Integrated Millimeter Wave and Sub-6 GHz Wireless Networks: A Roadmap for Ultra-Reliable Low-Latency Communications
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Emerging wireless services such as augmented reality require next-generation wireless networks to support ultra-reliable and low-latency communication (URLLC), while also guaranteeing high data rates. Existing wireless networks that solely rely on the scarce sub-6 GHz, microwave (μW) frequency bands will be unable to meet the low-latency, high capacity requirements of future wireless services. Meanwhile, operating at high-frequency millimeter wave (mmWave) bands is seen as an attractive solution, primarily due to the bandwidth availability and possibility of large-scale multi-antenna communication. However, even though leveraging the large bandwidth at mmWave frequencies can potentially boost the wireless capacity and reduce the transmission delay for low-latency applications, mmWave communication is inherently unreliable due to its susceptibility to blockage, high path loss, and channel uncertainty. Hence, to provide URLLC and high-speed wireless access, it is desirable to seamlessly integrate the reliability of μW networks with the high capacity of mmWave networks. To this end, in this paper, the first comprehensive tutorial for integrated mmWave-μW communications is introduced. This envisioned integrated design will enable wireless networks to achieve URLLC along with high data rates by leveraging the best of two worlds: reliable, long-range communications at the μW bands and directional high-speed communications at the mmWave frequencies. To achieve this goal, key solution concepts are developed that include new architectures for the radio interface, URLLC-aware frame structure and resource allocation methods along with learning techniques, as well as mobility management, to realize the potential of integrated mmWave-μW communications. The opportunities and challenges of each proposed scheme are discussed and key results are presented.
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