| 摘要 |
A frequency-division-multiplex transmitter for carrying an OFDM signal on a large number of closely-spaced carriers receives the digital data at an input (12), applies coding such as convolutional coding (14), time interleaves (16) the signals, and assembles them frame-by-frame in a matrix (18). The data is converted to parallel form by a shift register (18), frequency interleaved, (24) differentially encoded (26), and quadrature phase modulated (28) on several hundred or more closely-spaced carriers. A first inverse Fast Fourier Transform circuit (30) transforms this information in the frequency domain into the time domain. Instead of being transmitted directly, the resultant signals are then amplitude limited (42) and applied to an FFT (44) to reconvert them to the frequency domain. The phases of the wanted signals are then re-set, and the amplitudes of the signals near the edges of the band reduced, in correction circuits (46). The resultant signals are applied to a second inverse FFT (48) for transmission. The output of the second inverse FFT contains smaller power peaks than the output of the first inverse FFT (30). The output is converted to serial form by a shift register (32), a guard interval added (34), and the resultant converted (36) to analogue form.
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