Recently, several MAC protocols using directional antennas, typically referred to as directional MAC protocols, have been proposed for wireless ad hoc networks. Although directional transmissions are expected to provide significant improvements, directional MAC protocols introduce new kinds of problems. One such problem is deafness. Deafness is caused when a transmitter repeatedly attempts to communicate with its intended receiver, but it fails because the receiver has its beam pointed towards a direction away from the transmitter. This paper proposes RI-DMAC (Receiver-Initiated Directional MAC) to address the issue of deafness in directional MAC protocols. RI-DMAC is a combination of sender-initiated and receiver-initiated operations.The sender-initiated mode is the default mode and the receiverinitiated mode is triggered when the transmitter experiences deafness. In RI-DMAC, each node maintains a polling table and polls a potential deafness node using the RTR (Ready To Receive) frame after the completion of every dialog. The experimental results show that RI-DMAC improves throughput and fairness performance compared to existing directional MAC protocols.

No abstract

To examine the applicability of hematite ore to the ironmaking by microwave heating, the carbothermic reduction of hematite powders by microwave heating were elucidated using the gas analysis of exhausted gas, and were compared with that of magnetite powders. The temperature of the hematite -graphite mixed powders moderately increases at the beginning, and then, starts to increase abruptly at around 400°C owing to the thermal runaway of Fe2O3. Once the reduction reaction starts to take place, the reduction reaction rate of hematite is even faster than that of magnetite, which is the same behavior as that observed by conventional heating. Hematite ore could be a possible raw material for microwave ironmaking: When hematite ore is utilized, the ore should be preheated up to around 400°C prior to the feeding to a microwave furnace.

No abstract

Directional antennas are expected to provide significant improvements over omni-directional antennas in wireless ad hoc networks. Directional MAC protocols, however, introduce new kinds of problems arising from directivity. One major problem is deafness, caused by a lack of state information from neighbor nodes (i.e., idle or busy). This paper proposes DMAC/DA (Directional MAC with Deafness Avoidance) to overcome the deafness problem. In DMAC/DA, WTS (Wait To Send) frames are transmitted by the transmitter and the receiver after the successful exchange of directional RTS (Request To Send) and CTS (Clear To Send) to notify the on-going communication to potential transmitters that may experience deafness. Furthermore, DMAC/DA is enhanced by the next packet notification to distinguish transmitters from neighbors. We evaluate our protocol through extensive simulation study with different values of parameters such as the number of flows, data size and beamwidth. The experimental results show that DMAC/DA outperforms existing directional MAC protocols, such as DMAC (Directional MAC) and MDA (MAC protocol for Directional Antennas), in terms of throughput, RTS failure ratio, and control overhead.

No abstract

Full-duplex (FD) wireless communication is evolving into a practical technique, and many studies are being conducting in this area, especially regarding the physical layer. However, to exploit FD benefit successfully, efficient medium access control (MAC) protocols are crucial as well as physical layer advances. Numerous FD-MAC protocols have been proposed, but these MAC protocols cannot address all the issues encountered in this area. In addition, many half-duplex (HD) capable devices are present in existing wireless local area networks (WLANs), so there is an urgent need to integrate FD clients and HD clients in the same WLAN. We refer to this type of WLAN as a heterogeneous WLAN (Het-WLAN). In this paper, we propose an FD-MAC for Het-WLAN, which considers all possible types of FD transmissions. Our proposed FD-MAC protocol suppresses inter-user interference. Simulation results demonstrated that a significant throughput gain (about 96%) could be achieved by using our proposed FD-MAC compared with traditional HD communications. Moreover, our proposed MAC obtained better performance (average throughput gain of about 11%) compared with another existing FD-MAC design. In addition, probability analysis suggested that the total probability of FD transmissions increased rapidly as the WLAN approached saturation conditions.

No abstract