This paper studies the performance of large-scale cache-enabled device-to-device (D2D) networks with homogeneous Poisson point process distributed mobile helpers(MHs) and user equipments (UEs). The MHs are assumed to have caching capabilities and able to serve the random requests from the UEs within the collaboration distance of D2D transmission. To avoid collisions among the concurrent transmissions, a contention-based multimedia delivery protocol is proposed, under which a MH is allowed to transmit only if its back-off timer is the smallest among its associated contenders. By applying tools from stochastic geometry, the transmission probability of MHs is derived and analyzed. We then characterize the coverage probability of the randomly requested files and thereby the successful content delivery probability of the cache-enabled D2D network. Based on the obtained results of successful content delivery probability, the optimal probabilistic caching strategy of MHs is investigated. Particularly, under the proposed contention-based multimedia delivery protocol, it is recommended to simply cache the most popular file at each MH to maximize the successful content delivery probability of the cache-enabled D2D network. Simulations are provided to validate our analysis.

The services of enhanced mobile broadband (eMBB) and the ultra-reliable low-latency communication (URLLC) enabled by 5G new radio (NR) are considered as the essential prerequisites of the future intelligent transportation systems. Particularly, the eMBB service is designed to provide extremely high data rate for content delivery and thereby can significantly enhance the quality of experience (QoE) of the bandwidth-hungry in-vehicle entertainment applications. On the other hand, the URLLC is designed to tackle the stringent requirements on the latency and reliability of the critical packets transmissions, and thereby can facilitate the autonomous driving of the connected vehicles. In this paper, under the scenario of a one-way highway vehicular network, we address the issue of joint resource allocations of the eMBB and URLLC traffics for the enhancement of the network performance. The eMBB traffic is assumed to be full-buffered and scheduled at the boundary of each time slot for multimedia transmissions. During each eMBB transmission interval, random arrivals of URLLC traffics are assumed. To satisfy the latency constraint of the URLLC transmissions, the eMBB time slot is divided into minislots and the newly arrived URLLC traffic is promptly scheduled in the next minislot by puncturing the on-going eMBB traffics. Further, to guarantee the reliability of the URLLC traffic, guard zones are deployed around the vehicle receivers as protections and the eMBB transmissions inside the guard zones are prohibited. Under this context, we first derive the transmission probability of the RSU nodes. Then, based on the obtained results, we capture association probabilities of the vehicle receivers for URLLC and eMBB traffics, respectively. Finally, the coverage performance of the vehicle-to-vehicle (V2V) links and the rate coverage performance of the vehicle-to-infrastructure (V2I) links are analyzed.

Sequences with low/zero ambiguity zone (LAZ/ZAZ) properties are useful in modern communication and radar systems operating over mobile environments. This paper first presents a new family of ZAZ sequence sets motivated by the “modulating” zero correlation zone (ZCZ) sequences which were first proposed by Popovic and Mauritz. We then introduce a second family of ZAZ sequence sets with comb-like spectrum, whereby the local Doppler resilience is guaranteed by their inherent spectral nulls in the frequency domain. Finally, LAZ sequence sets are obtained by exploiting their connection with a novel class of mapping functions. These proposed unimodular ZAZ and LAZ sequence sets are cyclically distinct and asymptotically optimal with respect to the existing theoretical bounds on ambiguity functions.

In this paper, a novel opportunistic spectrum access (OSA) protocol, namely the primary receiver assisted interference avoidance (PRA-IA) protocol, is proposed and analyzed in cognitive radio (CR) networks to simultaneously exploit the underutilized positions of the primary network and avoid transmission collisions among secondary transmitters (STs). Particularly, the proposed PRA-IA protocol is comprised of two processing phases, i.e., the qualification phase and the contention phase. The qualification phase is designed to preselect the set of STs (denoted by eligible STs) which are in the “spatial holes” of the active primary receivers (PRs) to guarantee the primary transmissions. The contention phase, on the other hand, aims to improve the performance of secondary transmissions by further resolving the potential collisions among the eligible STs based on the randomly generated back-off timer. With mathematical tools from stochastic geometry, the transmission probability of active STs, the coverage probability and thereby the spatial throughput of the CR network under the PRA-IA protocol are characterized and analyzed. Further, simulations are provided to verify the accuracy of the derived analytical results and demonstrate the impacts of key network parameters on network performance. From the numerical results, it is shown that the proposed PRA-IA protocol is superior to the PRA protocol on the spatial throughput trade-off of the primary and secondary networks.

In this paper, we develop a novel framework to analyze the successful content delivery performance of device to device (D2D) networks with cache-enabled and self-sustained mobile helpers (MHs). Particularly, to facilitate the access of multimedia services for user equipments (UEs) under intermittent energy arrivals, an energy based content delivery strategy, namely the energy dependent nearest MH transmission (ED-NMT) strategy is considered. Under the proposed ED-NMT strategy, a MH is capable of delivering the content to the requesting UE if sufficient energy is harvested in its battery and it is the nearest MH of the tagged UE. Assuming infinite battery capacity, with ED-NMT strategy, we characterize the the energy availability and thereby the transmission probability of MHs which cache the ƒ-th file at the local storage. Then, we derive the cache-hit probability and the coverage probability of the ƒ-th file. Finally, with the obtained results, we evaluate the successful content delivery probability (SCDP) of the D2D network with cache-enabled and self-sustained MHs. It is shown through both analytical and numerical results that under certain conditions, there is no performance loss due to stochastic and intermittent energy arrivals.