Patent GB-1452029-A (GB)
Title: Vehicle monitoring radio communication system
IPC: G08G1/0967
Filed: 1974-11-08
Abstract: 1452029 Interrogation systems MULLARD Ltd 8 Nov 1974 48561/74 Heading H4L In a vehicle monitoring system, e.g. for keeping track of and communicating with buses, there is a main transmitting/receiving station and a number of beacon stations having transmission powers such that their transmissions do not overlap, and the vehicles are able to store information transmitted by the beacons and transmit information including the stored information to the main station on request. The system operates in response to control signals from the main station such that beacon stations only transmit when the main station is inactive and vice-versa, and the main and beacon station transmitters transmit in the same carrier channel. In the vehicle, data, which may be from a beacon, is received at 21, demodulated at 23 and passed to a register 27. The beacon data consists of a start code, stored in elements 1-5 of the register, a series of five binary "1"s, stored in elements 6-10 and a code identifying the particular beacon, stored in elements 11-15. The data is clocked into the register using a clock pulse extractor 24, the pulses from which pass via an AND gate 25 which is kept open by the Q output from a bi-stable 55. When the start code is detected by comparator gates 29 and a series of "1"s (indicating a beacon signal) by AND gate 38, gate 34 opens and the content of elements 11-15 (identifying the beacon) of register 27 are fed into elements 11-15 of register 46. In this register, other data can be entered into elements 6-10 via terminals 59 and the terminals 60 are prewired to the vehicle address code. When a subsequent transmission including a start code in elements 1-5 and the vehicle address code in elements 6-10 identifying the vehicle, is received from a central station the gates 36, which are prewired to the vehicle address code, deliver a "1", such that AND gate 33 is opened to switch the bi-stable 55, thus cutting off the control pulses for the register 27, starting the timer 39 and opening gate 42. The timer delivers an output for a controlled time, to read-out the contents of register 46 into data modulator 52 and thence to transmitter 53 so that they are transmitted back to the central station. Furthermore, the contents of elements 11-15 of the register 27 are read-out into store 43 so that information/instructions/control signals sent to the vehicle from the central station can be read-out. At a beacon station (Fig. 2, not shown) a similar but simpler arrangement enables a central station transmission identifying all  beacons to be received and stored at the beacon, and to cause the beacon transmission code to be clocked out of the register 46 and transmitted to any adjacent vehicles. The central station repetitively sends out beacon transmissions to actuate the beacons periodically, and contains control arrangements to cause it to shut down during beacon transmissions. A computer may control the codes sent out in time elements 6-10 so that all vehicles are polled, whilst periodically all beacons are activated. As well as vehicle location, information relating, e.g. to odometer readings (entered in stages 6-10 of register 46 on the vehicle) can be returned to the master station.