Patent Publication Number: US-2023164694-A1

Title: Method for low-power v2x based on early reception termination

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Patent Application No. 63/281,699 filed on Nov. 21, 2021, which is expressly incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The disclosure relates generally to a low-power vehicle-to-everything (V2X) communications (or simply “V2X”) operation scheme for a battery-operated device, and in particular to a scheme minimizing a V2X reception operation for Vulnerable Road User (VRU) protection to reception of messages from safety-relevant vehicles. As used herein, the term “safety-relevant” as applied to a vehicle refers to a vehicle that can potentially endanger the VRU within a few seconds. 
     BACKGROUND 
     V2X can protect all road users through direct communication. Vehicles are the first to deploy V2X. Vulnerable road users should be part of the V2X network, since the number of road fatalities of vehicle occupants is lower than that of non-occupants in many places including Europe. Motorcyclists, cyclists, eScooter riders, and pedestrians are all VRUs. 
     One of the major challenges of a VRU safety device is power consumption. VRUs typically carry battery-operated handheld devices, like smartphones, smartwatches, fitness trackers, and other wearables. In all such devices, battery life, as measured by days between charges, is a key selling point. V2X can be added to a battery-operated device only if it does not shorten battery life noticeably. 
     Some wireless standards, like Bluetooth, are designed to operate with a battery. Common properties of a low-power wireless standard are low bandwidth, simple modulation, and operational cycles allowing shut-down of the device. V2X wireless standards, either 802.11p, 3GPP C-V2X Rel. 14/15 (LTE-V2X) or Rel. 16/17 (NR-V2X), were designed for other purposes, in particular, long communication range, short latency, and high channel capacity even in presence of congestion. A V2X solution without low-power modifications cannot be used in battery-operated handheld devices due to the high power consumption. 
     Power consumption can be reduced by configuring V2X to transmit-only operation without any reception capability. However, this will reduce the safety benefit because the VRU will not be alerted of endangering vehicles. 
     It is desired to receive all messages from safety-relevant vehicles while limiting the duration of V2X reception operation (i.e. minimizing the reception of non safety-relevant vehicles) to lower power consumption. This can be referred to as “limited reception V2X”. 
     SUMMARY 
     In various example embodiments, there is provided a method, comprising determining, using V2X communications, that a vehicle is a safety-relevant vehicle posing a potential danger to a VRU, and receiving only transmisssions of the safety-relevant vehicle and skipping reception of transmissions of non-safety-relevant vehicles, thereby lowering V2X reception power consumption of a device carried by the VRU. 
     In some examples, the determining that a vehicle is a safety-relevant vehicle includes receiving V2X messages from a plurality of vehicles during a predetermined period and grading the safety-relevance of each vehicle using a respective respective location, speed, and heading of each vehicle. 
     In some examples, the receiving of only transmisssions of the safety-relevant vehicle while skipping the reception of transmissions of non-safety-relevant vehicles includes: identifying periodically a slot and a respective subchannel for V2X transmission of the safety-relevant vehicle and receiving the current slot and respective subchannel if the current slot and respective subchannel are identified as allocated to the safety-relevant vehicle, or skipping the reception of the current slot and respective subchannel if the current slot and respective subchannel are not identified as allocated to the safety-relevant vehicle, terminating the reception of the current slot and respective subchannel if the current slot and respective subchannel are identified as allocated to the safety-relevant vehicle but do not include transmissions of the safety-relevant vehicle, and if the current slot and respective subchannel do not include transmissions of the safety-relevant vehicle, scanning for transmissions of the safety-relevant vehicle in slots and respective subchannels proximal to the current slot and subchannel and, upon finding such proximal slots and respective subchannels, updating a database with the found slots and respective subchannels. 
     In some examples, the terminating of the reception current slot and respective subchannel includes activating a V2X receiver, measuring subchannel energy received during an AGC symbol, comparing the measured energy of each subchannel with a threshold, and if, the measured energy is lower than the threshold, terminating the reception. 
     In various example embodiments, there is provided a device, comprising a V2X receiver configured to determine, using V2X communications, that a vehicle is a safety-relevant vehicle posing a potential danger to a VRU, and to receive only transmisssions of the safety-relevant vehicle and skip reception of transmissions of non-safety-relevant vehicles, thereby lowering V2X reception power consumption of a device carried by the VRU. 
     In some examples, the V2X receiver includes an AGC unit configured to measure subchannel energy and the device further comprises a slot filter that provides an input used by the AGC unit to decide whether to receive or stop reception of the packet. 
     In some examples, the V2X receiver includes a data channel receiver and a control channel receiver, and the device further comprises a L1 ID filter configured to hold an expected L1 ID value and to match the expected L1 ID value with a L1 ID value received in a physical sidelink control channel (PSCCH) by the control data receiver. 
     In some examples, if the AGC unit did not stop reception and if the expected L1 ID value matched the received L1 ID value, the L1 ID filter is further configured to store a physical sidelink data channel (PSSCH) only for the given subchannel. 
     In some examples, the device further comprises a safety-relevant vehicles controller configured to determine that a vehicle is to be monitored with a given periodicity and to provide to the V2X receiver an input to determine that the vehicle is a safety-relevant vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting examples of embodiments disclosed herein are described below with reference to s attached hereto that are listed following this paragraph. Identical structures, elements or parts that appear in more than one figure are generally labeled with a same numeral in all the figures in which they appear. If identical elements are shown but numbered in only one figure, it is assumed that they have the same number in all figures in which they appear. The drawings and descriptions are meant to illuminate and clarify embodiments disclosed herein and should not be considered limiting in any way. In the drawings: 
         FIG.  1    illustrates a block diagram of a device for low-power V2X based on early reception termination disclosed herein; 
         FIG.  2 A  of a method for low-power V2X based on early reception termination disclosed herein; 
         FIG.  2 B  illustrates more details of the method of  FIG.  2 A ; 
         FIG.  3    illustrates a flow chart for identifying slots and subchannels allocated for transmission of safety-relevant vehicles; 
         FIG.  4    illustrates a flow chart for receiving a safety-relevant vehicle; 
         FIG.  5    illustrates a flow chart for terminating the reception if not including the transmission of a safety-relevant vehicle; 
         FIG.  6    illustrates a flow chart for scanning for the missing safety-relevant vehicle in proximal slots; 
         FIG.  7    illustrates a flow chart of vehicle safety relevance calculation; 
         FIG.  8    illustrates low-power reception stages. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    illustrates a block diagram of a device (or “system”) for low-power V2X based on early reception termination disclosed herein and numbered  100 . Device  100  may be used for NR-V2X (defined by 3GPP C-V2X standard Rel. 16/17) operation. The transmit functionality is omitted from the diagram because transmit is unmodified from any other V2X device. Device  100  comprises a radio-frequency integrated circuit (RFIC)  102  and a receive part of a modem (also referred to as “V2X receiver”)  104  which includes an adaptive gain control (AGC) unit  106 , a control channel receiver  108  and a data channel receiver  110 . Device  100  further comprises a security check layer  112  and a V2X stack  114  as defined by the respective ETSI or IEEE protocols. Device  100  further comprises a slot filter  122 , a L1 ID filter  124 , and a safety-relevant vehicles controller  126  The functionality/operation of each components is described below. Exemplarily, device components  102 ,  104 ,  112 ,  122  and  124  are implemented in hardware. 
     Modem,  104  embeds 3 major subblocks— 106 ,  108  and  110 . AGC  106  sets the gain of the RF front end. In known art, AGC measures the energy of the entire first symbol of the packet to obtain the most accurate measurement. 
     During operation, a packet is first received by RFIC  102 . The RFIC is optimized for low-power consumption even at the expense of higher noise. The RFIC demodulates signals of the received packet and forwards quadrature signal (IQ) samples to the receiving part of the modem  104 . The modem reception processing capacity is lowered for power consumption reduction. In a regular V2X device, the modem is capable of continuously receiving all messages, which could sum to 10 messages per 0.5 msec slot, reaching thousands of messages per second. For pedestrian safety, assume that only 3 vehicles are posing a maximal risk. Therefore, only ˜30 “safety-critical” messages per second need typically be received. A bicycle is moving faster than a pedestrian, therefore one can assume that the number of vehicles putting it at risk is doubled to six. For a motorcycle which moves even faster, the number of vehicles putting it at risk may be tripled to 9. All of this is far lower than the theoretical channel capacity of 200 vehicles reception. 
     In addition to receiving the safety-critical messages, device  100  needs to scan the V2X channel to identify vehicles that become safety-relevant and scan slots of their transmissions. Overall, the modem (V2X receiver)  104  implementation disclosed herein can be scaled down to receiving only one or two messages per slot. The reduction of requirements enables shrinking the modem memory and using weaker hardware, with only 5-10% of the capacity of a regular V2X device. That translates linearly to lower power consumption and a smaller silicon area. 
     The limited-reception V2X disclosed presents a first modification vs known reception by obtaining an early indication of specific slot and subchannels reception, by associating the specific slot and subchannels with a safety-relevant vehicle, and by determining early if the slot should be terminated for power reduction. The association between a specific subchannel and vehicle identity is performed during the scan. A second modification enables quickly obtaining energy indication for terminating the remainder of AGC operation if the energy is far below a threshold. With these two modifications, the AGC is the prime gate for packet reception and the most important contributor to power reduction by activity reduction. The AGC is configured by slot filter  122 , which determines an action taken per each subchannel: process, ignore, or scan.
         Process: energy is measured only for the subchannels of the safety-relevant vehicle. If the energy level in those subchannels is too low, the reception is terminated.   Ignore: the slot is not received at all. The AGC is inactivated.   Scan: energy is measured for all subchannels.       

     If the AGC had not stopped packet reception, next, a PSCCH is received by control channel receiver  108 . During a periodic scan, PSCCH operates on the strongest subchannels and L1 ID filter  124  is inactivated. After PSCCH content is processed and parsed, the received L1 ID is used to determine if reception should be aborted as configured by L1 ID filter  124 . The L1 ID filter holds the expected value of L1 ID, as recorded during the scan. If the received L1 ID value does not match the expected L1 ID value, this means the transmitter changed the slot to another slot in proximity. The L1 ID is searched in potential new slots in proximity. Alternatively, if the L1 ID filter matched the expected L1 ID value, the remainder of the slot (the PSSCH) is received by data channel receiver  110  and stored in an embedded memory (not shown) in the device. Known art implementations first store all received data. Only afterwards does a digital signal processor (DSP) start processing. Here, only the PSSCH of the relevant subchannels is stored, for reducing the required memory size, cost, and power. 
     After completion of PSSCH processing, the resulted data is forwarded to security layer  112  which checks (verifies) the authenticity of the data The processing capability of the security layer is scaled down from full line rate capacity (which is typically over 2,000 per second), to the amount of safety of relevant messages for power and area reduction. Scanned packet verification can be skipped, since even a false decision to monitor a vehicle would not prevent the monitoring of safety-relevant vehicles and alerting of the VRU when needed. After the received packet was verified, it is forwarded to V2X stack  114 . The V2X stack is adapted for low-power operation by adding the capability to partially parse a packet, extracting only location fields during the scan, and skipping irrelevant fields during application parsing. 
     The parsed location, speed, and heading fields are forwarded to safety-relevant vehicles controller  126 , which determines which vehicles should be monitored and at what periodicity, based on their potential safety risk, by applying a safety relevancy check. Entries of each slot are stored in a database in controller  126  (not shown). The database contains an entry per 0.5 msec slot in the 100 msec cycle, totaling 200 entries. Each slot entry contains the following fields:
         Vehicle #1: Information on the first vehicle monitored in slot   Subchannel [4-bits]: index of subchannel carrying vehicle #1   Periodicity [2/3-bits]: Representation of vehicle #1 monitoring periodicity: 1, 2, 4, or 8 cycles   L1 ID [24-bits]: ID of vehicle #1   Vehicle #2: Information on the second vehicle monitored in slot   Subchannel [4-bits]: index of subchannel carrying vehicle #2   Periodicity [2/3-bits]: vehicle #2 monitoring periodicity   L1 ID [24-bits]: ID of vehicle #2   HARQ subchannels [10-bits]: bitmap of subchannel indices to ignore during a scan since those contain the second copy of a message that was already supposed to be received from the first copy       

     The database entry suits hardware capable of receiving 2 subchannels in a slot. The number of monitored vehicles should be adjusted according to actual hardware capacity. Slot filter  122  and L1 ID filter  124  receive the respective entry from the database before the beginning of the slot. The slot filter indicates to the AGC unit which subchannel to process. The L1 ID filter provides the L1 ID value to match with the value received in the PSCCH. 
       FIG.  2 A  illustrates general steps of a method for low-power V2X based on early reception termination disclosed herein. In step  202 , a device like device  100  determines, using V2X communications, that a vehicle is a safety-relevant vehicle posing a potential danger to a VRU. In step  204 , the device receives only transmisssions of the safety-relevant vehicle and skips reception of other, non-safety-relevant vehicles, thereby lowering V2X reception power consumption. 
       FIG.  2 B  illustrates a flow chart with more details of the method in  FIG.  2 A . The method basically restricts reception to only messages of safety-relevant vehicles, and terminates reception in other slots (with messages from vehicles that are not safety-relevant) as soon as possible (for example, immediately after the AGC or immediately after control channel PSCCH reception). The operation begins in step  210  every 0.5 mSec slot. Next, in step  212 , slots and respective subchannels allocated for transmissions of safety-relevant vehicles are identified periodically (e.g. every few seconds) by scanning all slots, grading the safety relevance of the vehicle, and selecting the most safety-relevant vehicles for reception. Next, in step  214 , a current slot and respective subchannel identified as allocated to a safety-relevant vehicle and received, or, if a current slot and respective subchannel are not identified as allocated to a safety-relevant vehicle, the reception is skipped. In case a safety-relevant vehicle expected to be found in the received current slot and respective subchannel is not found, in step  216 , the reception is terminated if the subchannel energy received during the AGC is low (for a “low” criterion, see step  506  below), or after reception of the control channel PSCCH if the received L1 ID does not match the expected value. Next, in step  218 , continuing to search for the missing safety-relevant vehicle, a scan of transmissions of the safety-relevant vehicle is performed in proximal slots (i.e. the ID of the safety-relevant vehicle is searched in nearby slots). If the ID of the safety-relevant vehicle is found in a proximal slot, then the database (not shown) in safety-relevant vehicles controller  126  is updated for the next cycle (100 mSec) in which the same slot will be received, i.e. where the safety-relevant vehicle is supposed to transmit again. 
       FIG.  3    illustrates a flow chart for identifying slots and subchannels allocated for transmission of safety-relevant vehicles, i.e. provides details on the operation in step  212 . The operation begins periodically in step  300  in each slot. In step  302 , a check if a periodic scan is due is made by controller  126 . Each subchannel of the slot is scanned periodically. The periodic scan spans all 0.5 msec slots in the 100 msec cycle. The period is set statically, typically between 1 second and 3 seconds. A longer period lowers the power consumption but increases the latency of detecting a danger from an unmonitored vehicle. If a scan is not due, the operation ends in step  320 . Otherwise, if a scan is due, the operation continues to step  304 , where modem  104  is activated and subchannel energy is measured during reception of the AGC symbol (see  801  in  FIG.  8   ). Next, in step  306 , the energy of each subchannel is compared with a threshold by slot filter  122 . The threshold is set as the typical energy received from vehicles 100 m away, for example around −80 dBm. If the energy is lower than the threshold, then the reception is terminated in step  318  and operation ends in step  320 . If the measured energy is higher than the threshold, the operation continues to step  308 , where the control channel PSCCH is received by control channel receiver  108 . Next, step  310  checks if a second copy of the packet (HARQ) is not contained in another slot. If HARQ is contained in the current reception of the control channel, then the reception is terminated in step  318 . If not contained, the operation continues to step  312  where the data channel PSSCH is received by data channel receiver  110 . The location, speed, and direction fields are parsed, while security validation can be skipped, as explained above. Those location, speed, and direction fields are used in step  314  to determine the safety relevancy of the received vehicle, quantifying the potential risk the received vehicle imposes on the VRU. The safety risk for self-VRU is based on two factors, as explained in  FIG.  7   : 
     Time-To-Collision (TTC): The time it would take the received vehicle to reach the VRU. The relevancy increases when TTC is shorter. 
     Perpendicular distance from received vehicle (i.e. the distance of the vertical axis of the road between the VRU and vehicle): when walking as a pedestrian or riding in parallel to vehicle, the shorter the perpendicular distance between the VRU&#39;s future path to the vehicle&#39;s future path, the higher the risk. The calculated risk determines if the received vehicle should be monitored and how often. 
     After the relevancy was calculated in step  314  (see also  FIG.  7   ), and if the vehicle is determined to be indeed a safety-relevant vehicle, then controller  126  adds in step  316  the slot and respective subchannel to the database (not shown) in safety-relevant vehicles controller  126  to process. The operation then ends at step  320 . 
       FIG.  4    illustrates a flow chart for receiving a safety-relevant vehicle, i.e. details of step  214 . The operation begins in step  400 . Next, step  402  checks if the current slot and respective subchannel are allocated to a safety-relevant vehicle. If yes, reception begins in step  404 . If no, reception is skipped in step  406 . Operation ends in step  408 . 
       FIG.  5    illustrates a flow chart for terminating the reception if the received message does not include a transmission of the expected safety-relevant vehicle, i.e. details of step  216 . The operation begins in step  500 . Next, step  502  checks if reception is ongoing. If not, the operation ends in step  518 . If reception is ongoing, the operation continues to step  504 , where the subchannel energy is measured during the AGC symbol. Next, in step  506 , the energy is compared with a threshold, as explained re. step  306 . If the measured energy is lower than the threshold, then the reception is terminated in step  516  and the safety-relevant vehicle is reported as missing. That is, the safety-relevant vehicle that was supposed to transmit in the slot and respective subchannel has selected a new slot for transmission. Next, the operation ends in step  518 . If the measured energy is higher than the threshold, the operation continues to  508 , where the control channel PSCCH is received by control channel receiver  108 . Next, step  510  checks if the received L1 ID is matching the expected value. If not matched, while CRC is good, then the reception is terminated in step  516 . If L1 ID matched, the operation continues to step  512  where the data channel PSSCH is received by data channel receiver  110 . Next, the vehicle safety relevance is updated in step  514 , as was explained in  314 . The operation ends in step  518 . 
       FIG.  6    illustrates a flow chart for scanning for the missing safety-relevant vehicle in proximal slots. The operation begins in step  600 . Next, step  602  checks if the current slot is in proximity to a slot of a missing vehicle. C-V2X specification defines the possible span of slots to select, from −5 mSec (10 slots before) to 15 mSec ahead (30 slots after). If the current slot is not within that range, the operation ends in step  616 . Otherwise, the operation continues to step  604 . The allocated subchannels in the slot are received. In addition, the scan is applied on the strong subchannels in the slot. Next, step  606  checks if the scan identified the L1 ID of the missing vehicle. If no, reception is terminated in step  614 , followed by ending in step  616 . If yes, step  608  receives the data channel PSSCH, step  610  updates vehicle safety relevancy, and step  612  updates the allocated slot and subchannels based on the location in which the L1 ID was found. The operation ends in step  616 . 
       FIG.  7    illustrates a flow chart of vehicle safety relevance calculation, i.e. identification if a vehicle is safety-relevant or not, implemented by safety-relevant vehicles controller  126 . This expands on steps  314  and  514 . The flow chart represents processing a single packet from a single vehicle. The operation begins at step  700  after parsing only certain fields such as location, speed, and heading of a vehicle as relayed in a message. The operation continues from step  702 , which checks if the vehicle is driving away from the VRU. The test can be performed using two different methods. The more reliable method is to compare the current distance between the vehicle and VRU with a previous distance. The second method is to compare the headings of the VRU and of the vehicle. 
     If the vehicle is driving away from the VRU, it has no safety relevance, and the operation ends at step  708 . Otherwise, the operation continues from step  704 . The period for monitoring the vehicle is adjusted based on TTC to lower power consumption. The period is a criterion for safety relevance. If the vehicle is safety-relevant, then the period is short, and the vehicle is received often to track its progress. If the vehicle is not safety-relevant, then period is high, and the vehicle is received rarely (similar to a scan) to track its progress. For example, under 4 seconds the period is adjusted to just 100 msec, under 5 seconds the period is adjusted to 200 msec, under 7 seconds the period is adjusted to 800 msec, and above 7 seconds the subchannel is not monitored. TTC requires prediction of the VRU movement. This can be performed for a motorcycle or a bicycle, but not for pedestrian, for which the current location is used in all predictions. Next, the operation continues from step  706  in which the perpendicular distance is calculated and the period calculated in step  704  is adjusted. If the VRU is pedestrian and, for example, if the distance is greater than 3 meters, the periodicity is doubled, and if the distance is greater than 9 meters the periodicity is quadrupled. For motorcycles and bicycles, the step is performed only if the angle between the heading of the vehicle and the heading of a motorcycle or bicycle is smaller than 10°, meaning riding in parallel. Next, the operation ends at step  708 . 
       FIG.  8    illustrates the low-power reception stages in a limited-reception V2X device like device  100 . As specified, a slot is composed of 13 C-V2X symbols,  801  to  813 . NR-V2X defines multiple slot structure options. For simplicity, the relevant slot structure option shows the processing stages. As explained above, a regular C-V2X receiver stores the data of all symbols in a memory and then processes stored symbols  801 - 813 . In the low-power receiver of a limited-reception V2X device, there are 3 possible reception stages. Each stage operates on specific symbols, as shown by the line boundaries. The first, energy measurement stage  820 , operates on AGC symbol  801  and is performed in real-time without waiting for the subsequent symbols. The reception ends if the measured subchannel energy is too low or if there is a subchannel process. If continuing to the second, control channel stage  822 , this stage receives and processes the PSCCH symbols  802  and  803  also in real-time, to terminate reception as early as possible if the packet needs to be ignored, for example, when the vehicle is not safety-relevant or when a HARQ packet copy is received. The third and last stage, data channel stage  824 , completes the reception of the entire packet using symbols  804 - 813 . 
     It is appreciated that certain features of the presently disclosed subject matter, which are, for clarity, described in the context of separate examples, may also be provided in combination in a single example. Conversely, various features of the presently disclosed subject matter, which are, for brevity, described in the context of a single example, may also be provided separately or in any suitable sub-combination. 
     Unless otherwise stated, the use of the expression “and/or” between the last two members of a list of options for selection indicates that a selection of one or more of the listed options is appropriate and may be made. 
     It should be understood that where the claims or specification refer to “a” or “an” element, such reference is not to be construed as there being only one of that element. 
     Some stages of the aforementioned methods may also be implemented in a computer program for running on a computer system, at least including code portions for performing steps of a the relevant method when run on a programmable apparatus, such as a computer system or enabling a programmable apparatus to perform functions of a device or system according to the disclosure. Such methods may also be implemented in a computer program for running on a computer system, at least including code portions that make a computer execute the steps of a method according to the disclosure. 
     While this disclosure has been described in terms of certain examples and generally associated methods, alterations and permutations of the examples and methods will be apparent to those skilled in the art. The disclosure is to be understood as not limited by the specific examples described herein, but only by the scope of the appended claims.