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The IEEE 802.11 MAC protocols have been implemented in many wireless ad hoc and infrastructure networks. Most of the IEEE 802.11-based networks adopt a one-hop transmission mechanism (the source and destination communicate using a direct link). While this strategy is simple, it degrades network performance as it limits the number of data transmissions that can concurrently take place. The performance of IEEE 802.11 MAC in terms of delay and overall achieved throughput can be improved when the overall transmission time for each data transmission from the access point (AP) to any node in the network is minimized. Occupying the time-frequency resources for a shorter time period results in more available resources for other potential downlink transmissions to take place. In this work, we present a modified MAC protocol for IEEE 802.11 infrastructure-based networks with device-to-device transmission strategy. The main goal of our proposed protocol is to minimize the transmission time for individual downlink transmissions while maximizing the utilization of network resources by using D2D multi-hop transmissions, thereby improving the overall achieved throughput. In our proposed mechanism, the AP selects the multi-hop path that requires the minimum transmission time to deliver the data packets to destination. This path is selected even though the direct path exists. Compared to the IEEE 802.11 standard, simulation results show significant performance improvements in terms of throughput and fairness. [ABSTRACT FROM AUTHOR]

Summary: Wireless sensors are considered the key elements in enabling efficient Internet of Things (IoT) networking and services. One of the key objectives in designing a WSN is increasing network lifetime by reducing the overall network energy consumption. To achieve this, several techniques have been proposed to extend the network lifetime, such as clustering. Clustering divides the network into several clusters, each with its own member nodes and a cluster‐head (CH) node. In this paper, a novel clustering mechanism is developed with the objective of extending network lifetime through load balancing in wireless sensor networks (WSNs). This is achieved by electing a new node to a provides specific tasks in the WSN to decrease energy consumption and enhance network lifetime. This node is called a relay node that is responsible of delivering the received data packets from the CHs, and then forwards them to the central node (sink). Unlike previous clustering schemes, the proposed algorithm consists of three main processes: CH selection, relay node selection, and medium access control processes. These processes depend on energy level and user's distributions. The performance of the proposed algorithm is investigated through simulation experiments in terms of network lifetime under various network parameters. The results reveal that the proposed mechanism significantly enhances network lifetime compared to previously proposed algorithms. [ABSTRACT FROM AUTHOR]

Cognitive radio (CR) is a new intelligent wireless technology that aims at improving spectrum utilization by allowing opportunistic access to the underutilized licensed spectrum. Wireless CR operating environment is typically characterized by its unreliable and unpredictable channel conditions and time availability due to fading and the randomness of primary radio (PR) activities. In such environment, packet fragmentation is needed to enhance the probability of success/packet delivery and reduce the needed number of packet re-transmission attempts. Specifically, the quality and availability of the PR channels along with the data packet size should be considered when designing communication protocols for CR networks (CRNs) such that the packet success probability is improved. Based on the quality and availability of the PR channels, an optimal-packet size metric is derived, which is defined as the packet size that can be transmitted over a selected channel while guarantying a predefined probability of success. In this paper, we propose three fragmentation-based channel assignment algorithms: fixed-fragment size algorithm, first-fit algorithm and near-exact fit algorithm. The first algorithm divides the packet equally over the selected channels while the other algorithms use variable fragment size. The main objectives of the algorithms are to enhance network throughput, decrease the number of dropped packets and reduce the average number of retransmission attempts. This preserves more channels for potential future CR transmissions, resulting in higher network throughput with less energy consumption. Simulation results show that the proposed algorithms significantly outperform existing CRN channel assignment algorithms with no fragmentation. [ABSTRACT FROM AUTHOR]