# How can satellites serve a large number of devices on earth?

Say we have a LEO satellite. There are 5000 low power devices on earth (They are in the close vicinity, can be served by same satellite) which needs to be communicated with the satellite.

Now my question is:

1) With the number of devices on earth, the number of channels changes so does the bandwidth of operation ? so what is the band of operation in this case ? If after few years the number of devices double then how will satellite expert go on expanding their system?

2) How does the frequency allocation actually works in this case ?

3) How does the satellite respond to the simultaneous queries ?

4) Can we use combination of FDM and TDM for this operation ? or DS-CDMA ? or which is the most suitable standard (Access Method) for this case ?

5) What is the lowest power with which the devices on earth can operate on ?

• This sounds like a homework question, and without all the necessary info - What have you done to solve this yourself? Jun 20, 2017 at 14:20
• @EugeneStyer...I calculated free space path loss (Considering frequency of operation is at 4.2GHz and satellite is at a distance of 400km). I can derive EIRP and with some assumed gains and power even calculate a value for it. The questions which I am asking, came into my mind after being gone through several materials. If you need "Necessary Info" please ask, I will share. Jun 20, 2017 at 14:31
• Please ask one question per post... Jun 21, 2017 at 13:24

for question 1: bandwidth required depends on what kind of communications you want. Telephone can be done in something like 9.6 kbit/s for one device, video needs hundreds of kbit/s.

The satellite (and its ground station) is designed with a certain load in mind (X devices * Y kbit/s), and the satellite owner buys/negotiates enough bandwidth to use this capacity.

When you exceed the design load, there's not much you can do. You can't transmit more data inside your allocated bandwidth without replacing all the devices in the chain ground station-satellite-end user devices.

There's some information on bandwidth allocation here:

Who/What is the international authority to assign/refuse orbit to a satellite/space-craft?

What frequency wavebands are used for communication in LEO?

Not a full answer, but some starting points on the relationship between bandwidth, data load and number of devices:

The Shannon-Hartley theorem gives an upper bound to the amount of data that can be sent over a given bandwidth.

Techniques like Quadrature Amplitude Modulation can be used to transmit more information in a single clock pulse.

• Consider my operation is in IEEE S-band. Jun 20, 2017 at 16:15