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 multi-connectivity 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.

5G will transform the cellular network from a generic supplier of high-speed data to a flexible, super-fast, and highly-reliable communications medium that supports diverse sets of services and applications. Low packet latency is a critical enabler for the interactivity features of many of these applications, but maybe compromised in saturated packets buffers if the buffers are oversized, as is often the case in the RLC layer of the 3GPP RAN stack. To protect all interactive applications from excessive buffering, we completely revise the flow-control component of a prior solution of ours that splits the per-bearer buffer between the RLC and PDCP layers and regulates the packet flow between the two buffers so that queue build-up in the RLC layer is constrained. On a cellular link shared with a greedy TCP flow, our new enhanced bearer buffer (EBB) design with continuous flow control (CFC) reduces the latency of packets from low-bandwidth interactive applications by at least 80% compared to previous EBB versions, and by orders of magnitude compared to the default bearer configuration with a large RLC buffer. The CFC also benefits throughput-intensive interactive applications like augmented and virtual reality because it confines the buffering within the PDCP layer, where it can be effectively controlled with active queue management techniques.

With the new emerging throughput-intensive ultralow latency applications, there is a need for a transport layer protocol that can achieve high throughput with low latency. One promising candidate is TCP BBR, a protocol developed by Google, with the aim of achieving high throughput and low latency by operating around the Bandwidth Delay Product (BDP) of the bottleneck link. Google reported significant throughput gains and much lower latency relative to TCP Cubic following the deployment of BBR in their high-speed wide area wired network. As most of these emerging applications will be supported by Millimeter Wave (mmWave) wireless networks, BBR should achieve both high throughput and ultra-low latency in these settings. However, in our preliminary experiments with BBR over a mmWave wireless link operating at 60 GHz, we observed a severe degradation in throughput that we were able to attribute to high delay variation on the link. In this paper, we show that “throughput collapse” occurs when BBR's estimate of minimum RTT is less than half of the average RTT of the uncongested link (as when delay jitter is large). We demonstrate this phenomenon and explain the underlying reasons for it using a series of controlled experiments on the CloudLab testbed. We also present a mathematical analysis of BBR, which matches our experimental results closely. Based on our analysis, we propose and experimentally evaluate potential solutions that can overcome the throughput collapse without addina sianificant latency.

Millimeter wave communication systems can provide high data rates, but the system performance may degrade significantly due to interruptions by mobile blockers, such as humans or vehicles. High-frequency interruptions and lengthy blockage durations will degrade the quality of the user's experience. A promising solution is to employ the macrodiversity of base stations (BSs), where the user equipment (UE) can handover to other available BSs if the current serving BS gets blocked. However, an analytical model to evaluate the system performance of dynamic blockage events in this setting is unknown. In this paper, we develop a line-of-sight (LOS) dynamic blockage model and evaluate the probability, duration, and frequency of blockage events considering all the links to the UE which are not blocked by buildings or the user's own body. For a dense urban area, we also analyze the impact of non-LOS links on blockage events. Our results indicate that the minimum density of the BS required to satisfy the quality of service requirements of ultra-reliable low-latency communication applications will be driven mainly by blockage and latency constraints, rather than coverage or capacity requirements.

Fifth Generation (5G) Millimeter Wave (mmWave) cellular networks are expected to serve a large set of throughput-intensive, ultra-reliable, and ultra-low latency applications. To meet these stringent requirements, while minimizing the network cost, the 3rdGeneration 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.

5G is expected to expand the set of interactive applications enabled by the mobile network. Low end-to-end packet latency is a fundamental requirement for proper operation of those applications, but may be compromised in packet buffers shared with elastic applications that use greedy TCP sources for end-to-end transport. The accumulation of queuing delay by the elastic application degrades the latency for the interactive application, however light the throughput of the latter may be (as is the case with online gaming and over-the top voice). Buffer sharing is unavoidable in the RLC layer of the 3GPP RAN stack. To minimize its negative effect on interactive applications, we split the buffering between the RLC and PDCP layers. Then we equip the PDCP buffer with per-flow queues, and apply to the RLC buffer a new dynamic sizing mechanism that enforces the lowest queuing delay that is compatible with the existing configuration of the RLC connection. On a cellular link shared with a greedy TCP flow, our dynamic sizing solution can reduce the queuing delay of PING packets by up to two orders of magnitude compared to the default configuration with an RLC-only buffer of fixed size.

The bandwidth required for TV content distribution is rapidly increasing due to the evolution of high definition TV (HDTV) and ultra HDTV. Service providers are constantly trying to differentiate themselves by innovating new ways of distributing content more efficiently with lower cost and higher penetration. We propose a cost-efficient wireless architecture [wireless live TV (WiLiTV)], consisting of a mix of wireless access technologies [satellite, Wi-Fi, and LTE/5G millimeter wave (mmWave) overlay links], for delivering live TV services. In the proposed architecture, live TV content is injected into the network at selected locations, consisting of some homes and/or cellular base stations, using satellite antennas. The content is then further distributed to other homes using a house-to-house Wi-Fi network or an LTE/5G mmWave overlay. We construct an optimal content distribution network with the minimum number of satellite injection points, while preserving the highest quality of experience, for different neighborhood densities. We evaluate the framework using time-varying demand patterns and a diverse set of home location data provided from an operational content distribution network. Our study demonstrates that this architecture reduces the overall cost by 60% compared with the traditional architecture. We have also shown that the WiLiTV is robust in its support for several TV formats.

Unlike in the developed countries, TV white spaces are abundant in India and rural broadband coverage is negligible. Government of India has an ambitious plan to connect 250,000 rural offices (Gram Panchayat) using optical fiber based point of presence (PoP); this will allay, but not solve the rural broadband coverage problem. In this work, a middle-mile multihop mesh network operating in the TV UHF band is presented as a solution to providing seamless connectivity between the Gram Panchayat and village users. This network can coexist with TV broadcasting via the License Shared Access mechanism. The main contribution of this paper is a throughput optimization tool. Given the demography information of rural areas, the desired broadband speed and contention ratio, available frequency, location of fiber PoP, and propagation path-loss models of the TV UHF band - our optimization tool computes optimal power and routing for the multihop mesh network. The analysis is performed at the physical layer. Time division multiple access and spatial reuse of frequency are used for interference management in this work. Simply put, given demography information, our optimization tool determines at what power will broadband coverage will be feasible in the rural areas. This tool's design is separable and it can be utilized in other areas of the world, where demography and path-loss models can be replaced. Our optimization tool will be exemplified using results from one demographic region in India.