Compact non-linear modulation processor
Original Publication Date: 2007-May-24
Included in the Prior Art Database: 2007-May-24
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The efficiency in a transmitter can be improved by peak reduction of the baseband modulation while minimizing the impact on the modulation accuracy. This technique is known from prior art. A general block diagram of this technique is given in Figure 1. Using this technique (see above) the following is proposed: Referring to Figure 2, the baseband symbols are passed both to the Main lowpass filter, Filter 1, and also to a copy of the same filter, Filter 2. The Main lowpass filter is used to define the spectrum of the modulation sidebands, and is usually defined as part of the specifications of the radio system being implemented. The prediction filter, Filter 2, is a truncated version of the main filter, so it has less delay (and not so much out-of-band rejection), but its peak response is substantially identical to the first filter. Therefore, its output can be used to calculate a peak correction to be applied at the main filter's output. The fact that the copy filter is truncated means that it can produce an output before the main filter does. As a further enhancement, the prediction filter can be adjusted so that it includes the effect of the modulator bandwidth, for example any analog filtering after the DACs which may modify the peak amplitudes.