In an automotive prototype, having a telemetry system is of great importance since it allows measuring and recording its behavior under real operating conditions. For this reason, a telemetry system was developed, composed of hardware and software stages. For the system's development process, first, the variables to be measured were defined, and the data transmission networks and communication stages were chosen. Both the RF communication cards and the 915 MHz band were chosen.
For this application, we use data packet formats, communication protocols, encryption algorithms, and Red Solomon coding to increase the transmitted data's reliability and efficiency. The radio system developed comprises a transmitter chipset (CC1101), coupling networks, amplifiers, duplexers, and an antenna (see Fig. 1). The transfer of information to the transmitter and receiver card is done through the CAN 2.0 protocol and the telemetry card, as shown in Fig.1.Transmitter and receiver card Figure 2.
using chip CC1101.
Communication protocol CC1101
The information packets coming from the CAN bus are transferred to the RF module via SPI protocol. The captured information is stored in registers depending on the packet type. These packets are assigned an identification command,
Fig.2. Control card of transmitter and length, and CRC16 polymode, encrypted using AES. After
the receiver based on chip CC1101 passing through this process, the packets are separated into
128-byte blocks. Each block is encoded using Reed Solomon, forming three blocks of 160 bytes to which an identifier is assigned. The new block encoding is transferred via SPI to the chipset in 256-byte blocks. The maximum data buffer size of the CC1101 is 256 bytes.
At the hardware level, the telemetry system has the following characteristics:
- Modulation type: 2-FSK.
Communication technique: FHSS 510 hops/s.
- ∆f = 80 KHz.
- Fc = 915 MHz.
- Rb = 125 kbps.
- Modulation index: 0.64.
- Channel frequency: 200 kHz.
- Number of channels 16.
- Minimum output power: +0dBm.
- Maximum output power: +27dBm.
- Sensitivity: -86.5 dBm.
- Network losses: 2dB.
- Free space losses 97.748dB.
- Maximum range: 1Km
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