Relative to designs assuming no channel knowledge at the transmitter, considerably improved communications become possible when adapting the transmitter to the intended propagation channel. As perfect knowledge is rarely available, transmitter designs based on partial (statistical) channel state information (CSI) are of paramount importance not only because they are more practical but also because they encompass the perfect- and no-knowledge paradigms. In this paper, we first provide a partial CSI model for orthogonal frequency division multiplexed (OFDM) transmissions over multi-input multi-output (MIMO) frequency-selective fading channels. We then develop an adaptive MIMO-OFDM transmitter by applying an adaptive two-dimensional (2-D) coder-beamformer we derived recently on each OFDM subcarrier, along with an adaptive power and bit loading scheme across OFDM subcarriers. Relying on the available partial CSI at the transmitter, our objective is to maximize the transmission rate, while guaranteeing a prescribed error performance, under the constraint of fixed transmit-power. Numerical results confirm that the adaptive 2-D space-time coder-beamformer (with two basis beams as the two "strongest" eigenvectors of the channel's correlation matrix perceived at the transmitter) combined with adaptive OFDM (power and bit loaded with M-ary quadrature amplitude modulated (QAM) constellations) improves the transmission rate considerably.
Bibliographical noteFunding Information:
Manuscript received December 22, 2002; revised April 30, 2003. This work was supported by the ARL/CTA under Grant DAAD19-01-2-011 and the National Science Foundation under Grant 01-0516. This work was presented in part at the IEEE Signal Processing Workshop on Signal Processing Advances in Wireless Communications (SPAWC), Rome, Italy, June 15–18, 2003. The associate editor coordinating the review of this paper and approving it for publication was Dr. Rick S. Blum.
- Adaptive modulation
- MIMO OFDM
- Partial channel state information