Finding the Perfect Blend of Full and Half Duplex for Future Cell Phone Networks

A proper mix of full and half duplex cells will maintain high-quality coverage and deliver greater spectrum efficiency

2 min read
Finding the Perfect Blend of Full and Half Duplex for Future Cell Phone Networks
Image: Saul Herrera/iStock

The sales pitch for full duplex is a powerful one: these new radios could instantly double the capacity of today’s wireless networks by transmitting and receiving signals on the same frequency, at the same time. That promise has made network engineers eager to deploy it in cellular base stations and mobile devices ever since the technology began to pick up steam around 2007.

But in reality, transmitting and receiving messages at the same time on the same frequency has an unfortunate side effect. It causes twice as much interference as performing each function in turn or on separate bands. So while full duplex radios can dramatically improve spectrum efficiency, the resulting interference means more connections would be lost if a network were constructed wholly of them.

Knowing this, a team of researchers from New York University in the U.S. and Ireland’s Trinity College is studying how wireless engineers can get the best of both worlds by blending full and half duplex radios into the same network. They say that doing so can will allow designers to balance spectrum efficiency and top-notch coverage for the area they wish to serve.

Sanjay Goyal, a coauthor and PhD student at New York University, says service providers will inevitably confront this tradeoff when they construct future base stations featuirng full duplex technology. It might make more sense to include more full duplex components in a crowded area, for example where bandwidth demand is skyhigh. Rural communities, meanwhile, should probably use fewer full duplex cells in order to maximize coverage.

Goyal and his colleagues demonstrated the concept by toying with the ratio of half and full duplex base stations in a model network. Their simulation included 1,000 base stations in a square kilometer, which is similar in structure to many dense networks found in cities.

They adjusted the ratio of full and half duplex cells (low-powered radio nodes with a shorter range than traditional cell towers) in their simulated network and recorded the results in coverage and spectrum efficiency. All the handheld devices in their model were assumed to be half duplex because full duplex radios are too expensive and require more power than is considered practical for smartphones and tablets.

Their results showed that wireless engineers could tweak the mix of full and half duplex cells in a network to prioritize greater efficiency or better coverage to suit their purposes. Including more full duplex cells delivered higher spectrum efficiency at the cost of a few more dropped calls. On the other hand, featuring more half duplex units improved coverage at the expense of overall efficiency.

Goyal hopes wireless engineers will find this result useful and perhaps even freeing as they plot tomorrow’s wireless networks. “If you don't need spectrum efficiency gain, don't use full duplex,” he says. “But if you want spectrum efficiency gain and you want coverage, you need to tune the number of full duplex base stations according to that.” Goyal presented the group’s work on Thursday at the IEEE International Conference on Communications in Kuala Lumpur, Malaysia.

The team also tested whether it was possible within a full duplex system to enable a faster connection only for those users trying to download data versus those wishing to send it. After all, the average network has about five times as much traffic in downloads than uploads. Indeed, by lowering the transmission power of nearby devices and thereby eliminating interference, the group showed that recipients’ devices enjoyed speedier downloads than they would otherwise.

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How the FCC Settles Radio-Spectrum Turf Wars

Remember the 5G-airport controversy? Here’s how such disputes play out

11 min read
This photo shows a man in the basket of a cherry picker working on an antenna as an airliner passes overhead.

The airline and cellular-phone industries have been at loggerheads over the possibility that 5G transmissions from antennas such as this one, located at Los Angeles International Airport, could interfere with the radar altimeters used in aircraft.

Patrick T. Fallon/AFP/Getty Images

You’ve no doubt seen the scary headlines: Will 5G Cause Planes to Crash? They appeared late last year, after the U.S. Federal Aviation Administration warned that new 5G services from AT&T and Verizon might interfere with the radar altimeters that airplane pilots rely on to land safely. Not true, said AT&T and Verizon, with the backing of the U.S. Federal Communications Commission, which had authorized 5G. The altimeters are safe, they maintained. Air travelers didn’t know what to believe.

Another recent FCC decision had also created a controversy about public safety: okaying Wi-Fi devices in a 6-gigahertz frequency band long used by point-to-point microwave systems to carry safety-critical data. The microwave operators predicted that the Wi-Fi devices would disrupt their systems; the Wi-Fi interests insisted they would not. (As an attorney, I represented a microwave-industry group in the ensuing legal dispute.)

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