric losses, the atmospheric attenuation is taken into consideration for the FSO link. The performance of the ground-train communications system in terms of bit-error-rate is evaluated under weak turbulence conditions via numerical simulation.

In this work, the authors consider the communication network of a power substation, where multiple intelligent electronic devices (IEDs) transmit their delay sensitive control and monitoring messages to a common receiver over a wireless network; in the presence of a broadband jammer, which is capable of jamming multiple channels simultaneously. The objective of the IEDs is to successfully transmit their messages within a specified time, whereas the jammer wants to obstruct IED's transmission. A novel utility function is designed for the players, that addresses the time-critical nature of communication. Due to the conflicting interest of the IEDs and the jammer, they model the interaction between them as a repeated Bayesian zero-sum game, which also addresses the repeated interaction among the IEDs and the jammer, and the unavailability of exact information about the jammer. The equilibrium strategies for both the scenarios of perfect and imperfect monitoring are derived and verified through simulation results. Further, the performance of the proposed game model in various scenarios is thoroughly compared in the result section. Finally, the efficacy of the proposed defence strategies is tested in a practical communication network of a power substation under jamming, which is simulated in Optimised Network Engineering Tool (OPNET).

In this study, the authors propose a novel virtual full-duplex relaying scheme, which is referred to as centre-partition max-link relaying by using buffer-aided half-duplex relays for multi-hop decode-and-forward cooperative networks. In the proposed scheme, they aim to select two independent available links for data packet transmission in the same time slot, which, in turn, improves the overall performance of the system. By modelling the evolution of buffer state transition as a Markov chain, the performance of the system is analysed in terms of outage probability and end-to-end average packet delay. The state transition matrix of the Markov chain is constructed and its steady-state distribution is obtained to derive the outage probability. Numerical results demonstrate that the proposed scheme has a potential to provide significant outage performance with reduced average packet delay as compared to that of buffer-aided multi-hop decode-and-forward relaying networks using the conventional max-link scheme.

Multi-hop relaying is used to extend the reach of wireless communication systems whereas cooperative relaying is used to improve the performance gain by exploiting the spatial diversity. In this study, the authors combine these two techniques to improve the range as well as the performance gain of cognitive radio networks (CRNs). Selective decode-and-forward relays are considered and two relay selection schemes are used to study the performance of multi-hop CRNs over Rayleigh fading channels. The exact outage probability and throughput of the considered system are derived for both the schemes by considering the effect of both peak-power and peak-interference constraints. By using the derived outage probability, the diversity gains for both considered schemes are determined. Numerical results show that the outage probability monotonically improves, whereas the throughput has concave behaviour with respect to increasing number of relaying hops.

In this work, a mathematical modelling of M-ary Poisson reception processes in molecular communication (MC) environment is performed. A lower bound of the capacity of MC system is derived using maxentropic capacity-approaching distributions; and the variation of the capacity with distance, drift velocity, and diffusion coefficient is analytically studied. Average symbol error probability (ASEP) of the considered system is analysed using maximum likelihood (ML) detection criterion. In order to improve on the error performance, an ML sequence detector employing hard decision Viterbi decoding is proposed. The proposed detection allows for a significant improvement in ASEP with some increase in system complexity.

In this study, the authors have analysed the performance of selection relaying at each hop in a decode-and-forward (DF)-based multi-hop cognitive radio (CR) system deploying cooperative spectrum sensing. The decisions on spectrum availability are taken by a number of sensing CRs (SCRs) at the first level and are sent to a fusion centre (FC) over pre-existing clusters of relaying CRs (RCRs). The RCRs are being used in a secondary role for relaying the spectrum decision besides sensing their own area primary user. The decision of each SCR is relayed to FC one-by-one via number of RCR clusters by selecting a maximum signal-to-noise ratio link at each cluster independently. The selected RCR forwards the decision to the next level using DF protocol. The closed-form expressions for probability of missed detection and false alarm are derived at the FC. An optimal combining rule is devised at the FC. A comparative graphical analysis of power saving in case of multi-hop transmission to that of single-hop transmission is also presented. The number of hops for the considered system is optimised based on a trade-off relation between error rate and transmission delay.

In this study, the error performance and the capacity analysis is performed for the decode-and-forward based dual-hop asymmetric radio frequency-free space optical communication (RF-FSO) system. The RF link is characterised by Nakagami- m fading and the FSO link is characterised by path loss, Gamma-Gamma distributed turbulence and pointing error. For this mixed RF-FSO cooperative system, novel closed-form mathematical expressions are derived for cumulative distribution function, probability density function and moment generating function of the equivalent signal-to-noise ratio in terms of Meijer-G function. Using these channel statistics, new finite power series based analytical expressions are obtained for the outage probability, the average bit error rate for various binary and M -ary modulation techniques and the average channel capacity of the considered system in terms of Meijer-G function. As a special case, the analytical framework can also be obtained for channel statistics and performance metrics of dual-hop mixed Rayleigh-Gamma-Gamma system. Simulation results validate the proposed mathematical analysis. The effects of fading, turbulence and pointing error are studied on the outage probability, average bit error rate and channel capacity of the asymmetric RF-FSO system.

The maximum-likelihood (ML) decoder is derived for diagonal unitary space-time block code (STBC) matrices based double-differential modulation for multiple-input multiple-output systems. The ML decoder is obtained on the basis of maximising the joint probability density function of three consecutively received data matrices.

Joint transmitter and receiver design problem for frequency-selective, time-invariant fading channels are studied. The authors first propose a simple approximate maximum likelihood serial decision-feedback equaliser (A-ML-SDFE) through DFE, a Gaussian approximation, a pre-whitening filter and a matched filter. Secondly, assuming full channel knowledge available at the transmitter side, the authors perform pre-equalisation in a downlink scenario by moving the decision-feedback part of the A-ML-SDFE to the transmitter. The proposed A-ML-SDFE achieves much better performance than linear minimum mean square error (MMSE) and MMSE-DFE with a lower complexity. The pre-equaliser further improves the system performance at low signal-to-noise ratio with a reduced receiver complexity.