Non-uniform User Distribution Research Articles

Non-Uniform Full-Dimension MIMO: New Topologies and Opportunities

Different from traditional massive MIMO arranging ULA only in the azimuth direction, FD-MIMO offers a practical means of realizing massive MIMO in limited space by equipping URA at the base station, which provides extra spatial degree of freedom in elevation domain and eliminates inter-cell interference considerably. Consequently, FD-MIMO draws much attention from both academia and industry for future 5G wireless communication systems. However, the spectral efficiency of URA is lower than its ULA counterpart when adopting the same number of antenna elements due to low resolution caused by the non-uniform distribution of users in the elevation domain. In this article, the concept of NUFD-MIMO is proposed for the first time, which inherits the advantages and is capable of handling the challenges of traditional FD-MIMO. Structured NURA is designed to enhance the spatial resolution of FD-MIMO in the elevation domain and the corresponding two-dimensional precoding is introduced as well. Moreover, some insights on actual NUFD-MIMO implementations in millimeter-wave systems are provided, including non-uniform multi-beam and two-layer phase shifter feeding network. Finally, future work

Optimal Relay Station Placement with Non-uniform User Distribution

An relay station (RS) is a low-cost alternative to upgrading a conventional communication infrastructure. It can cope with ever-increasing wireless traffic demand and eliminate shadow areas efficiently. Accordingly, relay-based networking is a key technology for the next generation wireless communication infrastructure. In a relay-based network, the signal to interference plus noise ratio (SINR) and the throughput of the mobile stations (MSs), especially those located at cell edges, heavily depend on the location of the RSs. Hence, it is important to determine the optimal RS locations. In this paper, we address an anomaly which causes a serious fairness problem among MSs when the RS locations are determined only by throughput maximization. Moreover, RS locations were considered for a non-uniform geographical user distribution environment, because in the real world users are not uniformly distributed. We propose a utility optimal RS placement scheme based on a genetic algorithm (GA), which considers both the fairness problem and the non-uniform user distribution. An extensive simulation study verified that the proposed scheme extends cell coverage and maximizes utility while guaranteeing fairness among MSs.

5G Ultradense Networks With Nonuniform Distributed Users

User distribution in ultradense networks (UDNs) plays a crucial role in affecting the performance of UDNs due to the essential coupling between the traffic and the service provided by the networks. Existing studies are mostly based on the assumption that users are uniformly distributed in space. The nonuniform user distribution has not been widely considered despite that it is much closer to the real scenario. In this paper, radiation and absorbing model (R&A model) is first adopted to analyze the impact of the nonuniformly distributed users on the performance of 5G UDNs. Based on the R&A model and queueing network theory, the stationary user density in each hot area is investigated. Furthermore, the coverage probability, network throughput, and energy efficiency are derived based on the proposed theoretical model. Compared with the uniformly distributed assumption, it is shown that nonuniform user distribution has a significant impact on the performance of UDNs.

DNA-GA: A Tractable Approach for Performance Analysis of Uplink Cellular Networks

In this paper, we propose a tractable semi-analytical approach for the network performance analysis of uplink (UL) cellular networks, which is based on a deterministic network analysis using a Gaussian approximation (DNA-GA). The key contribution of this paper is to investigate the UL signal-to-interference ratio (SIR) performance using the DNA-GA analysis. In particular, the SIR is modeled as a ratio of two random variables (RVs), representing the signal power and the aggregate interference power, respectively. The signal power is further characterized by a product of two RVs, i.e., a lognormal RV and an RV with an arbitrary distribution. The former RV comes from a common assumption of lognormal shadow fading, and the latter one takes the rest of random factors into account, such as random user positions, arbitrary types of multi-path fading, and so on. The aggregate interference power is approximated by an RV with a power lognormal distribution. The proposed DNA-GA analysis has several desirable features: 1) it naturally considers lognormal shadow fading; 2) it can treat arbitrary shape and/or size of cell coverage areas; 3) it can handle non-uniform user distributions; 4) it can cope with any type of multi-path fading; and 5) it can be applied to multi-antenna base stations. These features make the DNA-GA analysis very useful for the network performance analysis of the 5th generation systems with general cell deployment and user distribution.

Teletraffic Analysis of OFDMA Cellular Systems With Persistent VoIP Users and Maximum SIR Scheduling Based on Order Statistics

Voice over IP (VoIP) is the multimedia service with the fastest growth on current cellular systems and this trend will continue in the future. Voice transmission by VoIP users with traditional dynamic scheduling schemes could become a bottleneck in the signaling channels due to the periodic transmission of signaling small packets. To solve this problem, persistent scheduling has been proposed. Since the resource allocation information is indicated in the first burst of persistent data, no information resource allocation is required for the duration of the data bursts. This paper presents a performance study of the persistent scheduling based on the transmission of VoIP traffic, using as mathematical tools order statistics and teletraffic analysis. A combination of interference analysis and birth and death processes is performed to obtain the average transmission rate in the system using the Shannon equation. We obtain the order statistics of band signal-to-interference ratios (SIRs) by considering the co-channel interference. The order statistics are then used to analyze a best-m band feedback scheme, in which every user reports the index of their best-m bands to the base station. If multiple users present a band as their best band, two different approaches are analyzed: 1) random allocation and 2) Maximum SIR allocation. The probability density function of the SIR was obtained; it is observed that the Maximum SIR allocation has a significant gain of up to 20% in regard to the random allocation. After that, the probability of using a specific modulation and coding scheme is obtained. In order to obtain the probability of forced termination and the average data rate, these probabilities are introduced in the birth and death process as a different arrival rates and service times. It is observed that the order statistics model the cellular systems are more accurate. As an example for uniform user distribution and voice over VoIP traffic, the numerical results shown that the probability of forced termination is corrected by more than 70% in comparison without order statistics. Moreover, using the methodology developed with order statistics, an evaluation is made for a non-uniform user distribution with Skype traffic, considered as a very important service for 5G cellular systems.

Cooperative resource management and power allocation for multiuser OFDMA networks

Mobile network operators are facing the challenge to increase network capacity and satisfy the growth in data traffic demands. In this context, long-term evolution (LTE) networks, LTE-advanced networks, and future mobile networks of the fifth generation seek to maximise spectrum profitability by choosing the frequency reuse-1 model. Owing to this frequency usage model, advanced radio resource management and power allocation schemes are required to avoid the negative impact of interference on system performance. Some of these schemes modify resource allocation between network cells, while others adjust both resource and power allocation. In this study, the authors introduce a cooperative distributed interference management algorithm, where resource and power allocation decisions are jointly made by each cell in collaboration with its neighbouring cells. Objectives sought are: increasing user satisfaction, improving system throughput, and increasing energy efficiency. The proposed technique is compared with the frequency reuse-1 model and to other state-of-the-art techniques under uniform and non-uniform user distributions and for different network loads. They address scenarios where throughput demands are homogeneous and non-homogeneous between network cells. System-level simulation results demonstrate that their technique succeeds in achieving the desired objectives under various user distributions and throughput demands.

On the performance of a virtual user pairing scheme to efficiently utilize the spectrum of unpaired users in NOMA

This paper evaluates the performance of a virtual user pairing scheme that efficiently utilizes the spectrum of unpaired users in non-orthogonal multiple access (NOMA), termed as VP-NOMA. The scheme aims at utilizing the frequency bands of those users which remain unpaired due to the non-uniform distribution of users in a cellular area. We consider a case where the cell edge users are more than the cell center users, so that complete one-to-one correspondence does not exist between all cell center and cell edge users to be accommodated/paired using conventional NOMA (C-NOMA) user pairing. Thus, some cell edge users remain unpaired, and are served using conventional multiple access (OMA) schemes. In such scenario, VP-NOMA pairs a single cell center user with two or more clustered (closely located) cell edge users over non-overlapping frequency bands, thus enabling the cell center user to efficiently use the frequency bands of these previously unpaired cell edge users. Performance of VP-NOMA in terms of ergodic sum capacity (ESC), outage probability (OP), and outage sum capacity (OSC), is analyzed through comprehensive mathematical derivations and simulations for a generalized system model. Moreover, the mathematical analysis is validated through close concordance between analytical and simulation results of ESC, OP, and OSC.

Toward green 5G heterogeneous small-cell networks: power optimization using load balancing technique

The overwhelming demand for data by an ever-increasing number of users is a great challenge wireless cellular networks are faced with. One potential solution to this issue is deploying a massive number of small cells (SCs) in the existing macro network. As SC overlay has a big role in the future wireless networks that can overcome the data traffic upsurge at little power cost, heterogeneous network (HetNet) has been viewed as a promising technology for 5G networks that extends cell coverage, improves network capacity and offloads the network traffic from the macro cell (MC) to the SCs. However, the hyper-dense SCs and their uncorrelated operation raise an important question about the joint power consumption of the macro base station (MBS) and the small base stations (SBSs) in the HetNet since the aggregate power consumption of the dense SBSs cannot be ignored. Recently, the SC sleeping technique has become a hot topic for saving energy in HetNets. To minimize power consumption in HetNets, we propose three algorithms to dynamically adapt the operation of the SBSs to active/sleep (on/off) for non-uniform user distribution in the HetNet. We investigate the general optimal power minimization problem for HetNet that requires relatively high computational complexity. Taking into account the additional increase of the traffic load brought to the MBS, a key design principle of the proposed algorithms is to switch off the SBSs gradually based on their locations, user densities in their coverage areas or the highest power that can be saved by switching some of them off, respectively. Then, we enhance the mathematical framework to make the analysis more realistic by considering the offloading between the SCs and the MBS that occurs when the traffic load exceeds SCs’ capacity. In this paper, based on the fact that user densities of SCs and MC change with time, we model the traffic on the European traffic profile and portray the power consumption of the HetNet throughout the day. Simulation results show that by applying SC sleeping and our proposed algorithms, the HetNet can save about 20% power daily. The performances of our proposed algorithms are close to that of the optimal algorithm and their computational complexities are remarkably lower.

Efficient and scalable execution of smart city parallel applications

SummaryRecent research efforts in the field of urban computing aim to develop innovative services for citizens through the application of ubiquitous and pervasive computing paradigms in urban spaces. Smart city applications need to cope with a large number of involved users and devices. Since data and objects are strictly related to the territory on which they are defined and used, it is preferable, when possible, to perform computation locally through the adoption of dispersed computing nodes such as CPU‐equipped sensors. In this context, the computation related to smart city applications can be profitably and efficiently parallelized by partitioning the territory into regions and assigning the computation related to each single region to a local node. Nevertheless, the adoption of parallel computing models poses several communication and synchronization issues, especially when the number of nodes is large and the time constraints of applications are compelling. This paper presents and analyzes a parallel computing model for smart city applications in which each node needs to exchange information only with a subset of neighbor nodes, allowing the synchronization overhead to be significantly reduced. As sample application, we consider the analysis and prediction of internet traffic generated by vehicle and pedestrian devices moving on a smart avenue equipped with distributed computing nodes. This work offers a detailed performance evaluation in a number of scenarios, including uniform and nonuniform user distribution and different types of user mobility behavior. The results show that the presented computation model offers notable advantages in terms of computation efficiency and speedup, with respect to a classical all–to‐all synchronization paradigm, in which the nodes need to coordinate with a central entity.

Optimal Non-Uniform Deployments in Ultra-Dense Finite-Area Cellular Networks

Network densification and heterogenisation through the deployment of small cellular access points (picocells and femtocells) are seen as key mechanisms in handling the exponential increase in cellular data traffic. Modelling such networks by leveraging tools from Stochastic Geometry has proven particularly useful in understanding the fundamental limits imposed on network coverage and capacity by co-channel interference. Most of these works however assume infinite sized and uniformly distributed networks on the Euclidean plane. In contrast, we study finite sized non-uniformly distributed networks, and find the optimal non-uniform distribution of access points which maximises network coverage for a given non-uniform distribution of mobile users, and vice versa.

Performance of ZF precoder in downlink massive MIMO with non-uniform user distribution

In this paper, we investigate the achievable sum rate and energy efficiency of downlink massive multiple-input multiple- output antenna systems with zero-forcing precoding, by taking into account the randomness of user locations. Specifically, we propose two types of non-uniform user distributions, namely, center-intensive user distribution and edge-intensive user distribution. Based on these user distributions, we derive novel tight lower and upper bounds on the average sum rate. In addition, the impact of user distributions on the optimal number of users maximizing the sum rate is characterized. Moreover, by adopting a realistic power consumption model which accounts for the transmit power, circuit power and signal processing power, the energy efficiency of the sys- tem is studied. In particular, closed-form solutions for the key system parameters, such as the number of antennas and the optimal transmit signal-to-noise ratio maximizing the energy efficiency, are obtained. The findings of the paper suggest that user distribution has a significant impact on the system performance: for instance, the highest average sum rate is achieved with the center-intensive user distribution, while the lowest average sum rate is obtained with the edge-intensive user distribution. Also, more users can be served with the center-intensive user distribution.

Joint Scheduling and Beamforming Coordination in Cloud Radio Access Networks With QoS Guarantees

The cloud radio access network (C-RAN) is a promising architecture for future radio access networks (RANs) due to its advantages in cost efficiency, flexibility, and utilization efficiency. To fully reap these benefits, this paper focuses on joint optimization of user grouping, virtual base station (VBS) clustering, and transmit beamforming in C-RAN downlink networks for maximizing the system utility, subject to the diverse quality-of-service (QoS) requirements of users and the power constraints of distributed remote radio heads (RRHs). To tackle the high computational complexity in solving the nonconvex combinatorial optimization problem, a two-stage solution is proposed. Specifically, a dynamic user-centric scheduling algorithm is developed to form user groups and cluster RRHs into VBSs by exploiting the nonuniform distribution of users. Then, an iterative transmit beamformer optimization algorithm is devised to coordinate the transmit beamforming among the VBSs to mitigate the intracell and intercell interference, hence further enhancing the overall system utility. Evaluation results demonstrate that the proposed algorithm achieves significant performance gain over various reference algorithms in terms of system utility, system throughput, and energy efficiency.

CoSFR: coordinated soft frequency reuse for OFDMA-based multi-cell networks with non-uniform user distribution

Inter-cell interference coordination (ICIC) technology has been extensively studied to improve service quality of users near cell boundaries. Most ICIC schemes available make an assumption that users in the same cell are distributed uniformly. This is reasonable but incomplete. Mobility may result in users distributed non-uniformly, so this paper proposes a novel semi-static ICIC scheme, coordinated soft frequency reuse (CoSFR), for multi-cell networks with non-uniform user distribution. A finer cell partition structure with a tunable parameter r is proposed. With this structure, dedicated user classification rules and opportunistic scheduling strategies are designed for different cells. Assisted by a simple but efficient coordination scheme, a cell with overloaded cell-edge traffic, named aggressor cell, calls adjacent neighboring cells for help. Some reuse opportunities can be created after coordination and the aggressor cell can expand its cell-edge band to alleviate the overloaded state. No additional entity is required for being compatible with the flat network structure of LTE/LTE-Advanced. In addition, CoSFR can deal with the scenario that more than one cell suffering overloaded cell-edge traffic and it can also be applied to irregular cells with minimal modifications. Simulation results show that more than 97.4 % users are satisfied with their data rate. Average cell-edge user throughput is raised substantially and the outage probability declines significantly.

Spectrum sharing model for OFDMA macro-femtocell networks

Enhancing the network throughput while supporting non-uniform user distribution and dense femtocell deployment is a challenge in OFDMA networks. Previous research works focus on spectrum partitioning or spectrum sharing with interference managements regardless the user distribution or mobility. In this paper, we propose a spectrum sharing approach that maximises the network throughput using Linear Programming. Power adaptation is performed to mitigate the interference and to guarantee QoS downlink transmissions. Our solution is able to: 1 fairly allocate resources to each macrocell zone taking into account the user distribution; 2 optimally reuse the bandwidth allocated to inner MC zones inside femtocells located in outer zones; 3 optimally determine the serving base station, subcarriers and transmitted power for downlink transmissions taking into account user locations and demands. Simulations are conducted to show a comparison of our solution with two SP approaches with and without partial bandwidth reuse incorporating user mobility.

Uplink outage performance of linear cellular networks with non‐uniform user distribution

The Wyner model has been extensively used in the literature for analysing cellular networks. Recent studies show that when compared with a grid-based model, this simple model fails to capture key features of a cellular network under different scenarios. Without increasing complexity, a linear network model which uses an average user distance and considers a non-uniform user distribution scenario within cells is proposed. Simulation results show that despite the simplicity, the proposed model can provide a close insight when compared with a grid-based model.

Path-loss Based Power Suppression for Spectral and Energy Efficient Inter-cell Interference Coordination

The inter-cell interference problem is a key challenge in OFDMA-based cellular networks because it significantly decreases the throughput of the users at the cell edge. Mitigating this problem requires an inter-cell interference coordination (ICIC) scheme that divides the spectrum into a power constant band and a power limited band for the cell edge users. Overall, static ICIC or frequency reuse schemes are effective when users are uniformly distributed across the network, whilst non-uniform user distributions suggest semi-static ICIC schemes where the power levels in the power limited bands are effectively set based on the interference situation from neighboring cells. In this paper we define a method that uses path-loss statistical measures to describe the non-uniform distribution between adjacent cells. Based on this method, we devise a new distributed algorithm that derives the suppression levels of transmit power a cell may set at a neighboring cell’s cell edge band based on the path-loss to the cell edge users of that neighboring cell. Our algorithm is evaluated by means of simulations and compared to reference frequency reuse schemes based on a non-uniform user distribution scenario where users are distributed in clusters. Simulation results show that the power suppression levels derived by our algorithm greatly improve spectral and energy efficiency as compared to 7-reuse and 1-reuse schemes respectively. It is also shown that our algorithm exploits the non-uniformity in the user distribution to improve the user throughput of cell edge users without any losses in the user throughput of the cell center users. Keywords: ICIC, interference coordination, frequency partitioning, orthogonal frequency division multiplexing (ofdm), soft frequency reuse system capacity, 3GPP LTE standardization.

Large Scale Cooperation in Cellular Networks with Non-uniform User Distribution

Large Scale Cooperation in Cellular Networks with Non-uniform User Distribution

Towards an end-to-end delay analysis of LEO satellite networks for seamless ubiquitous access

LEO satellite networks, with moderate propagation delay and low terminal power requirement, are considered as a promising solution to providing global seamless access services for ubiquitous computing. In order to satisfy the requirement of accessing computing resource for users, end-to-end delays should be bounded for a continual and reliable connectivity. But given dynamic topology and non-uniform distribution of terrestrial users, end-to-end delays within LEO satellite networks are liable to fluctuate. Hence, to examine the delay constraint, an analytical model based on a tandem queue is established under a hot-spot traffic pattern, which is unfavorable for bounded delays. The departure interval moments of a target flow are calculated and fitted for the next link as input parameters, from which queuing delays under cross flows are iteratively obtained. The analytical results show that this model is able to depict the influence by the traffic pattern with satisfying accuracy, which is valuable for the design of routing schemes in satellite networks.

Base Station Placement Optimization Algorithm for Heterogeneous Distributions of Mobile Users with Multi-Service Requirements

In this paper the placement of base station within a cellular network is addressed as an optimization problem. A genetic algorithm is used as the optimization tool. This optimization issue is particularly important and critical in the multi-service environment commonly found in new generation cellular communications systems. Particularly, the goal of the algorithm presented in this work is to minimize the interference between base stations. It is shown that, by using the so proposed weighted objective function, it is possible to specify the base station locations, the cell coverage in terms of traffic and area, as well as the overlap levels between base stations. The weighted objective function is based on a preliminary analysis of the load factor for the base stations involved. The proposed algorithm is verified by means of a simulation scenario that considers a non-uniform distribution of users with different types of service. The presented results show an adequate tradeoff between the total traffic serviced and overlap level that allows transfers and minimizes the interference levels. Thus, our algorithm provides a useful tool for finding a near optimal solution for base station placement and efficiently determines number of base stations required in a cell planning procedure.

Fair Single Code and Multi Code Designs for 3G and Beyond CDMA Systems

Multimedia rates are handled in 3G and beyond CDMA networks using orthogonal variable spreading factor (OVSF) codes. Multimedia rates can have non uniform distribution of real time and non real time users. The paper describes fair single code and multi code designs to handle these rates. The single code design is for quantized rates and divides the OVSF code tree capacity according to the arrival distribution. The change in the distribution is dynamically reflected in the division of the code tree capacity for different rates. The multi code design is preferred for the system dominated by non quantized rates. Simulation results are presented to show the superiority of the proposed designs with its existing counterparts.