N-gram based language models are very popular and extensively used statistical methods for solving various natural language processing problems including grammar checking. Smoothing is one of the most effective techniques used in building a language model to deal with data sparsity problem. Kneser-Ney is one of the most prominently used and successful smoothing technique for language modelling. In our previous work, we presented a Witten-Bell smoothing based language modelling technique for checking grammatical correctness of Bangla sentences which showed promising results outperforming previous methods. In this work, we proposed an improved method using Kneser-Ney smoothing based n-gram language model for grammar checking and performed a comparative performance analysis between Kneser-Ney and Witten-Bell smoothing techniques for the same purpose. We also provided an improved technique for calculating the optimum threshold which further enhanced the the results. Our experimental results show that, Kneser-Ney outperforms Witten-Bell as a smoothing technique when used with n-gram LMs for checking grammatical correctness of Bangla sentences.
The IEEE 802.11ax (Wi-Fi 6) and IEEE 802.11be (Wi-Fi 7) adopt the OFDMA technology to provide high-speed and uninterrupted communications in the dense network. Until the advent of IEEE 802.11ax standard, Wireless LAN (WLAN) predominantly uses the Random Access (RA) mechanism to access the network. IEEE 802.11ax and IEEE 802.11be (proposed) provide another access mechanism for WLAN (i.e., Wi-Fi), which is known as Scheduled Access (SA). This mechanism utilizes the OFDMA technology to provide highspeed and smooth communications in congested areas. By the way, the performance of the OFDMA based wireless LAN largely depends on the scheduling protocol. Many researchers propose RA and SA protocols independently, which do not consider the simultaneous implementation of both mechanisms. This paper proposes a Proportional Resource Scheduling (PRS) scheme for the OFDMA-based wireless LAN that simultaneously implements RA and SA mechanisms for data transmission. We design two algorithms for the resource scheduling for the PRS protocol. Algorithm 1 provides the initial scheduling information, which is received by Algorithm 2 as the input. After performing revision, Algorithm 2 provides the final scheduling information to the access point. The PRS distributes the channel resources proportionally to the stations according to their available loads. Thus, it utilizes the resources efficiently and increases the throughput and fairness in accessing the channel. We construct analytical models both for the SA and RA mechanisms and conduct rigorous simulations to measure the efficiency of the PRS protocol. The analyses validate the robustness of the proposed protocol in throughput, goodput, fairness, and retransmissions. The main contribution of the proposed protocol is that it provides a framework for simultaneous implementation of RA and SA mechanisms for the future wireless LAN.
Two types of MAC mechanisms i.e., random access and reservation could be adopted for OFDMA-based wireless LANs. Reservation-based MAC is more appropriate than random access MAC for connection-oriented applications as connectionoriented applications provide strict requirements of traffic demands. On the other hand, random access mechanism is a preferred choice for bursty traffic i.e., data packets which have no fixed pattern and rate. As OFDMA-based wireless networks promise to support heterogeneous applications, researchers assume that applications with and without traffic specifications will coexist. Eventually, OFDMA-based wireless LAN will deploy hybrid MAC mechanisms inheriting traits from random access and reservation. In this article, we design a new MAC protocol which employs one kind of hybrid mechanism that will provide high throughput of data as well as maintains improved fair access policy to the medium among the terminals. The protocol works in two steps, where at step 1 sub-channels are approximately evenly distributed to the terminals and at step 2 terminals within in a subchannel will contend for medium randomly if the total number of terminals of the system is larger than the number of sub-channels. The details of the protocol is illustrated in the paper and we analyze the performance of our OFDMA-based multi-channel hybrid protocol using comprehensive computer simulations. Simulation results validate that our proposed protocol is more robust than the conventional CSMA/CA protocol in terms of throughput, collision reduction and fair access. In addition, the theoretical analysis of the saturation throughput of the protocol is also evaluated using an existing comprehensive model.
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