Automatic frequency control circuit and automatic frequency control method

Abstract

A frequency control circuit for correcting the frequency difference of a received PSK-modulated signal composed of a data sequence where two-symbol period signal section formed of a two-symbol period signal is arranged at a predetermined position. The frequency control circuit has offset removing means (17) that subtracts the phase rotation amount of the modulated component for a (2xM) symbol period from the phase rotation amount for the (2xM) symbol period and extracts the phase rotation amount for the (2xM) symbol period due to the frequency difference between the transmitter and the receiver. By using the periodicity of the two symbol period section which is a known pattern, the frequency difference can be corrected in a short time with high accuracy even if bit-timing synchronization is not established.

Description

technical field [0001] The present invention relates to a PSK modulated signal of a digital wireless communication system using a PSK (Phase-Shift-Keying: phase-shift keying method) modulation method, in particular to an automatic frequency control circuit for correcting frequency deviation when receiving the PSK modulated signal and Automatic frequency control method. Background technique [0002] In recent years, digital wireless communication systems using the PSK modulation method have been put into practical use. For example, there is a technology disclosed in Non-Patent Document 1 as a differential detection demodulator using the PSK modulation method. The automatic frequency control circuit described in this document performs frequency offset correction on a received signal that is PSK-modulated on an arbitrary data sequence. [0003] figure 1 It is a block diagram showing the configuration of a conventional automatic frequency control circuit disclosed in the afor...

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Problems solved by technology

[0017] However, in the conventional automatic frequency control circuit, since the correction operation is performed assuming that the received signal is an arbitrary data sequence modulated by PSK, the SN ratio of the received signal may be misjudged by the judging unit 94 under a harsh environment.

Furthermore, for example, even when a preamble signal of a known pattern is received, it is difficult to perform high-precision frequency offset correction in a short time.

[0018] In addition, the existing automatic frequency control circuit needs to assume that the bit timing synchronization has been established. If the bit timing synchronization is not established, there is also a problem that the frequency deviation estimation characteristic is degraded due to the influence of intersymbol interference, etc.

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