Abstract: A system and device for, and method of, detecting, characterizing, and mitigating deterministic distortion in a communication system. An exemplary communication system includes a digital adaptor for sending octets on to a backbone of a PSTN, which then sends, and potentially distorts the octets, received by a line interface. The line interface converts the octets to baseband signals received by an analog adaptor. Several mechanisms and methods are described in which the analog and digital adaptor cooperate to detect the presence of distortion, in particular, robbed bit signaling, on the communication system. The characterization may then be used to mitigate the effects of the distortion. Several receive constellations are provided, each constructed in view of the transmit constellation and in view of the manner in which the deterministic distortion will distort signals transmitted over the system. The receive constellations differ from the transmit constellation.

Abstract: An efficient and power-saving method of converting serial in-phase (I) and quadrature-phase (Q) symbols at the IS-54 standard symbol rate, to time-aligned IQ pairs at the CDPD standard symbol rate. A FIFO buffer stores the serial in-phase (I) and quadrature-phase (Q) symbols at the IS-54 standard symbol rate. A DSP performs CDPD demodulation by reading time-aligned IQ pairs directly from the FIFO buffer, even though the FIFO buffer contains serial in-phase (I) and quadrature-phase (Q) symbols at the IS-54 standard symbol rate. This is accomplished by performing a rate conversion method between the DSP pointer and the FIFO buffer. The rate conversion combines, symbol rate conversion, sample timing alignment, and sign corrections in one calculation, resulting in an efficient method of generating the desired time-aligned IQ pairs at the CDPD symbol rate. A look-up table is used for several of the variables in the rate conversion calculation.

Abstract: A transceiver including a receiver having a sequential amplifier that includes at least first and second RF amplifier stages coupled together by a delay line. A transmitter in the transceiver includes an oscillator for generating an RF carrier and the oscillator includes the delay line as a phase shifting element. A modulator is coupled to the oscillator for modulating the RF carrier either AM, OOK modulated, FM, FSK modulated, PM, and PSK modulated.

Abstract: The voice over data component of a personal communications system enables the operator to simultaneously transmit voice and data communication to a remote site. This voice over data function directly encodes digitized voice samples onto the carrier using quadrature amplitude modulation to transmit multiple bits of the voice sample for every baud. The system also allocates selected bauds of the carrier to voice and to data so the voice over data may be transmitted using the same allocated bandwidth. The system may also dynamically reallocate the bandwidth over the telephone line depending on the demands of the voice grade digitized signal.

Abstract: A system for the transmission of data, and a modem for use in such a system, utilize variable shift keying (VSK), in which a data signal is modulated to form a continuous phase signal in which successive symbols are represented by successive signal segments of constant phase angle, typically 180.degree. or one half cycle, different symbols being distinguished by the segments being of different duration, i.e. at different frequencies. The ratios of the frequencies may be chosen to facilitate signal modulation and demodulation, and to control the frequency spectrum of the transmitted signal. Each symbol may represent one or more bits of the data signal. The lengths of half cycles used to represent different symbols may be adjusted by introducing flat peaks into the half cycles whilst maintaining uniform the profile of their flanks so as to facilitate generation and reduce zero crossing detection jitter during reception.

Abstract: A modem unit includes a data communication modem having data communication functions, a facsimile communication modem having facsimile communication functions, and a controller which is coupled to the data communication modem and the facsimile communication modem. The controller controls the data communication modem and the facsimile communication modem so that non-image facsimile data is communicated via the data communication modem and image facsimile data is transferred via the facsimile communication modem. Communication time is thus shortened through the provision of both the data communication modem and the facsimile communication modem in communicating facsimile data.

Abstract: A technique for reliable passage of handshaking information between a cellular modem and a land modem. Instead of bare transmission over a voice channel connection highly susceptible to signal fading and dropout, the initial modem handshaking exchange is instead FSK-encoded and broadcast using a network data signalling methodology already used to reliably pass signalling information between the base and registered mobiles. Automatic retransmission request signalling and transmission redundancy may be implemented to insure successful receipt at the receiving end of the radio link. Once received and verified, handshaking information is decoded and delivered to the destination modem in the appropriate format along cleaner fixed pathways. Reliable handshaking operations are contemplated whether the destination modem is a cellular modem registered in auto-answer mode (land-originated data call), or a land modem (mobile-originated data call).

Abstract: An improved Phase-Locked Loop (PLL) radio receiver circuit includes a phase detector, either an active loop filter or a set of parallel, alternately selectable loop filters, and a Voltage-Controlled Oscillator (VCO) whose input is connected to the output of the loop filter. The output of the VCO is fed to frequency divider. The output of the frequency divider and a reference frequency signal form the inputs to the phase detector/comparator. Toggling among the loop filters occurs such that the loop limit frequency, defined by a loop amplification of 1, is altered by this toggling without significantly changing the gradient of the amplification to the frequency, in a frequency range which includes the limit frequency.

Abstract: A facsimile apparatus determines whether a frame to be transmitted is an image block or an error retransmission frame, and transmits a short training sequence or a long training sequence based on the results of the determination. The long training sequence is sent if a TCF signal is transmitted and the short training sequence is sent if the image block is transmitted. If the facsimile apparatus is on the receiving side, a training sequence in accordance with the frame from the transmitting side is received. After a carrier signal is detected, the apparatus then makes a transition to a mode for receiving the TCF signal or image block.

Abstract: A data transfer arrangement by which variable-rate data transfer can be effected between a modem and a synchronous data terminal has a plurality of terminal-connected accesses. Namely, the first access for receiving data from the terminal, a second access for supplying clock signals to the terminal which fix the rate of the received data, a third access for supplying data to the terminal, and a fourth access for supplying clock signals to the terminal which fix the rate of the supplied data. Further accesses are connected via the modem to the transmission line for transmission and reception of data thereon at a uniform rate. A variable rate clock generator supplies clock signals to the second access, the clock rate being adjusted in accordance with the rate at which data is to be received from the data terminal.

Abstract: An apparatus automatically determines the frequency deviation of a transmitter by analyzing a signal received from the transmitter. The apparatus automatically corrects the incoming signal for the improper deviation and maintains a record of the frequency deviation errors. Transmitters which consistently exhibit errors may then be recalled for servicing. This device increases data transmission reliability, improves compliance with FCC licensing regulations and reduces maintenance costs.