Effect Of User Mobility Research Articles

Effect of user mobility under Rician fading on power allocation for non-orthogonal multiple access strategy

Effect of user mobility under Rician fading on power allocation for non-orthogonal multiple access strategy

Effect of User Mobility under Rician Fading on Power Allocation for Non-Orthogonal Multiple Access (PA-NOMA) Strategy

Effect of User Mobility under Rician Fading on Power Allocation for Non-Orthogonal Multiple Access (PA-NOMA) Strategy

Handover Approach for Heterogeneous Networks with Improved K-Partite Graph

Vertical handovers (VH) is said to be a significant effect of user mobility in a diverse wireless network as it causes a major effect on network performances, like call blocking probability, packet delay, or throughput. On the other hand, the analysis of VH meets a lot of complexities when it comes to investigation, including network modeling that was very complex owing to the diversity in topology. This article aims to present a VH method by means of graph theory. At first, the improved k-partite graph is exploited to model the VH issues in HetNets. Second, improved Dijkstra’s algorithm (DA) is deployed for choosing the best path. Further, the analytic hierarchy process is used for estimating the adaptive weights among nodes. Accordingly, optimal selection of weights in DA is performed depending on a hybridized model named as grey wolf upgraded CSO. Ultimately, several metrics such as throughput, packet jitter, and delay and packet losses indicate that the created strategy is efficient.

Adding edge dynamics to bipartite random-access networks

We consider random-access networks with nodes representing transmitter-receiver pairs whose signals interfere with each other depending on their vicinity. Data packets arrive at the nodes over time and form queues. The nodes can be either active or inactive: a node deactivates at unit rate, while it activates at a rate that depends on its queue length, provided none of its neighbors is active. In order to model the effects of user mobility in wireless networks, we analyze dynamic interference graphs where the edges are allowed to appear and disappear over time. We focus on bipartite graphs and study the transition time between the two states where one part of the network is active and the other part is inactive, in the limit as the queue lengths become large. Depending on the speed of the dynamics, we are able to obtain a rough classification of the effects of the dynamics on the transition time.

Influence of User Mobility and Antenna Placement on System Loss in B2B Networks

In this paper, the influence of user mobility and on-body antenna placement on system loss in body-to-body communications in indoor and outdoor environments and different mobility scenarios is studied, based on system loss measurements at 2.45 GHz. The novelty of this work lies on the proposal of a classification model to characterise the effect of user mobility and path visibility on system loss, allowing to identify the best set of on-body antenna placements. To quantify the influence of visibility and mobility on the average system loss, a combined score is proposed, allowing to map system loss onto the degree of visibility and mobility that depends on the scenario being considered and on on-body antenna placements. Overall, a good agreement is observed between the proposed classification model and the average measured values of system loss, with the higher values of combined scores being associated with lower values of systems loss. For the cases under study, the average values of system loss are 61.6 dB for the cases of the antennas being positioned only on the front of the body and/or the head, and 64.5 dB if at least one of the antennas is placed on an arm.

Rate-Splitting Multiple Access to Mitigate the Curse of Mobility in (Massive) MIMO Networks

Rate-Splitting Multiple Access (RSMA) is a robust multiple access scheme for downlink multi-antenna wireless networks. RSMA relies on multi-antenna Rate-Splitting (RS) at the transmitter and Successive Interference Cancellation (SIC) at the receivers. In this work, we study the performance of RSMA under the important setup of imperfect Channel State Information at the Transmitter (CSIT) originating from user mobility and latency/delay (between CSI acquisition and data transmission) in the network. We derive a lower bound on the ergodic sum-rate of RSMA for an arbitrary number of transmit antennas, number of users, user speed and transmit power. Then, we study the power allocation between common and private streams and obtain a closed-form solution for optimal power allocation that maximizes the obtained lower bound. The proposed power allocation greatly reduces precoder design complexity for RSMA. By Link-Level Simulations (LLS), we demonstrate that RSMA with the proposed power allocation is robust to the degrading effects of user mobility and has significantly higher performance compared to conventional multi-user (massive) Multiple-Input Multiple-Output (MIMO) strategies. The work has important practical significance as results demonstrate that, in contrast to conventional multi-user (massive) MIMO whose performance collapse under mobility, RSMA can maintain reliable multi-user connectivity in mobile deployments.

Distributed MIMO for Li-Fi: Channel Measurements, Ray Tracing and Throughput Analysis

LiFi has been considered as a promising candidate for future wireless indoor networks. The IEEE P802.15.13 and P802.11bb standardization groups agreed upon channel models generated using the non-sequential ray tracing approach of OpticStudio. In this paper, in order to validate the channel modelling approach, at first 2×2 multiple-input multiple-output (MIMO) channel measurements are carried out over 200 MHz bandwidth using a channel sounder. The experimental scenario is also modeled in 3D by applying ray tracing. The obtained results indicate good agreement between simulations and measured channel impulse responses, from which parameters such as path loss and delay spread are derived. After validating the channel modeling approach, we investigate the singular values and the effect of user mobility onto the performance in a 4×4 distributed multi-user MIMO scenario.

Performance Analysis of Dynamic Downlink PPP Cellular Networks Over Generalized Fading Channels With MRC Diversity

This paper proposes novel and generalized expressions to characterize the performance of modern cellular networks under realistic user mobility behavior. The η-μ distribution is employed to derive the received power probability density function, the average bit error rate for different modulation schemes, and the coverage probability assuming a Poisson point process spatial distribution of base stations in downlink. The user is assumed to experience fading with Maximum Ratio Combining (MRC) and move according to a random way-point mobility model. The proposed expressions are applicable to different widely-used fading environments, such as Rayleigh and Nakagami-m as particular cases, by an appropriate selection of the η-μ parameters. Monte Carlo simulation was used to show the validity of the proposed expressions. The generalized expressions allow the system designer to quantify the effects of user mobility on the cellular network performance, in different propagation environments, and network topologies as a function of the number of base stations and MRC branches.

Reducing Offloading Latency for Digital Twin Edge Networks in 6G

6G is envisioned to empower wireless communication and computation through the digitalization and connectivity of everything, by establishing a digital representation of the real network environment. Mobile edge computing (MEC), as one of the key enabling factors, meets unprecedented challenges during mobile offloading due to the extremely complicated and unpredictable network environment in 6G. The existing works on offloading in MEC mainly ignore the effects of user mobility and the unpredictable MEC environment. In this paper, we present a new vision of Digital Twin Edge Networks (DITEN) where digital twins (DTs) of edge servers estimate edge servers’ states and DT of the entire MEC system provides training data for offloading decision. A mobile offloading scheme is proposed in DITEN to minimize the offloading latency under the constraints of accumulated consumed service migration cost during user mobility. The Lyapunov optimization method is leveraged to simplify the long-term migration cost constraint to a multi-objective dynamic optimization problem, which is then solved by $Actor$ - $Critic$ deep reinforcement learning. Simulations results show that our proposed scheme effectively diminishes the average offloading latency, the offloading failure rate, and the service migration rate, as compared with benchmark schemes, while saving the system cost with DT assistance.

On the Impact of User Mobility on the Performance of Wireless Receivers

In this paper we study the effect of user mobility on the performance of wireless digital receivers operating in the presence of fading, shadowing, and path loss. Recently, it was shown in (Lopez-Fernandez et al., 2018) that the distribution of the received power of a mobile receiver is given by the incomplete moment of the underlying static fading distribution. In this paper, we consider the random waypoint mobility model and show that, in fact, other performance metrics of the mobile receiver can be expressed in terms of statistical characterizations of the fading distribution in the static case. We consider the moment generating function of the received signal-to-noise ratio (SNR), the average bit error rate and the average channel capacity and present analytical results for these performance metrics in different generalized fading environments. Asymptotic expressions are also derived that converge to the exact performance at high values of the SNR. Numerical results are provided to quantify the effects of network dimension, path loss coefficient and fading model parameters on the performance metrics of the mobile receiver.

Effect of User Mobility and Channel Fading on the Outage Performance of UAV Communications

Many wireless networks operate in a mobile environment with randomly moving user terminals. This letter analytically characterizes the impact of ground user mobility, propagation environment and channel fading on the outage performance of unmanned aerial vehicle (UAV) communications. Closed-form expressions for the outage probability using the random waypoint model for ground user mobility, UAV channel models for different propagation environments and the Nakagami-m model for fading channels are derived. Furthermore, the outage analysis takes into account the effect of co-channel interference by both the stationary and mobile users. Numerical results are presented to demonstrate the interplay between the communication performance and the system parameters.

Handover Rate Characterization in 3D Ultra-Dense Heterogeneous Networks

Ultra-dense networks (UDNs) envision the massive deployment of heterogeneous base stations (BSs) to meet the desired traffic demands. Furthermore, UDNs are expected to support the diverse devices e.g., personal mobile devices and unmanned aerial vehicles. User mobility and the resulting excessive changes in user to BS associations in such highly dense networks may however nullify the capacity gains foreseen through BS densification. Thus, there exists a need to quantify the effect of user mobility in UDNs. In this paper, we consider a three-dimensional $N$ -tier downlink network and determine the association probabilities and inter/intra tier handover rates using tools from stochastic geometry. In particular, we incorporate user and BSs’ antenna heights into the mathematical analysis and study the impact of user height on the association and handover rate. The numerical trends show that the intra-tier handovers are dominant for the tiers with shortest relative elevation w.r.t. the user and this dominance is more prominent when there exists a high discrepancy among the tiers’ heights. However, biasing can be employed to balance the handover load among the network tiers.

Exploiting Mobility in Cache-Assisted D2D Networks: Performance Analysis and Optimization

Caching popular content at mobile devices, accompanied by device-to-device (D2D) communications, is one promising technology for effective mobile content delivery. User mobility is an important factor when investigating such networks, which unfortunately was largely ignored in most previous works. Preliminary studies have been carried out but the effect of mobility on the caching performance has not been fully understood. In this paper, by explicitly considering users’ contact and inter-contact durations via an alternating renewal process, we first investigate the effect of mobility with a given cache placement. A tractable expression of the data offloading ratio, i.e., the proportion of requested data that can be delivered via D2D links, is derived, which is proved to be increasing with the user moving speed. The analytical results are then used to develop an effective mobility-aware caching strategy to maximize the data offloading ratio. Simulation results are provided to confirm the accuracy of the analytical results and also validate the effect of user mobility. Performance gains of the proposed mobility-aware caching strategy are demonstrated with both stochastic models and real-life data sets. It is observed that the information of the contact durations is critical to design cache placement, especially when they are relatively short or comparable to the inter-contact durations.

Effect of User Mobility upon Trust Building among Autonomous Content Routers in an Information‐Centric Network

The capability of proactive in‐network caching and sharing of content is one of the most important features of an information‐centric network (ICN). We describe an ICN model featuring autonomous agents controlling the content routers. Such agents are unlikely to share cached content with other agents without an incentive to do so. To stimulate cooperation between agents, we adopt a reputation and trust building scheme that is able to explicitly account for both objective current content availability and subjective willingness to cooperate. The scheme is further complemented with a so‐called one‐time goodwill mechanism introduced to avoid penalizing agents failures to provide temporarily unavailable content. In a simulated ICN environment under a modified Random Waypoint user mobility model, we investigate the resiliency of the reputation and trust building scheme to subversion, that is, strategic (selfish or malicious) agents acquiring higher trust values than honest ones, for varying user mobility scenarios. The scheme proves resilient in low‐mobility scenarios, while increased user mobility is shown to have a negative effect. The one‐time goodwill mechanism partly remedies this for high‐mobility scenarios. We validate the results by comparison with an existing reputation and trust building scheme and with an alternative user mobility model.

Effect of User Mobility on the Performance of Device-to-Device Networks With Distributed Caching

We consider a distributed caching device-to-device network in which a user’s file of interest is cached as several portions in the storage of other devices in the network. Assuming that the user needs to obtain all these file portions, the portions cached farther away naturally become the performance bottleneck. This is due to the fact that dominant interferers may be closer to the receiver than the serving device. Using a simple stochastic geometry model, we concretely demonstrate that this bottleneck can be loosened if the users are mobile. Gains obtained from mobility are quantified in terms of coverage probability.

Dynamic Analysis of Load Balancing Algorithms in LTE/LTE-A HetNets

The performance of load balancing algorithms in HetNets is investigated in this paper. We performed a comparative analysis of three load balancing algorithms, including our previously proposed algorithm based on local optimization. We evaluated the offloading capabilities, fairness of the distribution of the load across base stations and spectral efficiency gains in the downlink. As opposed to previous studies were the evaluation of such algorithms was carried out under static conditions, in this study we performed the analysis in a dynamic and more realistic scenario. We quantified the effects of user mobility and the triggering of handovers during the load balancing process on the gains provided by the algorithms. We were able to show that the resulting gains in spectral efficiency after balancing the load are not as high as previously reported under static conditions. Our study shows that user mobility does affect the benefits of load balancing algorithms, particularly in the case of iterative algorithms. However, balancing the load in a HetNet still leads to faster downlink data rates, up to 80% gain for cell edge users was achieved according to our study. Our results show that our load balancing algorithm was able to provide similar benefits compared to the other two algorithms, however our approach is substantially less complex. Additionally, our load balancing algorithm was superior in terms of its practicality due to a minimum level of coordination and exchange of information among base stations.

Impact of General Channel Aging Conditions on the Downlink Performance of Massive MIMO

Recent works have identified massive multiple-input-multiple-output (MIMO) as a key technology for achieving substantial gains in spectral and energy efficiency. Additionally, the turn to low-cost transceivers, being prone to hardware impairments is the most effective and attractive way for cost-efficient applications concerning massive MIMO systems. In this context, the impact of channel aging, which severely affects the performance, is investigated herein by considering a generalized model. Specifically, we show that both Doppler shift because of the users' relative movement as well as phase noise due to noisy local oscillators (LOs) contribute to channel aging. To this end, we first propose a joint model, encompassing both effects, in order to investigate the performance of a massive MIMO system based on the inevitable time-varying nature of realistic mobile communications. Then, we derive the deterministic equivalents (DEs) for the signal-to-noise-and-interference ratios (SINRs) with maximum ratio transmission (MRT) and regularized zero-forcing precoding (RZF). Our analysis not only demonstrates a performance comparison between MRT and RZF under these conditions, but most importantly, it reveals interesting properties regarding the effects of user mobility and phase noise. In particular, the large antenna limit behavior depends profoundly on both effects, but the burden due to user mobility is much more detrimental than phase noise even for moderate user velocities ($\approx30$ km/h), while the negative impact of phase noise is noteworthy at lower mobility conditions.

Direct Connection on the Move: Characterization of User Mobility in Cellular-Assisted D2D Systems

Next-generation device-to-device (D2D) communication technology, in which a cellular network assists proximal users at all stages of their interaction, is rapidly developing. Previous research has thoroughly characterized D2D performance aspects from discovery to connection establishment, security, and service continuity; however, prospective D2Denabled applications and services envision highly opportunistic device contacts as a consequence of unpredictable human user mobility. Therefore, mobility's impact on D2D communication requires careful investigation to understand the practical operational efficiency of future cellular-assisted D2D systems. This article offers a first-hand tutorial on various implications of D2D mobility across different user movement patterns and mobility-related parameters and proposes an assessment methodology for D2D-enabled systems. The rigorous system-level evaluation conducted for this study delivers important conclusions on the effects of user mobility in emerging D2D-centric systems.

Mobility Aware Virtual Network Embedding

Over the last years, network virtualization has become one of the most promising solutions for sustainability towards the ongoing increase of data demand in mobile networks. Within that context, the virtual network embedding problem has recently been studied extensively and many different solutions have been proposed; but, mainly these studies have focused on wired networks. The main purpose of this paper is to provide an optimization framework for optimal virtual network embedding, including a heuristic algorithm with low computational complexity, by explicitly considering the effect of supporting the actual user mobility, assuming the emerging Distributed Mobility Management (DMM) scheme as well as a traditional Centralized Mobility Management (CMM) scheme. In addition to that, service differentiation is introduced, giving higher priority to time-critical over-the-top (OTT) services compared to more traditional elastic Internet applications. The performance of the proposed framework is compared to mobility agnostic greedy algorithms as well as virtual network embedding algorithms from the literature. Numerical investigations reveal that the effect of user mobility has a significant impact on the design of virtual networks. Additionally, the mobility aware scheme can provide tangible gains in the overall performance compared with the previous proposed schemes that do not take explicitly into account the effect of user mobility.

A novel security-centric framework for D2D connectivity based on spatial and social proximity

Device-to-device (D2D) communication is one of the most promising innovations in the next-generation wireless ecosystem, which improves the degrees of spatial reuse and creates novel social opportunities for users in proximity. As standardization behind network-assisted D2D technology takes shape, it becomes clear that security of direct connectivity is one of the key concerns on the way to its ultimate user adoption. This is especially true when a personal user cluster (that is, a smartphone and associated wearable devices) does not have a reliable connection to the cellular infrastructure. In this paper, we propose a novel framework that embraces security of geographically proximate user clusters. More specifically, we employ game-theoretic mechanisms for appropriate user clustering taking into account both spatial and social notions of proximity. Further, our information security procedures implemented on top of this clustering scheme enable continuous support for secure direct communication even in case of unreliable/unavailable cellular connectivity. Explicitly incorporating the effects of user mobility, we numerically evaluate the proposed framework by confirming that it has the potential to substantially improve the resulting system-wide performance.