Blind Channel Estimation and Blind Block Synchronization in OFDM Systems by Repeated Use of Remodulated Received Blocks
Date Issued
2012
Date
2012
Author(s)
Huang, Si-Syuan
Abstract
Digital signal processing (DSP) techniques have played an important role in channel equalization and estimation in communication systems. While channel equalization and estimation are usually done by pilot-assisted methods in most systems,algorithms for blind channel estimation have also been largely studied due to high bandwidth efficiency. In communication systems employed with cyclic prefixes (CP),
subspace-based (SS) methods are among the most popular categories of blind channel estimation schemes. Existing SS methods, however, either require a large amount of received data or possess a high computational complexity. These drawbacks have made many consider blind methods as inapplicable in modern communication systems which feature fast-varying channels.
In the first part of this thesis, a new algorithm for blind channel estimation in orthogonal frequency division multiplexing (OFDM) systems that require few received blocks with a reasonable complexity is proposed. The idea is based on combining advantages from two previously reported SS methods, namely, remodulation and repeated use of each received block. The combination of the two separated ideas turns out to be superior to each of them alone in many facets. Simulation results not only confirm the capability of the proposed method to work properly with very few received blocks, but also show that it outperforms all previously reported methods.
Another important problem, namely the blind block synchronization, is also studied in the second part of this thesis. Most existing blind estimation methods in linear
redundancy precoder systems assume the block boundaries of the received streams are perfectly known to the receiver, but this assumption is usually not true in practice since no extra known samples are transmitted. Two algorithms for blind block synchronization are proposed for CP-based OFDM systems. The first proposed algorithm declares block synchronization when a certain autocorrelation matrix, constructed from the received signal, achieves minimum rank. It has a much lower computational complexity. The second proposed algorithm exploit the concept of remodulation and
repeated use of each received block. Simulation results suggest their advantages over all previously reported algorithms, especially when the amount of received data is
limited.
Subjects
Blind channel estimation
Blind block synchronization
Subspace method
OFDM
Type
thesis
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