Tandem duplication (TD) errors occur when data is stored in the DNA of living organisms. The construction of codes to correct these errors was previously considered. A method was proposed to construct codes for TD errors of length at most k, , based on the uniqueness of -roots. It was shown that there exist words which have more than one -root when . As a consequence, the previous approach to correcting TD errors of length at most k cannot be extended to . In this study, -hinge-free irreducible words are introduced and used to construct codes for TD errors of length at most k where . Furthermore, it is conjectured that the proposed approach can be extended to .

This study addresses the energy efficiency (EE) maximisation problem in multi-input multi-output cognitive relay networks, where a secondary transmitter–receiver pair communicates through an amplify-and-forward relay using the licenced spectrum of a primary user. The authors aim to maximise the EE of the secondary system by jointly designing the source and relay precoding matrices, subject to transmit power, interference, and quality-of-service constraints. The resultant problem is non-convex in the precoding matrices; it is converted into a much simpler vector-valued problem using singular value decomposition. A combination of iterative optimisation, fractional programming, and Lagrangian multiplier is used to further tackle the problem. Numerical results are presented to evaluate the EE performance of the proposed scheme. Impact of transmit power, interference threshold, and minimum rate requirement on the EE is analysed.

In this study, the authors propose a learning-based approach to improve the security of the authors' considered communication system in a dynamic environment, where a source transmits information to a legitimate receiver in the presence of an active eavesdropper. Additionally, they assume that the source has to harvest energy from the environment to support its communication. Due to the dynamic of the environment, both the harvested energy and the channel vary over time, requiring a dynamic transmission strategy that follows the changes. In order to improve the security performance, they first analyse how to select the optimal transmission parameters in hindsight, and then they propose to combine the Q-learning algorithm and the expert advice method to maximise the cumulative reward in the dynamic environment. They also introduce an improved learning-based approach, which accelerates the convergence of their approach. The simulation results show that their proposed learning-based approach helps the legitimate nodes learn a beneficial transmission strategy to obtain a larger cumulative reward.

Achieving reliable and energy-saving broadcast is the main issue discussed in this study. Firstly, a multi-hop broadcast model is introduced, and the energy consumption and reliability of the network are defined in this study. Then five broadcast-based automatic repeat request (ARQ) protocols (automatic retransmission N times, stop-and-wait end-to-end-ARQ, stop-and-wait hop-by-hop-ARQ, stop-and-wait hop-by-hop oriented implicit ARQ, stop-and-wait hop-by-hop implicit and explicit ARQ) are proposed to realise the reliable transmission. Secondly, based on five protocols, the relationship between the system reliability and the number of retransmissions of the root node is established analytically, and the maximum number of retransmissions is solved under the required system reliability. Thirdly, the energy consumptions of the root node are calculated, and then the analytical expressions of the minimum system energy consumption are obtained separately according to five broadcast-based retransmission mechanisms. Finally, the relationships between the maximum number of retransmissions, energy consumption and reliability, the broadcast probability and feedback probability are discussed in the numerical analysis. Specially, for better energy-saving, the modulation technique should be adopted to choose suitable protocol based on a dynamic hop threshold.

The broadcasting services of vehicles in both vehicular networks and unmanned aerial vehicle (UAV) networks can be seen as the typical applications of all-to-all (A2A) scenario. In order to achieve efficient information broadcasting in A2A scenarios, this study proposes a two-stage resource allocation scheme. In the first stage, to improve the frequency spectrum reusability, the communication area is divided into as many non-overlapping square regions as possible based on the reliability requirements and power constraints of the vehicles, where the nonadjacent square regions share the same frequency spectrum. In the second stage, the vehicles belonging to the same region broadcast information with distributed time division multiplexing, and an improved coded slotted ALOHA scheme is proposed based on full-duplex, where each vehicle can detect whether its broadcasted information is successful. Thus, the number of retransmissions and collision probability can be reduced and therefore the system energy can be saved. Results indicate that the two-stage resource allocation scheme significantly improves the resource reusability while guaranteeing the communication reliability.

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 wireless sensor networks, multi-way relaying is a very common network configuration, where multiple nodes exchange information via a single relay over uncorrelated fading channels. In such configuration, node pair-wise communication together with physical-layer network coding (PNC) at the relay node provides a good trade-off between spectral efficiency and error performance. A joint channel decoding-PNC algorithm employed at the relay can further improve the bit error rate performance. This study proposes an improved joint channel decoding-PNC algorithm for M-ary phase shift keying modulated multi-way wireless relay systems. The proposed algorithm can achieve an additional diversity gain by exchanging bit-level or symbol-level soft information between the constitute decoders decoding different information pairs. Moreover, several schemes are proposed for exchange of the soft information between the parallely operating channel decoders. Simulation results demonstrate improved error and convergence performance of the proposed algorithm over the existing algorithms at the expense of non-significant increase in computational complexity.

In this study, a cognitive radio network is considered in which multiple secondary users intend to detect a primary user frequency band in order to specify whether it is occupied or not. To this end, a blind Bayesian framework is proposed by which secondary users cooperatively perform spectrum sensing. In practice, it is impossible to estimate the noise variance accurately (noise uncertainty problem) and this can degrade the performance of some previous spectrum sensing algorithms like energy detection (ER). To overcome this issue, unlike the conventional ER, the proposed algorithm utilises marginalisation to eliminate the effect of uncertainty in noise variance estimation. By computer simulations using MATLAB, it can be seen that the authors' algorithm reaches the ideal case for by improving the level of cooperation (increasing the number of secondary users) and yet its is also improved compared to ER in practical situations (presence of noise uncertainty).

Conventional beamforming transmission techniques can enhance physical layer secrecy performance while requiring the full channel state information (CSI) of legitimate users and even that of eavesdroppers at the transmitter. However, providing full CSI of legitimate users at the transmitter can be challenging in practice. Thus, it is of considerable interest to enhance secrecy performance with partial CSI of legitimate users at the transmitter. Random unitary beamforming (RUB) is a low-complexity multiple antennas transmission scheme requiring limited CSI. In this study, the authors investigate the secrecy performance of RUB transmission over multiple-input single-output single-eavesdropper and multiuser multiple-input multiple-output single-eavesdropper channels. They also propose a novel RUB-based artificial noise (AN) method for multiple antennas communication system. They derive the closed-form expressions of the exact and the asymptotic ergodic secrecy rate and the secrecy outage probability for these transmission scenarios. Numerical results are presented to illustrate the trade-off between performance and complexity of the resulting physical layer security design. They show that the deployment of RUB and RUB-based AN offers an attractive solution for enhancing the security of wireless transmission systems.

In this study, a new modulation method defined as Ramanujan periodic subspace division multiplexing (RPSDM) is proposed using Ramanujan subspaces. Each subspace contains an integer-valued Ramanujan sum and its circular downshifts as a basis. The proposed RPSDM decomposes the linear time-invariant wireless channels into a Toeplitz stair block diagonal matrices, whereas orthogonal frequency division multiplexing (OFDM) decompose the same into diagonal. Advantages of such structured subspaces representation are studied and compared with an OFDM representation in terms of a peak-average power ratio and bit error rate. Zero-forcing and minimum mean square error detectors are applied to evaluate the performance of OFDM and RPSDM techniques. Finally, the simulation results show that the proposed design (with an additional receiver complexity) outperforms OFDM under both detectors.

The direction of arrival (DOA) and amplitude-phase (AP) of source signal can be estimated through array signal processing, while the process of information acquisition has not been described by information theory yet. In this study, the authors propose a novel spatial information theory framework to describe the DOA and AP estimation process. Firstly, they give a sensor array system model, where the spatial information is defined mathematically. Furthermore, in a single source scenario, the derivations of theoretical expression and an asymptotic upper bound for DOA information are presented. It also proves that the AP information accords with Shannon channel capacity when the source follows complex-Gaussian distribution. In addition, when in an uncorrelated multi-sources scenario, the AP information is the sum of that of each source for Gaussian distributed sources. Finally, they propose a definition of entropy error to evaluate the information acquisition capability of a sensor array. Numerical results verify that the entropy error is consistent with mean square error and approaches Cramér–Rao bound in high signal-to-noise ratio. It also verifies the correctness of theoretical derivation and shows that the spatial information can be employed as an evaluation index to quantitatively analyse the system performance which has significant guidance.

Space-time block coded spatial modulation (STBC-SM) with cyclic structure (STBC-CSM) employs cyclical rotation of activated transmit antenna pairs to transmit Alamouti codewords taken from two different constellation sets to improve the spectral efficiency of STBC-SM. Furthermore, existing literature has shown that media-based modulation (MBM), which employs radio frequency (RF) mirrors demonstrate significant improvement in error performance of wireless systems. Hence, this study proposes the application of MBM to STBC-CSM and STBC-SM in the form of media-based STBC-CSM (MBSTBC-CSM) and MBSTBC-SM, respectively. The theoretical framework of the union-bound on average bit-error probability of M-QAM MBSTBC-CSM and MBSTBC-SM, for the maximum-likelihood (ML) detector is formulated and agrees well with Monte Carlo simulations. Furthermore, due to the large computational complexity of the ML detector, the authors propose a low-complexity near-ML detector for MBSTBC-CSM and MBSTBC-SM, which achieves a near-ML bit error rate performance with reduction in computational complexity.

This study presents a spectral approach to estimate the time difference of arrival (TDOA) between a reference unit, composed of a pair of very close antennas (small baseline regarding the operating bandwidth), acting as a known fixed location transmitter, and a mobile unit acting as a single antenna receiver. It uses the channel frequency response (CFR) based on an orthogonal frequency division multiplexing multicarrier communications in a multiple-input-single-output antenna configuration. By handling the CFR responses, seen as wideband interferometric signals, the authors minimise a cost function expressed as the difference between measured channel response and a predefined direct model. Effects of noise and multipath are evaluated and mitigated by the averaging process. The overall performances of the system are analysed, and the experimental validation is systematically led. In a small-scale indoor environment, it has been shown that the TDOA can be accurately estimated with higher accuracy than the conventional techniques. The proposed method allows, for example, estimating TDOAs of about 2 ns when using a null-to-null bandwidth of 100 MHz. Such an approach, based on existing communication systems, and suitable for the 5G norm, can be useful for several applications needing accurate positioning, without requiring complex dedicated infrastructure.

A three-user two-way channel in which three users exchange their messages through a two-way communication is considered by applying the physical-layer network coding and the superposition coding. The equivalent squared minimum distance (ESMD) is derived as a criterion for power allocation by analysing the average symbol error probability (SEP). Optimal and suboptimal power allocations are proposed based on the ESMD maximisation under total power constraint. Inspired by the result, a proportional power allocation is proposed under per-node power constraint. This scheme improves SEP at high signal-to-noise ratio (SNR) and consumes significantly less power. The average power consumption for each node is mathematically derived as a closed form. Furthermore, a compensation algorithm is introduced, which saves power and simultaneously achieves remarkable SEP improvement over entire SNR range. The numerical simulations over Rayleigh fading channels confirm the superiority of the proposed algorithms.

Resource allocation problem is a key issue in multi-carrier non-orthogonal multiple access (NOMA) networks. Maximum access problem and power allocation problem are two important problems in resource allocation problem. In this study, two algorithms are proposed to solve the two problems for multi-carrier NOMA networks, namely mixed integer programming algorithm (MIPA) and dynamic power allocation algorithm (DPAA). In order to solve the maximum access problem, a MIPA is proposed in uplink multi-carrier NOMA networks. For the power allocation problem, a DPAA is proposed in downlink multi-carrier NOMA networks. Simulation results show that MIPA can increase the number of supported users compared to other schemes, DPAA can improve user data rate by increasing mean channel quality indicator and make power allocation more reasonable. According to DPAA, the gains of weighted sum-rate utility per subcarrier can be improved with the increase in the number of subcarriers. Simulation results also show that the proposed scheme is superior to reservation channel technique in terms of the probability of call dropping and probability of call blocking.

A new multilevel modulation scheme centred on Manchester signalling known as four-level modified Manchester (4-MM) modulation format is envisioned and proven statistically for high-speed optical fibre transmission links. Similarly, the bit error rate (BER) assessment version has been developed for the envisioned 4-MM format. The performance of new 4-MM is examined and compared with conventional Manchester modulation, binary MM modulation, and four-level pulse amplitude modulation (4-PAM) formats in relation to receiver sensitivity, spectral efficiency, and chromatic dispersion tolerance. Therefore, the computed receiver sensitivity and chromatic dispersion tolerance at 10⁻⁹ BER of the envisioned 4-MM are −21.5 dBm and 95 ps/nm, respectively. The receiver sensitivity of 4-MM was improved by 3 dB in comparison with 4-PAM in a back-to-back configuration. Similarly, assessment of results indicates that 4-MM technique has a distinct benefit in comparison with binary MM and 4-PAM in achieving a dynamic role in the subsequent generation of high-speed optical access and short reach networks where power efficiency is of critical important.

Studies have shown that most of the flows in data centres are mice flows and last short time. However, existing green networking solutions do not consider this traffic characteristic. A mass of mice flows may be rerouted after network equipment is put into sleep mode and this can result in significant degradation of network performance. In this study, the authors propose a novel solution for green networking called energy-efficient flow scheduling approach (EFSA). EFSA aggregates mice flow into a minimal set of links, and the largest flows that result in an overload of links in the set are rerouted in time. Instead of managing every mice flows, only a few numbers of largest flows are rerouted. Unused switches/links will be put into sleep mode for energy saving. The evaluation of EFSA shows that it can significantly reduce the number of rerouted flows and improve the performance of data centre networks while saving network energy efficiently.

Sensor node communications are usually the most energy consuming among its activities. Therefore, reducing those communications necessarily preserves the node limited energy. One successful approach to this end is to reduce both the number of transmissions made by the node and the payload of each transmission. Numerous proposals have recently been made to achieve this reduction by approximating the node data at the sink via forecasting. However, many of these proposals are plagued with one or more of three problems: intensive computations, excessive delays and backtracking. In this study, the authors introduce the lightweight energy-efficient real-time (LEERT) framework, which avoids all three problems while saving considerably on energy consumption. The savings are achieved by both reducing immensely the number of transmissions and reducing the payload of each transmission to only one element. This is actually the minimum any framework would hope for. LEERT is also extremely light, performing only four primitive operations per measurement on average. Its storage requirements are even lighter – only one past measurement needs to be retained in memory. LEERT has passed extensive validation tests using real-world data. Its performance has been evaluated against two recent energy-efficient frameworks and found to have an astounding edge.

An energy-harvesting decode-and-forward cooperative system over correlated Rayleigh fading channels is investigated. Simultaneous wireless information and power transfer (SWIPT) technology is employed at the relay to improve energy efficiency. To overcome the spatial correlation among the transmit antennas, precoding spatial modulation (PSM) is formulated. The average bit-error probability (ABEP) upper bound is derived and it matches closely with the Monte Carlo simulation results. The influence of the parameters, such as the power-splitting factor and transmit correlation coefficient, on system performance is studied. The results show that the proposed PSM-SWIPT system can achieve better ABEP performance than SM-SWIPT, space shift keying-SWIPT and multiple-input–multiple-output-SWIPT systems under the same spectral efficiency.

A new end-to-end communication system is proposed to increase transmission speed, robustness, and security in order to meet the requirements of mobile systems that know an exponentially increasing data amount over time. The design relies on the use of compressed sensing-source coding instead of the supported speech coding standards in actual mobile communication systems. The proposed compressed sensing-source coding method allows reducing the speech coding complexity by using simple quantisation and binary encoding, saving communication system resources, and encrypting communications without additional costs. The performance of the resulting communication system is evaluated for speech communication via 10 dB Rayleigh environment in terms of perceptual evaluation of speech quality (PESQ) scores and coherence speech intelligibility index (CSII) when convolutional coding, orthogonal frequency division multiplexing, and diversity schemes are used. Results report that for a bit rate of 12.8 kbit/s the proposed scheme achieves fair speech intelligibility justified by a CSII value of 0.5, and offers good output speech quality measure, providing a PESQ of 3.33 for the same bit rate.

In this study, the authors analyse and provide new insights into the problem of multi-cell minimum mean square error (MMSE) detector in massive multiple-input multiple-output (MIMO) systems. Their system combines pilot hopping and pilot reuse strategy in the multi-cell scenario.They obtain a deterministic expression of rate bounds of the uplink system when MMSE is used for channel estimation and data detection. Their result is different from the existing MMSE bounds in massive MIMO literature in that they obtain an achievable rate that is simply a scaled version of that of the matched filter (MF) detection, i.e. the achievable rate of the MF detection can be scaled with a constant, which is a function of the number of antennas and users as well as the power allocation to directly obtain the achievable rate of the MMSE detection. This new finding saves a significant amount of work needed when analysing MMSE detection in massive MIMO since it reduces the problem to obtaining simpler results (using MF analysis) and then extending the result to the MMSE case in a straightforward manner. Simulation results show how tight the achievable rate bound to the actual one at a large number of BS antennas.

In this study, the authors formulate a non-cooperative game approach in which all base stations compete in a selfish manner to transmit at higher power. Each base station in the network is considered as a player in the game. The solution of the game is obtained by finding the optimal point, namely the Nash equilibrium. The proposed method, named efficient handover game theoretic, targets to manage the handover in dense small cell heterogeneous networks. Each player in the game optimises its payoff by adjusting the transmission power so as to enhance the overall performance in terms of throughput, handover, energy consumption, and load balancing. In order to choose the preferred transmission power for each player, the payoff function takes into account the gain of increasing the transmission power, energy consumption, base station load, and unnecessary handover. The cell selection is performed using the technique for order preference by similarity to an ideal solution (TOPSIS). A game theoretical approach is implemented and evaluated for dense small cell heterogeneous networks to validate the enhancement achieved in the proposed method. Results show that the proposed game theoretical approach provides a throughput enhancement while reducing the power consumption in addition to minimise the unnecessary handover and balance the load between base stations.