(Received: 2017-05-01, Revised: 2017-06-03 , Accepted: 2017-07-19)
Orthogonal frequency division multiplexing (OFDM) is a promising candidate for cognitive radio transmission. OFDM supports high data rates that are robust to channel impairments. However, one of the biggest problems for OFDM transmission is high out-off-band radiation, which resultes from the sidelobes of the OFDM sub-carriers. These sidelobes are a source of interference to neighbouring transmissions. This paper focuses on reducing out-of-band radiation by reading and extracting the radiation power in the sidelobes. This is done by extending the time domain OFDM signal by zeros in both sides. The resulting signal is then transformed to the time domain and extended samples are removed to obtain the N-samples of time domain signal representing the out-of-band radiated signal. The resulting signal is Fourier transformed and high frequency sub-carriers are removed to obtain pilots that are inverted and added to the original OFDM data sub-carriers, resulting in reducing the Adjacent Channel Interference (ACI), which affects the adjacent systems. The added signal represents a noise signal to the desired OFDM signal that reduces the BER performance of the desired system, thus a weighing factor is applied to the added signal in order to get a better BER performance with good out-of-band radiation reduction. Matlab/Simulink simulation is adopted to perform an assessment of the proposed technique with different weighing factors and different frequency separation between the desired signal and the adjacent one. For 0 dB attenuation on the added signal, a 10 dB reduction in out-of-band radiation is obtained, while 6 dB reduction is obtained when the weighing factor reduces the input signal power by 3 dB. BER performance is better by performing the reduction technique and depends on the frequency distance between the adjacent signal and the desired one.

[1] V. K. Garg and J. E.Wilkes, Wireless and Personal Communications Systems, Upper Saddle River, NJ: Prentice - Hall PTR, 1996.

[2] A. Goldsmith, Wireless Communication, New York: Cambridge University Press, 2005.

[3] G. Jiann-Ching, A. Khayrallah and G. E. Bottomley, "Adjacent Channel Interference Rejection for Land Mobile Radio Systems," in the 48th IEEE Vehicular Technology Conference (VTC 98), pp. 1715-1719, vol. 3, 1998.

[4] P. Dely, M. C. Castro and A. J. Kassler, "Impact of Adjacent Channel Interference on Performance of Multi-Radio Multi-Channel Mesh Networks," European Collaborative Innovation Centres for Broadband Media Services, 2014.

[5] H. Holma and A. Toskala, 1970-WCDMA for UMTS: Radio Access for Third Generation Mobile Communications, 2nd Ed., Chichester: Wiley, 2002.

[6] W. C. Y. Lee, Mobile Communications Design Fundamentals, 2nd Ed., New York; Chichester: Wiley, 1993.

[7] W. C. Y. Lee, Mobile Communications Engineering: Theory and Applications, 2nd Ed., New York; London: McGraw-Hill, 1998.

[8] J. Kimery, "802.11ac Adjacent Channel Interference (ACI)," 14-April-2016, [Online], Available:

[9] L. Hanzo, M. Münster, B. J. Choi and T. Keller, OFDM and MC-CDMA for Broadband Multi-User Communications, WLANs and Broadcasting, John Wiley & Sons, Ltd., July 2003.

[10] R. V. Nee and R. Prasad, OFDM for Wireless Multimedia Communications, Boston; London: Artech House Publisher, 2000.

[11] R. Prasad, OFDM for Wireless Communications Systems: Artech House, Universal Personal Communications Series, 2004.

[12] K. G. Samarah, High Bit Rate Air Interface for Next Generation Mobile Communication Systems, Ph.D. Dissertation, School of Engineering, Design and Technology, University of Bradford, Bradford, 2007.

[13] I. A. Glover and P. M. Grant, Digital Communications, London: Prentice-Hall, 1998.

[14] D. J. Defatta, J. G. Lucas and W. S. Hodgkiss, Digital Signal Processing: A System Design Approach, Chichester: Wiley, 1988.

[15] J. G. Proakis and D. G. Manolakis, Digital Signal Processing: Principles, Algorithms and Applications, 2nd Ed., New York; Toronto; New York: Macmillan; Maxwell Macmillan Canada; Maxwell Macmillan International, 1992.

[16] S. Pagadarai, Sidelobe Suppression for OFDM-Based Cognitive Radios in Dynamic Spectrum Access Networks, M.Sc. Thesis, Department of Electrical Engineering & Computer Science, Jawaharlal Nehru Technological University, India, 2007.

[17] A. Zubow and R. Sombrutzki, "Adjacent Channel Interference in IEEE 802.11n," in the 2012 IEEE Wireless Communications and Networking Conference (WCNC), pp. 1163-1168, 2012.

[18] S. Brandes, I. Cosovic and M. Schnell, "Techniques for Reducing Out-of-band Radiation in OFDM-Based Transmission Systems," European Transactions in Telecommunications, vol. 21, p. 11, March 2010.

[19] S. Technote, "Communication - OFDM," [Online], Available: Communication_OFDM.html.

[20] A. D. S. Jayalath and C. Tellambura, "Reducing the Out-of-band Radiation of OFDM Using an Extended Guard Interval," in the 54th IEEE Vehicular Technology Conference (VTC), pp. 829-833, vol. 2, 2001.

[21] I. Cosovic, S. Brandes and M. Schnell, "Subcarrier Weighing: A Method for Sidelobe Suppression in OFDM Systems," IEEE Communications Letters, pp. 444-446, vol. 10, 2006.

[22] S. Pagadarai, R. Rajbanshi, A. M. Wyglinski and G. J. Minden, "Sidelobe Suppression for OFDM-Based Cognitive Radios Using Constellation Expansion," in the IEEE Wireless Communications and Networking Conference, pp. 888-893, 2008.

[23] J. G. Proakis, Digital Communications, 4th Ed., London: McGraw-Hill, 2001.

[24] K. Pahlavan and P. Krishnamurthy, Principles of Wireless Networks: A Unified Approach, Prentice Hall PTR, 2001.

[25] P. Wang, J. An and Y. Wu, "Reduction of Out-of-band Radiation in OFDM-Based DRM Simulcast Systems," International Conference on Wireless Communications, Networking and Mobile Computing, pp. 1-4, 2006.

[26] A. W. Mustafa and K. G. Samarah, Adjacent Channel Interference Reduction in OFDM Systems, Un-published Master Thesis, Electrical Engineering Department, Mutah University, 2017.

[27] M. D. A. R. Chung, M. Dohler, M. Fiacco, S. Saunders, J. Brown, SMR. Jones, T. Harrold and A. Nix, "Propagation Models Final Report," London, 26 Jan. 2000.