Mojtaba Mansour Abadi

Bio: Mojtaba Mansour Abadi is an academic researcher from Northumbria University. The author has contributed to research in topics: Free-space optical communication & Visible light communication. The author has an hindex of 11, co-authored 32 publications receiving 356 citations. Previous affiliations of Mojtaba Mansour Abadi include University of Glasgow.

FSO Detection Using Differential Signaling in Outdoor Correlated-Channels Condition

Abstract: In this letter, we introduce a detection technique based on differential signaling scheme for outdoor free space optical communications. This method requires no channel state information (CSI) and does not suffer from the computational load compared with the conventional receivers, where adjusting dynamically the detection threshold level (either based on CSI knowledge, or by using pilots) leads to increased computational time and reduced link throughput. This letter shows that the performance of the proposed technique only depends on the correlation of propagating optical beams. Especially under highly correlated-channels condition the fluctuation of the detection threshold level in the receiver is significantly small. We also show experimentally that under weak turbulence regime the variance of detection threshold level reduces for the correlated channel.

Tackling Africa's digital divide

Abstract: Innovations in ‘sustainable’ photonics technologies such as free-space optical links and solar-powered equipment provide developing countries with new cost-effective opportunities for deploying future-proof telecommunication networks.

Quantized Feedback-Based Differential Signaling for Free-Space Optical Communication System

Abstract: We propose a quantized feedback-based differential signaling scheme for $2 \times 1$ free space optical (FSO) multiple-input single-output communication systems. The analytical bit error rate (BER) for the proposed differential signaling scheme is derived and compared with the existing differential signaling scheme for FSO systems. The asymptotic BER of the proposed scheme is also determined and it is shown by using the asymptotic BER expression that the proposed scheme achieves full spatial diversity of two. Moreover, the effect of the feedback error on the performance of the proposed scheme is studied and it is demonstrated by simulation-based and analytical results that the proposed scheme significantly outperforms a previously proposed differential signaling scheme in terms of turbulence fades reduction for tolerable feedback errors.

Impact of link parameters and channel correlation on the performance of FSO systems with the differential signaling technique: Errata

Abstract: We investigate the effects of link parameters and the channel correlation coefficient on the detection threshold, Q-factor, and bit-error-rate (BER) of a free-space optical system employing a differential signaling scheme. In systems employing differential signaling schemes, the mean value of the signal is used as the detection threshold level, provided that differential links are identical or highly correlated. However, in reality, the underlying links are not essentially identical and have a low level of correlation. To show the significance of the link parameters as well as the correlation coefficient, we derive analytical relations describing the effect of weak turbulence and we determine the improvement of Q-factor with the channel correlation. Further, for the same signal-to-noise ratio, we demonstrate that a link with a higher extinction ratio offers improved performance. We also propose a closed-form expression of the system BER. We present experimental results showing improved Q-factor for the correlated channel case compared to the uncorrelated channel.

A space division multiplexed free-space-optical communication system that can auto-locate and fully self align with a remote transceiver.

Abstract: Free-Space Optical (FSO) systems offer the ability to distribute high speed digital links into remote and rural communities where terrain, installation cost or infrastructure security pose critical hurdles to deployment. A challenge in any point-to-point FSO system is initiating and maintaining optical alignment from the sender to the receiver. In this paper we propose and demonstrate a low-complexity self-aligning FSO prototype that can completely self-align with no requirement for initial manual positioning and could therefore form the opto-mechanical basis for a mesh network of optical transceivers. The prototype utilises off-the-shelf consumer electrical components and a bespoke alignment algorithm. We demonstrate an eight fibre spatially multiplexed link with a loss of 15 dB over 210 m.

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Art of electronics

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A Key 6G Challenge and Opportunity—Connecting the Base of the Pyramid: A Survey on Rural Connectivity

Abstract: Providing connectivity to around half of the world population living in rural or underprivileged areas is a tremendous challenge, but, at the same time, a unique opportunity. Access to the Internet would provide the population living in these areas a possibility to progress on the educational, health, environment, and business levels. In this article, a survey of technologies for providing connectivity to rural areas, which can help address this challenge, is provided. Although access/fronthaul and backhaul techniques are discussed in this article, it is noted that the major limitation for providing connectivity to rural and underprivileged areas is the cost of backhaul deployment. In addition, energy requirements and cost-efficiency of the studied technologies are analyzed. In fact, the challenges faced for deploying an electricity network, as a prerequisite for deploying communication networks, are huge in these areas, and they are granted an important share of the discussions in this article. Furthermore, typical application scenarios in rural areas are discussed, and several country-specific use cases are surveyed. The main initiatives by key international players aiming to provide rural connectivity are also described. Moreover, directions for the future evolution of rural connectivity are outlined in this article. Although there is no single solution that can solve all rural connectivity problems, building gradually on the current achievements in order to reach ubiquitous connectivity, while taking into account the particularities of each region and tailoring the solution accordingly, seems to be the most suitable path to follow.

Performance Analysis of Gamma–Gamma Fading FSO MIMO Links With Pointing Errors

Abstract: The bit error rate (BER) performance of the free space optical (FSO) link suffers from the atmospheric turbulence. By employing additional transmit and receive apertures at the transmitter and receiver, respectively, the error rate of the FSO communication system can be significantly improved. However, the pointing errors (PEs), generated because of the building sway, have the potential to eradicate the benefits of the multiple transmit and/or receive apertures-based FSO communication system. Therefore, for a general and realistic study of the FSO multiple-input multiple-output (MIMO) system, the effect of PEs in the Gamma–Gamma (GG) fading atmospheric fluctuations is considered in this paper. We study two schemes for the FSO MIMO systems: 1) equal gain combining (EGC), and 2) maximal ratio combining (MRC). A new power series-based representation is proposed for the probability density function of the GG fading FSO links with PEs. This new series representation contains only the terms with exponent of the random variable (RV) as compared to the closed-form representation, which contains the Meijer-G function of the RV. Then, we derive the average BER for both combining schemes over the GG fading FSO links with PEs. By using the derived BER expressions, we derive the asymptotic BER for both schemes. The analytical diversity order and combining gains for both systems are also obtained. The effect of PEs over the performance of the schemes is analyzed under different scenarios and it is observed that the PEs significantly degrade the diversity of the FSO MIMO system. It is deduced by simulation and analysis that though the EGC scheme is simpler to implement in practice but the MRC scheme is more rugged to the large PEs.