A modified contention resolution algorithm for W-CDMA

The emergence of wireless and personal communications has brought random access protocols for packet radio networks back to the research fore fronts. Most of the protocols are based on ALOHA protocol. Unfortunately this protocol is inherently unstable and requires sophisticated schemes to stabilize it. Another class of random access schemes, called limited sensing or stack algorithms, has been proposed that is stable and allows for the dynamic incorporation of new stations into the network. Indeed, after the second generation networks supporting voice service only, the third generation systems, UMTS (Universal Mobile Telecommunication System), should offer more services with quality. We analyze the possibility to apply the tree random access protocol for the W-CDMA (wideband-code division multiple access) part in the UTRA (UMTS Terrestrial Radio Access) radio interface proposition. The analytical model uses a modified version of the tree protocol which can be represented by a simple Geom/G/1 queue. We analyze this simple Geom/G/1 queue to predict the performance of the new random access protocol. It Is found that random access procedure is very stable and has higher channel capacity and lower access delay than the conventional slotted ALOHA access. It was also inferred that the protocol is insensitive to the way in which the tree runs, either breath first search or depth first search, thus giving the implementation flexibility. Also, simulation results are presented and show the predominance of this protocol compared with the conventional tree access mechanisms.