Method and apparatus for controlling the modulation index of continuous phase modulated (CPM) signals
US5832022A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Jun 2, 1995 |
| Grant date | Nov 3, 1998 |
| Priority date | — |
| Expiry date | Jun 2, 2015 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L27/201
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
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…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.