With a nod to recent advances in self-interference cancellation (SIC), researchers at New York University Tandon School of Engineering and Trinity College in Dublin, Ireland, set out to propose a mixed multi-cell system composed of full duplex and half duplex radios.
A full duplex radio system developed
They point out that the so-called "half duplex" radios that comprise today's cellular base stations perform two functions: They send signals and receive signals. However, they can only perform one of these functions at a time.
Full duplex radios, on the other hand, are capable of sending and receiving on the same frequency simultaneously, potentially doubling spectral efficiency. If used in smartphones, they would allow simultaneous uploading and downloading. The problem is, they also generate double the amount of interference.
Shivendra Panwar, professor of electrical and computer engineering at NYU Tandon, says the use of full duplex in a cellular network is similar to 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 via a press release. "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 researchers hypothesized that mixing full and half duplex cells could allow wireless providers to customize networks to meet demand and improve spectral efficiency as needed without excess interference.
To the researchers' knowledge, this is the first study to investigate the impact of mixed-cell base stations on spectral efficiency and outages. Their models are readily applicable for wireless engineers seeking to 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, in the release. "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 crucial.
The NYU Tandon and the Trinity College researchers' paper, Throughput and Coverage for a Mixed Full and Half Duplex Small Cell Network, recently won Best Paper at the IEEE International Conference on Communications (ICC) in Kuala Lumpur, 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.
Others have devoted R&D to similar work in trying to address the transmit and receive issues. Kumu Networks, a startup that was founded by a team of Stanford University professors and Ph.D graduates, developed a self-interference cancellation technology that isolates the receiver from the transmitter, allowing radios to transmit and receive simultaneously on the same frequency. The company has drawn backing from the likes of Cisco, Verizon Ventures and Deutsche Telekom, among others.
- see the press release
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