MULTIPLE ACCESS IN CELLULAR COMMUNICATION SYSTEMS To examine the problem of multiple access in cellular communications, first the relevant OSI layers need to be identified, which is not necessarily straightforward. A split into basic multiple access schemes such as CDMA, TDMA, and FDMA, associated with the physical layer, and multiple access protocols, situated at the medium access control layer, is adopted here. After a discussion of basic multiple access schemes, approaches chosen for medium access control in 2G cellular communication systems are briefly reviewed | Multiple Access Protocols for Mobile Communications GPRS UMTS and Beyond Alex Brand Hamid Aghvami Copyright 2002 John Wiley Sons Ltd ISBNs 0-471-49877-7 Hardback 0-470-84622-4 Electronic 3 MULTIPLE ACCESS IN CELLULAR COMMUNICATION SYSTEMS To examine the problem of multiple access in cellular communications first the relevant OSI layers need to be identified which is not necessarily straightforward. A split into basic multiple access schemes such as CDMA TDMA and FDMA associated with the physical layer and multiple access protocols situated at the medium access control layer is adopted here. After a discussion of basic multiple access schemes approaches chosen for medium access control in 2G cellular communication systems are briefly reviewed. The main effort will be invested in the identification of medium access control strategies suitable for systems that serve a substantial amount of packet-data users starting with systems such as GPRS but mainly focussing on 3G and beyond. It was pointed out in the introductory chapter that in the specific case of CDMA systems certain types of packet traffic might be best served on dedicated channels. We will briefly reconsider this issue here but defer a more detailed discussion on this topic to later chapters. Here the main focus is on multiple access protocols for common or shared channels. A case is made for reservation ALOHA-based protocols. As a representative of this family of protocols PRMA is considered in more detail and possible enhancements to PRMA are discussed leading to the identification of design options available in the wider reservation ALOHA framework. Appropriate design choices are made and an outline is provided of the extent to which they will be investigated in subsequent chapters. Multiple Access and the OSI Layers A company wishing to operate a licensed cellular communications system will normally have to obtain from a national regulator through a beauty contest or an auction for instance a .
