Everything is Duplexing

When you talk to someone on the phone typically someone makes a statement or asks a question then the other party responds. We take turns. You talk then I talk, then you talk then I talk – back and forth. That is also how many internet services and wireless communications work as well — they either take turns sending then receiving data (time division duplex or TDD) or will use separate frequencies for transmitting and receiving (frequency division duplex or FDD).

What if they could send and receive data in the same frequency at the same time? Try it — talk to someone on the phone at the same time they are talking to you. Not so easy to carry on a conversation, is it? This is because of a couple of reasons — first of all, our brains are not able to handle thinking about what someone is saying to us while simultaneously talking about some other topic. Computers can do this fairly easy but humans cannot. The second reason is feedback and interference. The combination of listening to someone speak while simultaneously speaking about something else creates a jumbled mess of voices where some speech frequencies interfere or cancel making it more difficult to hear. Add in the fact that your own voice is also recycling into your ear and you end up not able to concentrate on what you are speaking about. The same thing happens to most data communication.

When data is being transmitted at the same time it is being received the frequencies collide, interfere, and cancel making some bits more powerful and others subdued. There is also an “echo” that happens where the data being send is also echoed back to the sender the same way your voice leaves your mouth and enters back into your ear when ¬†you talk. Until recently, it was not possible (in most cases) for computers to “talk” and “listen” at the same time on the same frequency.

However, there have been many advancements in eliminating interference – mostly using magnets (called circulators). The problem with using circulators is two fold: 1. They are big and bulky and not able to fit into small devices and 2. When in close quarters to other electronic circuits, magnets cause their own interference. However, a new silicon chip has been enhanced by a grad student at Columbia University to require a single antenna. To achieve this he created a circulator out of transistors on a CMOS chip combined with a receiver designed to cancel out echos that had previously been developed by the university.

The current problem is that the new chip is not capable of broadcasting with high enough power for a mobile network — It just barely meets the bottom end of power requirements for a WiFi network. Researchers are working on solving this issue so that the chip can eventually be embedded in mobile/cellular phones as well as in the high-powered equipment of the cellular network antennas. Once viable it can effectively double current wireless network capacity:

http://spectrum.ieee.org/tech-talk/telecom/wireless/new-full-duplex-radio-chip-transmits-and-receives-wireless-signals-at-once

In fact, wireless chip-set builders are already testing and advancing full-duplex technology for future 5G networks:

http://www.zdnet.com/article/lg-trials-wideband-full-duplex-radio-tech-for-5g/

Cable networks have also had their eye on this technology since their coaxial cables are also only half-duplex. Upcoming DOCSIS standards are expected to include full duplex technology enhancements that can also double the bandwidth of cable networks and bring the consistently slow upload speeds up to par with download speeds (symmetric upload and download speeds). CableLabs is testing their own full duplex technology based on the research being done for wireless networks:

http://www.cablelabs.com/full-duplex-docsis-3-1-technology-raising-the-ante-with-symmetric-gigabit-service

Both wireless and non-optical wired technologies are vying for the top spot in bandwidth and are likely to be competing with each other in future multi-gigabit networks.

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