Vehicle speed determination from audio input for dead reckoning determination in a portable navigation device

#1. Field of the Invention

#The invention relates to a portable navigation device used to make a dead reckoning determination, and more particularly, to a portable navigation device utilizing an audio input to determine a vehicle's speed and thereby make a dead reckoning determination.

#2. Description of the Prior Art

#FIG. 1 is a diagram of a portable navigation device connected to a vehicle's wiring loom according to the prior art.

#FIG. 2 is a diagram of a portable navigation device containing a microphone used to determine a vehicle's speed according to the present invention.

#FIG. 3 is a functional block diagram of the portable navigation device according to the present invention.

#The present invention provides a simplified method to determine the speed of a vehicle that a portable navigation device is placed in when GPS signals cannot be received by the navigation device. The present invention advantageously makes use of hardware already present in a typical personal navigation device, and eliminates the need for connecting wires to a vehicle's wiring loom.

#Please refer to FIG. 2. FIG. 2 is a diagram of a portable navigation device 100 containing a microphone 104 used to determine a vehicle's speed according to the present invention. Like conventional portable navigation devices, the portable navigation device 100 contains a display 102 for displaying map information and has a plurality of control buttons 120 for enabling a user to operate the portable navigation device 100. Differing from the conventional portable navigation device 10, the portable navigation device 100 of the present invention utilizes the microphone 104 for obtaining sound signals from inside the vehicle, analyzing the sound signals, and thereby determining a speed at which the vehicle is moving. Once the speed of the vehicle is obtained, dead reckoning calculations can be made to estimate the current location of the vehicle using the determined speed, the elapsed time since a last reliable GPS signal was received, and the course of the vehicle.

#Please refer to FIG. 3. FIG. 3 is a functional block diagram of the portable navigation device 100 according to the present invention. The portable navigation device 100 additionally contains a processor 106 for analyzing the sound signals received from the microphone 104, determining the speed at which the vehicle is moving according to the analyzed received sound signals, and estimating a current location of the vehicle based on the determined speed of the vehicle. A memory 108 is used to store map and route information, as well as software executed by the processor 106. A speaker 110 can be used to output audio messages to a user, such as indications that a required turn is quickly approaching. The portable navigation device 100 optionally contains a General Packet Radio Service (GPRS) modem 112, a Universal Serial Bus (USB) port 114, a gyroscope 116, or an accelerometer 118, as will be explained below.