Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
1998-07-02
2001-07-17
Chin, Stephen (Department: 2734)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C375S142000, C370S320000
Reexamination Certificate
active
06263031
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to digital communication systems and, more particularly, to systems utilizing reference symbols to assist in the demodulation of transmitted information.
2. Description of the Related Art
Digital communication systems typically utilize bandwidth-efficient modulation schemes to maintain high bit rates for a number of user channels. Such systems transmit bursts of information symbols that may include both reference symbols and data symbols. The reference symbols are known by a receiver to assist in the demodulation of the data symbols.
Some signal bursts are designed to provide control information only. For instance, FACCH (fast access control channel), SDCCH (stand-alone dedicated control channel), and SACCH (slow associated control channel) bursts provide messaging information for upper layer protocols. These and other types of signal bursts are to be distinguished from data bursts that carry voice and/or other data information, such as TCH (normal traffic channel) and RACH (random access channel) bursts. In order to benefit from these different types of bursts, the receiving portion of the communication system must be capable of distinguishing between burst types. Past systems have classified incoming bursts by devoting a portion of a preamble segment to identification data.
In order to demodulate the identification data (and the rest of the data contained in the signal burst), the clock in the receiver must be synchronized with the clock in the transmitter and, further, the oscillator in the receiver must be aligned with the actual frequency of the carrier signal. With certain modulation schemes (e.g., QPSK), the receiver is capable of deriving timing and frequency information from the information symbols themselves subsequent to removing the modulation. These conveniences are not available with modulation schemes such as GMSK (Gaussian Minimum Shift Keying), in which modulated information is transmitted over a plurality of bit periods, inasmuch as no single non-linearity exists for modulation removal. However, such memory-inducing modulation schemes provide several advantages, not the least of which is the constant envelope of the transmitted signal. This advantage is particularly useful for satellite communication systems, inasmuch as cheaper Class C amplifiers may be used in both the satellites and the receivers.
In past systems utilizing memory-inducing modulation schemes, the preamble segment of each signal burst also included portions for estimating the timing and frequency of the signal burst. For the timing variable, a first portion provided reference symbols having considerable variation such that the transmitted signal has high frequency components. A second portion provided symbols all set to “1” to obtain high resolution for the frequency variable. However, evaluation of these portions of the preamble became an undesirable prerequisite to burst type classification. Moreover, allocating separate bits to timing and frequency estimation as well as burst type classification has limited the data throughput of such systems.
SUMMARY OF THE INVENTION
The present invention is useful in a digital communication system transmitting a signal burst of a plurality of different burst types. According to one aspect of the present invention, a burst classifier includes a plurality of filters associated with the plurality of different burst types, respectively. Each filter generates correlation data based on the signal burst and a respective plurality of reference signals offset by a plurality of time offsets. The respective pluralities of reference signals are indicative of a corresponding burst type of the plurality of different burst types. The burst classifier further includes a comparator that analyzes quantities based on the correlation data from each filter to determine the burst type of the signal burst.
According to another aspect of the present invention, a method of classifying a signal burst as one of a plurality of burst types transmitted in a digital communication system includes the step of calculating correlation data based on the signal burst and a respective plurality of reference signals offset by a plurality of time offsets. The respective pluralities of reference signals are indicative of a corresponding burst type of the plurality of different burst types. The inventive method further includes the step of comparing quantities based on the correlation data to determine the burst type of the signal burst.
According to yet another aspect of the present invention, a method is useful for classifying a signal burst modulated by a modulation scheme that induces memory therein as one of a plurality of burst types transmitted in a digital communication system. The inventive method includes the step of comparing the signal burst with a respective plurality of reference signals to generate comparison data not reflecting the memory induced by the modulation scheme. The respective pluralities of reference signals are indicative of a corresponding burst type of the plurality of different burst types. The inventive method further includes the step of combining the comparison data non-coherently over a plurality of reference segments distributed within the signal burst to generate combined comparison data for each of a plurality of time offsets and for each burst type. The inventive method still further includes the step of removing uncertainty associated with a timing offset of the signal burst by generating a maximum comparison value for each burst type from the combined comparison data for the plurality of time offsets. Lastly, the inventive method includes the step of determining the burst type of the signal burst from the maximum comparison values.
REFERENCES:
patent: 4007331 (1977-02-01), Flanagan
patent: 4450531 (1984-05-01), Kenyon et al.
patent: 4843562 (1989-06-01), Kenyon et al.
patent: 5117441 (1992-05-01), Weitgand
patent: 5210820 (1993-05-01), Kenyon
patent: 5561431 (1996-10-01), Peele et al.
patent: 5577056 (1996-11-01), Malik et al.
patent: 5696762 (1997-12-01), Natali et al.
patent: 5809009 (1998-09-01), Matsuoka et al.
patent: 5991632 (1999-11-01), Guillame
patent: 6067295 (2000-05-01), Taubenheim et al.
patent: 6128331 (2000-10-01), Struhsaker et al.
Antia Yezdi F.
Beidas Bassel F.
Hammons, Jr. A. Roger
Al-Beshrawi Tony
Chin Stephen
Hughes Electronics Corp.
Sales Michael W.
Whelan John T.
LandOfFree
Method and apparatus for signal burst classification does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for signal burst classification, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for signal burst classification will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2564147