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System Design for Cognitive Radio Communications

System Design for Cognitive Radio Communications. Mustafa Emin Şahin Hüseyin Arslan ELECTRICAL ENGINEERING DEPARTMENT UNIVERSITY OF SOUTH FLORIDA TAMPA, FL, USA. Outline. Cognitive Radio Concept Opportunistic Spectrum Usage Spectrum Sensing Cooperation of Transmitter and Receiver

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System Design for Cognitive Radio Communications

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  1. System Design for Cognitive Radio Communications Mustafa Emin Şahin Hüseyin Arslan ELECTRICAL ENGINEERING DEPARTMENT UNIVERSITY OF SOUTH FLORIDA TAMPA, FL, USA

  2. Outline • Cognitive Radio Concept • Opportunistic Spectrum Usage • Spectrum Sensing • Cooperation of Transmitter and Receiver • Spectrum Shaping by Adaptive Pulse Design • Range of Cognitive Communications • Numerical Results

  3. Current State of Wireless • Wireless communication systems are evolving substantially • New mobile radio systems aim at higher data rates and a wide variety of applications • Higher capacity and performance required through a more efficient use of limited resources • Two cutting edge solutions are UWB and cognitive radio • UWB is considered to supplement Cognitive Radio

  4. Cognitive Radio • Traditional system design allocates fixed amounts of resources to the user • Adaptive design identifies the requirements of the user, and then allocates just enough resources • Introducing advanced attributes to the adaptive design • Multi-dimensional awareness • Sensing • Learning  Cognitive Radio

  5. Cognitive Radio Concept • Opportunistic Spectrum Usage • Spectrum Sensing • Cooperation of Transmitter and Receiver • Spectrum Shaping by Adaptive Pulse Design • Range of Cognitive Communications • Numerical Results

  6. Opportunistic Spectrum Usage • Opportunistic Spectrum Usage: • licensed bands can be utilized by secondary users when they are not being used by their owners • leads to the most efficient exploitation of the entire spectrum • The operation of unlicensed systems should not affect the primary users

  7. Spectrum Sensing • Cognitive radios periodically scan the spectrum and detect the white bands • The target spectrum to be sensed should be limited • The received signal can be sampled (after the down-conversion) at or above the Nyquist rate and can be processed digitally • The computational burden associated with spectrum sensing can be restricted to a reasonable level  limited hardware complexity • The analog front-end required for a very wide spectrum scan (wideband antenna, wideband amplifiers and mixers), which have a rather high cost, can be avoided • It can be prevented that a single type of cognitive radio occupies the majority of the bands that are open to opportunistic usage

  8. Spectrum Sensing • Spectrum allocation for different types of cognitive radios can be done by regulatory agencies depending on • the intended range and • the throughput requirements • high data rate cognitive radios aiming at wide range applications (like TV broadcast systems) wider target spectra at lower frequency bands • relatively low rate, short range communication devices (like cordless phones) narrower bands at higher frequencies

  9. Cooperation of Transmitter and Receiver • Both the transmitter and the receiver have transmission and reception capabilities • In order to match the results of the spectrum sensing, each of them transmits the information regarding the white spaces they have detected • The transmission of spectrum sensing results is done via low power UWB signaling • Since UWB transmission will be underlay, it can be done simultaneously with the real data communication without affecting each other

  10. Cooperation of Transmitter and Receiver • A low-complexity and low cost solution is OOK based impulse radio UWB signaling using energy detector receivers • Once both parties receive the spectrum sensing information from the other party, they logically ’AND’ the white spaces Depending on these common white spaces, each party designs a new pulse shape • what the receiving party uses as the template to match the received pulse will be (almost) the same as the transmitted pulse by the other party  a successful matched filtering

  11. Spectrum Shaping • Cognitive transceiver has to be able to dynamically shape the spectrum of the transmitted pulse to fill the spectrum opportunities • possible options • employing OFDM carriers as in the case of UWB-OFDM • employing Prolate Spheroidal Wavelet Functions (PSWF) • leakage from the opportunity bands to the licensed systems in the adjacent bands should be kept at a negligible level

  12. Spectrum Shaping

  13. Spectrum Shaping • An alternative method based on the usage of raised cosine filters • The center frequencies and bandwidths of each opportunity are determined • The most suitable raised cosine filters are selected • The selected filters are multiplied with digitally generated cosine signals • Sum of the separately generated signals is transmitted

  14. Spectrum shaping via raised cosine filtering

  15. Cognitive Radio Concept • Opportunistic Spectrum Usage • Spectrum Sensing • Cooperation of Transmitter and Receiver • Spectrum Shaping by Adaptive Pulse Design • Range of Cognitive Communications • Numerical Results

  16. Range of Cognitive Communications • In order to exchange the sensing information, there should not be a gap between the sensing ranges of both parties • the receiving sensitivity of both parties has an important role in determining the range of communication • We assume a rather high sensitivity around −120dBm to −130dBm and free space propagation  according to the Friis equation the range of one-to-one cognitive communication is limited to 50m to 150m

  17. Range of Cognitive Communications • Network of Cognitive Transceivers

  18. Range of Cognitive Communications • A network of collaborating cognitive nodes may be an effective solution • if the targeted range is wider than 50-150 m, or • if the cognitive devices are experiencing shadowing (and are hardly able to detect the primary users) • Consider a cognitive network whose nodes communicate with each other using UWB to exchange spectrum information

  19. Range of Cognitive Communications • Looking at the BER expression for OOK modulated UWB signals • it is seen that increasing Ns results in lower BER,  a very advantageous feature of UWB called processing gain • By applying enough processing gain, farthest nodes in a cognitive network can share the spectrum sensing information

  20. Range of Cognitive Communications • processing gain lowered throughput; not a limiting factor because a quite low data rate is enough to transmit the spectrum sensing information • By enabling all the nodes in a cognitive network talk to each other via UWB, there is no need • to allocate a separate channel for sharing the sensing information, • or to employ a centralized controller • The sensing information received from all the other nodes in the network can be combined in each node, and pulse design can be done • This way, the range of cognitive communications can be extended to the coverage area of a medium-sized network

  21. Cognitive Radio Concept • Opportunistic Spectrum Usage • Spectrum Sensing • Cooperation of Transmitter and Receiver • Spectrum Shaping by Adaptive Pulse Design • Range of Cognitive Communications • Numerical Results

  22. Numerical Results • List of Simulation Parameters

  23. Numerical Results • BER vs. the distance between the nodes for UWB signaling

  24. Numerical Results • Repetition rate required for reliable UWB signaling vs. distance (taking the BER at 40m as a reference)

  25. Numerical Results • Probability of the licensed transmitter (transmitting at -60 dBm) being detected by the cognitive network at different node sensitivity levels

  26. Thanks for attending ! ANY QUESTIONS?

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