Method for transmitting digital data by means of continuous phase modulation
AssigneeBBC Brown, Boveri & Company, Limited
InventorDacfey Dzung
Life of this patent
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Abstract
A method for transmitting digital data by means of continuous phase modulation (CPM), wherein the transmission signal s(t) is generated by retrieving stored digital values, which are allocated to a continuous sequence of symbols a.sub.i present at the transmitter input, from storage in a memory. In contrast to the conventional method, these stored digital values are not calculated from a predetermined frequency-base-band pulse g(t) by linear superposition but are optimized with respect to the in-band power emitted by means of an iterative method. This non-linear method leads to distinctly improved spectral characteristics of the transmission signal s(t).
Claims4
Method for transmitting digital data by means of continuous phase modulation of a carrier oscillation, comprising:
- presenting the digital data in the form of a continuous sequence of symbols (a.sub.i) which occur at a rate of 1/T and can assume M possible discrete values;
- transmitting the information items with a carrier frequency f.sub.c and a time-dependent phase .PHI.(t) in a transmission signal s(t) having the form
- s(t)=cos .vertline.2.pi.f.sub.c t+.PHI.(t).vertline.;
- before transmission, subjecting the symbols a.sub.i to a shaping process in accordance with the determination of a frequency-baseband pulse extending over L symbol intervals L.multidot.T;
- permanently storing, for each possible sequence of L symbols, a plurality of digital values which, for generating the transmission signal s(t) are allocated to the symbol sequence present in each case at the transmission input, are retrieved from storage and converted into an analog signal;
- and
- using only values for which the power of the transmission signal s(t) located within a fixed frequency band around the carrier frequency (fZc) is a maximum as stored digital values.
Dependencies are inferred from the claim text.