III. NETWORK MODEL
A. Node Model
In a laser transceiver system, the volume, weight, manufacturing
and installation difficulty of a receiver antenna
(referred as receiver for short) are much greater than those
of a transmitter antenna (referred as transmitter for short).
Currently, laser nodes only have one receiver but could have
multiple transmitters under current technology. In this case,
how to flexibly utilize the different features of the transmitter
and receiver is our motivation for such a new laser system.
Due to the constraints on the receivers as mentioned before,
we believe it is valuable to study a new node model to expand
the application scenario for future laser networks. Therefore,
we propose a laser node model based on receiver multiplexing
by transmitters.
In this node model, all transmitters and receiver have
independent rotation axes. When a node communicates with
different neighbors, it requires the receiver to point with one of
the transmitters at each neighbor by rotating its axis - a basic
process in APT. Multiple transmitters on a node can share one
receiver, so with a given time, the receiver can point with up to
one transmitter. When the node receives the reply beacon from
its neighbor, it will initiate the pointing and tracking process.
The dominating difficulty in the realization of this node
model is to achieve acquisition and pointing between the
transmitter and receiver within a reasonable time constraint,
which, especially, poses a strict requirement on the sensibility
and responsiveness for axis rotation.
A laser node L is composed by N independent transmitters
TA1 TAN and a receiver RA, which can be formulated as