Enhanced transponder programming in an open road toll system

A method of directing communications with transponders in moving vehicles in a roadway, the roadway having a plurality of antennas having a coverage area that includes at least a portion of the roadway, the antennas being configured to operate in a time division multiplexed sequence, the time division multiplexed sequence being comprised of successive superframes, each superframe being comprised of a series of frames, each frame corresponding to communications on one of the antennas, each superframe having a fixed number of frames available for reading data from a memory of the transponder and a fixed number of frames available for writing data to the memory of the transponder, the method comprising:

• determining which of the transponders need to be programmed;
• selecting for immediate programming at least some of the transponders that need to be programmed based on the fixed number of frames available for writing data;
• determining which of the antennas to use for communicating with the transponders that need to be programmed;
• determining which frames correspond to the antennas to be used;
• allocating the frames of a first superframe which have been determined to correspond to the antennas to be used as writing slots, for writing data to the memory of the transponder;
• and
• allocating a predetermined number of the unallocated frames of the superframe as reading slots.

A transponder communication system for use in an electronic toll collection system for programming a transponder located in a moving vehicle travelling in a roadway, the transponder having a memory, the system comprising:

• a plurality of narrow beam reading antennas, each antenna having a coverage area that includes at least a portion of the roadway for transmitting trigger signals and receiving signals transmitted by the transponders in response to the trigger signal;
• at least one wide beam programming antenna having a coverage area that includes at least a portion of the roadway for transmitting signals to the transponders, the coverage area of the wide beam antenna being larger than the coverage area of any one of the narrow beam antennas;
• and
• a control device connected to the antennas, the control device being configured to control communications on the antennas, the control device being configured to initiate a reading sequence by causing one of the narrow beam antennas to transmit a trigger signal and awaiting a response on that antenna, the control device being further configured to initiate a writing sequence by causing the wide beam antenna to transmit a programming signal.