Dynamic Channel bandwidth allocation

GNU Radio
1

So, I’m trying tomake a system where nodes communicate, not on set
channels,
but on as much of the spectrum as they can use based on the level of
interference. For example, we know that 802.11 divides the spectrum into
13
channels with the center frequencies set at 5MHz apart. In my ideal
situation, a network with only two nodes would be able to use the entire
spectrum to send data, a network with 4 nodes and two transmissions
would
divide the spectrum in half for each transmission, and so on and so
forth.

In order to do this, I need to be able to scan for interference at
specific
channels/frequencies to determine whether or not they’re available.
Before I
get too deep into the project, is this even possible with the USRP
motherboard and the RFX2400 transceiver board? I know we have the RSSI
circuit onboard, but I don’t know on which frequencies it scans.

-Michael F.-

2

Michael F. wrote:

specific channels/frequencies to determine whether or not they’re
available. Before I get too deep into the project, is this even
possible with the USRP motherboard and the RFX2400 transceiver board?
I know we have the RSSI circuit onboard, but I don’t know on which
frequencies it scans.

The RSSI on the motherboard will tell you the power within approx. +/-
15 MHz from your carrier. You can also get a digital RSSI which will
tell you the power within your signal of interest.

Matt

3

Matt,

I’ll actually want to be able to control how far I can detect
interference
from my carrier, and the carrier I’ll be detecting interference from. Do
I
have no choice but to cover ~30Mhz at a time?

-Michael F.-

4

The way we have envisioned RSSI is as a 3-part measurement:
Analog RSSI
Digital RSSI in FPGA (from output of ADCs)
Digital RSSI in host (computed however you like, from the
channelized signal sent over the bus by the USRP)

If you want to use the measured analog RSSI, it will measure whatever
passes through the analog channel filter. You can only change that
bandwidth by changing inductors and capacitors.

Note also that analog RSSI is only on the RFX900, RFX1200, RFX1800, and
RFX2400. The RFX400, TVRX, and DBSRX do not have that capability.

Matt

5

If I can’t change the bandwidth covered, that’s okay, as long as I can
be
confident in that the analog RSSI will cover the constant ~30MHz that
you
say it does, and that I can cover different ~30 MHz chunks based on what
I
set the carrier frequency to be.

-Michael F.-