Tech Briefs

Multiplexed data from multiple sources can be reconstructed in original temporal relationships.

A method of time coding of asynchronously transmitted data from multiple sources has been invented. The method is especially applicable to a data-acquisition and transfer system that operates in a standard asynchronous transfer mode (ATM), in which, at a transmitter, streams of data acquired simultaneously from multiple sources are time-multiplexed, packaged into cells that are sent sequentially over a single wide-band transmission line or other channel to a receiver. The packaging destroys the original temporal relationship among the data streams, but the method enables reconstruction of the data streams in their original temporal relationships at the receiver.

This Generic Data-Acquisition-and-Transfer System is an example of systems in which the present invention could be applied. The invention applies primarily to processing in the data formatter.

A typical generic system in which the method could be utilized acquires data streams consisting of the digitized outputs of X+1 sensors (see figure). The sampling period of the analog-to-digital converter (ADC) that processes the output of each sensor is controlled by a system clock that is synchronized with an external real-time clock known to have requisite high precision. Also connected to the system clock is a sample counter, which is so named because it counts system- clock cycles and thereby indirectly counts samples. The output of the sample counter also serves as a record of the time of acquisition of each sample. The output of each ADC is fed to a buffer, along with a partial count (consisting of the least significant bits) from the sample counter. In each buffer, the partial sample count is combined sequentially with the sample data. The outputs of all the buffers are fed to a multiplexer, wherein they are combined sequentially into a single larger stream. The multiplexer must operate at a clock rate significantly greater than that of the buffers in order to be able to multiplex all the data acquired during a given sampling period, before the arrival of data from the next sampling period.