Aug 2018     Issue 8
To Reach Where Optical Fiber Cannot

Prof. Raymond W. YEUNG, Department of Information Engineering

In the newly released Smart City Blueprint for Hong Kong, the government is launching a multi-functional smart lampposts pilot scheme at urban locations to provide convenient data services and collect real time city management data like transportation, weather and environment.  Equipped with sensors, data networks and related facilities, the smart lampposts can help transform Hong Kong into a smart city through the provision of information and digital services such as Wi-Fi and future 5G networks and base stations.  The transmission rate and installation cost of communication networks is a significant factor to consider.

A major problem for the installation of smart lampposts is to be able provide highspeed connections between these lampposts and the Internet backbone. This is essential because i) the data collected at the lampposts need to be transmitted back to the data center for storage and analysis; ii) if 4G/5G base stations are put on the lampposts, they need to be connected to the Internet backbone; iii) if the lampposts provide WiFi services, the access points need to be connected to the Internet backbone.

The ideal solution is to lay optical fiber to each smart lampposts.  However, this solution not only is expensive but also not very feasible in many situations. The process of laying optical fiber causes much disturbance to the shops and pedestrians nearby. Moreover, it can take 2 to 3 years to obtain all the necessary permits for laying optical fiber in the city center, which is too long a waiting time for most deployments.

Another solution is to put a 4G/5G SIM card on each of the lampposts so that the lampposts are connected to the Internet backbone through the cellular network. The drawbacks of this solution are two-fold. First, the operating cost is high because one needs to pay the monthly fee for the cellular service for each lamppost. Second, since the cellular network is a public network, the bandwidth share of the lampposts would drop drastically during the peak hours. This would severely impair the quality of the services provided by the smart lampposts.

The third solution is to connect a group of consecutive lampposts by a WiFi multi-hop network to a point that has access to the Internet backbone (for example an office building nearby, or one of the lampposts). However, due to accumulation of packet loss in the wireless links and the inefficiency of Internet protocols in a lossy environment, with existing technologies it is not possible to build such a network with more than 3 to 4 hops, because beyond that the throughput of the network would drop very drastically. 

To tackle this so-called "multi-hop curse", our team at the Institute of Network Coding invented an advanced network coding scheme called BATched Sparse codes (BATS codes) in 2011. With BATS codes, the throughput of a wireless multi-hop network can be maintained after tens or even hundreds of hops. During the past few years, our team has developed BATS codes into a technology that can readily be deployed.

The attached figure depicts a possible user case. The lamppost on the left, referred to as the first lamppost, is connected to the Internet backbone through optical fiber.  The other lampposts in the same street are collected to the first lampposts through a wireless multi-hop network powered by BATS codes.  This provides a low-cost solution for a smart lamppost system that requires the installation of very few or even no new optical fiber links.

The applications of BATS codes are not limited to smart lampposts. They can be applied to any multi-hop network with packet loss. Other potential applications of BATS code include internet of things, 5G cellular networks, vehicle-to-vehicle communication, underwater communication, satellite communication, power line communication, and disaster communication, breaking geographical boundaries with technologies.



The illustration was originally designed by the CUHK Communications and Public Relations Office.

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