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MULTIDIMENSIONAL PRMA The PRMA protocol extended for operation on a hybrid CDMA/TDMA air interface is defined in the following. This extended version of PRMA is referred to as multidimensional PRMA or MD PRMA. First, the basic protocol suitable for frequency-division duplexing is described. Then, the implications of different approaches to time-division duplexing on the protocol operation will be discussed. Finally, the two investigated approaches to access control, namely load-based access control and backlog-based access control, will be introduced | 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 6 MULTIDIMENSIONAL PRMA The PRMA protocol extended for operation on a hybrid CDMA TDMA air interface is defined in the following. This extended version of PRMA is referred to as multidimensional PRMA or MD PRMA. First the basic protocol suitable for frequency-division duplexing is described. Then the implications of different approaches to time-division duplexing on the protocol operation will be discussed. Finally the two investigated approaches to access control namely load-based access control and backlog-based access control will be introduced. Before tackling the main issues of interest a little digression is required to discuss the terminology used in conjunction with the research efforts presented here or more precisely the names used in previous publications when referring to this PRMA-based protocol. A Word on Terminology The following comments are provided to avoid potential confusion when looking at some of our earlier publications since although the investigations documented in the next few chapters on MAC strategies are centred fundamentally on one protocol this protocol has evolved over time and so did the names we used when referring to it. Initially the protocol was referred to as the Joint CDMA PRMA protocol in References 28-31 where random coding was considered single time-slots could carry several packets but individual code-slots were not discerned. In References 48 and 49 we suggested a protocol for operation on a rectangular grid of resource units where the basic unit would normally be a code-time-slot but it could also be a frequency-time-slot if the protocol were to be used with a hybrid FDMA TDMA multiple access scheme. Apart from the different channel models considered as discussed in detail in the previous chapter and a different approach to channel .