| 摘要 |
Apparatus and method for digital frequency discrimination are provided that only require one sample per data symbol (e.g. one bit for BPSK or 2 bits for QPSK). This is accomplished by determining the difference between the carrier phase error on successive data symbols. The difference in phase error is then used as an approximation to the derivative of the phase error, which is the frequency error between the carrier and the local oscillator of the receiver. An important advantage of this apparatus and method is that they allow the maximum symbol rate to be processed by the receiver for a given digital technology. In other words, maximum symbol rate can now be equal to the maximum clock rate of the digital technology, if so desired by the user. In contrast, conventional digital frequency discriminators limit the maximum symbol rate to one-half or one-fourth of the maximum clock rate for a given digital technology. A key feature is the use of a threshold apparatus and method that allows the discriminator to ignore phase shifts that are due to data modulation, and only use phase shifts that are due to carrier frequency errors. Thus, when successive data symbols are identical, frequency error information can be obtained for carrier recovery. When successive data symbols are different, no updates are made to the carrier recovery. This allows a carrier recovery loop to operate at a rate of one sample per data symbol.
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