Importance

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Abstract

A transceiver uses feedback control to monitor a transmitted continuous phase modulation (CPM) waveform, such as a spread spectrum CPM waveform, and adjust the modulation index in response thereto. Codewords are selected from a table according to a data signal and applied to a pulse shaping network. The pulse shaping network outputs a CPM waveform to a prefilter. The prefilter is connected to an FM modulator, such as a voltage controlled oscillator. In one embodiment, a correlator in the transceiver monitors the transmitted waveform during times when the transceiver is not receiving signals, and provides a correlation signal to a feedback control circuit. The feedback control circuit dynamically adjusts the gain of the prefilter, and may comprise, e.g., a second order tracking loop filter. The feedback control signal thereby tracks the amplitude of the transmitted waveform and adjusts the output gain of the prefilter so as to maintain a constant signal envelope. A tau-dither algorithm may be employed as part of the tracking circuit. In an alternative embodiment, a gradient search is used to adjust the output amplitude of the transmitted signal, wherein the step size of the gradient search is based on the slope of the signal amplitude and varied dynamically over time. In another embodiment, a two bandwidth differencing circuit is used to adjust the output amplitude of the transmitted signal.

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First Claim