| 摘要 |
PURPOSE: To speed up the setting of AGC, a phase, etc., on the receiving side, to improve the efficiency of a frame and to reduce the error rate of a frame by setting up a prescribed information field in a preamble area in a low frequency hopping communication system using a multi-valued orthogonal amplitude modulation system. CONSTITUTION: A transmitting station switches the frequency of a synthesizer in accordance with a set frequency hopping pattern, successively transmits respective fields of a ramp 701, receiving power measurement 702 and carrier reproduction 703 in a preamble area 741 and then transmits an information transfer area. When a non-modulated wave with an envelope of fixed size is used for the field 702 for setting up AGC, averaging time can be shortened and field length can also be shortened. The field 703 can be detected by using a non-modulated wave without generating ambiguity of phases between a reproduced carrier and a received wave and a timing extracting field 704 charges the phase of a carrier by π in each symbol and maximizes a phase change on a symbol boundary to improve the detection sensitivity of phase shift. |
