Dynamic Spectrum Access Using Audio

By: Samuel HendersonAmos Ajo

Advised By: Dr. DietrichDr. Beex

Project Objective

This project demonstrates the application of Software Define Radio (SDR) and Cognitive Radio (CR) to perform Dynamic Spectrum Access (DSA) using an audio communication system.

What is Wireless Spectrum ?

Licensed User

Radio

Cell Tower

Federal Communications Commission

FCC

Cartoon pic Posted by John Klossner on Apr 18, 2013 at 12:10 PM

http://fcw.com/blogs/fcw-insider/2013/04/klossner_spectrum.aspx

Spectrum data collected using GNU Radio

Cognitive communication Group Project collecting data @ Radford park

Spectrum Utilization

Data collected from VT parking garage across Whitmore building by Cognitive Communication group

Spectrum Hole

Primary User @ 854 MHz Primary User Inactive @ 854 MHz

FFT Plot FFT Plot Spectrum Hole

Dynamic Spectrum Access (DSA)

• DSA: Ability of a Secondary User (SU) radio to opportunistically access spectrum allotted to a Primary User (PU).

• SDR: Are radios which are implemented and controlled in software.

• CR: SDR’s which can sense its environment and use software algorithms to configure and adjust itself dynamically

• Spectrum Sensing: Find spectrum holes

System Setup

PU TX

PU RX

SU RX

SU TX

Primary User Link• PU transmitter sends binary data over a sound

wave– This is made possible by a process called digital

modulation.

• PU receiver demodulates this wave to recover the data

Primary User Link (cont.)

• Coded in MATLAB:– PU TX transmits periodically in bursts– Occupy a channel of spectrum centered at 4 kHz

Primary User Performance

• How accurately does PU receiver recover the bits? Bit Error Rate (BER)

• Of 100k bits, 1.59% are in error• Errant Data caused by carrier incoherence

00.05

0.10.15

0.20.25

0.30.35

0.40.45

0.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

BER

SAMPLES

Bit Error Rate Plot

Secondary User

• The SU is a transmitter whose task is to– Employ spectrum sensing to:

• Occupy PU channel when available.• Vacate PU channel when PU returns.

– Cognitive Radio! – Implemented in software using GNU Radio– Spectrum sensing and control logic scripted in

Python

SU GNU Radio Flowgraph

SU DSA

SU Occupying PU Channel SU Vacating PU Channel

SUPU

SU

System Performance

• The performance of our total system is measured by PU BER

• Factors influencing performance are:– Power of SU– Burst length of PU

Results

With 2 second PU burst length:-Avg. BER of 13.24%

With 3 second SU burst length:-Avg. BER of 5.24%

100k bits of data transmitted and received by PU

Conclusion

• In our research we accomplished the following:– Established a workable model for DSA audio

communication system– PU: Used MATLAB to transmit and receive BPSK

modulated data– SU: Used GNU Radio to implement SDR systems,

and learned to use Python to program implement a cognitive radio

Discussion

• Our research taught us that DSA algorithms, though promising and increasingly necessary, can be difficult to efficiently implement

• Smarter and faster algorithms for spectrum sensing and cognition can be developed to ensure non-intrusive navigation of the spectrum.

Further Work

• Implement proper carrier recovery in PU RX• Add more SU’s to the network• Implement entire system in RF using CORNET

Acknowledgements

• Special Thanks:– Mentorship of Dr. Beex and Dr. Dietrich– Assistance of Tamoghna Roy and Jason Snyder– NSF for sponsoring our research

References

• 1.) "Simulink Exercises for "Digital Communications: A Discrete-Time Approach," by M. Rice." Simulink Exercises for "Digital Communications: A Discrete-Time Approach," by M. Rice. N.p., n.d. Web. 25 July 2013.

Questions?