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Phase noise problem in oscillators can degrade the performance of high-speed communication systems. The author analysed the impact of phase noise problem on multi-input–multi-output (MIMO) systems under common and independent oscillators. The estimation of system parameters (i.e. phase noise and channel gains) is a challenging task. In this study, a data-aided least square estimator based compressed sensing Kalman filter (KF)-based compressed sensing (CS) scheme is proposed for tracking phase parameters. The signal model and estimation problem for the system are mathematically derived. Also, Bayesian Cramer–Rao lower bound (BCRLB) scheme is also derived. For joint estimation, the mean square error (MSE) and bit error rate (BER) performances of the BCRLBs and proposed scheme are compared. Results demonstrate that the proposed KF-based CS scheme gives low BER values and better performance compared to other estimation schemes. The utilisation of the proposed scheme helps in reducing the MSE of the MIMO system. Finally, the proposed scheme enhances the estimation of phase noise parameters for the MIMO system.

A symbol-asynchronous uplink non-orthogonal multiple access (NOMA) model is considered, where K users transmit codewords to a common receiver according to their local clocks. As the complicated user location and the dynamic transmission environment, the exact time offsets of users are not always available at the base station (BS). To ensure the efficiency of the system, linear minimum mean square error algorithm and partial message passing (P-MP) algorithm are designed based on iterative detection. The signal to interference plus noise ratio is also applied to analysis the effect of estimated time offsets on the P-MP algorithm. Then simulation results show that when the variance of estimation error is 0.1 , the symbol-asynchronous NOMA systems with imperfect time offsets can achieve the same or even better bit error rate performance than the NOMA system.

Massive multiple-input multiple-output (M-MIMO) is one of the cutting edge technologies that provides significant improvement in throughput, coverage and spectral efficiency. The challenge with M-MIMO systems is to extract individual signals from the composite signal, thus making optimal detectors prohibitively complex. Recently, approximate message passing (AMP) and its variant detectors have gained substantial importance due to their decreased complexity and improved performance. However, AMP algorithm does not always converge. Non-linear detectors like vertical Bell-Labs layered space-iime improve the bit error rate (BER) but with high complexity, whereas, linear minimum mean square error (MMSE) detector offers low complexity while compromising on BER performance. Neumann series based MMSE detectors further reduce MMSE computational complexity, however, the BER performance remains the same. In this work, the authors propose a hybrid Neumann series based MMSE detector which decomposes the detected signal into its constituent components and apply a neighbourhood selection algorithm on the obtained components thus improving the overall performance. Another contribution of this work is derivation of an off-set value for optimised neighbourhood set selection that enables more accurate detection while further reducing computational complexity. Simulation results confirm that the proposed scheme outperforms aforementioned algorithms in terms of BER performance and computational complexity in a continuously changing Rayleigh channel.

This study presents the design analysis and correlation properties of a new spreading code for the incoherent synchronous pulse position modulation-optical code division multiple access (PPM-OCDMA) networks. The proposed code called optimised modified prime code (OMPC), which refers to the modified prime codes (MPCs) family. Additionally, this new code designed at a higher code length, optimised code weight and good correlation characteristics to enhance communication security and improve the bit error rate (BER) performance. In this study, the proposed code is used as source code for different kinds of multimedia services such as data, voice, and video. Furthermore, the characteristics and correlation properties of the OMPC in comparison with the other MPCs families that utilised in the PPM-OCDMA networks are presented. Moreover, for the PPM-OCDMA networks, the effect of OMPC auto- and cross-correlation properties on the multiple access interference (MAI) was investigated. Consequently, the MAI is considered in the BER analysis and calculations. Finally, the results show that the proposed OMPC is better than the other existing codes with respect to the channel capacity and system performance.

Amplify-and-forward cooperative underwater optical wireless communication employing optical improved quadrature spatial modulation (OIQSM) is proposed in this study. It uses multiple signal constellations, thereby improving the system performance. It uses multiple lasers but it activates only a few of them depending on the message bits and can transmit double modulated symbols in a single symbol interval. The OIQSM system performance is compared in terms of bit error rate (BER) with other existing schemes in the literature. The analysis is conducted for weak oceanic turbulence conditions, which is generally prevalent in deep oceans. The cost and power consumption analysis of OIQSM is performed to highlight its benefits over other schemes. It is observed that OIQSM yields a signal-to-noise ratio gain of at least 5.5 dB over the conventional optical spatial modulation scheme for any BER value between 10 − 2 and 10 − 4 .

Non-orthogonal multiple access (NOMA) is an attractive candidate for future wireless networks. Recently, vehicular communications with NOMA have received substantial research attention owing to their appealing advantages. In this study, the authors investigate the performance of downlink power-domain NOMA-enabled vehicular communications, in which a base station communicates with two users UE1 (far user) and UE2 (near user). Since all the nodes are moving vehicles, the channels for vehicular links experience independent and non-identically distributed double-Rayleigh fading. Specifically, the authors derive the outage probabilities of individual users and overall system under two scenarios of interest, viz. (i) when the rate of NOMA system falls below the fixed target rate and (ii) when NOMA system achieves lower rate than orthogonal multiple access (OMA) rate. The authors also derive the average bit error rate (ABER) and ergodic capacity expressions for the considered system. The numerical and simulation results validate the proposed analytical findings, and demonstrate the impacts of various parameters on the system performance. The authors further show that NOMA scheme is superior than OMA in terms of outage probability and ergodic capacity, whereas OMA outperforms NOMA in terms of ABER because OMA users do not have inter-user interferences.

Error performance of hybrid subcarrier intensity modulation (hybrid-SIM) in optical free-space satellite downlink has been studied in this work. Bit error rate (BER) is improved by aperture averaging and spatial receiver diversity and it is found out be effective in strong turbulence regime. Subsequently, the reduction in scintillation index has been investigated by implementing a single large receiver and an array of point receivers of length n R with the same effective aperture area. Moreover, the BER at different turbulence conditions is compared with minimum shift keying and multiple levels of pulse position modulation pertaining to aperture averaging. Upon analysing the single input multiple outputs (SIMO) system, the desired response is obtained above a certain threshold in average received irradiance. At different zenith angles and turbulence strengths for n R = 4 , the threshold is 4.59 and 3.35 dB, respectively, and it rises by 13.6 and 26.43 dB when n R is increased to 9. This constraint can be exploited to optimise the number of receivers concerning system requirement and availability. Further, the pointing error effects are also investigated for SISO and SIMO systems, which takes into account both atmospheric turbulence and misalignment induced fading.

The acoustic signal transmission over the underwater channel has a limited sum rate and it consumes high power due to the properties of the underwater environment. This study attempts to use the non-orthogonal multiple access (NOMA) technologies for underwater communications. NOMA can be an attractive candidate for underwater communication due to its high spectral efficiency, resistance for carrier frequency offset, and efficient energy consumption. To cope with the hard-recharging capability of the underwater wireless sensor nodes caused by the ocean environment, this study proposes a novel transmission scheme called time-reversed NOMA (TR-NOMA) for underwater communication. In the proposed TR-NOMA, a single-input multiple-output NOMA scheme with a passive-time reversal technique is proposed to reduce the time–frequency dispersion of the underwater acoustic channels. Consequently, simultaneous wireless information and power transfer (SWIPT) can be applied for underwater TR-NOMA. In this study, a SWIPT-NOMA is postposed to harvest energy in downlink transmission from the transmitted signal. The bit error rate (BER) and the outage probability are used to characterise the performance of the proposed TR-NOMA scheme and simulation results show how the proposed TR-NOMA significantly outperforms the conventional NOMA schemes. Additionally, a mathematical framework for the average BER of TR-NOMA is delineated.

The authors propose an integrated Mach-Zehnder interferometer and diversity combining receiver to mitigate the atmospheric turbulence-induced fading in a millimetre-wave (mmW) radio-over-free-space optics (RoFSO) link. They use a carrier frequency of 28 GHz as recommended for the fifth-generation wireless access networks and consider two optical mmW signal generation schemes, namely double-sideband (DSB) and single-sideband (SSB). In direct detection (DD)-based RoFSO, the link performance is limited by atmospheric turbulence. They show that the proposed Rx can overcome this detrimental effect, which is verified by investigation of a 10 Gb/s 16-quadrature amplitude modulation orthogonal frequency-division-multiplexing signal at 28 GHz over a 1 km free-space optics link under weak and strong turbulence regimes. For the DSB scenario, the proposed Rx offers improved error vector magnitudes of about 0.8 and 5.7%, and modulation error ratios of 1.3 and 4.9 dB under weak and strong turbulence regimes, respectively, compared with the DD receiver (DD Rx). For the SSB scenario under weak turbulence, the proposed Rx achieves a 4 dB improvement in the receiver sensitivity and four orders of magnitude enhancement in the bit error rate over the DD Rx. The proposed Rx can be integrated on a single chip for further cost reduction.

Free space optical (FSO) inter-satellite links could often be non-reliable due to the imperfect line of sight (LOS) links. To achieve more reliable communication, the authors propose hybrid inter-satellite links. However, this leads to new challenges like switching physical (PHY) layers at the satellite's transmitter. In this work, they propose a novel hybrid radio frequency-FSO (RF/FSO) satellite system. For it, they develop a novel best beam selection policy (BBSP) and switching of FSO and RF to improve the reliability of the inter-satellite links. To obtain more insights, they investigate the performance of BBSP by deriving expressions for the outage probability, average spectral efficiency, and average bit error rate of the BBSP. For the PHY switching, they compare the instantaneous error probabilities of RF and FSO links and find the signal-to-noise ratio threshold at which it is more efficient to switch to RF. They further improve this threshold by considering a satellite transmitting multiple beams and choosing the best source beam. To validate the analytical findings, they simulate the proposed model with CubeSat level parameters. They and that the BBSP delivers superior performance in terms of various performance measures, which shows its applicability in next-generation satellite systems.

In the present paper, the bit error rate (BER) performance of hybrid power line communication (PLC) and multiple-input multiple-output (MIMO) visible light communication (VLC) system (HPMV) has been investigated using line-of-sight (LOS) and LOS plus first reflection (L-R1) signals for room size of 5 m × 5 m × 3 m (configuration A) and 7.5 m × 7.5 m × 3.5 m (configuration B). In the work, Rayleigh fading and Barry channel models have been considered for PLC and VLC channels respectively. The BER has been analysed by varying separations between LEDs as 0.2 m, 0.6m and 1m for both configurations. The results show that the BER for LOS and L-R1 signals decreases upto optimal separation of 0.6 m for configuration A. However, the result indicates that the required optimal separation for configuration B is more than configuration A. The channel frequency response of MIMO-VLC and HPMV system has been inspected and it supports the results of BER simulation. It has been found that, with increase in spatial separation between LEDs, the deep notches and attenuation in the frequency response of MIMO-VLC system decrease. The overall investigation shows that even though OFDM is resilient to frequency selective fading, an optimum separation between LEDs must be chosen according to the room size for the HPMV system.

With the increasing demand for high-speed mobile transmissions for 5G networks, the cooperative relay-aided non-orthogonal multiple access (CR-NOMA) has been highly considered. An efficient and reliable CR-NOMA not only depends on the network mechanism but on the network coding strategy at the relay. Even though conventional strategies have broadly been studied, they suffer from noise accumulation and interference. Lately, the compute-and-forward (CpF) strategy has been identified as a potential technique to mitigate interference and enhance outage probability. In this study, the authors present a mathematical formulation to examine the performance of CpF on downlink CR-NOMA. In the proposed formulation, a two-stage downlink cooperative relay network is considered to obtain analytical closed-form expressions of outage probability and bit error rate. The outage probabilities and bit error rates of existing relaying strategies are compared regarding the network model. The theoretical analysis shows that CpF requires half the number of relays desirable in amplify-and-forward and decode-and-forward strategies to achieve a proportionate outage probability in CR-NOMA. Finally, we present results to show that at a lower signal-to-noise ratio, the integration of CpF and NOMA enhances error performance irrespective of the number of users.

In this study, the authors have developed an analytical model for reducing the peak-to-average-power ratio (PAPR) using non-linear companding transform (NCT) based on inverse hyperbolic sine function. As a consequence of non-linear transform, this study compensates the system bit error rate (BER) degradation with the help of an error efficient hybrid modulation. By means of an inflexion point and companding parameter, more design flexibility is achieved; as a result, a trade-off between PAPR and BER has reasonably been more precise. To the best of the authors’ awareness, no findings have yet been reported on the performance evaluation of the optical orthogonal frequency division multiplexing (OOFDM) system using a hybrid modulation technique. To find out the advantages of hybrid modulation with NCT, the authors inspect the nature of PAPR reduction, and BER improvement through numerical simulations. The numerical BER results exhibit roughly 3 dBm decay in the power efficiency of hybrid modulation with NCT over discrete Fourier transform (DFT) precoding technique. On the other hand, the NCT technique with hybrid modulation has 6 dB less PAPR than the DFT precoding technique.

The authors incorporate Alamouti space-time block coded orthogonal frequency division multiplexing (OFDM) with signal space diversity (SSD) in order to significantly strengthen the physical layer security of the communication network. The coordinate interleaving step of SSD is performed amongst OFDM subcarriers, according to distinct strategies that make the correlation coefficients between the subcarrier channel gains equal to zero. The proposed system model can improve the security by enabling a legitimate user to have much less error than an eavesdropper, even under the worst-case scenario where the unauthorised receiver somehow captures the interleaving strategy compromised by the transmitter and legitimate receiver. It is shown that a legitimate user with the introduced scheme can provide up to 14% more performance gain as compared to an unauthorised receiver for a bit error rate (BER) of 10−4 under worst-case scenarios with different parameters. An exact closed-form expression of the BER is derived for the legitimate user and shown to match with the simulation results. Finally, it is demonstrated that the system is also capable of enhancing the resistance against channel estimation errors at the receiver. The proposed system does not require high complexity or additional bandwidth or time resources.

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.

Ambient backscatter which utiliees the ambient radio-frequency signals to enable transmissions between battery-less devices has attracted considerable attention in academia and industry. This study addresses the questions of full-duplex (FD) and self-interference cancellation (SIC) for ambient backscatter which adopts dual-antenna structure to achieve persistent information transmission and energy harvesting. The authors construct the physical-layer network coding (PNC) mapping principle of on–off keying in the dual-antenna structure and propose the PNC-based FD algorithm to eliminate the self-interference in the information domain. Furthermore, the bit-error-ratio and throughput performances are analysed under conventional half-duplex mode and the proposed FD mode, respectively. In order to facilitate system complexity and reduce power consumption, they design a hardware prototype to achieve SIC which consists of low-power passive analogue components. Numerical results are provided to confirm the theoretical studies. Circuit simulations demonstrate that the circuit is commendably consistent with the design concept.

Presently, the single-carrier frequency division multiplexing (SCFDM)-based visible light communication (VLC) system is extensively implemented for secure and high-speed data transmission. However, the effect of additive white Gaussian noise in VLC with white light-emitting diode is high, due to a high peak to average power ratio (PAPR). To address this difficulty in 5G networks, two objectives were carried out in this research article. Initially, selective mapping (SLM) scheme was applied for PAPR reduction, because it considerably selects the effective phase rotation factors that help in the reduction of system complexity. Besides, binary crow search algorithm was used for sub-block partition optimisation in SLM for enhancing the convergence speed of the proposed SCFDM-based VLC system. In the experimental investigation, the proposed SCFDM-based VLC system was analysed in terms of complementary cumulative distribution function, bit error rate and signal-to-noise ratio by varying the equalisation techniques for 5G networks.

A design of 4/6 intertrack-interference (ITI)-mitigating error correction modulation code for bit-patterned media recording systems is proposed in this Letter. Generally, coding schemes in data storage devices are usually accomplished using a combination of error-correction coding and modulation coding. However, an interesting approach is that the modulation code itself has the capability of correcting errors. Such a modulation code design will reduce the total size and complexity of the data storage devices. In this Letter, the authors design a new 4/6 modulation code, where the code not only mitigates the effect of ITI but also maintains minimum Hamming distance of 2 to build up a trellis structure providing error correction capability of the proposed code. Simulation results show that the proposed design outperforms prior arts. For instance, the performance of the proposed design is better than that of a conventional 4/6 modulation code about 8 dB at a bit error rate of 10 −7 under 20% read-head offtrack for the area density of 4 Tb/in 2 .

With the high mobility, flexibility and manoeuvrability, unmanned aerial vehicles (UAVs)-enabled mobile edge computing (MEC) plays an important role in many applications that lack of available terrestrial infrastructures, such as disaster response, emergency relief and military scenarios. However, the high mobility of UAVs may severely degrade the implementation of UAV-enabled MEC in computation-intensive or delay-sensitive scenarios from a physical layer signalling perspective, e.g. frequency selective fading effect caused by the low altitude and low elevation angle routes of UAVs. In this study, a generalised weighted-type fractional Fourier transform (GWFRFT) based signal energy-spreading transmission (EST) scheme is proposed for signalling and quality of service (QoS) provisioning for UAV-enabled MEC. In the proposed scheme, the communication signal energy is redistributed evenly at the time-frequency plane to enhance the robustness of UAV communications against the severe fading channels. The signalling provisioning mechanism of the GWFRFT-EST scheme is analysed and simulated under poor air-to-ground channels with low Rician K-factor. Simulation results show that the proposed method greatly improves the bit error rate performance with a negligible computational complexity increase.

Faster-than-Nyquist (FTN) signalling is regarded as a promising technology in satellite communications for the past few years, however, existing inter-symbol interference (ISI) elimination algorithms for FTN signalling cannot eliminate the linear distortion caused by the input-multiplexing and output-multiplexing filters, which are very common in satellite communications. On the strength of the fractionally-spaced equaliser (FSE), the authors propose a precoding-based frequency-domain linear distortion equaliser (PFLDE) to eliminate the above-mentioned linear distortion in FTN systems. On the one hand, by virtue of fast Fourier transform (FFT) and inverse FFT, the proposed PFLDE lends itself naturally to high-throughput parallel architectures, which are quite essential in high throughput satellite communications. On the other hand, the mean square error performance of the proposed PFLDE is superior to that of the existing time-domain FSEs. Furthermore, combining PFLDE with the existing ISI elimination algorithms for FTN signalling, the satisfactory bit error ratio performance can be obtained.

This Letter proposes a reliable and lightweight key generator based on a novel bit-self-test arbiter physically unclonable function (BST-APUF). The BST-APUF adds a delay detection circuit into a classical APUF to automatically test the delay deviation that produces each bit of the PUF response and generates a reliability-flag for each response to indicate its reliability. The key generator collects robust responses and produces a secure key using a cryptographic entropy accumulator. FPGA implementation results show that the overhead and the helper data length of the authors proposed key generator are significantly lower than that of the state-of-the-art schemes when generating a 128-bit key with a bit error rate of 10−9.

This study accessed the performance of the four-level Manchester coding (4-MC) and four-level modified Manchester (4-MM) technique at the bit rates of 20 and 40 Gb/s for the first-order and second-order optical equalisers. The performances were evaluated with respect to bit error rate (BER), power penalty, eye diagrams, and dispersion tolerance. Based on the results by utilising the second-order optical equaliser, at 20 Gb/s, the transmission distance of 4-MC and 4-MM was extended by 25 and 27 km of standard single-mode fibre (SSMF), respectively, while at the bit rate of 40 Gb/s, the 4-MC and 4-MM transmission distance was extended by 6.5 and 7.5 km of SSMF, respectively. Hence, the second-order optical equaliser can adequately compensate for the fibre dispersion and consequently the overall BER performance. Therefore, the proposed system could serve as an alternative to the next-generation high-speed optical transmission links.

The performance of multiple-input and multiple-output (MIMO) flip-orthogonal frequency division multiplexing (flip-OFDM) for indoor optical wireless communications (OWCs) is studied here. To improve the system performance in terms of the bit error rate (BER), the singular value decomposition (SVD)-based MIMO technique is applied together with the bit loading technique. The authors, especially, focus on optimising the BER performance of SVD-based MIMO-OFDM OWC systems under the impact of the OFDM symbol design, the configuration of MIMO transmitters, the required data rates, the available bandwidth, and the angular diversity based on tilting receiver photo detectors (PDs). The system BER expressions are analytically derived and verified to be accurate through comparison with simulation results. The authors find that the 9 × 4-MIMO system is the optimal configuration in terms of a large coverage of low BER regions and low computational complexity for the 5 m × 5 m room. In addition, polar angle tilting of PDs can effectively improve the BER performance. Finally, in case of light dimming control with a low total transmit optical power, the system can benefit from a high multiplexing gain with a large tilting polar angle, as indicated by improved condition numbers of MIMO channel matrices.

Millimetre-wave (mmWave) communications have been regarded as a key technology for the next-generation cellular systems since the huge available bandwidth can potentially provide the rates of multiple gigabits per second. Conventional precoding and combining techniques are impractical at mmWave scenarios due to manufacturing costs and power consumption. Hybrid alternatives have been considered as a promising technology to provide a compromise between hardware complexity and system performance. This study examines, using a semi-analytic approach, the downlink performance of massive MU-MIMO mmWave systems in terms of the bit error rate (BER). Also, a general expression is derived to estimate an upper bound/approximation to the BER performance via the Monte Carlo method, which can be used for any hybrid precoder/combiner, modulation and different data detectors. Numerical results evidence that the approximate BER expressions provide values very close to the ones obtained through simulation using only two statistical moments related to parameters of the system, mean and variance.

In this study, the audio transmission performance of some block coding methods in wavelet and non-wavelet cases is compared. For this purpose, a communication system has been established in the MATLAB environment for the transmission of the audio signal for 5 s. The comparison of the transmission performance of the block codes was performed separately in different parameters of additive white Gaussian noise, Rician and Rayleigh channels. At the same time, it is determined which discrete wavelet transform (DWT) family is suitable in terms of transmission performance for block coding methods and how DWT level affects transmission performance is investigated. Four DWT families at different levels were applied to the audio signal for linear block coding, Hamming, Cyclic, Bose–Chaudhuri–Hocquenghem, Reed–Solomon, encoded channels, and bit error rate and mean squared error performances were compared.

In this study, the authors consider the effect of multiple access interference (MAI) on the performance of a quasi-synchronous multicarrier direct-sequence code-division multiple access (QS-MC-DS-CDMA) system. An analytical expression of the bit error rate (BER) is derived for a QS-MC-DS-CDMA system over additive white Gaussian noise channel. The BER performance degradation is proportional to the squares of the even correlation function (ECF) and odd correlation function (OCF) of the spreading codes. The obtained results show that the adequate spreading code is a set of binary zero correlation zone sequences with both zero ECF and OCF. The construction of the latter codes remains a challenge for researchers in the field of code design.

In the 5G system, different units probably do cooperation to satisfy the communication requirements. However, when network configuration is limited, these units may be difficult to adopt the globally cooperative style. In this case, local cooperation is considered. This study focuses on local cooperation, and mainly aims at interference mitigation between different units and receiving performance improvement for each unit. Generally, a two-step scheme is proposed. First, channel decomposition is acted on interference mitigation through the design of first-step transmitters and receivers. Second, channel diagonalisation with symbol processing and selection principle is executed for receiving performance improvement, and the second-step transmitters and receivers are generated. The authors' contributions are: (i) they present the general scenario of local cooperation, and propose the corresponding strategies of interference mitigation and receiving performance improvement; (ii) they do not apply any iterative algorithm, and can adjust the quantity of information interaction between multiple units; (iii) they can make the symbol processing rule, modulation mode and signal-to-noise ratio metric flexible for each data stream. Numerical results illustrate the proposed scheme efficiently reduces the bit error rate, which means the proposed scheme can achieve the satisfactory effect in the locally cooperative network.

Besides promotion in the spectrum efficiency, orbital angular momentum (OAM) can bring additional benefits to physical layer security. In this study, the authors will highlight the benefit of covert transmissions to deal with the contradiction between transmission rate and security in the traditional direct sequence spread spectrum (DSSS) system. Based on OAM, a secure high-speed spread spectrum (SS) transmission system is proposed. Specifically, the system architecture and mathematical models are established. Afterwards, the detection method for the proposed OAM SS system is investigated. Meanwhile, the corresponding bit error rate (BER) and performance of anti-interception are analysed. The performance of data anti-interception is evaluated based on computational complexity, while the performance of signal anti-interception is studied by Neyman–Pearson criterion. Furthermore, Monte–Carlo simulations are also implemented to show the effectiveness of the proposed system. Compared with the traditional DSSS system, the higher security can be achieved by the proposed system. Besides, the transmission rates and BERs are the same for the traditional DSSS system and proposed system. Therefore, the proposed OAM SS transmission system successfully handles the contradiction of the transmission rate and security. In other words, the secure high-speed transmission can be achieved by the proposed OAM SS system.

In this study, a two-way full-duplex amplify-and-forward relay network is considered in which two multi-antenna fullduplex user nodes manage to exchange their information via a full-duplex multi-antenna relay. The users and relay can concurrently transmit their symbols in all time slots in the same frequency band, which leads to self-interference (SI) at all nodes. The joint beamforming algorithm is used in which the relay and users beamforming matrices are updated in each time slot to suppress the SI. This algorithm needs the channel state information (CSI) of all previous time slots, so the complexity increases as time lapses. To decrease the complexity, an algorithm is proposed in which the beamforming matrix is computed recursively. Moreover, the channel estimation error is considered when the relay and users have partial CSI. Thus, a robust algorithm, i.e. an algorithm that takes the estimation error into account is proposed to decrease the effect of estimation error. The proposed algorithm has been evaluated in terms of mean square error, achievable sum rate and BER for various values of the estimation error variances and compared with the non-robust algorithm. The results show that the superiority of the recursive robust algorithm in terms of SNR and complexity.

Multi-carrier faster-than-Nyquist (MC-FTN) signalling, which is a non-orthogonal data transmission scheme, is broadly viewed as one of the potential candidates for the future high spectral-efficient communications. In this study, a discrete time-frequency packing scheme based on the discrete Fourier transform (DFT) block transmission for MC-FTN signalling (DBT-MC-FTN) is proposed. Firstly, by transforming the blockwise MC-FTN signalling into the frequency domain, an efficient implementation transceiver structure incorporating a bank of DFTs, circular expanding operation, and cyclic shift summation operation is obtained. Thus, flexible packing in both time and frequency domains can be achieved efficiently within a DBT-MC-FTN block. Secondly, to deal with the inter-symbol interference (ISI) introduced by time packing and inter-carrier interference (ICI) introduced by frequency packing in the proposed DBT-MC-FTN scheme, a subcarrier-level equalisation combined with a soft interference cancellation scheme operated in the frequency domain is further proposed to detect the DBT-MC-FTN signals at the receiver. Simulation results show that the proposed DBT-MC-FTN scheme performs close to the corresponding orthogonal system with negligible bit error rate performance loss in the case of moderate ISI and ICI. Additionally, the post-processing signal-to-interference-plus-noise ratio of the proposed scheme is also given in detail.

Sparse code multiple access (SCMA) is one of the non-orthogonal multiple access schemes to meet the demands of massive connection and high spectral efficiency in the 5G communications. Since the sparsity of the codebook, the message passing algorithm (MPA) can be utilised for multi-user detection. However, the high computational complexity of MPA hinders the practical application of SCMA. The extended Max-Log MPA (EML-MPA) and the channel-adaptive extended Max-Log MPA (CAD-EML-MPA) help to reduce the complexity of conventional Log-MPA with trellis representation. On this basis, the authors propose a dynamic trellis based MPA (DT-MPA) in this study. DT-MPA selects symbols dynamically according to a specific threshold τ in each iteration of MPA. The impact of the threshold on the complexity and convergence behaviour is analysed. Simulation results show that the DT-MPA with variable τ which is related to bit signal-to-noise can achieve better bit error rate performance and lower complexity than EML-MPA and CAD-EML-MPA.

This Letter proposes a symbol cyclic reconstruction scheme for universal-filtered multi-carrier (UFMC) systems. In this scheme, the overlap-add technique is employed to reduce the computational complexity of the system transmitter. At the receiver, ISI cancellation is performed to remove the interference between neighbouring overlapped symbols. Then, a cyclic reconstruction algorithm is proposed to eliminate the interference caused by the linear shift. This scheme effectively improves the transmission efficiency in multipath channel environments while ensuring the bit error rate performance. Simulation results show that the TE of the proposed scheme is much higher than that of standard UFMC and cyclic prefix -OFDM systems.

In this study, the authors have proposed a low complexity companding function for peak-to-average-power ratio (PAPR) reduction in orthogonal frequency division multiplexing systems. This function transforms the signals into a probability density function with a cumulative distribution function an anti-trigonometric function. By carefully choosing the transform parameters, the bit error rate (BER) performance can be improved significantly during the reduction of PAPR. In addition, the proposed companding function offers design flexibility. Simulation results show that for the same PAPR performance, the proposed companding scheme can offer better BER performance. For example, upon assigning BER = 10−4 in an additive white Gaussian noise channel without a solid-state power amplifier, the minimum required bit energy to noise power spectral ratio (E b/N o) for the proposed companding scheme with c = 0 and A = 1.414 is 11 dB. It is 5, 4.2, and 3 dB lower than exponential companding function, root-based μ-law companding function, and amplitude limiting companding schemes, respectively. Also, their PAPR performance is the same.

This work presents an analogue equaliser with digital tuning. It compensates the losses introduced by up to 120 m long category 5 unshielded twisted pair cables and baseline wander (BLW). The equaliser is designed for Fast Ethernet with a symbol rate of 125 MHz. A g m -C filter, based on three first-order high pass filters, is used to compensate the cable loss. To minimise power consumption, three operational transconductance amplifiers (OTAs) are merged into a novel multi-input OTA structure. Additionally, a robust digital control logic is presented to automatically adjust the parameters of the equaliser for different cable lengths. A fast settling time below 250 µs is demonstrated for different scenarios. The equaliser is fabricated as part of a Fast Ethernet PHY chip in a 180 nm CMOS technology of GLOBALFOUNDRIES. Measurement results demonstrate error-free data transmission (bit error rate below 10 −12 ) for cable lengths up to 120 m. The power consumption of the analogue equaliser ranges from 2.3 mW (short cable) to 6.5 mW (120 m cable). To the best of the authors’ knowledge, this is the lowest power consumption of an analogue equaliser for Fast Ethernet, supporting additional BLW and flat loss compensation reported to date.

In this Letter, the authors introduce optimisation design technique of systematic Luby transform (SLT) codes over binary erasure channel (BEC). SLT codes are more efficient than Luby transform (LT) codes since the former ones can recover source symbols more quickly. There was some work about designing degree distribution in LT codes and it was shown that erasure probability barely impact performances of LT codes. Using degree distributions designed for LT codes directly in SLT codes does not provide satisfied performances. For the first time, they introduce erasure probability as a parameter to establish a linear programming model in SLT codes. By applying And-or Tree analysis, they propose the asymptotic analysis formulae of SLT codes over BEC. To achieve the goal of recovering source symbols as soon as possible, the authors' objective of optimisation is to minimise overhead. Simulations are offered to validate the performance of their optimisation result. Besides, their degree distribution outperforms other distributions with respect to bit error ratio.

This study introduces an accurate design and optimisation of a passive optical code division multiple access (OCDMA) network encoder using the coupled cavity waveguide (CCW) as an optical delay line. Such CCW has the capability of providing more time delay with minimum encoder size. The proposed design and analysis are based on the two-dimensional (2D) photonic crystal (PhC) structure. Additionally, two different 2D-PhC structures are studied, in which a silicon material with an effective refractive index of 3.487 is used. The first structure is a silicon bar in air background, whereas the second one is air holes in a silicon substrate. Furthermore, the behaviour of the proposed 2D-PhC structures is studied over the wavelength, ranging from 1300 to 1600 nm. Since the structure geometry is simple with a clear operating principle, it is sufficient to use in the photonic integrated circuits. Moreover, the performance analysis of such design is investigated in terms of the bit error rate (BER) calculations. Finally, the results showed that a 21% BER performance enhancement was achieved using the optimised silicon bars in air background encoder model and this model can be utilised for the multimedia applications in the OCDMA networks.

This study investigates cooperative inter-lighting interference cancellation (C-ILIC) in indoor multiple-input single-output (MISO) visible light communication (VLC) to overcome co-channel interference (CCI) and provide connectivity, even if there is link blockage. C-ILIC exhibits great improvement in the average bit error rate (BER) performance and the transmission capacity. VLC plays an important role in handling the increasing data traffic in indoor environments. When the transmitters simultaneously send unique data over the same frequency resources, and the receiver obtains the different signals, CCI occurs because the signals interfere with each other. C-ILIC employs cooperative transmission to forward a composite data, which consists of the high received power data and the low received power data, and ILIC to decode the high received power data and reduce CCI in the low received power data before decoding. Through computer simulations, the BER performance of C-ILIC overcomes the conventional ILIC in any position because the receiver power ratio always complies with the threshold. Despite the BER performance deteriorating in the presence of link blockage, the data connection is guaranteed when the obstruction is not severe. Therefore, C-ILIC can provide reliable communication and full connectivity within a room.

In this work, a comparative analysis is performed to study the bit error rate and error vector magnitude achieved with the least-squares (LS), the minimum mean squared error (MSE), and the Kalman filter (KF) channel estimators when these are applied to the maximum-ratio combining (MRC) and the regularised zero-forcing (RZF) receivers. The MSE achieved with the different channel estimators was also compared by varying the noise and interference power at the receiver. The proposed methodology relies on the characterisation of a massive multiple-input multiple-output (MIMO) channel with a quasi-deterministic radio channel generator and a cyclic prefix orthogonal frequency division multiplexing link-level radio simulation. The fifth-generation (5G) new radio (NR) frame structure was used to perform channel estimation and equalisation for operation frequencies below 6 GHz. Numerical results show that the MRC receiver achieves its maximum performance with the KF estimator, especially at low signal-to-noise ratio scenarios, while the RZF receiver achieves its maximum performance with the LS estimation even in high interference scenarios.

In this study, a construction analysis and design of a new spreading code set are presented. This code is designed to be used as a source code in optical wireless communication (OWC) system to achieve better performance and security enhancement. The new proposed code is called double length modified prime code (DLMPC), which is constructed based on the popular modified prime code that is commonly applied in the optical code division multiple access (OCDMA) networks. The correlation properties and characteristics of the DLMPC are investigated in this study. Based on the new code, the OWC system architecture and channel model are illustrated and further analysed. Additionally, the transmitted and received data bits encoding and decoding scenarios are discussed. Moreover, a low power consumption optical light source and photo-detector are utilised for a transmitter and receiver, respectively. The overall OWC performance in terms of the bit error rate (BER) has been evaluated considering the multi-user interference as the only source of noise. Finally, the results show that the proposed DLMPC outperforms the popular codes with respect to the channel capacity, security, and system BER performance.

This study presents a multiuser (MU) multiple-input multiple-output (MIMO) downlink transmission scheme based on the quadrature spatial modulation (QSM) concept, which uses the indices of the non-zero entries in its transmission vector to modulate and transmit an independent sequence of bits for each user in the system. The MU interference is removed by using a matrix precoding technique based on channel state information (CSI) known as block diagonalisation (BD). The performance of the proposed scheme is compared with the conventional MU-MIMO-BD system for uncorrelated Rayleigh fading channels and correlated fading channels with imperfect CSI in the reception. Additionally, a low-complexity near maximum likelihood (ML) detection algorithm for the MU-MIMO-QSM signal's detection is proposed. For the considered cases, the proposed MU-MIMO-QSM scheme exhibits gains up to 1 dB in bit error rate performance and a reduction in detection complexity up to 93% as compared to the conventional MU-MIMO-BD scheme for the optimal ML detection. The proposed algorithm performs very near to the optimal ML detector whilst achieving a complexity reduction of up to 58%.

The main objective of this study consists in reducing the correlated background radiations along with minimising the bit error rate (BER) for a multiple aperture 2 × 1 free-space optical (FSO) communication system based on differential signalling scheme. Instead of performing the conventional equal gain combining (EGC) of the two wavelengths, here, the authors propose to efficiently combine them at the receiver by using non-equal channel-dependent weighting factors. To this aim, they first derive the analytic expression of the BER of the considered system, which is necessary for optimising the background radiations. Second, by considering ON–OFF keying modulation, they optimise the decision threshold and the weighting factors of the two wavelength by minimising the BER. The performance merit of the proposed scheme is contrasted to the zero threshold scheme and to the EGC scheme in terms of the average BER, the average signal-to-noise ratio (SNR) and the background rejection at the receiver. They show that the proposed scheme can improve the SNR up to 17 dB, based on the correlation coefficient of the background radiations at two wavelengths. Moreover, simulation results confirm the superiority of the proposed scheme in terms of achievable BER compared to the aforementioned conventional methods.

In the proposed random communication system (RCS), the alpha-stable (α-stable) noise as a random carrier drives the transmitter which is modelled by the linear dynamical system and the skewness parameter of the random carrier encodes the binary messages. By selecting the receiver as the inverse system of the transmitter, the output of the receiver is ensured to be α -stable noise whose skewness parameters are then estimated to decode the binary messages. The response of a linear system to an α-stable process is again α -stable process, however, the skewness parameters of the response differs from that of the input which can only be recovered at the output of the inverse system. Hence, estimation of skewness parameter by an eavesdropper, without using the inverse system, will not reveal the true binary messages while the intended receiver truly decodes the binary messages. The proposed inverse system based RCS provides efficient performance which is shown by comparing the bit error rate of the intended receiver and an eavesdropper where the enhancement in covertness is shown by evaluating the covertness values of the proposed RCS.

In this paper, a novel dual-hop relay-assisted hybrid Free Space Optical / Radio Frequency (FSO / RF) communication system is presented. In this structure an access point connects users within the building to the Base Station via a hybrid parallel FSO / RF link, this link is proposed firstly. The parallel combination of FSO and RF links and use of an access point will increase capacity, reliability and data rate of the system. It is the first time that the effect of the number of users on the performance of a dual-hop relay-assisted hybrid parallel FSO / RF system is investigated. FSO link is considered in GammaGamma atmospheric turbulence with the effect of pointing error and RF link is considered in Rayleigh fading. For the first time, closed-form expressions are derived for Bit Error Rate (BER) and Outage Probability (P out ) of the proposed system. Derived expressions are verified through MATLAB simulations. It is shown that performance of the proposed system is almost independent of atmospheric turbulence intensity, thereby when atmospheric turbulence strengthens, low power consumption is required for performance maintenance. Hence the proposed structure is suitable for mobile systems in which a small battery supplies transmitter power.

One of the prime concerns regarding multi-tier architecture in heterogeneous networks (HetNets) is the interference between users in macrocells and femtocells. Interference mitigation (IM) in femtocells is of critical importance due to high power interfering signals from macrocells. However, such IM techniques generally demand intensive signalling overhead that adversely affect the benefits of multi-tier network architecture. A novel interference cancellation technique with very low signalling overhead that does not require global channel state information at the transmitter is proposed in this study for the uplink of HetNets. The proposed subspace nulling (SN)-based method projects the composite received signal onto the intersection space of the left null space of the interfering space and the row space of desired space to cancel the cross-tier interference. This is achieved both in the presence and absence of macrocell user channel state information at receiver (MU-CSIR). The authors also propose a low complexity subspace method that works with the knowledge of MU-CSIR. Exhaustive simulation studies show that the proposed schemes fully cancel the cross-tier interference in femtocell tier resulting in better bit error rate performance for the FU receiver.

In this study, multi-user (MU) underwater acoustic communication is investigated using massive multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM)-based orthogonal time frequency space modulation (OTFS) systems. The performance of a 4-user scenario is evaluated over a simulated 1 km vertically-configured time-varying underwater acoustic channel (UAC) in terms of bit error rate and maximum achievable bit rate. Considering 64-QAM and frequency-domain pilot-based channel estimation, it is shown that the underwater vehicles employing the OFDM-based OTFS modulation outperform those using the conventional OFDM modulation in a dynamic UAC. The application of massive MIMO allows the four underwater vehicles to use the same time and frequency resources to transmit their information reliably to a surface station. Furthermore, it is shown that each underwater vehicle in the MU-massive MIMO transmission scenario can achieve an effective bit rate as high as 198.7 kbps over the 1 km UAC using four transmitting transducers.

In 1975, J. E. Mazo showed the potential faster-than-Nyquist (FTN) gain of the single-carrier binary signal. If the inter-symbol interference is eliminated by an optimal detector, FTN single-carrier binary signal can transmit 24.7% more bits than the Nyquist signal without loss of bit error rate performance, which is known as the Mazo limit. In this study, the authors apply sphere decoder (SD) with box optimisation (BO) to reduce inter-carrier interference (ICI) in the FTN non-orthogonal frequency division multiplexing (FTN–NOFDM) system. Compared with the commonly used SD algorithm, SD with BO can achieve the same ICI cancellation performance, and the computational complexity is significantly reduced. When the bandwidth compression factor α is set to 0.802, the transmission rate of FTN–NOFDM is 24.7% faster than the Nyquist rate, and quadrature phase shift keying (QPSK)-modulated FTN–NOFDM has almost the same performance as QPSK-modulated orthogonal frequency division multiplexing (OFDM), which agrees well with Mazo limit. In the simulation, the QPSK-modulated FTN–NOFDM with α = 0.5 outperforms 16-quadrature amplitude modulation (16-QAM)-modulated OFDM by about 1.5 dB, and the 16-QAM-modulated FTN–NOFDM with α = 0.67 and 0.5 outperforms 64- and 256-QAM-modulated OFDM by about 1.5 and 2 dB, respectively.

Recently non-orthogonal multiple access (NOMA) technique has been proposed for boosting spectral efficiencies in 5G cellular networks. In NOMA the transmitter maps a predefined number of user symbols on to the same resources. The conventional receiver for NOMA is the well-known serial interference cancellation. To overcome the problem of high overhead signalling, a receiver with an automatic modulation classification (AMC) algorithm for a K-user NOMA which identifies the modulation scheme of users before symbol detection is proposed. First, a two-user NOMA (TU-NOMA) scheme is treated and the receiver is extended to more general cases. For evaluating the performance of the proposed receiver its bit error rate (BER) for TU-NOMA case has been driven and shown that this can be approximated as the sum of the demodulator BER and the AMC algorithm error probability. The simulation results show the BER degradation can be neglected if an enough number of symbols with sufficiently large SNR values are available.

In multiple-input multiple-output (MIMO) systems, rank deficient channels are the most common and key areas of research. In these channels, the number of transmit antennas (M Tx) is higher than receive antennas (M Rx) and subsequently the unknown variables are more than the number of equations. In such situations, the conventional sphere decoder (SD) fails due to the presence of zero diagonal elements in Cholesky decomposition. This study analyses the quasi-orthogonal space-time block code (QOSTBC) of symbol rate-2 for M Tx = 4 with modified double-layer SD detection to overcome rank deficiency problem. The first half of transmitted symbols is detected using two partially dependent SDs with optimised search radii. The remaining half is detected by employing single symbol maximum likelihood detection. Simulation and analytical results indicate that the proposed detection scheme reduces bit error rate and complexity compared to existing techniques.

The growing interest in underwater explorations has stimulated considerable interest in advancing the enabling technologies of underwater wireless communication (UWC) systems. The study presents the design and implementation techniques of a short-range unidirectional UWC system which uses optical camera communication (OCC) principles. OCC systems have light emitting diodes at the transmitter, with the receiver being a camera. Overall system design considerations, synchronisation and frame selection, and a novel spatial position-based image processing algorithm to decode data from frames are discussed. Also, the optimisation techniques used in the image processing algorithm are also elaborated. Importance of few of key features of an OCC system, namely camera quality, transmission distance and the threshold value used for image binarisation are demonstrated through numerical results using simulations via synthetically generated images. Further, the bit error rate (BER) performance of the system is evaluated using the experimental proof of concept setup in clear water, muddy water and under turbulence conditions. Overall BER performance in the order of 10 -3 within the communication distance of 1 m is observed, and it shows that the proposed system design and algorithms can be used to realise an UWC link for short-range applications successfully.