Modeling Ordered Subcarrier SNR in MIMO-OFDM Wireless Links
Robert C. Daniels and Robert W. Heath, Jr.
R. C. Daniels and R. W. Heath, Jr., ``Modeling Ordered Subcarrier SNR in MIMO-OFDM Wireless Links,'' Physical Communication, Vol. 4, Issue 4, pp. 275-285, December, 2011.
Recent results show that the error-rate of coded and bit-interleaved multiple-input, multiple-output (MIMO-OFDM) links are characterized by the ordered post-processing signal-to-noise ratio (SNR). In this paper, we show that the per-stream ordered SNR asymptotically converges (with delay spread) to the inverse, marginal cumulative distribution function (CDF) of post-processing SNR. Using channel- informed precoding, we derive a new approximation of the post-processing SNR marginal inverse CDF through an approximation of the marginal CDF of ordered eigenvalues in Wishart random matrices. Further, by evaluating the independence of subcarriers in terms of the power delay profile we show that the inverse marginal CDF is also an important characterization of post-processing SNR in practice. We exploit this structure to improve principal component regression algorithms that empirically infer a low-dimension basis for ordered SNR. Numerical simulations show high accuracy of this basis with just three dimensions for arbitrary power delay profiles. Consequences of this work include high-resolution limited channel feedback, simpler channel models for system simulation and algorithm design, as well as the reduction of dimension in link quality metrics for link adaptation. The latter is demonstrated through simulations in IEEE 802.11n with constellations that may be adapted per spatial stream.
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