Content Delivery Probability Research Articles

Mathematical Modeling and Validation of Retransmission-Based Mutant MQTT for Improving Quality of Service in Developing Smart Cities

Unreliable networks often use excess bandwidth for data integration in smart cities. For this purpose, Messaging Queuing Telemetry Transport (MQTT) with a certain quality of service (QoS) is employed. Data integrity and data security are frequently compromised for reducing bandwidth usage while designing integrated applications. Thus, for a reliable and secure integrated Internet of Everything (IoE) service, a range of network parameters are conditioned to achieve the required quality of a deliverable service. In this work, a QoS-0-based MQTT is developed in such a manner that the transparent MQTT protocol uses Transmission Control Protocol (TCP)-based connectivity with various rules for the retransmission of contents if the requests are not entertained for a fixed duration. The work explores the ways to improve the overall content delivery probability. The parameters are examined over a transparent gateway-based TCP network after developing a mathematical model for the proposed retransmission-based mutant QoS-0. The probability model is then verified by an actual physical network where the repeated content delivery is explored at VM-based MQTT, local network-based broker and a remote server. The results show that the repeated transmission of contents from the sender improves the content delivery probability over the unreliable MQTT-based Internet of Things (IoT) for developing smart cities' applications.

Performance Analysis of Hybrid UAV Networks for Probabilistic Content Caching

Caching content in small-cell networks can reduce the traffic congestion in backhaul. In this article, we develop a hybrid caching network comprising of unmanned aerial vehicles (UAVs) and ground small-cell base stations (SBSs), where UAVs are preferred because of their flexibility and elevated platform for line of sight. First, we derive the association probability for the ground user affiliated with a UAV and ground SBS. Then, we derive the successful content delivery probability by considering both the intercell and intracell interference. We also analyze the energy efficiency of the hybrid network and compare it with the separate UAV and ground networks. We further propose the caching scheme to improve the successful content delivery by managing the content popularity, where the part of the caching capacity in each UAV and ground SBS is reserved to store the most popular content (MPC), while the remaining stores less popular contents. Numerical results unveil that the proposed caching scheme has an improvement of 26.6% in content delivery performance over the MPC caching, which overlooks the impact of content diversity during caching.

Cache-Enabled HetNets With Limited Backhaul: A Stochastic Geometry Model

With the rapid explosion of data volume from mobile networks, edge caching has received significant attentions as an efficient approach to boost content delivery efficiency by bringing contents near users. In this article, cache-enabled heterogeneous networks (HetNets) considering the limited backhaul is analyzed with the aid of the stochastic geometry approach. A hybrid caching policy, in which the most popular contents are cached in the macro BSs tier with the deterministic caching strategy and the less popular contents are cached in the helpers tier with the probabilistic caching strategy, is proposed. Correspondingly, the content-centric association strategy is designed based on the comprehensive state of the access link, the cache and the backhaul link. Under the hybrid caching policy, new analytical results for successful content delivery probability, average successful delivery rate and energy efficiency are derived in the general scenario, the interference-limited scenario and the mean load scenario. The simulation results show that the proposed caching policy outperforms the most popular caching policy in HetNets with the limited backhaul. The performance gain is dramatically improved when the content popularity is less skewed, the cache capacity is sufficient and the helper density is relatively large. Furthermore, it is confirmed that there exists an optimal helper density to maximize the energy efficiency of the cache-enabled HetNets.

Ultra Dense Edge Caching Networks With Arbitrary User Spatial Density

Cache-enabled small cells can be an effective solution to deliver contents to mobile users with much lower power and latency. While the trend for getting smaller and denser cells is clear, interference will soon become unmanageable and an obstacle when the number of content requests is massive. Moreover, content request is seldom a spatially homogeneous process due to physical impediments (e.g., buidings) and social activities, which makes resource allocation for content delivery more challenging. In this paper, we consider an ultra-dense network (UDN) in which content requests are served by cache-enabled access nodes which can either be active for delivering contents to users, or inactive to reduce interference and network energy consumption. Our aim is to devise an approach that can locally adapt the caching node density and content caching probabilities to accommodate any arbitrary user density and content request for maximizing the network's successful content delivery probability (SCDP). With a non-homogeneous spatial distribution for user equipments (UEs), we find that user-load, a parameter at the access node, plays a major role in the overall optimization. Simulation results illustrate that the proposed method can obtain superior performance against the considered benchmarks, with up to 150-160% increase, and our optimized solutions effectively adapt to the spatial-dependent user density.

On LOS Contribution to Ultra-Dense Network

Ultra-dense networks (UDNs) are widely considered as an effective solution to greatly improve coverage by shortening the communication distance between user equipments (UEs) and base stations (BSs). The reality of UDN is that line-of-sight (LOS) communication becomes more likely to occur but this desirable result also complicates the performance analysis of random UDNs and puts an obstacle on the design and optimization of UDNs. The aim of this paper is to derive analytical results that take into account the phenomenon of having mixed LOS and non line-of-sight (NLOS) links in UDNs. In particular, the use of an arbitrary shaped thinning process to model the LOS wireless links allowed us to investigate a wide set of scenarios for what concerns the desired and interfering power levels. Our contribution is an accurate approximation in closed form for the success content delivery probability (SCDP) that decouples the contribution from LOS and NLOS links. Simulation results corroborate the accuracy of the proposed approximation.

Toward a Connected Sky: Performance of Beamforming With Down-Tilted Antennas for Ground and UAV User Co-Existence

Providing connectivity to aerial users (AUs) such as cellular-connected unmanned aerial vehicles (UAVs) is a key challenge for tomorrow’s cellular systems. In this letter, the use of conjugate beamforming (CB) for simultaneous content delivery to an AU co-existing with multiple ground users (GUs) is investigated. In particular, a content delivery network of uniformly distributed massive multiple-input multiple-output (MIMO)-enabled ground base stations (BSs) serving both aerial and ground users through spatial multiplexing is considered. For this model, the successful content delivery probability (SCDP) is derived as a function of the system parameters. The effects of various system parameters such as antenna down-tilt angle, AU’s altitude, number of scheduled users, and number of antennas on the achievable performance are then investigated. Results reveal that, whenever the AU’s altitude is below the BS height, the antennas’ down-tilt angles yield an inherent tradeoff between the performance of the AU and the GUs. However, if the AU’s altitude exceeds the BS height, down-tilting the BS antennas with a considerably large angle improves the performance of both the AU and the GUs.

Fog-aided wireless networks for content delivery: A file-level carrier sensing based approach

We investigate a novel file-level carrier sensing based content delivery (FL-CSBCD) protocol to accommodate the transmission of multimedia files in fog-aided wireless networks. Particularly, the proposed FL-CSBCD protocol contains two phases, i.e., the file contention phase and the communication contention phase. The file contention phase aims to resolve the contentions among the requested multimedia files at each fog user equipments (F-UEs), such that the cache-hit performance is maximized. The communication contention phase is designed to resolve the collisions among concurrent content deliveries of the same file, such that the mutual interference can be suppressed. By modeling the fog-aided wireless networks with Poisson point process, we capture the density of active F-UEs, and evaluate the successful content delivery probability (SCDP) with the FL-CSBCD protocol. We show by simulations that the FL-CSBCD protocol can enhance the cache-hit performance while guarantee the coverage probability of content delivery.

Fog Radio Access Networks With Hierarchical Content Delivery

We investigate a novel hierarchical content delivery strategy for F-RAN in this paper to accommodate the acquisition of popular multimedia files. Particularly, the studied F-RAN is assumed to be formed by base stations (BSs), cache-enabled fog user equipments (F-UEs), and conventional cellular user equipments (C-UEs), where the BSs, F-UEs, and C-UEs are spatially distributed as independent HPPPs. Furthermore, we assume the presence of a multimedia content library F:= {1,2,...,F}. To facilitate the repetitive downloading of multimedia files in F for C-UEs, a novel hierarchical content delivery strategy, which comprises of the BS transmission phase and the F-UE transmission phase, is proposed. Particularly, under the proposed hierarchical content delivery strategy, a C-UE with a random file request is jointly and hierarchically served by its associated BS and the F-UEs within a distance of R d . Furthermore, to resolve the contentions among the F-UEs, a carrier sensing-based collision avoidance scheme is adopted in the F-UE transmission phase, and only the F-UEs which have the minimal back-off timer among their respective competitors are selected to deliver the cached file. As such, the proposed hierarchical content delivery strategy can substantially enhance the quality of experience of the F-RAN. In order to analyze the performance of the proposed hierarchical content delivery strategy, we derive the network successful content delivery probability of the F-RAN based on the HPPP approximation of active F-UEs. The simulation examples are presented to verify our analytical results.

Device to Device Networks With Cache-Enabled and Self-Sustained Mobile Helpers

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, an 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 energy availability, and thereby, the transmission probability of MHs which cache the f-th file at the local storage. Then, we derive the cache-hit probability and the coverage probability of the f-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.

Physical-Layer Security in Cache-Enabled Cooperative Small Cell Networks Against Randomly Distributed Eavesdroppers

This paper explores the physical-layer security in a small cell network (SCN) with cooperative cache-enabled small base stations (SBSs) in the presence of randomly distributed eavesdroppers. We propose a joint design on the caching placement and the physical-layer transmission to improve the secure content delivery probability (SCDP). We first put forward a hybrid caching placement strategy in which a proportion of the cache unit in each SBS is assigned to store the most popular files (MPFs), while the remaining is used to cache the disjoint subfiles (DSFs) of the less popular files in different SBSs as a means to enhance transmission secrecy and content diversity. We then introduce two coordinated multi-point (CoMP) techniques, namely, joint transmission (JT) and orthogonal transmission (OT), to deliver the MPFs and DSFs, respectively. We derive analytical expressions for the SCDP in each transmission scheme, considering both non-colluding and colluding eavesdropping scenarios. Based on the obtained analytical results, we jointly design the optimal transmission rates and the optimal caching assignment for maximizing the overall SCDP. Various insights into the optimal transmission and caching designs are further provided. Numerical results are also presented to verify our theoretical findings and to demonstrate the superiority of the proposed caching and transmission strategies.

Content Placement in Cache-Enabled Sub-6 GHz and Millimeter-Wave Multi-Antenna Dense Small Cell Networks

This paper studies the performance of cache-enabled dense small cell networks consisting of multi-antenna sub-6 GHz and millimeter-wave (mm-wave) base stations. Different from the existing works which only consider a single antenna at each base station, the optimal content placement is unknown when the base stations have multiple antennas. We first derive the successful content delivery probability by accounting for the key channel features at sub-6 GHz and mm-wave frequencies. The maximization of the successful content delivery probability is a challenging problem. To tackle it, we first propose a constrained cross-entropy algorithm which achieves the near-optimal solution with moderate complexity. We then develop another simple yet effective heuristic probabilistic content placement scheme, termed two-stair algorithm, which strikes a balance between caching the most popular contents and achieving content diversity. Numerical results demonstrate the superior performance of the constrained cross-entropy method and that the two-stair algorithm yields significantly better performance than only caching the most popular contents. The comparisons between the sub-6 GHz and mm-wave systems reveal an interesting tradeoff between caching capacity and density for the mm-wave system to achieve similar performance as the sub-6 GHz system.

Mitigating Interference in Content Delivery Networks by Spatial Signal Alignment: The Approach of Shot-Noise Ratio

Multimedia content, especially videos, is expected to dominate data traffic in next-generation mobile networks. Caching popular content at the network edge, namely content helpers (base stations and access points), has emerged as a solution for low-latency content delivery. Compared with traditional wireless communication, content delivery has a key characteristic that many signals coexisting in the air carry identical popular content. However, they can interfere with each other at a receiver if their modulation-and-coding (MAC) schemes are adapted to individual channels following the classic approach. To address this issue, we present a novel idea of content adaptive MAC (CAMAC) where adapting MAC schemes to content ensures that all signals carrying identical content are encoded using an identical MAC scheme to achieve spatial MAC alignment. Consequently, interference can be harnessed as signals to improve the reliability of wireless delivery. In the remaining part of the paper, we focus on quantifying the gain that CAMAC can bring to a content-delivery network by using a stochastic-geometry model. Specifically, content helpers are distributed as a Poisson point process and each of them transmits a file from a content database based on a given popularity distribution. Given a fixed threshold on the signal-to-interference ratio for successful transmission, it is discovered that the successful content-delivery probability is closely related to the distribution of the ratio of two independent shot noise processes, named a shot-noise ratio . The distribution itself is an open mathematical problem that we tackle in this work. Using stable-distribution theory and tools from stochastic geometry, the distribution function is derived in closed form. Extending the result in the context of content-delivery networks with CAMAC yields the content-delivery probability in different closed forms. In addition, the gain in the probability due to CAMAC is shown to grow with the level of skewness in the content popularity distribution.

Energy Efficiency Analysis of Cache‐Enabled Cellular Networks with Limited Backhaul

Caching in the cellular networks has been proposed as a promising technology for reducing the content delivery latency and backhaul cost. Since the backhaul capacity is limited in the practical scenario, the network performance analysis of base station (BS) caching should address the effects of the limited backhaul. This paper investigates the energy efficiency of the cache‐enabled cellular networks with the limited backhaul based on the stochastic geometry method. First, the successful content delivery probability (SCDP), which depends on the successful access delivery probability, successful backhaul delivery probability, and cache hit ratio, is analyzed under the limited backhaul. Based on the obtained SCDP results, we derive the analytical expressions of throughput, power consumption, and energy efficiency for various scenes including the general case, the interference‐limited case, and the mean load approximation case. The accuracy of theoretical analysis is verified by the Monte Carlo simulation. The simulation results show that BS caching can dramatically improve energy efficiency when the content popularity is skewed, the content library size is small, and the backhaul capacity is relatively small. Furthermore, it is confirmed that there exists an optimal BS density which maximizes the energy efficiency of the cache‐enabled cellular networks.

Cooperative Caching and Transmission Design in Cluster-Centric Small Cell Networks

Wireless content caching in small cell networks (SCNs) has recently been considered as an efficient way to reduce the data traffic and the energy consumption of the backhaul in emerging heterogeneous cellular networks. In this paper, we consider a cluster-centric SCN with combined design of cooperative caching and transmission policy. Small base stations (SBSs) are grouped into disjoint clusters, in which in-cluster cache space is utilized as an entity. We propose a combined caching scheme, where part of the cache space in each cluster is reserved for caching the most popular content in every SBS, while the remaining is used for cooperatively caching different partitions of the less popular content in different SBSs, as a means to increase local content diversity. Depending on the availability and placement of the requested content, coordinated multi-point technique with either joint transmission or parallel transmission is used to deliver content to the served user. Using Poisson point process for the SBS location distribution and a hexagonal grid model for the clusters, we provide analytical results on the successful content delivery probability of both transmission schemes for a user located at the cluster center. Our analysis shows an inherent tradeoff between transmission diversity and content diversity in our cooperation design. We also study the optimal cache space assignment for two objective functions: maximization of the cache service performance and the energy efficiency. Simulation results show that the proposed scheme achieves performance gain by leveraging cache-level and signal-level cooperation and adapting to the network environment and user quality-of-service requirements.

Cache-Enabled Device to Device Networks With Contention-Based Multimedia Delivery

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.