The 5G New Radio (NR) standard for wireless communications supports the millimetre-wave (mmWave) spectrum to yield unprecedented improvement of the access network capacity. However, intermittent blockages in the mmWave signal may degrade the system performance and lead to the under-utilisation of the allocated resources. To circumvent this problem, the transmission slot-time shall be adjusted according to the blockage condition, avoiding the resource under-utilisation. In this paper, we propose that the 5G NR flexible numerology should be applied to adapt the slot-time in order to mitigate the blockage effects. We validate this claim by analysing the expected data rate of a mmWave system, under a range of blockage scenarios. We show that different blockage scenarios may require different numerologies to produce best performance, and that the correct choice of numerology may improve this performance by as much as hundreds of Mbps. Our results carry insights important for the design of blockage-aware scheduling mechanisms for 5G.
The literature on blockage mitigation in mmWave communication is mostly focused on techniques that rely on spatial macro-diversity. Such techniques allow the transmitter to find an alternative physical path for the mmWave signal when the primary LOS path fails due to a blockage event. The main techniques considered are: (i) : usage of surfaces made of materials that reflect the mmWave signal to cover an obstructed spot through a NLOS path @cite_17 @cite_28 ; (ii) : forwarding the transmission to a relay node that has a LOS path with the UE @cite_19 @cite_18 ; (iii) : moving the AP location during the transmission to a position where there is a LOS path @cite_24 ; (iv) : associating the UE with multiple AP , so the UE can have a LOS path served by a backup AP @cite_9 @cite_2 .
@cite_18 @cite_28 @cite_9 @cite_24 @cite_19 @cite_2 @cite_17
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Millimeter wave (mmWave) is recognized as a promising technology for the fifth generation cellular networks as it can increase system capacity significantly due to its abundant spectrum resources. Since mmWave signals are highly sensitive to blockages, received signals can experience severe none-line-of-sight (NLOS) pathloss if there are blockages between a mmWave base-station (mBS) and a user equipment (UE). Relay nodes (RNs) can be used in a mmWave cellular network to help alleviate blockages and provide alternative line-of-sight (LOS) links when blockage occurs. In this paper, we provide coverage study in a mmWave network with various distributions of mBSs, UEs, blockages, and RNs. Both analytical and simulation results show that with the assistance of RNs more LOS links are expected and the network signal-to-noise ratio (SNR) or signal-to-interference-noise ratio (SINR) performance can be improved significantly. Due to high propagation loss and directivity, mmWave links are very susceptible to obstacles blocking the direct line-of-sight path for communication. In this case, indirect communication via a relay may help to circumvent the blockage. In this paper, we propose a two-hop relay selection algorithm for mmWave communications. For the relay selection, we analyze the probability that an indirect path is available given that the direct path is blocked trough geometric analysis. We then choose the most promising node among neighbors as relay. The analysis shows that the probability of an indirect path is a function of the obstacle density as well as the location of relay nodes. When the density is low, the correlation between the direct path and an indirect path is dominant, i.e., the angle between the direct path and the path to relay should be large, whereas the blockage probability of an indirect path becomes more dominant as the density increases, i.e., relay links should not be too long. The probability analysis also allows to decide an initial antenna angle for beam-training in mobile mmWave environments. Through numerical studies, we verify our analytical results. Blocking objects (blockages) between a transmitter and receiver cause wireless communication links to transition from line-of-sight (LOS) to non-LOS propagation, which can greatly reduce the received power, particularly at the higher frequencies such as millimeter wave. We consider a cellular network in which a mobile user attempts to connect to two or more base stations (BSs) simultaneously, to increase the probability of at least one LOS link, which is a form of macrodiversity. We develop a framework for determining the LOS probability as a function of the number of BSs, when taking into account the correlation between blockages: for example, a single blockage close to the device—including the user’s own body—could block multiple BSs. We consider the impact of the size of blocking objects on the system’s @math th order LOS probability and show that macrodiversity gains are higher when the blocking objects are small. We also show that the BS density must scale as the square of the blockage density to maintain a given level of LOS probability. Millimeter wave (mmWave) communications systems are promising candidate to support extremely high data rate services in future wireless networks. MmWave communications exhibit high penetration loss (blockage) and require directional transmissions to compensate for severe channel attenuations and for high noise powers. When blockage occurs, there are at least two simple prominent options: 1) switching to the conventional microwave frequencies (fallback option) and 2) using an alternative non-blocked path (relay option). However, currently it is not clear under which conditions and network parameters one option is better than the other. To investigate the performance of the two options, this paper proposes a novel blockage model that allows deriving maximum achievable throughput and delay performance of both options. A simple criterion to decide which option should be taken under which network condition is provided. By a comprehensive performance analysis, it is shown that the right option depends on the payload size, beam training overhead, and blockage probability. For a network with light traffic and low probability of blockage in the direct link, the fallback option is throughput- and delay-optimal. For a network with heavy traffic demands and semistatic topology (low beam-training overhead), the relay option is preferable.