Abstract
Subcarrier weighting (SW) is a recognized technique for sidelobe suppression in OFDM systems. In this paper SW is discussed in the context of cognitive radios where some portion of the spectrum is shared with primary users so it is required to notch that portion. A major disadvantage with SW scheme is bit error rate (BER) degradation due to unequal power distribution among different subcarriers therefore the primary objective of the paper is to enhance the performance of SW without additional degradation in BER performance. To this extent we propose an Elliptical-SW scheme by expanding the locus of weights to elliptical region. Simulation results show that the proposed scheme can produce deeper notch as compared to Conventional-SW for same BER performance. In second part we present a Partial-SW scheme by applying SW to lesser number of subcarriers. It can enhance BER performance significantly with negligible loss in sidelobe suppression capacity. Another scheme namely Guarded-SW is also proposed in this paper to provide further means to obtain very deep notches without any additional degradation in BER however it has to scarify some throughput. Finally an effective way of implementing SW in MIMO systems is presented by jointly optimizing weights over selected number of antennas.
Similar content being viewed by others
References
FCC. (2002). Spectrum policy task force report. ET Docket no. 02–135.
Haykin, S. (2005). Cognitive radio: Brain-empowered wireless communications. IEEE Journal on Selected Areas in Communications, 23(2), 201–220.
Weiss, T.A., & Jondral, F. K. (2004). Spectrum pooling: An innovative strategy for the enhancement of spectrum efficiency.IEEE Commununications Magazine, Radio Commununications, Suppl., 8–14.
Budiarjo, I., Lakshmanan, M. K., & Nikookar, H. (2008). Cognitive radio dynamic access techniques. Wireless Personal Communications, Springer, 45(3), 293–324.
Standard for Wireless Regional Area Networks (WRAN)—Specific requirements—Part 22: Cognitive Wireless RAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Policies and procedures for operation in the TV Bands. The Institute of Electrical and Electronics Engineering, Inc., Std. IEEE 802.22.
Luo, Jian, Kortke, Andreas, & Keusgen, Wilhelm. (2014). Guardband optimization for cellular systems applying raised cosine windowed OFDM. Wireless Personal Communications, Springer, 78(2), 1375–1390.
Mahmoud, H. A., & Arslan, H. (2008). Sidelobe suppression in OFDM-based spectrum sharing system using adaptive symbol transition. IEEE Communications Letters, 12(2), 113–135.
Yamaguchi, H. (2004). Active interference cancellation technique for MB-OFDM cognitive radio. In 34th European microwave conference, 2, 1105–1108.
Brandes, S., Cosovic, I., & Schnell, M. (2006). Reduction of out-of-band radiation in OFDM systems by insertion of cancellation carriers. IEEE Communications Letters, 10(6), 420–422.
Cosovic, I., Brandes, S., & Schnell, M. (2006). Subcarrier weighting: A method for sidelobe suppression in OFDM system. IEEE Communications Letters, 10, 444–446.
Cosovic, I., Brandes, S., & Schnell, M. (2005). A technique for sidelobe suppression in OFDM systems. IEEE Global Telecommunications Conference, 1, 204–208.
Zhang, J. A., Huang, Xiaojing, Antonio, Cantoni, & Guo, Y. J. (2012). Sidelobe suppression with orthogonal projection for multicarrier systems. IEEE Transactions on Communications, 60(2), 589–599.
Kumar, R., & Tyagi, A. (2013). Improvement in active interference cancellation technique using guard carriers in MB-OFDM UWB system. International Conference on Signal Processing and Communication, 487–489. doi:10.1109/ICSPCom.2013.6719840
Schmidt, J. F., Costas-Sanz, S., & Lopez-Valcarce, R. (2013). Choose your subcarriers wisely: Active interference cancellation for cognitive OFDM. IEEE Journal on Emerging and Selected Topics in Circuits and Systems, 3(4), 615–625.
Sarabchi, F., & Nerguizian, C. (2010). Interference cancellation technique for MIMO MB-OFDM UWB cognitive radio. In 6th international conference on wireless and mobile communications, 472–477.
Alian, E. H. M., Saffar, H. E., & Mitran, P. (2012). Cross-band interference reduction trade-offs in SISO and MISO OFDM-based cognitive radios. IEEE Transactions on Wireless Communications, 11(7), 2436–2445.
Kumar, R., & Tyagi, A. (2014). Antiphase tones across transmitting antennas: A spectrum sharing technique for cognitive CO-STFC MB-OFDM UWB system. Wireless Personal Communications, Springer, 79, 437–451. doi:10.1007/s11277-014-1866-0
Xu, R., Zhang, J., Chen, M., Wu, B., & Wang, H. (2012). Pairwise subcarriers weighting for suppressing out-of-band radiation of OFDM. International Journal of Communication Systems, 25, 16–29.
Selim, A., & Doyle, L. (2013). Real-time sidelobe suppression for OFDM systems using advanced subcarrier weighting. IEEE Wireless Communications and Networking Conference (WCNC), 4043–4047.
Boyd, S., & Vandenberghe, L. (2010). Convex optimization. Cambridge: Cambridge University Press.
Grant, M., & Boyd, S. (2011). CVX: Matlab software for disciplined convex programming, version 1.21. http://cvxr.com/cvx.
Proakis, J. Digital communication (5th ed.). New York: McGraw-Hill.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Kumar, R., Tyagi, A. Extended Subcarrier Weighting for Sidelobe Suppression in OFDM Based Cognitive Radio. Wireless Pers Commun 87, 779–796 (2016). https://doi.org/10.1007/s11277-015-2623-8
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11277-015-2623-8