Abstract: A method and apparatus for aligning a test signal to a frame interval of a communication system in which an alignment test signal having an alternating pattern of frequencies is generated and transmitted over a communication link that carries the alignment test signal in a sequence of frames. The alignment test signal is received over the communication link as a return alignment test signal and then evaluated for frequency content. The start time of the alignment test signal is adjusted until the frequency content of the return alignment test signal corresponds to the alternating pattern of frequencies.

Abstract: The present invention teaches an equalizer preprocessor for a mobile telephone speech coder that adapts to the characteristics of its input transducer. The equalizer determines the frequency response of the input transducer by measuring the long term characteristics of the input signal and estimating the spectral envelope of that signal. The equalizer then adapts so that the output signal has a spectral response closer to a perceptually ideal response in accordance with the calculated spectral envelope. In a first embodiment of the present invention, the adaptive equalizer is implemented using digital filtering techniques. The equalizer determines a set of long term autocorrelation coefficient values and from these values generates a set of filter taps which serve to whiten or flatten the spectral response of the input signal. This whitened signal is then passed through a target filter which impresses upon the whitened signal the target spectral response.

Abstract: A method and apparatus for the selection of an encoding mode for speech frames in a variable rate encoding system. For each speech frame, the method and apparatus selects the encoding mode which provides for rate efficient coding. A mode measurement element receives a speech signal and a signal derived from the same speech signal, and generates a set of parameters which are ideally suited for operational mode selection. Rate determination logic receives the set of parameters and selects an encoding rate using predetermined selection rules. The selection rules further distinguish between unvoiced speech and temporally masked speech, which are encoded at the same rate but with different encoding strategies.

Abstract: When one vocoding system is coupled to another vocoding system, a tandem arrangement results. The tandem configuration results in voice quality degradation as speech is encoded and decoded, then encoded and decoded again. One reason for the degradation is that postfiltering performed at the output of the speech decoding process introduces distortions in the spectral content of the reconstructed speech as compared to the original speech. The present invention prevents the degradation due to the use of postfilters by modifying the postfiltering within the vocoders where a tandem configuration exists. A detection code is embedded within the data signal to indicate the existence of a tandem configuration. If the detection code is received at a vocoder, modified vocoding is established within the vocoders to prevent the degradation due to the postfiltering.

Abstract: A method and apparatus are described for controlling the data rates for communications to and from a base station and a plurality of remote users. The usage of the communications resource whether the forward link resource (from base station to remote users) or reverse link resource (from remote users to base station) is measured. The measured usage value is compared against at least one predetermined threshold value and the data rates of communications or a subset of communications on said communications resource is modified in accordance with said comparisons.

Abstract: An improved method and apparatus for canceling echo is disclosed. The echo canceller of the present invention compensates for the existence of quantization error in the echo signal that does not exist in the reference signal by introducing the quantization effects into the reference signal. The quantization effects are typically companding quantization errors caused by the A-law and .mu.-law quantizers prevalent in digital communications equipment.

Abstract: A method and apparatus for characterizing a communications link. An apparatus is disclosed for performing a series of tests that measure delay time, frequency response, background noise, frame error rate and sample slipping and repetition measurements. A signal generator generates a series of signal optimally selected for the particular test. The generated signal is transmitted through the communication system and then sent back through the system by a loop back element remotely placed. The return signal is then analyzed by a monitor means.

Abstract: A method for selecting a code vector in an algebraic codebook wherein the analysis window for the coder is extended beyond the length of the target speech frame. By extending the analysis window, the two dimensional impulse response matrix can be stored as a one dimensional autocorrelation matrix greatly saving on the computational complexity and memory required for the search.

Abstract: It is a first objective of the present invention to provide a method by which to reduce the probability of coding low energy unvoiced speech as background noise. The present invention determines an encoding rate by examining subbands of the input signal, by this method unvoiced speech can be distinguished from background noise. A second objective of the present invention is to provide a means by which to set the threshold levels that takes into account signal energy as well as background noise energy. In the present invention, the background noise is not used to determine threshold values, rather the signal to noise ratio of an input signal is use to determine the threshold values. A third objective of the present invention is to provide a method for coding music passing through a variable rate vocoder. The present invention examines the periodicity of the input signal to distinguish music from background noise.

Abstract: A method and apparatus for controlling transmission power in a variable rate communication system is disclosed. The method disclosed provides for a closed loop power control method. A first remote station controls the transmission power of a second remote station by transmitting a rate dependent power control signal to the second remote communication station. Since only the second communication knows its transmission rate a priori, it must determine its course of action in accordance with both the received power control signal and the knowledge of its transmission rate. In the present invention, the power control system reduces the amount of overhead required by restricting the possible rate transition of the variable rate communication system.

Abstract: In a variable rate vocoder a method for determining a higher encoding rate of a set of encoding rates for unvoiced speech. The method is accomplished by generating an encoding rate indication based upon a first characteristic of an audio signal, determining a second characteristic of the audio signal, and modifying the encoding rate indication when the second characteristic of the audio signal is representative of unvoiced speech to provide a modified encoding rate indication corresponding to a higher encoding rate of the set of encoding rates.