AUTOMATIC BAR CODE SYMBOL READING SYSTEM AND METHOD OF READING BAR CODE SYMBOLS USING THE SAME

摘要

Disclosed is a fully automatic bar code symbol reading system having at least one automatic (i.e., triggerless) portable bar code symbol reading device, and an associated base unit positioned within the data transmission range thereof without a physical wiring connection thereto. After each successful reading of a bar code symbol, the bar code symbol reading device automatically produces symbol character data representative of the decoded bar code symbol, synthesizes a group of data packets each containing the symbol character data, and then transmits the synthesized group of data packets to the base unit. Upon the successful receipt of one of the transmitted data packets and the recovery of symbol character data therefrom, the base unit generates an acoustical acknowledgement signal that is perceptible to the user of the bar code symbol reading device and indicates the transmitted symbol character data has been successfully received. In typical applications, a plurality of such bar code systems are used in physical proximity with each other, such as in conventional retail point-of-purchase (POS) environments. In accordance with the present invention, radio frequency(RF) carrier signals of the same frequency are used by each hand-supportable bar code symbol reading device to transmit groups of data packets to respective base units. Data packet interference at each base unit is minimized during data packet reception by using a novel data packet transmission scheme. In accordance therewith, each bar code symbol reading device transmits the data packets in each of its data packet groups with a unique time delay imposed therebetween, thus creating data packet transmission "slots" or "windows" on the time domain, during which other groups of data packets may be transmitted from neighboring bar code symbol reading devices and received at their respective base units without data packet interference. Each base unit in the resultant system is also able to distinguish data packets associated with consecutively different bar code symbols read by its mated bar code symbol reading device. This capability is provided by using a novel data packet encoding scheme during data packet synthesis, and a novel data packet decoding scheme during data packet reception and symbol character data recovery. Significantly, the bar code symbol reading system of present invention eliminates the need for electromagnetic signal receiving and processing circuitry aboard each portable bar code symbol reading device. Advantageously, the automatic bar code symbol reading system of the present invention can be inexpensively manufactured, and reliably operated with a significant reduction in battery power consumption which is critical in most portable bar code symbol reading applications.