Cognitive Radio Presentation

COGNITIVE RADIO

INTRODUCTION 

Cognitive radio is a paradigm for wireless communication in which either a network or a wireless node changes its transmission or reception parameters to communicate efficiently avoiding interference with licensed or unlicensed users. This alteration of parameters is based on the active monitoring of several factors in the external and internal radio environment, such as radio frequency spectrum, user behavior and network state.

ARCHITECTURE OF CR

A. Physical Layer Functions 1)

Spectrum Sensing: The main function of the physical layer is to sense the spectrum over all available degrees of freedom (time, frequency and space) in order to identify sub-channels currently available for transmission.

2) Channel Estimation In

order to set up the link, channel sounding is used to estimate the quality of subchannels between SUs that want to communicate. The transmission parameters (transmit power, bit rate, coding, etc.) are determined based on the channel sounding results

3) Data Transmission CR’s

optimally uses the available spectrum as determined by the spectrum sensing and channel estimation functions. Therefore it should have the ability to operate at variable symbol rates, modulation formats (e.g. low to high order QAM), different channel coding schemes, power levels and be able to use multiple antennas for interference nulling, capacity increase (MIMO) or range extension

B. Link Layer Functions Group 

It is assumed that any secondary station will belong to a SU Group. A newly arriving user can either join one of the existing groups or create a new one through the Universal Control Channel.

Link 

Management

Management

covers the setup of a link in order to enable the communication between two SUs and afterwards the maintenance of this SU Link for the duration of the communication.

Medium 

Access Control

As long as it can be assured that all Sub-Channels are used exclusively, i.e. all Sub-Channels used by one SU Link cannot be used by any other SU Link this problem comes down to a simple token-passing algorithm ensuring that

.

only one of the two communication peers is using the link

Types of Cognitive Radio Depending

on the set of parameters taken into account in deciding on transmission and reception changes, we can distinguish certain types of cognitive radio. The main two are: Full cognitive radio  Spectrum sensing cognitive radio

(Contd.) depending

on the parts of the spectrum available for cognitive radio, we can distinguish: Licensed Band Cognitive Radio (IEEE 802.22) Unlicensed Band Cognitive Radio (IEEE 802.15)

FUNCTIONS OF CR The

main functions of Cognitive Radios are: Spectrum Sensing : detecting the unused spectrum and sharing it without harmful interference with other users.

(Contd.) Spectrum

sensing techniques can be classified into three categories: ◦ Transmitter detection: cognitive radios must have the capability to determine if a signal from a primary transmitter is locally present in a certain spectrum, there are several approaches proposed: matched filter detection energy detection

Match filter detection is

obtained by correlating a known signal, or template, with an unknown signal to detect the presence of the template in the unknown signal.

(Contd.) ◦ Cooperative detection: refers to spectrum sensing methods where information from multiple Cognitive radio users are incorporated for primary user detection.

(Contd.) Spectrum

Management: Capturing the best available spectrum to meet user communication requirements management functions can be classified as: ◦ spectrum analysis ◦ spectrum decision

(Contd.) 

Spectrum Mobility: is defined as the process when a cognitive radio user exchanges its frequency of operation. Cognitive radio networks target to use the spectrum in a dynamic manner by allowing the radio terminals to operate in the best available frequency band, maintaining seamless communication requirements during the transition to better

(Contd.) Spectrum

Pooling :is a resource sharing strategy that organizes the available spectrum into a spectrum pool which is then optimized for a given application . Once a primary user appears, secondary users need to cease transmission if they will cause interference.

Cognitive radio network

The

cognitive radio network is an intelligent multi user wireless communication system that embodies the following list of primary tasks: •to perceive the radio environment (i.e., outside world) by empowering each user’s receiver to sense the environment on a continuous-time basis •to learn from the environment and adapt the performance of each transceiver

(Contd.) •to

facilitate communication between multiple users through cooperation in a self-organized manner •to control the communication processes among competing users through the proper allocation of available resources

Software defined radio Software-Defined

Radio (SDR) system is a radio communication system where components that have typically been implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors. etc.) are instead implemented using software on a personal computer or other embedded computing devices.

(Contd.) A

basic SDR may consist of a computer (PC) equipped with a sound card, or other analog-to-digital converter, preceded by some form of RF front end. Significant amounts of signal processing are handed over to the general purpose processor, rather than done using special-purpose hardware. Such a design produces a radio that can receive and transmit a different form of radio protocol (sometimes referred to as a waveform) just by running different software. It is the enabler of Cognitive

Functions provided by SDRs 1.

The radio hardware. The radio hardware includes radio frequency circuitry and signal processing devices. 2. Software modules. Software modules represent code that has been loaded into field programmable gate arrays (FPGAs), digital signal processors (DSPs), or embedded general purpose processors.

(Contd.) 3.

Middleware. The middleware layer attempts to reduce the details of specific devices and software modules to common abstractions.

4.

Device Manager: The device manager loads radio configurations into the hardware components and sets-up the

(Contd.) 5. Logical Radio Layer: Depending on the radio configuration, the hardware and software can be programmed to act like multiple radio links . 6. Module Libraries: The module libraries are collections of radio functions.

(Contd.) 7.

Rules Engine and Policies: Policies are used to limit the operation of the radio due to regulatory, geographical, or physical constraints.

8.

Smart Controller: A “smart controller” manages all of the radio resources outlined above.

ISSUES IN CR Spectrum

management Spectrum utilization: presence of white spaces Spectral co-existence  Spectrum sharing

Spectrum management spectrum

management involves assigning particular frequencies to specified users. This can be done through administrative methods or by means of a market process, such as an auction. Additionally, some spectrum may be reserved for unlicensed use (this is sometimes referred to as the spectrum commons). All users satisfying certain

Spectral utilization white

spaces refer to frequencies allocated to a broadcasting service but not used locally unlicensed devices that can guarantee that they will not interfere with assigned broadcasts can use the empty white spaces in spectrum

Spectral coexistence Two

approaches have been given: Collaborative approach: radio of different technologies exchange information regarding the frequency usage of the spectrum. Non collaborative: radio devices sense the frequency spectrum occupancy and determine by itself the channel definition

Spectral sharing Stringent

spectrum sensing requirements ◦ Various types of primary users ◦ Low SNR environment ◦ Fast wideband sensing ◦ Robust sensing (to noise uncertainty, interference …) Can the acquired on/off status be used to protect primary users? ◦ Channel asymmetry ◦ Shadowing, hidden terminal issue ◦ Transmission power asymmetry

CONCLUSION There

are opportunities to explore “spectrum white spaces” To promote white space reuse ◦ technically, though challenging, effective solutions are needed to protect the primary users ◦ economically, good business models are needed to make both primary users and secondary users happy!

(Contd.) Cognitive

networks

radio -> cognitive radio

◦ How to acquire cognition PHY sensing Network layer traffic sensing

◦ Cognitive MAC: Control information sharing, cooperation, … ◦ Distributed processing ◦ Other issues (security, trust, …) Let

us work together to make cognitive radio (networks) from imagination to reality!

(Contd.) Cognitive

radio can be used in the following fields: Signal processing Communication theory Radar systems Control theory

bibliography Wikipedia.org IEEE xplore www.technologyreview.com www.cognitiveradio.wireless.vt.e du IEEE papers

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