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Purpose: This study aims to investigate the influence of corporate social responsibility (CSR) on corporate sustainable performance (CSP) of small- and medium-sized enterprises (SMEs) by looking into the significance of mediating factors, namely, brand image (BI) and brand loyalty (BL), within the context of an emerging economy. Design/methodology/approach: The authors conduct an extensive literature study on the subjects of CSR, BI and BL to assess their influence on the sustainable performance of SMEs in an emerging market. The study adopts a quantitative methodology. A total of 438 answers were obtained from a sample size of 513. The data of the SMEs in Vietnam was analyzed using the smart partial least squares structural equation modeling software, specifically version 3.3.2. Findings: The results of the authors demonstrate notable and favorable correlations between CSR and CSP, CSR and BI and CSR and BL. Importantly, the findings contribute to existing knowledge by looking into the mediating influence of BI and BL in the relationship between CSR and CSP. Originality/value: According to the authors' understanding, a number of research have investigated the correlation between CSR and CSP within the realm of SMEs. Nevertheless, there is a scarcity of scholarly research examining the mediating function of BI and BL in this association. The study's findings have important implications for entrepreneurs and senior management in effectively guiding their enterprises and improving their business strategies with an emphasis on sustainability in emerging markets. The outcome of this study has the potential to significantly contribute to SMEs in Vietnam as well as other emerging countries. [ABSTRACT FROM AUTHOR]

The increasing development and utilisation of optical camera communications offer an excellent opportunity for the implementation of the smartphone‐to‐smartphone‐based visible light communications (S2SVLC) system. In this study, the authors experimentally demonstrate that the S2SVLC system can support high‐quality multimedia transmissions by the investigation of the mean square error estimation, peak signal‐to‐noise (PSNR) degradation, bit error rate (BER), and data rate achieved. The experimental analysis has been carried out for different typical practical background illuminations (i.e., normal illumination and dark condition), distances, tilting, and rotation angles. The PSNR and BER are determined for different frame sizes in the S2SVLC system to provide an insight of system performance. Those results indicate that the data transmission at different conditions significantly impacts the system's performance. [ABSTRACT FROM AUTHOR]

This paper proposes a novel approach to provide a privately secured multiple-input and multiple-output visible light communication (VLC) in the mobility conditions. In the proposed system, a private secured VLC link is adaptively allocated to a mobile user all the time thanks to the movement tracking assistance by a camera-based detection system. The generation of the dynamic location-based scrambling matrix will be introduced providing a secured communication zone within a full normal coverage illumination area. An extensive range of numerical evaluation and practical experiments is carried out to demonstrate and evaluate the proposed system performance in different environment configurations including the mobility, camera resolutions, link range, and environment light intensity. We demonstrate that the proposed system is fully capable of securely steering the information with respect to a receiver location with a high level of reliability. [ABSTRACT FROM AUTHOR]

Underwater Acoustic Communications (UWAC) is an emerging technology in the field of underwater communications, and it is challenging because of the signal attenuation of the sound waves. Multiple Input and Multiple-Output (MIMO) is introduced in UWAC because of its support in enhancing the data throughput even under the conditions of interference, signal fading, and multipath. The paper presents the concept and analysis of 2x2 MIMO UWAC systems that uses a 4-QAM spatial modulation scheme thus minimizing the decoding complexity and overcoming the Inter Channel Interference (IChI). Bit Error Rate (BER) investigation is carried out over different link distances under acoustic Line of Sight (LOS). The utilization of Zero Forcing (ZF) and Vertical-Bell Laboratories Layered Space-Time (VBLAST) equalizers, which estimates the transmitted data proves a success of removing Inter Symbol Interference (ISI). The ISI caused due to multipath effect and scattering in UWAC can be reduced by iterative process considered in VBLAST. A study is made on how the distance between the transmitter and the receiver and the Doppler Effect has its impact on the performance of the system. [ABSTRACT FROM AUTHOR]

Erratum corrects an error in Fig. 8. [ABSTRACT FROM AUTHOR]

We propose an adaptive localization and channel state information (CSI) estimation model using the distance vector for indoor multiple-input multiple-output (MIMO) visible light communication (VLC). Under normal conditions, receivers (Rxs) require the CSI of all channels [formed by multiple transmitters (Txs) and multiple Rxs] to recover the original data, and the received signal strength (RSS) obtained from Txs, i.e., light-emitting diodes (LEDs) to predict the Rx's location. A beacon [or pilot signal (PS)] with CSI is periodically broadcasted from each LED to MIMO Rxs for constructing the CSI matrix and measuring the RSS. However, in an abnormal condition, PSs from one or multiple Txs might not reach Rxs due to shadowing, thus resulting in a failure in positioning and data recovery. To combat this, the proposed model enables the Rx to predict its location without the need for all PSs based on the construction of the distance vectors at Rx. Simulations conducted for two scenarios of user's mobility, i.e., lattice and random direction mobility, show a low positioning error of ∼0.1 and 0.2 m, respectively. Based on predicted positions, MIMO VLC is capable of fulfilling the CSI matrix and assists the Rx in recovering transmitted data with a very low bit error rate. [ABSTRACT FROM AUTHOR]

This paper studies zero-forcing (ZF) precoding designs for multi-user multiple-input single-output visible light communication (VLC) broadcast channels. In such broadcast systems, the main challenging issue arises from the presence of multi-user interference (MUI) among non-coordinated users. In order to completely suppress the MUI, ZF precoding, which is originally designed for radio frequency (RF) communications, is adopted. Different from RF counterpart, VLC signal is inherently non-negative and has a limited linear range, which leads to an amplitude constraint on the input data signal. Unlike the average power constraint, obtaining the exact capacity for an amplitude-constrained channel is more cumbersome. In this paper, we first investigate lower and upper bounds on the capacity of an amplitude-constrained Gaussian channel, which are especially tight in the high signal-to-noise regime. Based on the derived bounds, optimal beamformer designs for the max-min fairness sum-rate and the maximum sum-rate problems are formulated as convex optimization problems, which then can be efficiently solved by using standard optimization packages. [ABSTRACT FROM AUTHOR]

Indoor positioning or localization based on visible light communications (VLC) is an emerging technology with wide applications. In conventional localization schemes, the trilateration technique is widely used with at least three separate lighting sources to determine the user's location. An indoor VLC positioning scheme based on the optical power distributions of only two light emitting diodes (LEDs) is reported for different environments. We have used two received signal strength indications to determine the user's position based on the LEDs configuration offering less complexity. We propose comprehensive mathematical models for the VLC localization system considering the noise and its impact on the user's location, and numerically evaluated it over a range of signal-to-noise ratios (SNRs). In addition, it is compared to the results with the exiting trilateration technique. The performance of the proposed system is evaluated with a reported accuracy of <20 cm for an SNR of >13 dB. [ABSTRACT FROM AUTHOR]

In this paper, a 10-Gb/s hybrid optical fiber (OF) and free-space optics (FSO) link as part of a bidirectional long-haul OF transmission for application in outdoor environments such as bridges is proposed. A fiber-Bragg-grating (FBG) sensor head is used for monitoring the condition of a bridge, and in the case of the bridge being damaged, the transmission path is changed over from OF to the FSO link to ensure link connectivity. An Erbium-doped fiber amplifier is used to compensate for losses due to the fiber cable and the free-space channel. At a bit error rate (BER) of 10e-9, the power penalty between the OF and FSO paths is < 1 dB, and the power variations for both paths are ±0.07 and ±0.12 dB, respectively. [ABSTRACT FROM PUBLISHER]

We present recent progress on visible light communication systems using polymer light-emitting diodes as the transmitters and a commercial silicon photodetector as the receiver. In this paper, we use transmitters at red, green, and blue wavelengths to investigate the maximum on-off keying link performance of each device type as the first steps toward a wavelength-division multiplexed link. We show that a total transmission speed of 13 Mb/s is achievable when considering the raw bandwidth of each of the RGB PLEDs. Such a rate represents a 30% gain over previously demonstrated systems. Further capacity improvement can be achieved using high performance artificial neural network equalizer offering a realistic prospect for transmission speeds up to 54.9 Mb/s. [ABSTRACT FROM PUBLISHER]

This study introduces a routing model which has the ability to detect the mobile ad‐hoc network (MANET) mobility states and self‐adapt routing metrics accordingly. In this model, nodes rely on theirs mobility indicator to detect whether the network is relatively static or mobile and hence switch the routing metric to either expected transmission count (ETX) or mobility factor (MF), respectively. The proposed model takes advantages of both ETX and MF metrics thus enhancing the overall routing performance for MANET in different mobility states. Packet delivery ratio increases 10% in both static and mobile conditions whereas the number of drop packets reduces half compared with the original optimised link state routing protocol. [ABSTRACT FROM AUTHOR]

In this study, a compact design of a highly efficient, and a high luminosity light‐emitting diode (LED)‐based visible light communications system is presented, which is capable of providing standard room illumination levels and also wide‐coverage Ethernet 10BASE‐T optical wireless downlink communications over a distance of 2.3 m using commercial white light phosphor LEDs. The measured signal‐to‐noise ratio of the designed Ethernet system is >45 dB, thus allowing error‐free communications with both on–off keying non‐return zero and differential Manchester‐coded modulation schemes at 10 Mbps. The uplink has been provided via a wireless infra‐red link. A comparative study of a point‐to‐point wired local area network (LAN) and the optical wireless link confirms no discernible differences between them. The design of the transmitter is also shown to be scalable, with the frequency response for driving 25 LEDs being almost the same as driving a single LED. LED driving units are designed to match with the Ethernet sockets (RJ45) that conform to the existing LAN infrastructures (building and portable devices). [ABSTRACT FROM AUTHOR]

The demand for access to broadband data services in high‐speed trains is increasing as more people are travelling to and from work, which is not met by the existing radio frequency technology. Therefore an alternative technology known as free space optics (FSO) could be readily adopted that could overcome the bandwidth bottleneck problem. The study presents a mathematical model of an FSO link for ground‐to‐train communications link and analyses the system performance in terms of the signal‐to‐noise ratio and the bit error rate (BER). The authors show that the simulated BER is in good agreement with the predicted results for bit rates up to 50 Mbps. The link budget analysis for the proposed system is also presented showing a link margin of 17.75 dB. [ABSTRACT FROM AUTHOR]

In this letter, we propose a tuned elliptical Lambertian beam (ELB) model to achieve a higher transmission bandwidth than the conventional circular Lambertian beam (CLB) model for indoor optical wireless communication systems. ELB is generated by employing a M^\circ\times N^\circ light shaping diffuser, and its power distribution is investigated. We first derive new expressions of the power distribution and the multipath impulse response for ELB. From the precise frequency responses of CLB and ELB sources, we show that the tuned ELB model offers a higher transmission bandwidth than CLB. [ABSTRACT FROM PUBLISHER]

In this paper, we propose and validate an artificial neural network-based equalizer for the constant power 4-level pulse amplitude modulation in an optical camera communications system. We introduce new terminology to measure the quality of the communications link in terms of the number of row pixels per symbol N pps , which allows a fair comparison considering the progress made in the development of the current image sensors in terms of the frame rates and the resolutions of each frame. Using the proposed equalizer, we experimentally demonstrate a non-flickering system using a single light-emitting diode (LED) with N pps of 20 and 30 pixels/symbol for the unequalized and equalized systems, respectively. Potential transmission rates of up to 18.6 and 24.4 kbps are achieved with and without the equalization, respectively. The quality of the received signal is assessed using the eye-diagram opening and its linearity and the bit error rate performance. An acceptable bit error rate (below the forward error correction limit) and an improvement of ~66% in the eye linearity are achieved using a single LED and a typical commercial camera with equalization. [ABSTRACT FROM AUTHOR]

The accuracy of the received signal strength-based visible light positioning (VLP) system in indoor applications is constrained by the tilt angles of transmitters (Txs) and receivers as well as multipath reflections. In this paper, for the first time, we show that tilting the Tx can be beneficial in VLP systems considering both line of sight (LoS) and non-line of sight transmission paths. With the Txs oriented towards the center of the receiving plane (i.e., the pointing center F), the received power level is maximized due to the LoS components on F. We also show that the proposed scheme offers a significant accuracy improvement of up to ~66% compared with a typical non-tilted Tx VLP at a dedicated location within a room using a low complex linear least square algorithm with polynomial regression. The effect of tilting the Tx on the lighting uniformity is also investigated and results proved that the uniformity achieved complies with the European Standard EN 12464-1. Furthermore, we show that the accuracy of VLP can be further enhanced with a minimum positioning error of 8 mm by changing the height of F. [ABSTRACT FROM AUTHOR]

This letter reports an experimental demonstration of an indoor angle-diversity optical wireless communications system. This operates at 1.25 Gb/s and provides bidirectional communications between two terminals. Each terminal uses three transmitting “cells” giving a field of view of approximately 25^\circ\times 8^\circ over a range of approximately 3 m. Data is transmitted to a terminal that uses three receivers to obtain a similar reception field of view. Link operation at a bit-error rate < 10e\-9 is reported, together with an overview of the system configuration. [ABSTRACT FROM PUBLISHER]