Progress Report on OWDM-Based Cognitive Radio System

1. Progress Report on OWDM-Based Cognitive Radio System Presenter: Kuan-Hung Chen Adviser: Tzi-Dar Chiueh March 28, 2005

2. Outline • Why Cognitive Radios? • Motivation • Orthogonal Wavelet Division Multiplexing (OWDM) • OWDM-Based Cognitive Radio System • Simulation Results • Conclusions

3. Why Cognitive Radios? • In the near future, it is expected that the demand for bandwidth will increase substantially due to • more and more sophisticated wireless applications, • explosive increase of wireless LAN availability, and • growing demands on ubiquitous wireless access to Internet. • Scarcity of spectral resources reminds us spectrum should be used more efficiently. • Cognitive Radio draws lots of attention. • It is proposed to improve spectrum utilization. • It should be smart enough to find out free spectrum it can use.

4. Inefficiency on Spectrum Utilization [1]

5. … … T I M E Frequency Motivation • Cognitive radio  OFDM • OFDM modulation has some disadvantages when only fragmentary spectrum is available. [2]

6. IEEE 802.22 • In Dec. 2002, FCC begins to consider allowing unlicensed operation in licensed band [3][4]. • TV bands below 900 MHz and in 3650-3700 MHz band • It seems that the technology is not ready to support unlicensed operation in TV broadcast spectrum [5]. • A new working group is created in Nov. 2004 for cognitive wireless regional area network (WRAN) standardization. • Provide fixed, point to multi-point air interface • Prevent harmful interference to the licensed services

7. OWDM and Cognitive Radio • OWDM modulation has been studied extensively for xDSL applications or wireless communications. • Better sidelobes attenuation is achievable by OWDM. • A cognitive radio system applies the OWDM is proposed. • Target band: TV band, GSM band, etc.

8. Orthogonal Wavelet Division Multiplexing

9. Introduction on Wavelet • A wave is usually defined as an oscillating function of time, such as a sinusoid. • A wavelet is a “small wave”, which has its energy concentrated in time. [6]

10. Orthogonal Wavelet Division Multiplexing • Wavelet based multichannel modulation scheme. • Implemented via overlapped waveforms to preserve data rate. • Guard interval does not make sense in OWDM. Symbol Duration: T T T

11. Subchannel Spectrum Property • The energy of each subchannel is much more concentrated in mainlobe than that in OFDM case. OFDM Subchannel Spectrum OWDM Subchannel Spectrum

12. OWDM-based Cognitive Radio System • Indoor low-mobility wireless communication system • Target band: TV band, GSM band, etc.

13. Advantages and Drawbacks • Advantages • Higher spectral containment • More robust to narrowband interference • Drawbacks • Higher complexity • More complex equalization • Challenges • Low-complexity architecture development

14. System Specification

15. Packet Format • Short Preamble: CFO estimation • Long Preamble: Symbol timing estimation • Training Symbol: Channel estimation for FEQ initialization

16. System Architecture • Exponentially-modulated synthesis/analysis bank (EMSB/EMAB) are used to realize the OWDM modulation/demodulation.

17. Channel Model • Multipath Rayleigh fading, SCO, CFO, AWGN

18. CFO Estimator • The length N used for moving average is adjustable.

19. Simulation Setups • Parameters • Carrier frequency: 2.4 GHz • Sampling frequency: 80 MHz • CFO: 40 ppm • The CFO estimator is randomly enabled during the first 64 samples of the second symbol in the short preamble. • Three cases are simulated. • Case 1: CFO estimation is done using 256+N-1 samples. • Case 2: CFO estimation is done using 288+N-1 samples. • Case 3: CFO estimation is done using 320+N-1 samples. • 5 schemes are done for each case. • 10000 runs are simulated for each scheme.

20. Simulation Results Case I Case II Case III

21. Histogram of Percentage CFO Estimation Error • Case I: Without moving average, SNR = 5dB

22. Bit Error Rates • 100 symbols are transmitted for each run • 300 runs are simulated for each SNR • 2dB degradation under low SNR

23. Conclusions • An OWDM-based cognitive radio system is proposed to operate in the bands where only fragmentary spectrum is available. • Lower interference to primary systems can be achieved by OWDM modulation. • Moving average is useless to improve the accuracy of CFO estimation.

24. Reference [1] E. Tsui, “What are Adaptive, Cognitive Radios?” in BWRC Winter Retreat, Jan. 13, 2004. http://bwrc.eecs.berkeley.edu/Presentations/Retreats/Winter_Retreat_2004/Tuesday%20AM/ACR%20E%20Tsui.ppt [2] B. Fette, “SDR Technology Implementation for the Cognitive Radio,” in Workshop on Cognitive Radio Technologies, Washington, DC, May 19, 2003. ftp://ftp.fcc.gov/pub/Bureaus/Engineering_Technology/Documents/cognitive_radio/fcc_cognitive_radio_fette_v8.ppt [3] B. Lane, “Cognitive Radio Technologies in the Commercial Arena,” in Workshop on Cognitive Radio Technologies, Washington, DC, May 19, 2003. ftp://ftp.fcc.gov/pub/Bureaus/Engineering_Technology/Documents/cognitive_radio/lane_cognitive_radio_5-19-03.ppt [4] FCC, ET Docket 02-328. [5] Joint reply comments of the association for maximum service television, Inc., the national association of broadcasters, and the association of public television stations. http://gullfoss2.fcc.gov/prod/ecfs/retrieve.cgi?native_or_pdf=pdf&id_document=6514088793 [6] C. S. Burrus, R. A. Gopinath, and H. Guo, Introduction to Wavelets and Wavelet Transforms, Prentice-Hall, Inc., 1998.