Researchers combine full- and half-duplex in same network

Study by NYU and Trinity College Dublin argues that full duplex alone has too many trade-offs, but hybrid network can deliver huge gains

Full duplex technology – which allows radios to transmit and receive on the same frequency at the same time – is seen as one of the most important ways to improve spectral efficiency in emerging wireless networks. However, it has downsides including more limited coverage, so researchers at New York University Tandon School of Engineering and Trinity College, Dublin are proposing a hybrid scheme.

Full duplex – as pioneered by various start-ups, most notably Kumu Networks, which has attracted investment from Cisco, Deutsche Telekom, Swisscom and Verizon –effectively doubles spectral efficiency, by using self-interference cancellation (SIC) to reduce the noise of transmission.

But Shivendra Panwar, professor of electrical and computer engineering at NYU Tandon, says full duplex networks create higher levels of interference, despite SIC. He said in a statement recently that it would be impossible to tune out the extra noise of simultaneous transmission and reception, adding “The same is true in a full duplex system. There are many more outages and dropped calls due to the high level of interference.” Traditional half dupex radios also support wider coverage areas.

The researchers believe the advantages of both systems could be realized with a hybrid network that mixes full and half duplex cells. Carriers could then optimize their networks to meet their particular levels of demand and spectral efficiency without excess interference. They believe theirs is the first study to investigate the impact of mixed-cell base stations on spectral efficiency and outages and to create models to help wireless engineers improve their networks.

“The beauty of this system is that it’s tunable and would allow providers to adjust the mix of cells based on the needs of a region,” said Sanjay Goyal, a doctoral student. “If you’re designing an urban network, the demand for bandwidth is much greater than the need for wide area coverage. More full duplex cells would provide that bandwidth, even at the cost of a few more dropped calls.” The reverse is true in less dense areas, where spectral efficiency is less important but a carrier might prioritize excellent QoS.

The paper resulting from the study, entitled ‘Throughput and Coverage for a Mixed Full and Half Duplex Small Cell Network’, recently won Best Paper at the IEEE International Conference on Communications in Malaysia. The research team was led by Panwar and Goyal, along with Assistant Professor Nicola Marchetti and doctoral student Carlo Galiotto, both of Trinity College.

In October, Deutsche Telekom conducted the world’s first public operator trial of self-interference cancellation (SIC), a technology which has been defined as a Technology Building Block for 5G by the NGMN Alliance, working with Kumu. DT said SIC technology could be used in existing networks and potentially solve small cell issues by ususing the same spectrum for access and backhaul.

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