Wireless communication over terahertz (THz) frequency bands is envisioned as the key enabler of many applications and services offered in 6G networks. The abundantly available bandwidth in THz frequencies can satisfy the ultra-high user throughput requirements and accommodate a massive number of connected devices. However, poor propagation characteristics, shadowing, and blockages may result in sudden outages and necessitate frequent handovers. Therefore, an inefficient handover procedure will impose severe challenges in meeting the ultra-high reliability and low latency requirements of emerging applications. In blockage driven mmWave and THz networks, a higher multiconnectivity degree and efficient handover procedures are needed to reduce the data plane interruptions and to achieve high reliability. We present an analytical model to study the impact of handover procedures and multi-connectivity degree on the latency and reliability of blockage driven wireless networks. From the network protocol design perspective, our study offers a quick and accurate way to envisage how network architecture and protocols should evolve in terms of multi-connectivity degrees and handover procedural efficiency. Our results suggest that, for THz systems, coverage range should be increased even if it comes at the cost of increased initial access and base station discovery times.

Fifth Generation (5G) Millimeter Wave (mmWave) cellular networks are expected to serve a large set of throughputintensive, ultra-reliable, and ultra-low latency applications. To meet these stringent requirements, while minimizing the network cost, the 3 rd Generation Partnership Project has proposed a new transport architecture, where certain functional blocks can be placed closer to the network edge. In this architecture, however, blockages and shadowing in 5G mmWave cellular networks may lead to frequent handovers (HOs) causing significant performance degradation. To meet the ultra-reliable and low-latency requirements of applications and services in an environment with frequent HOs, we propose the Fast Inter-Base Station Ring (FIBR) architecture, where Base Stations (BSs) that are in close proximity are grouped together, interconnected by a bi-directional counter-rotating buffer insertion ring network. FIBR enables high-speed control signaling and fast-switching among BSs during HOs, while allowing the user equipment to maintain a high degree of connectivity. We demonstrate that the FIBR architecture efficiently handles frequent HO events in mmWave cellular systems, and thus more effectively satisfies the QoS requirements of 5G applications.

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The high data rates required for next generation applications necessitate the use of millimeter wave and terahertz bands where bandwidth is abundant. Due to high path loss in these bands, antenna arrays (AAs) are needed to focus the signal in highly directional beams in the desired directions. However, highly directional communication links in these bands are vulnerable to misalignment and blockages due to mobility. Thus, both mobile blockers and user equipment (UE) rotations can significantly increase the handover (HO) frequency, while HO delays and HO failures jeopardize system latency and reliability. Furthermore, the scanning angle of each AA is limited by the orientation of the device, the mounting angle of the AA, the element spacing and the grating sidelobes formed during beamforming, which is referred as Field-of-View (FoV). In scenarios with UE rotational mobility, limited FoV may lead to loss of connection with the source next-generation NodeB (gNB).In this paper, we analyze current HO and radio link monitoring protocols in scenarios with UE rotational mobility and mobile blockers. We use a Markov Chain based analytical model as well as MATLAB based system level simulations to show how user rotation can significantly increase the outage duration under various deployment configurations. We propose enhancements to enable faster HO under user rotations and demonstrate significant performance improvements using simulations.