Abstract:
Sensing vehicle speed is disclosed. A speed sensor is self powered. The speed sensor measures a speed data of multiple vehicles with one Doppler pulse. A sample is taken of speed sensor data from the speed sensor. The sample of speed sensor data is processed to calculate speed. The calculated speed is wirelessly transmitted to a server.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to sensing vehicle speed. More specifically, a self-powered vehicle speed sensor is disclosed. 
   BACKGROUND OF THE INVENTION 
   Vehicle speed sensors are frequently expensive and require power, a dedicated communication line, or both. Thus, these wire connections for the vehicle speed sensors require substantial infrastructure (and hence investment) in order to widely proliferate speed sensors. It would be helpful to have a vehicle speed sensor that was self-powered so that it does not require a wire connection for power. In addition, it would also be helpful to have a vehicle sensor that does not require a wire connection to communicate its information. 
   Vehicle speed sensors usually have very specific mounting requirements. Some are buried in the road pavement; others must be mounted very close to the vehicle lane on a separate pole. It would be very helpful to have a speed sensor with a long sensing range, enabling it to be mounted in many different locations and still work effectively. 
   Self-powered speed sensors are usually very bulky. They require large solar panels and lots of batteries for backup power. Often, they are too bulky and weigh too much to be installed on existing light poles or sign posts. It would be helpful to have a self-powered speed sensor that used very little power, shrinking the amount of batteries required and reducing the load on the pole. 
   Current vehicle speed sensing equipment measures the speed of one vehicle at a time. It would be helpful to measure the speed of multiple vehicles at once on a section of road while distinguishing vehicle direction and whether or not the vehicle was using a high-occupancy vehicle (HOV) lane. 
   Many vehicle speed sensors are difficult to install and calibrate. It would be helpful to have a speed sensor that is self-calibrating and could be installed in a matter of minutes. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings. 
       FIG. 1  is a block diagram illustrating a self-powered vehicle speed sensor system. 
       FIG. 2  is a flow chart illustrating the steps of operation of the self-powered vehicle speed sensor system. 
       FIG. 3  is a flow chart illustrating the steps for preparing the speed sensor system. 
       FIG. 4  is a circuit diagram illustrating a preamplifier in the speed sensor system. 
       FIG. 5  is a flow chart illustrating the steps for acquiring speed sensor data. 
       FIG. 6  is a flow chart illustrating the steps for processing the speed sensor data. 
   

   DETAILED DESCRIPTION 
   The invention can be implemented in numerous ways, including as a process, an apparatus, a system, a composition of matter, a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication links. In this specification, these implementations, or any other form that the invention may take, may be referred to as techniques. In general, the order of the steps of disclosed processes may be altered within the scope of the invention. 
   A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured. 
     FIG. 1  is a block diagram illustrating a self-powered vehicle speed sensor system. In one embodiment, speed sensor  100  sends its signal to front end  102 . Front end  102  includes a preamp and filter  104 , which amplifies and filters the data signal from the sensor, and an analog-to-digital (A/D) converter  106 , which digitizes the data signal from the sensor. Digital signal processor (DSP)  108  then processes the digitized data signal. The processed information is then sent using wireless data modem  110  to a centralized server. DSP  108  also controls the battery manager  1   18 , which is part of the overall battery management system  112 . The battery management system  112  controls a) charging of battery  114  from solar panel  116  and also b) providing power from either battery  114  or solar panel  116  to the rest of the speed sensor system. Power manager  120  intelligently turns on and off subsystems to efficiently use the power provided by the battery management system  112 . The battery management system  112  and the power manager  120  allow the speed sensor system to be self-powered from the solar panel. It is not necessary to attach the speed sensor system to an electric power supply wire. This also makes the speed sensor system easy to install because no wires need to be connected to the speed sensor system. In addition, because of the power management system, the battery can be small and this reduces the weight of the speed sensor system. 
   In some embodiments, speed sensor  100  is a Doppler speed sensor, which has a microwave source and receiver that is designed to measure the speed of objects using the Doppler shift in the back-reflected microwaves. 
   The power manager  120  intelligently controls the frequency and duration of the speed measurements. If the traffic is moving at a normal speed, the measurements, or samples, are less frequent than if the traffic is very slow. In addition, the power manager  120  would also lower the frequency of samples when the battery power is low to preserve power until the next charging time. 
     FIG. 2  is a flow chart illustrating the steps of operation of the self-powered vehicle speed sensor system. In step  200 , the speed sensor system prepares to take a measurement. Because the power manager turns off power hungry circuitry except when necessary, the system needs to turn on and stabilize the measurement electronics. In step  202 , the speed data sample is acquired. In step  204 , the speed data sample is processed. In step  206 , the speed information is transmitted to a centralized server. 
     FIG. 3  is a flow chart illustrating the steps for preparing the speed sensor system. In step  300 , the microwave source of the speed sensor and the preamplifiers are turned on. In step  302 , the system waits in order to stabilize the electronics after the microwave source is turned on. In step  306 , the in-line capacitor is pre-charged. In step  308 , the charge saver switch is closed. 
   The speed sensor has a calibration system that can be used at power up to check the speed sensor. Using a known oscillating target in front of the speed sensor a speed measurement can be made and compared against the known speed achieved for that target. 
     FIG. 4  is a circuit diagram illustrating a preamplifier in the speed sensor system. Preamplifier  406  is designed to take the speed sensor signal input  408  and produce an amplified output  410 . When switch  400  is closed the capacitor  404  is rapidly charged. When switch  402  is closed the charge saver function is off for capacitor  404 . This method is used to rapidly stabilize the preamplifier signal path to prepare it for the data signal. 
     FIG. 5  is a flow chart illustrating the steps for acquiring speed sensor data. In step  500 , the acquisition system electronics is allowed to stabilize. In step  502 , the analog-to-digital (A/D) converter is turned on. In step  504 , the data samples required to measure speed and direction are taken. For direction, the sine and cosine components of the back-reflected microwave signal are sampled. In step  506 , the microwave source, preamplifiers, and A/D converter are turned off again to preserve power, and the charge saver switch is opened to preserve the capacitor charge until the next measurement. 
     FIG. 6  is a flow chart illustrating the steps for processing the speed sensor data. In step  600 , the digital signal processor (DSP) is placed in high-power mode. In step  602 , the DSP calculates speed information in both directions by performing FFT analysis on the sine and cosine components of the speed sensor data. The DSP processes the return signal by separating it into its component frequencies, and splitting the frequencies into cohorts that correspond to 0.1 mph increments. The average speed is calculated by averaging the speed of all of the cohorts which were found to have a positive return from the Doppler radar signal. In step  604 , the DSP is returned to low-power mode. In step  606 , the average speeds for both directions of the traffic are calculated. In some embodiments, several traffic lanes are measured simultaneously. In addition in step  606 , the high occupancy vehicle traffic speed can be separately calculated from the non-high occupancy vehicle traffic speed. In step  608 , the speed information is averaged over a number of samples (e.g. four samples where a sample is taken every 250 milliseconds). In step  610 , the average speed information is corrected for the angle that the speed sensor is placed at with respect to the road. In some embodiments, the angle correction is performed after the information is sent to the server. In step  612 , the calculated speed information is placed into a psuedo-RS232 packet to be transmitted over the wireless data modem to a server. 
   Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative and not restrictive.