Ofdm
Channel Tracking in Wireless OFDM Systems
Heiko Schmidt, Volker K¨ hn, and Karl-Dirk Kammeyer u University of Bremen, FB-1, P.O. Box 33 04 40, D-28334 Bremen, Germany, e-mail: schmidt@comm.uni-bremen.de and Reinhard R¨ ckriem and Stefan Fechtel u Infineon Technologies AG, P.O. Box 80 09 49, D-81609 Munich, Germany e-mail: reinhard.rueckriem@infineon.com
Abstract— In the presented paper, the principle of frequency domain channel estimation for wireless OFDM systems will be shown. A well known noise reduction technique will be adapted to HIPERLAN/2 and IEEE802.11a standards, and its positive effects will be demonstrated by simulation results. Channel tracking has not been considered by the WLAN standards named above, although it is well known that time-variant indoor radio channels can change their characteristics within one PHY burst. This paper presents some techniques for decision directed channel tracking, applicable in wireless OFDM systems. Keywords— HIPERLAN, IEEE802.11, OFDM, channel estimation, channel tracking, noise reduction
I. I NTRODUCTION The American IEEE802.11a standard and the European equivalent HIPERLAN/2 are two similar concepts for broadband wireless LANs (WLAN) in the 5 GHz band. Both standards are based on the multicarrier modulation technique OFDM (orthogonal frequency division multiplexing) combined with convolutional channel coding. The baseband modulation schemes of both standards are very similar, which simplifies implementation considerably. Challanges and difficulties considered in this paper regard both systems. Except for slight differences in signal mapping, most discrepancies between the standards regard the higher protocol layers. Section II presents some fundamentals of OFDM and the WLAN standards. Here we focus on the baseband modulation in the PHY layer and explain parts of the PHY burst structure relevant to channel estimation. Section III describes a frequency domain channel estimator. Assuming channel impulse responses being
Heiko Schmidt, Volker K¨ hn, and Karl-Dirk Kammeyer u University of Bremen, FB-1, P.O. Box 33 04 40, D-28334 Bremen, Germany, e-mail: schmidt@comm.uni-bremen.de and Reinhard R¨ ckriem and Stefan Fechtel u Infineon Technologies AG, P.O. Box 80 09 49, D-81609 Munich, Germany e-mail: reinhard.rueckriem@infineon.com
Abstract— In the presented paper, the principle of frequency domain channel estimation for wireless OFDM systems will be shown. A well known noise reduction technique will be adapted to HIPERLAN/2 and IEEE802.11a standards, and its positive effects will be demonstrated by simulation results. Channel tracking has not been considered by the WLAN standards named above, although it is well known that time-variant indoor radio channels can change their characteristics within one PHY burst. This paper presents some techniques for decision directed channel tracking, applicable in wireless OFDM systems. Keywords— HIPERLAN, IEEE802.11, OFDM, channel estimation, channel tracking, noise reduction
I. I NTRODUCTION The American IEEE802.11a standard and the European equivalent HIPERLAN/2 are two similar concepts for broadband wireless LANs (WLAN) in the 5 GHz band. Both standards are based on the multicarrier modulation technique OFDM (orthogonal frequency division multiplexing) combined with convolutional channel coding. The baseband modulation schemes of both standards are very similar, which simplifies implementation considerably. Challanges and difficulties considered in this paper regard both systems. Except for slight differences in signal mapping, most discrepancies between the standards regard the higher protocol layers. Section II presents some fundamentals of OFDM and the WLAN standards. Here we focus on the baseband modulation in the PHY layer and explain parts of the PHY burst structure relevant to channel estimation. Section III describes a frequency domain channel estimator. Assuming channel impulse responses being