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Journal Article•DOI•

A survey on spectrum management in cognitive radio networks

Ian F. Akyildiz1, Won-Yeol Lee1, Mehmet C. Vuran1, S. Mohanty1•
Georgia Institute of Technology1
01 Apr 2008-IEEE Communications Magazine (IEEE)-Vol. 46, Iss: 4, pp 40-48
TL;DR: Recent developments and open research issues in spectrum management in CR networks are presented and four main challenges of spectrum management are discussed: spectrum sensing, spectrum decision, spectrum sharing, and spectrum mobility.
Abstract: Cognitive radio networks will provide high bandwidth to mobile users via heterogeneous wireless architectures and dynamic spectrum access techniques. However, CR networks impose challenges due to the fluctuating nature of the available spectrum, as well as the diverse QoS requirements of various applications. Spectrum management functions can address these challenges for the realization of this new network paradigm. To provide a better understanding of CR networks, this article presents recent developments and open research issues in spectrum management in CR networks. More specifically, the discussion is focused on the development of CR networks that require no modification of existing networks. First, a brief overview of cognitive radio and the CR network architecture is provided. Then four main challenges of spectrum management are discussed: spectrum sensing, spectrum decision, spectrum sharing, and spectrum mobility.

Summary (5 min read)

Jump to: [INTRODUCTION] – [COGNITIVE RADIO TECHNOLOGY] – [A Survey on Spectrum Management in Cognitive Radio Networks] – [NETWORK COMPONENTS] – [SPECTRUM HETEROGENEITY] – [NETWORK HETEROGENEITY] – [SPECTRUM MANAGEMENT FRAMEWORK] – [SPECTRUM SENSING] – [PRIMARY TRANSMITTER DETECTION] – [PRIMARY RECEIVER DETECTION] – [INTERFERENCE TEMPERATURE MANAGEMENT] – [SPECTRUM SENSING CHALLENGES] – [SPECTRUM DECISION] – [CHANNEL CHARACTERISTICS IN COGNITIVE RADIO NETWORKS] – [DECISION PROCEDURE] – [SPECTRUM DECISION CHALLENGES] – [SPECTRUM SHARING] – [SPECTRUM SHARING CHALLENGES] – [SPECTRUM MOBILITY] – [SPECTRUM MOBILITY CHALLENGES] and [CONCLUSION]

INTRODUCTION

  • CR networks are envisioned to provide high bandwidth to mobile users via heterogeneous wireless architectures and dynamic spectrum access techniques.
  • Select the best available channel Coordinate access to this channel with other users .
  • The authors explain the concept of spectrum management and the required functionalities.

COGNITIVE RADIO TECHNOLOGY

  • The key enabling technologies of CR networks are the cognitive radio techniques that provide the capability to share the spectrum in an opportunistic manner.
  • From this definition, two main characteristics of cognitive radio can be defined [3] : Cognitive capability: Through real-time interaction with the radio environment, the portions of the spectrum that are unused at a specific time or location can be identified.
  • The best spectrum can be selected, shared with other users, and exploited with-.

A Survey on Spectrum Management in Cognitive Radio Networks

  • Through this capability, the best spectrum band and the most appropriate operating parameters can be selected and reconfigured.
  • In order to provide these capabilities, CR requires a novel radio frequency (RF) transceiver architecture.
  • In the RF front-end the received signal is amplified, mixed, and analogto-digital (A/D) converted.
  • In the baseband processing unit, the signal is modulated/ demodulated.
  • This functionality is related mainly to the RF hardware technologies, such as wideband antenna, power amplifier, and adaptive filter.

NETWORK COMPONENTS

  • The primary network (or licensed network) is referred to as an existing network, where the primary users have a license to operate in a certain spectrum band.
  • If primary networks have an infrastructure, primary user activities are controlled through primary base stations.
  • Due to their priority in spectrum access, the operations of primary users should not be affected by unlicensed users.
  • CR networks also can be equipped with CR base stations that provide single-hop connection to CR users.
  • Finally, CR networks may include spectrum brokers that play a role in distributing the spectrum resources among different CR networks [6] .

SPECTRUM HETEROGENEITY

  • CR users are capable of accessing both the licensed portions of the spectrum used by primary users and the unlicensed portions of the spectrum through wideband access technology.
  • The licensed band is primarily used by the primary network.
  • Hence, CR networks are focused mainly on the detection of primary users in this case.
  • The channel capacity depends on the interference at nearby primary users.
  • Furthermore, if primary users appear in the spectrum band occupied by CR users, CR users should vacate that spectrum band and move to available spectrum immediately.

NETWORK HETEROGENEITY

  • As shown in Fig. 2 , the CR users have the opportunity to perform three different access types: CR network access: CR users can access their own CR base station, on both licensed and unlicensed spectrum bands.
  • Because all interactions occur inside the CR network, their spectrum sharing policy can be independent of that of the primary network.
  • CR users can also access the primary base station through the licensed band, also known as Primary network access.
  • Unlike for other access types, CR users require an adaptive medium access control (MAC) protocol, which enables roaming over multiple primary networks with different access technologies.
  • An overview of the spectrum management framework and its components is provided next.

SPECTRUM MANAGEMENT FRAMEWORK

  • CR networks impose unique challenges due to their coexistence with primary networks as well as diverse QoS requirements.
  • To address these challenges, the authors provide a directory for different functionalities required for spectrum management in CR networks.
  • The spectrum management process consists of four major steps: Spectrum sensing: A CR user can allocate only an unused portion of the spectrum.
  • This allocation not only depends on spectrum availability, but is also determined based on internal (and possibly external) policies.
  • It is evident from the significant number of interactions that the spectrum management functions require a cross-layer design approach.

SPECTRUM SENSING

  • Spectrum sensing enables CR users to adapt to the environment by detecting spectrum holes without causing interference to the primary network.
  • This can be accomplished through a real-time wideband sensing capability to detect weak primary signals in a wide spectrum range.
  • Generally, spectrum sensing techniques can be classified into three groups: primary transmitter detection, primary receiver detection, and interference temperature management as described in the following.

PRIMARY TRANSMITTER DETECTION

  • Three schemes are generally used for transmitter detection: matched filter detection, energy detection, and feature detection [5] : Matched filter detection:.
  • When the information of the primary user signal is known to the CR user, the optimal detector in stationary Gaussian noise is the matched filter.
  • Also, energy detectors often generate false alarms triggered by unintended signals because they cannot differentiate signal types.
  • It is computationally complex and requires significantly long observation times.
  • Hence, transmitter detection techniques alone cannot avoid interference to primary receivers because of the lack of primary receiver information as depicted in Fig. 4a .

PRIMARY RECEIVER DETECTION

  • The most efficient way to detect spectrum holes is to detect the primary users that are receiving data within the communication range of a CR user.
  • Usually, the local oscillator (LO) leakage power emitted by the RF front-end of the primary receiver is exploited [9] .
  • Because the LO leakage signal is typically weak, implementation of a reliable detector is not trivial.

INTERFERENCE TEMPERATURE MANAGEMENT

  • Traditionally, interference can be controlled at the transmitter through the radiated power and location of individual transmitters.
  • Therefore, recently a new model for measuring interference, referred to as interference temperature, has been introduced by the Federal Communications Commission (FCC) [1] .
  • This model limits the interference at the receiver through an interference temperature limit, which is the amount of new interference the receiver could tolerate.
  • As long as CR users do not exceed this limit, they can use the spectrum band.
  • The difficulty of this model lies in accurately determining the interference temperature limit.

SPECTRUM SENSING CHALLENGES

  • There exist several open research challenges that must be investigated for the development of spectrum sensing techniques: Interference temperature measurement:.
  • Due to the lack of interactions between primary networks and CR networks, generally a CR user cannot be aware of the precise locations of the primary receivers.
  • Thus, new techniques are required to measure or estimate the interference temperature at nearby primary receivers.
  • The multi-user environment, consisting of multiple CR users and primary users, makes it more difficult to sense spectrum holes and estimate interference.
  • Moreover, because sensing time directly affects transmission performance, novel spectrum sensing algorithms must be developed such that the sensing time is minimized within a given sensing accuracy.

SPECTRUM DECISION

  • CR networks require the capability to decide which is the best spectrum band among the available bands according to the QoS requirements of the applications.
  • This notion is called spectrum decision and constitutes a rather important but as yet unexplored topic in CR networks.
  • Spectrum decision is closely related to the channel characteristics and operations of primary users.
  • Then, based on this characterization, the most appropriate spectrum band can be chosen.
  • In the following the authors investigate the channel characteristics, decision procedures, and research challenges in CR networks.

CHANNEL CHARACTERISTICS IN COGNITIVE RADIO NETWORKS

  • Because available spectrum holes show different characteristics that vary over time, each spectrum hole should be characterized considering both the time-varying radio environment and spectrum parameters, such as operating frequency and bandwidth.
  • Hence, it is essential to define parameters that can represent a particular spectrum band as follows: Interference: From the amount of interfer- ence at the primary receiver, the permissible power of a CR user can be derived, which is used for the estimation of channel capacity.
  • As the operating frequency increases, the path loss increases, which results in a decrease in the transmission range.
  • Depending on the modulation scheme and the interference level of the spectrum band, the error rate of the channel changes, also known as Wireless link errors.
  • This results in different link layer delays.

DECISION PROCEDURE

  • After the available spectrum bands are characterized, the most appropriate spectrum band should be selected, considering the QoS requirements and spectrum characteristics.
  • Accordingly, the transmission mode and bandwidth for the transmission can be reconfigured.
  • Because of the operation of primary networks, CR users cannot obtain a reliable communication channel for a long time period.
  • This method can create a signal that is not only capable of high data throughput, but is also immune to interference and primary user activity.
  • Even if spectrum handoff occurs in one of the current spectrum bands, the rest of the spectrum bands will maintain current transmissions.

SPECTRUM DECISION CHALLENGES

  • In the development of the spectrum decision function, several challenges still remain unsolved: Decision model: Spectrum capacity estimation using signal-to-noise ratio (SNR) is not sufficient to characterize the spectrum band in CR networks.
  • Thus, design of application-and spectrum-adaptive spectrum decision models is still an open issue.
  • Even if SNR is changed, bit rate and bit error rate (BER) can be maintained by exploiting adaptive modulation instead of spectrum decision.
  • Spectrum decision over heterogeneous spectrum bands: Currently, certain spectrum bands are assigned to different purposes, whereas some bands remain unlicensed.

SPECTRUM SHARING

  • The shared nature of the wireless channel requires the coordination of transmission attempts between CR users.
  • Moreover, the unique characteristics of CRs, such as the coexistence of CR users with licensed users and the wide range of available spectrum, incur substantially different challenges for spectrum sharing in CR networks.
  • Spectrum allocation and access are based on local (or possibly global) policies that are performed by each node distributively [11], also known as Distributed spectrum sharing.
  • This localized operation provides an effective balance between a fully centralized and a distributed scheme.
  • These solutions do not require frequent message exchanges between neighbors as in cooperative solutions.

SPECTRUM SHARING CHALLENGES

  • There are many open research issues for the realization of efficient and seamless open spectrum operation in CR networks, such as: Common control channel: A common control channel (CCC) facilitates many spectrum sharing functionalities.
  • Either CCC mitigation techniques must be devised or local CCCs must be exploited for clusters of nodes.
  • And sharing techniques consider a channel as the basic spectrum unit.
  • An important assumption in the existing work is that secondary users know the location and transmit power of primary users so that interference calculations can be performed easily.

SPECTRUM MOBILITY

  • The fourth step of spectrum management, as explained earlier, is spectrum mobility management.
  • Protocols for different layers of the network stack must adapt to the channel parameters of the operating frequency.
  • Moreover, they should be transparent to spectrum handoff and the associated latency.
  • The purpose of the spectrum mobility management in CR networks is to ensure smooth and fast transition leading to minimum performance degradation during a spectrum handoff.
  • This information can be provided by the sensing algorithm.

SPECTRUM MOBILITY CHALLENGES

  • The following are the open research issues for efficient spectrum mobility in CR networks: Spectrum mobility in the time domain: CR networks adapt to the wireless spectrum based on the available bands.
  • Because these available channels change over time, enabling QoS in this environment is challenging.
  • The available bands also change as a user moves from one place to another.

CONCLUSION

  • By exploiting the existing wireless spectrum opportunistically, CR networks are being developed to solve current wireless network problems resulting from the limited available spectrum and the inefficiency in spectrum usage.
  • CR networks, equipped with the intrinsic capabilities of cognitive radio, will provide an ultimate spectrum-aware communication paradigm in wireless communications.
  • In particular, the authors investigate novel spectrum management functionalities such as spectrum sensing, spectrum decision, spectrum sharing, and spectrum mobility.
  • Many researchers are currently engaged in developing the communication technologies and protocols required for CR networks.
  • To ensure efficient spectrumaware communication, more research is required along the lines introduced in this survey.

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DigitalCommons@University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln
CSE Journal Articles
Computer Science and Engineering, Department
of
2008
A Survey on Spectrum Management in Cognitive Radio Networks A Survey on Spectrum Management in Cognitive Radio Networks
Ian F. Akyildiz
Georgia Institute of Technology
Won-Yeol Lee
Georgia Institute of Technology
Mehmet C. Vuran
Georgia Institute of Technology
, mcvuran@cse.unl.edu
Shantidev Mohanty
Georgia Institute of Technology
Follow this and additional works at: https://digitalcommons.unl.edu/csearticles
Part of the Computer Sciences Commons
Akyildiz, Ian F.; Lee, Won-Yeol; Vuran, Mehmet C.; and Mohanty, Shantidev, "A Survey on Spectrum
Management in Cognitive Radio Networks" (2008).
CSE Journal Articles
. 87.
https://digitalcommons.unl.edu/csearticles/87
This Article is brought to you for free and open access by the Computer Science and Engineering, Department of at
DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in CSE Journal Articles by an
authorized administrator of DigitalCommons@University of Nebraska - Lincoln.
IEEE Communications Magazine • April 2008
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0163-6804/08/$25.00 © 2008 IEEE
INTRODUCTION
Current wireless networks are characterized by a
static spectrum allocation policy, where govern-
mental agencies assign wireless spectrum to
license holders on a long-term basis for large
geographical regions. Recently, because of the
increase in spectrum demand, this policy faces
spectrum scarcity in particular spectrum bands.
In contrast, a large portion of the assigned spec-
trum is used sporadically, leading to underuti-
lization of a significant amount of spectrum [1].
Hence, dynamic spectrum access techniques
were recently proposed to solve these spectrum
inefficiency problems.
The key enabling technology of dynamic spec-
trum access techniques is cognitive radio (CR)
technology, which provides the capability to
share the wireless channel with licensed users in
an opportunistic manner. CR networks are envi-
sioned to provide high bandwidth to mobile
users via heterogeneous wireless architectures
and dynamic spectrum access techniques. This
goal can be realized only through dynamic and
efficient spectrum management techniques. CR
networks, however, impose unique challenges
due to the high fluctuation in the available spec-
trum, as well as the diverse quality of service
(QoS) requirements of various applications.
In order to address these challenges, each CR
user in the CR network must:
• Determine which portions of the spectrum
are available
• Select the best available channel
• Coordinate access to this channel with other
users
• Vacate the channel when a licensed user is
detected [2]
These capabilities can be realized through spec-
trum management functions that address four
main challenges: spectrum sensing, spectrum deci-
sion, spectrum sharing, and spectrum mobility.
This article presents a definition, the func-
tions, and the current research challenges of
spectrum management in CR networks. More
specifically, we focus our discussion on the
development of CR networks that require no
modification in existing networks. An overview
of CR technology is provided, and the CR net-
work architecture is presented. We explain the
concept of spectrum management and the
required functionalities. Then we describe spec-
trum sensing, spectrum decision, spectrum shar-
ing, and spectrum mobility concepts.
COGNITIVE RADIO TECHNOLOGY
The key enabling technologies of CR networks
are the cognitive radio techniques that provide
the capability to share the spectrum in an oppor-
tunistic manner. Formally, a CR is defined as a
radio that can change its transmitter parameters
based on interaction with its environment [1].
From this definition, two main characteristics of
cognitive radio can be defined [3]:
• Cognitive capability: Through real-time
interaction with the radio environment, the
portions of the spectrum that are unused at
a specific time or location can be identified.
As shown in Fig. 1a, CR enables the usage
of temporally unused spectrum, referred to
as spectrum hole or white space. Conse-
quently, the best spectrum can be selected,
shared with other users, and exploited with-
ABSTRACT
Cognitive radio networks will provide high
bandwidth to mobile users via heterogeneous
wireless architectures and dynamic spectrum
access techniques. However, CR networks
impose challenges due to the fluctuating nature
of the available spectrum, as well as the diverse
QoS requirements of various applications. Spec-
trum management functions can address these
challenges for the realization of this new net-
work paradigm. To provide a better understand-
ing of CR networks, this article presents recent
developments and open research issues in spec-
trum management in CR networks. More specif-
ically, the discussion is focused on the
development of CR networks that require no
modification of existing networks. First, a brief
overview of cognitive radio and the CR network
architecture is provided. Then four main chal-
lenges of spectrum management are discussed:
spectrum sensing, spectrum decision, spectrum
sharing, and spectrum mobility.
COGNITIVE RADIO COMMUNICATIONS
AND NETWORKS
Ian F. Akyildiz, Won-Yeol Lee, Mehmet C. Vuran, and Shantidev Mohanty, Georgia Institute of Technology
A Survey on Spectrum Management in
Cognitive Radio Networks
VURAN LAYOUT 3/24/08 2:36 PM Page 40
IEEE Communications Magazine • April 2008
41
out interference with the licensed user.
• Reconfigurability: A CR can be programmed
to transmit and receive on a variety of fre-
quencies, and use different access technolo-
gies supported by its hardware design [4].
Through this capability, the best spectrum
band and the most appropriate operating
parameters can be selected and reconfig-
ured.
In order to provide these capabilities, CR
requires a novel radio frequency (RF) transceiv-
er architecture. The main components of a CR
transceiver are the radio front-end and the base-
band processing unit that were originally pro-
posed for software-defined radio (SDR), as
shown in Fig. 1b [4]. In the RF front-end the
received signal is amplified, mixed, and analog-
to-digital (A/D) converted. In the baseband pro-
cessing unit, the signal is modulated/
demodulated. Each component can be reconfig-
ured via a control bus to adapt to the time-vary-
ing RF environment. The novel characteristic of
the CR transceiver is the wideband RF front-end
that is capable of simultaneous sensing over a
wide frequency range. This functionality is relat-
ed mainly to the RF hardware technologies, such
as wideband antenna, power amplifier, and
adaptive filter. RF hardware for the CR should
be capable of being tuned to any part of a large
range of spectrum. However, because the CR
transceiver receives signals from various trans-
mitters operating at different power levels, band-
widths, and locations; the RF front-end should
have the capability to detect a weak signal in a
large dynamic range, which is a major challenge
in CR transceiver design [5].
COGNITIVE RADIO
NETWORK ARCHITECTURE
A comprehensive description of the CR network
architecture is essential for the development of
communication protocols that address the
dynamic spectrum challenges. The CR network
architecture is presented in this section.
NETWORK COMPONENTS
The components of the CR network architec-
ture, as shown in Fig. 2, can be classified as two
groups: the primary network and the CR network.
The primary network (or licensed network) is
referred to as an existing network, where the pri-
mary users have a license to operate in a certain
spectrum band. If primary networks have an
infrastructure, primary user activities are con-
trolled through primary base stations. Due to
their priority in spectrum access, the operations
of primary users should not be affected by unli-
censed users.
The CR network (also called the dynamic
spectrum access network, secondary network, or
unlicensed network) does not have a license to
operate in a desired band. Hence, additional
functionality is required for CR users to share
the licensed spectrum band. CR networks also
can be equipped with CR base stations that pro-
vide single-hop connection to CR users. Finally,
CR networks may include spectrum brokers that
play a role in distributing the spectrum resources
among different CR networks [6].
SPECTRUM HETEROGENEITY
CR users are capable of accessing both the
licensed portions of the spectrum used by prima-
ry users and the unlicensed portions of the spec-
trum through wideband access technology.
Consequently, the operation types for CR net-
works can be classified as licensed band operation
and unlicensed band operation.
• Licensed band operation: The licensed band
is primarily used by the primary network.
Hence, CR networks are focused mainly on
the detection of primary users in this case.
The channel capacity depends on the inter-
ference at nearby primary users. Further-
more, if primary users appear in the
spectrum band occupied by CR users, CR
users should vacate that spectrum band and
move to available spectrum immediately.
• Unlicensed band operation: In the absence of
primary users, CR users have the same
right to access the spectrum. Hence, sophis-
ticated spectrum sharing methods are
required for CR users to compete for the
unlicensed band.
NETWORK HETEROGENEITY
As shown in Fig. 2, the CR users have the oppor-
tunity to perform three different access types:
• CR network access: CR users can access
their own CR base station, on both licensed
and unlicensed spectrum bands. Because all
interactions occur inside the CR network,
■ Figure 1. Overview of cognitive radio: a) the spectrum hole concept; b) cognitive radio transceiver architecture.
Time
Dynamic
spectrum
access
Frequency
Spectrum in use
“Spectrum hole”
Power
Transmit Receiver
From user To user
RF front-end
(wideband sensing)
Radio
frequency
(RF)
Baseband
processing
Analog-to-digital
converter
(A/D)
Control
(reconfiguration)
VURAN LAYOUT 3/24/08 2:36 PM Page 41
IEEE Communications Magazine • April 2008
42
their spectrum sharing policy can be inde-
pendent of that of the primary network.
• CR ad hoc access: CR users can communi-
cate with other CR users through an ad hoc
connection on both licensed and unlicensed
spectrum bands.
• Primary network access: CR users can also
access the primary base station through the
licensed band. Unlike for other access types,
CR users require an adaptive medium
access control (MAC) protocol, which
enables roaming over multiple primary net-
works with different access technologies.
According to the CR architecture shown in
Fig. 2, various functionalities are required to
support spectrum management in CR net-
works. An overview of the spectrum manage-
ment framework and its components is
provided next.
SPECTRUM MANAGEMENT FRAMEWORK
CR networks impose unique challenges due to
their coexistence with primary networks as well
as diverse QoS requirements. Thus, new spec-
trum management functions are required for CR
networks with the following critical design chal-
lenges:
• Interference avoidance: CR networks should
avoid interference with primary networks.
• QoS awareness: To decide on an appropri-
ate spectrum band, CR networks should
support QoS-aware communication, consid-
ering the dynamic and heterogeneous spec-
trum environment.
• Seamless communication: CR networks
should provide seamless communication
regardless of the appearance of primary
users.
To address these challenges, we provide a
directory for different functionalities required
for spectrum management in CR networks. The
spectrum management process consists of four
major steps:
• Spectrum sensing: A CR user can allocate
only an unused portion of the spectrum.
Therefore, a CR user should monitor the
available spectrum bands, capture their
information, and then detect spectrum holes.
• Spectrum decision: Based on the spectrum
availability, CR users can allocate a chan-
nel. This allocation not only depends on
spectrum availability, but is also determined
based on internal (and possibly external)
policies.
• Spectrum sharing: Because there may be
multiple CR users trying to access the spec-
trum, CR network access should be coordi-
nated to prevent multiple users colliding in
overlapping portions of the spectrum.
• Spectrum mobility: CR users are regarded as
visitors to the spectrum. Hence, if the spe-
cific portion of the spectrum in use is
required by a primary user, the communica-
tion must be continued in another vacant
portion of the spectrum.
The spectrum management framework for
CR network communication is illustrated in Fig.
3. It is evident from the significant number of
interactions that the spectrum management
functions require a cross-layer design approach.
In the following sections we discuss the four
main spectrum management functions.
■ Figure 2. Cognitive radio network architecture.
Spectrum band
Spectrum broker
Other
cognitive
radio
networks
Primary user
Primary
network
access
CR
network
access
CR user
CR user
CR ad hoc
access
CR
base station
Primary user
Primary networks
Cognitive radio
network (without
infrastructure)
Cognitive radio
network(with
infrastructure)
Primary
base station
Unlicensed band
Licensed band I
Licensed band II
CR networks impose
unique challenges
due to the
coexistence with
primary networks, as
well as diverse QoS
requirements. Thus,
new spectrum
management
functions are
required for CR
networks to meet
critical design
challenges.
VURAN LAYOUT 3/24/08 2:36 PM Page 42
IEEE Communications Magazine • April 2008
43
SPECTRUM SENSING
A CR is designed to be aware of and sensitive to
the changes in its surroundings, which makes
spectrum sensing an important requirement for
the realization of CR networks. Spectrum sens-
ing enables CR users to adapt to the environ-
ment by detecting spectrum holes without
causing interference to the primary network.
This can be accomplished through a real-time
wideband sensing capability to detect weak pri-
mary signals in a wide spectrum range. General-
ly, spectrum sensing techniques can be classified
into three groups: primary transmitter detection,
primary receiver detection, and interference
temperature management as described in the
following.
PRIMARY TRANSMITTER DETECTION
Transmitter detection is based on the detection
of a weak signal from a primary transmitter
through the local observations of CR users.
Three schemes are generally used for transmitter
detection: matched filter detection, energy detec-
tion, and feature detection [5]:
• Matched filter detection: When the informa-
tion of the primary user signal is known to
the CR user, the optimal detector in sta-
tionary Gaussian noise is the matched filter.
However, the matched filter requires a pri-
ori knowledge of the characteristics of the
primary user signal.
• Energy detection: If the receiver cannot gath-
er sufficient information about the primary
user signal, the optimal detector is an ener-
gy detector. However, the performance of
the energy detector is susceptible to uncer-
tainty in noise power. Also, energy detec-
tors often generate false alarms triggered
by unintended signals because they cannot
differentiate signal types.
• Feature detection: In general, modulated sig-
nals are characterized by built-in periodicity
or cyclostationarity. This feature can be
detected by analyzing a spectral correlation
function [7]. The main advantage of feature
detection is its robustness to uncertainty in
noise power. However, it is computationally
complex and requires significantly long
observation times.
Due to the lack of interactions between pri-
mary users and CR users, transmitter detection
techniques rely only on weak signals from the
primary transmitters. Hence, transmitter detec-
tion techniques alone cannot avoid interference
to primary receivers because of the lack of pri-
mary receiver information as depicted in Fig. 4a.
Moreover, transmitter detection models cannot
prevent the hidden terminal problem. A CR user
(transmitter) can have a good line of sight to a
CR receiver but may not be able to detect the
primary transmitter due to shadowing, as shown
in Fig. 4b. Therefore, sensing information from
other users is required for more accurate prima-
ry transmitter detection — referred to as cooper-
ative detection.
Cooperative detection is theoretically more
accurate because the uncertainty in a single
user’s detection can be minimized through col-
laboration [8]. Moreover, multipath fading and
shadowing effects can be mitigated so that the
detection probability is improved in a heavily
shadowed environment. However, cooperative
approaches cause adverse effects on resource-
constrained networks due to the overhead traffic
required for cooperation.
PRIMARY RECEIVER DETECTION
Although cooperative detection reduces the
probability of interference, the most efficient
way to detect spectrum holes is to detect the pri-
mary users that are receiving data within the
■ Figure 3. Spectrum management framework for cognitive radio networks.
Application
Application control
Handoff delay, loss
Routing
information
Link
layer
delay
Spectrum
sharing
Sensing
information
Spectrum
sensing
Spectrum
mobility
function
Spectrum
decision
function
Transport
Network layer
QoS
requirements
Reconfiguration
Scheduling
information/
reconfiguration
Sensing
information/
reconfiguration
Routing information/
reconfiguration
Link layer
Physical layer
Handofff decision,current and candidate spectrum information
A cognitive radio is
designed to be
aware of and
sensitive to the
changes in its
surroundings, which
makes spectrum
sensing an important
requirement for the
realization of CR
networks.
VURAN LAYOUT 3/24/08 2:36 PM Page 43
Citations
More filters
Journal Article•DOI•
Advances on Spectrum Sensing for Cognitive Radio Networks: Theory and Applications

[...]

Abdelmohsen Ali1, Walaa Hamouda1•
Concordia University1
22 Jan 2017-IEEE Communications Surveys and Tutorials
TL;DR: This survey paper focuses on the enabling techniques for interweave CR networks which have received great attention from standards perspective due to its reliability to achieve the required quality-of-service.
Abstract: Due to the under-utilization problem of the allocated radio spectrum, cognitive radio (CR) communications have recently emerged as a reliable and effective solution. Among various network models, this survey paper focuses on the enabling techniques for interweave CR networks which have received great attention from standards perspective due to its reliability to achieve the required quality-of-service. Spectrum sensing provides the essential information to enable this interweave communications in which primary and secondary users are not allowed to access the medium concurrently. Several researchers have already considered various aspects to realize efficient techniques for spectrum sensing. In this direction, this survey paper provides a detailed review of the state-of-the-art related to the application of spectrum sensing in CR communications. Starting with the basic principles and the main features of interweave communications, this paper provides a classification of the main approaches based on the radio parameters. Subsequently, we review the existing spectrum sensing works applied to different categories such as narrowband sensing, narrowband spectrum monitoring, wideband sensing, cooperative sensing, practical implementation considerations for various techniques, and the recent standards that rely on the interweave network model. Furthermore, we present the latest advances related to the implementation of the legacy spectrum sensing approaches. Finally, we conclude this survey paper with some suggested open research challenges and future directions for the CR networks in next generation Internet-of-Things applications.

483 citations

Cites background from "A survey on spectrum management in ..."

  • ...In fact, a countable number of survey papers exist in the literature in the context of cognitive radio communications covering a wide range of areas such as spectrum occupancy measurement [13], spectrum sensing [6][7][14][15], cognitive radio under practical imperfections [16], spectrum management [17], emerging applications for cognitive radios [18], spectrum decision [19], spectrum access strategies [20], and CR networks [21]....

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Journal Article•DOI•
A Survey on Machine-Learning Techniques in Cognitive Radios

[...]

Mario Bkassiny1, Yang Li1, Sudharman K. Jayaweera1•
University of New Mexico1
23 Jan 2013-IEEE Communications Surveys and Tutorials
TL;DR: The learning problem in cognitive radios (CRs) is characterized and the importance of artificial intelligence in achieving real cognitive communications systems is stated and the conditions under which each of the techniques may be applied are identified.
Abstract: In this survey paper, we characterize the learning problem in cognitive radios (CRs) and state the importance of artificial intelligence in achieving real cognitive communications systems. We review various learning problems that have been studied in the context of CRs classifying them under two main categories: Decision-making and feature classification. Decision-making is responsible for determining policies and decision rules for CRs while feature classification permits identifying and classifying different observation models. The learning algorithms encountered are categorized as either supervised or unsupervised algorithms. We describe in detail several challenging learning issues that arise in cognitive radio networks (CRNs), in particular in non-Markovian environments and decentralized networks, and present possible solution methods to address them. We discuss similarities and differences among the presented algorithms and identify the conditions under which each of the techniques may be applied.

455 citations

Cites background from "A survey on spectrum management in ..."

  • ...Several surveys on the DSA techniques and the medium access control (MAC) layer operations for the CRs are provided in [56]–[60]....

    [...]

Journal Article•DOI•
A Survey on MAC Strategies for Cognitive Radio Networks

[...]

A. De Domenico, Emilio Calvanese Strinati, M.-G. Di Benedetto1•
Sapienza University of Rome1
21 Jan 2012-IEEE Communications Surveys and Tutorials
TL;DR: The fundamental role of the MAC layer is shown and its functionalities in a cognitive radio (CR) network are identified and a classification of cognitive MAC protocols is proposed and advantages, drawbacks, and further design challenges of Cognitive MAC protocols are discussed.
Abstract: Dynamic spectrum policies combined with software defined radio are powerful means to improve the overall spectral efficiency allowing the development of new wireless services and technologies. Medium Access Control (MAC) protocols exploit sensing stimuli to build up a spectrum opportunity map (cognitive sensing). Available resources are scheduled (dynamic spectrum allocation), improving coexistence between users that belong to heterogeneous systems (dynamic spectrum sharing). Furthermore, MAC protocols may allow cognitive users to vacate selected channels when their quality becomes unacceptable (dynamic spectrum mobility). The contribution of this survey is threefold. First, we show the fundamental role of the MAC layer and identify its functionalities in a cognitive radio (CR) network. Second, a classification of cognitive MAC protocols is proposed. Third, advantages, drawbacks, and further design challenges of cognitive MAC protocols are discussed.

423 citations

Cites background or methods from "A survey on spectrum management in ..."

  • ...However, this approach is only suitable in the detection of TV receivers [5]....

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  • ...A general overview of critical issues in CR network spectrum management is provided in [5]....

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Journal Article•DOI•
Spectrum Sharing for Device-to-Device Communication in Cellular Networks

[...]

Xingqin Lin1, Jeffrey G. Andrews1, Amitava Ghosh2•
University of Texas at Austin1, Nokia2
18 May 2013-arXiv: Information Theory
TL;DR: A tractable hybrid network model where the positions of mobiles are modeled by random spatial Poisson point process is proposed and derived analytical rate expressions are applied to optimize the two D2D spectrum sharing scenarios under a weighted proportional fair utility function.
Abstract: This paper addresses two fundamental and interrelated issues in device-to-device (D2D) enhanced cellular networks. The first issue is how D2D users should access spectrum, and we consider two choices: overlay (orthogonal spectrum between D2D and cellular UEs) and underlay (non-orthogonal). The second issue is how D2D users should choose between communicating directly or via the base station, a choice that depends on distance between the potential D2D transmitter and receiver. We propose a tractable hybrid network model where the positions of mobiles are modeled by random spatial Poisson point process, with which we present a general analytical approach that allows a unified performance evaluation for these questions. Then, we derive analytical rate expressions and apply them to optimize the two D2D spectrum sharing scenarios under a weighted proportional fair utility function. We find that as the proportion of potential D2D mobiles increases, the optimal spectrum partition in the overlay is almost invariant (when D2D mode selection threshold is large) while the optimal spectrum access factor in the underlay decreases. Further, from a coverage perspective, we reveal a tradeoff between the spectrum access factor and the D2D mode selection threshold in the underlay: as more D2D links are allowed (due to a more relaxed mode selection threshold), the network should actually make less spectrum available to them to limit their interference.

416 citations

Cites background from "A survey on spectrum management in ..."

  • ...Existing research relevant to this paper includes spectrum sharing in cognitive radio networks, where secondary cognitive transmitters may access the primary spectrum if the primary transmitters are not active or they do not cause unacceptable interference [13]....

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Journal Article•DOI•
Emerging cognitive radio applications: A survey

[...]

Jianfeng Wang1, Monisha Ghosh1, Kiran Challapali1•
Philips1
01 Mar 2011-IEEE Communications Magazine
TL;DR: This article presents a high-level view on how cognitive radio (primarily from a dynamic spectrum access perspective) would support such applications, the benefits that cognitive radio would bring, and also some challenges that are yet to be resolved.
Abstract: Recent developments in spectrum policy and regulatory domains, notably the release of the National Broadband Plan, the publication of final rules for TV white spaces, and the ongoing proceeding for secondary use of the 2360-2400 MHz band for medical body area networks, will allow more flexible and efficient use of spectrum in the future. These important changes open up exciting opportunities for cognitive radio to enable and support a variety of emerging applications, ranging from smart grid, public safety and broadband cellular, to medical applications. This article presents a high-level view on how cognitive radio (primarily from a dynamic spectrum access perspective) would support such applications, the benefits that cognitive radio would bring, and also some challenges that are yet to be resolved. We also illustrate related standardization that uses cognitive radio technologies to support such emerging applications.

381 citations

References
More filters
Journal Article•DOI•
Cognitive radio: brain-empowered wireless communications

[...]

Simon Haykin1•
McMaster University1
07 Feb 2005-IEEE Journal on Selected Areas in Communications
TL;DR: Following the discussion of interference temperature as a new metric for the quantification and management of interference, the paper addresses three fundamental cognitive tasks: radio-scene analysis, channel-state estimation and predictive modeling, and the emergent behavior of cognitive radio.
Abstract: Cognitive radio is viewed as a novel approach for improving the utilization of a precious natural resource: the radio electromagnetic spectrum. The cognitive radio, built on a software-defined radio, is defined as an intelligent wireless communication system that is aware of its environment and uses the methodology of understanding-by-building to learn from the environment and adapt to statistical variations in the input stimuli, with two primary objectives in mind: /spl middot/ highly reliable communication whenever and wherever needed; /spl middot/ efficient utilization of the radio spectrum. Following the discussion of interference temperature as a new metric for the quantification and management of interference, the paper addresses three fundamental cognitive tasks. 1) Radio-scene analysis. 2) Channel-state estimation and predictive modeling. 3) Transmit-power control and dynamic spectrum management. This work also discusses the emergent behavior of cognitive radio.

12,172 citations

"A survey on spectrum management in ..." refers background in this paper

  • ...From this definition, two main characteristics of cognitive radio can be defined [3]: • Cognitive capability: Through real-time interaction with the radio environment, the portions of the spectrum that are unused at a specific time or location can be identified....

    [...]

Journal Article•DOI•
NeXt generation/dynamic spectrum access/cognitive radio wireless networks: a survey

[...]

Ian F. Akyildiz1, Won-Yeol Lee1, Mehmet C. Vuran1, Shantidev Mohanty1•
Georgia Institute of Technology1
15 Sep 2006-Computer Networks
TL;DR: The novel functionalities and current research challenges of the xG networks are explained in detail, and a brief overview of the cognitive radio technology is provided and the xg network architecture is introduced.

6,608 citations

"A survey on spectrum management in ..." refers background in this paper

  • ...In order to address these challenges, each CR user in the CR network must: • Determine which portions of the spectrum are available • Select the best available channel • Coordinate access to this channel with other users • Vacate the channel when a licensed user is detected [2] These capabilities can be realized through spectrum management functions that address four main challenges: spectrum sensing, spectrum decision, spectrum sharing, and spectrum mobility....

    [...]

Proceedings Article•DOI•
Implementation issues in spectrum sensing for cognitive radios

[...]

Danijela Cabric1, S.M. Mishra1, Robert W. Brodersen1•
University of California, Berkeley1
07 Nov 2004
TL;DR: To improve radio sensitivity of the sensing function through processing gain, three digital signal processing techniques are investigated: matched filtering, energy detection and cyclostationary feature detection.
Abstract: There are new system implementation challenges involved in the design of cognitive radios, which have both the ability to sense the spectral environment and the flexibility to adapt transmission parameters to maximize system capacity while coexisting with legacy wireless networks. The critical design problem is the need to process multigigahertz wide bandwidth and reliably detect presence of primary users. This places severe requirements on sensitivity, linearity and dynamic range of the circuitry in the RF front-end. To improve radio sensitivity of the sensing function through processing gain we investigated three digital signal processing techniques: matched filtering, energy detection and cyclostationary feature detection. Our analysis shows that cyclostationary feature detection has advantages due to its ability to differentiate modulated signals, interference and noise in low signal to noise ratios. In addition, to further improve the sensing reliability, the advantage of a MAC protocol that exploits cooperation among many cognitive users is investigated.

2,806 citations

"A survey on spectrum management in ..." refers background or methods in this paper

  • ...Three schemes are generally used for transmitter detection: matched filter detection, energy detection, and feature detection [5]: • Matched filter detection: When the information of the primary user signal is known to the CR user, the optimal detector in stationary Gaussian noise is the matched filter....

    [...]

  • ...However, because the CR transceiver receives signals from various transmitters operating at different power levels, bandwidths, and locations; the RF front-end should have the capability to detect a weak signal in a large dynamic range, which is a major challenge in CR transceiver design [5]....

    [...]

Journal Article•DOI•
Decentralized cognitive MAC for opportunistic spectrum access in ad hoc networks: A POMDP framework

[...]

Qing Zhao1, Lang Tong2, Ananthram Swami3, Yunxia Chen1•
University of California, Davis1, Cornell University2, United States Army Research Laboratory3
01 Apr 2007-IEEE Journal on Selected Areas in Communications
TL;DR: An analytical framework for opportunistic spectrum access based on the theory of partially observable Markov decision process (POMDP) is developed and cognitive MAC protocols that optimize the performance of secondary users while limiting the interference perceived by primary users are proposed.
Abstract: We propose decentralized cognitive MAC protocols that allow secondary users to independently search for spectrum opportunities without a central coordinator or a dedicated communication channel. Recognizing hardware and energy constraints, we assume that a secondary user may not be able to perform full-spectrum sensing or may not be willing to monitor the spectrum when it has no data to transmit. We develop an analytical framework for opportunistic spectrum access based on the theory of partially observable Markov decision process (POMDP). This decision-theoretic approach integrates the design of spectrum access protocols at the MAC layer with spectrum sensing at the physical layer and traffic statistics determined by the application layer of the primary network. It also allows easy incorporation of spectrum sensing error and constraint on the probability of colliding with the primary users. Under this POMDP framework, we propose cognitive MAC protocols that optimize the performance of secondary users while limiting the interference perceived by primary users. A suboptimal strategy with reduced complexity yet comparable performance is developed. Without additional control message exchange between the secondary transmitter and receiver, the proposed decentralized protocols ensure synchronous hopping in the spectrum between the transmitter and the receiver in the presence of collisions and spectrum sensing errors

1,709 citations

"A survey on spectrum management in ..." refers background in this paper

  • ...• Distributed spectrum sharing: Spectrum allocation and access are based on local (or possibly global) policies that are performed by each node distributively [11]....

    [...]

Proceedings Article•DOI•
Cooperative Sensing among Cognitive Radios

[...]

Shridhar Mubaraq Mishra1, Anant Sahai1, Robert W. Brodersen1•
University of California, Berkeley1
11 Dec 2006
TL;DR: This work proposes light-weight cooperation in sensing based on hard decisions to mitigate the sensitivity requirements on individual radios and shows that the "link budget" that system designers have to reserve for fading is a significant function of the required probability of detection.
Abstract: Cognitive Radios have been advanced as a technology for the opportunistic use of under-utilized spectrum since they are able to sense the spectrum and use frequency bands if no Primary user is detected. However, the required sensitivity is very demanding since any individual radio might face a deep fade. We propose light-weight cooperation in sensing based on hard decisions to mitigate the sensitivity requirements on individual radios. We show that the "link budget" that system designers have to reserve for fading is a significant function of the required probability of detection. Even a few cooperating users (~10-20) facing independent fades are enough to achieve practical threshold levels by drastically reducing individual detection requirements. Hard decisions perform almost as well as soft decisions in achieving these gains. Cooperative gains in a environment where shadowing is correlated, is limited by the cooperation footprint (area in which users cooperate). In essence, a few independent users are more robust than many correlated users. Unfortunately, cooperative gain is very sensitive to adversarial/failing Cognitive Radios. Radios that fail in a known way (always report the presence/absence of a Primary user) can be compensated for by censoring them. On the other hand, radios that fail in unmodeled ways or may be malicious, introduce a bound on achievable sensitivity reductions. As a rule of thumb, if we believe that 1/N users can fail in an unknown way, then the cooperation gains are limited to what is possible with N trusted users.

1,562 citations

"A survey on spectrum management in ..." refers background in this paper

  • ...Cooperative detection is theoretically more accurate because the uncertainty in a single user’s detection can be minimized through collaboration [8]....

    [...]

Related Papers (5)
Cognitive radio: brain-empowered wireless communications

[...]

07 Feb 2005-IEEE Journal on Selected Areas in Communications
Simon Haykin
NeXt generation/dynamic spectrum access/cognitive radio wireless networks: a survey

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15 Sep 2006-Computer Networks
Ian F. Akyildiz, Won-Yeol Lee, Mehmet C. Vuran, Shantidev Mohanty 
Cognitive radio: making software radios more personal

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01 Aug 1999-IEEE Personal Communications
Joseph Mitola, Gerald Q. Maguire Jr.
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[...]

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Frequently Asked Questions (17)
Q1. What are the contributions in "A survey on spectrum management in cognitive radio networks" ?

In this paper, the authors present a survey of spectrum management in cognitive radio ( CR ) networks, including spectrum sensing, spectrum decision, spectrum sharing, and spectrum mobility. 

CR networks are envisioned to provide high bandwidth to mobile users via heterogeneous wireless architectures and dynamic spectrum access techniques. 

To address different path loss, wireless link error, and interference, different types of link layer protocols are required at different spectrum bands. 

The purpose of the spectrum mobility management in CR networks is to ensure smooth and fast transition leading to minimum performance degradation during a spectrum handoff. 

The key enabling technology of dynamic spectrum access techniques is cognitive radio (CR) technology, which provides the capability to share the wireless channel with licensed users in an opportunistic manner. 

Due to the lack of interactions between primary users and CR users, transmitter detection techniques rely only on weak signals from the primary transmitters. 

spectrum sensing techniques can be classified into three groups: primary transmitter detection, primary receiver detection, and interference temperature management as described in the following. 

A comprehensive description of the CR network architecture is essential for the development of communication protocols that address the dynamic spectrum challenges. 

By exploiting the existing wireless spectrum opportunistically, CR networks are being developed to solve current wireless network problems resulting from the limited available spectrum and the inefficiency in spectrum usage. 

The third classification for spectrum sharing in CR networks is based on the access technology [14]: • Overlay spectrum sharing: Nodes access thenetwork using a portion of the spectrum that has not been used by licensed users. 

because of the operation of primary networks, CR users cannot obtain a reliable communication channel for a long time period. 

if primary users appear in the spectrum band occupied by CR users, CR users should vacate that spectrum band and move to available spectrum immediately. 

The following are the open research issues for efficient spectrum mobility in CR networks: • Spectrum mobility in the time domain: CRnetworks adapt to the wireless spectrum based on the available bands. 

There exist several open research challenges that must be investigated for the development of spectrum sensing techniques: • Interference temperature measurement: Dueto the lack of interactions between primary networks and CR networks, generally a CR user cannot be aware of the precise locations of the primary receivers. 

There are many open research issues for the realization of efficient and seamless open spectrum operation in CR networks, such as: • Common control channel: A common con-trol channel (CCC) facilitates many spectrum sharing functionalities. 

In particular, the authors investigate novel spectrum management functionalities such as spectrum sensing, spectrum decision, spectrum sharing, and spectrum mobility. 

The CR network (also called the dynamic spectrum access network, secondary network, or unlicensed network) does not have a license to operate in a desired band.