In communication physical layer means the layer in which the following items occur:

modulation, channel coding, source coding, channel estimation, resource allocation, power calculation..

There is another layer called MAC layer which includes:

QOS, the algorithmes that organize and handle the data transmission of each device in the system over the given channels

In addition to what Radwa answered, in the 7-layer OSI model, the physical layer is layer 1. That's the layer which describes how the bits are transferred over the medium. In the case of satellite, it will typically be PSK, QPSK, or 16-QAM at most, single carrier, to achieve robustness with the least demands on transmit power.

The next layer up in the OSI model is the data link layer, which describes how the data frames are arranged. Such as MAC addresses, the type of frame being transmitted (meaning what the payload consists of), the size of the payload, payload size limits, and frame error checking.

So in principle, one can conceive of a satellite link only being different from other links, such as Ethernet let's say, at layer 1. And all the upper layers, from data link on up to the application layer, being the same. Although frequently, satellite links use MPEG2-TS at layer 2, as opposed to Ethernet or other.

Radwa and Albert summed all. Thanks

Good answers (and correct). But if you are not aware of what the 7 layer model of communication is; the OSI (Open Systems Interconnect) model: study this first. It will help you understand all types of communications systems between machines.

Thank you all for your kind information. I have some idea about OSI model. And I am finding the differences if there any for satellite communications.