The tremendous growth of worldwide data traffic over the past years means that the future access network architectures will be revised. The flexibility of wireless links, compared with wired ones, makes them more adequate and cost efficient in several scenarios. Consequently, high-capacity wireless interfaces must be integrated with optical networks without imposing a capacity bottleneck. The millimeter-wave (30â€“300 GHz) band is postulated as the main candidate to extend the capacity of wireless interfaces because of highly available bandwidth resources. However, a high-gain directive antenna with beam steering capabilities must be used in this spectrum region to overcome large free space attenuation.
Researchers from Eindhoven University of Technology, The Netherlands and Tektronix AB, Sweden proposed that the optical true time delay beamforming technique is the best candidate to provide beam steering capabilities to an antenna array at millimeter-wave frequencies within a hybrid millimeter-wave/photonic system. This scheme offers broadband operation, low loss, and straightforward integration into optical distribution networks. Traditionally, the beamformer network is situated at the antenna unit. This work proposes a scheme that shifts this functionality to a central entity to control the beamforming configuration remotely. A multicore fiber is used to transmit different replicas of the signal to each array element keeping the relative time delay between different cores. This system is validated by an experimental demonstration and the measurement of the relative delay after the transmission over 2 km of the multicore fiber. This work has been published in Chinese Optics Letters, Volume 16, No. 4, 2018 (Álvaro Morales, et al., 50 GHz optical true time delay beamforming in hybrid optical/mm-wave access networks with multicore optical fiber distribution)
The shift of the beamformer network to a remote central entity is completely different from common approaches. The main advantages are the central management of the beamformer configuration for different antenna units and the reduction in the deployment costs of new base stations. The results serve as engineering guidelines for the design of a hybrid optical/millimeter-wave access network with centralized beamforming capabilities.
"Most researches agree that new paradigms for the next generation of radio access networks will rely on the deployment of a large number of radio stations, multi-antenna systems, and millimeter-wave communications," said Prof. Idelfonso Tafur Monroy from Eindhoven University of Technology, "The ideas proposed in this work are in accordance with this philosophy."
Further work will be focused on the end-to-end design of the radio frequency segment and the reconfigurability of the beamformer to make the proposed system suitable for implementations.
荷兰埃因霍温理工大学（Eindhoven University of Technology）和瑞典泰克公司（Tektronix AB）的研究人员提出，在混合毫米波/光子系统中，光纤真时延波束成形技术是向毫米波天线阵提供波束控制能力的最佳方案。该方案使光分配网络具有高宽带、低损耗和直接集成等特性。传统上，波束成形器网络位于天线单元处。该研究团队则将此功能转移到控制中心，来远程控制波束成形的配置，并将信号的不同副本通过多芯光纤传输到每个阵列单元，以保持不同副本之间的相对时延。该研究团队还测量了信号在多芯光纤中传输超过2 km后的相对延迟，并实验验证了该系统。相关研究结果发表于Chinese Optics Letters 2018年第4期第16卷（Álvaro Morales, et al., 50 GHz optical true time delay beamforming in hybrid optical/mm-wave access networks with multicore optical fiber distribution)。
荷兰埃因霍温理工大学光子集成技术中心太赫兹系统与指示器系统的Idefonso Tafur Monroy教授指出：“大多数学者认为，下一代无线接入网将依赖于大量无线电台、多天线系统和毫米波通信的部署。该团队提出的想法与这一理念不谋而合。”