Delay distributions of slotted ALOHA and CSMA

We derive the closed-form delay distributions of slotted ALOHA and nonpersistent carrier sense multiple access (CSMA) protocols under steady state. Three retransmission policies are analyzed. We find that under a binary exponential backoff retransmission policy, finite average delay and finite delay variance can be guaranteed for G<2S and G<4S/3, respectively, where G is the channel traffic and S is the channel throughput. As an example, in slotted ALOHA, S<(ln2)/2 and S<3(ln4-ln3)/4 are the operating ranges for finite first and second delay moments. In addition, the blocking probability and delay performance as a function of r/sub max/ (maximum number of retransmissions allowed) is also derived

Cooperative Jamming in Wireless Networks - Turning Attacks into Privacy Protection

Generally, collisions between packets are undesired in wireless networks. We design this scheme, Cooperative Jamming in Wireless Networks (CJWN), to make use of collision to protect secret DATA packets from being sniffed by a nearby eavesdropper. We are intending to greatly increase the Packet Error Rate (PER) at the eavesdropper when the PER at the receiver is maintained at an acceptable level. This scheme is not intended to completely take the place of various encryption/decryption schemes which are working based on successfully received packets. Adding CJWN to the popular CSMA/CA adopted in IEEE 802.11 will add more security even the key for encryption/decryption is already exposed. Because the overhead of CJWN is very big, we do not suggest using it on every transmission. When some secret packets have a high requirement of confidentiality, CJWN is worth trying at the cost of throughput performance and power

A Simulation Study of Medium Access Control Protocols of Wireless Networks

A thesis presented to the faculty of the College of Science and Technology at Morehead State University in partial fulfillment of the requirements for the Degree of Master of Science by Rohan Uddhav Patel on May 8, 2008

Construction of a LAN for the Turkish Naval Base

This research discusses the design issues and fundamental techniques of a local area network (LAN). It then constructs and chooses a LAN for the Turkish Naval Base. Three ships and headquarters will have their own PCs, and they need to rapidly and accurately exchange information among them. The thesis examines the issues for designing a LAN and discusses four fundamental technical issues. These are (1) topology, (2) transmission media, (3) access control, and (4) transmission techniques. Finally we introduce PC LANs, and select and recommend a PC LAN broadband system with coaxial cable. Theses. (fr)http://archive.org/details/constructionofla00oylaTurkish Navy author

A particle system in interaction with a rapidly varying environment: Mean field limits and applications

We study an interacting particle system whose dynamics depends on an interacting random environment. As the number of particles grows large, the transition rate of the particles slows down (perhaps because they share a common resource of fixed capacity). The transition rate of a particle is determined by its state, by the empirical distribution of all the particles and by a rapidly varying environment. The transitions of the environment are determined by the empirical distribution of the particles. We prove the propagation of chaos on the path space of the particles and establish that the limiting trajectory of the empirical measure of the states of the particles satisfies a deterministic differential equation. This deterministic differential equation involves the time averages of the environment process. We apply our results to analyze the performance of communication networks where users access some resources using random distributed multi-access algorithms. For these networks, we show that the environment process corresponds to a process describing the number of clients in a certain loss network, which allows us provide simple and explicit expressions of the network performance.Comment: 31 pages, 2 figure

Efficient collision resolution protocol for highly populated wireless networks

An efficient Medium access control (MAC) protocol is an important part of every wireless system. It prevents multiple devices from accessing the channel at the same time by defining rules for orderly access. Due to the fact that wireless networks have received enormous popularity in the last 10 - 15 years, number of users in these networks increased dramatically. Thus, support of large user population for modern MAC protocol is not an option anymore but a necessity, especially for dense Wireless Sensor Networks (WSNs). This work proposes a novel random MAC protocol for wireless networks named BCSMA/CA that can provide high channel throughput for very large number of users. The main idea of the protocol is based on the absence of backoff intervals where the channel is idle and using this time for active collision resolving. By presented analytical model and means of simulation, performance of the proposed protocol itself as well as in the framework of 802.11 Distributed Coordination Function (DCF) is explored. Corresponding comparison shows that 802.11 under BCSMA/CA is more suitable for applications where number of users is large compared to the traditional DCF approach

Collision-free Time Slot Reuse in Multi-hop Wireless Sensor Networks

To ensure a long-lived network of wireless communicating sensors, we are in need of a medium access control protocol that is able to prevent energy-wasting effects like idle listening, hidden terminal problem or collision of packets. Schedule-based medium access protocols are in general robust against these effects, but require a mechanism to establish a non-conflicting schedule. In this paper, we present such a mechanism which allows wireless sensors to choose a time interval for transmission, which is not interfering or causing collisions with other transmissions. In our solution, we do not assume any hierarchical organization in the network and all operation is localized. We empirically show that our localized algorithm is successful within a factor 2 of the minimum necessary time slots in random networks; well in range of the expected (worst case) factor 3-approximation of known first-fit algorithms. Our algorithm assures similar minimum distance between simultaneous transmissions as CSMA(/CD)-based approaches