Michael P Spratt

An overview of positioning by diffusion

Positioning by Diffusion is a method by which mobile and static devices can calculate their positions, by means of exchanging information over short range wireless links. It is intended for deployment within shopping malls, corporate buildings, theme parks, etc. The implementation is in software, and does not impose extra hardware requirements on mobile or static devices. Another objective is to minimize the system administration and deployment costs, by minimizing the required number of devices which have their position programmed into them – devices we define as Access Points – for the system to operate. The positioning system works instead by a seamless inter-working of the algorithm across Access Points, static devices which learn their position rather than having it pre-programmed, and mobile devices. Positioning by Diffusion is being adopted by the Bluetooth Local Positioning Working Group as its positioning algorithm.

IEEE 802.12 Demand Priority and Multimedia

This paper introduces the 100Base-VG LAN technology that is being standardised in the IEEE 802.12 committee. The network is designed as a low-cost 100Mb/s upgrade for IEEE-802.3 10Base-T and key features of the network are discussed such as its support for installed Category 3 cable and cascading to cover campus areas without bridges. The access protocol, Demand Priority, supports two priorities and the paper considers in some detail how this can be used to provide guaranteed bandwidth and delay services for emerging applications such as real-time multimedia.

A CSMA/CD compatible MAC for real-time transmissions based on varying collision intervals

Abstract This paper suggests a CSMA/CD compatible MAC protocol for real-time transmissions in a shared Home or Small Office Local Area Network. The new MAC is based on the distributed assignment of special TAG numbers to the stations transmitting real-time traffic. These TAG numbers determine a Round Robin order of transmissions among the real-time stations. They also help in resolving collisions among real time stations by setting the length of the Jam signal, transmitted in case of a collision, to be a function of the TAG number. In a collision the station with the highest TAG number, and so with the longest Jam, is persisting with its Jam transmission for the longest until all the other stations defer. Thus, the collision terminates and the longest persisting station can transmit its packet successfully. The new protocol enables stations implementing the IEEE 802.3 MAC standard to transmit on the same network with stations implementing the new protocol. After introducing the protocol, we compute an upper bound on the access delay that the protocol guarantees and prove the correctness of the distributed TAG assignment procedure. Finally, we simulate the protocol in a network consisting stations implementing the new protocol together with stations implementing the standard IEEE 802.3 MAC. We show that the access delays of the stations transmitting real-time traffic are indeed bounded as predicted.