Design and implementation of a v2x tag for iot based smart on street parking system

The test results show that, with low power consumption, the V2X-Tag proposed in this paper is suitable for use in IoT systems such as street parking management systems.. Therefore, when

Design and Implementation of a V2X-Tag for IoT-Based Smart On-Street Parking System

1st Vinh Tran-Quang, Member, IEEE,

School of Electrical and Electronic Engineering (SEEE)

Hanoi University of Science and Technology, Vietnam

vinh.tranquang1@hust.edu.vn

2nd Duc Nguyen-Dinh School of Electrical and Electronic Engineering (SEEE) Hanoi University of Science and Technology, Vietnam

duc.nd167138@sis.hust.edu.vn

Abstract—In this paper, we propose to design and develop

a device called V2X-Tag with compact dimensions suitable

for mounting on vehicles such as cars, allowing these cars to

communicate with each other through a mobile cellular network

We also develop firmware for the V2X-Tag and propose a

communication protocol between the V2X-Tag and Server We

also built prototypes of the V2X-Tag and tested these devices in a

smart street parking management system The test results show

that, with low power consumption, the V2X-Tag proposed in this

paper is suitable for use in IoT systems such as street parking

management systems

Index Terms—C-V2X-Tag, IoT system, mobile communication,

parking system, wireless network

I INTRODUCTION

V2X stands for Vehicle to Everything, is a communication

system that supports the exchange of information between

vehicles and other entities in the system that can affect

vehicles such as other vehicles, traffic lights, infrastructure,

or any entity equipped with V2X technology [1], [2] The

goal of V2X technology is to improve road traffic safety,

save energy, and improve traffic efficiency Communication

between entities in the system requires high accuracy and

reliability By sharing information, such as speed and direction

with objects around the vehicle, V2X technology improves the

driver’s awareness of potential hazards on the road, helping

the driver to know and be aware of the traffic situation ahead,

helping to minimize the possibility of traffic accidents [3],

[4] The obvious benefits of the V2X technology are alerting

drivers of upcoming road conditions, suggesting alternative

routes to avoid traffic congestion, and identifying available

street parking The V2X technology is developing in two

directions [2], [5]: V2X based on the LTE/5G mobile

commu-nication network infrastructure (C-V2X) and V2X based on

IEEE802.11p technology (DSRC) [6] In particular, C-V2X

technology [7], [8] is considered the strongest development

direction in the future, especially when 5G technology will

be used as an inevitable trend in the 4.0 era However, in

Vietnam, up to now, the 5G network is still in the research

and development stage and has not yet provided commerce

services Therefore, in this paper, we choose the C-V2X

technology based on the LTE mobile communication network

to develop a V2X tag mounted in the car, which serves as a

smart parking management system on the street Developed

for both short-term deployment and long-term development,

C-V2X is flexible enough to support both today’s use cases and future use cases Compatible with 4G and 5G mobile networks, it is designed to be scalable and interoperable Over time, C-V2X will support advanced driver assistance systems (ADAS), where vehicles can cooperate, coordinate, and share the information collected by sensors and ultimately drive the connected vehicle autonomous vehicle (CAD) [1]–[3], [9]

In this paper, our aim is to design and develop a device called V2X-Tag with compact dimensions suitable for mount-ing on vehicles such as cars, allowmount-ing these cars to commu-nicate with each other through a mobile cellular network At the same time, we also develop firmware for the V2X-Tag and propose a communication protocol between the V2X-Tag and Server We also built prototypes of the V2X-Tag and tested these devices in a smart street parking management system (sParking) The actual test results show that the V2X-Tag works well and meets the designed technical requirements, providing accurate information about parking location (parking slot), parking time, vehicle identification, etc., serving the functions of parking management, parking space notification, route navigation, and service charge

II LTE-BASEDV2X-TAGHARDWAREDESIGN

A Technical Requirements

To manage the smart parking spot system on the street, registered cars that use the service will be fitted with a V2X-Tag device Since the V2X-tag device uses the vehicle’s power via the USB port, when the vehicle is turned off, the device’s power supply is cut off Therefore, when the vehicle enters / exits the parking spot, the user needs to press the register / release button on the device to confirm the time to start using the parking slot or end using the parking slot When the register/release button on the tag is pressed, the tag will send user information (including the tag’s ID, the time to start using the slot / time to end the use of the slot, the location of the slot, etc.) to the system via the 4G LTE module Requires the V2X-Tag to be equipped with a touch-sensitive button to communicate with the user The user will press and release this button to notify the car entering the parking slot and hold the button (about 1.5 seconds) to notify the car out of the parking lot The V2X-Tag will have two main data transmission interfaces: transmitting and receiving data

by SIM7600 [10] module and by WiFi via ESP32 module

The ESP32 module in V2X-Tag acts as the main controller of

the tag and plays the role of transmitting and receiving data

The V2X-Tag is time-synchronized via LTE network and is

located using the built-in GPS receiver on the SIM7600CE

module The management center (Server) will listen for socket

connection requests to receive messages from V2X-Tag, save

them in the database, process the messages, and return ACKs

for the tag with the respective use cases application The server

data are accessible by authorized user applications Such data

may be used by third parties to analyze, design, and develop

related applications V2X-Tag uses a 5V USB power source

that plugs directly into the car, so it requires a compact

V2X-Tag design and saving power consumption The V2X-V2X-Tag is

plugged into the car, so it will likely affect the GPS data

capture function, so Tag needs to design a loose

V2X-Tag cover, leaving the GPS antenna part open to minimize the

case of failure to get GPS

In summary, the technical requirements for V2X-Tag in this

project include:

• Has touch buttons and status LED

• Communicate with Server via LTE/WiFi

• Has GPS navigation

• 5V USB power supply

• Compact size, suitable for car mounting

B Block Diagram Design

With the above functional requirements, we propose a

general diagram of the LTE-based V2X-Tag, as shown in

Figure 1, consisting of the following main blocks:

• Power block: The device’s power block performs the

function of converting 5V power from the USB

connec-tion port to lower voltage levels such as 3V3 and 3V8

The power block is required to operate stably and meet

the necessary amperage for the operation of hardware

modules

• Communication block: The communication block uses

the SIM7600CE module to send/receive data between the

system and the device The main function of the LTE

radio communication block in V2X-Tag is to send user

data and receive system control commands In this paper,

we use the SIM7600CE module of SIMCOM [10] The

SIM7600CE module has the appropriate specifications for

V2X-Tag in the smart parking system

• Control block: The control block uses the ESP32

mi-crocontroller, which controls the reception of user data,

encapsulates data, controls the LTE module, and performs

control of the device’s operations At the same time, it

also plays the role of a WiFi communication module

• User interaction block: This block includes one touch

button and LEDs that show device status (status of

4G-LTE and WiFi, GPS, and parking register or release),

parking suggestion, parking confirmation

Within the scope of this paper, we do not present the detailed

schematics of the V2X-Tag’s principle design

USER Interface

LED state, Button

MCU

ESP32-D0WDQ6

LTE MODULE

SIM7600CE-M1S

Power Supply

Fig 1 Block Diagram of the V2X – Tag.

C Design Layout and Sample Product Images Due to the compactness requirements of the V2X-tag, we design the V2X-Tag board as two separate subboards and then connect them on top of each other via jumps

• MCU & Touch sub-board: includes ESP32, buttons, LED status display, flash, shift level IC, and 5V power con-verter block from the USB port in the vehicle to 3V3

• 4G & Power sub-board: includes SIM7600CE module, 5V to 3V8 power converter block

The PCB layout image and the 3D product image from the design software are shown in Figure 2 Figure 3 is the image

of the V2X tag prototypes after they are manufactured and assembled

III COMMUNICATIONPROTOCOLBETWEENV2X-TAG

ANDSERVER

A Design Message Structure

We propose to design the message structure and commu-nication protocol between the V2X-tag and the monitoring center (Server) as follows The server and the V2X-Tag device exchange information with each other using encrypted TCP/UDP packets through the LTE SIM7500E module The maximum packet size is 64 bytes, consisting of two parts: SIGN (header) and MESSAGE as depicted in Figure 4 and Table I To determine whether the message exchanged between the V2X-tag and the Server is a data message or an ACK message, we rely on the MTI (Message Type Identifier) field

as defined in Table II To reduce transmission costs and save energy, the data packet is transmitted only according to events when a vehicle approaches the parking slot or leaves the parking lot Data messages with payload containing the information described in Table III The entry / exit status

of the parking slot or the server processing status will be encapsulated in the STATE field as defined in Table IV and Table V, respectively

B Operation Mechanism Communication on V2X-Tag is designed to be event-driven When connecting the V2X-Tag to the 5V power source via the car’s USB port, the LED LTE and LED GPS RED lights are turned on and the SIM7600 module starts During the booting process, LED LTE will blink continuously and will only stop blinking when the SIM module is successfully started The

Top layer Bottom layer

Fig 2 The PCB layout of (a) 4G & Power board and (b) MCU & Touch board.

Fig 3 Image of the V2X tag prototypes.

SIGN

SEQ

(4 bytes) (1 byte)MTI (15 bytes)ID/IMEI (40 bytes)DATA

LAT

(11 bytes)

DATA

(1 bit) (1 bit)ACK

Undefine Value

(6 bits) (12 bytes)LONG (8 bytes)DATE (8 bytes)TIME (1 byte)STATE

Fig 4 Message Structure (RAW DATA).

device is then ready to operate V2X-Tag will search for WiFi

access points every 5 seconds If V2X-Tag can connect to

WiFi to access the Internet, the LED WiFi will light up and

TABLE I

D EFINES THE STRUCTURE OF MESSAGES EXCHANGED BETWEEN

V2X-T AG AND S ERVER (LTE P ACKET ).

Field Name Description Length (bytes) SIGN Mark the start of the message 4 SEQ Sequence number of messages 5 MTI Specify Data/ACK message type 1 ID/IMEI Device ID or IMEI string 15

the LED LTE light will turn off (preferably using WiFi to transmit and receive data) The status of the LEDs on the V2X-Tag and their meanings are defined as shown in Figure 5 The operation flow of the V2X-Tag in the smart parking

TABLE II MTI FIELD DEFINITION

Bit Order Description Sending Direction

0 ACK: Acknowledgment Downlink (Server to V2X-Tag)

1 DATA: Send data Uplink (V2X-Tag to Server)

TABLE III DATA FIELD DEFINITION

Field Name Description Length (bytes)

STATE Processing status (depends on MTI) 1

TABLE IV

D EFINES THE STATE FIELD OF UPLINK (V2X-T AG TO S ERVER ).

STATE Description

0 Vehicle exit notification (slot release / unoccupied)

1 Vehicle entry notification (slot register / occupied)

TABLE V

D EFINES THE STATE FIELD OF DOWNLINK (S ERVER TO V2X-T AG ).

STATE Description

0 Vehicle exit parking slot

1 Vehicle entry parking slot

2 V2X-Tag is not registered in the system

3 Parking slot are not in the system

system is described in Figure 6

As shown in Figure 6, the operation of V2X-Tag in the

IoT-based smart street parking system is divided into 2 phases: the

search for space and the drive into the parking lot (VEHICLE

IN) and the exit from the parking phase (VEHICLE OUT)

VEHICLE IN: Register parking slot process:

• When there is a need to park on the street, the user,

with a V2X-Tag device registered on the system and

connected to the car’s USB power port, opens a sParking

application on a smartphone (the sParking application

is not present in this paper) to search for the nearest

available slot When the user approaches the parking

slot, the V2X-Tag compares its GPS coordinates with

the coordinates of the parking slot that is predefined

in the parking spot management system If it matches,

the device will issue a parking confirmation message

by turning the LED GPS GREEN status to green and

waiting for the user to confirm

• When LED GPS GREEN is on, the user presses and

RED: active LTE (no WiFi) BLUE: WIFI ON (inactive LTE)

GPS_BLUE: good GPS signal GPS_RED: no GPS

LED_PARK_REGISTER LED_PARK_RELEASE

Fig 5 LEDs status on the V2X-Tag and their defined meanings.

SIGN, SEQ, MTI, ID, STATE

SIGN, SEQ, MTI, ID, LAT, LONG, DATE, TIME, STATE SIGN, SEQ, MTI, ID, STATE

SIGN, SEQ, MTI, ID

VEHICLE IN

[parameters]

VEHICLE OUT

[parameters]

CLICK IN

CLICK OUT LED NOTIFY

LED NOTIFY

SIGN, SEQ, MTI, ID, LAT, LONG, DATE, TIME, STATE

SIGN, SEQ, MTI, ID

Fig 6 The operation flow of the V2X-Tag in the smart parking system.

releases the register/release button on the V2X-Tag, LED PARK REGISTER will flash continuously for 1 second, indicating that the user has pressed the request button, a data message will be generated and send it to the server The data message includes the device’s ID, vehicle location, the date, and time of sending

• Server receives the data message sent from the V2X-Tag, will authenticate the user, and checks the validity of the received message Next, the Server will generate and send

an ACK message to V2X-Tag for confirmation During

a predefined timeout period, if the tag receives an ACK message, LED PARK REGISTER will turn on, meaning parking is successful V2X-Tag saves GPS location and other status information to its internal memory If no ACK is received the LED PARK REGISTER will turn off The user needs to press the touch button to send the parking request again

VEHICLE OUT: Release parking slot process:

• When the user starts the vehicle engine, the V2X-Tag

is also booted and reloaded with the previous status information (parking success status)

• To end the parking session, the user presses and holds the register/release button for about 2 seconds, the LED PARK RELEASE light will flash continuously for

3 seconds to confirm that the user has just pressed the request button to get out of the parking lot, a data message

will be generated and send to the Server including the

ve-hicle location, the date and time of sending the message

If sending is successful, LED PARK RELEASE will be

lit If it fails, the LED PARK RELEASE will turn off

Users must press the touch button to send a request to

end the parking session again

C Data Processing Procedures

The data processing process is shown in Figure 7 In which

the main functions/procedures to process data include:

• secure_encrypt(): Encrypt the data block to be sent

with the predefined secret key “sPKGPWD”,

correspond-ing to each device With V2X-Tag, the key is stored in the

firmware of the V2X-TAG In Server, the key is stored

in the database The authentication function checks the

secret key match in V2X-Tag and Server

BASE85 method to convert all binary data to text, suitable

for communication with the GSM/GPRS/LTE modem

• pack_data(): Pack data according to the LTE Packed

standard

• send_data(): Procedure for sending data

• receive_data(): Procedure for receiving data (which

is an LTE packed block)

method to convert data from text to binary

• secure_decrypt(): Decryption with the secret key

“sPKGPWD”

• process_data(): Process the original data received

DataParked

(RAW Pack)

Encrypted

(ARC-4)

Text

(Base 85)

Encrypted

(AES)

LTE Packed

(Send)

LTE Packed

(Received)

Decrypted

(AES)

Text

(Base 85)

Decrypted

(ARC -4)

DataPacked

(RAW Pack) (a) Process of sending data

(b) Process of receiving data

Fig 7 Process of handling data sent/received via LTE Module.

D Flowchart of the V2X-Tag Communication Algorithm

The V2X-Tag device in the sParking system uses the 4G

LTE communication standard to exchange data with the server

The flowchart of the V2X-Tag communication algorithm is

illustrated in Figure 8 The following events will trigger

V2X-Tag to send packets to the Server:

• The device enters the parking lot

• The device leaves the range of the parking lot

• The user presses the register/release parking button

At the end of the data sending phase, the device establishes

a receive window for a pre-configured fixed period of time to

wait for an ACK or ACK + CMD response from the Server

If the timeout period has passed but the ACK has not been

received, the device will proceed to re-send the packet The

device receives the message within the timeout period, and it will proceed to process the packet The device first checks the SIGN (@V2X - Device Identifier), and ID/IMEI (Device Iden-tifier), CMD ID (MTI) fields The communication between the device and the server will end when the V2X-Tag sends an ACK packet to the server

Start

New period has started

Normal State

Event?

Start Rx, Wait for ACK

Msg?

Cond?

Time out?

Decrypted Data Excute & send ACK

New period has started End

SIGN?

ID/IMEI?

MTI?

YES YES

NO NO

NO

Register/

Release?

YES

Packing Data

Start Tx, Led warning

STATE?

Encrypted Data

Fig 8 Flowchart of the V2X-Tag Communication Algorithm.

IV TESTRESULTS

A Power Consumption Evaluation The power consumption tests of the V2X-Tag used a GW Instek GPS 4-channel DC output power supply (30V, 3A, 4CH) When starting to supply 5V power to V2X-Tag, the SIM7600 module performs network registration This is the highest power consumption process of V2X-Tag, the mea-sured current is 280mA Power consumption is P = U I =

5 × 0.28 = 1.4W After successful network registration, the current consumed in the V2X-Tag will gradually decrease to the waiting state for user interaction At this time, the power consumption of V2X-Tag reaches the minimum value; the measured current consumption is 40 mA Power consumption

is P = U I = 5 × 0.04 = 0.2W When the user starts interacting with the V2X-Tag by pressing the touch button,

the process of sending a confirmation message will be sent

to the server and waiting for the ACK message This process

consumes more power than the standby state, the measured

current value is 120 mA, corresponding to the power

con-sumed in the active state (sending/receiving data) of V2X-Tag

is P = U I = 5 × 0.12 = 0.6W

B Field Test Results

The experimental deployment takes place at the parking lot

location at latitude 21.192401, longitude 105.825735 Parking

radius is 200 meters along the street As the LED signaling

system function is described in Figure 6, the LED status after

it has been started and GPS data has been obtained is shown

in Figure 9 (a) The WiFi light is green, the GPS light is on,

and the LED that has not sent the vehicle is red

Fig 9 Image of V2X-Tag in action during a field test: (a) Standby state when

GPS position is obtained, (b) Successfully sending a start parking request, and

(c) Successfully sending a stop parking request.

STT SysTime SIGN SEQ MTY ID LAT LONG DATE TIME STATE

263 27-06-2021 23:26:16 @V2X 5 1 000000000012345 21.19247442 105.82557962 28/06/21 06:26:16 1

STT SysTime SIGN SEQ MTY ID LAT LONG DATE TIME STATE

264 27-06-2021 23:37:08 @V2X 6 1 000000000012345 21.19247442 105.82557962 28/06/21 06:37:08 0

263 27-06-2021 23:26:16 @V2X 5 1 000000000012345 21.19247442 105.82557962 28/06/21 06:26:16 1

(a) Register parking request message

(b) Release parking request message

Fig 10 Register/Release parking request message exchange between

V2X-Tag and Server.

the LED state before when the car engine was turned off

After entering the parking lot, to send a parking request, the

user presses and releases the touch button on the V2X-Tag, a

message will be sent to the server as shown in Figure 10

(a) After successful sending, an ACK message from the

server returns the V2X-Tag to confirm that the server has

received the message At the same time, on the V2X-Tag, the

LED PARK REGISTER will turn off, and the LED PARK

RELEASE will turn green (Figure 9 (b)) At this time, the

user can completely turn off the engine and get off the car,

the parking status, as well as the parking position will be

saved in the EEPROM memory The process of taking the

car out is the opposite of the parking process, the user starts

the car, V2X-Tag will get the data in the EEPROM to set

The user will press and hold the touch button on the V2X-Tag for about 1.5 seconds to send a request to confirm the removal of the vehicle, a message will be sent to the server as shown in Figure 10 (b), message number 264 After successful registration, an ACK message from the server returns the V2X-Tag to acknowledge the server has received the message At the same time, on the V2X-Tag, LED PARK REGISTER will turn off, and LE PARK RELEASE will be red (Figure 9 (c)) The sending process is over

V CONCLUSION

In this paper, we have proposed the design and proto-type manufacture of the V2X-Tag, proposed to develop the firmware, and design the radio communication protocol for the V2X-Tag device V2X-Tag prototypes have been tested and evaluated for power consumption, communication, and parking registration, parking release activities in the on-street smart parking management system The test results show that, with low power consumption (0.2W in standby mode and 0.6W in data sending/receiving mode, respectively), the proposed V2X-Tag is suitable for use in IoT systems such as street parking systems The proposed V2X-Tag is also suitable for extending use to other V2X applications in the future

ACKNOWLEDGEMENT

This work was supported by Vingroup Innovation Founda-tion (VINIF) under Project VINIF.2019.DA16

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