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Adaptive OFDM System Employing a New SNR Estimation Method  

Kim Myung-Ik (Dept. of Electronics and Information Engineering, Korea Univ.)
Ahn Sang-Sik (Dept. of Electronics and Information Engineering, Korea Univ.)
Publication Information
Journal of the Institute of Electronics Engineers of Korea TC / v.43, no.3, 2006 , pp. 59-67 More about this Journal
Abstract
OFDM (Orthogonal frequency Division Multiplexing) systems convert serial data stream to N parallel data streams and modulate them to N orthogonal subcarriers. Thus spectrum utilization efficiency of the OFDM systems are high and high-speed data transmission is possible. However, with the OFDM systems using the same modulation method at all subcarriers, the error probability is dominated by the subcarriers which experience deep fades. Therefore, in order to enhance the performance of the system adaptive modulation is required, with which the modulation methods of the subcarriers are determined according to the estimated SNRs. The IEEE 802.11a system selects various transmission speed between 6 and 54 Mbps according to the modulation mode. There are three typical methods for SNR estimation: Direct estimation method uses the frequency domain symbols to estimate SNR directly by minimizing MSE (Mean Square Error), EVM method utilizes the distance between the demodulated constellation points and received complex values, and the method utilizing the Viterbi algorithm uses the cumulative minimum distance in decoding process to estimate the SNR indirectly. Through comparison analyses of three methods we propose a new SNR estimation method, which employs both the EVM method and the Viterbi algorithm. Finally, we perform extensive computer simulations to confirm the performance improvement of the proposed adaptive OFDM systems on the basis of IEEE 802.11a.
Keywords
OFDM; Adaptive modulation; SNR estimation;
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1 W. Webb and R . Steele, 'Variable rate QAM for mobile radio,' IEEE Transactions on Communications, vol. 43, pp. 2223-2230, July 1995   DOI   ScienceOn
2 J. Heiskala and J. Terry, 'OFDM Wireless LANs: A Theoretical and Practical Guide,' pp. 48-83, SAMS, 2000
3 L. Hanzo, C. L. Wong and M. S. Yee, 'Adaptive Wireless Transceivers,' WILEY, pp. 535-578, 2002
4 ETSI BRAN, TS 101 475, 'HIPERLAN Type 2; Physical (PHY) layer,' Apr. 2000
5 Shousheng He and Torkelson M. 'Effective SNR estimation in OFDM system simulation', IEEE Globecom'98, pp. 945-950, Nov. 1998   DOI
6 IEEE Std 802.11a-1999, 'Part 11: Wireless LAN ？Medium Access Control (MAC) and Physical Layer (PHY) specifications,' Sep. 1999
7 ETSI EN 300 799, 'Digital video broadcasting (DVB); framing, structure, channel coding, and modulation for digital terrestrial television,' June 1999
8 ETSI EN 300 401, 'Radio broadcasting systems: digital audio broadcasting (DAB) to mobile, portable and fixed receivers,' Sep. 2000
9 Joint TC of Committee T1 R1P1.4 and TIA TR46.3.3/TR45.4.4 on Wireless Access, 'Draft Final Report on RF Channel Characterization,' Paper no. JTC (AIR)/94.01.17-238R4, Jan. 17, 1994
10 Tang, C., Stolpman, V., 'An adaptive learning approach to adaptive OFDM,' IEEE WCNC 2004, pp, 1406-1410, March 2004
11 Sklar, 'How I learned to Love the Trellis,' IEEE Magazine, pp. 87-102, May 2003   DOI   ScienceOn
12 H. Matsuoka, S. Sampei, N. Morinaga, and Y. Kamio, 'Adaptive modulation systems with variable coding rate concatenated. code for high quality multi-media communications systems,' Proceedings of IEEE VTC'96, pp. 487-491, 1996   DOI
13 A. Czylwik, 'Adaptive OFDM for wideband ratio channels,' IEEE Globecom'96, pp. 713-718, 1996   DOI
14 V. Lau and M. Macleod, 'Variable rate adaptive trellis coded QAM for high bandwidth efficiency applications in Rayleigh fading channels,' Proceedings of IEEE VTC'98, pp. 348-352, 1998   DOI