Abstract: In an encryption system comprising DES in a cipher feedback mode of k bits, a plain text bit stream is fed into n individual DES encryptors. The DES encryptor operates in parallel from a common input register containing cipher text bit streams so that the overall throughput of the system is increased approximately by a factor of n. If k=1 then the system is self-synchronizing.

Abstract: A phase and gain corrector is described for a modem for receiving QAM or PSK-encoded signals. An ideal vector corresponding to the received vector is generated and the difference or error vector is resolved into a radial component in the direction of the ideal vector a tangential component. A gain corrector and a phase corrector variable are calculated from said radial and tangential components of the error vector and used to correct the gain and phase of the received signals. A secondary detector is also used to detect signals corresponding to extreme points of the signal constellation. The output of the secondary detector is used to modify the gain corrector variable thereby compensating for large gain hits.

Abstract: In the transmitter of a data communication system using QAM, a plurality of trellis coders with delay units are used for forward error correction. The output of each encoder is modulated using QAM to generate sequential baud signal elements. The redundant data bits generated are distributed among several non-consecutive bauds. At the receiver a distributed convolutional decoder individually addressed having sectioned memory elements is utilized to decode the received signal element. The distributed trellis decoder is self-synchronizing.

Abstract: In the transmitter of a data communication system using QAM, a trellis coder with k-baud delay units is used for forward error correction. The output of the encoder is modulated using QAM to generate sequential baud signal elements. The redundant data bits generated are distributed among several non-consecutive bauds. At the receiver a plurality of distributed convolutional decoders are utilized to decode the received signal element. The distributed trellis decoder is self-synchronizing.

Abstract: In the transmitter of a data communication system using QAM, a plurality of trellis coders with delay units are used for forward error correction. The output of each encoder is modulated using QAM to generate sequential baud signal elements. The redundant data bits generated are distributed between several non-consecutive bauds. Likewise, at the receiver a plurality of distributed convolutional decoders are utilized to decode the received signal element. The distributed trellis decoder is self-synchronizing.

Abstract: A modem is operated in a half-duplex mode having various elements which are trained on data and which are locked up while data is not exchanged, thereby eliminating the need for a preamble. A preamble is used only if the period between successive transmissions exceeds a preselected threshold.

Abstract: A method of determining the data rate of signals received on a communication line is disclosed. The method analyzes the training signals which normally precede each data transmission to determine whether they contain a preselected pattern of phase reversals. The presence or absence of the pattern indicates the data rate.

Abstract: This invention provides a method of measuring the characteristics of the channel of a communication system using modems without automatic equalization. The method consists of preceeding a data string sent between modems by a set of TRAINING signals followed by a set of TEST signals. Preferably the TEST signals are chosen to eliminate intersymbol interference on the channel, so that the signals do not have to be equalized.

Abstract: This invention pertains to a disk channel controller for controlling data transfer to and from a disk drive formed of several disks. The controller includes data ports for receiving and transmitting data, head tracking circuits for tracking the heads which store and retrieve data to and from the disks, temporary memories and a microprocessor. Except for the microprocessor, all the controller elements are hardwired. A novel disk formatting is also described.

Abstract: In a system in which data between a master and remote location is encrypted by using the DES algorithm, the status of security devices at the remote location is monitored from a centralized security station. A message indicative of the status of the security devices is used to generate an initializing vector (IV). This IV is then used to encrypt the data from the remote to the master.

Abstract: In a QAM digital modem decoder section, the received signals (after equalization) are transposed to a preselected quadrant of the signal constellation to generate an index pointer. The index pointer and the actual quadrant are used to decode the QAM signals. The index pointer is also used to update the equalizer taps and to operate a phase tracking loop used to reduce or eliminate phase jitter.

Abstract: A modem receiver used in a QAM or PSK data communication system is provided with various circuits generating error or monitoring signals indicative of the status of the system. These signals and the in-phase and quadrature components of the received signals are fed to an interface circuit which generates display signals suitable for driving a display unit such as an oscilloscope. These display signals define an image composed of the signal constellation of the received signals and various error or monitoring points.

Abstract: A modem for exchanging information between a plurality of remote DTE's and a plurality of local master DTE's is disclosed having multiple line interface and DTE interface circuits. Preferably a single microprocessor is used to process all the signals between the respective lines and DTE interface circuits. Furthermore the microprocessor is also used to calculate and update the operational parameters of the line interface circuits such as equalizer coefficients, A/D or D/A attenuator coefficients.

Abstract: This invention provides a receiver for a QAM modem with a phase tracking loop for eliminating phase errors due to phase jitter and frequency offset. The instantaneous phase error of the received signal is monitored and if it is below a certain preselected value, indicating the presence of white noise, the gain of the phase tracking loop is reduced.

Abstract: A phase and gain corrector is described for a modem for receiving QAM or PSK-encoded signals. An ideal vector corresponding to the received vector is generated and the difference or error vector is resolved into a radial component in the direction of the ideal vector a tangential component. A gain corrector and a phase corrector variable are calculated from said radial and tangential components of the error vector and used to correct the gain and phase of the received signals.

Abstract: A method of adding a secondary channel to a QAM signal mapped in the complex plane is provided. A pair of positions in the mapped complex plane is determined such that one-half the sum of the square of the distances to such positions from the origin is no greater than the square of the distance from the origin to the position of the furthest mapped data point. For secondary channel communication, a data point is shifted from a normal position to one or the other of the new positions with one of said positions assuming a binary "1" for the secondary channel and the other of said positions assuming a binary "0".

Abstract: This invention pertains to a method and system for transmitting high speed data from a transmitter to a receiver over several low speed data channels. At the receiver end the differences in the transmission times between data channels are detected and the signals from the faster data channels are delayed to insure that the output high speed data stream is correctly assembled. The differences in the transmission times are monitored during data transmission and if a change is detected the transmission is interrupted and retraining is requested.

Abstract: A method of adding a secondary channel to a QAM signal mapped in the complex plane is provided. A pair of positions in the mapped complex plane is determined such that the positions are equi-distant from the origin and no greater from the origin than the distance from the origin to the position of the furthest mapped data point. For secondary channel communication, a data point is shifted from a normal mapped position to one or the other of the new positions with one of said positions assuming a binary "1" for the secondary channel and the other of said positions assuming a binary "0".

Abstract: This invention relates to a demodulator for an FSK signal having a baud rate which is independent of the signal's bandwidth. The demodulator multiplies the received FSK signal with two quadrature signals having a frequency which lies between the two frequencies of the FSK signal, to obtain the real and imaginary components of a phasor. The phasor rotates in the complex plane, the direction of the rotation depending on whether the frequency of the quadrature signals is above or below the frequency of the received signal. The demodulator determines the direction of rotation of the phasor and generates binary data corresponding to the frequency change in the FSK signal.

Abstract: Digital transmission service offerings provided by common carriers are characterized by digital terminations at two or more user locations. The user has access only to the digital clock and data signals. A modem is described which when attached to the digital terminations provides three functions. First it allows the user to pass his data over the digital service channel. Second it measures the digital communication error rate and availability. Third it permits the user to pass a low speed telemetry channel over the digital service in addition to normal user data. The modem measures the digital channel bit error rate and provides a secondary or side channel without interfering with the transmission of normal data.