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COGNITIVE RADIO
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CHAPTER 1
INTRODUCTION
Interest is rapidly growing in lowering barriers to spectrum access and
improving spectrum efficiency. The introduction of software-defined radios
and the realization that new levels of computational performance applied to
radios creates exciting new possibilities for wireless devices. This has resulted
in explosive growth in interest in cognitive radios. The term cognitive radio
was first used by Joe Mitola. The concept and the term cognitive radio quickly
caught the interest of many in the communications field.
Cognitive radio technology enables a number of capabilities to
improve the usefulness and effectiveness of wireless communications. Those
functions include:
Exploit locally vacant or unused radio channels, or ranges of radiospectrum, to provide new paths to spectrum access.
Roam across borders and perform self-adjustment to stay incompliance with all local radio operations and emissions
regulations.
Negotiate as a broker on behalf of the radio user with multiple serviceproviders to give network access best matched to the user needs at the
lowest cost.
Adapt itself without user intervention to save battery power or toreduce interference to other users.
Make use of location awareness to ensure that radio emissionsdo not interfere with licensed broadcasters.
Understand and follow the actions and choices taken by theirusers to become more responsive and anticipate user needs over
time.
Formulate and issue queries, one radio to another. Execute commands sent by another radio. Fuse contradictory or complementary information.
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This proliferation of the term cognitive radio is validation of the strong
interest in the industry and government for communications systems that can
operate with more intelligence and improved performance. This interest leads
to a need for a common terminology for manufacturers, regulators,researchers, and users all to be able to advance the development of cognitive
radios.
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CHAPTER 2
DEFINITION
Tautologically, a cognitive radio could be defined as A radio that is
cognitive.In the absence of a turing test for radios, applying this definition is
nontrivial and implies a level of functionality that many researchers consider
excessive. Indeed, while many researchers and public officials agree that
upgrading a software radios control processes will add significant value to
software radio, there is currently some disagreement over how much
cognition is needed which results in disagreement over the precise definition
of a cognitive radio. The following provides some of the more prominently
offered definitions of cognitive radio.
In the 1999 paper that first coined the term cognitive radio, Joseph
Mitola defines a cognitive radio as A radio that employs model based
reasoning to achieve a specified level of competence in radio-related
domains.However, Simon Haykin defines a cognitive radio as An intelligent
wireless communication system that is aware of its surrounding environment,
and uses the methodology of understanding-by-building to learn from theenvironment and adapt its internal states to statistical variations in the
incoming RF stimuli by making corresponding changes in certain operating
parameters in real-time, with two primary objectives in mind:
Highly reliable communications whenever and wherever needed; Efficient utilization of the radio spectrum.
Cognitive radio (CR) is type of wireless communication which is used
to receive and identify the channels of communication sharply that which
channels can be operated or which cannot be operated. It progress immediately
into available channels although preventing occupied anyone. This radio-
frequency (RF) spectrum is available for the optimistic users and decreasing
the interference to another client.
Cognitive radio is capable to identify its geological area, recognize and
approve its user, encode and decode the signals, awareness of connecting the
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wireless devices in process and manage the power of output and intonation
components.
2.1. Types of cognitive radio (CR)
Depending on the set of parameters taken into account in deciding on
transmission and reception changes, and for historical reasons, we can
distinguish certain types of cognitive radio. The main two are:
Full Cognitive Radio: Radio in which every possible parameterobservable by a wireless node or network is taken into account. Also
known as Mitolas Radio.
Spectrum Sensing Cognitive Radio: Radio in which only the radiofrequency spectrum is considered.
Also, depending on the parts of the spectrum available for cognitive
radio, we can distinguish:
Licensed Band Cognitive Radio: cognitive radio which is capableof using bands assigned to licensed users, apart from unlicensed bands,
such as U-NII band or ISM band.
Unlicensed Band Cognitive Radio: Cognitive radio which canonly utilize unlicensed parts of radiofrequency spectrum.
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CHAPTER 3
FUNCTIONS
3.1. Spectrum Sensing
Spectrum sensing refers to the action of a wireless device measuring
characteristics of received signals, which may include RF energy levels as part
of the process of determining if a particular section of spectrum is occupied.
Sensing in the spectrum domain is the detection of some signal
features indicating the presence (or absence) of other users/services. These can
include signal energy, periodic features (pilots, preambles, and chip rates),
likely identity of the other users/services, estimation of interference-tolerance
capabilities and estimation of the duration of spectrum occupancy.
Spectrum sensing techniques is divided into three components:-
1. Transmitter detection: The capability must be in cognitive radio
to identify the signals which come from basic transmitter either is nearby in
specific spectrum. There are many accesses are suggested:
Coordinated filter recognition Force or power recognition Cyclostationary characteristics recognition2. Cooperative detection: it specifies the methods of spectrum
sensing at which information is included to detect the main user from multiple
users of cognitive radio.
3. Interference based detection.
3.2. Spectrum Management
Capturing the finest accessible spectrum to fulfill the communication
needs of the user. Cognitive radio must have the capability to settle on the
finest spectrum band to fulfill the needs of quality of advantage over the
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accessible spectrum bands, although spectrum authority affairs are necessary
for Cognitive radios. These management affairs can be divided as:
Spectrum/Range analysis Spectrum/Range decision
3.3. Spectrum Mobility
When cognitive radio user interacts the frequency of process is called
spectrum mobility. The main objective of cognitive radio networks is to use in
energetic manner as a spectrum that will be available from the radio stations to
process in finest frequency band, retain faultless communication needsthroughout the switch to improved spectrum.
3.4. Spectrum Sharing
Spectrum sharing is the method where spectrum that has been assigned
to a license holder is made available to other users on a secondary, non-
interfering basis. The secondary users may have arrangements with the license
holders that are arrived at through some kind of cooperation agreement. Thesecondary users may, by following a set of rules designed to prevent the
possibility of interference, access the spectrum either with the cooperation
of, or alternatively without the knowledge of license holders depending
on the relevant policies and protocols.
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CHAPTER 4
LEVELS OF FUNCTIONALITY
The differences in the definitions for cognitive radio can be largely
attributed to differences in the expectations of the functionality that a
cognitive radio will exhibit. Joseph Mitola considers the nine levels of
increasing cognitive radio functionality shown in the table 4.1, ranging from a
software radio to a complex self-aware radio.
Table 4.1: Levels of cognitive radio functionality.
LEVEL CAPABILITY COMMENTS
0 Pre-programmed A software radio
1 Goal Driven Choose waveform according
to goal. Requires
environment awareness
2 Context Awareness Knowledge of what the User
is trying to do
3 Radio Aware Knowledge of radio and
network components,
Environment Models
4 Capable of Planning Analyze situation(level2&3)
to determine
goals(QoS,power), Follows
prescribed plans
5 Conducts Negotiations Settle on a plan with another
radio
6 Learn Environment Autonomously determines
structure of environment
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7 Adapts Plans Generates new goals
8 Adapts Protocols Proposes and negotiates
new protocols
As a reference for how a cognitive radio could achieve these levels of
functionality, Mitola introduces the cognition cycle, shown in Figure 4.1, as a
top-level control loop for cognitive radio. In the cognition cycle, a radio
receives information about its operating environment (Outside world) through
direct observation or through signaling. This information is then evaluated
(Orient) to determine its importance. Based on this valuation, the radio
determines its alternatives (Plan) and chooses an alternative (Decide) in a way
that presumably would improve the valuation. Assuming a waveform change
was deemed necessary, the radio then implements the alternative (Act) by
adjusting its resources and performing the appropriate signaling. These
changes are then reflected in the interference profile presented by the
cognitive radio in the Outside world. As part of this process, the radio uses
these observations and decisions to improve the operation of the radio (Learn),
perhaps by creating new modeling states, generating new alternatives, or
creating new valuations.
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Figure 4.1: Cognition Cycle
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CHAPTER 5
ARCHITECTURE
Cognitive radios are capable of making decisions and selecting or
modifying the operating parameters of a radio. In the most abstract view of the
Cognitive Radio Working Group, there are two major subsystems in a
cognitive SDR radio; a cognitive unit that makes decisions based on various
inputs and a flexible SDR unit whose operating software provides a range of
possible operating modes.
The Cognitive Radio Working Group developed a conceptual model
that uses a layered architecture where the SDR radio is at the base and is
closest to the physical RF channel. The cognitive layer is above the SDR
layer and below the application layer. One goal of this architecture is to hide
the complexity of the SDR radio from the applications. The combination of a
cognitive "engine" and the SDR together comprise a "cognitive radio" or a
cognitive SDR radio. The cognitive layer acts to optimize or control the SDR
with minimal user interaction or oversight. In this model the cognitive engine
accepts inputs, makes decisions and inferences from a pool of current and
historical contextual knowledge and issues control or configuration
commands to the flexible-architecture SDR radio.
The basic function of a cognitive radio is matching the radio link
requirements of a higher layer application or user need with the available
device, spectral and infrastructure resources. The cognitive layer could also
be aware of the data rates and quality of service requirements of the
application.
The cognitive layer would be aware of the radios hardware resources
and capabilities. It would store an inventory of the software modulation
schemes available and the capabilities and characteristics of these
modulation and spectrum access schemes. The cognitive layer could know
the measurement utilities available to allow it to collect information to feed the
decision process.
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In this model the rules or decision algorithms are stored separately
from the engines to enable them to be updated easily. The cognitive function
is further separated into two parts as shown in the block diagram in Figure 5.1
below. The first labeled the cognitive engine tries to find a solution oroptimize a performance goal based on inputs received from other parts of the
radio. These other parts can supply information that is the basis for
awareness as described above.
The second engine is the policy engine and is used to ensure that the
solution is in compliance with regulatory rules and other policies external to
the radio. Each of these engines has a separate rule-set or algorithm-set. The
reason we have shown them separately is that these subsystems perform two
different tasks. The policy engine isolates policy or regulatory rules from the
operational capability rules of the radio as regulatory policies apply to all
radios. The purpose of the policy engine is to veto, if necessary,
adaptation choices made by the cognitive engine.
Cognitive rules are likely to be written to be compatible with the
specific capabilities of a particular radio.
The cognitive engine strives to find ways to adapt the radio to best
meet a goal or a set of priorities based in awareness of both internal and
external conditions. This view is a conceptual one and implementations may in
practice share processing hardware and memory.
The cognitive layer, using the available radio resources, could monitor
RF environment and gain awareness of external users and the presence of
unused spectrum. It could monitor and be aware of the presence of relay
nodes or infrastructure access points that the radio could use. It could also
utilize other criteria in the decision process, such as whether to maximize
battery life or minimize operating expense.
It is envisioned that in the future, advanced cognitive SDR radios could
learn and innovate, meaning they test new hypotheses, store and recall
adaptations that resulted in successful outcomes in addition to those that may
not have improved performance in future, similar situations.
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The inputs come from both the lower SDR layer and from the upper
application layers. The SDR, or special monitoring subsystems, provide inputs
including the status and current capabilities of the radio and the results of
spectrum scans. The upper layers will provide inputs including informationabout the desired data rates, QoS and inputs from other sensors such as GPS
based location.
The decisions can be simple or complex. The decision making activity
can also make use of some memory along with the external inputs. This makes
it possible for the radio to learn and possibly improve the quality or speed of
its decisions. Decisions can be derived using declarative languages combined
with inference engines. In other systems, decision systems can be
implemented using game theoretic or genetic algorithms. Of course, simple if-
then-else decision trees can be implemented in imperative languages such as C
or Java.
Figure 5.1: Conceptual view of Cognitive Radio Architecture
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A less flexible hardware radio may have some degree of cognitive
ability but will be limited by the ability of hardware to adapt to different
frequencies and modulations. A radio that can operate on only a handful of
channels in a single band using a single modulation will have limitedinterference avoidance ability if all the channels are occupied. A radio that
can only connect to a single radio network cannot change modes to avoid
congestion.
To the extent allowed by the RF hardware a cognitive SDR radio may
be capable of multitasking and can simultaneously receive and spectrum scan.
The interface between the cognitive layer and the application layer can
be a simple known list or array of available modes or a highly abstracted
interface. The abstracted interface of the cognitive layer would appear to
applications in terms of a client requesting a communications service
possibly with particular latencies or data rates.
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CHAPTER 6
FEATURES
6.1. Energy (battery) awareness
Refers to including knowledge or awareness of the remaining amount
of energy in a radios power supply(e.g. available battery charge) to influence
decisions about which operating mode or frequency to use.
6.2. Spatial awareness
A very significant role for a CR may be viewed as personal assistant.One of its key missions is facilitating communication over wireless links. The
opposite key mission is impending communication when appropriate. As an
example most people do not want to be disturbed while in church, in an
important meeting. A CR could learn to classify its situation into user
interruptible and user non interruptible. The radio accepting aural inputs
can classify a long running exchange in which only one person is speaking at a
time as a meeting or classroom and autonomously put itself into vibration only
mode. If the radio senses its primary user is speaking continuously or even
50% of time, it may autonomously turn off the vibration mode.
6.3. Self-correction, Fault tolerance
Refers to the ability of a radio to discover that, for some reason,
something is wrong, and that it can reconfigure itself and thereby recover and
re-establish communications.
6.4. Recovery after incorrect decision, error condition sensing
It is expected that cognitive radios will in some situations adapt their
operating characteristics in a way that worsens performance or possibly
increases the likelihood of causing interference. Decisions should be
followed up with checks where possible to detect these situations and initiate
corrective action. Awareness of error conditions could be part of the input set
of the cognitive engine.
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6.5. Negotiation
Negotiation refers to radios that can adapt to new operating
characteristics based not only on knowledge of their own priorities and goals
and environmental state. Radios and networks that can share knowledge and
negotiate with each other to select mutually optimal operating characteristics
may perform better. A negotiation language that can express the concepts of
and offer and counter-offer may prove useful
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Unrestricted roaming for consumers using different types of wireless
services such as GSM, CDMA, and WCDMA in addition to WLAN networks
could become more common with the introduction of cognitive radios and
systems. These consumer radios could listen for the presence of accessnetworks and select the carrier that best meets a users needs.
Management of identity and authentication are also important aspects
of interoperability. The identity of the users of radios who wish to join a
network needs to be assured. Authentication that the devices themselves are
suitable and authorized for use on a network is critical. The SDR Forum
Public Safety SIG has explored some of these issues in greater detail and has
published a document describing improvements in interoperability.
7.2. Reduced demand on user, reduced user control burden
Another potential benefit of cognitive radios is the reduction and
simplification of the tasks needed to set up and use a radio. Cognitive radios
aware of a users goals and priorities, and capable of independently acting,
could simplify the operation of radios. A flexible SDR radio needs some form
of input or command to set the operating frequency, power level, modulation,
bandwidth, and possibly many other radio parameters. For example, filters
may need to be tuned and different subsystems may need to be switched in to
enable certain operating modes. Software routines may need to be selected,
loaded and run to facilitate operation using a new waveform. Enhanced
flexibility in a wireless device offers a greater number of possible
options and settings. There is value in significantly reducing the burden of
technical knowhow on the part of the user using cognitive functionality. Usersshould be able to utilize the capability of the radio with a minimum level of
detail over radio operating parameters, with the radio making appropriate
choices among options.
7.3. Greater spectrum efficiency through improved access
The term spectrum efficiency, as used in the SDR Forum Cognitive
Radio Working Group, refers to increasing the efficiency of how spectrum isassigned and used to support one or more wireless services in one or more
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geographical locations in either a concurrent or time-based manner. New
methods provide ways of accessing spectrum that would have been excluded
by regulatory policy and licensing rules in the past. One scenario involves
use of licensed spectrum by unlicensed users using protocols and etiquettes tominimize the potential for interference to licensed users.
Wireless devices that are aware of their spectral environment provide
benefits by being able to access previously unused, unavailable, or restricted
spectrum segments that may be available for usage in other geographical areas
or under other regulatory regimes. Spectral awareness may enable the use of
this spectrum without causing interference to the radios originally operating in
the spectrum. Radio spectrum is perceived to be a scarce resource: there may
be a shortage of spectrum available for dedicated allocation without displacing
current users. Interest is high to find ways to use spectrum more efficiently.
Utilization levels vary widely between services and geographic areas, with
some having substantial amounts of white space, or unused spectrum
segments at any point in time. Radios capable of exploiting unused or lightly-
used spectrum without introducing interference will improve efficiency of
spectrum utilization.
Figure 7.1: Opportunistic spectrum utilization
To improve spectrum utilization, opportunistic spectrum utilization has
been proposed wherein devices occupy spectrum that has been left vacant. An
illustrative example of opportunistic spectrum utilization is shown in Figure
7.1. In the left half of the figure, a pair of transmitted carrier signals is presentin the lower frequency bands while a random access system and a TDMA
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system are operating in the upper bands. After observing the spectrum holes -
points in time and frequency where spectrum is underutilized opportunistic
devices could fill in these holes to support concurrent services as illustrated in
the diagram on the right.
7.4. Improved application interface for communications tasks
A Cognitive radio can provide communications services that allow
users to designate a priority or a value for each particular communications
task. For example, email might be given a higher priority than streaming
video. Cognitive radios could be aware of the requirements that different
applications on a radio have for data throughput rates, latencies, and quality ofservice (QoS) levels. These services become increasingly important as users
multiplex applications (e.g. streaming audio and video while simultaneously
text messaging) and executing applications in parallel. The cognitive SDR can
support communications by using prioritized connection use rules (i.e. drop
streaming audio if incoming call), time of transmission optimization (i.e. batch
low priority uploads/downloads until low cost, high bandwidth connections),
appropriate channel bandwidth to match endpoint coding/decoding schemes,
and adaptive compression to balance bandwidth usage (i.e. increase
compression in voice over IP (VOIP) conference call scenario). The cognitive
radio can also gracefully degrade the supplied services according to
environmental conditions such as link quality changes, interference, and
energy-source degradation in order to help maximize the useful operating
lifetime of the device
7.5. Dynamic Regulatory Compliance
Radios that are aware of their locations and current regulatory
jurisdiction can update and maintain compliance with local regulations. This is
important for radios that are likely to cross borders. This awareness combined
with the ability to update a radios knowledge of regulatory rules could
allow regulations to adapt more quickly to new technologies.
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7.6. Radio performance optimization
A radio that is aware of its internal state can improve its performance
compared to a traditional radio. For example, a radio aware of its remaining
energy level could adapt its data rates or modulation type to maximize its
operating time. A radio that was aware that its decoder was operating near the
limits of its abilities may adapt its data rate or bandwidth to increase the
operating margins of the communications link.
7.7. User based Cognitive Adaptation
An additional level of cognition may be the radios awareness of its
user. Soft biometrics enables a CR node to recognize user identity. Sensors for
medical triage and first responder health may indicate to a wearable CR the
health of its user, enabling the radio to adjust even its physical layer (power)
or network layer (routing parameters from forwarding to flooding) to call for
help if a first responder is in need. The robotics industry is developing robots
for health care, and these robots will have different priorities for use of
wireless services for various forms of service and assistance. Although the
radio itself would not take on the job of assessing the state of the user, the
cognitive radio that is user-aware may autonomously adjust air interface,
application, and protocol stack agility to provide the most appropriate mode of
communications on a scale of assured connectivity to better bandwidth
without the user having to explicitly program or control the SDR.
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CHAPTER 8
DISADVANTAGES
With any emerging technology there are drawbacks that can potentially
affect the development of the system. Key problems that arise for CR include:
Encompasses the same drawbacks as software defined radio Loss of control Regulatory concerns Significant research remains to be done to realize commercially
practical cognitive radios
With any software define radio based technology there are always
complexity drawbacks. Since the core of CR resided with software defined
radio, CR inherits most of the same problems associated with software defined
radio. Some of the drawbacks associated with software defined radio are:
Security Software reliability Keeping up with higher data ratesThe process of CRs sense, learns, and adapt cycle changes the outside
world for other cognitive radios with each cycle. This can potentially result in
loss of control if a group of radios interact with each other causing chaotic
networks. As far as regulatory concerns apply to CR the current FCC
regulations are not specified or designed for CR use. The fear is that
regulations will retard the development of cognitive radio or actually reduce
available spectrum. The concept of CR is still evolving and there are many
research areas that need to be addressed for the systems. This includes:
information collection and modeling; decision processes; learning processes;
hardware support
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CHAPTER 9
FUTURE OF COGNITIVE RADIO
Today engineers are trying to make further adaptable operating
capacity to upcoming radios, mobiles and other wireless communication
accessories. In future, it will be permitted that cognitive radio technology
almost wireless networking that will use to establish and to connect to any
nearby accessible unused radio spectrum that facilitates the customer.
Cognitive radio technology can improve interoperability by enabling
devices to bridge communications between jurisdictions using different
frequencies and modulation formats. Such interoperability is crucial to
enabling public safety agencies to do their jobs. Example: National Public
Safety Telecommunications Council (NPSTC) supported by U.S. DOJs
AGILE Program for the public safety.
Planning applications are one of the new attractive technologies that
CR will enable. Navigation using databases and GPS signals will increase.
Some of the planning applications envisioned are:
Route planning Battery Management Noise Discipline Light Discipline Management of Information Flow Role Assignment as a function of the operators skills Talk Group Assignment Smart Calibration Smart Bridge (recognize the need for two or more legacy to
communicate and connect them through a bridge)
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CHAPTER 10
CONCLUSION
We have discussed a number of different considerations of the use of
Cognitive Radio technology. The challenge is to understand its implications,
and make use of its capabilities to specify, design, and operate
communications systems that provide users with capabilities they need,
enhance their applications, and make them more effective. Gaining more
utility from existing spectrum or minimizing the acquisition cost of additional
spectrum for additional services is shown to have a huge monetary
value. And in the commercial world, time is also critical. Systems must
complete their communications tasks within an acceptable time frame to suit
the users purposes. All of these goals are substantially enabled by cognitive
radio capabilities.
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CHAPTER 11
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