Articles written in Sadhana

    • ANN-based optimization framework for performance enhancement of Restricted Access Window mechanism in dense IoT networks


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      IEEE 802.11ah, marketed as Wi-Fi HaLow, operates at Sub 1 GHz spectrum to provide broad coverage, high throughput, energy efficiency and scalability. This makes IEEE 802.11ah a promising candidate for the Internet of Things (IoT). One of the major enhancements in the MAC layer is the Restricted AccessWindow (RAW) mechanism, which focuses on mitigating the channel contention in dense networks. The RAW mechanism reduces the channel contention among the group of devices by restricting their channel access to the allocated RAW slots. Since the standard does not specify the optimal RAW configuration parameters, choosing the number of RAW slots has significant impact on the performance of the RAW mechanism. In this paper, we develop an optimization framework by exploiting the Multilayer Perceptron Artificial Neural Network (MLPANN)to find the optimal number of RAW slots that can maximize the performance of the RAW mechanism in terms of throughput, delay and energy consumption. We train the ANN using the network size, Modulation and Coding Schemes, duration of the RAW period and the optimal number of RAW slots found using the analyticalmodel presented in this paper. Further, we evaluate the performance of the RAW mechanism by choosing the optimal number of RAW slots provided by the ANN-based optimization framework. Results show that the proposed scheme significantly enhances the performance of the RAW mechanism. Finally, the analytical results are corroborated using extensive simulations done in ns-3.

    • Stochastic modelling and performance analysis of cooperative HARQ in multi-cluster underwater acoustic sensor networks


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      Cooperative hybrid automatic repeat request (C-HARQ) scheme based on multi-hop relaying has been adopted as an efficient strategy in underwater acoustic sensor networks (UASNs) to extend network coverage and to enhance the performance by utilizing spatial diversity gain. In this letter, we develop a stochastic model for multi-cluster transmissions in UASNs, considering the underwater-specific characteristics such as frequency-dependent signal attenuation, acoustic spreading, multi-path fading and underwater noises. From this generalized stochastic model, we derive accurate analytical expressions to analyse the end-to-end packet error rate (PER) and energy efficiency. Analytical results demonstrate that the C-HARQ scheme can significantly improve the performance of UASNs, especially with the increase in number of relay nodes. Analytical results are corroborated with extensive simulation studies.

    • A novel channel access scheme for NOMA based IEEE 802.11 WLAN


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      In this letter, we propose a novel channel access scheme based on non-orthogonal multiple access (NOMA) for IEEE 802.11 to improve the throughput performance and connectivity of wireless local area network (WLAN). We consider a wireless network with NOMA at the physical layer and distributed coordination function (DCF) in the medium access control (MAC) layer. The proposed scheme allows the simultaneous transmission of multiple nodes using NOMA as well as reduces the number of contending nodes. In addition, we present a simple yet accurate analytical model for NOMA based IEEE 802.11 multi-rate WLAN. The analytical findings show that the aggregate throughput and connectivity are significantly improved compared with conventional IEEE 802.11multi-rate WLANs. The analytical results are corroborated with extensive simulation studies.

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