Telecommun Syst (2013) 52:2599–2609
DOI 10.1007/s11235-011-9600-7
On the optimization of the contention resolution mechanism
for IEEE 802.16 networks
Jesús Delicado · Francisco M. Delicado ·
Luis Orozco-Barbosa
Published online: 24 August 2011
© Springer Science+Business Media, LLC 2011
Abstract The IEEE 802.16 standard defines a contention
bandwidth request mechanism offering QoS-aware broad-
band access through a wireless medium. According to the
standard, the Base Station (BS) is responsible for granting
the requests issued by the Subscriber Stations (SSs). The
SSs communicate their requests to the BS by placing their
requests into the uplink subframe, using the contention pe-
riod defined within the subframe for this purpose. The size
of contention period, defined in minislots, is fixed by the BS
on a frame by frame basis. The remaining part of the uplink
subframe is used to carry the data frames. A tradeoff be-
tween these two periods of the uplink subframe is required
for an effective operation of the system. On the contrary, if
the size of the contention is shorten below a certain thresh-
old, the SSs may be unable to place their requests within the
time required by the end-user applications.
In this paper, we introduce an adaptive mechanism of the
contention period size. The proposed mechanism takes into
account the varying operation conditions of the system by
estimating the number of stations that may be placing a re-
quest. Simulation results confirm that our proposal outper-
forms other mechanisms having recently been reported in
the literature.
Keywords Resource request · Contention resolution ·
QoS · IEEE 802.16 · WiMAX
J. Delicado ( ) · F.M. Delicado · L. Orozco-Barbosa
Instituto de Investigación en Informática de Albacete (I³A),
Universidad de Castilla-La Mancha (UCLM), 02071 Albacete,
Spain
e-mail: jdelicado@dsi.uclm.es
F.M. Delicado
e-mail: franman@dsi.uclm.es
L. Orozco-Barbosa
e-mail: lorozco@dsi.uclm.es
1 Introduction
In the recent years, the development of Broadband Wire-
less Access (BWA) systems has been spurred by the in-
creasing demand for high-speed Internet access and deploy-
ment of applications characterized by stringent requirements
on bandwidth and delay. Their flexibility and low installa-
tion cost have made possible the widespread deployment
of such BWA systems. Nowadays, one of the main BWA
standards is the IEEE 802.16 standard, whose release is
called IEEE 802.16-2004 [1], being an amalgamation of pre-
vious releases [2–4]. IEEE 802.16e [5] upgrades the stan-
dard from fixed BWA systems to mobile service at vehic-
ular speeds, appearing in 2009 a revision of IEEE 802.16-
2004 [6]. These IEEE 802.16 standards are widely known
under the acronym WiMAX, Worldwide Interoperability for
Microwave ACCess.
The IEEE 802.16 standard defines two layers: the physi-
cal (PHY) and medium access control (MAC) layers. In this
paper, we focus on the study of the MAC protocol and con-
sider the use of a frequency-division duplexing (FDD) mode
and the mandatory point-to-multipoint (PMP) topology. For
an in depth description on the IEEE 802.16 standard, the
reader may refer to [6, 7].
The IEEE 802.16 MAC protocol is a centralized control
based mechanism, defining two types of nodes: the Base Sta-
tion (BS), responsible for granting the bandwidth requests to
each and every connection running at the SSs, and the Sub-
scriber Stations (SSs), which describe devices which are ori-
gin and destination of connections. The bandwidth require-
ments on the downlink direction are known by the BS. In
the case of uplink connections, the estimation on the current
bandwidth requirements of the SSs, these latter ones have
to communicate their needs to the BS. The standard defines
the signaling mechanisms for this purpose. These mecha-
nisms operate following one of two well-known principles,