One of the key features of 5G is the NR V2X (vehicle to everything) sidelink that has been first standardized during Release 16. V2X is designed to operate in a distributed manner, enabling operation independent of wireless network coverage. This differs fundamentally from traditional cellular networks where resources are centrally managed by gNodeBs. For distributed operation, 3GPP has defined a set of pre-configuration parameters in the Radio Resource Control (RRC) specification which can be set by the network, or pre-provisioned in the UE for OOC operation. The standard does not assign values for the pre-configuration parameters, but rather defines value ranges to provide flexibility and accommodate a rich span of applications and environments. To enable efficient and inter-operable operation these parameters need to be set carefully. In this paper, we evaluate pre-configuration parameter selection for several key aspects of NR Release-16 sidelink operations. In particular, we focus on distance-based quality of service, congestion control and resource reservation. Our results suggest parameter values suitable for various V2X applications, traffic types and operating conditions.

Two-hop relay transmissions can be exploited to improve the coverage and spectral efficiency of cellular networks. Using stochastic geometry, we develop analytical models for the uplink coverage probability and spectral efficiency of two-hop device-to-device (D2D) relay-assisted cellular networks, in which user equipments (UEs) with poor direct links to the base station (BS) can complete their transmissions with the help of a relay UE. We assume overlay inband D2D operation such that D2D link transmissions (from the source UE to the relay UE) use uplink spectrum, but do not interfere with uplink transmissions in the same cell. We model the base stations (BSs) and candidate relay UEs as Poisson point processes (PPPs) and derive the two-hop coverage probability capturing the correlation of the two links in two-hop transmission. We then model the uplink spectral efficiency, which takes into account the D2D link resource usage and depends on the mode selection strategy. Numerical results show that the analytical models provide reasonable approximations of the cellular uplink performance with a Rayleigh fading assumption. They also reveal insights into the coverage and spectral efficiency gains achievable when leveraging D2D relays on the uplink of a cellular network.

The susceptibility of millimeter waveform propagation to blockages limits the coverage of millimeter-wave (mmWave) signals. To overcome blockages, we propose to leverage two-hop device-to-device (D2D) relaying. Using stochastic geometry, we derive expressions for the downlink coverage probability of relay-assisted mmWave cellular networks when the D2D links are implemented in either uplink mmWave or uplink microwave bands. We further investigate the spectral efficiency (SE) improvement in the cellular downlink, and the effect of D2D transmissions on the cellular uplink. For mmWave links, we derive the coverage probability using dominant interferer analysis while accounting for both blockages and beamforming gains. For microwave D2D links, we derive the coverage probability considering both line-of-sight and non-line-of-sight (NLOS) propagation. Numerical results show that downlink coverage and SE can be improved using two-hop D2D relaying. Specifically, microwave D2D relays achieve better coverage because D2D connections can be established under NLOS conditions. However, mmWave D2D relays achieve better coverage when the density of interferers is large because blockages eliminate interference from NLOS interferers. The SE on the downlink depends on the relay mode selection strategy, and mmWave D2D relays use a significantly smaller fraction of uplink resources than microwave D2D relays.

Millimeter-wave (mmWave) communications is one of the most promising candidate technologies for next generation cellular networks due to the global bandwidth shortage for mobile broadband access. The susceptibility of millimeter waveform propagation to blockages, however, may largely restrict the coverage of mmWave signals. To overcome blockages, we propose to leverage two-hop device-to-device (D2D) relaying. Using stochastic geometry, we develop a coverage probability model for the downlink of a relay- assisted mmWave cellular network using dominant interferer analysis, which accounts for both beamforming gains and blockages. Theoretical analysis and simulation results show that the downlink coverage of a mmWave cellular network can be improved by using two-hop D2D relay transmissions.