Spectrum Sensing Techniques and Cognitive Radio

This study material explores the spectrum sensing techniques and cognitive radio technology. It discusses the challenges faced by mobile multimedia networks, such as scarce resource allocation and interference, and how cognitive radio networks can address these challenges. The material also covers the benefits of cognitive radio networks in terms of dynamic spectrum access, co-existence of wireless networks, and interference management.

SPECTRUM SENSING TECHNIQUES AND COGNITIVE RADIO
STUDENT NAME
STUDENT REGISTRATION NUMBER
DATE OF SUBMISSION
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ABSTRACT
The mobile communication networks in the modern age are adopting a level of intelligence to
ensure that they sense and automatically adapt to the environment accordingly. The mobile
multimedia networks are faced with several challenges like the scarce resource allocation of the
frequency spectrum and the interference of channels during communication. There is a lot of
wastage when a given section of the frequency spectrum is allocated yet unused. Most of the
cognitive networks are applied to enable dynamic spectrum access, co-existence of different
wireless networks, and interference management. The cognitive radio paradigm is set to drive the
next generation of standards and principles governing the mobile communication and cellular
networks. The cognitive radio technology ensures that the communication systems have flexible
development and there is the deployment of the highly adaptive radios where systems are built
upon the software defined radio technology.
The cognitive radio technology opens several frontiers that can be explored to develop better and
more efficient wireless communication systems for wireless and mobile computing. The systems
end up forming the cognitive radio networks in the cellular mobile communication networks by
extending the radio link features and attributes to a given network layer function. The system
classifies the CRN architecture into a number of unidirectional links and structures. This paper
seeks to carry out an analysis on the MATLAB software for the cognitive network and the
performance analysis of the spectrum-reuse. Common networks introduce issues for the protocol
design, power efficiency, spectrum management and detection, for the emotional awareness and
improved algorithm design. The radio resource allocation policies and economic considerations
are posed by the inherent transmission misappropriations on the wireless links and mobility of
the mobile network end users.
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TABLE OF CONTENTS
INTRODUCTION.....................................................................................................................................4
LITERATURE REVIEW.........................................................................................................................6
Cognitive radio networks.........................................................................................................................6
Digital modulation.................................................................................................................................11
Spectrum sensing...................................................................................................................................12
Signal detection & Link budgets and cognitive radio network design...................................................18
Agile transmission techniques in cognitive radio networks...................................................................20
SYSTEM MODELLING & MATLAB IMPLEMENTATION............................................................20
CONCLUSION........................................................................................................................................21
REFERENCES........................................................................................................................................21
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INTRODUCTION
There is a growing need for the wireless applications and services and as a result the spectrum
resources are needed to meet this demand. The spectrum is allotted to services where the service
provider acquires a frequency band or block from the telecommunication regulatory body in a
given nation. All the services provided require some frequency block which is expected to
increase rapidly and it is able to move towards a fully wireless system where the spectrum is
enhanced. It is very difficult to find a frequency block years later as the primary spectrum is
already assigned to several existing services. The regulatory bodies do not allow the unlicensed
users to access the licensed spectrum. These unlicensed users are required to use a highly
complex, interference-prone frequency band with other unlicensed users. There is indeed a huge
spectrum scarcity problem for the primary frequency spectrum band. A swift scan of the
frequency bands allocated for services in urban settings reveals many unoccupied frequency
bands in the spectrum while those occupied may only be partially occupied. The remaining parts
are heavily used. The radio spectrum, for instance, is quite a limited resource. The resource is
governed by telecommunication bodies and national communication regulatory bodies such as
the federal communication commission in the United States of America.
Cognitive networks are used in the development of the experimental protocol stack to be
implemented in system networks, for instance, cognitive radios. The networks are developed to
have scalable auto-configuration and network management. The dynamic network layer seeks to
support the functionality of the system such that there is IP, group messaging, and rich queries
for the system. The network build on the foundation of the cognitive radio using the GNU radio,
KU agile radio, and the Rutgers radio which has a protocol stack built upon it. The network layer
has an overlay with structured and unstructured for the P2P and the DHT. The services are used
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to map better and particular overlays. The overlay is used to determine the appropriate
application layer of the semi-persistent links between participating nodes that is used to forward
messages between the distributed application elements.
The current wireless communication systems are implemented in the telephony and interactive
internet data for the multimedia type of application. All communication systems desire improved
data rate during transmission and little or no interference. The frequency spectrum is a very
scarce resource that is allocated by telecommunication bodies to the different service providers.
These service providers are able to transmit information to the different mobile users using their
allocated frequency range in the spectrum with a guard band aimed at avoiding interference
between different channels. The technology used in cognitive radio networks presents a new
approach to the use of the scarce resource, that is, the frequency spectrum.
The concept is implemented in the wireless communication networks to ensure that the available
radio spectrum is used comprehensively and that the frequencies can be re-used in different cells
on the mobile communication networks. The cognitive radio technology opens several frontiers
that can be explored to develop better and more efficient wireless communication systems for
wireless and mobile computing. The systems end up forming the cognitive radio networks in the
cellular mobile communication networks by extending the radio link features and attributes to a
given network layer function. The system classifies the CRN architecture into a number of
unidirectional links and structures. This paper seeks to carry out an analysis on the MATLAB
software for the cognitive network and the performance analysis of the spectrum-reuse. Common
networks introduce issues for the protocol design, power efficiency, spectrum management and
detection, for the emotional awareness and improved algorithm design.
The system provides a solution to the crowding problem that results when too many service
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providers have purchased the frequency bands and the remaining bands are limited. The
cognitive radio networks perform the cognitive operations such as the sensing of the spectrum to
determine unused sections of the spectrum. The analysis seeks to determine interference spots,
noise temperature in the transmission network, radio channel characteristics, and the availability
of power in the spectrum. The mobile communication field has encountered advancements in
technology by adopting intelligent systems to have features such as smart antennae, cognitive
packets, smart radios, smart packets, and ultimately cognitive networks. The cognitive networks
employ a wide knowledge base to ensure that the networking technology is addressed using the
common aspect of the technology implemented. The cognitive radio is analysed as the most
preferred cognitive network within the system level scope of mobile communication. The
network intelligence ensures that the resources implemented are understood from a user
requirement point of view and the resources are only allocated to meet these requirements. The
model seeks to improve performance in the networks as well as ensure quality services. The
paper seeks to define the spectrum sensing techniques employed in the efficient implementation
of the fixed frequency spectrum allocation for the wireless communication networks while
utilizing the unused channels or frequency blocks in the network.
LITERATURE REVIEW
Cognitive radio networks
The cognitive network for the radio spectrum is a novel technology that seeks to improve the
spectrum utilization. It allows another user to borrow the unused portion of the frequency band in
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the radio spectrum and in this case, the unlicensed services share the frequency band with
primary licensed users. The cognitive radio operates in a radio frequency environment and it
selects the communication parameters needed to optimize the spectrum usage as well as to adapt
the transmission and reception accordingly. The communication parameters under focus in the
implementation of the cognitive radio are the carrier frequency of a signal, the type of
modulation employed, and the transmission power alongside the signal bandwidth. The cognitive
radio network has a level of intelligence that enables it to sense its surrounding in order to easily
adapt to the current radio environment. The cognitive radio snoops to find holes in the spectrum.
The system provides the frequency in the spectrum holes to the unlicensed users without
interfering or causing harm to the primary user. The cognitive radio is constantly sensing the
spectrum to ensure that once the primary user is back online, the unlicensed user is denied of
service or is transferred to yet another identified spectrum hole. The move seeks to reduce any
form of interference or breach of spectrum use. The allocation to the spectrum holes for the
unlicensed users is a challenge as the different spectrum holes may have the primary users on
different modulation schemes, data rates depending on the transmission device or mobile
equipment being used, and the transmission power in that channel. The secondary users or those
assigned by the cognitive radio network may cause some form of interference such that the
variable propagation environment may be different from their inherent parameters.
The cognitive radio can provide the spectral awareness technology to support FCC initiatives in
spectral use. The software defined radio is developed as a basic platform on which the cognitive
radio is established or built. The software defined radios are the result of the evolutionary
process based on the purely hardware-based equipment to fully support the software-based
equipment. The process is defined that the hardware driven radios, digital radios, and the
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software defined radios are involved. The hardware driven radios constitute the transmit
frequencies, type of modulation, and the radio frequency parameters where the hardware may
have changes. The digital radio in the process is concerned with proper signal processing and
transmission of the digital signals. The signal may be programmed for use in the given system.
This paper discusses the software defined radios for all the functions, modes, and applications to
be configured and reconfigured by the software. Cognitive radio network reference a smart and
alert network that knows what services are available and it can identify them. The system goes
ahead to use the empty spectrum to communicate even more efficiently. The services that
interest the users in a given proximity are easily identified and the system is able to know the
current degree of needs and the future likelihood of the user requirements. The system is able to
learn and recognize the usage patterns of the users so that the Model based reasoning is
employed to meet this objective.
Applications are continuously changing and allocated frequency blocks have diminished the
available limited spectrum. Frequency is a key communication parameter alongside time and
space which run on the 3 degrees of freedom for a communication system for support. The
frequency separates users on the variation of the different frequency bands. The traditional
method requires analog filtering and the system is able to exploit wide bandwidths and DSP as
well as higher frequencies. They tend to present CMOS technology which allows the
communication system to implement up to 100GHz for the system allocation. There is a space
and angle factor that reduces the transmit power. It decreases the radius of omnidirectional cells.
The implementation of the UWB, 60 GHz cognitive radio on the 3 degrees of freedom exploits
the angular nature of the spatial channel by implementing multiple channels. The implementation
further focuses on the use of impulse filtering and sense interference and avoidance.
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The illustration below seeks to describe the cognitive cycle employed for a flexible mobile
multimedia communication scheme such that,
The SDR products and technique are implemented in modern mobile communication systems
and they are actively being improved by standard bodies and organizations. The cognitive radios
have the ability to implement the protocols and policies beyond traditional communications. The
software defined radio defines the type of radio that digitizes its radio frequency and
intermediate frequency functions. Some of the functions that are set up in the digital domain
include the waveform synthesis. The model seeks to obtain a greater flexibility of the system for
the radio operation modes. The SDR does not exhibit the level of intelligence in spectrum
synthesis and sensing as the cognitive networks do.
Mitola’s research defined the cognitive radio as a growing research area with increased interest
in being the next generation of the software defined radio which lacked the intelligence to
navigate through unused spaces in the radio spectrum. The cognitive radio network makes smart
decisions on the frequency and bandwidth that the ISP configures to ensure the communication is
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highly reliable and efficient for the spectrum being used. The radio network has been analyzed
for years with the aim of defining the radio environment and its own behavior. Simon Haykin, in
signals and communication, defined the cognitive radio networks as an intelligent wireless
communication system that is in sync with the radio surroundings. The system that uses the
mode of understanding to build and learn from the environment while adapting to its internal
state of the statistical variation for the incoming radio frequency stimuli. The system seeks to
provide highly reliable communication at all times while efficiently implementing the radio
spectrum.
The mobile communication networks in the modern age are adopting a level of intelligence to
ensure that they sense and automatically adapt to the environment accordingly. The mobile
multimedia networks are faced with several challenges like the scarce resource allocation of the
frequency spectrum and the interference of channels during communication. There is a lot of
wastage when a given section of the frequency spectrum is allocated yet unused. Most of the
cognitive networks are applied to enable dynamic spectrum access, co-existence of different
wireless networks, and interference management. The cognitive radio paradigm is set to drive the
next generation of standards and principles governing the mobile communication and cellular
networks. The cognitive radio technology ensures that the communication systems have flexible
development and there is the deployment of the highly adaptive radios where systems are built
upon the software defined radio technology.
Digital modulation
The carrier signal in a cellular network undergoes modulation such that the message signal is
superimposed to a carrier signal. The sine wave on which the attributes of the information signal
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when the signal is modulated. During modulation any reliable message signal can be detected by
an appropriate demodulator sub-system. There are two types of modulation are the analog and
digital modulation. The following block diagrams illustrate the digital and analog modulation
techniques:
Modulation ensures the digital and analog information is converted to a waveform that is suitable
for transmission over a given medium. It involves the variation of different parameters of a
signal as a function of time or frequency. Some of the common analog modulation techniques
employed in common systems are the amplitude shift keying, frequency shift keying, and phase
shift keying.
Spectrum sensing
The cognitive cycle performs spectrum sensing, management, mobility, and sharing. The
cognitive radio system detects the unused sections of the spectrum, also known as the spectrum
holes. It initiates sharing the spectrum holes with unlicensed users while the primary users of the
frequency blocks do not encounter harmful interference from these new users. The cognitive
radio network senses these using the best techniques to ensure no interference with the primary
users. The network seeks to analyze the communication parameters in a given spectrum hole
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before assigning it to a new service. The service needs to be accommodated in the
communication attributes of a given spectrum hole as sensed. The service assigned to these
unused portions of the spectrum need to demonstrate a match between the user communication
requirements and the communication parameters of the unused spectrum portions. The cognitive
network users are able to exchange frequency of operation once the user requires of the
frequency block or channel. The cognitive users must share the limited spectrum holes hence the
sharing process is scheduled using different scheduling methods. The spectrum sharing is quite a
challenge for the implementation of the cognitive radio network in many mobile communication
networks.
The cognitive radio exploits the time degree of freedom by sensing if a signal is present before
taking the relevant measures to assure that there is no interference. The cognitive radio may opt
to use the time and frequency communication parameters to sense the spectral environment over
the wise bandwidth and transmit signals within the white spaces. It detects if a primary user is in
the frequency block at a given time or if the primary users wishes to use the block and moves to
another new white space. The system ensures that the service moved to a new white space is able
to adapt bandwidth and power levels with the aim of meeting QOS requirements. The spectrum
sensing is key in enabling the functionality and it must be very sensitive to limit unwanted
interference.
When sensing very weak signals,
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The cyclostationary feature detector is able to set a new radio functionality which requires new
algorithms and understanding over the spectrum density and focusing on the spectral correlation.
The sensing performance is evaluated on the basis of the log time against the input SNR.
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The coherent sensing conducts the correlation of the fixed header using the adaptrum in the FCC
trials to result in the highest performance levels. The sensing is tested in a laboratory setting
using the ATSC sensitivity measurement equipment such that,
Using the Adaptrum software to plan a bay area for cognitive area using the 400MHz frequency
band experimental testbed, the geographic output was obtained as,
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The spatial degree of freedom is used to improve the spectral sensing in the cognitive radio
network. The spatially separated sensing radios can make independent measurements. The single
radio sensitivity can be improved by the use of the multiple antennae using the beam forwarding
technique. When the network spectrum sensing is tested to determine the probability of detection
against the probability of recording a false alarm, the spacing parameter outputs,
The wide band sensing quickly senses an open band in the radio network. The small signals need
to be sensed in the presence of strong interference and then processed digitally. The technique
places difficult requirements on RF front end and for the analog or digital conversion. The muti-
antenna spatial processing provides several solutions. It aids the improvement of the N antennas
by allowing the suppression of the up to N-1 large signals and it further provides for not less than
N times. The results is that the sensitivity is increased for the different arrays.
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According to Yang, The time domain interference cancellation is set to address the dynamic
range problem. The signal system is as illustrated in the block diagram below,
The system can be implemented to yield N+M equivalent bits having being passed through
digital modulation for the dynamic range,
Signal detection & Link budgets and cognitive radio network design
It is important to calculate how far any equipment can transmit signals with all the loss
parameters taken into consideration. It enables one to understand why mobile communication
networks erect very high masts for long links. There is software used to help automate the
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Time Domain
Wideband Signal
Interference Estimation
A/D Digital
Processing
Attenuate Strong Interference
and Reduce DR to ADC
+ -

RX

process of planning the radio links. Signal power is diminished by geometric spreading of the
wave front using the free space loss and the power of the signal is spread over a wave front. The
area of which increases as the distance from the transmitter increases is measured for the
diminishing power density. In a mobile communication network, the power in a wireless system
is evaluated from the transmitter to the receiver with the receiver sensitivity taken into
consideration such that,
The performance of the mobile communication system link depends on the quality of the
equipment being used. The link budget is the most preferred technique for the link performance
quantification. The received power in an 802.11 link is determined by the transmit power, the
transmitting antenna gain, and the receiving antenna gain. The power transmitted must be greater
than the minimum received signal level of power factoring in the free space loss for the link to be
qualified as a viable means of transmission. The difference between the minimum received
signal power level and the actual received power level defines the link margin.
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For the viable transmission link, the link margin is desired positive and should be designed to be
at least 10dB for the links. In such mobile communication links there are Fresnel zones. These
are defined as the ellipsoid-shaped volume around the line of sight path between the transmitter
and the receiver. The Fresnel zone is the region of integrity of the radio frequency link which
defines the volume around the line of sight that must be clear of any obstacle for the maximum
power to reach the receiving antenna. The objects that are considered to attenuate the received
signal within the Fresnel Zone and which are considered to be stumbling blocks to transmission
of wireless signals are the trees, hilltops, and buildings especially in a rural and urban setting
respectively. Radio waves are not confined to a perfectly straight line, they tend to occupy a
volume in space. The Fresnel Zone theory describes the propagation of a wave which may causes
the interference and the Fresnel Zone is partially blocked by obstructions with the signals
arriving at the far end tending to diminish.
Agile transmission techniques in cognitive radio networks
There are some infrastructure based approaches where the spectral awareness etiquette is
implemented on the existing mobile communication network such that it supports reuse- spread
economic support base. There are examples of spectrum sharing protocols such as the trunked
radio, cellular spectrum borrowing, demand assigned multiple access and the infrastructure
support on the different range of spectrum management policies. Some of the most common
policies implemented for management purposes in the infrastructure support include the match
requirements, definition of priorities, and the spectral mask of the different owners. In the
implementation of the cognitive network, there is a waveform orthogonality where the signal
parameters are manipulated. The CSMA sensing is involved in the waveform orthogonality to
ensure high priority users are support. The very distinct modes implemented are the adaptive
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frequency, spatial beam steering and null steering, and the adaptive TDMA.
For the mode that considers time, frequency, and space, the spectral reuse is based on the
operation where the transmitter forms a beam towards the intended recipient receiver while it
leaves a null towards the interference sources. For a digital communication, there is an additional
waveform orthogonality technique known as the adaptive bit loading onto the OFDM carries
based on the signal to noise ratio. The OFDM interference avoidance is implemented in the
cognitive radio networks such that,
The OFDM technique is implemented where small spectral holes are filled by one or a few
carriers that fit the time-frequency hole. The OFDM carriers are selected for use that fall into
available spectrum and the interference suppression and multi-user decomposition. The
importance of adaptive power control and the Ad hoc network provides the shortest hop routing
for the wireless APC.
SYSTEM MODELLING & MATLAB IMPLEMENTATION
While using the time domain cancellation in CDMA systems, the analysis is in the analog
domain. The time domain wideband signal is obtained from the antenna. An interference
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estimation is generated and it is used to determine the attenuation with reference to the strong
interference to reduce the DR to analog to digital converter. The system employs digital
techniques and assumptions to determine the interference levels in the transmission and receiver
systems. The attenuation of the strong interference and reduction of the dynamic range to the
residue ADC is extended by the effective number of bits for the system which is nearly 6 bits.
The goal of spectrum sensing is to determine which of these hypothesis holds,
The cognitive radio may opt to use the time and frequency communication parameters to sense
the spectral environment over the wise bandwidth and transmit signals within the white spaces. It
detects if a primary user is in the frequency block at a given time or if the primary users wishes
to use the block and moves to another new white space. The system ensures that the service
moved to a new white space is able to adapt bandwidth and power levels with the aim of meeting
QOS requirements. There are Grey spaces in the spectrum which is modeled as,
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The software radios permit the network or the users to control the operation of the software
radio. On the other hand, the cognitive radio seeks to enhance the control process by adding a
level of intelligence and autonomy to the control of the radio. It provides a sense of environment
awareness with a goal to improve the operations. It ensures that there is an awareness of the radio
capabilities to negotiate waveforms with other radios. The radio has control over certain
processes that permit the radio to leverage situational knowledge and intelligent processing to
autonomously adapt towards the given goal.
The RF components are expensive and their cheaper analog alternatives are more and they spur
out-of-band emissions. The system is able to process the cognitive radios which are able to adapt
around spurs while teaching the radio to reduce the spurs. The cognitive radio provides an
improved link reliability as the radio takes action to compensate for the loss of signals and the
radio learns best course of action from situation. The system is able to aid cellular system to
inform systems and other radios of identified gaps.
The radio network observes the environment, learns from it and ensures that the environment is
in an automated fashion to ensure automated interoperability. The underutilized spectrum can be
traded to support the huge demand for service. The faster spectrum trading may permit for the
significant increase in the available bandwidth. The radio is able to leverage the services that it
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provides to other radios and the system has goals to identify the potential collaborators while
implying the observations of processes. The system has classes of collaboration known as
distributed processing and distributed sensing. The Matlab implementation is given such as,
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RESULTS
The angular isolation of the beam formed signal requires not only co-location but also it must be
in the same angle. It essentially eliminates the interference by incorporating other unlimited
capacity techniques such as UWB for spectrum sharing and cognitive techniques to achieve the
unlimited nature of the spectrum. There is an increase in the number of users with the multiple
antennas that provide an unlimited increase in the frequency or the antenna area for increase.
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To obtain the complementary ROC of cooperative sensing with the AND rule considering the
additive white Gaussian noise. The simulation has the theoretical n factor at 10 and 5
respectively. The spectrum sensing does not rely on any external system hence there is no need
to change the primary system which is simple and affordable for the service provided. It is
suitable for dynamic spectrum bands. The wide range of spectrum sensing algorithms such that
detection performance, complexity, computation cost, and applicability.
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CONCLUSION
The spectrum sensing works on the multiuser frequency-hopping primary network. The cognitive
network users are able to exchange frequency of operation once the user requires of the
frequency block or channel. The cognitive radio technology opens several frontiers that can be
explored to develop better and more efficient wireless communication systems for wireless and
mobile computing. The systems end up forming the cognitive radio networks in the cellular
mobile communication networks by extending the radio link features and attributes to a given
network layer function. The system classifies the CRN architecture into a number of
unidirectional links and structures. This paper seeks to carry out an analysis on the MATLAB
software for the cognitive network and the performance analysis of the spectrum-reuse. Common
networks introduce issues for the protocol design, power efficiency, spectrum management and
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detection, for the emotional awareness and improved algorithm design. The cognitive users must
share the limited spectrum holes hence the sharing process is scheduled using different
scheduling methods. The spectrum sharing is quite a challenge for the implementation of the
cognitive radio network in many mobile communication networks.
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