Performance Analysis of ACO-OFDM NOMA for VLC Communication

Visible light communication (VLC) is seeking a lot of attention in the recent years due to high bandwidth, low cost, ease of implementation. VLC can be used for illumination as well as communication at the same time. Light emitting diode (LED) acts as a transmitter for data transmission and photo detector is used at the receiver side. Intensity Modulation (IM) is used to convert electrical signal into optical signal where only real and positive signal need to be transmitted. Optical orthogonal frequency division multiplexing (O-OFDM) is used in the VLC to enhance the bandwidth limitation due to LED. Using OOFDM for VLC does not provide the massive connectivity in an multi-user environment. A Non orthogonal multiple access (NOMA) is the further expansion where user can use both the time and frequency resources but distinguished in power domain with successive interference cancellation (SIC) at the receiver to decode the signal of each user. Also, Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) is used to get positive signal with enhanced spectral efficiency. The proposed method is evaluated analytically and using simulation in terms of bit error rate (BER).

Robust Hybrid Beam-Forming for Non-Orthogonal Multiple Access in Massive MIMO Downlink

This paper presents hybrid precoding for a non-orthogonal multiple access (NOMA) transmission scheme in a millimeter wave (mmWave) massive MIMO (mMIMO) downlink. In hybrid precoding, the analog precoder is obtained by the orthogonalization of the users’ channel vectors to minimize inter-beam interference. The digital precoder consists of a zero-forcing precoder to minimize inter-user interference. In order to break the barrier of one user per beam, we utilize the NOMA within the beam for power domain multiplexing among users. Simulation results show the proposed scheme’s efficacy compared to the state-of-the-art schemes and provide 1.48 times better sum-rate performance at 10 dB received SNR.

Statistical Beamforming Techniques for Power Domain NOMA System

Power-domain non-orthogonal multiple access (NOMA) assigns different power levels for near and far users in order to discriminate their signals by employing successive interference cancellation (SIC) at the near user. In this context, multiple-input-single-output NOMA (MISO-NOMA), where the base station (BS) is equipped with multiple antennas while each mobile user has a single antenna receiver, is shown to have a better overall performance by using the knowledge of instantaneous channel state information (CSI). However, this requires prior estimation of CSI using pilot transmission, which increases the transmission overhead. Moreover, its performance is severely degraded in the presence of CSI estimation errors. In this work, we provide statistical beamforming solutions for downlink power-domain NOMA that utilize only knowledge of statistical CSI, thus reducing the transmission overhead significantly. First, we derive the outage probabilities for both near and far users in the multi-user NOMA system without imposing strong assumptions, such as Gaussian or Chi-square distribution. This is done by employing the exact characterization of the ratio of indefinite quadratic form (IQF). Second, this work proposes two techniques to obtain the optimal solution for beam vectors which rely on the derived outage probabilities. Specifically, these two methods are based on (1) minimization of total beam power while constraining the outage probabilities to the QoS threshold, and (2) minimization of outage probabilities while constraining the total beam power. These proposed methods are non-convex function of beam vectors and, hence, are solved using numerical optimization via sequential quadratic programming (SQP). Since the proposed methods do not require pilot transmission for channel estimation, they inherit better spectral efficiency. Our results validate the theoretical findings and prove the supremacy of the proposed method.

Undergraduate Nursing Students Endorse Education Standards in Blended e-Learning Theory Teaching during COVID-19 Pandemic

Aim: The aim of this study was to survey student learning perspectives as measured by ‘student satisfaction’ following the rapid introduction of remote blended e-learning into the existing undergraduate nursing curriculum at Umm Al-Qura University, Saudi Arabia. Background: National legislation resulting from the spread of Covid-19 required all theoretical and practical nurse training to move immediately to online provision using an unfamiliar e-learning environment and associated tools. Objective: The objective of this study was to use a validated satisfaction questionnaire developed elsewhere, but within a similar educational context involving both theoretical and practical components, for the purpose of checking that educational objectives were being satisfactorily achieved across five relevant domains of educational enquiry, and to use survey findings to improve the online delivery of the nursing program in future academic years. Methods: A validated 35 item questionnaire was circulated online to all male and female nursing students in their 2nd, 3rd and 4th years of study. The questionnaire content was subdivided into the five domains of ‘Interaction’, ‘Instruction’, ‘Instructor’, ‘Course Management’ and ‘Technology’. Descriptive and comparative statistics were used to compare levels of satisfaction between genders and among undergraduate years of study, and against findings from undergraduate information technology undergraduates. Results: 199 female and 84 male students completed the questionnaire (response rate 59.2%). Mean satisfaction scores for male and female nursing undergraduates were significantly greater than 3 (neutral score) in all domains of enquiry, indicating good satisfaction with blended e-learning (p<0.001). However, multivariate regressions of domain satisfaction scores taking gender and year of study as explanatory variables had poor resolving power. Domain scores were also significantly greater than those of a comparator study in three of the five domains (p<0.030) and similar in the domains of course management (p=0.717) and technology (p=0.677). Levels of satisfaction in males and females were similar in 80% of the survey questions, but in females, satisfaction was significantly lower in some questions concerning technology (p<0.003), willingness to interrupt the instructor (p=0.021), comparison of blended learning and face-to-face teaching (p=0.002) and timely feedback on tests and assignments (p=0.031). Fourth-year students showed the highest levels of satisfaction across all five domains. Conclusion: Undergraduate nursing students reported above-average satisfaction levels across all five domains of education provision. Despite an unfamiliar blended e-learning curriculum environment, they demonstrated compatible technological skills, satisfactory interaction with teachers and other students and engagement in the learning process. A number of recommendations identified in the literature as underlying a successful program of blended e-learning are recorded for the benefit of readers.

Joint power control and user grouping for uplink power domain non-orthogonal multiple access

Orthogonal multiple access schemes based on assignment of communication resource blocks among multiple contenders, although widely available, still necessitate an upper limit on the number of concurrent users for minimization of multiple-user interference. The feature thwarts efforts to cater for pressing connectivity demands posed by modern-day cellular communication networks. Non-orthogonal multiple access, regarded as a key advancement towards realization of high-speed 5G wireless communication networks, enables multiple users to access the same set of resource blocks non-orthogonally in terms of power with controllable interference, thereby allowing for overall performance enhancement. Owing to the combinatorial nature of the underlying optimization problem involving user pairing/grouping scheme, power control and decoding order, the computational complexity in determining optimal and sub-optimal solutions remains considerably high. This work proposes three novel alternative approaches (Randomly, 2-Opt and Hybrid) for arriving at a near-optimal solution for the problem of user pairing/grouping. The algorithms not only offer reduced computational complexity but also outperform orthogonal multiple access and existing schemes reported in the literature for uplink non-orthogonal multiple access systems.

Spectral efficiency analysis of two-user Downlink PD-NOMA with LTE modulation and coding schemes

Non-orthogonal multiple access (NOMA) is a promising user multiplexing technique for future wireless networks that allows increasing their spectral efficiency (SE). Power-Domain NOMA (PD-NOMA) is one of the most perspective techniques in the NOMA group. It makes it possible to perform the transmission of information symbols of several users within the same time-frequency resource segment (RS) without a spreading code. Many research works show the high efficiency of PD-NOMA compared to the orthogonal multiple access (OMA). However, these results are obtained analytically using Shannon’s formula and not taking into account the real performance of existing modulation and coding schemes (MCS). The issue is that it is impossible to obtain the achievable practical performance of PD-NOMA systems in this way. We obtain the SE in RS of a PD-NOMA system with Long Term Evolution (LTE) MCS’s and compare it with OMA. As a result, we conclude that PD-NOMA gains the system SE when the multiplexed user’s signal-to-noise ratio (SNR) outreaches the threshold of the highest performing MCS provided for the transmission by a MCS table.