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Can You Hear Me Now? Doubling Wireless Capacity with Full Duplexing

Ashutosh Sabharwal, Professor of Electrical and Computer Engineering at Rice University, has come up with an innovative solution to an age-old problem in the telecom space that has set the industry on its ear. The good professor, along with graduate students Melissa Duarte and Chris Dick, came up with a low cost, easily implemented ‘full-duplex’ capability on the same carrier frequency without the need to add additional cell sites. All that would be needed is some additional hardware both on the handset and at the transmission tower, along with a clever software hack.

Current communication happens at ‘half-duplex’ in the telecoms space. At a given frequency, only half of the bandwidth can be used since cell sites can either send or receive information, but it cannot do both at the same time. People talking on mobile phones get the impression of full interaction, but that is due to networks being able to quickly string data packets together on both ends. However, once networks become congested, you start to get drop-out due to the fact that there is not enough bandwidth to move all the data packets.

The problem with ‘full duplex,’ however, is that you end up with both streams of data being sent and received at the same time on both ends, leading to garbled data. An analogy would be like two people shouting at each other at the same time and each not being able to hear clearly what the other person is saying. The solution found by Professor Sabharwal, utilizes a concept called MIMO or Multiple-In-Multiple-Out which was popular in the wireless router space several years ago before the 802.11n standard became finalized.

MIMO, as the name implies, simultaneously sends and receives data on multiple antennas, which increases the effective bandwidth and improves signal quality. The Rice researchers found that the addition of a second antenna in a handset would allow simultaneous send and receive on the same frequency. And through a clever software trick, the data being sent at both ends is electronically cancelled – think active noise cancellation – at the local handset so each side only hears what the other side is transmitting.

This clever hack allows full speed transmission and reception at the same time, therefore effectively doubling the data bandwidth. An additional beneficial side effect to this is that the second antenna helped boost reception quality about 10x greater than normal, which is a good thing considering how prevalent signal dropouts are on celluar networks.

These wizards of wireless also perfected yet another previously thought to be impossible feat, again via software, by enabling asynchronous full-duplex operation. Keep in mind that while ‘full-duplex’ means both sides can be sending and receiving data at the same time, the handsets still have to sync with each other. An analogy here would be like a baton pass during track and field competitions. One runner prepares to handoff the baton, while the second prepares to receive it. It is a specific timed event and has to be done in sync, otherwise the baton gets dropped. The time that it takes to set up this specific timed event is basically the wasted bandwidth on the cellular network.

Asynchronous operation, however, means that both sides can start to send or receive whenever they are ready without having to wait for the other side to agree. It would be like the baton being teleported from one runner to the next whenever you hit the teleport switch regardless of where both runners are on the track. Since this happens instantaneously, bandwidth is preserved, which maximizes the amount of data that can be transmitted over the wireless network.

What this means is that in the next few years as 4.5G and even 5G network rollouts take place, we will have faster and more reliable connections for our voice and data being transmitted wirelessly. And all this can be done using existing equipment and existing frequencies which saves costs for both the carriers and the end consumer.

Source: Futurity

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