Abstract: A strict commercial time synchronization system, method and apparatus therefore is provided. Transmission information data and N bits data in a PN signal generated from a PN generator are transmitted to a down stream station by multiplexing circuit. Then, the transmission information data and N bits data are demultiplexed by a demultiplexing circuit into the transmission information data and the PN signal. An error between this PN signal and generated by a PN generator is detected by a timing detection circuit. The operation timing of the PN generator is corrected corresponding to this error. The corrected PN signal and the transmission information data are transmitted by a multiplexing circuit to an upstream station. The timing of the PN-signal is shifted ahead by half the time corresponding to the error detected.

Abstract: Upon voice processing in an ATM network, processing delay in a real-time voice telecommunication processing is avoided. Voice data to be processed by a CPS processing unit and by an IuUP processing unit is subjected to protocol conversion based on an IuUP protocol and a CPS protocol. The IuUP protocol is defined as an upper protocol of the CPS protocol according to the standard (3GPP 3G TS 25.415). Upon receiving and processing the voice data, the CPS processing unit does not execute CRC check; meanwhile, the IuUP processing unit executes the CRC check instead. Since a CPS header only uses UUI=26, the CPS header and an IuUP header are always added in combination. Although the CRC check for the CPS header is not executed, it is possible to confirm normality of an ATM cell just by checking IuUP header CRC. Accordingly, it is possible to avoid delay in signal processing by omitting check for the CPS header CRC.

Abstract: In a CDMA transmitter operable in response to a plurality of input data signals to produce a transmission signal, a dummy symbol is generated by a dummy symbol generator to reduce a peak value of a synthesized signal obtained by subjecting the input data signals to spread spectrum modulation. The dummy symbol is attained by spreading the peak value by spread codes which are not used for the spread spectrum modulation and is subtracted from the synthesized signal to suppress the peak value. A level adjustment value is multiplied by a peak suppressed signal so as to compensate a variation of average power which might occur due to the dummy symbol.

Abstract: A random access channel receiver used in a base station of a CDMA mobile communication system is provided. The receiver is only provided with a single signal decoding part for performing burst reception of control request signals having different off-set timing each other. A synchronizing circuit calculates correlation value at each off-set timing, and a synchronism determining and establishing circuit determines the off-set timing to be used for a synchronizing signal for receiving the signal frame currently arriving by monitoring correlation values of respective off-set timings, and alters the off-set timing for the synchronizing signal to better quality of signal if a plurality of signal frames of different off-set timing are arrived. The signal frame of less quality is discarded, or abandoned its decoding processing.

Abstract: A voice encoder which pauses outputting codewords in accordance with the absence of voice activity. An input aural signal is divided into frames and inputted to the voice encoder. The voice encoder has a voice activity detection circuit for determining at each frame whether voice activity is absent or present, a voice encoding circuit, a background noise update judging circuit for detecting a change in the characteristics of the input aural signal, and a control circuit. If the absence of voice activity is detected, the control circuit causes the frame at that time to be encoded as a background noise frame, and then pauses the operation of the voice encoding circuit. If the presence of voice activity is detected, the operation of the voice encoding circuit is resumed.

Abstract: In a LPC speech signal decoder, background noise is simulated during periods of silence at the transmitting end based upon a background noise frame containing information about the background noise at the sending end. When the silence persists, the transmitter periodically updates the background noise frame previously send by transmitting an updating background noise frame. When an update background noise frame is received, an interpolation is performed so as to make the simulated background noise sound natural to the listener. The interpolation process includes a step of selecting between interpolation spectrum parameters which are produced by the interpolation process and the updated spectrum parameters which are based solely upon the most recent updated background noise frame.

Abstract: An artificial echo signal generator generates an artificial echo signal from received voice signal data stored in a first data memory and a presumed impulse response outputted from a tap coefficient updater. The artificial echo signal is subtracted from an echo signal from a four-wire/two-wire converter by a subtractor, which then outputs a remainder signal that is stored in a second data memory. An updating time controller determines and outputs an updating time based on the data stored in the second data memory. An updating element selector selects one time element of the updating time from the updating time controller. The tap coefficient updater updates the presumed impulse response so as to approach the impulse response of a true echo path at the selected time element, and outputs the updated presumed impulse response to the artificial echo signal generator.

Abstract: An echo canceller includes echo signal canceling sections, first level detection sections, second level detection sections, third level detection sections, and priority decision section. The echo signal canceling sections are independently provided to echo paths of speech communication paths to learn and update the estimated values of impulse responses on the echo paths and cancel echoes generated in the corresponding speech communication paths on the basis of the updated estimated values of the impulse responses. The first level detection sections detect the levels of transmission speech signals. The second level detection sections detect the levels of residual signals obtained by removing echo components from the transmission speech signals. The third level detection sections detect the levels of reception speech signals.

Abstract: High frequency components of input digital speech samples are emphasized by a preemphasis filter (11). From the preemphasized samples a spectral parameter (a.sub.i) is derived at frame intervals. The input digital samples are weighted by a weighting filter (13) according to a characteristic that is inverse to the characteristic of the preemphasis filter (11) and is a function of the spectral parameter (a.sub.i). A codebook (18, 19) is searched for an optimum fricative value in response to a pitch parameter that is derived by an adaptive codebook (16) from a previous fricative value (v(n)) and a difference between the weighted speech samples and synthesized speech samples which are, in turn, derived from past pitch parameters and optimum fricative values, whereby the difference is reduced to a minimum. Index signals representing the spectral parameter, pitch parameter and optimum fricative value are multiplexed into a single data stream.