Cognitive Radio Network Introduction.pptx

Brief Introduction of the Cognitive Radio Network and its Types.

1. CONTENTS Introduction Cognitive Radio Networks Types Of Cognitive Radio Network Users Spectrum Division How The Cognitive Radio Cycle Functions Cognitive Radio System Models Implementation Of CR Network Channel Capacity Capacity Analysis of CRN Conclusion References

2. INTRODUCTION In the today’s scenario the radio spectrum is a very precious resource on which all the wireless services are dependent. The radio resource is allocated to various license holders for their exclusive use of the spectrum. The spectrum licensing policy[1] eliminates the interference problem among various users of the spectrum. This result in a very inefficient use of the spectrum, which has become scarce resource today due to increasing number of users of the wireless services and requirements of high data rates. Thus Cognitive radio networks (CRN) allow the new wireless systems to dynamically access or share the licensed band on a negotiated or opportunistic basis[2]. Cognitive Radio (CR) is considered as the key technology to improve the spectrum utilization.

3. COGNITIVE RADIO NETWORKS CRN is an intelligent wireless communication system. It is aware of its environment and uses the technique of understanding by developing to learn from the environment and adapt to statistical variations in the input characteristics[3]. The two main objectives in mind Highly reliable communication whenever and wherever needed, also Effective utilization of the radio spectrum.

4. COGNITIVE RADIO NETWORKS USERS Primary or licensed users. Secondary or unlicensed or cognitive users. The primary users have greater priority of using the licensed spectrum whereas the secondary users opportunistically communicate in the licensed spectrum by varying their communication parameters adaptively when the spectrum holes are available[4].

5. SPECTRUM DIVISION The spectrum is divided into three broad categories: Black Spaces : these are portions of licensed spectrum being used by primary users and is occupied by high power signals. Grey Spaces : these are temporary occupied by low power interfaces White spaces : are free from RF interferences and are purely unutilized portion of licensed spectrum. These white and grey spaces are the goals of the secondary users.

6. HOW THE COGNITIVE RADIO CYCLE FUNCTIONS There are four main functions of the CR including: Spectrum Sensing : To sense the unutilized frequency bands. It is the most important function of CR system. Spectrum Management : It is the process of deciding the best available spectrum considering the user and QOS requirements. Spectrum Mobility : It is the transition of Cognitive user from one frequency to another. This happens when primary user tries to occupy the same spectrum band and so the secondary user transits due to detection of some other best spectrum. Spectrum Sharing : It enables the CR user to efficiently utilize and share the used licensed spectrum[5].

7. COGNITIVE RADIO SYSTEM MODELS Three main approaches[6] according to which a secondary user access spectrum without interfering with the primary user are: Underlay system : In this secondary and primary user transmits simultaneously by maintaining interference at primary receiver by secondary users below certain threshold level. Here the interference problem can be solved by using multiple antennas by which secondary user transmission could be guided away from primary receiver. Also, we can use wide bandwidth on which secondary transmitter could be spread while dispreading signals at secondary receiver.

8. Cotnd.. Overlay system : Here the interference is reduced and sometimes completely cancelled as the primary users assist the secondary user for simultaneous transmission by using portion of their transmitting power. Interweaver system : Works on the primary idea of CRs. They sense the unused spectrum opportunistically, utilizes it for communication and leave the spectrum when primary user is detected thus avoiding the considerable interference.

9. IMPLEMENTATION OF CR NETWORK There are two ways in which a CR user may coexist with the primary users: Non- interfering basis : Here exclusive frequency band is allocated to the primary users and CR users can only operate in the unused frequency bands i.e. Spectrum holes or White Spaces. Interference tolerant basis : It works by allowing the CR users to operate on the frequency bands assigned to primary user until the total interference power received at primary user is below certain threshold. This network requires the primary network to be aware of the CR network and send back the interference levels of all the primary receivers to CR transmitters. This system has more implementation challenges than the previous system but is more efficient due to more effective utilization of spectrum[7].

10. CHANNEL CAPACITY For Wireless communication system the channel capacity is used as a basic performance measurement tool for the analysis and design of new and more efficient techniques to improve the spectral efficiency. The channel capacity is the maximum rate at which information may be sent reliably over a channel.

11. CAPACITY ANALYSIS OF CRN Channel Capacity has been analyzed for Interference tolerant CR network under received interference power constraints. The received interference power can be specified as Average power or peak power[8][9] and the channel capacities are studied AWGN channels in the absence of fading as well as in the presence of different fading environments[10][11][12]. The capacity analysis is done at different levels of communication system At link level where only one CR transmitter opportunistically communicates with one CR receiver in presence of single or multiple primary receivers. At system level of CR networks where the system consists of multiple CR transmitters and multiple primary receivers.

12. USE OF MIMO NETWORK The purpose of the CR network is to improve the radio access ability of a cellular system. The current and future cellular networks are challenged by users’ increasing demand of high quality and high data rate multimedia services. MIMO i.e. Multiple Input Multiple Output is a key technology to meet this challenge[13][14]. By deploying multiple antennas at both transmit & receive ends Capacity can be significantly increased. But this becomes a problem at the mobile terminals. So, Virtual MIMO system is an alternative which cordinate multiple single antenna users to form a virtual antenna array[15][16].