Tip:
Highlight text to annotate it
X
Hi, my name is Erik Luther, I'm an SDR manager here at National Instruments, and we're at
NIWeek 2013. I'd like to show you an ALOHA MAC demo using the USRP, which is a low-cost
software-defined radio platform that's great for both teaching and research. In this particular
demo, we have three different USRPs, and the reason we've got three is we actually want
to create a network between these three different devices so that they can all send one another
information. To do that, we've actually written one LabVIEW VI that runs exactly the same
code on each one of the three devices. I'll go ahead and run my application, and it's
going to open up three windows. All three of these windows are showing exactly the same
VI, but each one has its own place and memory and is talking to its own USRP device. This
represents a traditional network, an ALOHA MAC is a famous MAC. You can actually look
it up online to learn more information about the ALOHA MAC. There are two different types
of MAC architectures. The MAC is the next layer up above the physical layer. An ALOHA
MAC is designed for collision correction. There are two different types of MACs. The
first one is called collision avoidance, so you would typically detect whether signals
were apparent and only transmit when there was free space. An ALOHA MAC is actually collision
recovery. If there's a collision between packets, it will actually retransmit. The way it achieves
that is it transmits a packet and waits for an acknowledgement before it sends the next
packet. To show that in action, we can actually choose a different device. They all have IP
address references. We're going to transmit from this device to this device, so transmit
on 10.4 and receive on 10.2. We can change our data, which is a picture, and we can go
ahead and transmit that data. You'll see that transmitted down here. So you see the tree
was transmitted to this device. We can actually transmit from this device to this device,
and from this device to this device at the same time and actually create packet collisions,
and whenever a packet collision occurs, it will detect that collision and retransmit
that packet until the entire message has been transmitted. So we want to send to 10.4 from
this device, which is 10.3. We want to send it to 10.2. So I can go ahead and press "send"
and we actually see packet collisions taking place. Eventually that image will be transmitted
to the other device once all of the packets arrive at the destination successfully. I'm
glad you were able to see our demo. Enjoy more of the great demos at NIWeek 2013. To
learn more about the software-defined radio products, visit ni.com/sdr.