The spectrum scarcity can be resolved using the paradigm of Cognitive Radio Networks (CRNs). In CRNs, the Secondary Users (SUs) having no spectrum licenses can benefit from spectrum opportunities spatiotemporally left over by Primary Users (PUs) if these SUs do not make any harmful interference to the PUs. Due to the ease of deployment, the ad hoc CRNs are expected to attract the future applications of the secondary spectrum usage [1]. However, the new challenges in ad hoc CRNs should be tackled first to visualize the new revolution of this kind of networks. The spectrum availability variation over time and locations creates a unique trait of the CRNs. This key trait poses great challenges in different aspects in the basic design of ad hoc CRNs. One of the major challenges is how the SUs can exchange their control signaling to coordinate their spectrum sensing, spectrum allocation and access, and traffic routing. The intuitive way is to have a Common Control Channel (CCC), which can be in-band or out-of-band channel. In the literature, there are different approaches of choosing the CCC, and the readers may refer to [1] for more details. However, the spectrum heterogeneity seen by the SUs in multi-hop ad hoc CRNs makes using a CCC an embarrassing challenge. Network clustering can be used to overcome the spectrum heterogeneity by grouping the nearby users that may experience the same activities of the same set of PUs; moreover, the clustering can help to reduce the signaling overhead required for operating the network and maintaining its connectivity. Almost all the existing clustering approaches in CRNs aim to avoid using a global CCC and instead rely on in-band CCCs to coordinate their processes, and form clusters... ... middle of paper ... ...stems that are expected to cover larger area of communications than the SUs, so each group of nearby SUs is expected to be almost under the coverage of the same set of PUs. The nearby SUs are clustered with 1-hop from a central user based on the geographical locations of the users and their time occurrence orders, so each cluster covers a geographical part of the whole communication region. The SUs in each cluster cooperate to sense the spectrum in their vicinity and then access the available channels using a MAC framework. As shown in Fig. 1, each cluster consists of a Cluster Head (CH) user that initiates the cluster, Cluster Member (CM) users, and Cluster Gateway (CG) users that join the cluster with its neighboring clusters. We assume that the SUs rarely move, and when they do, they move slowly, so the topology of the network is dynamic with stable status.
4. When a CS is not followed by a UCS, the subsequent fading of a CR is called:
Research suggests that managers and employees in the wireless industry have faced tough challenges in their daily work. Managers have had the difficult job of crafting appropriate business strategies and human resource practices in the face of technological uncertainty, volatile demand, and heightened price competition in markets plagued by overcapacity (Batts, Colvin, Katz & Keefe (2005). This paper will examine the challenges facing the wireless industry the near future and recommend ways in which my new organization, Twenty1Wirless, can meet those challenges. First we will discuss the challenges we are facing as an organization. Next, we will explore the opportunities Twenty1 Wireless has to overcome these challenges. Finally, we will discuss
“The Spanning Tree Protocol (STP) is an older network protocol that ensures a loop-free topology for any bridged Ethernet local area network. The basic function of STP is to prevent bridge loops and the broadcast radiation that results from them.”
J. A. Gutierrez ,M. Naeve , E. Callaway , M. Bourgeois ,V. Mitter and B. Heile "IEEE 802.15.4:adeveloping standard for low-power low-cost wireless personal area networks", IEEE Network, vol. 15, no. 5, pp.12 -19 2001
Johnson, D., Maltz, D. (1996). Dynamic Source Routing in Ad-hoc Wireless network. Print ISBN: 0 79239697 0
Wireless Local Area Network (WLAN) is one of the most successful technologies in IEEE 802.XX standards family. WLAN provides free connectivity, mobility, and flexibility with a relatively low cost for users. The widespread use of WLAN technology in streaming videos and voice applications stimulated high bandwidth capacity for WLANs. Recently IEEE has announced latest WLAN standard 802.11ac. For 802.11ac to be effective, it requires minimum 80 MHz wide channel with optionally up to 160 MHz. The increase in bandwidth leads to problems like OBSS. OBSS problem occur when two or more BSSs operate in same channel and are close to hear each other. This is an undesirable situation where two or more BSSs compete for channel access and increase contention which ultimately degrades performance/efficiency of the WLAN system [1]. The problem was not critical with 802.11a/b/g/n where the channel bandwidth was reasonable. ...
8) Ian F. Akyildiz, Ismail H. Kasimoglu, “Ad Hoc Networks’’, Wireless sensor and actor networks: Research Challenges, Georgia Institute of Technology, USA, May-2004.
Analysis of the Environment of the Mobile Network System Executive Summary 3 Glossary of Abbreviations 4 Introduction 5 Recent History
An Open Shortest Path First (OSPF) protocol is the most used interior gateway protocol and computation intensive protocol where energy consumption in Internet Protocol (IP) networks is the main concern. The energy in an IP network can be saved by allowing a subset of IP router interfaces on sleep mode setting during the low traffic hours through the model of “move” by dint of an Energy Aware Routing (EAR) strategy, which is completely compatible with OSPF and is based on the “Shortest Path Tree (SPT) exportation” techinque or “Dijkstra's Algorithm”. In case of heavy traffic hours, the EAR strategy is not usable and may cause denial of service. The strategy implemented can help a network operator to control the network performance and allow a smoothed QoS degradation. This performance evaluation study permits to save about 30% of network links with a insignificant rise of link loads and network path lengths.
Wireless local area networks (WLANs) have the potential to improve the flexibility, productivity, and the quality of work life of an enterprise (Sage Research Staff, 2001). Berean Institute is a typical two year college with about a staff of sixty eight employees and 250 students per semester. Berean teaches cosmetology, barbering and the latest software and hardware technology, which is located in Philadelphia, Pennsylvania. Berean currently has two locations in the Philadelphia area and using a Local Area Network (LAN).
Star topology networks require more cabling than bus, but the tradeoff comes in the form of a more solid network topology. A break in the network media will only affect a single node, since every node has a dedicated connection to the central device; a hub or switch. This also makes the central device a Single Point of Failure (SPOF). Redundant or failover switches are often used to eliminate the SPOF in a star LAN.
Print. The. Gordon A. Gow, and Richard K. Smith. Mobile and wireless communications: an introduction, McGraw-Hill International, 2006. Print.
When looking at wireless communications, there are many standards to discuss as there are so many types all used for different purposes. I am going to talk about a range of communications used for different ways to communicate; for example Bluetooth can be used to send files between mobile devices. Cellular broadband, which is used on mobile phones and tablets to be able to access the internet while out of reach of a Wi-Fi signal. I will also look at satellite, which can be used to provide Internet to remote areas and Wi-Fi which is widely used to access Internet and local networks without having to have a physical connection. I will finally assess WiMAX (Worldwide Interoperability for Microwave Access) that is used to provide Internet over a large distance.
Thus, I would like to discuss all the above mentioned topics as a part of my survey report on IEEE 802.11n with the help of the references mentioned above.
In today’s world there is an increasing demand for wireless connectivity. But with the present technology there is an inefficient use of the available. A large part of the spectrum is underutilised as shown in Fig 1. Due to the inefficient use of spectrum by the current spectrum allocation methods there is a need for developing new methods which aids in efficient use of available spectrum.