Abstract: An encoding/decoding method for a signal having at least two different positive and negative levels. Each symbol representing, for instance, two binary bits is encoded in each symbol period. During each symbol period, the encoded signal transitions between a level of one polarity to a level in the opposite polarity. The levels and transitions are selected so that there is no DC component. The frequency spectrum is shifted away from the lower frequencies with this encoding.

Abstract: Binary data is transmitted to a network physical layer from a media access controller as a series of multibit nibbles and is encoded into a multi-level data stream and split among a number of transmission channels, thereby reducing the signal frequency necessary to carry the data on each one of the transmission channels. The multi-level signal is then translated at a receiver back into a binary data stream. In a specific embodiment, the symbol transmission frequency on each of the transmission channels is at the same frequency as the nibble transfer rate between the media access controller and the physical layer.

Abstract: A single flexible mount and a simple adjustment system are used to provide the means to focus the collective outputs of multiple light-emitting elements.

Abstract: An apparatus and method for transmitting an 8-bit binary format data word as a 6-trit ternary code word includes an encoder, a decoder, and a code assignment that produce, for each 8-bit data word value, an unique 6-trit ternary code word that is particularly optimized for transmission over twisted-pair cable. The logic circuitry of the invention is optimized to accomplish the translation using a small number of combinatorial logic gates. The present invention thus has advantages in size, speed and performance over other possible means for encoding an 8 bit data word to a 6 trit code word.

Abstract: A power line communication (PLC) apparatus wherein a carrier is derived to avoid determinable interference harmonics. In order to transmit data on a power line containing the television interference or other determinable interference harmonics, the present invention uses redundant carriers at a frequency between the television interference harmonics. In the preferred embodiment, the first carrier is positioned at 118 KHz and the redundant carrier is positioned at 133.7 KHz for the PLC apparatus designed for use in the United States. Other carrier frequencies are used for other countries in order to avoid interference harmonics at a slightly different frequency. The present invention includes a waveshaping and modulation circuit for generating the modulated data waveform for output over the power line. In the preferred embodiment, the waveshaping and modulation circuit includes a waveshape ROM for storing samples that represent the appearance of the carrier waveshape.

Abstract: In a power line communication apparatus, data is redundantly transmitted on a first and a second carrier where the carriers are separated by a predetermined number of Hz. In the receiver two channels are used, one for each of the carriers. The noise level in each channel is independently determined. A switching network is used to allow the selection of the channel with the lesser noise or if the noise is approximately equal in both channels, the signals in the channels are combined.

Abstract: A power line communication (PLC) apparatus wherein transmission mode information is encoded into each data packet while maintaining immunity from single bit errors. In the present invention, a power line communication system includes a transmitter/receiver (i.e. transceiver) which is coupled to a power distribution network. Data is transmitted through the power line by the transceiver in packets. The transceiver includes a preamble generator which creates a preamble for each of the data packets and a preamble decoder that decodes the preamble of a data packet and determines word sync for the packet. The preamble generated by the preamble generator consists of a carrier detect interval, a carrier sync interval, a bit sync interval, and a word sync pattern. The transceiver may select either BPSK or QPSK transmission modes on a data packet by data packet basis by encoding information into the packet preamble.

Abstract: An improvement in an apparatus which uses a carrier detection threshold level for detecting a carrier signal modulated with binary data. The threshold level is dynamically changed and generally seeks a level above the background noise. The threshold level is maintained constant when the detected signal exceeds the threshold level. An evaluation circuit is able to examine the detected signal to determine whether it contains data or only noise, and if it contains only noise, a possible trapped condition is avoided by raising the threshold level to a level higher than the background noise.

Abstract: A method and apparatus for power line communications which utilizes common mode transmission and reception of communication signals over power lines. The communication signals are sent and received between the power and neutral lines, and the ground line. A common mode choke in the power lines presents a relatively high impedance to the communication signals and prevents them from being shorted to the ground line. The choke is substantially transparent to the power delivery current.

Abstract: In a power line communications apparatus an improvement for blanking or snubbing impulse noise. The impulse noise is detected and used to snub the detected signal. The duration of the snubbing pulses is controlled to assure complete blanking of noise including the trailing noise signals following a main noise pulse which may not otherwise be detectable. Also, the number of snubbing pulses which can occur are limited to prevent too much energy from being snubbed during any given baud period.

Abstract: An error detection and correction method and apparatus is described which permits the correction of double errors using a (15,11) Hamming code and a parity bit. The Hamming code and parity bit allows the detection of double errors. A modulated waveform carrying the binary data is examined for anomalies such as noise pulses. A hint signal is generated based on the anomalies which points to a suspect bit. The state of this bit is changed to correct for double errors.

Abstract: A phase detector particularly suited for high speed, digital data. The data is auto-correlated with the data shifted through a flip-flop where the flip-flop is clocked by the clocking signal. The data is also delayed by one period by an analog delay line. The output of the flip-flop is auto-correlated with the data and with the data shifted by one period to provide an error signal for a VCO. Ordinary ECL circuits in leaded packages may be employed with data rates in the 300 MHz range.

Abstract: An improved architecture for a computerized branch exchange particularly for a time division multiplexed bus used in the exchange. An intershelf bus includes a unidirectional source bus which receives signals from expanders and a unidirectional destination bus which transmits signals to the expanders. The expanders, through another bus, communicate with line cards which interface with telephone station sets, commercial lines, etc. A time division multiplexed controller updates distributed connection tables contained in each of the expanders and controls the flow of data onto and from the unidirectional buses. The distributed connection tables eliminate the need to broadcast addresses during each time slot. The arrangement is particularly useful in reducing blocking associated with prior art bidirectional buses.