Tier Heterogeneous Network Research Articles

On the Statistical Delay Performance of Large-Scale IoT Networks

Large-scale Internet of things (IoT) networks have shown great advantages and attracted much attention in 5G networks due to its high-speed Internet connectivity, high data rate, ultra reliability and low latency. However, the diversity of ubiquitous IoT devices and complex transmission environment lead to the difficulty of theoretical analysis of delay performance. In order to capture the characteristics of large IoT networks, a novel integrated analysis framework is developed to build the performance model and analyze the statistical delay performance in this paper. Specifically, we model the spatial distribution of IoT devices with heterogeneous Poisson point processes. With the Laplace transform of signal-to-interference-plus-noise ratio, the service capability of the wireless channel with multiple interferes is determined with a mathematical stochastic-network-calculus aided approach in the exponential domain for Poisson bipolar and cellular networks. Then, the upper bound of delay is achieved by the Mellin transform of the service incremental process. We extend our work to a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$k$</tex-math></inline-formula> -tier heterogeneous network and apply the analysis results to a practical two-tier cognitive radio IoT network. Simulation results validate the theoretical analysis of delay performance with various network parameters.

Sum-rate optimization for NOMA based two-tier hetnets with massive MIMO enabled wireless backhauling

In this paper, massive MIMO and NOMA techniques are jointly considered in a two tier heterogeneous network for accommodating huge traffic. In addition, full duplex communication is used at SBS to enhance system performance. First, SINR and rate equations are modeled while considering imperfect channel state information and zero-forcing beamforming. In the proposed framework, both macro base station and small cell base station can serve multiple users by using NOMA. Since, existing literature mainly focuses on orthogonal multiple access (OMA) based UA schemes, it is necessary to re-design user association (UA) schemes for NOMA. Hence, based on the proposed framework, a joint UA and power allocation (PA) optimization problem is designed with the perspective of optimizing the sum-rate of the system while accounting for quality of service and backhaul constraints. Since, the initially formulated problem is non-convex, a distributive algorithm is propounded where a joint problem is separated into two convex subproblems (viz., UA and PA). Furthermore, the complexity of the proposed algorithm is examined and Jain’s fairness index is measured. Simulation results demonstrate the effectiveness of the proposed algorithm by comparing with optimal solution and other base-line algorithms.

User Association in Limited Quota Het-Nets Aided Massive MIMO Networks

Massive multiple-input-multiple-output (MIMO) and heterogeneous networks are two leading concepts in the emerging 5G technology. Practical systems may employ massive MIMO macro-cells along with several small-cells in different tiers to increase the coverage and system capacity. The effect of limited quota on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${K}$ </tex-math></inline-formula> -tier heterogeneous networks is investigated under Rayleigh fading channel. The users admit to the considered system following the college admission model. In particular, closed-form expressions for the user association probability, coverage probability, and average rate are derived for both macro base stations and small base stations. Numerical results demonstrate that the size of the quota has a significant impact on the considered system performance.

Hierarchical power control model for interference mitigation in a two – Tier heterogeneous network

The heterogeneous deployment of different base stations has increased the overall network capacity and reduced excess traffic from the macrocell network. However, this improved system performance i...

2-to-&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$M$ &lt;/tex-math&gt; &lt;/inline-formula&gt; Coordinated Multipoint-Based Uplink Transmission in Ultra-Dense Cellular Networks

The ongoing densification of small cells, i.e., ultimately evolving toward ultra-dense networks (UDNs), yields an unprecedented paradigm shift in network design by bringing the base stations (BSs) and users to approximate the spatial scale and number magnitude. To address the super-frequent handovers of mobile users in such UDNs, the coordinated multipoint (CoMP) then becomes a feasible solution by effectively improving communication reliability. In this paper, we consider CoMP-based uplink transmission in heterogeneous UDNs. As our first step, a CoMP uplink transmission scheme is proposed for each user to transmit to multiple (2 to $M$ ) cooperating BSs with channel inversion power control in a multi-channel scenario. The performance of the proposed uplink CoMP is analyzed in the context of UDNs using stochastic geometry, in terms of outage probability and ergodic capacity, considering the effects of BS intensity, power control, number of cooperating nodes, and network tiers, first in a single-tier network, and later extended to a $K$ -tier heterogeneous network. Performance evaluation through extensive simulations is conducted and it is shown that the simulation results fit well with the analytical ones. The performance of the proposed scheme is then compared with that of the non-CoMP scheme, and it is found that the proposed scheme can significantly improve outage probability and ergodic capacity of mobile users.

Coordinated Multipoint-Based Uplink Transmission in Internet of Things Powered by Energy Harvesting

Energy harvesting techniques extend the lifetime of Internet of Things (IoT), whereas yield an unprecedented paradigm shift in network design. Base stations (BSs), being powered by self-contained energy harvesting modules, may keep OFF during recharging, leading to super-frequent handovers for nodes and high network dynamics. Under such dynamics, multiple cooperating BSs for the service of a “smart thing,” referred to as coordinated multipoint (CoMP), become a feasible solution by effectively improving communication reliability. To the best of knowledge, this is the first work to consider CoMP uplink transmission to alleviate outage caused by energy harvesting of BSs in IoT. A simple CoMP uplink transmission scheme is proposed for each node of IoT to transmit to two cooperating BSs in a $K$ -tier heterogeneous network. The performance of the proposed scheme is analyzed using tools of stochastic geometry, in terms of availability and average rate, considering the effect of energy capacity, energy charging rate, in a $K$ -tier heterogeneous network. Performance evaluation through extensive simulations are conducted and it is shown that the simulation results fit well with the analytical ones. The performance of the proposed scheme is then compared with that of the non-CoMP scheme, and it is found that the proposed scheme can significantly improve availability and average rate.

Feedback Design for Multi-Antenna &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$K$ &lt;/tex-math&gt; &lt;/inline-formula&gt;-Tier Heterogeneous Downlink Cellular Networks

We characterize the ergodic spectral efficiency of a non-cooperative and a cooperative type of $K$ -tier heterogeneous network with limited feedback. In the non-cooperative case, a multi-antenna base station (BS) serves a single-antenna user using maximum-ratio transmission based on limited feedback. In the cooperative case, a BS coordination set is formed by using dynamic clustering across the tiers, wherein the intra-cluster interference is mitigated by using multi cell zero-forcing also based on limited feedback. Modeling the network based on stochastic geometry, we derive analytical expressions for the ergodic spectral efficiency as a function of the system parameters. Leveraging the obtained expressions, we formulate feedback partition problems and obtain solutions to improve the ergodic spectral efficiency. Simulations show the spectral efficiency improvement by using the obtained feedback partitions. Our major findings are as follows: 1) in the non-cooperative case, the feedback is only useful in a particular tier if the mean interference is small enough; 2) in the cooperative case, allocating more feedback to stronger intra-cluster BSs is efficient; and 3) in both cases, the obtained solutions do not change depending on the instantaneous signal-to-interference ratio.

The Connectivity of Millimeter Wave Networks in Urban Environments Modeled Using Random Lattices

Millimeter-wave (mm-wave) communication opens up tens of giga-hertz spectrum in the mm-wave band for use by next-generation wireless systems, thereby solving the problem of spectrum scarcity. Maintaining connectivity stands out as a key design challenge for mm-wave networks deployed in urban regions due to the blockage effect characterizing mm-wave propagation. In this paper, we set out to investigate the blockage effect on the connectivity of mm-wave networks in a Manhattan-type urban region modeled using a random regular lattice, while base stations (BSs) are Poisson distributed in the plane. In particular, we analyze the connectivity probability that a typical user is within the transmission range of a BS and connected by a line-of-sight. First, we consider a single-tier network. By jointly applying the random lattice and stochastic geometry theories, a lower bound on the connectivity probability is derived as a function of building parameters (e.g., size and site occupancy probability) and BS parameters (e.g., transmission range and BS density). For the case of dense buildings, the bound is derived in a simpler form. Next, the preceding lower bounds are tightened based on the geometric technique of partitioning the irregular blockage-free region around the typical user. Moreover, the analysis is generalized to mm-wave channels with both LoS and NLoS paths. Finally, the results are extended to a $K$ -tier heterogeneous network (HetNet), where building heights are random, and depending on its height, a building can block the signals transmitted by a subset of BS tiers but not all. The analysis shows that the connectivity probability of the $K$ -tier HetNet increases linearly with the number of tiers. In general, our work quantifies the relation between the coverage of an mm-wave network and the parameters of building and BS processes, providing useful guidelines for deploying practical networks in a Manhattan-type region.

Coverage Analysis and Load Balancing in HetNets With Millimeter Wave Multi-RAT Small Cells

We characterize a two tier heterogeneous network, consisting of classical sub-6 GHz macro cells, and multi radio access technology (RAT) small cells able to operate in sub-6 GHz and millimeter-wave (mm-wave) bands. For optimizing coverage and to balance loads, we propose a two-step mechanism based on two biases for tuning the tier and RAT selection, where the sub-6 GHz band is used to speed-up the initial access procedure in the mm-wave RAT. First, we investigate the effect of the biases in terms of signal-to-interference-plus-noise ratio (SINR) distribution, cell load, and user throughput. More specifically, we obtain the optimal biases that maximize either the SINR coverage or the user downlink throughput. Then, we characterize the cell load using the mean cell approach and derive upper bounds on the overloading probabilities. Finally, for a given traffic density, we provide the small cell density required to satisfy system constraints in terms of overloading and outage probabilities. Our analysis highlights the importance of deploying dual-band small cells, in particular, when small cells are sparsely deployed or in case of heavy traffic.

Optimization and Analysis of Probabilistic Caching in $N$ -Tier Heterogeneous Networks

In this paper, we study the probabilistic caching for an $N$ -tier wireless heterogeneous network (HetNet) using stochastic geometry. A general and tractable expression of the successful delivery probability (SDP) is first derived. We then optimize the caching probabilities for maximizing the SDP in the high signal-to-noise ratio regime. The problem is proved to be convex and solved efficiently. We next establish an interesting connection between $N$ -tier HetNets and single-tier networks. Unlike the single-tier network where the optimal performance only depends on the cache size, the optimal performance of $N$ -tier HetNets depends also on the base station (BS) densities. The performance upper bound is, however, determined by an equivalent single-tier network. We further show that with uniform caching probabilities regardless of content popularities, to achieve a target SDP, the BS density of a tier can be reduced by increasing the cache size of the tier when the cache size is larger than a threshold; otherwise, the BS density and BS cache size can be increased simultaneously. It is also found analytically that the BS density of a tier is inverse to the BS cache size of the same tier and is linear to BS cache sizes of other tiers.

Traffic Management for Heterogeneous Networks With Opportunistic Unlicensed Spectrum Sharing

This paper studies how to maximize the per-user-based throughput in an $M$ -tier heterogeneous wireless network (HetNet) by optimally managing traffic flows among the access points (APs) in the HetNet. The APs in the first $M-1$ tiers can use the licensed spectrum at the same time whereas they share the unlicensed spectrum with the APs in the $M$ th tier by the proposed opportunistic CSMA/CA protocol. We characterize the statistical property of the cell load and channel access probability of each AP using a general AP association scheme. For an AP in each tier, the tight bounds on its mean spectrum efficiencies in the licensed and unlicensed spectra are derived in a low-complexity form for general random channel gain and AP association weight models and they can give some insights on how channel gains, AP association weights and void AP probabilities affect the mean spectrum efficiencies. We define the per-user link throughput and per-user network throughput based on the derived the mean spectrum efficiencies and maximize them by proposing the decentralized and centralized traffic management schemes for the APs in the first $M-1$ tiers under the constraint that the per-user link throughput of the tier- $M$ APs must be above some minimum required value. Finally, a numerical example of coexisting LTE and Wi-Fi networks is provided to validate our derived results and findings.

Downlink and Uplink Decoupling in Two-Tier Heterogeneous Networks With Multi- Antenna Base Stations

In order to improve the uplink performance of future cellular networks, the idea to decouple the downlink (DL) and uplink (UL) association has recently been shown to provide significant gain in terms of both coverage and rate performance. However, all the works are limited to a single input single output (SISO) network. Therefore, to study the gain provided by the DL and UL decoupling in multi-antenna base stations (BSs) setup, we study a two tier heterogeneous network consisting of multi-antenna BSs, and single antenna user equipments (UEs). We use maximal ratio combining (MRC) as a linear receiver at the BSs and tools from stochastic geometry, and we derive tractable expressions for both signal-to-interference ratio (SIR) coverage probability and rate coverage probability. We observe that as the disparity in the beamforming gain of both tiers increases, the gain in terms of SIR coverage probability provided by the decoupled association over non-decoupled association decreases. We further observe that when there is asymmetry in the number of antennas of both tiers, then we need further biasing toward femto-tier on the top of decoupled association to balance the load and get optimal rate coverage probability.

Spectrum and Energy Efficiency in Massive MIMO Enabled HetNets: A Stochastic Geometry Approach

This letter focuses on the spectrum efficiency (SE) and energy efficiency (EE) of $K$ -tier heterogeneous networks (HetNets), in which massive multiple-input multiple-output (MIMO) is employed in the macro cells. We consider the impact of massive MIMO on flexible cell association. We develop an analytical approach to examine SE and EE of HetNets. We confirm that using flexible cell association can improve the EE of HetNets by offloading data traffic to small cell. This is due to an increase of EE in the macro cell. Moreover, we show that serving moderate number of users in the macro cells with massive MIMO can boost both SE and EE.