On-vehicle equipment for dedicated short-range communication in intelligent transport system
In an on-vehicle equipment for Dedicated Short-Range Communication (DSRC) in Intelligent Transport System (ITS), a priority sequence for switching local frequencies of f 1 to f 7 in correspondence with types of on-road equipment is previously set, the local frequencies are sequentially outputted at a predetermined cycle in accordance with the priority sequence, a received frequency signal is compared with a selected frequency signal, and when the received frequency signal is the same as the selection frequency signal, the local frequency corresponding to these is determined as a desirable communication frequency, and the communication frequency is fixed as being this local frequency with high efficiency.
1. An on-vehicle equipment for Dedicated Short-Range Communication (DSRC) in an Intelligent Transport System (ITS) comprising:
a receiving antenna for receiving a radio wave signal transmitted from on-road equipment;
a frequency converting unit for converting a receiving frequency for the radio wave signal to a predetermined local frequency among a plurality of local frequencies;
a channel selecting filter unit for filtering a signal received at the predetermined local frequency to obtain only a signal in a predetermined channel;
a demodulator for digitizing the predetermined channel signal obtained by the channel selecting filter unit;
a normal reception determining unit for judging whether the radio wave signal is normally received based on an output from the demodulator;
a phase locked loop (PLL) oscillating unit for outputting the predetermined local frequency to the frequency converting unit according to a selected frequency signal; and
a frequency switching determining means for selecting the predetermined local frequency, generating the selected frequency signal by sequentially switching the local frequencies at a predetermined cycle in accordance with a preset priority sequence for switching the local frequencies corresponding to different types of on-road equipments, comparing a receiving frequency signal generated based on the frequency of the received radio wave signal with the selected frequency signal, and setting the local frequency output from the PLL oscillating unit if the receiving frequency signal and the selected frequency signal are equal.
2. The on-vehicle equipment for DSRC in the ITS according to claim 1 , wherein the frequency switching determining means is configured to switch to a local frequency of high priority more often than a local frequency of low priority.
3. The on-vehicle equipment for DSRC in the ITS according to claim 1 , wherein the frequency switching determining means determines the priority sequence for switching the local frequencies based on the vehicle speed.
4. The on-vehicle equipment for DSRC in the ITS according to claim 1 , wherein the frequency switching determining means is configured to operate under a first control mode of selecting only a local frequency or frequencies of high priority and a second control mode of selecting at least a local frequency of low priority, and a control mode of the frequency switching determining means is changed from the first control mode to the second control mode when a switching command is externally inputted.
5. The on-vehicle equipment for DSRC in the ITS according to claim 4 , wherein the control mode of the frequency switching determining means is changed from the second control mode to the first control mode after a lapse of a predetermined time period from a change from the first control mode to the second control mode.