Abstract: A dual-reflector antenna system (40) is provided for generating a shaped main beam radiation pattern (20) and at least one additional secondary spot beam radiation pattern (30,32). The antenna system (40) includes a main shaped reflector (10) having a shaped reflective surface (11) operatively coupled to a subreflector (12) for communicating therewith. A main feed horn (14) communicates directly with the subreflector (12) so as to reflect first energy to and from the main reflector (10) within a shaped beam radiation pattern (20). In a preferred embodiment, the subreflector (12) has an ellipsoidal reflective surface (13) which communicates directly with the main reflector (10) via an inverted reflective path (17) which has a converging focal point (18). One or more auxiliary feed horns (24,26) are operatively coupled directly to the main reflector so as to directly communicate therewith and reflect second energy within one or more additional radiation patterns (30,32).

Abstract: A cellular system has base stations in which diversity transmission is controllably employed to improve voice communications as needed. Normal signal transmission is employed in each voice channel unless it is detected that quality has dropped to a point where diversity transmission is needed to enhance the quality. When it is detected that a voice channel needs diversity transmission, a diversity (delayed) signal is automatically transmitted for that channel over an independent path. A common diversity transmitter is employed for all channels, whereas individual transmitters are employed for the normally transmitted signals in the respective voice channels.

Abstract: The present invention provides for sample timing adjustment using channel impulse response which is particularly well adapted for use in a receiver for digital cellular mobile telephones. The sample timing adjustment includes storing samples in time slots, generating estimates of the transmission channel impulse response, and using a subset of the samples received during the time slot, and generating error measurements of the degree to which the estimated channel impulse responses match the actual channel impulse responses. The different measures use simultaneously recorded samples having different time offsets. At least one sample used for each measure is advanced in time and one sample used for each measure is retarded in time relative to the samples used for generating the first measure. Then, a sample time setting that minimizes the error measurement is determined and the sampling is adjusted to reflect the newly determined sample time setting.

Abstract: A digital discontinuous cellular communication system has a transmitter that transmits two frames of data following detection of voice inactivity. A receiver includes a comfort noise generator that uses the two frames of data to output noise to the speaker during period of voice inactivity. The comfort noise generator includes synthesis codebook with samples scaled by actual background noise and excitation codebook with samples filtered and scaled by the background noise that are combined to produce comfort noise having attributes and loudness level of the received background noise prior to interruption of transmission. The scaled signals are weighted to vary the loudness level and spectral attributes.

Abstract: A method and device for canceling frequency offsets in received modulated signals. The frequency offset cancellation device includes a downconverter module, a channel unit and a control module. The downconverter module shifts received signals to a lower frequency. The channel unit searches the shifted received signals and demodulates them, and the control module adjusts the downconverter in accordance with frequency offset information generated by the channel unit, thereby continuously cancelling out any frequency offsets that may have occurred during frequency shifting.

Abstract: A DTMF digit detecting method and apparatus includes signal state identifier (32) for identifying whether the received signal is in a DTMF-digit-detect state, a no-detect high-energy state, or a no-detect low-energy state, digit candidate identification processor (34) for identifying a digit candidate when the presence of a state other than the no-detect low-energy state is detected following a detection of the presence of the no-detect low-energy state for a first predetermined period of time, digit identifier (32) for identifying a DTMF digit corresponding to a sample group in a DTMF-digit-detect state, and valid digit identifier (34) for identifying a valid DTMF digit when at least a first predetermined number of sample groups are all in the DTMF-digit-detect state or in an allowable combination of states.

Abstract: An adaptive pitch pulse enhancer and method, adaptive to a voicing measure of input speech, for modifying the adaptive codebook of a CELP search loop to enhance the pitch pulse structure of the adaptive codebook. The adaptive pitch pulse enhancer determines a voicing measure of an input signal, the voicing measure being voiced when the input signal includes voiced speech and the voicing measure being unvoiced when the input signal does not include voiced speech, modifies a total excitation vector produced by the CELP search loop in accordance with the voicing measure of the input signal, and updates the adaptive codebook of the CELP search loop by storing the modified total excitation vector in the adaptive codebook.

Abstract: The present invention switch transcoder (18) provides transcoding of speech for a cellular system in which speech from a plurality of E1 lines (7) may be compressed for outputting to a much smaller number of T1 lines (8) so that multiple conversations greater in number than previously possible can be carried on at the same time. The transcoding and switching of speech between the E1 and T1 lines are effected on a single module (30) which has thereon the control processor (42), voice processors (44) and appropriate interfaces (36, 40).

Abstract: A symbol timing recovery method and device which aligns the received data with a free-running symbol clock such that the aligned data sampling error is minimized. The symbol timing recovery process consists of detecting the timing phase error between the transmitters symbol clock and the receiver symbol clock, filtering the error, and then using the filtered error signal to control a block which changes the phase of the data relative to the timing reference signal. A data zero-crossing phase error detector drives a loop filter whose most significant bits form the address of the FIR coefficient ROM, which allows the FIR to interpolate data at sub-symbol resolution. The FIR coefficients are then used to synchronize the received data with the receiver clock.

Abstract: A system is described which integrates terminal traffic in a digital voice cellular radio communication system. Data is conveyed from remote data stations and remote radio telephone stations over a reverse channel TDMA frame. The allocation of time slots in the reverse channel TDMA frame is controlled at the base station. The base station provides priority to radio telephones having digitized voice traffic. The base station assigns time slots within the reverse channel TDMA frame based upon allocation requests received from radio telephone stations and remote data stations. Remote data stations may contend on a random access for a minority of a set of time slots in the reverse channel data frame. Additionally, they may request an assigned slot by inserting an allocation request in a control slot of the reverse channel data frame. The base station allocates time slots on a voice radio telephone priority, and assigns any excess time slots to data stations waiting for access to the reverse channel.

Abstract: A multimedia codec for a frame relay network. Multiple information media from different sight equipment is converted to a standard packet for transmission over said frame relay network. Incoming frames are processed on a priority basis and stored in an elastic buffer. Tests of pointers are kept for each media type identifying the location in the elastic buffer of the various packets for the different media. Applications running in the frame relay processor retrieve the stored media data and forward it to a digital signal processor connected to respective terminal equipment.

Abstract: A decision feedback multiple symbol differential demodulator for Gaussian filtered Minimum Shift Keying (GMSK) has a performance very close to theoretical limit even under a fading channel. The demodulator implements a non-coherent, maximum likelihood (ML) search over multiple bit-time intervals. The past bit decisions are fed back to the ML decision logic. The improved performance of the demodulator is achieved by using old decisions in the ML decision logic.

Abstract: A device and method of adjusting an equalizer in a digital communications receiver in response to relative velocity between the communications receiver and a communications transmitter. A radio frequency receiver receives a radio frequency signal from the communications transmitter through a communications channel, and an analog to digital converter digitizes a first portion of the radio frequency signal during a first time period, and generates a first data signal made up of digital samples. The analog to digital converter also digitizes a second portion of the radio frequency signal during a second time period and generates a second data signal, also made up of samples. A channel estimator estimates characteristics of the communications channel in response to a portion of the first data signal, and generates a first channel estimate in response thereto.

Abstract: A mobile telephone system multiplexes plural voice traffic channels on a single carrier using a TDMA protocol. The capacity of the mobile telephone system is increased by assigning voice traffic capacity, not on a conversation basis, but on an information burst basis. In order to avoid compromising the voice transmission capacity, control signals (for the allocation and deallocation of both forward and reverse traffic channels) are sent using multiple diversity, i.e. both time and frequency. In addition, to increase the number of available control channels, a control channel comprises a sub-divided portion of an otherwise equivalent voice traffic slot. For reverse allocation requests, which are transmitted over a contention access channel, power diversity is used in addition to time and frequency diversity.

Abstract: A system for controlling forward error correction of a VSAT earth station is disclosed. A hub earth station communicating with the VSAT earth station transmits digital data representing a propagation condition measured at the hub earth station. The VSAT earth station computes an estimated inroute fade from the transmitted information, as well as from the VSAT demodulator's estimate of propagation condition. When the total inroute fade is below a selected margin, a higher FEC encoding rate is selected for the VSAT transmitter in which to transmit its data packets to the hub earth station. As the estimated inroute fade exceeds a high FEC rain margin, a lower rate of FEC encoding is employed at the VSAT earth station. By permitting a higher FEC encoding rate, digital throughput is increased between the VSAT earth station and the hub station.

Abstract: Each cell has an assigned classification that determines its inclusion in a measurement list for handing off. The candidate cells, which are selected from the measurement list are given priority level assignments. The priority levels are implemented by the candidate neighboring cells measured RF signal strength; and the order of handing off is arranged in accordance with the adjusted RF signal strength.

Abstract: A cellular automated test set for testing cellular telephones consists of a RF interface coupled to an RF input/output of the cellular telephone and a transmitter-receiver coupled at an RF input/output of the transmitter-receiver to the RF interface. The transmitter-receiver transmits a first message signal to and receives a second message signal from the cellular telephone via the RF interface. The second message signal is generated by the cellular telephone in response to the first message signal. A data interface is coupled to a data port of the transmitter-receiver; and a processor is coupled to the data interface. The processor transmits a first data signal to and receives a second data signal from the transmitter-receiver via the data interface. The first message signal is generated in response to the first data signal and the second data signal is generated in response to the second message signal.

Abstract: A method and apparatus for use in estimating phase error in a phase-modulated carrier. The method and apparatus of the present invention may be embodied in a phase-error-estimator circuit which is typically incorporated into a demodulator of a digital communications receiver. In general, the phase-error-estimator circuit receives the I and Q components of a phase-modulated signal, and outputs an estimate of the phase error, if any, in the phase-modulated carrier signal associated with the received I and Q. Preferably, the phase-error-estimator circuit includes an index/polarity generator circuit coupled to a look-up table. The index/polarity generator receives I and Q and maps them onto a reduced range of phase angles represented by values X and Y. X and Y are fed to a reduced and substantially triangular look-up table which outputs the stored phase-error-estimate for the particular X and Y inputs.

Abstract: Code excited linear prediction (CELP) is performed using two voiced and unvoiced sets of windows, each set is used both for linear prediction and pitch determination. The accompanying degradation in voice quality is comparable to the IS54 standard 8.0 Kbps voice coder employed in U.S. digital cellular systems. This is accomplished by using the same parametric model used in traditional CELP coders but determining, quantizing, encoding, and updating these parameters differently. The low bit rate speech decoder is like most CELP decoders except that it operates in two modes depending on the received mode bit. Both pitch prefiltering and global postfiltering are employed for enhancement of the synthesized speech. In addition, built-in error detection and error recovery schemes are used that help mitigate the effects of any uncorrectable transmission errors.

Abstract: There is provided an elastomeric switching device for use with electrical circuits, such as those on a printed circuit board. The elastomeric switching device comprises an elastomeric pad constructed from a plurality of parallel strips of conductive material between layers of non-conductive or insulating material together with a moveable conductive contact which is aligned with the elastomeric pad. The elastomeric pad is predisposed in contact with the circuits on the printed circuit board. The moveable conductive contact establishes electrical connections between the affected circuits via the conductive strips of the elastomeric pad. The proper alignment and orientation of the elastomeric pad and moveable conductive contact relative to the circuits is maintained by the structural and mechanical features of a housing.