Wireless local area networks (WLAN) are expected to be a major growth facto
r for communication networks in the upcoming years. They an expected to pro
vide a transparent connection for mobile hosts to communicate with other mo
bile hosts, and wired hosts on the wired LAN and broadband networks. Recent
ly there have been two WLAN projects, which are undergoing standardization
process: the IEEE 802.11 and the ETSI HIPERLAN. Most of the existing study
of the two MAC protocols focused on simulation results, and none of them ha
s formally analyzed the hidden-terminal effect, which is both crucial and u
navoidable in wireless/mobile environment. In the first part of this paper,
we formally analyze the hidden-terminal effect on HIPERLAN. Through mathem
atical analysis, we formulate network throughput under hidden-terminal infl
uence in terms of the original (clear-channel) throughput, hidden-terminal
probability, and other protocol parameters. We show that when hidden probab
ility is greater than zero, the achievable throughput is reduced by more th
an the percentage of hidden probability.
In the second part of the paper, we evaluate and compare the two WLAN MAC p
rotocols by simulation on the effect of hidden terminals on: (1) network th
roughput; (2) real-time voice delay; and (3) number of voice and data stati
ons supported while guaranteeing delay for voice. We also evaluate how well
the two MAC protocols support real-time traffic while considering the effe
cts of frame size and other network parameters, and measure: (1) the distri
bution of voice delay; (2) number of voice and data stations supported whil
e guaranteeing their quality of service. We found that, comparing with IEEE
802.11, HIPERLAN provides real-time packet voice traffic with shorter dela
y, and at the same time provides the non-real-time packet data with higher
bandwidth.
We believe that the formal analysis presented in this work would provide a
significant reference for wireless/mobile network community; the comparison
study of the two MAC protocols would also aid the future enhancement of WL
AN MAC protocols. (C) 2000 Elsevier Science B.V. All rights reserved.