Search

As a last resort for radio frequency communication, Terahertz bands (0.1-10 THz) are targeted thanks to their ability to provide ultra-wide bandwidth satisfying varieties of emerging applications. However, the waves propagating at THz frequencies suffer from high losses due to absorption in air molecules which forces their use into short-range links. We propose a multi-hop system to extend the range of THz links with the aid of multiple passive reconfigurable intelligent surfaces (RIS). In contrast with existing literature, we address the challenge of the over-determined system of equations arising from optimizing the phases of cascaded RISs taking into account the practical case of highly directional antennas and spatially correlated channels in THz bands. We propose an efficient method to jointly optimize the phases induced by the RISs in order to maximize the power at the receiver side Scopus

The need for energy-efficient routing and data gathering protocols in large-scale environments becomes very challenging. Hierarchical routing in WSNs is a very important topic. It has been widely investigated relative to energy efficiency based routing protocols. LEACH (Low Energy Adaptive Clustering Hierarchy algorithm) is the pioneering cluster routing protocol in WSNs. However, it is not suitable for large scale network and wireless channel conditions are ignored during packet forwarding. To address this issue, we proposed a novel multi-hop clustering cross layer protocol based on LEACH. It considers both the SNR of different links and the residual energy of sensor nodes. Simulation results in terms of the average energy consumption, the network lifetime and the Packet Delivery Ratio show clearly the outperformance of the proposed algorithm versus the conventional LEACH.

This paper proposes an optimal hops-based adaptive clustering algorithm (OHACA). The algorithm sets an energy selection threshold before the cluster forms so that the nodes with less energy are more likely to go to sleep immediately. In setup phase, OHACA introduces an adaptive mechanism to adjust cluster head and load balance. And the optimal distance theory is applied to discover the practical optimal routing path to minimize the total energy for transmission. Simulation results show that OHACA prolongs the life of network, improves utilizing rate and transmits more data because of energy balance.

Wireless ad hoc nodes are freely and dynamically self-organize in communicating with others. Each node can act as host or router. However it actually depends on the capability of nodes in terms of its current power level, signal strength, number of hops, routing protocol, interference and others. In this research, a study was conducted to observe the effect of hops count over different network topologies that contribute to TCP Congestion Control performance degradation. To achieve this objective, a simulation using NS-2 with different topologies have been evaluated. The comparative analysis has been discussed based on standard observation metrics: throughput, delay and packet loss ratio. As a result, there is a relationship between types of topology and hops counts towards the performance of ad hoc network. In future, the extension study will be carried out to investigate the effect of different error rate and background traffic over same topologies., {"references":["Samal, C.K., TCP Performance through Simulation and Testbed in\nMulti-Hop Mobile Ad hoc Network. International Journal of\nComputer Networks & Communications (IJCNC) 2010. 2 (4): p.\n109-124.","Leung, K.C. and V.O.K. Li, Transmission control protocol (TCP) in\nwireless networks: issues, approaches, and challenges.\nCommunications Surveys & Tutorials, IEEE, 2006. 8(4): p. 64-79.","Paxson, V., End-to-end internet packet dynamics. IEEE/ACM\nTransactions on Networking (TON), 1999. 7(3): p. 277-292.","Jain, R., Congestion control in computer networks: issues and\ntrends. Network, IEEE, 1990. 4(3): p. 24-30.","Xu, K., Y. Tian, and N. Ansari, TCP-Jersey for wireless IP\ncommunications. Selected Areas in Communications, IEEE Journal\non, 2004. 22(4): p. 747-756.","Jindal, A. and K. Psounis, Wireless contention in mobile multi-hop\nnetworks. 2007, Citeseer.","Chen, K., Y. Xue, and K. Nahrstedt. On setting TCP's congestion\nwindow limit in mobile ad hoc networks. 2003: IEEE.","Floyd, S. and V. Paxson, Difficulties in simulating the internet.\nIEEE/ACM Transactions on Networking (TON), 2001. 9(4): p. 392-\n403.","Gerla, M., K. Tang, and R. Bagrodia. TCP performance in wireless\nmulti-hop networks. 1999: IEEE.\n[10] Jacobson, V. Congestion avoidance and control. 1988: ACM.\n[11] Li, T. and D.J. Leith, Buffer sizing for TCP flows in 802.11 e\nWLANs. Communications Letters, IEEE, 2008. 12(3): p. 216-218.\n[12] Ali, M.M., A.K.M.S. Alam, and M.S. Sarker, TCP Performance\nEnhancement in Wireless Mobile Ad Hoc Networks. International\nJournal, 2011. 1.\n[13] Low, S.H., F. Paganini, and J.C. Doyle, Internet congestion control.\nControl Systems Magazine, IEEE, 2002. 22(1): p. 28-43.\n[14] Postel, J., RFC 793: Transmission control protocol. 1981,\nSeptember.\n[15] Aaron, A. and S. Tsao, Techniques to improve TCP over wireless\nlinks. Final Report, EE. 359.\n[16] Ho, C.Y., Y.C. Chen, and Y.C. Chan, Fast retransmit and fast\nrecovery schemes of transport protocols: A survey and taxonomy.\nComputer Networks, 2008. 52(6): p. 1308-1327.\n[17] Floyd, S. and T. Henderson, The NewReno modification to TCP's\nfast recovery algorithm. 1999.\n[18] Prabakaran, M., A. Mahasenan, and A. Kumar. Analysis and\nenhancement of TCP performance over an IEEE 802.11 multi-hop\nwireless network: single session case. 2005: IEEE.\n[19] Al Hanbali, A., E. Altman, and P. Nain, A survey of TCP over ad hoc\nnetworks. IEEE Communications Surveys & Tutorials, 2005. 7(3): p.\n22-36.\n[20] Hallani, H. and S. Shahrestani, Improving the Performance of\nWireless Ad-hoc Networks: Accounting for the Behavior of Selfish\nNodes. Communications, 2011. 2011.\n[21] Gupta, S., C.K. Nagpal, and C. Singla, Impact of Selfish Node\nConcentration in MANETs. International Journal, 2011. 3.\n[22] Fu, Z., et al. The impact of multihop wireless channel on TCP\nthroughput and loss. 2003: IEEE.\n[23] Fu, Z., X. Meng, and S. Lu. How bad TCP can perform in mobile ad\nhoc networks. 2002: IEEE.\n[24] Information Sciences Institute, The NS-2 simulator,\nwww.isi.edu/nsnam/ns.\n[25] Breslau, L., et al., Advances in network simulation. Computer, 2000.\n33(5): p. 59-67.\n[26] Habbal, A.M.M. and S. Hassan. Loss Detection and Recovery\nTechniques for TCP in Mobile Ad Hoc Network. 2010: IEEE.\n[27] Nahm, K., A. Helmy, and C.C.J. Kuo, Cross-layer interaction of\nTCP and ad hoc routing protocols in multihop IEEE 802.11\nnetworks. IEEE Transactions on Mobile Computing, 2007: p. 458-\n469.\n[28] Ikeda, M., et al. Mobility effects of wireless multi-hop networks in\nindoor scenarios. 2010: IEEE."]}