Satellite Communication

NetSim satellite library simulates end-to-end, full stack, packet level communication between terrestrial nodes and Geostationary satellites. Geo satellites have the unique property of remaining permanently fixed in exactly the same position in the sky as viewed from any fixed location on Earth. This means ground-based antennas do not need to track them but can remain fixed in one direction. These satellites have orbital period that is the same as Earth’s rotation period and are the most common type of communications satellites.

NetSim Satellite Communication

The Satellite MAC layer protocol supported in NetSim is TDMA for forward link and MF-TDMA for return link (based on the DVB S2 standards). The forward link is in the Ku band (12 – 18 GHz) while the return link is in the Ka band (24 – 60 GHz).

The satellite can be thought of as a relay station. It operates on the bent-pipe (transparent star) principle, sending back to Earth what comes in, with only amplification and a shift from uplink to downlink frequency.

The PHY layer models include:

  • Channel model: Friis free space path loss with Loo Markov fading model
  • Modulation: QPSK, 8PSK, 18APSK, 16QAM, 32APSK with appropriate coding rates
  • Tx, Rx Antenna gains
  • Antenna gain to noise temperature

All the choices of transport protocols, and all types of applications in unicast mode can be run.

In NetSim, the satellite communication network library interfaces with Internetworks library. This means users can connect Satellite gateway and User Terminals to devices such as Routers, Switches and Wired nodes.

Modulation and coding schemes supported

  1. QPSK with coding rates 1/3, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9, 9/10
  2. 8PSK with coding rates 3/5, 2/3, 3/4, 5/6, 8/9, 9/10
  3. 16APSK with coding rates 2/3, 3/4, 4/5, 5/6, 8/9, 9/10
  4. 16QAM with coding rates 3/4, 5/6
  5. 32APSK with coding rates 3/4, 4/5, 5/6, 8/9

Propagation

The distance between the ground nodes and the satellite determines the propagation delay and path loss of the radio signal. The distance is computed based on the cartesian distance between the ground nodes and the satellite. NetSim computes the propagation delay of the radio signal traveling from the source node to the destination node at the speed of light. The propagation model calculates the weakening of the radio signal as it propagates from the source node per the pathloss and fading model.

  1. Pathloss: Friis Free Space
  2. Fading: Three state Markov process obeying the Loo distribution

Protocol Source C Code

NetSim’s protocol source C code shipped alongwith (standard / pro versions) is modular and customizable to help researchers to design and test their own sat-com protocols.