WSEAS TRANSACTIONS ON COMMUNICATIONS Issue 11. Volume 4, November 2005 ISSN 1109-2742 Priority to Low Moving Terminals in TETRA Networks E. DIMITRIADOU 1 , K. IOANNOU 1 , I. PANOUTSOPOULOS 1 , A. GARMPIS 2 and S. KOTSOPOULOS 1 1 Wireless Telecommunication Laboratory, Department of Electrical and Computer Engineering, University of Patras, Rion 26500, Patras GREECE 2 Department of Applied Informatics in Management & Economy, Technological Educational Institution of Messolonghi, Messolonghi, 30200 GREECE ioannou@ee.upatras.gr Abstract: - In this paper is presented a channel management scheme that gives priority to Low Moving Terminals in Tetra Networks. The proposed scheme is based on a two-layer cellular architecture. The lower layer is based on a microcellular solution, for absorbing the traffic loads of both the handoff and new calls of the Low Moving Terminals (LMT). The higher layer is based on a macro-cell umbrella solution, for absorbing the traffic load of the handoff and new calls of the Fast Moving Terminals (FMT). The simulation results show that assigning the optimum number of channels in each layer, the QoS of the LMT is optimized having the minimum negative effect on the QoS of the HMT. Key-Words: - Mobile communication, Tetra Network, Channel Assignment Scheme, Velocity 1 Introduction For decades, radio communication has been the solution for flexible and efficient communication in the field. Radio enables instant communication between two or more people simply by pressing a button. This push-to-talk feature and the ability of people to communicate in groups is fundamental for authority communication. In most Public Safety organisations around the world, communication is a hot item - in many countries old equipment must be renewed during the next few years. The change from conventional analogue to intelligent digital radio networks is a big one, involving both technical and financial complexity, especially for the users. One of the leading standards in digital radio is TETRA, an abbreviation of TErrestrial Trunked RAdio. It has been defined and approved by the European Telecommunications Standards Institute (ETSI) to be the only official European Standard for digital Professional Mobile Radio (PMR). Accordingly, TETRA is a global standard for radio communication in the same way that GSM is the mobile telephony standard. In their every day activities, public safety organisations need various kinds of communications services. TETRA offers both usual cellular services as well as professional radio services such as group communication, field workforce management services (dispatching) and efficient data services. TETRA is a unique combination of group voice communications, mobile telephony and mobile data services specifically designed for authority use. TETRA is a purpose built technology that offers public safety and security organisations major advantages over conventional radio systems to. It was developed to meet the needs of the most demanding professional radio users who need fast one-to-one and one-to-many radio communication using voice and data in their daily work. Users are typically public safety and security organisations such as police, fire and rescue forces. TETRA fulfils the needs of professional users and replaces old analogue and proprietary radio communication systems that no longer meet professional radio- communication needs. Commercial cellular services cannot provide the ultimate security needed by professional users. Security consists of several issues: Reliability 1228