Research

Unmanned aerial vehicles

The integration of unmanned aerial vehicles (UAVs) into spectrum sensing cognitive communication networks can offer many benefits for massive connectivity services in 5G communications and beyond; hence, this work analyses the performance of non-orthogonal multiple access-based cognitive UAV-assisted ultra-reliable and low-latency communications (URLLCs) and massive machine-type communication (mMTC) services. An mMTC service requires better energy efciency and connection probability, whereas a URLLC service requires minimising the latency. In particular, a cognitive UAV operates as an aerial secondary transmitter to a ground base station by sharing the unlicensed wireless spectrum. To address these issues, we derive the analytical expressions of throughput, energy efficiency, and latency for mMTC/URLLC-UAV device. We also formulate an optimisation problem of energy efficiency maximisation to satisfy the needs of URLLC latency and mMTC throughput and solve it using the Lagrangian method and the Karush-Kuhn-Tucker conditions. The algorithm is presented by jointly optimising the transmission powers of the mMTC and URLLC users. The derived expressions and algorithm are then used to evaluate the performance of the proposed system model. The numerical results show that the proposed algorithm improves the energy efficiency and satisfies the latency requirement of the mMTC/URLLC-UAV device.Source: [1] Sabuj, S. R., Ahmed, A., Cho, Y., Lee, K.-J., & Jo, H.-S. (2020). Cognitive uav-aided urllc and mmtc services: Analyzing energy efficiency and latency. IEEE Access, 9, 5011–5027.[2] Ahmed, S., Chowdhury, M. Z., Sabuj, S. R., Alam, M. I., & Jang, Y. M. (2021). Energy-efficient uav relaying robust resource allocation in uncertain adversarial networks. IEEE Access, 9, 59920–59934.[3] Rahul, A. R., Sabuj, S. R., Akbar, M. S., Jo, H.-S., & Hossain, M. A. (2021). An optimization based approach to enhance the throughput and energy efficiency for cognitive unmanned aerial vehicle networks. Wireless Networks, 27(1), 475–493.

Satellite communication

This paper discusses the significance and prospects of low-altitude small satellite aerial vehicles in order to ensure smooth aerial-ground communications for next-generation broadband networks. In order to achieve the generic goals of fifth-generation and beyond wireless networks, the existing aerial network architecture needs to be revisited. The detailed architecture of low-altitude aerial networks and the challenges in resource management have been illustrated in this paper. Moreover, we have studied the coordination between promising communication technologies and the low-altitude aerial networks to provide robust network coverage. We talk about the techniques that can ensure user-friendly control and monitoring of the low altitude aerial networks in order to bring forth wireless broadband connectivity to a new dimension. At the end, we highlight the future research directions of aerial-ground communications in terms of access technologies, machine learning, compressed sensing, and quantum communications.Source: [1] Sabuj, S. R., Alam, M. S., Haider, M., Hossain, M. A., & Pathan, A.-S. K. (2022). Low altitude satellite constellation for futuristic aerial-ground communications. Computer Modeling in Engineering & Sciences, 2022 .

Machine type communication in sub-terahertz band

There is a compelling need to address the problem of accommodating the rapidly growing number of machinetype devices engaging in communication within the scarce radio spectrum, in current and forthcoming generations of wireless networks. The coming decades will also witness various novel applications, demanding wireless communication at very high data rate and energy efficiency, which currently favored technologies andtechniques are inadequate to support. Because of these reasons, it seems inevitable that wireless communicationwill have to be facilitated by the efficient utilization of larger bandwidth at higher frequencies. Non-Orthogonal Multiple Access (NOMA) and shifting to higher frequency ranges such as the lower terahertz band, have beenconsidered as solutions to provide space to the increasing number of communicating devices while meeting performance requirements. In this paper a machine type communication system model, utilizing the promising technique NOMA and operating in the sub-terahertz band, is developed and analyzed for its performances ofdata rate, spectral efficiency and energy efficiency. Thereafter the energy efficiency of the proposed model isoptimized by using unconstrained optimization and then constrained (by threshold of data rate) optimization, the latter solving a multi-objective problem by the πœ–-constraint method. The optimal transmission power isalso derived for both optimization techniques. Finally, simulation results demonstrate that the energy efficiencycan be maximized by utilizing unconstrained optimization and the spectral efficiency can be maximized by utilizing constrained optimization for both machine-to-machine and base-to-machine communications.Source: Sabuj, S. R., Khan, A. M. S., & Hamamura, M. (2020). Application of non-orthogonal multiple access for machine type communication in sub-terahertz band. Computer Networks, 182, 107508.

Coordinated multipoint joint transmission at mmWave

A coordinated multipoint joint transmission (CoMP-JT) framework at mmWave for a cyclic prefix (CP)-free multiuser OFDM wireless communication system is developed and analyzed. The aim is to provide high-quality service to cell-edge users; otherwise, the cell-users would suffer from significant signal degradation due to undesired interference. The impact of complex Hadamard transform with block diagonalization channel precoding for multiuser interference reduction and designed subcarrier mapping for out-of-band (OOB) reduction are investigated. In addition, the paper studied the input back-off-aided high-power amplifier for peak-to-average power ratio (PAPR) reduction and forward error correction channel coding for improved bit error rate (BER) for cell-edge users at mmWave frequencies. Moreover, signal-to-interference-noise ratio and ergodic achievable rate are estimated both in the presence and absence of CoMP-JT-based transmission technique to verify their significance in terms of transmitted power. Source: Sadique, J. J., Sabuj, S. R., Ullah, S. E., Hossain, M., Raad, R., Islam, M., . . . Mahmud, M. et al. (2021). Analytical framework of cp-free multiuser ofdm system for coordinated multi-point at mmwave. Applied Sciences, 11(16), 7605.

Random cognitive radio networks

Cognitive radio networks have recently attracted significant research attention owing to their promise for application in future cellular communication. In this light, given the intense power consumption of wireless networks, considerable research is now being directed at designing random cognitive radio networks with enhanced energy efficiency. In this study, we investigate the outage probability and energy efficiency in a cognitive radio network, modeling the locations of the primary users and cognitive users as a Poisson point process. We derive closed-form expressions for the outage probability and energy efficiency with consideration of the probabilities of unoccupied (not utilized by the primary users) channel selection and successful transmission for imperfect detection in an interference-limited environment of cognitive radio network. Furthermore, we propose a transmit antenna selection method for the cognitive transmitter in such networks and accordingly develop closed-form expressions for the outage probability and energy efficiency. The study reported here highlights the importance of combining the capabilities of unoccupied channel selection and successful transmission in cognitive radio networks to achieve optimal performance regarding outage probability and energy efficiency.Source: [1] Sabuj, S. R., & Hamamura, M. (2017). Outage and energy-efficiency analysis of cognitive radio networks: A stochastic approach to transmit antenna selection. Pervasive and Mobile Computing, 42, 444–469.[2] Sabuj, S. R., & Hamamura, M. (2017). Uplink modeling of cognitive radio network using stochastic geometry. Performance Evaluation, 117, 1–15.

Energy harvesting cognitive radio networks

There has recently been substantial interest in applying the principles of wireless radio frequency energy harvesting in battery-operated devices to cognitive radio networks. Although implementation of energy harvesting technique increases the complexity of network planning, it reduces battery power usage and enables eco-friendly cognitive radio network. In this paper, we report a comprehensive study of energy harvesting cognitive radio network where locations of users of primary and secondary networks follow a Poisson point process. In the design of random cognitive radio network, we focus on the two-slope path-loss function so as to have a realistic scenario of propagation environments. First, a new expression of outage probability is theoretically derived for secondary receiver in active mode. Second, we obtain an explicit expression of harvested energy for secondary receiver in active and inactive modes. Finally, we investigate the harvested energy maximization problem under a particular outage probability constraint, and also obtain an optimal solution of transmission power and density of secondary transmitters.Source: Sabuj, S. R., & Hamamura, M. (2018). Two-slope path-loss design of energy harvesting in random cognitive radio networks. Computer Networks, 142, 128–141.

Physical-layer network coding

In cognitive radio networks, security issues arise when intelligent malicious users can attack and decrease the permitted channel for unlicensed users (secondary users). In this paper, we propose a novel scheme, based on friend or foe (FoF) detection technique with physical layer network coding, to enable discrimination between secondary users and intelligent malicious users. Theoretical expressions are derived for probabilities of detection of secondary user, miss detection, and false alarm. In addition, the effectiveness of the proposed approach is evaluated by theoretical analysis and Monte Carlo simulation. Furthermore, an algorithm is proposed for distinguishing between secondary user and intelligent malicious user. Finally, based on the outcome of simulation of probabilities and normalised cross-correlation, it is determined that the proposed scheme outperforms in terms of orthogonal frequency-division multiplexing signal compared with quadrature phase-shift keying signal over cognitive radio network. Source: [1] Sabuj, S. R., & Hamamura, M. (2019). Signal technique for friend or foe detection of intelligent malicious user in cognitive radio network. International Journal of Ad Hoc and Ubiquitous Computing, 32(1), 29–42.[2] Sabuj, S. R., Hamamura, M., & Kuwamura, S. (2015). Detection of intelligent malicious user in cognitive radio network by using friend or foe (fof) detection technique. In 2015 international telecommunication networks and applications conference (itnac) (pp. 155–160).

Cognitive Wireless Sensor Networks

This paper introduces an analytical uplink modeling for cognitive wireless sensor network (CWSN). For such network, we derive the outage probability, throughput, affected area, and delay-sensitive area spectral efficiency (DASE). In addition, we investigate the DASE maximization problem and also obtain an optimal solution of transmission power and code rate. Finally, numerical results demonstrate that DASE is maximized for optimal transmission power compared with code rate. Source: Nazneen, S., Chowdhury, M. M. J., & Sabuj, S. R. (2019). Analysis of delay-sensitive performance in cognitive wireless sensor networks. Internet Technology Letters, 2(3), 1–6.