Joint Temporal and Spatial Spectrum Sharing in
Cognitive Radio Networks: A Region-based
Approach with Cooperative Spectrum Sensing
Qian Li, Zhiyong Feng
Wireless Technology Innovation Institute
Beijing University of Posts and Telecommunications
Beijing, P. R. China 100876
Email: liqian198703@bupt.edu.cn, fengzy@bupt.edu.cn
Wei Li, T. Aaron Gulliver
Department of Electrical and Computer Engineering
University of Victoria
Victoria, Canada V8W 3P6
Email: weili@ieee.org, agullive@ece.uvic.ca
Abstract—Efficient spectrum utilization is of great
importance in cognitive networks, however current
spectrum sharing techniques in the temporal or spatial
domains all have deficiencies. In this paper, we propose a
joint spatial and temporal spectrum sharing scheme based
on the concept of regions. We define four regions, namely
a primary exclusive region (PER), a temporal spectrum
sharing region (T-SSR), a joint spectrum sharing region
(J-SSR), and a spatial spectrum sharing region (S-SSR). T-
SSR and J-SSR are proposed to utilize temporal spectrum
holes which have not previously been exploited.
Cooperative spectrum sensing is employed to expand the
J-SSR, which is beneficial for system design. Closed-form
bounds for the four regions are obtained, and conditions
on T-SSR existence and the presence of a transition zone
between the JSSR and S-SSR are determined. Both
analytical and simulation results are presented which show
how the key factors, including primary user interference
constraints, spectrum sensing factors, and secondary user
coverage constraints, influence these bounds. This has
great practical value in improving spectrum efficiency in
cognitive networks.
Keywords—Temporal and spatial spectrum sharing;
Transmission regions; Cooperative sensing
I. INTRODUCTION
Efficient spectrum utilization is one of the most important
issues in cognitive radio networks (CRNs). These networks
allow for dynamic spectrum sharing to address the spectrum
scarcity problem [1][2][3]. Current studies divide dynamic
spectrum sharing into two categories [4]. The first, called
spectrum underlay, always allows secondary users to access
the spectrum subject to interference threshold constraints [5]
[6][7]. Thus, spectrum underlay can also be considered as
spatial spectrum sharing. However, the achievable capacity of
secondary users in this case is limited because they must lower
their transmission power to satisfy the interference threshold
even when the spectrum is idle [8]. The second, called
spectrum overlay, allows secondary users to utilize the
spectrum when it is idle. This is determined by a technique
called spectrum sensing [5][9][10]. Thus, spectrum overlay
can also be considered as temporal spectrum sharing.
However, temporal spectrum sharing is very dependent on the
behavior of the primary users [8]. If the spectrum is always
busy (such as with TV channels), there will be no spectrum
access opportunities for secondary users. Thus, spatial
spectrum sharing ignores the temporal spectrum access
opportunity, while temporal spectrum sharing is restricted by
primary user behavior.
To overcome the disadvantages of the two spectrum sharing
techniques and utilize the spectrum more efficiently, joint
spatial and temporal sharing has been proposed. The first step
is detection in a multi-domain, i.e., the time-space domain.
Tandra et al. [11] proposed a new metric for evaluating
spectrum sensing in this domain, and a time-space spectrum
sensing scheme was designed to determine spectrum
availability. However, how to utilize the available spectrum in
the time-space domain was not considered. Mai et al. [12]
proposed the primary exclusive region (PER) model. Beyond
this region, secondary users (SUs) can share the same
spectrum as primary users (PUs). This model is practical as
the primary transmitter (PT) with multiple primary users
(PUs) scenario is similar to that of TV and cellular networks.
However, they do not consider spectrum holes in the time
dimension, so active SUs are not allowed in the
-band
which is adjacent to the PER [12], even though temporal
spectrum opportunities can exist in this band. If SUs in this
band implement spectrum sensing in the time domain and
opportunistically access the vacant spectrum, the spectrum
utilization and SU capacity can be improved. A similar region
based concept was proposed in [13][14], but bounds on the
regions were not investigated. Therefore, how to design an
appropriate spectrum sharing technique that can utilize the
available spectrum in a multi-domain (e.g. the time-space
domain), is still a major challenge for efficient spectrum
sharing in CRNs.
To solve the above challenge, this paper considers full
exploitation of time-space spectrum opportunities (also called
spectrum holes). A region based model for time-space
spectrum access in CRNs is developed. This model consists of
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