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442 C.-I. Badoi et al.

At the same time, a next generation mobile communication network (the fifth genera-

tion5G) is being discussed. 5G has been proposed to bring together the existing wireless

and wired communication techniques into an all IP (Internet Protocol) high performance

world wide network.

This paper proposes 5G through the CR technology: the CR offers the possibility to inter-connect in a functional way the existing wireless technologies and, thus, it offers a complete

integrated 5G wireless access network.

The paper is organized as follow:

Section 2 describes the mobile telephony standards evolution over the time, and presents

the 5G concept as shown in the literature (features and terminal/network requirements). The

WISDOM (Wireless Innovative System for Dynamic Operating Megacommunications) con-

cept, which is the main 5Gs improvement in comparison with the 4G technology, is also

discussed.

Section 3 presents the CR technology andits implications/changes in the open systeminter-

connection (OSI) layers functionality. The section gives the state-of-the-art of CR and high-

lights a cognitive communications world need, as response to the increasing users demands.

Section 4 puts face to face these two technologies, and underlies the similarities between

them. This section demonstrates that the CR terminal can successfully represent the future

5G terminal, and that CR is the best way to implement the WISDOM concept, by integrating

the wireless technologies and make them cooperate. Also, the CR can provide a new control

plane and new protocols, so that the 5G technology functions properly. It also provides a

strong network monitoring, environment adaptation, and performance increment solutions.

Finally, Sect. 5 concludes the paper by giving a short summary of the proposed CR based

5G advantages and the issues to be solved as future works.

2 5G Concept

The twenty-first century is surely the century of speed, and achieves a high evolution in

all the possible domains, especially in communication: a very large variety of services, soft-

ware, equipments, possibilities etc. But this huge and colored offer also brings a complicated

lifestyle and waste of time for the human beings, and needs to be integrated and achievable

in a simple manner.

Therefore, a new technology started to be delineated, that will provide all the possibleapplications, by using only one universal device, and interconnecting the already existing

communication infrastructuresthat is the fifth generation of the mobile communications

standards5G.

2.1 Evolution from 1G to 5G

The first steps were made at the beginning of the 1980s, with the first mobile standards

family development and implementation (the user was able to geographically move along its

session period).The mobile telecommunication phases as identified in [1,2] (see Fig. 1) are:

1Gthe 1st generation of the mobile telecommunications technology, characterized

by the voice service: an analog radio signal (the voice was modulated and transmit-

ted according to analog techniques), and a 14.4 Kbps data rate. The main standards

within the 1G family: NMT (Nordic Mobile Telephone), AMPS (Advanced Mobile Phone

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5G Based on Cognitive Radio 443

Fig. 1 Evolution towards 5G. Over the last 10 years, the mobile communications have the tendency to inter-

connect all the existing wireless system types, to build a terminal that should support all the voice, video,

and data applications, at very high data rates and users speeds, with the 5G technology as final result. The

figure follows this evolution by taking into consideration the achievable data rates (X axis) and the terminals

speed/mobility (Y axis). With ellipses are represented the 5Gs in time predecessors (see the main arrow)

and the most important wireless technologies (see the secondary arrows), the final goal being an universal

communication technology5G

System), TACS (Total Access Communications System), ETACS (European Total

Access Communications System), JTACS (Japanese Total Access Communications

System).

2Gthe 2nd generation of the wireless telephone technology.

The 2G technology presents significant improvements compared with 1G: the voice is

digital transmitted, a data service is introduced (SMSshort message service), and the

data rate is increased at 144 Kbps. The 2G standards are classified, depending on the

channel access method, in two categories: (1) TDMA (Time Division Multiple Access)

based, with the GSM (Global System for Mobile Communications) standard as the main

representative, and (2) CDMA (Code Division Multiple Access) based, with the IS-95(Interim Standard 95) standard as a main representative.

3Gthe 3rd generation of mobile telecommunications, also known as IMT-2000 (Inter-

national Mobile Telecommunications-2000) standards family:

3G presents a wide range of services: voice/video/data (IP Television, video on demand,

video conferencing, tele-medicine, etc.), higher data rates 2 Mbps5 Mbps/348 Kbps in

a low/high mobility case, a better encryption block and authentication function.

The main 3G standards:

CDMA2000 family of standards (in this family we recall EV-DO, Evolution-Data

Optimized, typically for broadband Internet access);

W-CDMA (Wideband Code Division Multiple Access) or UMTS (Universal Mobile

Telecommunications System).

4Gthe 4th generation of mobile telecommunications also known as IMT-A (Interna-

tional Mobile Telecommunications-Advanced) standards family.

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The IMT-A/4G brings more than a 3G capabilities value increase [2], and presents some

fundamental differences.

By definition [1], the 4G is a system of systems and network of networks, fully IP

integrated; if 3G is using both packet and circuit switching communication methods in

order to transmit data, 4G is a packet switching based technology, presenting the IPsflexibility advantage.

Also, 4G presents a connectivity convergence: (1) heterogeneous access networks con-

vergence and integration, and (2) user terminal convergence. The first convergence type

refers to the possibility of accessing the 4G network via a multitude of heterogeneous

wireless networks: DAB/DVB (Digital Audio Broadcasting/Digital Video Broadcasting),

cellular GSM, IMT-2000, WLAN (Wireless Local Area Network), short range connectiv-

ity with Bluetooth, IR (Infrared Radiation) and UWB (Ultra-Wideband), xDSL (Digital

Subscriber Line), etc.; the second convergence type (terminal convergence) advances

the idea of a smart terminal, able to connect at the 4G network (by selecting the proper

access network) any where and any time, and able to transmit and receive any content

type.

4G characteristics and requirements overview [3,4]:

very high mobility,

higher data rates: 100 Mbps (high mobility)/1 Gbps (low mobility),

large variety of applications and services,

cooperation between different networks/access systems, with an unified architecture

as result,

network detection and network selection (ABCAlways Best Connected concept),

technology and topology independence,

seamless handover and service continuity in case of horizontal/vertical handovers.

Nowadays the most advanced 4G candidate is represented by the IEEE 802.16m [4].

Remark IEEE 802.16e and 3GPPs LTE (3rd Generation Partnership Project Long Term

Evolution) technologies are considered to be 3.9G, not 4G.

By presenting the above mentioned features, 4G becomes the forerunner of a new and

more advanced technology that shall interconnect the entire communication worldthe 5G

technology.

2.2 5G Concept Definition

The 5G field was poorly approached by the researchers. The most of the related papers

are trying to define the 5G concept, properties and requirements, and to delineate the 5G

technology over the 4G technology.

In 2009 [5] proposed for the first time in the literature the WISDOM concept, and gave

an in point 5G definition:

4G & WISDOM 5G

The WISDOM principle brings unlimited wireless world interconnection, convergence, and

cooperation (geographically including cities, countries, continents, and finally, the whole

world), together with a large variety of multimedia services at very high data rates, and

becomes the main 5G definition point.

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2.2.1 5G Requirements

The related literature defines the 5G technology, especially by indicating the differences over

the 4G and the necessary improvements needed to accept the evolution towards a new mobile

telecommunications generation.The main differences are regarding the terminal and networks functionality, as given in

[5,6]:

Requirements related to the 5G terminal:

in order to connect at the 5G network, the 5G terminal must be able to access different

wireless technologies, and to choose the most suitable one (environment knowledge,

information collecting, and, according to some performance criteria, the best selection).

With this aim, the terminal shall include more adaptors, according to the access net-

works (WLAN, WiMAXWorldwide Interoperability for Microwave Access, 3G, 2G,

Bluetooth, etc.) adaptors. also, for a better performance, the 5G user terminal shall be able to switch on various

technologies, during the same session; each network must provide an user mobility

until the terminal will make a final choice in terms of wireless access systems.

the terminal shall combine different streams coming from different technologies.

an high-performance terminal: better modulation and error correction schemes.

Requirements related to the 5G network (regarding the OSI layers functionality):

the first and the second layers functionality is specific to the selected wireless access

technology.

a total IP integration at the third layer (Mobile IP).The terminal will have a single fixed address (most likely an IPv6 address) and sev-

eral temporary CoA (Care-of-Address) addresses, corresponding to the access networks

number to which it is connected.

The network layer (NL) will present three sub-layers: (1) lower NL (uses the CoA

address), (2) Middleware NL (performs address translation: CoAIPv6 fixed address),

(3) upper NL (uses the fixed terminals IPv6 address).

the transport protocol is given by the wireless technology (it appears the terminals need

to download and install the corresponding protocols).

the application layer must present an intelligent QoS (Quality of Service) management

over the networks variety.

Remark The 5G network is intended to also be a high security network (an Authentication,

Authorization & AccountingAAAprotocol integration between multiple systems).

2.2.2 WISDOM Concept: The Main 5G Over 4G Improvement

The objective of the WISDOM system is to create the enabling wireless infrastructure for

the human-centric communications at very high data rates (up to 1 Tbps communications);

specifically, WISDOM aims to design and develop novel technologies, systems and networks

that shall globally integrate, inter-connect, and communicate into a flexible and dynamically-operating architecture [5].

The requirements that WISDOM must accomplish (the WISDOM design requirements):

Network protocols and architectures for heterogeneous networks (new physical layer

techniques, MAC (Medium Access Control) and link layer techniques, cooperative trans-

mission, etc.)the observations made in the previous paragraph remain valid.

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in mind: highly reliable communication whenever and wherever needed; efficient utilization

of the radio spectrum. Haykin [7].

CR technology is based on the fact that the licensed systems (also named primary sys-

tems PS) are not always using their spectrum bands; CR brings new radio typescognitive

radiosthat should firstly, identify the existing spectrum holes, and secondly, utilize themin a flexible manner, according to an access medium scheme.

CRs implications as a new technology, its OSI layers redefinition, and protocols advanced

proposals (see Fig. 2) are presented in the section.

3.1.1 Spectrum Management Implications

By spectrum sensing, it is mainly understood the CRs capability to detect the available chan-

nels, within the pre-existing systems licensed bands.

As well, the CR must detect the PUs (primary users) behavior and act according to their

intentions; if the CR user detects that the PU wants to transmit in the same channel, it respects

its priority, and quits or modifies its transmission characteristics in that channel.

The spectrum sensing function can be seen as a three steps operation:

signal detection: does a signal exist on the sensed channel? (In this step is no need to

know the type of the existing signal);

signal classification: in the case when a signal exist, is the signal a PUs signal? (the

signal type is usually determined by extracting the sensed signal features);

RemarkOnly possible in coherent detection.

channel availability decision, based on some criterion or rule: the channel is or notavailable?

The spectrum sensing function can present optionally the CRs opportunity to exchange infor-

mation/to communicate with each other (see Fig. 2).

After identifying the free channels, the next step is to share the spectrum holes; this

involves a spectrum allocation scheme which may take or not into account the cooperation

between CR devices.

Spectrum sharing shows how the spectrum is shared and used by the radio devices (CR

and PU devices), in other words the CR access channels/medium techniques.

Based on the priority level of accessing the radio spectrum, the spectrum sharing methodscan be classified in different categories:

horizontal spectrum sharingthe radio devices have equal rights to access the spectrum

(between CR users with same priority value);

vertical spectrum handoverdifferent priorities to access the spectrum between PUs

(high priority) and CR users (low priority);

hierarchical spectrum sharingseveral priorities levels of accessing the spectrum (the

CRs, that are competing for the same available spectrum bands, can have different pri-

orities); the hierarchical access is an elevated variant for the vertical spectrum sharing.

Spectrum handovermeans the frequency change in order to maintain the transmission up

(dynamically channel switching); in the CR context, a secondary user changes its frequency

due to the appearance of a PU or because of the transmission degradation.

This dynamically frequency change may affect the CRs connection (it can even stop the

transmission); so, it is necessary to design a seamless handover spectrum scheme, and, when

the context is lost, an efficient recovery procedure.

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Fig. 2 CR-delimitation as a new technology. The figure follows the CR development over the years: a the

CR concept and properties demarcation; b a detailed CR properties analyze, resulting in sub-properties iden-tification; c research direction to approach in order to achieve the presented properties/sub-properties; d the

performance increasing expected results (see the text explanatory notes)

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3.1.2 Environment Adaptation

In this case (see Fig. 2) the sensed information refers to the environment changes (architec-

tures and topological changes, changes in the noise/interference power, etc.), and not at the

spectrum holes availability status.In order to adapt to those changes and to maintain a performance constant level (lets

say a constant noise or interference rate), researchers originate an environment adapta-

tion research field; this new approach consists in new adaptation techniques and switching

methods between different CR device configurations and parameters values.

3.1.3 Routing

CR routing research field [8] is based mostly on the CR requirement to interoperate with

different systems, and is strongly influenced by the spectrum sharing techniques.

Thus, new factors appear in the CR routing metrics design:

the CR need to adapt at the preexisting systems (very relevant are the already defined

protocols that run in the preexisting systems);

the way spectrum channels are allocated between the users. See the two arrows finishing

in the routing module (see Fig. 2).

CRNs inherit the PSs (Primary Systems) network characteristics: infrastructure-based,

mesh, ad-hoc, sensor networks, etc.; these architecture types impose a specific routing algo-

rithm, which must also include the CR devices and the possibility for a CR to be a relay node

for another CR.

Influence of the spectrum holes availability variable nature on the CRN (CR Network)

routing technique

According to [9], the time period that the spectrum bands are unused by the PUs impose

a specific routing technique.

Khalife et al. [9] identifies three cases:

(1) the period that the CRs need the spectrum bands is less than the idle PUs period: static

mesh routing (if the idle periods will permit, we will have proactive routing);

(2) the availability period of the channels is dynamically varying in time: new specific algo-

rithms (for example based on genetic algorithms, evolutionary programming, swarm

intelligence, etc.);(3) the idle PUs period is diminutive than the period that the CR needs the spectrum bands:

opportunistic forwarding without pre-established routes (on demand/reactive routing).

These new possibilities, together with a difficult and dynamic architecture, make the CRN

to be very complex and hard to control.

The CR technology also brings new security and pricing challenges (see Fig. 2):

new security threats appeared at the same time with the dynamic spectrum accessconcept,

as well as the CRs authentication needs [10,11];

the pricing is very much influenced by the used channel allocation scheme; also, CRsmust be designed with strong capabilities to negotiate the available channels price.

The possibilities to increase the performance are also briefly represented in Fig. 2.

All these above analyzed features (sensing, sharing, spectrum handover, routing, adap-

tation, security and pricing) implemented into a single device, offers a very smart and high

performant user terminalthe CR terminal.

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3.2 The Future: An Integrated and Cognitive World

System interoperability means that different systems (systems with different transmission

characteristics and different network architectures) coexist and cooperate.

The communications integration concept was engendered mainly by the society needsand increasing demands; the user wishes real time applications, any time, any where, and

also wants to save time, money and resources; as well, the possibility to successfully face

the special situations (emergency situations) imposed the CR progress.

As it can be seen, the main CR technology advantage is the possibility to adapt and to

cooperate with all the other wireless technologies.

CR proposes the interoperability and integration achievement through Cognition: I

observed my neighbors and now I know their possibilities; I can adapt my behavior to their

needs, and choose the ones that are suiting me.

Thus, CR brings the integration paradigm into the wireless environment, in a high per-

formance level: the CR terminal can download the suitable software, adapt its configuration

parameters, dynamically change the OSI protocols, be connected to all wireless networks

types, and chose the best one to serve its needs.

The result of radio communication technology based on cognition: the CR user can

choose the suitable primary network for its communications, and, very important, two

different wireless networks can be integrated and communicate each other via the CR

device.

4 Proposed Solution for 5G: CR Based 5G

The traditional communications systems present (as basic characteristic) the partition into

access-network and core network respectively.

The centralized manner of approaching the communication is no longer responding to the

increasing users demands. Todays communication world shows the need of a more tightly

integrated architecture.

Thus, by its design properties and possibilities, CR technology become the tool to obtain

this integrated architecture (see Fig. 3).

This papers idea is to use the CR technology as the modality to build the integrated 5G

network.The next subsections will justify this new concept proposal, and will present all the 5Gs

gained advantages/accomplished functionalities, when using the CR technology.

4.1 5GCR Similarities: Short Overview

After presenting in the previous paragraphs the 5G and CR concepts, it can be noted that the

essential similarities between them are:

inter-working with different systems/networks; adaptation: based on the access networks features (5G case), respective on the primary

system network characteristics (CR case);

Remark the 5G integrated access networks and CR primary systems networks have the

same meaning.

new and flexible protocols;

very advanced PHY (physical layer) and MAC technologies;

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Fig. 3 Traditional communication versus 5G communicationnetwork architecture. The figure presents the

difference between the existing communications systems (a) and the proposed 5G technology (b), regarding

the network architecture. The 5G essential improvement is that no longer presents the network splitting into

access/core parts, offering, thus, a more tightly integrated architecture in response to the applications and users

growing demands

a very advanced terminal, endowed with the possibility to scan the environment, with

intelligence and decision capabilities;

resources management (an end-to-end integrated resource management that should in-

clude all the networks involved in the data transmission process);

security (new technologies new security challenges).

Thus it can be summarized that the 5G goal is to integrate/inter-connectvarious types of

communication technologies, and the CR ability is to self integrate into the wireless world

diversity. (Basically 5Gthrough WISDOMintegrates and interconnects all the wireless

technologies, and CR adapts and works with all the wireless technologies.)

Synthesizing, 5G/WISDOM brings the convergence concept, and CR represents the tech-

nological tool to implement it.

4.2 The 5G Terminal is a CR Terminal

The mobile radio terminal had a similar and parallel evolution to that of the mobile tele-

communications standards (see Sect. 2.1), being modified and improved at every new added

functionality/service [1]:

micro-processor controlled analog radio (Voice);

digital radio (Voice and DataSMS);

software defined radioSDR (Multimedia);

CR nowadays proposal: support for all the existing applications and services, access to all

the wireless technologies/systems, and knowledge, reasoning, and decision possibilities

(see Fig. 4).

By definition, the cognitive terminal is a very smart terminal with possibilities to choose

the proper network from all the existing wireless networks, at a given time, adapt to its

demands, and use its resource. Besides the older radio terminals properties, the CR radio

terminal supports all the data types, on demand QoS, and adaptable data rates (knowledge,

reasoning, and decisions properties).

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Fig. 5 CR based 5G. The CR technology is an ideal way to interconnect, in the most flexible and adaptable

manner, the entire wireless medium (2G, 3G, WiMAX, WiFi, WLAN, short range wireless connectivity net-

works, DAB/DVB, xDSL, etc.)that is also the entire world. Until this moment, the CR technology is the

only strong candidate for a good WISDOM implementation, and thus, for a tangible uniform integrated 5G

access network

The technology which should implement WISDOM can only be a technology able to

utilize the already existing resources and communication infrastructures (without changing

them or theirs test procedures, on account of time and money issues), and, moreover, capable

to interconnect the different systems/technologies one to each other.

Thus, it should be noted that WISDOMs implementation demands comply with the cog-

nitive paradigm in the wireless environment:

CR connects and cooperates with all existing wireless networks/systems types, becominga liaison technology between different systems and architectures, and thus, making a

first step for homogenize the diversity (see Fig. 5).

CRN architecture type (CR nodes + pre-existing systems) is consistent with the WIS-

DOM requirements (see Fig. 5): WISDOM does not exclude the pre-existing systems

(on the contrary, it integrates them as access systems inside the 5G network).

CRN modelthe CRN presents two sides: the pre-existing wireless systems (WiMAX,

WiFiWireless Fidelity, etc.), and the CR nodes, operating in the free channels of those

systems [7]. Also, the network model is based on multi-hop CRN: this means that we can

have more CR nodes on the route between source and destination.

The primary users networks are not changed, and the CRs work without affecting or

modifying the pre-existing systems.

CRN is a self organizing and self healing network, based on the cognitive networking

principles; these features are 5G essential in order to manage the complexity induced by

a variety of possible usage scenarios, on the one hand, and to minimize the spectrum and

energy requirements, on the other hand.

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It presents the environment monitoring and adaptation functions (see the following par-

agraph), which are a must for a good 5G network functionality and performance.

4.3.2 WISDOM Shared Context: Challenges

Inter-technology shared context

In order to offer the services in a personalized form, the 5G technology must know some

primary information about its users: identity, location, and privacy issues.

As mentioned in the previous paragraph, the CR based 5G network includes all the exist-

ing networks types, and the CR technology as binding. Thus, the 5Gs challenge to know

every user context becomes a shared context problem between all its pieces technologies (CR,

WiMAX, WiFi, etc.): how the context will be transferred from one technology to another in

case of a CR user that makes an inter-technology spectrum handover?

At this moment is to soon to advance a stable solution for this problem, given the fact that

CR technology is not yet standardized.

Nevertheless, an aboriginal solution can be suggested:

regarding the old PUs, each technology will maintain its own database (the traditional

case);

for the universal new users (CR users), it must be provided a conjoint database, whereon

each 5G component technology grant access; therefore the CR users information can

be accessed by all the pre-existing communications systems in order to make possible a

seamless spectrum handover.

This primary solution present some disadvantages when considering the joint CR database

dimension and the time to transfer the context.

It is expected, after the CR standardization, to obtain a real-time solution when transferring

the context from one technology to another.

Context-Aware CRs

Beside the inter-technology shared context case (when approaching the CR based 5G context

transfer) an important aspect is also identified: in order to provide the universal interconnec-tion, the CRs must communicate one each other, exchanging all information types:

personal context (identity, location, etc.);

environmental observations;

sharing preferences: spectrum and technology preferences.

According to all this information the CRs will know to act properly, with the aim of a func-

tional WISDOM, and, further 5G network.

4.3.3 Monitoring and Adaptation in WISDOM: CR Solutions

The exclusive CRN (including only the CR nodes, and not the primary systems) is seen

with self-organized and re-configurable capabilities, very flexible and mobile, and able to

cooperate with the existing systems.

The CR self-organized and re-configurable character is determined especially by the nodes

high mobility and location independence (resulting in frequent topological changes), and by

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Fig. 6 An adaptive CR based

5Ga dynamic OSI layers

functionality. The different

wireless network characteristics

and demands, together with the

CR WISDOM implementation,

require a strong network

monitoring function, which shall

be supported mainly by the CR

sensing function: the 5G

terminal/CR terminal senses the

environment, chooses the proper

network, downloads the proper

software (if necessary), and

selects the proper physical

technology and MAC/Network

layer protocols, in order to

transmit the data

the spectrum opportunities availability and channels quality dynamic variation in time; thus,

each node should decide the proper behavior, according to its own/and neighbors observa-

tions.

The CRN offered solutions for a self-organized and re-configurable design, till this mo-

ment, are [21]:

the networkmonitoring function ( environment sensing + information collection), that

each terminal must present - the extreme case needed to achieve adaptation.

the adaptation function having as purpose a constant performance level;

based on the information provided by the network monitoring/sensing function each

terminal will decide its configuration and behavior.

the need for a strong correlation between the network sensing and real-time protocols

for each OSI layers (see Fig. 6). In response to the environment changes, the CR terminal

obtains the network topology and the available channels set and then dynamically recon-

figures the MAC and physical layersthat is select the correct MAC from a collection

and the proper values for the physical layer parameters [22,23], and selects the best

route towards the destination [22].

a new Control Plane design with a tight cross-layer approach between the layers, and

even some new layers in the OSI stack, like CCL (Cognitive Convergence Layer)

[24].

new protocols and new metrics which should include the implications listed above (e.g. a

routing metric will be influenced by the in time channels availability, the way to allocate

these channelssharing methods, the nodes mobility, the network architecture, etc.).

Therefore, by implementing the access network in a cognitive manner, 5G will also assumethe CR solutions regarding the manner in which the resource management and adaptation

are achieved.

CR resource management means how the resources are qualitatively and quantitatively

allocated between different users.

According to [25], the CR resources can be classified in three categories: radio

resources, computing resources (that are including the processing capabilities), and

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application resources (with regard to the CR functionalities). The main CR radio resources

are the spectrum bands (the sub-carriers in CR OFDM based systems) and the power.

Based on this classification, and taking into account the very closed interconnections

between these resources, it was proposed an Integrated Resources Management (IRM).

The resource management assumes a resource admission function (Is it or not allowedfor a user to utilize the resources?) and a resource control function strongly related to the

adaptation (How many/Which type of resources is the user allowed to use in order to maintain

a good performance threshold?):

The admission function has a relevant importance in spectrum sharing, between CR and

PUs (underlay versus overlay approaches), and between concurrent CRs trying to access

the same resources.

The admission function may oblige the CR to stop or modify the transmissions character-

istics, at the moment when the PU will start the transmission in the respective frequency

channel.

The control function implies that the CR users request is honored, but the CR terminal

should always scan the environment and reconfigure its parameters/replace the software

so to maintain a constant performance level.

Adaptation means selecting the proper values (out of a set of values) for the CR parameters,

in order to respond to the environment current status.

The main CR provided solutions, concerning the environment adaptation, are:

(1) power control, which allows to reduce or to increase the transmit power, according toenvironment status (the path loss, the interference value, the SNR/SNIR (Signal Noise

Ratio/Signal Noise Interference Ratio) thresholds, the network capacity, the link data

rate etc.).

In order to achieve an efficient power control, a lot of methods/algorithms were sug-

gested, involving different disciplines, like polynomial time algorithms [26], game

theory (cooperative or non-cooperative games [27]), water filling scheme (for OFDM

systems, the sub-carriers are allocated to the users with the best channel quality ini-

tially and then adjusted to improve the system performance) [28], fuzzy logic for

power allocation control [29], a joint power control and admission control schemes

[30] etc.The adaptive power control domain is a very approached field, and offers a lot of

research opportunities.

(2) link adaptation [31], which consists in:

adaptive modulationthe modulation type selection according to the channel

status (noisy or noiseless, the interference range); for example, for some digi-

tal modulation methods, this implies selecting the proper constellation size (a rich

constellation for clear channels, and a poor one for noisy channels);

adaptive codingoptimal loss-less data compression schemes, in order to adapt to

the previous determined data composition (the data will match a prediction modeland will be compressed according to that model).

The compression is very useful because increases the throughput, allowing to trans-

mit the same data using a lesser number of data bits than without using compression.

(3) adaptive waveform techniquesan adaptive waveform generation and control in the

data transceiver.

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4.3.4 Increasing the Performance in WISDOM/5G: CR Solutions

By definition, 5G is a high performance technology (see Sect. 2), with high-band demanding

applications and services, and without time or space limitations.

What performance increase methods sustain a CR WISDOM implementation?First of all, should be emphasized that a cognitive performance metric is more complex

because of the dynamic, mobile and flexible CR networks nature.

Thus, in the CR domain we encounter at once old performance radio metrics, completely

new metrics based on the cognitive new paradigm ideas, and also a mixture between these two.

The most presented performance metrics are:

interferencebetween CR and PU, and between different CRs;

SNR and SNIR;

channel quality: time varying nature, dispersion of the signal, shadowing, distance loss;

bit error rate;

end-to-end transmission latency/delay;

average detection time: the mean time to detect the signal on the sensed channel;

sensing duration influence on the throughput;

throughput;

capacity limits;

spectrum substitutabilityhow fast is the spectrum handover, with the possibility to have

a seamless handover for CRs;

coverage performancegeographic coverage and range (how long can be the distance

between source and destination in a CRN).

New and original methods, operating in one way or another on the above-listed metrics,

were advanced by the CR researchers:

Reducing the Interference

In order to realize an efficient spectrum pooling between different users, is necessary

to avoid the interference; the first interference cancellation techniques proposed in the

CR domain were: OFDM-based UWB solution (frequency-domain signal processing)

[32], rosettes systems (allowing the utilization of directive antennas, arranged in a cir-

cular form, and rotated each other in order to minimize co-channel interference) [33],

and channel feedback regarding the performance parameters, followed, if necessary, by

some parameters adaptation.The majority of the studies for reducing the interference are dedicated to:

CR parameters adaptation to the channels conditions: adaptive channel modulation

and selection, adaptive power control/power allocations schemes, power scaling con-

trol [34,35,20], DFS (Dynamic Frequency Selection) [35], TA (Time Agility) [35],

adaptive time/frequency spreading for the OFDM systems, adaptive packet sched-

uling algorithm with QoS, OFDM blind parameter identification [36], adaptation

of the operating parameters and developing new protocols with the corresponding

metrics: ACL (Adjacent Channel Leakeage) [37] and interference temperature [20]; reduction/deactivation of the sub-carriers located in the vicinity of the PUs, mak-

ing possible to transmit in the presence of these incumbent users (only possible in

OFDM/A);

filters utilization: band-pass filters, multi-channel poly-phase filter implementation at

the receiver, low accuracy ADCs (analog to digital conversions) with digital adaptive

filters in order to extract the unwanted signals;

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efficient decoding schemes in order to combat residual interference;

a good design of the CR, especially for the receiver (a CR transmitter equipped with

antenna array forms transmit beam-forming in order to keep the interference below

a given threshold [38]);

CR optimal signal design (e.g., in OFDM systems a windowed signal use); control of the time interval between a series of impulses/guard bands (not always

possible).

Improved PHY technologies

The CR physical layer candidates, with very good qualities, are proposed to be the

multi-carrier techniques:

OFDM-QAM (Orthogonal Frequency Division MultiplexingQuadrature ampli-

tude Modulation) is a digital modulation technique, with the sub-carriers orthogonal

one each other, and each sub-carrier modulated with the quadrature amplitude mod-

ulation scheme [39].

OFDMA (Orthogonal Frequency Division Multiple Access) is a multi-user channel

access technique, where each user has assigned a subset of sub-carriers (different

sub-carriers assigned to different users) [40]. One of the most important advantage

of using OFDMA is the different QoS data rates achievement, according to the

sub-carriers number allocated to one user.

MC DS CDMA (Multi-carrier Direct-Sequence Code Division Multiple Access) is a

multiple access scheme, where each user has a specific code and can utilize multiple

parallel sub-carriers [39]. Like OFDMA, it may offer different QoS levels.

It is also very important the type of the antenna used by the CR receiver/transmitter.

Instead of using single omni-directive antennas, the researchers proposed the use ofmul-

tiple antennas concurrently: directive and smart antennas.

A directive/beam antenna has the property to radiate a grater power only in one/more

specific direction(s), increasing in this way the performance and reducing the interfer-

ence (this only happens if the direction is the right one).

A smart antenna (MIMO) is an antennas array, that has the possibility to identify

the direction of the arrival signal and to transmit with spatial selectivity using beam-

patterns.

This property, of estimating the received signal direction, is very important in the sensingprocedure, due to the possibility of finding the PUs location, and to the possibility to

spatial localize the victims in a emergency scenarios.

The spatial selectivity of the transmission direction (related to the receivers location),

instead of spreading the information in all the directions, also reduce the interference

with other transmitters/receivers.

Increasing performance with adaptation and with a flexible resource management (see

the CR solutions proposed in 4.3.2).

The above-quoted cognitive radio functionalities like:

(1) CRthe best technology to interconnect the different wireless systems;

(2) a new architecture for heterogeneous networksCRN architecture;

(3) CR terminalthe best choice for the 5G terminal;

(4) CRa new functionality for the OSI layers together with new physical, MAC and

link layer techniques (5G needs protocols for an end-to-end performance optimization

rather than the ones based on the classical layered design);

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(5) CR technologystrong resources management, adaptation and performance

improvement solutions

are more than enough to proclaim the CR technology as the best solution, at least at this

moment, for the WISDOM implementation, and 5G network real achievement.

5 CR Based 5G: Commercial Issues

5.1 Spectrum Based Pricing

The 5G based on CR technology proposal, which implies both the spectrum users delimitation

into primary (licensed) users and secondary (CR) users, and the CRs ability to dynamically

use the spectrum owned by primary users, demands new financial and business models.

Both the CR and primary users must gain in the wake of CR technology:(1) the CRs dynamically utilize the PUs licensed spectrum;

(2) the PUs receive a payment in return of CRs opportunistic spectrum access.

In [41], three models and ways of seeing the spectrum pricing were proposed:

a market equilibrium approach (the CRs demands take priority and the purpose is to

satisfy their needs with the best QoS);

competitive approach (competition between PSs in order to obtain a better pay from

CRit is a selfish behavior on behalf of PSs);

cooperative approach (cooperation between PSs, the best solution regarding the entire

ensemble of CR and PUs).

The pricing field remains opened for research, till the CR spectrum sharing strategies and

other related issues will be finalized.

Though, it is expected to have a game theory based pricing, since the spectrum sharing

was often proposed to be modeled using dynamic game approach.

5.2 Security

Also, at the same time with the CR great possibility to dynamically utilize the wireless spec-trum and to uniform the communication into a 5G network, new security challenges and

threats appeared, the most of them related to the CR terminals performing [ 42]:

harmful interference (when both the primary and CR users are transmitting in the same

radio band, the CR user must emit below a given threshold, so that the primary users

transmission to not be affected);

selfish misbehaviors (a CR user can behave in a selfish manner, without taking into

account the others CR users demands and the utilized medium access method, when

distributing the available spectrum between them);

licensed user emulation(a wireless user may pretend that it is a user that owns licensedspectrum, thus deceiving a CR user who pays for that spectrum utilization);

eavesdropping (the possibility of an CR user to know the data transmitted by another

user, either primary or CR, thereby violating the privacy rights);

complete deny of a CR user (On one hand, an unsecured CR station can be a victim

to potential denial of service [43], and on the other hand can be easily manipulated to

attack legacy and wireless networks [44]).

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For this reasons, a Trusted Radio Infrastructure for Enforcing Spectrum Etiquettes

(TRIESTE) was proposed to ensure that the radio devices are only allowed to access/use

the spectrum in a manner that conforms to their privileges: restrict the potential violation

and assure the possibility to monitor and to report measurements, in order to punish CRs if

violations are detected [45].Also, authentication and re-authentication protocols were suggested to avoid the viola-

tions: a CR Radio-Independent Authentication Protocol, Radio-Independent Mutual Authen-

tication Protocol and Re-authentication Protocol (EAP-CRP re-authentication) [46].

As can be seen, even if the CR technology solves the 5G main design/implementation

problems, a lot of issues remain to be approached toward a commercial form.

6 Conclusions

In this paper, the 5G and CR technologies where presented and discussed, then the basic

similarities were identified, and finally 5G network based on the CR functionality has been

proposed.

The proposed CR-5G network is strongly sustained by the main 5G requirements achieve-

ment through the CR use, in a high-performance manner:

5G acquires the desirable terminal, that is precisely the CR terminal.

5G obtains the tool technology to interconnect and integrate all the wireless networks

types, and thus, gains the needed network infrastructure (CRN).

5G adopts (maybe with minor modifications) the already proposed CR protocols and

increasing performance techniques.

In order to satisfy the 5G technology defined requirements, some issues remain to be

solved:

how to reach the maximum 5Gs 1Tbps data rate threshold when using the CR technology

at the access level (CR does not yet offer a very high rate possibility, but the researchers

are trying to resolve this challenge and a high frequencies use was advanced as solution);

good techniques in order to combine the flows coming from multiple access networks (At

this moment, an important number of combining methods exist. Thus, with a attentive

analysis, a proper solution will be found in the 5G case); how to connect the cognitive radio terminal to the wired networks (This implies new

media interfaces definition between the wireless and wired environments).

Finally, the paper concludes that CR technology is the first step to uniform the different

communications technologies, i.e. to obtain the interoperability between the different net-

work types, and the CR based 5G represents a successful combination which will provide

us the real 5G network.

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Author Biographies

Cornelia-Ionela Badoi is currently working towards the Ph.D. at

POLITEHNICA University of Bucharest, Romania, Department of

Communications. Her research interests focus on routing protocols,

cognitive radio, wireless networks, IP Multimedia Subsystems, and

next-generation networks.

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Neeli Prasad Senior IEEE Member, Associate Professor and

Coordinator of Network Architecture Thematic Group, Center for

TeleInfrastruktur (CTIF), and Head of Wireless Security and Sensor

Networks Group, Aalborg University, Denmark. During her indus-

trial and academic career for over 13 years, she had lead and coor-

dinated several projects both industrial and EC-funded. At present,She is leading a industry-funded projects on reliable self organizing

networks REASON and STRONG on Security and reliable next gen-

eration networks, Project Coordinator of European Commission (EC)

Integrated Project (IP) ASPIRE on RFID and Middleware and EC Net-

work of Excellence CRUISE on Wireless Sensor Networks. She is

coordinating Internet of Things working group for European Commis-

sion Future of Internet Assembly and co-caretaker of real world inter-

net (RWI). She has lead EC Cluster for Mesh and Sensor Networks and

Counsellor of IEEE Student Branch, Aalborg. She is project leader for

EC funded IST IP e-SENSE on Wireless Sensor Networks and NI2S3

on Homeland and Airport security and ICT PSP ISISEMD on telehealth care. Her publications range from

top journals, international conferences and chapters in books. She has also co-edited and co-authored twobooks titled WLAN Systems and Wireless IP for Next Generation Communications and Wireless LANs

and Wireless IP Security, Mobility, QoS and Mobile Network Integration, published by Artech House, 2001

and 2005. Her current research interest lies in IoT, Future Internet/NWGN, Virtual Networks, Cognitive

Radio Networks, Management, IdM, Embedded Security and Privacy.

Victor Croitoru (M1990, SM97) was born in Bucharest, Romania,

on August 17, 1943. He graduated from the Polytechnic Institute

of Bucharest and received his Ph.D. degree in Telecommunications

from Polytechnic Institute of Bucharest, Romania, in 1974. He joined

the Department of Telecommunications, Faculty of Electronics, Tele-

communications and Information Technology, Politehnica Univer-sity of Bucharest as an Assistant Professor in 1967, where he is

now a full professor. His research interests focused on communication

techniques, intelligent terminals, voice data integrated transmissions,

programmed logic terminals testing, telephone terminal integrated

sensory keyboards, personal communications, network management.

Dr. V. Croitoru is currently an associated editor of Revue Roumaine des

Sciences Techniques, Serie Electrotechnique et Energetique, Roma-

nian Academy Publishing House, respectively of AGIR Publishing

House. He served as the chairs/co-chairs of some national/inter-

national conferences (e.g. IEEE ICT 2001, Communications 2000/

2002/2004/2006/2008), and has received some educational/research awards (e.g. tRAian Vuia Roma-

nian Academy Prize, National Order Loyalty in Serving the Countryin the position of officer, etc.).Dr. Croitoru is currently member of some scientific and technical academies and professional associations

(e.g. corresponding member of American Romanian Academy of Arts and Sciences, corresponding mem-

ber of Romanian Technical Sciences Academy, etc.) and Ph.D. advisor. He is a Senior member of IEEE

Communications Society.

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2011_5G Based on Cognitive Radio