I want to send message from one embedded system to another embedded system, like from one car to another without using phone number. just turn on the wifi.. connect and send message. There are ways to to send text to phone but not this kind of texting? Iam short of time. I only need to know what will be required to do this ? PLease help
You can use ESP8266 modules( like Wemos d1) for wifi connections. The good thing about those are that they are also programmable and you can use arduino IDE to program. You can get two of those and make first one a server/host and second on a client for connection. There is more options of course: Bluetooth, RF link etc. Google "short distance connection arduino"
ESP8266 WiFi Module is a WiFi serial transceiver module, based on ESP8266 SoC. This chip implements a full TCP/IP protocol stack and the very interesting feature is that it has also a great computational power onboard. You can easily program it using Arduino IDE. You can buy this development boards in town market and its very low cost also.
Bluetooth/BLE4.0 Bluetooth is a type of wireless communication used to transmit voice and data at high speeds using radio waves. It is a standard protocol for short-range radio communications between many different types of embedded devices. Devices need to be within approximately 10 meters of each other, and the typical data transfer rate is around 2 megabits per second (Mbps).
These two are the most preferable for shorter distance communication.