Medium Access Control Technique Research Articles

Medium access control protocol for CDMA ad hoc networks

Recently, ad hoc networks have obtained a growing interest because of their advantages in many practical applications. One of the most critical points is the definition of an efficient medium access control (MAC) protocol that allows the transmission of packets generated by a node and routing of packets arriving from other nodes. A MAC technique is presented based on the code division multiple access (CDMA) scheme that adapts the used spreading factor to the network congestion in order to minimise the energy consumption and maximise the network throughput.

Uplink–downlink design issues for next generation satellite networks

AbstractNext Generation Mobile Systems will implement one's dream of anywhere, anytime communications. Providing global coverage and mobility, satellite systems will play an important role in order for this to be achieved. The design options of satellite systems include several choices. The basic ones are the choice of orbit, processing and switching, intersatellite links, and link layers technologies. In addition to the network architecture, the protocols must be developed for efficient use of the satellite radio resources. The most important protocol design issues concentrate on Medium Access Control (MAC) techniques, routing and traffic management. In this paper some of the special features of satellite systems are considered. Emphasis is given in MAC protocols design, as well as in research programmes that led to their development. Finally, an adaptive hybrid access scheme that combines CDMA technology and random access techniques is presented. This new scheme is called CDMA/PRMA and from the results obtained it is a very promising access technique for next generation satellite systems. Copyright © 2002 John Wiley & Sons, Ltd.

Performance analysis of the IEEE 802.11 distributed coordination function

The IEEE has standardized the 802.11 protocol for wireless local area networks. The primary medium access control (MAC) technique of 802.11 is called the distributed coordination function (DCF). The DCF is a carrier sense multiple access with collision avoidance (CSMA/CA) scheme with binary slotted exponential backoff. This paper provides a simple, but nevertheless extremely accurate, analytical model to compute the 802.11 DCF throughput, in the assumption of finite number of terminals and ideal channel conditions. The proposed analysis applies to both the packet transmission schemes employed by DCF, namely, the basic access and the RTS/CTS access mechanisms. In addition, it also applies to a combination of the two schemes, in which packets longer than a given threshold are transmitted according to the RTS/CTS mechanism. By means of the proposed model, we provide an extensive throughput performance evaluation of both access mechanisms of the 802.11 protocol.

On the performance of the IEC 61158 Fieldbus

The IEC 61158 Fieldbus protocol merges two well-established medium access control techniques based respectively on a centralized arbitration method and on a token-passing distributed scheme. The first method is used to handle real-time (cyclic) traffic, while the second one allows to share out fairly the bandwidth left free by the cyclic traffic. This paper analyzes the behaviour of an IEC 61158 network to study how the acyclic message exchanges are affected by the selection of some relevant protocol parameters. In particular, two working conditions are considered in the paper. First case, a steady state situation is analyzed where the asynchronous requests for the system bandwidth are equally shared among the different nodes. Second, a transient condition is considered where the asynchronous message queues are temporarily overloaded and the offered load is higher than the available system bandwidth.

Implementation of Segnet and its experimental performance

This paper describes the hardware implementation of Segnet, a bus network based on the CSMA/CD medium access control technique having dynamic segmentation capability. A six-station PC-based network was set up and its performance evaluated. The experimental results obtained are compared with the simulation results; excellent agreement is achieved. It is also found that Segnet performs better under clustered traffic environments and as the number of clusters increases. The performance of individual source-destination pairs is also investigated and the effect of varying packet length examined.