Importance

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Abstract

A two-way packet radio-based electronic toll collection system is to be installed on a highway and includes a main communication tower for transmitting continuously downlink communication packets that contain information regarding available uplink communication channels, and an in-vehicle unit installed in each vehicle passing along the highway to receive the downlink communication packets. The in-vehicle unit is capable of selecting one of the available uplink communication channels. The in-vehicle unit and the main communication tower exchange toll collecting and payment information wirelessly via the available uplink communication channel selected by the in-vehicle unit and a downlink communication channel corresponding thereto. When collision occurs along the packets transmitted by a number of in-vehicle units, a retransmission scheme is applied for each in-vehicle unit to guarantee successful communication between the tower and the in-vehicle unit.

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First Claim