Current Issue : January - March Volume : 2013 Issue Number : 1 Articles : 5 Articles
In this paper, we present different types of technologies and their characteristics for underwater communication. With the world progressing with the speed of light, man has conquered the Earth, sky and now he has reached undersea to explore the world underneath. The underwater world presents us with many obstacles and complexities. The complexities include multipath fading, time variations, the motion of the water itself. The emerging technologies like Blue-Green Lasers are finding their ways to replace the conventional acoustic communication thus reducing their drawbacks....
In this article, we design and demonstrate a signaling architecture for multicast and broadcast services over a\r\nlaboratory-emulated worldwide interoperability for microwave access (WiMAX) network. WiMAX is a broadband\r\nwireless access technology which includes different quality of service levels. Currently, a significant research effort\r\nfocuses on data transmission optimization and mobility support for multicast and broadcast services. Our proposal\r\nis fully IP-based, and the relevant signaling architecture is modular in all its entities and extensible to other, non-\r\nWiMAX, IP access networks. We specifically address the non-trivial support of multicast services, which has been\r\ndemonstrated through a prototype implementation of our proposal for an Internet protocol television (IPTV)\r\nservice. This prototype has been implemented by using open source technologies and its signaling is orchestrated\r\nby a JAIN SLEE server. The results obtained show that the implemented system is scalable, can achieve both high\r\nsignaling throughput and low service latency, and has a signaling overhead lower than similar IMS-based solutions....
More and more devices are becoming wirelessly connected. Many of these devices are operating in crowded\r\nunlicensed bands, where different wireless technologies compete for the same spectrum. A typical example is the\r\nunlicensed ISM band at 2.4 GHz, which is used by IEEE 802.11bgn, IEEE 802.15.4, and IEEE 802.15.1, among others.\r\nEach of these technologies implements appropriate Media Access Control (MAC) mechanisms to avoid packet\r\ncollisions and optimize Quality of Service. Although different technologies use similar MAC mechanisms, they are\r\nnot always compatible. For example, all CSMA/CA-based technologies use Clear Channel Assessment (CCA) to\r\ndetect when the channel is free; however, in each case it is specifically designed to improve detection reliability of\r\nthe specific technology. Unfortunately, this approach decreases the detection probability of other technologies,\r\nincreasing the amount of cross-technology collisions. In this article, we introduce the concept of coexistence aware\r\nCCA (CACCA), which enables a node operating in one technology to backoff for other coexisting technologies as\r\nwell. As a proof of concept, we analyze the Packet Error Rate(PER) incurred by an IEEE 802.15.4 network in the\r\npresence of IEEE 802.11bg interference, and assess the PER reduction that is achieved by using CACCA....
In this article, we propose a novel loss recovery algorithm of transmission control protocol (TCP) using packet\r\ntransmission order, which shows a steady loss recovery ability even though packet loss rate increases. This leads to\r\na significant throughput increase of TCP with heavy packet loss. We have verified the performance increase of the\r\nnew TCP under various environments such as a wireless network, and multimedia transmission through simulation.\r\nMoreover, we implemented the proposed idea in Linux and conducted some experiments in a real environment.\r\nEven though the experiment results did not perfectly agree with the simulation results, we obtained a similar\r\nthroughput increase to that of the simulation....
Orthogonal frequency division multiple access (OFDMA) has been selected as the core physical layer access\r\nscheme for state-of-the-art and next-generation wireless communications standards. In these systems, scheduling\r\nand resource allocation algorithms, jointly assigning transmission data rates, bandwidth and power, become crucial\r\nto optimize the resource utilization while providing support to multimedia applications with heterogeneous quality\r\nof service (QoS) requirements. In this article, a unified framework for channeland queue-aware QoS-guaranteed\r\ncross-layer scheduling and resource allocation algorithms for heterogeneous multiservice OFDMA wireless networks\r\nis presented. The framework encompasses different types of traffic, uniform and continuous power allocation,\r\ndiscrete and continuous rate allocation, and protocols with different amounts of channel- and queue-awareness.\r\nSystem parameters and QoS requirements are projected into utility functions and the optimization problem is then\r\nformulated as a constrained utility maximization problem. Optimal solutions for this problem are obtained for the\r\nuniform power allocation schemes, and novel quasioptimal algorithms are proposed for the adaptive power\r\nallocation strategies. Remarkably, these techniques exhibit complexities that are linear in the number of resource\r\nunits and users. Simulation results demonstrate the validity and merits of the proposed cross-layer unified\r\napproach....
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