Abstract: A system and method for testing signal transmission quality within a digital communication system is disclosed herein. The system may be incorporated within a digital cellular communication system in which information is exchanged over spread spectrum communication channels, among a plurality of mobile users, via at least one cell-site. The system contemplates testing a digital communication channel by transmitting a test sequence of digital data over the communication channel. The test sequence of digital data transmitted over the communication channel is received at a receiving station, within which is also generated a replica of the test sequence of digital data. The accuracy of transmission over the communication channel is then determined by comparing the replica of the test sequence of digital data to the test sequence of data received over the communication channel.

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 and apparatus for implementing a vocoder in a application specific integrated circuit (ASIC) is provided. The apparatus contains a DSP core that performs computations in accordance with a reduced instruction set (RISC) architecture. The circuit further includes a specifically designed slave processor to the DSP core referred to as the minimization processor. The apparatus further comprises a specifically designed block normalization circuitry.

Abstract: A variable rate transmission system where a packet of variable is transmitted on a traffic channel if the capacity of the traffic channel is greater than or equal to the data rate of the packet. When the rate of the packet of variable rate data exceeds the capacity of the traffic channel, the packet is transmitted on a traffic channel and at least one overflow channel. Also described is a receiving system for receiving and reassembling the data transmitted on the traffic channel and at least one additional overflow channels.

Abstract: A novel and improved method and apparatus for encoding line predictive coding (LPC) data in a speech compression system using line spectral square root values is disclosed. A novel and computationally efficient procedure for determining the set of quantization sensitivities for the line spectral square root values is disclosed, which results in a computationally efficient error measure for use in vector quantization of the line spectral square root values. A novel method of weighting the quantization error is disclosed, which accumulates the quantization error in each line spectral square root value and weights that error by the sensitivity of that line spectral square root value.

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: The apparatus and method are employed in a communications system has a transmitter and a receiver, where the receiver determines at which of several rates individual frames in a signal have been transmitted by the transmitter. For example, if the transmitter employs four transmission rates, the receiver decodes each frame of the received signal based on the four rates to produce four cyclic redundancy check (CRC) bits, four symbol error rate (SER) values and one or more Yamamoto check values. If only two of the CRC bits check, then the receiver compares to each other the SER values for those two rates to determine at which of the two rates a current frame was transmitted. If only one of the CRC bits check for a given rate, then the SER value for that rate is compared with a maximum SER threshold for that rate. Additionally, SER values for the other rates can be compared to minimum SER thresholds.

Abstract: A method and system for allocating a set of orthogonal PN code sequences of variable length among user channels operative at different data rates in a spread spectrum communication system is disclosed herein. PN code sequences are constructed that provide orthogonality between users so that mutual interference will be reduced, thereby allowing higher capacity and better link performance. In an exemplary embodiment, signals are communicated between a cell-site and mobile units using direct sequence spread spectrum communication signals. Information signals communicated on the cell-to-mobile link channels are encoded, interleaved, and modulated with orthogonal covering of each information symbol. Orthogonal Walsh function codes of varying length are employed to modulate the information signals. Code assignments are made on the basis of channel data rates in a manner which results in improved utilization of the available frequency spectrum.

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 are described for detecting doubletalk in an acoustic echo canceller. The present invention examines the spectral characteristic of the near-end audio signal and the spectral characteristics of the far-end audio signal and determines from the comparison if a condition of doubletalk exists. An exemplary implementaion of the present invention is presented in an acoustic echo canceller wherein the adaptation of the adaptive filter taps is inhibited during periods of doubletalk.

Abstract: A method and apparatus for implementing a vocoder in a application specific integrated circuit (ASIC) is provided. The apparatus contains a DSP core that performs computations in accordance with a reduced instruction set (RISC) architecture. The circuit further includes a specifically designed slave processor to the DSP core referred to as the minimization processor. The apparatus further comprises a specifically designed block normalization circuitry.

Abstract: A method and apparatus for matching the location of the forward link handoff boundary to the reverse link handoff boundary. A system constant is chosen which defines the product of the received power and the transmitted pilot power at every base station. The reverse link power level is measured at the base station and the forward link power level is compensated for the reverse link loading to maintain the constant product. Thereby the forward link handoff boundary to the reverse link handoff boundary are aligned to the same location.

Abstract: An apparatus and method for controlling a final transmit power, y, of a base station in a cellular communications system that has several channels. The base station has a transmit power tracking gain, y', and a radio frequency transmit power, w. The apparatus comprises channel elements for calculating expected powers, P.sub.k,a -P.sub.k,i, each of which corresponds to a channel. The apparatus also comprises a transceiver system controller (BTSC) for generating a desired output power, y.sub.d, of the base station, including an adder for summing the expected powers. The apparatus also includes a transmit power detector for measuring y to obtain a measured transmit power. The apparatus further comprises a radio frequency interface card (RFIC) for generating y'. Finally, the apparatus includes a gain unit for processing y' and w to obtain the final transmit power, y.

Abstract: An integrated search processor used in a modem for a spread spectrum communications system buffers receive samples and utilizes a time sliced transform processor operating on successive offsets from the buffer. The search processor autonomously steps through a search as configured by a microprocessor specified search parameter set, which can include the group of antennas to search over, the starting offset and width of the search window to search over, and the number of Walsh symbols to accumulate results at each offset. The search processor calculates the correlation energy at each offset, and presents a summary report of the best paths found in the search to use for demodulation element reassignment. The search is done in a linear fashion independent of the probability that a signal being searched for was transmitted at any given time.

Abstract: A Viterbi decoder for recovering the original bit data stream that was convolutionally encoded as a code symbol stream in a Code Division Multiple Access (CDMA) mobile communication system. The decoder simultaneously decodes at the several data rates associated with certain multirate vocoders. The decoder can decode at an unknown data rate in either continuous or framed packet modes. It accomplishes this by simultaneously decoding at multiple rates and by creating one or more data quality metrics for each decoded data packet. Special input and output buffering is provided to isolate the decoder from system timing constraints. The input buffer includes selection and accumulation logic to organize code symbol data into the packet order for repeat mode or random burst mode at lower frame data rates.

Abstract: A corner reflector antenna array capable of being driven by a coaxial feed line is disclosed herein. The antenna array comprises a substantially right-angle corner reflector having first and second reflecting surfaces. A dielectric substrate is positioned adjacent the first reflective surface, and defines first and second opposing substrate surfaces. In the preferred implementation the dielectric substrate is oriented substantially parallel to, but spaced from, the second reflective surface. The antenna array further includes a plurality of dipole elements, each of the dipole elements including a first half dipole disposed on the first substrate surface and a second half dipole disposed on the second substrate surface. A twin line interconnection network, disposed on both the first and second substrate surfaces, carries signal energy to and from the plurality of dipole elements.

Abstract: A method and apparatus of determining signal strength, regardless of the signal data rate, in a receiver receiving signals from a variable rate transmitter. The incoming signal is comprised of a series of frames. Each frame is comprised of a number of power control groups containing data. The number of the power control groups containing data within each frame is dependent on the unknown data rate. The position of the power control groups within the frame is a pseudorandom. The signal strength of an incoming signal of unknown data rate is determined based upon an active set of power control groups within a frame. The active set of power control groups contain data independent of the unknown data rate. This signal strength information may be used to indicate that the signal strength is sufficient to perform further signal processing.

Abstract: A novel and improved method and apparatus for quantizing the line spectral pair (LSP) frequencies in a speech compression system is disclosed. A novel and computationally efficient procedure for determining the set of quantization sensitivities for the LSP frequencies is disclosed, which results in a computationally efficient error measure for use in vector quantization of the LSP frequencies. A novel method of weighting the quantization error is disclosed, which accumulates the quantization error in each LSP frequency and weights that error by the sensitivity of that LSP frequency.

Abstract: A method and system for performing an intersystem handoff of communication with a mobile station between base stations of first and second cellular systems is disclosed herein. At the mobile station, a quantifiable parameter of a signal transmitted by a second base station of the second system is measured. When the measured value of the quantifiable parameter passes through a first predetermined level, the mobile station communicates a signal quality message via a first base station of the first system to a first mobile switching control station. A channel request message is then communicated from the first mobile switching control station to a second mobile switching control station within the second system. At the second base station, a quantifiable parameter of the signal received from the mobile station is also measured. The second base station establishes communication with the mobile station when the measured value of the quantifiable parameter passes through a predetermined level.

Abstract: A method and apparatus for adaptively despreading a direct sequence spread spectrum signal. The direct sequence spread spectrum signal is provided to a transversal filter. The output of the filter is demodulated to provide a soft symbol. The soft symbol is provided to an error corrector which generates an error corrected version of the soft symbol, referred to as a hard symbol. The value of the hard symbol is subtracted from the soft symbol to generate an error symbol. The error symbol is then used to compute tap values of the transversal filter by an LMS algorithm.