US 5,832,022 A · Method and apparatus for controlling the modulation index of continuous phase modulated (CPM) signals

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.

Claims51

Dependent claims

A method for controlling a modulation index of a signal, said method comprising the steps of

receiving a data signal,
generating a pulse shaped signal in response to said data signal, said pulse shaped signal associated with a continuous phase modulated waveform,
applying said pulse shaped signal to a frequency modulator, and generating a modulated signal thereby,
correlating said modulated signal, and generating a correlation signal in response thereto, and
amplifying said pulse shaped signal in dependence upon said correlation signal.

2 more elements

Apparatus for adjusting a modulation index of a transmitter generating a signal having a nominally constant signal envelope, said apparatus comprising

means for receiving a data signal,
means for encoding said data signal and generating an encoded signal thereby,
a pulse shaping network connected to said encoded signal,
a variable gain amplifier connected to an output of said pulse shaping network,
a voltage-controlled oscillator connected to an output of said variable gain amplifier,
a coupler connected to an output of said voltage-controlled oscillator,
a correlator connected to said coupler, said correlator outputting a correlation signal,
a feedback control circuit connected to said correlation signal, and
a gain adjustment command signal output from said feedback control circuit to said variable gain amplifier, whereby a gain of said variable gain amplifier is adjusted in response to said gain adjustment command signal.

6 more elements

Dependencies are inferred from the claim text.

Method and apparatus for controlling the modulation index of continuous phase modulated (CPM) signals

Life of this patent

Method and apparatus for controlling the modulation index of continuous phase modulated (CPM) signals

Life of this patent

Abstract

Claims51