Today’s ‘half duplex’ radios send signals and receive signals, but can only perform one of these functions at a time. Full duplex radios have the potential to double spectral efficiency, but would also generate double the amount of interference.

Looking to address the problem, researchers from New York University (NYU) and Trinity College in Dublin, Ireland have conceived a method to improve spectrum efficiency by deploying a mix of half and full duplex radios in basestations.

According to Professor Shivendra Panwar from NYU’s Tandon School of Engineering, the use of full duplex in a cellular network is like being at a crowded party where everyone is attempting to talk and listen at the same time. “Even if you were capable of speaking and listening at the same time, everyone around you would be doing the same thing,” he said. “It would be impossible to tune out that extra noise – and the same is true in a full duplex system. There are many more outages and dropped calls due to the high level of interference.”

Noting the advantages of each system – full duplex radios offer superior efficiency, while half duplex radios provide a wider coverage area – the team hypothesised that mixing full and half duplex cells could allow wireless providers to customise networks to meet demand and improve spectral efficiency as needed without excess interference.

The team generated mathematical models of base stations with varying configurations of half and full duplex, then ran simulations to predict the trade offs in efficiency and coverage areas. To their knowledge, this is the first study to investigate the impact of mixed cell basestations on spectral efficiency and outages. The models are also said to be readily applicable for wireless engineers seeking to improve their networks.

“The beauty of this system is that it’s tuneable and would allow providers to adjust the mix of cells based on the needs of a region,” said researcher Sanjay Goyal. “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 said to hold in less dense areas, where spectral efficiency is less crucial.

Because download traffic far exceeds upload traffic on most networks, the team showed that a mixed cell system could enable faster downloads at the expense of upload speed, which is less likely to be noticed by customers.