10-04-2017, 08:11 PM
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 IEE802.11a 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
Presented By:
Heiko Schmidt, Volker K uhn, and Karl-Dirk Kammeyer
University of Bremen, FB-1,
P.O. Box 33 04 40, D-28334 Bremen, Germany,
And
Reinhard R uckriem and Stefan Fechtel
Infineon Technologies AG,
P.O. Box 80 09 49, D-81609 Munich, Germany
I. INTRODUCTION
The American IEE802.11a standard and the European equivalent HIPERLAN/2 are two similar concepts for broad- band wireless LANs (WLAN) in the 5 GHz band. Both standards are based on the multicarrier modulation tech- nique OFDM (orthogonal frequency division multiplexing) combined with convolutional channel coding. The base- band 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 dis- crepancies 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 modu- lation in the PHY layer and explain parts of the PHY burst structure relevant to channel estimation. Section II describes a frequency domain channel estima- tor. Assuming channel impulse responses being limited in time, correlations between adjacent subcarriers can reduce the noise influence on the estimated transfer function. Here, a new method for computing the correlations is shown. In case of time variant channel coefficients, a decision di- rected channel tracking algorithm for re-estimating the chan- nel coefficients is presented in section IV. The remodulation of the detected data can be done with or without exploiting channel decoding as demonstrated in section IV
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http://ant.uni-bremen.de/sixcms/media.ph...chmidt.pdf