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Full Duplex Wireless Tech Could Double Bandwidth
CWmike writes "Rice University researchers announced on Tuesday that they have successfully demonstrated full-duplex wireless tech that would allow a doubling of network traffic without the need for more cell towers. Professor Ahutosh Sabharwal said the innovative technology requires a minimal amount of new hardware for both mobile devices and networks. However, it does require new standards, meaning it might not be available for several years as carriers move to 5G networks, he added. By allowing a cell phone or other wireless device to transmit data and receive data on the same frequency, unlike with today's tech, the new standard could double a network's capacity. Rice has created a Wireless Open-Access Research Platform (WARP) with open source software that provides a space for researches from other organizations to innovate freely and examine full-duplex innovations."
I wish more than the simple abstract was available, I'm greatly interested to find out more in how they've done it. All I can seem to glean is they came up with some sort of cancellation technology. I'm going to assume its CSMA/CA evolved. Should be some neat tech if its not hyped media stuff.
It's called 802.11n (which has been working for quite some time now), this is just doing it with cell phones.
Rice's team overcame the full-duplex hurdle by employing an extra antenna and some computing tricks.
We repurposed antenna technology called MIMO, which are common in today's devices
Yup.
In a world where bandwidth demands are increasing exponentially, a simple doubling of capacity ought to get us by for, oh, I don't, know, 6 months? This needs to be paired with a more fundamental upgrade that will get us by for several years to be worthy of incrementing the 'G' number to 5G, for any reasons other than marketing blather that is.
In wired Ethernet topologies, going full duplex yields significantly more than double the throughput, since you no longer have collisions, back-offs, and re-sends. The article doesn't elaborate whether their full-duplex wireless would still be multi-access (think WiFi, with many clients on the same AP and same channels) or if each frequency would be carved out for one client and the base-station (in which case you'd see the same gains you did on wired Ethernet).
M point is that while they cite "allow a doubling of network traffic", the reality is even better than that. Full duplex gets you more than double throughput, as well as improved jitter/latency since you no longer have to randomly re-transmit frames (or randomly wait to transmit, as with WiFi collision avoidance).
The idea, as they mention, has been around for a while, in fact since at least the early 1970s, with some information-theoretic work putting bounds on ideal full-duplex operation. The main idea is that you can cancel your own transmitted signal locally because you know what you're transmitting. The difficulty is that the transmitted signal is much stronger locally than the received signal, so there is little margin for error for imperfect cancellation; even if you cancel out 99.9% of the signal, there might still be too much noise left to decode the incoming signal. Errors can come from nearly anything; slightly imperfect knowledge of the characteristics of your device, changes due to weather or motion, interference from surrounding objects, etc.
Also note that terminology here is a bit confusing. In some uses (esp. radio), "full-duplex" just means any system that is capable of having people speak in both directions simultaneously, even if it's done by using separate frequencies for each direction, or by using a multiplexing scheme. In contrast, this usage of full-duplex means that both directions are transmitting simultaneously on the same channel, without segmenting or multiplexing it.
I don't actually know how they solved the problem, though, and the article is light on details.
10 PRINT CHR$(205.5+RND(1)); : GOTO 10
MIMO uses multiple antennas and the Rice team was able to send two signals in a way that they cancel each other out, allowing a clear signal to go through over the single frequency.
Doesn't this sound an awful lot like the DIDO approach (pdf) that Steve Perlman was talking up recently?
Why would anyone engrave "Elbereth"?
When AT&T, et. al. are in a position where they are the DeBeers of wireless bandwidth. I think instead of actually spending money to upgrade infrastructure, they would rather just continue to artificially limit the amount of available bandwidth so they can keep it grossly overvalued. Gotta keep those profits rolling in for the shareholders somehow.
And I'll be able to reach my download caps in half the time!
SJW: Someone who has run out of real oppression, and has to fake it.
Seriously .... could it be any worse than it is now?
Very dangerous question. "just when you're thinking things couldn't possibly get any worse, they suddenly do."
However there's quite a difference between patenting the vague "A method of using phones Full Duplex" and patenting the actual implementation (which the article didn't actually explain).
And this is why we don't put Slashdot in charge of the patent system.
At least we have a way to identify prior art.
My God, it's Full of Source!
OUTSIDE_IP=$(dig +short my.ip @outsideip.net)
This is NOT a big deal. Every new wireless telephony increases bandwidth by at least 10x. Basic GSM to basic 3G (UMTS) did that. From EDGE to HSxPA same thing. From HSxPA to LTE same.
While doubling performance is good, 5G networks needs to increase bandwidth 5x fold at an absolute minimum in order to be of any interest to wireless carriers.
And notice that today's wireless is full duplex a far as the user is concerned, but it happens using separate upstream/downstream channels. The biggest bottleneck is that both channels are shared among hundreds of users and that's where the congestion lies.
The 5G idea that was discussed is having all phones act as intelligent repeaters, allowing for very low power transmissions where user density is highest, the lowest power transmissions are, the more often spectrum can be reused dynamically by those repeaters. Also this could help with the shadow spots, since all it would take is one user in contact with the tower and with a shadow spot to illuminate that spot with signal. Also it would be expected to involve 10x more basestations in the form of femtocells / nanocells, using the same low power principle.
Wireless communications will never ever be not even close as efficient as wired communications for bandwidth intensive applications. Unlimited plans were always a fish and bait scheme, designed to create interest and dependency, until they limited bandwidth to increase revenue (i.e. jack up the prices).
The idea sounds great. But when you think realistically, you will know there is always a tradeoff. If you look at the paper and ideas by ignoring all the marketing messages, you can see there are flaws and it cannot apply to MIMO solutions.
Basically, the idea is to place the 1 Rx antenna between two Tx antennas so that the signals from two Tx antennas are out of phases at the Rx antenna position. Yes, it works for the purpose that you want the Rx antenna receives no signal from Tx antennas. However, this also changes the antenna beam pattern which will reduce the coverage for the reception of the signal by half. The placement of 2 Tx antennas is the same as have a Uniform Linear Array (ULA) with 2 antennas with some inter-element distances. For example, if you place the antennas with lambda/2 away (where lambda is the wavelength), you will receive very weak signal at the broadside angle. In the other word, you trade the reception quality at broadside angle for the null-out effect at your Rx antenna.
Just look at the image here and you can choose the null wherever you like
Actually, you have two degrees of freedom here to choose any position/angles you want to have the weakest signals (null-out effect). 1) by changing the phase difference between two Tx antennas. For example, making them 180 degree out of phase, the null will happen at the middle between two antennas. In this case, you trade your reception along the direction perpendicular to your antenna array with the so-call single duplex. 2) by changing the inter-distance between two antennas. For example, you can make the distance with lambda*3/4 away to create the 180 degree out of phase. The drawback is the same. You trade the reception at certain area with this null-out at certain position.
People can argue, you can increase the inter-distance more, so that more grating lobes can be observed. Because there are multiple paths, eventually, the whole space can be covered. Yes, you are right. But how far away two antennas should be separated? It definitely depends on the environment. You can make it adaptive. So a dedicated engineer needs stand at the access point to change the antenna separations per request. And if you place the antennas so far away, is that really practical to have such systems?
So, they are just using one mode of the ULA to achieve the signal cancellation at the receiver point. But since they are twisting the antenna patterns, if you add more antennas trying to achieve 3x3 or 4x4, you are doomed. Because the degree of freedom has been used to cancel the signal at receivers, you have no more degree of freedoms for more spatial streams. So, yes, they can increase the capacity by two fold (in some area of coverage), but not beyond as in MIMO solution!
I believe there is an use case. But we should know the tradeoff and whether it is suitable for real deployment.