New AFC tracking algorithms for digital DBS receiver

Two new automatic frequency control (AFC) tracking algorithms are proposed for QPSK demodulation in a digital direct broadcasting satellite (DBS) receiver. These are called rotational decision directed AFC(RDDAFC) and decision device embedded AFC(DDEAFC). In order to prevent the presence of the residual phase difference by the CPAFC [Natali 1984] as well as the AFC based on the tan/sup -1/ circuit [Ishigawa 1992], the RDDAFC rotates the decision boundary for the kth received symbol by the frequency detector output of the (k-1)th received symbol while the DDEAFC uses the product of the kth received symbol and the decision device output before passing through the cross product discriminator. It is shown that the total pull-in time of the RDDAFC and PLL was 0.13 msec with a carrier frequency offset of 2.4 MHz when the S/N equals 2dB while 0.2 msec is for the DDEAFC.