Abstract: A data transmitting QAM modem with partitions incoming data into unequal frames. Some of the bits in each frame are encoded using fractional rate encoding and then recombined the rest of the bits to form frames of equal bits. Trellis encoding is then performed on the frames of equal bits. Advantageously the number of points in the QAM constellation is also increased to an integer divisible by a power of 2 to reduce the complexity of fractional rate encoding.

Abstract: A method and system for communicating data over a communications channel such as a telephone line includes the conversion of asynchronous data transmitted from a diagnostic microcomputer through a modem into synchronous data for transmission over the communications channel. The method includes the use of error vectors to shift the asynchronous data into a continuous synchronous stream of data bits.

Abstract: An apparatus and method calculates pre-emphasis coefficients for a transmitting modem based upon the noise spectrum as it is received at the receiving modem. A noise spectrum analysis circuit calculates a difference between the best-fit transmitted data and the actually received data. This difference is used to compute a discrete Fourier transform of the noise spectrum, which is transmitted back to the transmitting modem on the secondary channel. This data is used to calculate filter coefficients for the transmitting modem.

Abstract: An apparatus monitors the convergence of the equalization training sequence in a multipoint communication network. Various latches record the period of the incoming sequence and the time to convergence, if any. A counter records the number of periods free of convergence, and upon the counter exceeding a threshold, the network train time is doubled. A register records the longest required time to convergence. This value is periodically compared to the network train time, and, if less, substituted therefor.

Abstract: Apparatus and method for time division multiple access in a multidrop system with multiple host applications employing half-duplex polled protocols is disclosed. Ranging with respect to time is used so as to reduce guard time between successive transmissions thereby increasing system efficiency. Host applications can request extra time slots for long messages via a request bit within the message format.

Abstract: A method and system for a synchronized pseudorandom privacy modem makes use of a pseudorandom signal generator to index into a table of N signal spaces thereby altering gain and phase modifiers so or to modify both the gain and phase of portions of the data signal being transmitted from a QAM modem and thus transmit an encrypted signal pattern to the other end of the communications channel. The modem transmitter circuit includes a data scrambler, and QAM signal point mapper, connected in series, as well as a pair of mixers having inputs from the pseudorandom signal generator and functioning to modify the gain and phase of portions of the QAM signal point mapper output signal before they are pulse amplitude modulated, filtered, converted to analog form, and transmitted over the communications channel. Complementary circuit elements in the receiver, which have been synchronized with those of the transmitter by baud rate counters at both locations, demodulate and decode the received encrypted signal.