AAUSAT3 - AIS1

AIS1 is a hardware AIS receiver based on an ADF7021 series integrated radio serviced by a AT90CAN128 at 8MHz clock. The receiving frequency an radio configuration can be reconfigured on the fly.

The AIS1 hardware consists of

• An ADF7021 radio front-end which delivers a 9k6 bit stream through a SPI interface to...
• an AT90CAN128 which as the first steps carry out
  • Trainings sequence detection - when applicable
  • HDLC frame detection - <flag> <data> <crc> <flag>
  • NRZi decoding and bit de-stuffing
  • and last AIS frame validation (CRC-16)
• FreeRTOS OS and CSP network

Frames are fully stored as they are received according to selected filters and a flash storage system preserves information for later download.

The AIS1 subsystem is developed to be capable of running even with a damaged flash system(radiation). AIS1 can be configured to only receive inside a specific area of interest. To limit the amount of downlink data it is possible request only one AIS message per ship instead of downloading all received data.

AIS - Automatic Identification Systen

AIS is transmitted in the in the VHF maritime band on two channels around 162 MHz which is reserved for the AIS communication purpose worldwide. The transponders on ships and goundstations are developed to transmit either in high or low power mode according to the AIS transceiver class (A or B). The high power mode is transmitting with 12,5 W and the low are when transmitting with 2 W. The AIS system uses different types of of the TDMA scheme and are transmitted with 9600 baud. Standard messages are 168 bit of data(not including HLDC frame, training etc.) which gives 2250 standard slots a minuet per channel.