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INTRODUCTION

INTRODUCTION. Cognitive radio (CR) is one of the new long term developments taking place and radio receiver and radio communications technology.

iliana-sharpe
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INTRODUCTION

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  1. INTRODUCTION • Cognitive radio (CR) is one of the new long term developments taking place and radio receiver and radio communications technology. • After the Software Defined Radio (SDR) which is slowly becoming more of a reality, cognitive radio (CR) and cognitive radio technology will be the next major step forward enabling more effective radio communications systems to be developed.

  2. Cognitive radio definition • A cognitive radio may be defined as a radio that is aware of its environment, and the internal state and with a knowledge of these elements and any stored pre-defined objectives can make and implement decisions about its behaviour. • The idea for cognitive radio has come out of the need to utilise the radio spectrum more efficiently, and to be able to maintain the most efficient form of communication for the prevailing conditions. • it is possible to develop a radio that is able to look at the spectrum, detect which frequencies are clear, and then implement the best form of communication for the required conditions. In this way cognitive radio technology is able to select the frequency band, the type of modulation, and power levels most suited to the requirements

  3. histroy • There have been many factors that have lead to the development of cognitive radio technology. -The steady increase in the requirement for the radio spectrum along with a drive for improved communications and speeds -To make more effective use of the spectrum, often with an associated cost dependent upon the amount of spectrum used. -Flexibility has been required.

  4. Example that exemplified the need for flexible communications occurred in the Netherlands in 2000 when a fireworks factory exploded killing 23 people, destroying much of the town and injuring more than a thousand people. While dealing with this catastrophe, the emergency services (fire, medical, police, etc) experienced real communications difficulties because they all had different communications systems and were unable to communicate with the other services.

  5. Cognitive Radio* is Built on SDR* • We must start with a Software Defined Radio as a basic platform on which to build a Cognitive Radio • Cognitive Radio can provide the spectral awareness technology to support FCC initiatives in Spectral Use

  6. SDR Standardized Architecture Supports Both Current and Future Applications • FDMA, TDMA, CDMA, TDD • AM, FM, MFSK, MPSK, MQAM, CPM, SSB, • Trunked Radio, APCO-25, GSM, Iridium, 802.11 • Tone Coded Squelch, CVSD, LPC, VSELP, AMBE.

  7. Cognitive radio architecture • In addition to the level of processing required for cognitive radio, the RF sections will need to be particularly flexible. Not only may they need to swap frequency bands, possibly moving between portions of the radio communications spectrum that are widely different in frequency, but they may also need to change between transmission modes that could occupy different bandwidths. • To achieve the required level of performance will need a very flexible front end. Traditional front end technology cannot handle these requirements because they are generally band limited, both for the form of modulation used and the frequency band in which they operate. Even so called wide band receivers have limitations and generally operate by switching front ends as required. Accordingly, the required level of performance can only be achieved by converting to and from the signal as close to the antenna as possible. In this way no analogue signal processing will be needed, all the processing being handled by the digital signal processing.

  8. Cognitive radio networks • It is possible to build a network of radios - nodes by linking several cognitive radio nodes, performance can be enhanced. • In many instances a single cognitive radio will communicate with several non-cognitive radio stations as in the case of a femtocell which requires cognitive functionality to set itself up, and then communicate with non-cognitive cell-phones. In other cases, several cognitive radios will be able to form a network and act as an overall cognitive radio network.

  9. External Intelligence Sources Orient Establish Priority Infer on Context Hierarchy Normal Plan Generate Alternatives (Program Generation) Evaluate Alternatives Pre-process Immediate Urgent Parse Register to Current Time Learn Observe New States Receive a Message Decide Read Buttons Save Global States Prior States Alternate Resources Outside World Act Initiate Process(es) (Isochronism Is Key) Send a Message Set Display The Cognition Cycle How Does a Cognitive Radio Get So Smart?

  10. Cognitive radio network advantages • Improved spectrum sensing. • Improved coverage. Spectrum sensing • For the overall system to operate effectively and to provide the required improvement in spectrum efficiency, the Cognitive Radio spectrum sensing system must be able to effectively detect any other transmissions, identify what they are and inform the central processing unit within the Cognitive Radio so that the required action can be taken • The ability of CR systems to access spare sections of the radio spectrum, and to keep monitoring the spectrum to ensure that the Cognitive Radio system does not cause any undue interference relies totally on the spectrum sensing elements of the system.

  11. QPSK Interference Spectrum Shaped QPSK @ 128 kbps 0 -10 -20 -30 -40 -50 Power Spectrum Magnitude (dB) -60 -70 Tx Spectrum -80 Rcv Spectrum -90 -100 0 0.5 1 1.5 2 2.5 Frequency (Hz) 6 x 10 -20 0 -40 -20 -60 -40 -80 Power Spectrum Magnitude (dB) Power Spectrum Magnitude (dB) -60 -100 -120 -80 -140 Survive -100 Survive 3 2.5 3 2.5 2 2 1.5 Survive Survive 2 1.5 2 1 1 0.5 0.5 Normal Normal 0 1 0 1 6 Transmission Number x 10 Frequency (Hz) 6 Transmission Number Frequency (Hz) x 10 Interference Avoidance

  12. Types of CR spectrum sensing • Non-cooperative spectrum sensing:   This form of spectrum sensing, occurs when a cognitive radio acts on its own. The cognitive radio will configure itself according to the signals it can detect and the information with which it is pre-loaded. • Cooperative spectrum sensing :   Within a cooperative cognitive radio spectrum sensing system, sensing will be undertaken by a number of different radios within a cognitive radio network. Typically a central station will receive reports of signals from a variety of radios in the network and adjust the overall cognitive radio network to suit.

  13. CR spectrum sensing methodologies • There are a no of attributes that must be incorporated into any cognitive radio spectrum sensing scheme. These ensure that the spectrum sensing is undertaken to meet the requirements for the particular applications. The methodology and attributes assigned to the spectrum sensing ensure that the cognitive radio system is able to avoid interference to other users while maintaining its own performance. • Spectrum sensing bandwidth • Spectrum sensing accuracy • Transmission type sensing • Spectrum sensing timing windows

  14. Time - Frequency - Space Each Domain has Opportunities for Spectral Reuse Transmitter forms Beam Toward Intended Recipient Receiver forms Null Toward Interference Sources R1,R4 T2 T1 Interfering Signal Placed In Null R3,T4 T3 R3

  15. Acceptance • With wire-less and radio communications becoming far more widely used, and the current levels of growth looking to increase, ideas such as cognitive radio will become more important. Some areas of the spectrum are very heavily used while others are relatively free. • Additionally the ability to change modes, frequencies and power levels will not only make communication possible for the cognitive radio system itself, but should also reduce the overall levels of interference to other users. • This is because the most spectrum or interference efficient modes can be chosen by the cognitive radio system. • In view of the possibility of CR radio communications systems utilising the spectrum more efficiently some regulatory bodies such as the FCC in the USA is looking favourably at the idea of cognitive radio. When the idea becomes a reality it would enable greater efficient use of the radio spectrum, which is not an infinite resource as it once was considered.

  16. -It knows where it is-It knows what services are available, for example, it can identify then use empty spectrum to communicate more efficiently-It knows what services interest the user, and knows how to find them-It knows the current degree of needs and future likelihood of needs of its user-Learns and recognizes usage patterns from the user-Applies “Model Based Reasoning” about user needs, local content, environmental context Cognitive Radio Means “Smart” and “Alert”

  17. Cognitive radio (CR) versus intelligent antenna (IA)

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