Abstract:
Methods for pedestrian unit (PU) communication activity reduction in pedestrian-to-vehicle communication networks include obtaining safety risk information for a pedestrian at risk for involvement in an accident and using the risk information to adjust a PU communication activity. In some embodiments, the activity reduction is achieved without implementing understanding of surroundings. In other embodiments, the activity reduction is based on risk assessment provided by vehicles. In some embodiments, the activity reduction includes PU transmission reduction. In some embodiments the transmission activity reduction may be followed by reception activity reduction for overall power consumption reduction.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to and hereby claims the priority benefit of commonly-owned and co-pending U.S. Provisional Patent Application No. 61/494,977 titled “Method and apparatus for pedestrian to vehicle communication system” and filed Jun. 9, 2011, and U.S. Provisional Patent Application No. 61/598,982 titled “Method and apparatus for activity reduction in pedestrian-to-vehicle communication network” and filed Feb. 15, 2012. 
     
    
     FIELD 
       [0002]    Embodiments disclosed herein relate in general to activity reduction in a pedestrian-to-vehicle communication network, and more specifically to methods for reducing the transmission and reception activity of a pedestrian communication unit (referred to hereinafter as “pedestrian unit”, “personal unit” or “PU”) by applying local decisions and decisions driven by analysis of vehicles. 
       BACKGROUND 
       [0003]    The term “pedestrian-to-vehicle communication network” or “PVCN” refers to a scheme for detecting pedestrians by vehicles. It has many advantages over vision-based or radar-based systems, since pedestrians obstructed by vehicles can still be detected (observed). Each pedestrian is expected to have a small pedestrian communication unit associated therewith. The PU will interact with vehicles having integrated vehicle communication units. 
         [0004]    The biggest challenges facing implementation of a PVCN are cost, power and positioning accuracy: the PU must be extremely low cost, even at the expense of limiting functionality. For example, a GPS (or similar) receiver may be too costly, and placing the GPS antenna in a position with a clear view to the sky may be too challenging. However, if a GPS receiver is not included, a PU may not have no location/positioning capability. Even if a GPS receiver is included, the processing power and memory size need to be kept very low, severely limiting the ability of the PU to have an accurate map of all roads and vehicles in its surroundings. 
         [0005]    Power reduction may be achieved by limiting PU receive and transmit operations (referred to herein generally as “activity”). In Pus which include a GPS receiver, the “activity” may also refer to GPS receive activity. Achieving these without compromising the safety goals requires understanding of the road topology and assessment of risk from approaching vehicles. Road topology storage requires significant memory, while risk assessment requires extensive processing. Implementing these features will increase the PU cost beyond acceptability. 
         [0006]    Transmission from a PU of a person sitting inside a vehicle may confuse processing of proximal vehicles, which might trigger a false alert for pedestrian safety risk. The conditions for pedestrian safety risk are different than those for vehicle risk. The sensitivity to raising pedestrian alerts will be likely higher than that to raising vehicle alerts. Therefore, there is a difference in risk analysis between pedestrians and vehicles and the two must not be confused. Another reason to reduce activity in a PVCN is to reduce network load and to increase battery life of a PU belonging to a pedestrian who is not posing a threat, such as a person sitting inside a vehicle. 
         [0007]    There is therefore a need for, and it would be advantageous to have activity reduction in pedestrian-to-vehicle communication network without implementing understanding of surroundings in a pedestrian unit. It would also be advantageous to have such activity reduction even if the PU includes a GPS receiver. 
       SUMMARY 
       [0008]    In various embodiments, there are provided methods for activity reduction in pedestrian-to-vehicle communication networks. In some embodiments, the activity reduction is achieved in a PU without implementing understanding of surroundings. In other embodiments, the activity reduction is based on risk assessment provided by vehicles. In some embodiments, the activity reduction includes PU transmission reduction. Transmission is more power consuming than reception, and it increases network load. In some embodiments the transmission activity reduction may be followed by reception activity reduction and, optionally, GPS receiver activity reduction for overall power consumption reduction. 
         [0009]    In a first embodiment, a PU determines if the pedestrian is inside (“in”) a vehicle (when inside a vehicle, the “pedestrian” is referred to henceforth as “person”), and disables its own operation as long as the person remains in the vehicle. In a second embodiment, a PU determines a transmission activity factor based on risk assessment guidance from vehicles in order to reduce its own activity. In a third embodiment, a vehicle unit performs vehicle analysis of a pedestrian safety risk, and adjusts accordingly the transmission rate for a PU of a pedestrian not located in a vehicle. 
         [0010]    Pedestrians may transmit on the same channel used by vehicles. However, it is more likely that a dedicated channel will be allocated for this purpose. The actual transmission channel does not impact the methods described. The methods disclosed herein allow manufacturing of a low-cost pedestrian unit powered by a battery with or without a GPS receiver. 
         [0011]    In an embodiment, there is provided a method for activity reduction in a PVCN comprising steps of obtaining pedestrian safety risk information related to a particular person, and, based on the obtained pedestrian safety risk information, adjusting the communication activity of a PU associated with the particular person. 
         [0012]    In an embodiment there is provided a method for activity reduction in a PVCN comprising steps of monitoring over a predetermined time period a distance between a particular pedestrian who carries a respective PU and a vehicle closest to the particular pedestrian to determine a distance deviation, and, if the distance deviation is lower than a predetermined threshold, reducing transmission activity by the respective PU. 
         [0013]    In an embodiment there is provided a method for activity reduction in a PVCN comprising steps of identifying pedestrians at a given level of risk from accidents with vehicles, each pedestrian having a respective PU associated therewith, transmitting an activity control message which includes information related to the given level of risk relevant to a particular pedestrian, and adjusting the communication activity of a respective PU associated with the particular pedestrian based on the information received in the activity control message. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Non-limiting embodiments are herein described, by way of example only, with reference to the accompanying drawings, wherein: 
           [0015]      FIG. 1  shows schematically an embodiment of a method for activity reduction disclosed herein; 
           [0016]      FIG. 2  shows schematically an embodiment of a first implementation of a method for activity reduction disclosed herein; 
           [0017]      FIG. 3  shows schematically an embodiment of a second implementation of a method for activity reduction disclosed herein; 
           [0018]      FIG. 4  illustrates schematically an environment which includes pedestrians and vehicles; 
           [0019]      FIG. 5  shows an exemplary message for activity reduction in an embodiment of a third implementation of a method for activity reduction disclosed herein; 
           [0020]      FIG. 6  shows a flow chart of a pedestrian unit operation in the embodiment described in  FIG. 5 ; 
           [0021]      FIG. 7  shows a flow chart of a vehicle unit operation in the embodiment described in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  shows schematically an embodiment of a method for activity reduction disclosed herein. Safety risk information for a pedestrian at risk for involvement in an accident is obtained in step  100 . The risk information is used to adjust a PU communication activity (e.g. reduce transmission) in step  102 . The adjustment will lead to reduced network congestion and increased PU battery life. The description next provides three exemplary implementations of the steps for obtaining the risk information and adjusting the PU activity. 
         [0023]    In a first implementation, the obtaining of risk information includes detecting if a person is sitting inside a vehicle, in which case the person poses no risk as all or poses a lower risk than when outside the vehicle (when he is a “pedestrian”).  FIG. 2  shows schematically an embodiment of this implementation. The person is assumed to have a respective PU which includes a GPS receiver. If the person is found to be located inside a vehicle, transmission by his/her respective PU is adjusted (reduced or prevented by setting the PU to “inactive”). 
         [0024]    The operation begins in step  200 . Transmission is set to “active” in step  202 . A pedestrian speed for a particular pedestrian, determined from data obtained by his/her PU GPS receiver, is compared with a minimal speed value in step  204 . Exemplarily, the minimal value may be 10 km/h. If the pedestrian speed is below the minimal value (a situation which may arise if the pedestrian is immobile, e.g. stands next to a vehicle instead of being a person inside the vehicle), operation returns to step  204 . In addition, the distance between vehicles grows with increasing vehicle speed, rendering the correlation of pedestrian location with vehicle location more distinct. If the pedestrian speed in step  204  is higher than the minimal value, operation continues from step  206  in which a vehicle closest to the pedestrian is selected after checking the distance from the pedestrian to all vehicles in his/her proximity. In step  208 , a deviation of the distance (“distance deviation”) between the selected (closest) vehicle and the pedestrian is monitored over a certain time period, for example 10 seconds or more. The distance deviation can take the form of a maximal absolute value or of an average value and is used to declare an “alignment” between the selected vehicle and the pedestrian. In step  210 , the measured distance deviation is compared with a first deviation threshold (e.g. 5 meters). If the deviation is larger than the threshold, then a wrong vehicle was selected as “closest” in step  206  (i.e. the selected vehicle and the pedestrian are not “aligned”), and operation resumes from step  206 . Otherwise (selected vehicle and pedestrian are “aligned”), operation continues to step  212 , in which transmission is set to inactive. For the period the transmission is inactive, the PU reception may be activated periodically, e.g. less that 10% of the period. GPS tracking speed can be lowered as well. The measured deviation is then compared in step  216  with a second, larger deviation threshold (e.g. 10 meters), to accommodate high GPS errors after initial lock. If the measured deviation is smaller than the second threshold, the vehicle and pedestrian are still aligned and step  214  is repeated. Otherwise, operation returns to and is repeated from step  202 , turning the transmission back on to active after discovering that the closest vehicle selection in step  206  was wrong, or that the pedestrian is not a person inside the vehicle. 
         [0025]    In a second implementation, the PU does not have a GPS receiver, to reduce cost and remove the challenge involved in GPS antenna placement. As in the previous implementation, the obtaining of risk information includes determining whether a person is inside or outside a vehicle. This is done using a Receive Signal Strength Indication (RSSI). As in the first implementation, if it is determined that the person is inside a vehicle, transmission by his/her respective PU is inactivated. This embodiment is shown schematically in  FIG. 3 . The PU performs all the following actions. The operation begins in step  300 . Transmission is set to active in step  302 . The RSSI of surrounding vehicles is monitored in step  304 . The monitoring lasts for several seconds (for example 10 seconds or more). A high RSSI value, for example above −55 dBm, is used to identify vehicles with very short distance from the person associated with the PU. If, for a particular vehicle, the deviation of different RSSI measurements from a given value over the monitored period is low, then the person has a fixed location relative to that vehicle, not impacted by environment or vehicle movement. This indicates that the person is inside that vehicle. The vehicle with the lowest RSSI deviation is selected in step  306 . The measured RSSI deviation is compared with a threshold (limit) in step  308 . For example, the threshold may be 4 dB. If the deviation is greater than the threshold, the operation returns to step  300 , to keep looking for vehicles matching the criterion (RSSI higher than −55 dBm). If the deviation is lower than the threshold, operation continues to step  310  in which the difference between the lowest RSSI deviation and the second lowest RSSI deviation is calculated The difference between the two deviations should be larger than a predetermined value, for example 3 dB, or else the selection of a vehicle as the one with the most “stable” RSSI is not confident enough. If the difference is smaller than the predetermined value, the operation continues from step  300 , repeating the process. If the difference is larger, the person is considered as “aligned” with the vehicle and operation continues to step  312 . Consequently and paralleling step  212  above, in step  312  transmission is set to inactive (thereby reducing activity). The RSSI of the selected vehicle is further monitored to assure that the alignment between vehicle and person continues in step  314 . The RSSI deviation is compared with a second threshold in step  316 . The second threshold is chosen to be higher than the first threshold, to allow slack after initial alignment declaration. For example, the second threshold may be higher by 2 dB than the first. If in step  316  the deviation is smaller than the second threshold, then the selected vehicle is still aligned with the person and monitoring resumes from step  312 . If the deviation is larger, operation returns to step  302 , and transmission is turned back to active. This is followed by searching for and selecting a new vehicle. 
       Reducing Activity Based on Risk Assessment Provided by Vehicles 
       [0026]    In a third implementation, the obtaining of risk information includes obtaining and analyzing a pedestrian safety risk. The analysis includes determination that a person (here a pedestrian) is outside a vehicle and determination, from vehicle transmissions, that a particular pedestrian is not close to a road. The vehicles transmit “activity control” messages which are received at a PU associated with the particular pedestrian. Each message includes information which indicates whether a particular pedestrian is close or not close to the road. An “activity factor” between 0-100% is calculated by the PU based on the information. If a message indicated that a particular pedestrian is not close to a road, the calculated activity factor will be low (e.g. 10%). The transmission activity of the PU associated with that particular pedestrian is then set according to the factor (in the example to 10%). Since during most of the time a pedestrian does not impose any risk, the activity factor can be decreased significantly, achieving the goal of transmission power reduction. The following describes in more detail the actions above. 
         [0027]      FIG. 4  illustrates schematically an environment which includes pedestrians and vehicles. Two vehicles,  410  and  412 , drive on a road  400 . Ten pedestrians, marked  420  to  429 , are on a curb  430 . The pedestrians closest to the road ( 421 ,  425  and  427 ) are identified as posing the greatest safety risk. These three pedestrians should be more visible to vehicles than other pedestrians. Higher visibility is reflected by higher respective PU transmission rate. 
         [0028]    An exemplary activity control message which may be propagated by all units in a PVCN in this implementation is illustrated in  FIG. 5 . The message includes the following fields: 
         [0029]    Pedestrian imposing safety risk (field  500 ): Binary field with Yes/No possible values. 
         [0030]    Pedestrian activity control (field  502 ): Binary field with Enable/Disable possible values. 
         [0031]    Activity re-enable distance (field  504 ): Field [in meters] of movement till pedestrian unit should resume activity. 
         [0032]    Activity re-enable direction (field  506 ): Field [in angles] of movement direction which is considered for distance calculation mentioned above. 
         [0033]    A message including only a subset of these fields can also be designed. The fields can be refined to greater degree of description if needed. For example, safety risk can be graded, instead of a plain Yes/No. 
         [0034]      FIG. 6  shows a flow chart of PU operation in this implementation. All steps are performed by a “receiving” PU. In step  600 , a check is performed to determine if an activity control message was received from a vehicle. If such a message was received, it is processed in step  602  by the receiving PU. The processing includes parsing all fields. If an enable control message was received, then the receiving PU is enabled. If a disable control message was received, then the receiving PU is disabled unless prohibited by a recent message from a different vehicle. The condition for enabling is recorded by the PU. Operation continues from step  604  in which a check is performed to check if activity is disabled. If YES, the condition for re-enable is checked in step  606 . If the condition is satisfied, then activity is re-enabled and the operation returns to step  600 . If NO in step  604 , operation continues from step  608 . If no transmission of any message as above was received recently, for example over the last 5 seconds, then activity is stopped in step  616 . This is followed by returning to step  600 . If transmission was received, operation continues from step  610 , in which pedestrian network load is measured. Network load measurement is known in the art, and existing schemes of counting the number of received packets or measuring a period of time in which received energy is above a threshold can be applied. The operation is followed by calculating the activity factor in step  612  and setting the transmission activity accordingly in step  614 . The activity factor calculation considers the load of the pedestrian network (obtained e.g. from measuring the number of PUs which transmitted during the last 1 second, or using an equivalent method know in the art) and the information received from the vehicle control message, and in particular the number of vehicles that identified the pedestrian as posing a safety risk. The logic for calculation is exemplarily as follows: 
         [0035]    Increased pedestrian network activity should reduce PU activity to decrease load. 
         [0036]    Increased number of vehicles identifying a pedestrian as imposing a safety risk should increase PU activity for better visibility. 
         [0037]    These two statements are combined to a single table. Table 1 includes an example for possible values: 
         [0000]                                TABLE 1                           Pedestrian       Pedestrian   Pedestrian   Pedestrian   marked twice       communication   not marked   marked once   or more as       network load   as imposing risk   as imposing risk   imposing risk                   Low   Medium activity   High activity   High activity       Medium   Low activity   High activity   High activity       High   Low activity   Low activity   High activity                    
The table may be extended to include more input values for network load or consider the load as continuous, instead of the discrete classification applied here. The table may also include finer granularity for activity level instead of only “low, medium, high”.
 
         [0038]    The PU operations in  FIG. 6  must be kept very simple to meet the requirement of low processing power. As can be seen, the operations and decision elements are fairly simple, and meet the requirement. 
         [0039]    A flow diagram of vehicle operation in this implementation is shown in  FIG. 7 . The vehicles perform the complex calculations. The operation begins in step  700  by identifying the positions of all pedestrians within communication range. The positions may be transmitted by PUs (when these include a GPS receiver) or by positioning schemes applied by a particular vehicle, similar to radar mechanisms, for example as described PCT patent application PCT IB2009/051769. The pedestrians are placed on a map in step  702 . The map must be very accurate to detect exact road boundaries. The map may be provided from a database or learned by the vehicle. Various alternatives exist for placing pedestrians on a map. 
         [0040]    Step  704  considers the vehicle speed in determining the number of pedestrians to identify as posing a risk. The faster the vehicle drives, the greater potential danger it poses to pedestrians, and the greater is the responsibility of the vehicle to identify pedestrians, since the distance between vehicles grows, and the number of vehicles on road is lower. For these reasons, a fast moving vehicle should be able to identify more pedestrians posing a safety risk than a lower moving vehicle. An example for slow vehicles includes many vehicles stopping at intersection during a red light. If each vehicle identifies several pedestrians as posing a risk, then all the pedestrians crossing the road will be marked as posing a big risk, which is likely to overwhelm the network. More dangerously, this will prevent vehicles from selecting other pedestrians, not crossing on the crosswalk. An example for selection of a number of pedestrians at risk is described in Table 2: 
         [0000]                                TABLE 2                       Vehicle speed   Maximal number of selected pedestrians                           &lt;10 km/h   0           &lt;25 km/h   1           &lt;40 km/h   2           Else   3                        
Other values may be used. The pedestrians posing the safety risk are identified in step  706 . The criterion is the distance of a pedestrian from the road, with the risk increasing with decreasing distance. The challenge is to ignore all pedestrians except those (one or more) closest to the road, and to avoid repeated selection by all vehicles of the same pedestrians. For this reason, a criterion of distance from vehicle is applied to limit the range of identification, so as to limit overlapping decisions of different vehicles. An exemplary scheme could be to select the pedestrians closest to the road between a current vehicle location and a certain distance that the vehicle will travel on the road (“road segment”), for example 25 meters. If the number of pedestrians with distance to the road of less than the certain distance (for example, 2 meters) is below required, then operation continues to the next segment, (which may be between 25 meters to 50 meters ahead), then to the next, etc. Optionally, in step  708 , the vehicle can instruct a PU to disable its activity based on its location. For example, if the vehicle identifies that the pedestrian is 30 meters from the closest road (“not at risk”), then the vehicle can instruct the PU to disable until the pedestrian moves 20 meters from his/her current location. In this example, the pedestrian will be at least 10 meters from the road when his/her PU is re-enabled. Since the pedestrian movement direction is not specified, the pedestrian can be much further away. Optionally, the movement direction can be added to refine the condition. In step  710 , after the pedestrians posing a risk are identified by a vehicle, their identities are attached to vehicular messages as defined in  FIG. 5  and transmitted.
 
         [0041]    While this disclosure has been described in terms of certain embodiments and generally associated methods, alterations and permutations of the embodiments and methods will be apparent to those skilled in the art. The disclosure is to be understood as not limited by the specific embodiments described herein, but only by the scope of the appended claims.