Abstract—With the broadband services increasing, such as
video conference, interactive games and multimedia
applications, the broadband access network is experiencing a
rapid development. Compared with traditional access
technologies, Wireless-Optical Broadband-Access Networks
(WOBAN) can provide larger bandwidth, flexible access and
better support for the emerging multimedia applications so as
to better meet the users’ requirements. Therefore, WOBAN is a
promising solution for the “last mile” access networks and it has
become a hot issue in recent years. In WOBAN, the placement
of Optical Network Units (ONUs) is one of the key issues for the
network deployment since the ONU acts as the interface
between wireless front-end and optical back-end. To address
the existing problems in ONU placement in WOBAN, we
propose a novel ONU placement algorithm called Load
Balanced ONU Placement (LBOP) in this paper, aiming to
minimize the number of required ONUs under the constraints
of hop number and load balancing. According to the LBOP, the
procedure is divided into two stages: ONU placement and load
transfer. First, the greedy algorithm is adopted to determine the
minimum number of ONUs and the location of each ONU under
the constraint of hops number. Second, given the traffic load of
each router and the location of each ONU, the traffic load is
transferred strategically among different ONUs with the
purpose of load balancing. If the load balancing constraint is
not yet satisfied after the load transfer, we will place new ONUs
into the network according to the ONU placement stage and
repeat the load transferring. Simulation results demonstrate
that the proposed LBOP algorithm requires fewer ONUs than
the previous works, while maintaining better load balancing.
Index Terms—Wireless-optical broadband-access networks,
onu placement, load balancing, greedy algorithm.
I. I
NTRODUCTION
Optical access networks aim to provide long distance,
high-bandwidth communication, while wireless access
networks aim to provide ubiquitous, flexible
communications mainly in community areas. In view of
complementary features of both optical and wireless access
networks, Wireless-Optical Broadband Access Networks
(WOBAN) has been proposed to integrate the Passive
Optical Network (PON) and the Wireless Mesh Network
(WMN) to provide the high bandwidth, cost-efficient and
ubiquitous last mile Internet access [1]. A typical architecture
of WOBAN is shown in Fig. 1. In WOBAN, the optical
sub-network (i.e., PON) consists of an Optical Line Terminal
Manuscript received September 18, 2012; revised October 26, 2012.
The authors are with the College of Information Science and Engineering,
Northeastern University, Shenyang, 110819, P. R. China (e-mail:
haveball@gmail.com)
(OLT) at the central office, a Remote Node (RN), and a group
of Optical-Network-Units (ONUs). The wireless
sub-network (i.e., WMN) is responsible to support
ubiquitous and flexible access for the users in premises.
Generally, the WMN consists of multiple gateways
connected to the Internet, a group of wireless mesh routers
that provide multi-hop wireless communication and a group
of wireless mesh clients whose traffic will be aggregated into
mesh routers.
Fig. 1. The architecture of WOBAN
In WOBAN, the network traffic is divided into two parts:
traffic to the Internet and peer-to-peer traffic [2], [3]. When a
wireless client wants to communicate with another wireless
client, such peer-to-peer traffic in WOBAN has two
alternative routes. It could be routed either through the
multi-hop wireless path within the wireless sub-network or
through the wireless-optical-wireless mode. Specifically, in
the wireless-optical-wireless mode, the wireless client a first
routes its traffic to the closest ONU (i.e., ONU-1), which will
send traffic to the OLT, OLT then broadcasts the traffic back
to all ONUs. When receiving the broadcast traffic from the
OLT, each ONU will determine either to drop or to forward
the traffic according to the destination address of the wireless
client. Then, the ONU closest to the wireless client b (i.e.,
ONU-4) will send traffic to b. It is worth noting that the
wireless-optical-wireless mode helps reduce the interference
among different traffic flows in WMN. Therefore, the
network is able to carry more traffic from wireless clients to
the Internet, which contributes to the network throughput
improvement.
It is well known that ONU placement plays an important
role in improving the performance of WOBAN [4]. Recently,
it becomes a very hot topic. In order to find the optimal
Load Balanced Optical-Network-Unit (ONU) Placement
Algorithm in Wireless-Optical Broadband Access
Networks
Bing Li, Yejun Liu, and Lei Guo
Journal of Future Computer and Communication, Vol. 2, No. 2, April 2013
DOI: 10.7763/IJFCC.2013.V2.131
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