'Full-duplex' wireless could double network throughput, and vendors are taking notice

with Ashutosh Sabharwal, an associate professor of electrical and computer engineering at Rice
with Ashutosh Sabharwal, an associate professor of electrical and computer engineering at Rice

Last week researchers at Rice University in Houston announced a breakthrough in wireless technology called "full-duplex." In theory, it would allow mobile operators to double the throughput in their networks without adding any cellular towers by enabling devices to send and receive data at the time and on the same frequency. FierceWireless Editor Phil Goldstein spoke with Ashutosh Sabharwal, an associate professor of electrical and computer engineering at Rice and one of the lead researchers on the topic, about the technology, what it means for wireless carriers and how it might be incorporated into wireless standards.

Fierce: How did you and your team develop full-duplex?

Ashutosh Sabharwal: It's a difficult question, because we are academic researchers, always trying to push the boundaries of what can be done. Maybe why we could do it would be an easier one. We used this open-source platform called WARP [wireless open-access research platform], which allows us to make and break different kinds of configurations on radios. We built every piece of it. It's something that's open source and other researchers use it now. So that allowed us to ask questions and say, let's reevaluate this assumption, or what if we do this. We can ask a lot of "What if?" questions, which you can't ask otherwise if you don't actually have access to such a reconfigurable test platform.  

Fierce: How long did the development of the full-duplex technology take?

Ashutosh Sabharwal: From the inception it was somewhere in 2009 when we first started asking this question. We did very preliminary tests in the lab. And it was encouraging. But those were very controlled tests. Then we set up our first elaborate test and we published it in 2010. ... We published the results in conferences and other academic avenues.

But we wanted to see a full operational system working, as real-time and operational as we can make it in the lab. So we built that and added certain new capabilities which are very important before you talk about getting it in the field. So things like [being able to] send and receive asynchronously, which means can you start sending and then in the middle of the packet can you start receiving a packet. That's what happens in actual systems, because all of these data streams are not synchronized. And then we also thought about how it will get deployed on devices, your laptops, your tablets and things like that. We actually conducted tests with mockups of how these antennas might be placed or where they could be placed like what device manufactures would be doing. We combined all of these together and built a real system. And that's when we saw real results. And the results are going to be published in an academic forum.

Fierce: So how does it actually work from an antenna perspective and what are the key benefits?

Ashutosh Sabharwal: There are actually many different ways of achieving the same end result. The one we are proposing is repurposing an existing radio technology which has been developed for the last 10 to 15 years, which is the MIMO technology. Now, in MIMO, you have these multiple antennas on each node, which can either serve as the transmit antenna at the same time or they can receive a packet. And what that does is on the transmit side it can increase your throughput and on the receive side it increases your reliability. Instead of keeping all antennas in the transmit mode, we essentially reconfigured them to say, OK, how would I use one to transmit and another one to receive. And then I would find a way to use the similar architecture in the system to send another signal which is a cancelling signal, because my transmit signal on my own device is going to be so much stronger than my receive signal from another device or access point. I need to suppress my huge signal that I am sending. So how do we do that? We essentially built a cancelling circuit and we repurposed the MIMO hardware. And that was the idea.

When you are actually talking and receiving at the same time, even though your voice is so much louder and closer to your ear, you can actually make out what the other person is saying who is father from you. And the reason is your brain knows what words you are uttering. So in the brain it can cancel them out and you can hear what the other person is saying. The same thing applies to antennas essentially.

Fierce: And what are the key benefits of that for wireless carriers?

Ashutosh Sabharwal: The key benefit immediately becomes throughput, it's pure throughout gain. That's what we have demonstrated. We have come very close to doubling throughout in the cell. You can send and receive at the same time.

Right now the way it is done, in Wi-Fi, for example, you either send the packet or receive the packet. When you are sending you have to wait to finish sending before you can receive. Now you can do it simultaneously. So that cuts your time in half of finishing both the transactions. And in cellular networks, they put it in two different frequencies, the uplink is in a different band than the downlink, so now you can even talk about sending and receiving in the same band, so you double your capacity effectively.     

Fierce: How does your team plan to work with standards bodies like 3GGP to develop full-duplex standards for devices and how long do you think that process might take?

Ashutosh Sabharwal: We fortunately have a good relationship with different research entities and these different companies which participate in standardization activity. And our contribution is always supplying the technology side of things. And then what the companies do is actually go to the standardization community. So as academics we are one step away from that.

Essentially we are working with companies to refine this, to really test it out in different situations and build the actual protocols which will be used on top of this.

Fierce: Which companies did you either work with for the process up until now or do you plan on working with in the future to carry it forward?

Ashutosh Sabharwal: I can tell you who we have worked with--that's in the release. But unfortunately, for the new companies which are coming, we have a nondisclosure agreement. But they are all well-known wireless companies. So far we have been supported by the National Science Foundation, of course, and then Xilinx, which is a chip company which we work with.   

Fierce: You guys are down there in Texas, so I imagine there are some Texas-based firms that might be working with you guys. [AT&T (NYSE:T) is based in Dallas, Ericsson (NASDAQ:ERIC), Huawei and Nokia Siemens Networks have offices in Plano and ZTE has a facility in Richardson.]

Ashutosh Sabharwal: [Laughs] That's right.