US 6,185,259 B2 · Transmitter/receiver for GMSK and offset-QAM

Abstract

A transmitter encodes a number 2N data bits by using N data bits to select one of 2N levels of a cosine wave and the other N data bits to select one of 2N levels of a sine wave. The modulation attains the cosine wave levels at instants offset by half an N-bit symbol interval with respect to the sine wave levels, and is called Offset QAM (OQAM). A received OQAM signal is amplified, filtered and digitized at a sampling rate of preferably only one sample per N-bit half-symbol interval. Successive N-bit half-symbols comprise information modulated alternately on a cosine and a sine carrier wave. The receiver may remove this successive rotation by applying successive derotations of successive digitized samples by like amounts. The derotated samples are then correlated with known sync half-symbols. The sync correlations determine a set of channel coefficients describing the dependence of each digitized sample on one or more unknown half-symbols. The computed channel estimates are then used to predict the expected received sample values for all possible sequences of successive unknown half-symbols that are to be decoded. Received samples are then compared with all possible expected values and a measure of disagreement or error metric computed. That sequence with the lowest cumulative error metric is used to determine the decoded symbol output. In other aspects of the invention, dual mode transmitters and receivers are disclosed that enable different types of modulation to be alternatively utilized in a same apparatus.

Claims25

Dependent claims

A communications method for transmitting information bits from a transmitter to a receiver comprising the steps of:

assembling the information bits into N-bit groups of bits to form half-symbols;
encoding even numbered ones of said half-symbols into one of two to the power N possible amplitude levels of a cosine wave at even instants of a half-symbol clock and odd numbered ones of said half-symbols into one of the same number of amplitude levels of a sine wave at odd instants of said half-symbol clock;
using said cosine and sine waves together to form complex symbols for transmission, each complex symbol carrying 2N information bits;
transmitting said complex symbols as a transmission signal on a designated frequency channel to a receiver;
receiving said transmission signal on said designated frequency channel and converting said received transmission signal to representative complex numerical values at a sampling rate of one complex sample per half-symbol interval;
and
forming a set of prerotated samples from said representative complex numerical values by rotating alternate ones of said representative complex numerical values by plus or minus 90 degrees in phase angle relative to the representative complex numerical values in between the alternate ones of the representative complex numerical values;
processing said prerotated samples to recover said information bits.

5 more elements

A method of transmitting information bits to a receiver at either a first information rate or a second information rate, comprising the steps of:

assembling said information bits into groups of unknown half-symbols, each containing a first number N1 of information bits when transmission at said first information rate is desired, and alternatively containing a second number N2 of information bits when transmission at said second information rate is desired;
encoding even numbered ones of the unknown half-symbols into one of two to the power N possible amplitude levels of a cosine wave at even instants of a half-symbol clock and odd numbered ones of said unknown half-symbols into one of the same number of amplitude levels of a sine wave at odd instants of said half-symbol clock, wherein N=N1 when transmission at said first information rate is desired, and N=N2 when transmission at said second information rate is desired;
using said cosine and sine waves together to form complex symbols for transmission, each complex symbol carrying 2N information bits;
and
transmitting said complex symbols to the receiver in a transmission signal that conveys the unknown half-symbols interleaved with other half-symbols that are known to the receiver in advance, wherein the other half-symbols each comprise a number N3 of information bits known to the receiver, wherein further N3 may alternatively be equal to N1 or N2 independently of whether transmission at said first or second information rate is desired.

2 more elements

Dependencies are inferred from the claim text.

Transmitter/receiver for GMSK and offset-QAM

Life of this patent

Transmitter/receiver for GMSK and offset-QAM

Life of this patent

Abstract

Claims25