High-Accuracy Positioning Services for High-Speed Vehicles in Wideband mmWave Communications

It is expected that the sixth-generation (6G) cellular networks will provide high-accuracy positioning services. For the millimeter wave (mmWave) frequency band in 6G, both the Doppler and the spatial wideband effects can lead to channel variation in time and space domains, respectively. However, the impact of these effects on the positioning performance is not well studied. In this paper, we will investigate this issue and show that these two effects are not only challenges, but also provide great opportunities in terms of positioning in vehicular networks. Particularly, we will conduct system modeling, algorithm design, and fundamental performance analysis of simultaneous localization and communications (SLAC) in mmWave-based vehicular networks, exclusively dependent on channel state information. The major challenge in algorithm design is the high computational complexity that comes with the huge antenna arrays and bandwidth. For high-speed vehicle positioning, timeliness is as important as accuracy. For performance evaluation, the Cramer-Rao lower bounds (CRLB) will be derived as benchmarks. We will show that it is possible to achieve CRLB-level positioning accuracy, with almost linear complexity. With the closed-form theoretical results, we will evaluate how different system parameters contribute to positioning accuracy, such as bandwidth, carrier frequency, size and orientation of antenna arrays, etc. These results will shed light on system-level design and optimization of SLAC with ultra-wide frequency band in highly dynamic environments, i.e., very strong spatial wideband and Doppler effects. Comprehensive numerical results will also be presented to verify the theoretical analyses and the effectiveness of the proposed algorithms.