In a world with 7 billion cell phones, wireless service providers are always searching for ways to maximize the efficiency of wireless spectrum to improve services. Most celluar base stations today are based on half duplex radio technology i.e they can send signals and receive signals, however can only perform one operation at a time.
Full duplex radios have long been a tantalizing proposition because they 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. However, they also generate double the amount of interference, constraining their deployment.
Researchers from New York University Tandon School of Engineering and Trinity College in Dublin, Ireland, have come up with a method to improve spectrum efficiency by deploying a mix of half and full duplex radios in base stations. Their 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 Shivendra Panwar, professor of electrical and computer engineering at NYU Tandon, and Sanjay Goyal, a doctoral student, along with Assistant Professor Nicola Marchetti and doctoral student Carlo Galiotto, both of Trinity College.
Panwar likened the use of full duplex in a cellular network 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. 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", said Panwar.
Noting the advantages of each system - full duplex radios offer superior efficiency while half duplex radios provide a wider coverage area - these 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.
They 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 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.
Additionally, because download traffic far exceeds upload traffic on most networks, this 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.
This research was funded by the National Science Foundation; the Center for Advanced Technology in Telecommunications (CATT) at NYU; the NYU WIRELESS research center; the Higher Education Authority (Ireland); and Science Foundation Ireland.
