1712 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 12, NO. 4, APRIL 2013
Attachment-Learning for Multi-Channel Allocation
in Distributed OFDMA-Based Networks
Lu Wang, Student Member, IEEE, Kaishun Wu, Member, IEEE
Mounir Hamdi, Fellow, IEEE, and Lionel M. Ni, Fellow, IEEE
Abstract—Wireless technology has become ever more popular
in recent years, which results in a higher and higher density
of wireless devices. In order to cope with this high density,
researchers are proposing the provision of multiple concurrent
transmissions by dividing a broadband channel into separate
narrow band subchannels. In particular, a fine-grained channel
access approach calls for efficient channel allocation mechanisms,
especially in distributed networks. However, most of the current
multi-channel access methods rely on costly coordination, which
significantly degrades network performance. Motivated by this,
we propose a cross layer design, termed Attachment Learning
(AT-Learning), to achieve multi-channel allocation with low cost
and high efficiency in distributed OFDMA based networks.
AT-Learning utilizes a jamming and cancellation technique to
attach identifier signals to data traffic, without degrading the
effective throughput of the original data transmission. These
identifier signals help mobile stations learn the allocation strategy
by themselves. After the learning stage, mobile stations can
achieve a TDMA-like performance, where stations will know
exactly when to transmit and on which channel without further
collisions. We conduct comprehensive simulations, comparing AT-
Learning with a traditional multi-channel access method like
Slotted ALOHA. The experimental results demonstrate that AT-
Learning can improve the throughput by up to 300% over Slotted
ALOHA.
Index Terms—Multi-channel allocation, interference cancella-
tion, game theory, OFDMA.
I. INTRODUCTION
O
VER the last two decades, wireless technologies have
witnessed explosive growth. Accordingly, wireless de-
vices have been deployed everywhere with high density,
resulting in oversubscribed wireless resources. Consequently,
it is desirable to divide the current frequency band into
smaller channels and let more than one user share a given
frequency band. Researchers have examined variations of this
paradigm, such as Frequency Division Multiplexing (FDM)
and Orthogonal Frequency Division Multiplexing (OFDM).
Among these techniques, OFDM is considered to be the most
promising choice for the provision of multiple fin e-grained
Manuscript received May 4, 2012; revised September 29 and December
10, 2012; accepted December 11, 2012. The associate editor coordinating the
review of this paper and approving it for publication was R. Mallik.
L. Wang, M. Hamdi, and L. M. Ni are with the Department of Computer
Science and Engineering, Hong Kong University of Science and Technol-
ogy, Clear Water Bay , Kowloon, Hong Kong (e-mail: {wanglu, hamdi,
ni}@ust.hk).
K. Wu is with the Guangzhou HKUST Fok Ying Tung Research Institute.
He is also with the National Engineering Research Center of Digital Life,
State-Province Joint Laboratory of Digital Home Interactive Applications, Sun
Yat-sen University, Guangzhou 510006, China (e-mail: kwinson@ust.hk).
Digital Object Identifier 10.1109/TWC.2013.022013.120627
channels, since it is able to combat inter-symbol interference
and achieving multi-user diversity gain.
Multi-channel environments such as OFDM-based systems
call for efficient channel allocation protocols. In distr ibuted
networks, there are no authorities(e.g., Access Points) to des-
ignate the channel allocation, channel allocation simply relies
on coordination among stations (cooperative) o r historical
knowledge of themselves (non-cooperative). The former retails
with a rather high overhead, and the latter has relatively
low accuracy, thus neither of them can achieve the desired
utilization. Recently, a lo t of research is focusin g on Game
Theory to solve the contention problems in d istributed multi-
channel environments [1] [2]. They formulize the multi-
channel allocation problem as different games, and try to
achieve the Nash E quilibriu m (NE) of these games. Nash
Equilibrium is a solution co ncept of a game involving two or
more players. If each player is making the best decision that
he or she can, taking into account the decisions of the others,
then they are in Nash Equilibrium. Mahonen et al. [1] propose
a simple non-cooperative scheme for multi-channel allocation
based on Minority Game, where each station maintains an
access strategy for each channel based on transmission history.
However, with limited information of other stations’strategies,
their approach cannot ensure fairness among stations. Gao
et al. [3] formalize multi-channel allocation in multi-h op
networks as a Cooperative Game. They do achieve good
NE and fairness, yet have to consume certain resource for
coordination.
Therefore, we conclude that, for a multi-channel allocation
game in distributed networks, we need a non-cooperative
scheme with an efficient NE and guaranteed fairness. To be
specific, without coordination, stations are better off learning
an efficient access strategy b y themselves. Here we adopt a
Correlated Eq uilibrium (CE) instead of NE. CE is a probability
distribution over the joint strategy profiles of the game [4]. It
assumes a correlation device for all the players, which samples
the probability distribution and recommend s an action f or each
player. When none of the players can increase its payoff by de-
viating from the recommended action, the distribution reaches
CE. Since the corr e lation device services as an authority, it
can ensure both NE and fairness. However, it is non-trivial
to achieve CE in distributed networks: first, the coordination
device is not available in distributed networks. An alternative
that serves the same purpose is required. Second, we need a
complete MAC protocol to fully utilize a corre lation signal to
achieve CE for multi-channel allocation.
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2013 IEEE