Random access protocol for multi-media networks, US5453987, 09/26/1995

A protocol for mixed voice and data access to a synchronous broadcast communications channel is provided. Transmission on the broadcast communications channel is by means of a plurality of time division frames, each such frame being defined by a plurality of time slots. The protocol requires that a user determine whether a time slot is available. If a slot is available, a user transmits a preamble on the broadcast communications channel and then substantially simultaneously monitors the channel for determining whether a collision of the preamble has occurred. If a collision has occurred with a second user who has a higher priority, the first user reattempts to acquire an available time slot after a time delay, the time delay being equivalent to a random number of time slots. If on the other hand, the collision was with a second user of equal priority, both users will reattempt acquisition of available time slots after respective random time delays. The preambles of users of different priority are transmitted using a non-interfering code or modulation frequency, thereby allowing the higher priority user to continue transmission of the remaining fields which make up that user's information packet. Another key feature of the protocol is the use of the preamble to identify voice users that are in silence periods, transmitting no data. Under these circumstances, the protocol permits data users to utilize such identified time slots when they are encountered, thereby increasing the throughput of the data communications system.

Subcarrier communication system, US5442646, 09/15/1995

AA communication system is provided for transmitting data to mobile receivers utilizing a subcarrier within a commercial FM channel of a radio station.  The data transmitted is first encoded in encoder, utilizing a forward error correction code.  The sequence of the encoded data is altered in interleaver, subdivided into a plurality of subframes, in framing and synchronization circuit, which also adds channel state bits to each subframe.  The framed data is modulated onto the subcarrier in the differential quadrature phased shift keying modulator, the output of which is coupled to the FM modulator of radio station transmitter.  The transmitted radio frequency signals may be received by a vehicle antenna for coupling to the vehicle's FM receiver.  The modulated subcarrier is recovered from the FM demodulator of the receiver, the modulated subcarrier being demodulated to recover the encoded digital data therefrom.  The channel state bits included with the data are extracted from the digital data and utilized to form a data reliability factor for each bit of the encoded data.  The data reliability factors thus obtained are associated with each bit of the data in a deinterleaver.  Deinterleaver provides each data bit in proper sequence, with its associated data reliability factor to a decoder.  The decoded digital data is provided to a vehicle traffic computer for processing and presentation of traffic information to a user on a display.

Optical interconnects for high-speed backplanes using spectral slicing, US5446572, 08/29/1995

An n-channel optical interconnect is suitable for use as a high-speed, low-latency interconnect at a backplane of a parallel processing computer.  The interconnect uses spectral slicing to address the output of the processor to one or more other processors.  Each processor has an optical receiver and n optical sources that each produce the same spectrum.  The light output of the sources is directed to a wavelength division multiplexer (WDM) that produces an optical output signal in one or more portions of the spectrum.  A selected portion is produced by energizing a selected one of the n optical sources.  Each portion is associated with a single addressee processor.  A passive star coupler combines all of the outputs of all of the WDM's.  A wavelength division demultiplexer (WDDM) separates this composite signal back into the spectral portions.  Electronic gating logic enables the appropriate source or sources at each transmitting processor.  Control logic monitors transmissions from the star coupler to prevent collisions.