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Optimal rate and power allocation for OFDM in the presence of channel uncertainty

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3 Author(s)
Chunhui Liu ; Institute for Theoretical Information Technology, RWTH Aachen University, D-52056, Germany ; Daniel Bielefeld ; Rudolf Mathar

Adaptive modulation of subcarriers for orthogonal frequency division multiplexing (OFDM) has been shown to improve system performance significantly. As a prerequisite, accurate channel state information (CSI) must be available at the transmitter. For time varying, noisy channels, however, this is difficult to achieve in practical systems. In this paper, we consider optimal subcarrier assignment under incomplete CSI. Soft estimates and the Cramer-Rao bound are used to analyze the effect of CSI errors. As an important control parameter, the frame length is coming in. We investigate analytically its influence on the performance of adaptive modulation in OFDM systems for the rate and power optimization problems. Simulations demonstrate that the frame length may not be neglected as an important overall system performance parameter.

Published in:

2008 IEEE 19th International Symposium on Personal, Indoor and Mobile Radio Communications

Date of Conference:

15-18 Sept. 2008