C.-D. Chung (Taiwan)
Modulation, differential encoding, block detection, DC offset.
In this paper, a differential encoding and block detection technique is investigated for coherently demodulating the square-constellation quadrature amplitude modulation (QAM) signals in the presence of DC offset in the receiver baseband processing. By applying the maximum-likelihood decision argument to the differences of the received symbols within a block, the coherent block detection of differentially en coded square QAM signals is developed and analyzed on the additive white Gaussian noise channel. The proposed receiver is capable of completely eliminating the existent DC offset as long as the offset remains constant over an observation block length. By virtue of a union bound argument, an approximate BEP upper bound is derived and verified by simulation for the scheme using the Gray code labeling of bits to symbols and the block detection with an arbitrary block length. It is analytically shown that the pro posed block receiver for differentially encoded QAM performs, in the presence of DC offset, comparably with the ideal coherent QAM receiver in the absence of DC offset, as the block length is long enough.
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