Analysis of signal decoding and carrier frequency recovery in practical MIMO communications

Build a wireless testbed on a comprehensive hardware platform not only enables us fast prototyping wireless communications but also helps us understand the potential benefits and problems that come with real hardware and cannot be identified with only theoretical research. This dissertation presents three research topics developed from building such a wireless testbed: transient carrier frequency offset (CFO), a joint CFO and SFO estimator, and computational complexity of sphere decoding with greedy ordering. %We present the design and implementation of a close-loop time-division duplex (TDD) multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) wireless testbed on a hardware platform.;We consider the transient CFO observed on the wireless testbed working in TDD mode. We model the transient CFO as the response of an underdamped second order system. We propose a subspace based low complexity parametric estimation algorithm. Furthermore, a weighted subspace fitting (WSF) algorithm is derived to minimize the mean squared error of the estimated parameters. The performance of the proposed algorithms is compared to the traditional solutions as well as the Cramer-Rao lower bound (CRLB). It is also confirmed by the experimental results obtained from the wireless testbed.;The joint CFO and SFO estimator exploits the fact that the sampling clock and the local radio frequency are derived from a common reference frequency source. The proposed joint CFO and SFO estimator is capable of estimating CFO in a extended range without suffering from the phase ambiguity problem. CRLB of the estimated CFO is discussed and compared. The proposed algorithm is validated on the wireless testbed.;We further explore the computational complexity of the sphere decoding algorithm with the greedy ordering. The ordering of the channel matrix may have significant impact on the complexity of the sphere decoding. The computational complexity is studied based on the distance between a fixed pair of lattice points in k--dimensional space. We show that the distribution of the distance depends only on the first n -- k steps of ordering, and is independent from the remaining k steps of ordering. Then, we obtain the complexity of the k--dimensional sphere decoding by the partially sorted QR decomposition. The analytical results are verified with the numerical simulations.