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In this paper, the physical layer security aspects of a wireless framework over α − κ − μ shadowed (AKMS) fading channel are examined by acquiring closed-form novel expressions of average secrecy capacity, secure outage probability (SOP), and strictly positive secrecy capacity. The lower bound of SOP is derived along with the asymptotic expression of SOP at the high signal-to-noise ratio regime in order to achieve secrecy diversity gain. Capitalizing on these expressions, the consequences due to the simultaneous occurrence of fading and shadowing are quantified. Finally, Monte-Carlo simulations are demonstrated to assess the correctness of the expressions.

In this paper, we mathematically analyze bit-error rate (BER) and diversity order of physical-layer network coding (PNC) scheme in the two-way relay channel (TWRC) under the assumption of multiple antennas at relay node. We assume the quadrature phase shift keying (QPSK) modulation for simple data transmission in IoT applications, and max–min transmit antenna selection (TAS) scheme in the broadcast (BC) phase for achieving full diversity gain. In particular, we obtain the upper bound of BER at the multiple access (MA) phase, while deriving the exact BER performance at the BC phase. To the best our knowledge, the mathematical analysis in this paper is the first analytical results in the literature. Through computer simulations, the analytical results are validated.

The need for wireless communication is growing at an unprecedented pace, making the wireless spectrum at a premium. To use the spectrum more efficiently, a promising solution was proposed to enable two concurrent users to transmit their signals in the same frequency at the same time, and then decode the superimposed signal. In current systems, the superimposed signal is decoded by successive interference cancellation (SIC) that requires strict power control upon each individual user. However, this requirement is infeasible for many IoT devices that are heterogeneous and often low cost. For other superimposed signal decoding technologies that require no power control, a reliable performance can be only achieved by introducing repetitive information in each transmission, which, in turn, reduces the spectrum efficiency. In this article, we introduce Chitchat, a new solution to decode the superimposed signal from two concurrent transmitters without any power control nor repetitive transmissions. Chitchat presents a rotation-code-based idea to provide both the diversity gain and the coding gain, so that it can achieve high reliability while preserving the spectrum efficiency. We implement Chitchat on a software-defined radio platform, and evaluate its performance in various scenarios.

Scarcity of frequency spectrum is one of the main issues in wireless communications. Cognitive radio networks (CRNs) have been considered as an effective way of improving the spectrum efficiency by opportunistically using the spectrum resources through appropriate cooperation between primary and secondary networks. Exploitation of content caching in CRNs can enhance the system performance and reduce the backhaul cost and delay. In this paper, we propose a combined caching strategy and base station coordination in CRNs to achieve a proper balance between the signal cooperation gain and the content diversity gain. Depending on the availability and placement of the requested content, we propose a zero‐forcing coordinated beamforming technique to simultaneously transmit the most popular contents that are cached in every secondary base station and achieve the signal cooperation multiplexing gains, also we propose a maximum ratio transmission technique to deliver the less popular contents which are cached in different secondary base stations and achieve the caching diversity gain. Enumeration of the solution space search is used to obtain the optimal cache solution. Numerical results show that our proposed solution outperforms the cooperative caching and transmission solution proposed where only a maximum ratio transmission technique is used.

In this paper, we propose an optimal user selection scheme for cooperative non-orthogonal multiple access (NOMA) networks with simultaneous wireless information and power transfer (SWIPT). By considering decode and forward (DF) protocol, SWIPT is employed at near users to relay information to far users via applying a user selection scheme that selects an optimal pair of near and far users and ensures the correct information decoding at the near user within an adaptive power allocation coefficient (PAC) range. Closed-form expressions for the outage probability of the selected near and far users are derived. We show that the selected near and far users can achieve a diversity gain of N and N + F, respectively, with a significant coding gain, where N and F are the number of near and far users. Simulation results investigate that the proposed scheme can achieve an optimal outage performance over the state of arts.

In this paper a multiband modified ‘W’ shaped, Multiple input multiple output (MIMO) antenna with a metamaterial inspired isolator for enhanced isolation is proposed for 5G application. The two-element MIMO antenna comprises of a closely placed (edge to edge gap of 0.117λo, λo = highest operating wavelength) antenna elements that covers both sub-6 GHz (3.42–4.25 GHz) and millimeter wave (mmWave) range bands (24.8–26.5 GHz) of 5G with bandwidth of 821 MHz and 1630 MHz. The MIMO antenna also covers bands C (7.44–7.92 GHz), X (9.9–10.49 GHz), Ku (12.02–13.39 GHz & 15.92–17.492 GHz), K (19.49–22.42 GHz), partially. The isolation level in all resonating bands remain near to the acceptable value of (|S12|> −15 dB) however a very significant mutual coupling effect is observed in sub-6 GHz range (|S12|= −11.92 dB at 3.94 GHz). To improve the isolation in sub-6 GHz band, a metamaterial inspired isolator comprising of Double negative (DNG) unit cells is uniquely placed along the side of the closely positioned antenna elements. Simulated results indicate that isolation level improves to (|S12|= −16.1 dB at 3.94 GHz) after placing the DNG metamaterial based isolator. The antenna performance parameters such as gain, return loss, bandwidth, Envelope correlation coefficient (ECC), Diversity gain (DG) and radiation efficiency are not affected by placement of isolator. The metamaterial equipped MIMO antenna (Meta–MIMO antenna) has a compact structure of 70 × 40 × 0.8 mm3, with a high isolation in all bands (|S12|> −16 dB), peak gain of 7.8dBi, low ECC (

The limited wireless backhaul capacity has become the major bottleneck for UAV communications, while in existing researches of UAV networks, the relation between cell selection and backhaul capacity has not been modeled. This paper proposes cell group selection with backhaul-aware biasing for UAV networks and analyzes system performance by deriving the rate outage probability via stochastic geometry, where the user’s maximum data rate is constrained by backhaul capacity. Specifically, cell group selection is no longer distance-based and considered with backhaul capacity bias factor, where UAVs with higher backhaul capacity will have a larger bias factor to match the backhaul variance. In addition, the dynamic UAV group is organized with the N largest bias reference signal receiving power (BRSRP), where users can utilize the diversity gain by adjusting serving UAV dynamically as the channel conditions change. Analytical results show that the outage probability is decreased by 58% when cell group size N = 3 and UAV optimal density λ u = 600 / k m 2 when UAV height h = 150 m .

The recent emergence of orthogonal time frequency space (OTFS) modulation as a novel PHY-layer mechanism is more suitable in high-mobility wireless communication scenarios than traditional orthogonal frequency division multiplexing (OFDM). Although multiple studies have analyzed OTFS performance using theoretical and ideal baseband pulseshapes, a challenging and open problem is the development of effective receivers for practical OTFS systems that must rely on non-ideal pulseshapes for transmission. This work focuses on the design of practical receivers for OTFS. We consider a fractionally spaced sampling (FSS) receiver in which the sampling rate is an integer multiple of the symbol rate. For rectangular pulses used in OTFS transmission, we derive a general channel input-output relationship of OTFS in delay-Doppler domain without the common reliance on impractical assumptions such as ideal bi-orthogonal pulses and on-the-grid delay/Doppler shifts. We propose two equalization algorithms: iterative combining message passing (ICMP) and turbo message passing (TMP) for symbol detection by exploiting delay-Doppler channel sparsity and the channel diversity gain via FSS. We analyze the convergence performance of TMP receiver and propose simplified message passing (MP) receivers to further reduce complexity. Our FSS receivers demonstrate stronger performance than traditional receivers and robustness to the imperfect channel state information knowledge.

This paper presents the design of a highly integrated eight port broadband slot antenna. The proposed slot antenna has a smaller footprint (33 × 33 × 0.8 mm3) and is constructed using one-quarter of an annular slot ring antenna. The miniaturized antenna has a broadband impedance characteristics covering 3 GHz–9 GHz making the antenna suitable for broadcasting applications within the realized 6 GHz bandwidth. The unit cell antenna is made polarization diverse by exciting the unit cell antenna with two feeds. The antenna is then replicated to produce an eight-port MIMO antenna. Thus the proposed antenna provides both polarization and pattern diversity characteristics. The average peak gain of the proposed MIMO antenna is greater than 5.51 dBi and the efficiency is greater than 80% throughout the operating bandwidth. The prototype antenna is fabricated and the simulation results are validated. Furthermore, the MIMO parameters such as envelope correlation coefficient, diversity gain and mean effective gain are evaluated and presented.

This paper theoretically and empirically explores the reliability gain that can be obtained by installing multiple antennas in on‐vehicle broadcasting receivers. Analytical derivations reveal that maximal‐ratio‐combining‐based diversity allows a multi‐antenna receiver (MR) to achieve significantly better coverage probability than a single‐antenna receiver (SR). In particular, the notable MR gains for low‐power reception and high‐throughput services are highlighted. We also discuss various aspects of mobile MRs, including geometric coverage, volume of the users served, and impact of receiver velocity. To examine the feasibility of MRs in the real world, extensive field experiments were conducted, particularly with on‐air ATSC 3.0 broadcast transmissions. Relying on the celebrated erroneous second ratio criterion, MRs with two and four antennas were verified to achieve notable reliability gains over SRs in practice. Furthermore, our results also prove that layered‐division multiplexing can cope better with receiver mobility than traditional time‐division multiplexing when multiple services are intended in the same radio frequency channel.

This letter presents a detailed investigation on the performance of reconfigurable intelligent surface (RIS)-assisted communication system with user scheduling. Depending on the availability of channel state information (CSI) at the RIS, two separate scenarios are considered, namely without CSI and with CSI. Closed-form expressions are derived for the ergodic capacity of the system in both scenarios. It is found that CSI has a significant impact on the performance of the system. Without CSI, the RIS provides an array gain of N, where N is the number of reflecting elements, and user scheduling provides an multi-user gain of $\log \log \text {M}$ , where M is the number of users. With CSI, the RIS provides an array gain of $\text {N}^{2}$ , while no multi-user diversity gain can be obtained.

A novel design is introduced for dual-band operation at 28/38 GHz for improving microstrip antennas. Also, the design support circularly polarized antenna that works in millimetre band applications. This proposed antenna is attached to a circular hole in the centre of the patch with four slits embedded in the corners. Also, small holes are etched at sides of the patch to achieve the resonant frequencies and improve the return loss value with achieving very wide band at 38 GHz. A single-feed circularly polarized antenna at 28 GHz and 38 GHz with return loss − 30 dB and − 42 dB, respectively, which makes it suitable for operation at 5 G wireless communication designs. A single element design can cover the frequency ranges of 27.6–28.3 GHz at 28 GHz with bandwidth 2.5% and 35.2–47.2 GHz at 38 GHz with very wide bandwidth 32.4%. Simulated results show that the proposed antenna has good circular polarization in both frequencies of left-hand circular polarization (LHCP). On the other hand, MIMO antenna with four ports is constructed. The four ports are arranged at the corner and middle of substrate with dimension 100 × 75 × 0.508 mm3. Meanwhile, resonant implementation frequencies in a millimetre wave of the MIMO achieved more mutual coupling minimization that effectively accomplished

Purpose This paper aims to design a most demanding low profile and compact ultra-wide band (UWB) antenna system for various wireless applications. The performance (in terms of data rate) of UWB system is improved by using multiple-input-multiple-output (MIMO) technology with it. Owing to the overlap of other existing licensed bands with that of UWB, electromagnetic signals can interfere. So, notched band UWB MIMO antenna system reported here which is highly compact, bandwidth efficient, superior data rate and high inter-element isolation comparatively to other reported designs. Design/methodology/approach A 49 × 49 × 1.6 mm3 quad-port UWB MIMO antenna with specific bandwidth elimination property is designed. The proposed planar MIMO configuration comprises unique four identical “Cordate-shaped” monopole radiators fed by 2.3-mm thick microstrip-lines. The radiators are located right-angled to each other to enhance inter-element isolation. Further, a different approach of slitted-substrate is applied to minimize the overall size and mutual coupling of the MIMO antenna, as a substitute of decoupling and matching structures. The defected ground structure is used to obtain −10 dB impedance bandwidth in entire UWB band, without compromising with the lower cut-off frequency response. Further, to eliminate the undesired resonant band (WLAN at 5.5 GHz) from UWB, a rounded split ring resonator is introduced in monopole patch. Findings In the entire operating band of 2.8 to 11 GHz, isolation among elements is more than 24 dB, envelope correlation coefficient less than 0.002, diversity gain greater than 9.99 dB and TARC less than −7 dB are obtained at all 4-ports. Research limitations/implications The measured parameters of the fabricated prototype antenna on FR4 substrate are found in good agreement with the simulated results. The small variation in software results and hardware results are observed due to hardware design limitations. Practical implications The proposed design may be used for any wireless application following in the range of UWB. Originality/value It can be shown from graphs of measured parameters of the fabricated prototype antenna. They found to be in good agreement with the simulated results.

This paper presents a high-performance multiple-input multiple-output (MIMO) antenna with a compact size of 42 × 42 mm2. The proposed antenna operates in the frequency range of 3.2–12 GHz for ultra wide band (UWB) wireless communication systems. The proposed MIMO antenna has four identical elements arranged to be orthogonal to each other to achieve a good performance. To achieve high isolation, stubs between the four radiating elements were used. Measured and simulated results were analyzed to obtain the antenna performance in the form of studying radiation pattern, Envelope Correlation Coefficient (ECC), diversity gain, and channel capacity loss. Additionally, simulated peak gain and total efficiency are acquired. Results indicate that the proposed antenna has UWB bandwidth, high isolation higher than 17 dB, and low correlation coefficient; therefore, this antenna is suitable for UWB wireless applications.

The $${\kappa -\mu /}$$ Inverse Gamma (KMIG) and $${\eta -\mu /}$$ Inverse Gamma (EMIG) are recently introduced composite fading distributions for the precise design of the wireless systems, where multipath fading and shadowing occur concomitantly. Further, these composite fading models are competent to be employed in the performance investigation of the digital communication system as their mathematical formulations are quite tractable. Average symbol error probability (SEP) and channel capacity analysis are important parameters to investigate the performance of a digital communication system. The applicability of these fading models is illustrated by analysing the performance matrices of the digital communication channels in the present work. Various performance matrices such as the average SEP, the channel capacity under different adaptive schemes namely, optimum rate adaptation (ORA), channel inversion with fixed rate (CIFR) and truncated CIFR are derived. The asymptotic analysis of KMIG and EMIG composite fading models over average SEP performance matrices with coding gain and diversity gain is also carried out in this work. The simplified high and low signal-to-noise-ratio solutions to channel capacity are also provided as a by-product. In addition, approximate analysis to ORA and CIFR capacity are provided under realistic environmental conditions. The accuracy of the derived numerical formulations is validated with the use of Monte–Carlo simulation. The results of present work will be advantageous in the modelling and designing of popular wireless services such as vehicle-to-vehicle communication, wearable communication and wireless power transfer related technologies.

In this paper, a metasurface-based multiple-input multiple-output (MIMO) antenna with high isolation between antenna elements is presented. The main patch radiator is sandwiched between a metasurface and a ground plane to achieve performance enhancement. The fabricated single element antenna has a compact size of $0.85\lambda _{0} \times 0.85\lambda _{0} \times 0.038\lambda _{0}$ . The antenna exhibits a wideband operational bandwidth from 3.27 to 3.82 GHz for $\vert \text{S}_{11}\vert < -10$ , which corresponds to a fractional bandwidth of 15.5%. Moreover, stable radiation patterns with a peak gain of 8.1 dBi are also achieved across the operating band. The proposed single element antenna is characterized for $2 \times 2$ MIMO system by translating each antenna element orthogonal to each other. A decoupling structure consisting of slots and metallic strip with shorting pins is used to improve the isolation between the MIMO elements. The shorting pins connect the metallic strips (located between MIMO elements) on the metasurface and ground plane. These slots on ground plane and shorting pins affect the electromagnetic field distribution and consequently reduce the mutual coupling. The fabricated MIMO antenna has a compact size of $1.75\lambda _{0}\times 1.75\lambda _{0} \times 0.038\lambda _{0}$ . The proposed 4 port ( $2\times 2$ ) MIMO antenna provides 15.9% of 10 dB impedance bandwidth from 3.3 to 3.87 GHz with a peak gain of 8.72 dBi. Moreover, the proposed MIMO antenna offers excellent diversity performance, isolation between antenna elements is very high (>32dB), ECC is lower than 0.001, and diversity gain is 9.99 dB very close to the ideal value of 10dB. Owing to these features, the proposed MIMO antenna can be a good candidate for 5G Sub-6 GHz (n78 band) smart devices and sensors.

This paper proposes integrating multiple antennas into wearable devices for application in fifth-generation (5G) communications and the Internet of Things (IoT). The frequency bands covered were wireless local area network 2.4-GHz/5-GHz channels (2410–2484 MHz), the global positioning system (1575 MHz), narrowband IoT band 8 (880–960 MHz), Global System for Mobile Communications 850/900, and the 5G frequency range 1 n77/78/79 band (3300–5000 MHz). The antennas were configured as a $2\times2$ multiple-input multiple-output system (MIMO). The antenna resonance contribution integrates the slot mode, monopole mode of the three-dimensional frame, and loop coupling monopole mode. The configuration of the independent matching circuits facilitated the effective control of the desired mode and the coverage of the desired bands. All integrated antennas were placed in a watch device ( $37\times 43\times8$ mm3) with a metal body and a metal strap. An integrated miniaturized antenna was designed. The diversity gain and multiplexing efficiency between the MIMO antennas were 9.97dB and above −2dB, respectively. Favorable diversity performance was confirmed. The channel capacity of the $2\times $ 2 MIMO array was determined to be 8.8 bps/Hz. Moreover, its performance was evaluated through the addition of a hand tissue module. The impact of metal straps on antenna radiation performance was discussed. The specific absorption rate (SAR) was examined, and the best results obtained under an SAR of 1 g and 10 g were 0.25 and 0.58 W/kg, respectively. The findings demonstrate the suitability of the antenna for practical applications in 5G communication systems and the IoT.

The LoRa standard is currently widely employed for low-power long-range wireless sensor networks at sub-GHz frequency bands. The longer wavelengths associated with sub-GHz technology provide excellent radiowave propagation characteristics, yielding a much larger coverage than the higher frequency bands. In the case of wearable sensors, the 868 MHz band can be covered by textile substrate-integrated-waveguide antennas of a convenient size. In body-centric communication systems, front-to-back (F/B) diversity is an important asset to mitigate the shadowing of the antennas by the presence of the human body. This article describes a diversity textile-antenna-based LoRa platform with integrated transceivers. Outdoor measurement campaigns are conducted to assess the performance of the wearable LoRa nodes with F/B diversity in an urban radio propagation environment at walking and cycling speeds. These experiments prove that large ranges of 1.5 km can easily and reliably be achieved for off-body LoRa communication links. The results demonstrate a significant performance improvement in terms of packet loss in NLoS situations when comparing single-receiver performance with different spatial receiver diversity applications. In addition, link budget increases up to 5.5 dB, owing to the realized diversity gain.

The deployment of the Millimeter-Wave (mm-Wave) band in 5G and beyond wireless communications networks is one of the emerging fields owing to its potential of providing extensive bandwidth. Frequency Hopping (FH) has a high potential for use in wireless networks due to its key advantages of spreading the interference over wide bandwidth and of providing diversity gain in counteracting frequency-selective fading. Furthermore, Fast Frequency Hopping (FFH) intrinsically amalgamated with directional Beamforming (BF) may overcome the impairments because of the path-loss of mm-Wave communications. Thus, we propose FFH assisted base-band precoding aided BF for mitigating the mm-wave channel impairments imposed by both fading as well as path loss, whilst relying on a minimal range of radio frequency chains. The mathematical analysis and simulation results demonstrate that hybrid precoded FFH is indeed a promising high-capacity technique of attaining both time- and frequency-domain diversity gains for the mm-Wave communications.

In industrial Internet-of-Things (IoT) applications including smart factories, railway/aircraft operating and control systems, and so on, it is expected to deliver a bundle of packets with a delay constraint. In this paper, we study delay-constrained transmissions where a user or device is to send a bundle of short-length packets within a certain time limit through radio resource blocks shared with others. We first derive a closed-form expression for (a tight upper-bound on) the probability of decoding error when a short-length packet is transmitted through multiple channels (for a high diversity gain under fading). Using the expression, we then study the performance in terms of delivery delay for a bundle of packets using the notion of queuing systems. It is shown that the derived expressions agree with simulation results, which demonstrates that those can be used to design delay-constrained transmission systems to support industrial IoT applications where a bundle of packets has to be delivered within a certain short time limit with high reliability.

The Time Modulated Array (TMA) provides multiple radiation beams at different frequencies, by turning the radiating elements on and off. In this paper, we propose to add polarization diversity to a wireless communication link by leveraging the capabilities of the TMA. The proposed architecture switches between two orthogonal polarizations, instead of turning the antenna off, providing polarization diversity for the receivers. We show that the beams of each polarization at the sidebands are exactly the same. However, the switching sequence should be optimized for the fundamental frequency to provide the same radiation level at each sideband. Two different switching sequences are proposed, which are optimized for different conditions. To evaluate the switching sequences and the diversity order of the system, an 8-element array with dual polarization antennas is fabricated. The radiating antenna element is a dual feed ring slot antenna, designed for 5.8 GHz with 10% fractional bandwidth. Both the single antenna and the array are measured in an anechoic chamber. The measurements indicate that the prototype provides full diversity gain along with multiple beam generation and beam steering, while it is very low cost and has low complexity.

Due to the lack of spectrum resources, effective methods must be proposed to meet the needs of the Internet of Things (IoT) massive connectivity. In this paper, two effective techniques to improve spectral efficiency, namely, sparse code multiple access (SCMA) and wireless multicast, are used together for the IoT system to expand network capacity. Different from existing works, we introduce layered coding into the SCMA-based IoT system and consider two channel state information (CSI) feedback scenarios, which can make full use of the diversity gain of multiple receivers. The original multicast data are divided into one basic layer (BL) and several enhancement layers (ELs) by layered coding. IoT receivers with good channel gain can achieve better quality of service by receiving more data layers. In the transmission scheme with CSI, the physical resources allocated to the BL and ELs can be dynamically adjusted. In the transmission scheme without CSI, a fixed resource allocation scheme is performed because it is impossible to calculate the multicast rate of each codebook in real time. To further improve the system capacity, we have proposed resource allocation algorithms for these two schemes according to different requirements for computational complexity. The simulation results show that the proposed schemes can provide a higher system capacity than unicast SCMA and nonlayered multicast SCMA.

This article presents a novel decoupling technique for the circularly polarized multiple-inputmultiple- output (CP-MIMO) system composed of Guoshaped patch antennas. A comparative study has been conducted on antenna performance as a function of packing distance before and after applying the technique. A prototype of two-element Guo-shaped patch MIMO at a small inter-element spacing of 12.5 mm has devised aiming for the 5G new radio n38 (2.57-2.62 GHz) applications. Simulation reinforced with experimental results confirmed the effectiveness of the proposed technique, whereas the two Guo-shaped patch elements packed in such small spacing can be operated independently. Both the envelope correlation coefficient and diversity gain are approaching their ideal values.

In this article, a compact dual-port single element MIMO antenna is presented for millimeter wave (mmWave) 5G wireless applications. The presented antenna design consists of an annular ring slot that is fed by a Substrate Integrated Waveguide (SIW) at the two opposite sides of the substrate. The antenna resonates at 28GHz and its 10dB impedance bandwidth is 400MHz. The isolation between the ports is reduced by introducing additional annular slot that acts as a cavity which results in an isolation better than 20dB at 28GHz. The measured gain of both ports are 6.9 dBi which is the highest gain per unit element at 28GHz in the literature. The measured diversity gain and envelope correlation coefficient are 9.98dB and 0.065, respectively, at the band of interest. The measured and simulated results are in good agreement.

Wireless relay technology improves information capacity and brings diversity gain for wireless avionics intra-communications (WAIC) which will replace some cabling interconnections in aircraft. An amplify-and-forward(AF) relay selection scheme considering transmitter power level in the cabin has been proposed, with physical layer of multi-band Orthogonal Frequency-Division Multiplexing Ultra-wide band (MB-OFDM-UWB), of which outage probability performance is characterized in terms of the cluster and ray arrival rates. Furthermore, minimum power density principle based relay selection and power allocation scheme (MPRP) has been proposed to mitigate the limitation. In particular, Quasi-Newton method is used to solve nonlinear systems in the calculation of power distribution factor. Simulation results demonstrate that the proposed MPRP scheme achieves the optimized system energy efficiency.

This work presents a 4-element multiple-input multiple-output (MIMO) antenna with a single layered metasurface array for fifth generation (5G) millimeter-Wave (mm-Wave) communication systems. Each MIMO antenna element is composed of a $1\times 2$ array with a corporate feed network. Moreover, a metasurface array structure consisting of $9\times 6$ Circular Split Ring (CSR) shaped cells is employed to improve the gain and isolation between the MIMO antenna elements. The proposed antenna system is realized using 0.787 mm thick Rogers RT Duroid 5880 substrate. The performance of the antenna is investigated in terms of s-parameters, radiation characteristics, and MIMO parameters. The antenna operates at the mm-Wave frequency band ranging from 24.55 to 26.5 GHz. The incorporation of the metasurface layer enhanced the gain thus attaining a peak measured gain of 10.27 dBi. Additionally, isolation is also improved by 5dB after the employment of metasurface. The investigation of MIMO performance metrics such as Envelope Correlation Coefficient (ECC), Diversity Gain (DG), Channel Capacity Loss (CCL), and Mean Effective Gain (MEG) exhibits good antenna characteristics. The demonstrated radiation properties of the proposed antenna ascertain its suitability for the forthcoming 5G communication systems.

This paper investigates a secure transmission in the multiple-input multiple-output (MIMO) cognitive wiretap networks, where a secondary transmitter (Alice) sends data to a secondary receiver (Bob) in the presence of an eavesdropper (Eve). In order to solve the problems of inter channel interference and inter antenna synchronization encountered by traditional MIMO technologies, the antenna transmission scheme is adopted at the transmitter. As a comparison, we design two different antenna transmission schemes, namely transmit antenna selection maximal-ratio combining (TAS-MRC) scheme and differential spatial modulation maximal-ratio combining (DSM-MRC) scheme, respectively. Moreover, due to outdated channel state information (CSI) of the interference link from Alice to the primary user (PU), we propose power control mechanism to protect the quality of service (QoS) of PU. Furthermore, the closed-form for the secrecy outage probability and the secrecy throughput with TAS-MRC and DSM-MRC schemes are derived to evaluate the secrecy performance, respectively. What’s more, we explore the security diversity gain and coding gain based on the asymptotic secrecy outage probability. As the results, it demonstrates that DSM-MRC requires less CSI and is convenient for modulation and demodulation, but sacrifices some secrecy performance gains between two proposed schemes.

As an efficient supplement for terrestrial communications, e.g., fifth-generation communication networks, satellite communication has been proved as a promising choice to realize seamless coverage, due to its inherent superiority over common wireless communication systems, like large-scale coverage area and flexibility of deployment. In this article, a satellite-terrestrial transmission (STT) system including a satellite transmitter (S) and a group of terrestrial receivers (D) is focused on. Considering the randomness of D and employing stochastic geometry, the outage performance and diversity gain of three hybrid automatic repeat request (HARQ) schemes, generalized slotted ALOHA (GSA), repetition time diversity (RTD) and general incremental redundancy (IR), are respectively studied. In detail, the exact closed-form analytical expression for the outage probability (OP) is derived for the GSA scheme, while the approximated expression for the OP of RTD scheme is presented and a useful expression for the OP of IR scheme is derived. Furthermore, the diversity gains of the three considered HARQ schemes are respectively investigated in STT scenarios. Finally, some numerical results are provided to validate the proposed analysis models.

This paper investigates the diversity gain of a distributed cyclic delay diversity (dCDD) scheme for cyclic-prefixed single carrier systems in non-identical fading channels. Non-identical small-scale fading is assumed in the environment, in which non-identical line-of-sight and non-line-of-sight fading coexist. A condition for dCDD resulting in intersymbol interference free reception at the receiver, is extended to this new channel environment. For an overpopulated system setup, a generalized performance analysis, is not available from existing works, is conducted after developing closed-form expressions for the distribution of the signal-to-noise ratio (SNR) realized at the receiver. Since the order statistics are involved in the statistical properties of the SNR, the corresponding spacing statistics are utilized to derive feasible closed-form expressions. The finalized closed-form expressions are shown to provide very reliable outage probability and spectral efficiency of dCDD for underpopulated and overpopulated systems. An asymptotic performance analysis verifies the maximum achievable diversity of the dCDD even in the overpopulated case within the considered channel environment. Link-level simulations are conducted and these verify the maximum achievable diversity gain.

Free space optical (FSO) communication systems provide high bandwidth in unregulated spectrum and act as a powerful line-of-sight wireless connectivity solution. The performance of FSO systems can be seriously impaired by fading as a result of atmospheric turbulence and/or pointing errors due to misalignment. In the context of FSO systems, relaying was proposed as an effective fading mitigation technique due to the fact that the variance is distance-dependent in turbulence channels. In this article, we present a unified performance analysis of multi-hop FSO systems over Double Generalized Gamma (DGG) turbulence channels with pointing error impairments. We assume amplify-and-forward relaying and consider both heterodyne detection and intensity modulation with direct detection. We derive tight closed-form expressions for the outage probability and bit error probability of both fixed-gain and channel state information (CSI)-assisted relaying in terms of the bivariate Fox-H functions and Fox-H functions, respectively. We further analyze asymptotic behavior of the outage probability in terms of simple elementary functions and obtain the achievable diversity orders. Diversity gain is found to be a function of atmospheric turbulence parameters, pointing error, detection type and the number of hops. Monte Carlo simulation results are further provided to verify the accuracy of the derived expressions.

Rich scattering of ultraviolet signals enables the non-line-of-sight outdoor wireless connectivity and eliminates the line-of-sight requirement of free-space optical links. Besides scattering losses, ultraviolet signals also suffer from the atmospheric turbulence-induced fading. One of the strong fading mitigation techniques is the spatial diversity, which has been extensively studied in the context of wireless radio frequency and infrared networks. In this study, spatial diversity techniques for non-line-of-sight ultraviolet communication links are considered. In particular, multiple-input-single-output (MISO), single-input-multiple-output (SIMO), and multiple-input-multiple-output (MIMO) non-line-of-sight ultraviolet communication systems are derived. The BER performance of the single-input-single-output (SISO) link is also derived as a benchmark. The accuracy of the derivations is confirmed through Monte Carlo simulations. The results demonstrate the significant performance improvements in spatial diversity schemes over SISO counterparts. The authors further investigate the effect of spatial correlation on the performance of non-line-of-sight ultraviolet links with spatial diversity. They demonstrate that the spatial correlation degrades the performance significantly, and efficient separation between apertures is crucial to achieve the maximum diversity gain.

The unmanned aerial vehicle (UAV) assisted transmission can significantly improve the spectrum efficiency and coverage of the wireless communication network. The paper proposed a cooperative secrecy transmission mechanism, which can take advantage of transmitter signal of primary user (PU) as a dedicated radio frequency (RF) source with decode and forward (DF) UAV selection and energy harvesting (EH) under cognitive network. Specifically, the transmitting signal of PU in the cognitive network can be viewed and used as energy to drive secondary user (SU) nodes and multi-relay nodes to send signals. It was worth noting that the DF UAV relay may bring about the unexpected noise and decrease the received signal to noise ratio (SNR), therefore, the multiple UAV assisted relays selected with secrecy capacity maximization criteria under cognitive network was proposed and investigated in detail, where the destination node equipped with multiple antennas and adopted the optimal antenna selection receiver. Moreover, By using the function analysis method, the closed expressions of the system secrecy outage probability (SOP) and the probability of non-zero secrecy capacity were calculated and derived accurately. Furthermore, the asymptotic expressions of the UAV assisted relay system under the large SNR cases were analyzed in detail, where the expressions of secrecy diversity order and secrecy diversity gain of the UAV assisted relay cognitive system were obtained thoroughly. Simulation results verified the effectiveness of the proposed mechanism and the correctness of the calculation.

Industrial WSNs are gradually gaining space in industry due to low cost of installation and maintenance. However, RF communications systems are prone to several propagation phenomena which can compromise reliability in terms of missed message deadlines. This work aims to increase the robustness of industrial WSN. In order to achieve this goal, it is necessary to correct inherent problems in wireless communications, some of which are channel noise, interference, and multipath fading. Multipath can be considered the main factor that makes communications in wireless sensor networks a real challenge when compared to other types of mediums, such as optical fiber, cable, or even directional radio transmissions. In this sense, antenna diversity is proposed as a solution to deal with these effects, with the aim of improving radio reliability to make the use of dense industrial WSN feasible. The potential of antenna diversity in WSN is not fully exploited in industrial applications. This article presents the combination of selection technique for industrial WSN through an algorithm that selects the transceiver port that has the highest link quality indicator and performs antenna switching in the radio modules. The results obtained are analyzed to verify the diversity gain by using antenna spatial diversity at reception and thus reduce packet error rate. The results corroborate with theory by increasing radio reliability in terms of diversity gain, quadrupling the received signal power when the correct antenna is chosen.

A joint data and interference transmission scheme based on a new distributed asynchronous cyclic delay diversity (dACDD) technique is proposed for cooperative communication systems. Without any perfect channel state information from a legitimate user (LU) and an eavesdropping user (EU), joint remote radio head (RRH) selection for the data and jamming signal transmissions is proposed for dACDD to achieve the maximum diversity gain at the LU, while degrading the receive signal-to-interference-plus-noise ratio at the EU. The proposed dACDD is the extension of distributed cyclic delay diversity, which requires a tight synchronization among the central control unit and RRHs. Thus, processing at each RRH causing no intersymbol interference at the LU is developed. Then, the selection scheme for a data RRH is proposed, which selects a single RRH connected with the channel having the greatest channel magnitude as the data RRH to transmit a desired confidential message and controls the remaining RRHs to transmit an artificial interference sequence to the LU and EU. For the proposed distributed system, the marginal secrecy outage probability and marginal probability of non-zero achievable secrecy rate are analyzed by deriving closed-form expressions, whose correctness is verified via link-level simulations over non-identically distributed frequency selective fading channels.

This brief demonstrates the use of metamaterial absorber (MA) to achieve high isolation between two patch antennas in a 2-element multiple-input–multiple-output (MIMO) system operating at 5.5 GHz resonant frequency useful for WiMAX application. The proposed flower shaped MA, designed on a $9\times 9$ mm2 FR-4 substrate with 1 mm thickness, exhibits near unity normalized impedance at 5.5 GHz with an absorptivity of 98.7%. A four element array of the MA is arranged in the form of a line in the middle of the two radiating patches in order to suppress the propagation of surface current between them at the operating frequency. Using the proposed flower shaped MA, an isolation of nearly 35 dB is achieved. The MIMO structure is studied in terms of return loss, isolation, overall gain, radiation pattern, envelope correlation coefficient (ECC), diversity gain (DG), total active reflection co-efficient (TARC), etc. The structure is finally fabricated and measured to show good agreement with the simulated results.

In this paper, a very small size (20 × 14.75 mm2) triple-band multiple-input multiple-output (MIMO) microstrip patch antenna for WLAN (2.4/5.2/5.8 GHz) and WiMAX (2.5/3.5/5.5 GHz) wireless applications. The goal of this paper is to merge these two wireless standards into a single antenna that can be easily accommodated inside the devices operating in three different frequency ranges. The proposed MIMO antenna consists of an asymmetric coplanar strip (ACS) feedline loaded with an inverted L-shaped slot and a meanderline. The inverted L-shaped slot and the meanderline both having an electrical length 0.5λ, are responsible for the achieving the operating band around 3.5 and 2.4 GHz, respectively whereas the ACS feedline is responsible for the generation of 5 GHz frequency band. The fabricated prototype of the proposed MIMO antenna when tested, shows three distinct frequency bands; I from 2.38 to 3.00 GHz, II from 3.21 to 3.61 GHz and III from 5.02 to 6.18 GHz that covers entire frequency bands of WLAN and WiMAX wireless applications along with different standards of IEEE 802.11 including a/b/j/p/g/n/ac/ax. The peak gain in I, II and III frequency bands is 7.93, 4.23 and 7.57 dBi, respectively. In addition, the diversity performance in terms of envelope correlation coefficient, diversity gain, multiplexing efficiency, total active reflection coefficient, and mean effective gain is also performed for the proposed MIMO antenna.

In this paper, a reduced mutual coupling dual-band multiple-input-multiple-output (MIMO) antenna is reported. A thin rectangular slot is incorporated into an unlicensed 5.2 GHz band rectangular pat...

The main objective of a Cooperative Multiple-Input Multiple-Output (CMIMO) system is to improve network throughput and network coverage and save energy. By grouping wireless devices as virtual multi-antenna nodes, it can thus simulate the functions of multi-antenna systems. A Space-Time Block Code (STBC) was proposed to utilize the spatial diversity of MIMO systems to improve the diversity gain and coding gain. In this paper, we proposed a cooperative strategy based on STBC and CMIMO, which is referred to as Space-Time Block Coded Cooperative Multiple-Input Multiple-Output (STBC-CMIMO) to inherit the advantages from both STBC and CMIMO. The theoretical performance analysis for the proposed STBC-CMIMO is presented. The performance advantages of the STBC-CMIMO are also shown by simulations. In the simulations, it is demonstrated that STBC-CMIMO can obtain significant performance compared with the existing CMIMO system.

In this study, dual-port dual-frequency tuneable MIMO planar inverted-F antenna (PIFA) is presented for mobile handheld device applications. The proposed MIMO antenna consists of two symmetrical PIFAs with the centre-to-centre distance of 43.0 mm (0.1906λ 0 ). The dual-band tunability is achieved by changing the capacitance (V 1 and V 2 ) of 4.15 pF (0 V)-0.72 pF (15 V). The impedance bandwidth of -6 dB is realised from 0.8 to 0.98 GHz for the lower band and 1.65 to 2.2 GHz for the higher band. The proposed antenna provides the independent frequency tunability without disturbing the frequency bands. It shows the good isolation for both the tuneable bands >20 dB without using any coupling element between the antenna structure. It has a peak realised gain of 3.44 dBi, good efficiency of > 75% and envelope correlation coefficient of 0.007. In addition, the proposed PIFA performance is analysed with total active reflection coefficient, channel capacity, diversity gain, multiplexing efficiency, mean effective gain and specific absorption ratio for the tuneable range of frequencies. The good agreement is obtained between simulation and experimental performances to validate the antenna parameters.

Free space optical (FSO) communication has emerged to provide line of sight connectivity and higher throughput over unlicensed optical spectrums. Cognitive radio (CR), on the other hand, can utilize the radio frequency (RF) spectrum and allow a secondary user (SU) to share the same spectrum with the primary user (PU) as long as the SU does not impose interference on the PU. Owing to the potential of these emerging technologies, to provide full spectrum efficiency, this paper focuses on the mixed CR RF-FSO transmission scheme, where RF communication is employed at one hop followed by the FSO transmission on the other hop in a dual-hop decode-and-forward (DF) configuration. To quantify the performance of the proposed scheme, closed form error probability is derived over Rayleigh/Exponentiated Weibull (EW) fading distributions by considering the statistical and instantaneous feedback channel of the primary network. We also employed an asymptotic analysis to illustrate the diversity gain of the overall system. We believe that the proposed scheme can be applicable to the 5G+ networks where an unlicensed university student connects to the home computer with the aid of an FSO path.

In the present endeavor, a CPW-fed dome-shaped monopole radiating elements with 2 × 2 MIMO configuration is presented. The dual-band response of the antenna is obtained by embedding a pair of comb-...

A very compact Superwideband multiple-input–multiple-output antenna with dual notched band characteristics is presented. Superwideband characteristics is obtained by means of radiating patch and high isolation between two input ports are obtained by using T-shaped stub in ground plane. Two rejection bands (wireless interoperability for microwave access (WiMAX)/C-band and wireless local area network) are obtained by etching two elliptical slots on radiating patch. Antenna offers large measured useable bandwidth of 2.60–20.04 GHz. Diversity performance is studied in terms of envelope correlation coefficient, diversity gain and total active reflection coefficient. Antenna also offers desirable radiation pattern, gain and radiation efficiency which makes proposed antenna quite suitable for different wireless applications.

Non-orthogonal multiple access (NOMA) is a promising spectrally-efficient technology to satisfy the massive data requirement of the next-generation wireless communication networks. In this paper, we consider cooperative non-orthogonal multiple access (CNOMA) networks with relaying user selection, where a two-stage user selection scheme is adopted to optimize the received signal-to-noise ratio (SNR) of the weak user. We derive analytical expressions of the outage probability of the CNOMA users under two different types of channel estimation errors. Afterwards, we investigate the asymptotic characteristics the outage probability of the CNOMA systems in the high SNR regimes. Our results show that for the case of constant variance of the channel estimation error, the outage probability of each user is saturated and cannot be improved by increasing the transmit power of the access point. In contrast, there is no performance bottleneck of the outage probability for all the users when the variance of the channel estimation errors decease with SNR, whilst fully diversity gain is achieved by the weak user.

With the ever-growing requirement for higher data rates, terminals supporting multiple-input multiple-output (MIMO) technologies are being developed for next-generation. As for wireless device manufacturers, a radio performance evaluation of multi-antenna terminals in desired environments is mandatory before product release. This paper discusses the Over the Air (OTA) performance evaluation of antenna diversity systems in Indoor and Outdoor multi-path propagation channel models inside anechoic chamber, in terms of correlation coefficients and diversity gain (DG). These channel models have been emulated in terms of angles of arrivals (AoA) and cross-polarization ratio (XPR) with Rayleigh fading. For this purpose, SATIMO SG24 measurement system has been used. However, the actual configuration of this system is not able to emulate desired realistic environments. Therefore, an innovative methodology based on the SG24 probes control has been developed. The obtained results in simulations and measurements have shown a good agreement.

A four-element compact wide-band optically transparent MIMO antenna with a full ground plane is proposed. The four elements transparent MIMO system has a compact size of 24 × 20 mm2 with the undivided ground plane as most of the real-time systems demand a common reference. The complete antenna system achieves around 85% transparency due to a combination of AgHT-8 and Plexiglas which forms the transparent conductive patch/ground and substrate, respectively. The antenna geometry leads dual-band operation ranging from 24.10 - 27.18 GHz (Impedance bandwidth = 12%) and 33 - 44.13 GHz (Impedance bandwidth =28.86$ %) targeting the mm-wave 5G applications. The 4-element antenna system achieves isolation between inter-elements >16 dB and maximum gain value of greater than 3 dBi with more than 75% efficiency. The proposed transparent MIMO antenna is evaluated in terms of diversity gain (DG), envelope correlation coefficient (ECC), total active reflection coefficient (TARC), and mean effective gain (MEG) where decent MIMO performance with isolation more than >16 dB between the adjacent and other elements is achieved. Transparent MIMO antenna achieves directional patterns for the operating band with the value of DG >9, ECC

In this paper, we investigate the wireless powered multi-user multi-relay communication network, in which only relay nodes need energy harvesting with power splitting-based simultaneous wireless information and power transfer architecture. A low-complexity practical scheme, in which the best user selection and partial Nth best relay selection are adopted, is proposed and analyzed under the impact of outdated channel state information (CSI). The exact and lower bound closed-form expressions for the outage probability are derived over independent but not necessarily identical distributed (i.n.i.d) Rayleigh fading channel, and its asymptotic analysis is also given. The asymptotic analysis reveals that the diversity gain can achieve 2, which is different from the system without outdated CSI. The correctness of analytical result is validated by Monte Carlo simulations, and simulation results provide insights into the effect of system parameters, i.e., the impact of outdated CSI, the number of relays and users, average channel fading power, energy harvesting coefficient and power-splitting ratio, on the outage performance. At last, simulation results show that the outdated CSI and the number of relays also affect the optimal value of the power-splitting ratio.

Multi-antenna technologies have been widely used in modern wireless communication systems to achieve diversity gain, spatial multiplexing gain, and better interference suppression. Beamforming has been considered as a potential candidate for throughput maximization in MIMO cognitive radio networks. However, the efficient implementation of beamforming demands for accurate knowledge of channel estimate. Conventional spectrum sharing strategies treat the detection and estimation problems in uncoupled manner, which may not result in the overall optimum performance. In this paper, we propose a censored spectrum sharing strategy which considers both the detection and estimation performances simultaneously and is capable of improving the throughput of MIMO cognitive radio network. We derive analytical expressions for the critical parameters and provide simulation results to validate our derivations.

As millimeter wave (mmWave) beamforming (BF) system can increase the areal capacity in ultra-dense network (UDN), a joint design of user association and hybrid BF is challenging due to the high feedback overhead and complicated interference management where many communication nodes use large antenna arrays. In addition, the wireless backhaul should be incorporated because it allows a flexible design, while the wired backhaul is difficult to be installed as the number of small base stations increases. To integrate the wireless backhaul and access, the time resource partitioning between the backhaul and access transmissions is needed, which affects the network performance combined with the user association and BF design. In this regard, this paper deals with the joint problem of the time resource allocation, user association, and BF design to maximize the weighted sum rate. Then a two-stage design approach is proposed based on the limited channel feedback to reduce the complexity and overhead. Simulation results show that the proposed limited feedback hybrid BF scheme outperforms the baseline schemes. In addition, we find that the maximum spatial multiplexing gain can be achieved if the number of antennas of each node increases with an order of larger than the square of the number of RF chains. At the same time, the multi-node diversity gain can be obtained in mmWave UDN, which depends on the path loss exponent of line-of-sight.

In this paper, we investigate the security of a cache-aided multi-relay communication network in the presence of multiple eavesdroppers, where each relay can pre-store a part of the requested files in order to assist secure data transmission from source to destination. If the relays have cached the requested file, then they can directly send it to the destination; otherwise, traditional dual-hop data transmission is used. For both cases, relay selection is performed to assist the secure data transmission. We analyze the network secrecy performance in both scenarios of non-colluding and colluding eavesdroppers, and obtain a closed-form expression for the average secrecy outage probability (SOP), as well as an asymptotic expression for the high main-to-eavesdropper ratio (MER). Through minimizing the network SOP, we further optimize the cache placement by proposing a stochastic sampling based cache learning (SacLe) strategy, which can be implemented in parallel and thus reduces the implementation latency substantially. Numerical and simulation results are finally presented to verify the proposed analysis, and show that the caching strategy has a significant impact on the network secrecy performance through affecting the caching diversity gain and signal cooperation gain at the relays. The proposed SacLe strategy is shown to be able to achieve the optimal performance obtained by the brute force (BF) algorithm.