A Unidirectional Communication Architecture for Extended Location-Based Services

Abstract

Location-Based Service (LBS) is an information service based on locations of mobile users and two-way interactions. Most LBS communications follow the client-server architecture which enables bidirectional communication between the server and a client. The paper examines the limitations of the current client-server LBS framework for time critical LBS application scenarios and their system requirements for networking and computing. It presents the publish/subscribe communication paradigm for unidirectional connections that support decentralised device-to-server and device-to-device data services with low-latency and high scalability. A lightweight publish/subscribe application protocol, namely Message Queue Telemetry Transport (MQTT), is also introduced for high-rate vehicle RTCM data exchanges for timely-critical connected vehicle applications. To prove the concept of the extended LBS, experiments are performed to demonstrate how well the MQTT can support real time location-based data transfer. Results show that the MQTT Broker overwhelmingly outperforms the NTRIP Caster in delivering RTCM correction data in terms of CPU usage of the network computer server and performs similarly well in latency and packet losses. MQTT is also tested for device to device GNSS data exchanges. Results show that two mobile devices can exchange RTCM v3 data with the reliability of 99% within the latency of 1 s under 4G cellular connectivity. The results also show that the MQTT Quality of Services mode 1 can support the 10 Hz data transfer at the latency of less than 100 ms and the reliability of above 99%, showing the potential in support of connected vehicle safety applications.