Robust Algorithm Development and Demonstration for Agile mmWave MIMO Hybrid Beamforming

点击翻译按钮获取中文摘要

Communication at millimeter wave (mmWave) bands promises to enable the rapid growth of mobile data traffic. However, the major limitation of utilizing them is their high path loss that needs to be compensated by antenna arrays with many elements. In turn beamforming techniques need to be used to optimally distribute the signal energy towards the users. As a purely digital implementation might consume too much power, a good trade-off between complexity, hardware cost, and performance can be achieved by utilizing analog beamforming in conjunction with digital baseband processing, known as ‘hybrid’ beamforming.Assuming high carrier frequencies together with user mobility occurring in the radio access network, the coherence time of mmWave systems is expected to be much shorter than that of low-frequency systems, that are served not by strongly but only weakly anisotropic beam patterns. Therefore, algorithms that accelerate (analog) beam selection at mmWave bands will be of vital importance for the successful application of antenna arrays in general and for using the hybrid beamforming approach in particular. In this project, we plan to do fundamental research on adaptive and accelerated beam selection for hybrid beamforming systems, as well as to investigate of hardware-related issues and their compen-sation. Only on this basis, a practical system implementation appears feasible. Compared to conven-tional approaches, like beam selection using fixed length tests, hybrid adaptive algorithms with variable length training sequences can achieve higher temporal efficiency. We have shown this already for the case of a single user by our proposed ‘sequential competition’ test. Such a robust algorithm can also serve as a building block to extend standard adaptive algorithms well-known for digital beamforming to adaptive algorithms suitable in a hybrid beamforming context.Apart from algorithms the impact of hardware-related impairments on the hybrid beamforming performance needs to be characterized, especially for wide bandwidths as well as for MIMO setups with multiple RF-chains. This includes e.g. frequency-selectivity, phase noise etc. from sub-optimal hardware components, that can lead to degradation or failure of the theoretically proven algorithms if not properly accounted for. On the digital baseband level, efficient signal processing schemes that can simultaneously handle multiple streams and users with data rates of several Gbit/s need to be developed and a suitable control plane with low latency is required to coordinate the digital and analog beamforming sections.For verification of the developed system concept, a 60 GHz hardware demonstration will be undertaken in an access scenario. The analog beamforming part will be performed using vector modulators provided by project partners. This will provide valuable insights into the feasibility of hybrid beamforming and the impact of hardware constraints on performance.