Mumbai University > Computer Engineering > Sem 6 > Mobile Communication & Computing

Marks: 10 Marks

Year: Dec 2016

Handovers in satellite networks can be broadly classified as follows:

• Link-Layer Handover:

Link-layer handover occurs when we have to change one or more links between the communication endpoints due to dynamic connectivity patterns of LEO satellites. It can be further classified as:

1. Spotbeam Handover: When the end-point users cross the boundary between the neighboring spotbeams of a satellite, an intrasatellite or spotbeam handover occurs. Since the coverage area of a spotbeam is relatively small, spotbeam handovers are more frequent (every 1–2 min)

2. Satellite Handover: When the existing connection of one satellite with the end user’s attachment point is transferred to another satellite, an intersatellite handover occurs.

3. ISL Handover: This type of handover happens when interplane ISLs would be temporarily switched off due to the change in distance and viewing angle between satellites in neighbor orbits. Then the ongoing connections using these ISL links have to be rerouted, causing ISL handovers

Network-Layer Handover:

When one of the communication endpoints (either satellite or user end) changes its IP address due to the change of coverage area of the satellite or mobility of the user terminal, a network or higher-layer handover is needed to migrate the existing connections of higher-level protocols (TCP, UDP, SCTP, etc.) to the new IP address. This is referred to as network or higher-layer handover. Three different schemes can be used during this call transfer process They are:

1. Hard-handover schemes: In these schemes, the current link is released before the next link is established.
2. Soft-handover schemes: In soft handover schemes, the current link will not be released until the next connection is established.
3. Signaling-diversity schemes: These are similar to soft handover, with the only exception that, in signaling diversity schemes, signaling flows through both old and new links and the user data go through the old link during handover.

Several additional situations for handover in satellite systems compared to cellular terrestrial mobile phone networks caused by the movement of the satellites:

Intra Satellite Handover

• Handover from one spot beam to another
• Mobile station still in the footprint of the satellite, but in another cell

Inter Satellite Handover

• Handover from one satellite to another satellite
• Mobile station leaves the footprint of one satellite

Gateway Handover

• Handover from one gateway to another
• Mobile station still in the footprint of a satellite, but gateway leaves the footprint

Inter system handover

• Handover form the satellite network to a terrestrial cellular network
• Mobile station can reach a terrestrial network again which might be cheaper, has a lower latency etc