Re: [Discuss-gnuradio] shared SDR receivers at repeater sites

[Daniel Pocock]

On 04/02/16 21:10, Derek Kozel wrote:
> I believe that Daniel's use case is to have an SDR receiving the
> entirety of a band of interest, and sending those samples, pre any
> processing, to multiple remote users. The concern with just
> instantiating N udp streams is that it doesn't scale for wide bands and
> large numbers of users.
> 
> Merging multiple remote user's transmit streams into a single tx stream
> is of course another problem.
> 


To give a more specific example:

a) SDR device sampling the 2 meter band (144 - 148 MHz), this input
range is locked and can't be changed by users

b) using something like the USRP B200
- it can do 61 Million samples/sec, 12 bit samples, 732 Mbit/sec
- but maybe that sample rate is not needed for a band that is 4 MHz wide...

c) an instance of GNU Radio taking all the samples and encapsulating
them into packets

d) transmitting to local users
layer 1/physical: 23cm or 13cm, using 8 - 10 MHz bandwidth
layer 2: AX.25 (with repeater callsign)
layer 3: IP multicast (UDP packets)

e) Receiving stations would receive the UDP multicast packets and feed
them as input to a flow graph in a local instance of GNU Radio

I can imagine there may be risks with packet loss and the receiving
users may need directional antennas.  As it would be a licensed amateur
repeater, it would be able to legally put out more watts than a wifi
router though.

Regards,

Daniel