Carrier-recovery loop with stored initialization in a radio receiver
Granted: June 6, 2000
Patent Number:
6072842
A carrier-recovery loop for a receiver in a communication system with features that facilitate initialization of the loop. The carrier-recovery loop is a PLL that uses a feedback signal to keep a recovery oscillator phase-locked to the carrier of a received signal. In the present invention, an initializing value of the feedback signal is stored in a memory and provided to a digitally controlled recovery oscillator (DCO). This initializing value brings the recovered signal to an initial…
Passband DQPSK detector for a digital communications receiver
Granted: April 25, 2000
Patent Number:
6055281
A digital communications DQPSK passband detector having a matched filter, a differential decoder, and a slicer that use elementary circuit components. In the matched filter, recovered carrier reference signals are fed along with the received signal to a pair of XNOR gates. This arrangement effectively results in a multiplication operation without any complex circuit elements. The outputs of the XNOR gates control the direction of counting of a pair of binary counters that generate…
Programmable loop filter for carrier recovery in a radio receiver
Granted: January 25, 2000
Patent Number:
6018556
A digital loop filter in the carrier-recovery loop of a digital communications receiver. The recovery loop is a PLL that keeps the receiver oscillator locked to the carrier wave, and the loop filter provides control over the PLL's frequency response by conditioning an error signal that is fed back to the receiver oscillator. In the present invention, the error signal is a digital signal, and the loop filter is implemented in digital hardware. With this implementation the characteristics…
Verification of PN synchronization in a direct-sequence spread-spectrum digital communications system
Granted: December 14, 1999
Patent Number:
6002709
In a direct sequence spread spectrum digital communication receiver, a system and method for recovering and verifying the timing or phase of a pseudo-random noise (PN) sequence used for despreading received signals. In one embodiment, the method includes steps of: (a) determining an initial value of a received PN phase, (b) setting the receiver's PN phase equal to the initial value of the received PN phase, (c) a first testing to verify that the receiver identifies a SYNC field within a…
Timing recovery for a pseudo-random noise sequence in a direct-sequence spread-spectrum communications system
Granted: December 14, 1999
Patent Number:
6002710
In a digital communication system for voice signals, a system and method for recovering the timing of a pseudo-random noise (PN) sequence used for direct-sequence spreading and despreading of the communicated signals. In one embodiment, a received signal is a time-division duplexing (TDD) or time-division multiple access (TDMA) signal, and a receiver performs a complete "sliding correlator" examination of the received signal in a fixed time by using the timing of the TDMA or TDD frames.…
Verification of PN synchronization in a spread-spectrum communications receiver
Granted: October 12, 1999
Patent Number:
5966416
A system for recognizing degraded pseudo-random noise (PN) synchronization in a spread-spectrum receiver. The system uses a signal that indicates the correlation of the locally generated PN sequence with the received PN sequence. The correlation signal can be a symbol-length integration of the output from a square-law detector, or an appropriate similar signal. If the correlation signal is not degraded by demodulating with a deliberately shifted copy of the PN sequence, there is an…
Method for compensating filtering delays in a spread-spectrum receiver
Granted: August 17, 1999
Patent Number:
5940435
A method for configuring the receiver with an IF delay value that indicates the timing of symbol transitions in a received signal processed by the receiver. The receiver recovers a timing that has the same period as the symbol period, but which is out of phase with the received symbols. The received symbols are members of a constellation with elements that have purely I or purely Q components. A symbol-quality signal is generated by constructing the quantity…
System and method for compression and decompression of audio signals
Granted: September 30, 1997
Patent Number:
5673364
A speech compression/decompression system and method which do not require special hardware are described. The compression unit represents an input audio signal as a collection of parameters, wherein the parameters are a remnant excitation pulse sequence, a set of spectral coefficients and a set of pitch parameters. The decompression unit utilizes the pitch parameters and remnant excitation pulse sequence to produce a reconstructed excitation signal. The decompression unit also utilizes…
Speech pattern matching in non-white noise
Granted: January 23, 1996
Patent Number:
5487129
A system for matching an input signal, comprising non-white noise and a patterned signal corrupted by said non-white noise, to a plurality of reference signals, the system including an estimator estimating noise features of said non-white noise and producing from the noise features at least one noise whitening filter; a filter generally simultaneously filtering the input signal and the plurality of reference signals using the noise whitening filter and producing a filtered input signal,…
Data reception technique
Granted: June 20, 1995
Patent Number:
5426652
A data reception apparatus and technique for use with a modem and including the functions of receiving via the modem a signal including a plurality of datapoints and including therein desired data and inherently redundant data, wherein upon reception of each datapoint, the modem produces quality information regarding how accurately the datapoint was received and identifying and correcting errors introduced into the signal through use of the inherently redundant data and the quality…
Noise reduction system
Granted: April 30, 1991
Patent Number:
5012519
Noise in a speech-plus-noise input signal is suppressed by splitting the input signal into spectral channels and decreasing the gain in the each channel which has a low signal-to-noise ratio (SNR). A voice operated switch (VOX) acts to detect noise-only input to gate a background noise (input signal) estimator and also to gate a residual noise (output signal) estimator. The gain in each of the channels is controlled by the current value (a posteriori) input signal SNR estimate, modified…
A method for indicating the presence of speech in an audio signal
Granted: September 25, 1990
Patent Number:
4959865
A voice operated switch employs digital signal processing techniques to examine audio signal frames having harmonic content to identify voiced phonemes and to determined whether the signal frame contains primarily speech or noise. The method and apparatus employ a multiple-stage, delayed-decision adaptive digital signal processing algorithm implemented through the use of commonly available electronic circuit components. Specifically the method and apparatus comprise a plurality of…
Fast search method for vector quantizer communication and pattern recognition systems
Granted: March 6, 1990
Patent Number:
4907276
An encoder apparatus for communication and pattern recognition systems employing a nearest neighbor search method for signal and data compression, based on a vector encoding quantization technique which optimizes systems performance with substantially reduced computational complexity using a fast geometrically-oriented search procedure. The apparatus comprises pre-procesing apparatus for providing off-line reorganization of a codebook having a set of reference vector patterns…
Method for performing time-scale modification of speech information or speech signals
Granted: September 5, 1989
Patent Number:
4864620
Pre-recorded speech is played back at a different rate, without pitch change. Adjacent signal segments are combined with best match processing. Method and apparatus process time domain speech signals containing speech information, the rate of reproduction of which is to be varied without changing pitch, wherein the input signal is processed by capturing input time domain speech samples in frames wherein the number of samples per frame is a function of a desired speech change factor,…
