Adaptive modulation for variable-rate OFDM systems with imperfect channel information

Adaptive modulation has been shown to have significant benefits for high-speed wireless data transmission when orthogonal frequency division multiplexing (OFDM) is employed. However, accurate channel state information (CSI) is required at the transmitter to achieve the benefits. Imperfect CSI arises from noisy channel estimates, which may also be outdated due to a delay in getting the CSI to the transmitter. We study adaptive OFDM with both perfect and imperfect CSI for the variable bit rate case, where a target bit error rate is set. Performance results are provided for adaptive OFDM with imperfect CSI. The use of multiple estimates is shown to mitigate the effect of CSI delay. In addition, the fundamental error mechanisms which result in performance degradation are studied. Robust approaches are then proposed that are less sensitive to CSI errors.

[1]  R. Steele,et al.  Mobile Radio Communications , 1999 .

[2]  Michael R. Souryal,et al.  Adaptive modulation with imperfect channel information in OFDM , 2001, ICC 2001. IEEE International Conference on Communications. Conference Record (Cat. No.01CH37240).

[3]  Per Ola Börjesson,et al.  OFDM channel estimation by singular value decomposition , 1996, Proceedings of Vehicular Technology Conference - VTC.

[4]  L. Hanzo,et al.  Adaptive multicarrier modulation: a convenient framework for time-frequency processing in wireless communications , 2000, Proceedings of the IEEE.

[5]  Geoffrey Ye Li,et al.  Robust channel estimation for OFDM systems with rapid dispersive fading channels , 1998, IEEE Trans. Commun..

[6]  Irving Kalet,et al.  The multitone channel , 1989, IEEE Trans. Commun..

[7]  Andrea J. Goldsmith,et al.  Degrees of freedom in adaptive modulation: a unified view , 2001, IEEE Trans. Commun..

[8]  Dennis Goeckel,et al.  Adaptive coding for time-varying channels using outdated fading estimates , 1999, IEEE Trans. Commun..

[9]  Masahiro Morikura,et al.  New high-rate wireless LAN standards , 1999, IEEE Commun. Mag..

[10]  W. C. Jakes,et al.  Microwave Mobile Communications , 1974 .

[11]  John M. Cioffi,et al.  Multicarrier systems with imperfect channel knowledge , 1998, Ninth IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (Cat. No.98TH8361).