Maximizing Investment Income of SSP for
Spectrum Trading in Cognitive Radio Networks
Lu Wang, Zhong Zhou, Wei Wu
State Key Laboratory of Virtual Reality Technology and Systems
School of Computer Science of Beihang University
Beijing, China
luwang.buaa@gmail.com
Abstract—More and more researches have demonstrated the
benefits of cognitive radio technology in improving flexibility and
efficiency of spectrum utilization. In order to encourage primary
users (PUs) to share their idle spectrum resources with secondary
users (SUs), spectrum trading frameworks are developed. In this
paper, the investment problem of spectrum service provider (SSP)
is considered which obtains spectrum from PUs and provides
service to multiple SUs. The SUs’ actions are estimated according
to statistical data. A estimation method for channels number is
proposed basing on maximizing the SSP’s investment income. A
Markov chain model is used to analyze the SSP’s state transition
and calculate the SU’s waiting time and queuing size by queuing
theory. The optimal number of channels is deduced with marginal
analysis theory. In either spectrum purchase or auction, the SSP
could adjust its investment strategy timely and flexibly according
to these parameters.
I. INTRODUCTION
Traditional fixed spectrum allocation and usage mode has
blocked development of wireless communication technologies.
Currently cognitive radio (CR) is regarded as a revolution
in breaking the barrier [1]. More and more researches have
demonstrated the benefits of CR technology in improving flex-
ibility and efficiency of spectrum utilization. In a CR network,
the secondary users (SUs) can opportunistically access the
licensed spectrum of primary users (PUs). To encourage PUs
share their idle spectrum with SUs, researchers propose some
spectrum trading mechanisms, which transform spectrum from
resources to goods [2][3][4]. The PUs sell the use rights of
licensed spectrum for a period of time, meanwhile the SUs
could achieve available spectrum at certain costs.
The large organizational SUs are relatively easy to get
spectrum from PUs. They need more spectrum and are glad
to pay higher costs for monopolizing the use rights. But for
the small organizational or personal SUs, it is difficult to
participate in the spectrum trading directly due to limitations
of heterogeneity, complex trading rules, restricted spectrum
requirements and unequal informations. These SUs are called
as end-users. An effective solution is to develop some knowl-
edgeable and professional spectrum service providers (SSPs)
to trade with PUs and achieve vacant spectrum. Spectrum
with large bandwidth is divided into different channels. When
the end-users expect to work using spectrum, they apply for
channels from a SSP. The SSPs provide an easy, efficient and
equitable platform in spectrum tradings between PUs and end-
users. The operation mode among PUs, a SSP and end-users
is similar to a cellular network in some ways, and the role of
SSP approximates to a base station.
Obviously the SSP faces a significant dilemma: If it obtains
less spectrum, the available channels it could provide to end-
users are less. The deferred spectrum service perhaps causes
loss of end-users who turn to other SSPs in their communi-
cation regions. On the other hand, if the SSP purchases too
many spectrum goods but the channel selling is disappointing,
the investment of SSP will fail. And worse still, the spectrum
will be wasted once again.
Some studies use game theory to model the interactions
among PUs, SSPs and end-users [5][6][7]. In these papers,
the end-users are regarded as a whole game participator to
influence the SSP. However, the end-user’s spectrum requests
come gradually in stead of together in fact. Every request
influences the system state as an individual behaviour. This
paper use a Markov chain model to analyze the SSP’s state
transformation with the end-users coming gradually. The wait-
ing time and queuing size are calculated with queuing theory.
The optimal number of channels for SSP to earn the most
investment income is deduced with marginal analysis.
Our contributions are as follows:
• A Markov chain model and queuing theory are introduced
into the analysis of SSP’s states. The optimal number of
channels is calculated according to marginal analysis. The
results of optimal channel number and cost-performance ratio
data have guiding significance for the SSP to participate in
either spectrum direct purchases or auctions.
• The attention on spectrum utilization lasts after resource
reallocation, instead of ending formerly. And the user expe-
rience is concerned. If the utilization ratio is often below
80%, the spectrum is not taken full advantage of. And if
the customer churn is often above 10%, the user experience
is terrible. The optimal number of channels proposed in
this paper achieves desired balance among utility, spectrum
utilization and end-user experience.
The rest of paper is organized as follows: We introduce our
system model in section II. Section III does some theoretical
analysis to the model where we give the method to calculate
its parameters. In section IV, we evaluate our system with
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