Coverage Of Macro Base Station Research Articles

Enabling Soft Frequency Reuse and Stienen's Cell Partition in Two-Tier Heterogeneous Networks: Cell Deployment and Coverage Analysis

Heterogeneous cellular networks (HetNets) are one of the key enabling technologies for fifth generation (5 G) networks. In HetNets, the use of small base stations (SBSs) inside the coverage area of a macro base station (MBS) offers higher throughput and improved coverage. However, such multi-tier base station deployment introduces new challenges, e.g., (i) All users experience significant inter-cell interference (ICI) due to frequency reuse, (ii) SBS associated users experience severe MBS-interference due to higher MBS transmit power, and (iii) MBS coverage edge users receive lower signal-to-interference ratio (SIR) due to longer distances. To address the aforementioned challenges, this work proposes a framework, including a novel cell deployment strategy, which combines Stienen's model with soft frequency reuse (SFR) and the corresponding performance analysis. According to Stienen's cell based SBS deployment, SBSs are deployed in MBS coverage edge area to enhance downlink SIR. To further mitigate ICI and MBS-interference, SFR is employed along with Stienen's cell based SBS deployment. Based on stochastic geometry, we derive expressions for coverage probability with four different types of cell deployment and SFR employment combinations. Numerical results indicate that SFR-enabled Stienen's cell based SBS deployment leads to enhanced edge user coverage and, hence, improves network performance gain.

Joint user association and resource allocation in HetNets based on user mobility prediction

Virtual small cell (VSC) formed by directional beams is seen as an alternative for the small base station (SBS) within the coverage of macro base station (MBS), to increase system capacity and reduce site cost. However, the flexibility of development for VSC poses challenges to user association and resource allocation in heterogeneous networks. In this paper, we consider the joint problem of user association and resource allocation in VSC aided multi-tier heterogeneous networks. To better analyze the formation of VSC and the impact of user mobility on the system, a user mobility prediction model is firstly constructed based on the Markov model. Then the joint user association and resource allocation problem is formulated to maximize the system capacity. Since the aforementioned problem is a coupling problem, two different solutions, namely, a decoupling solution and a coupling solution, are proposed based on the multi-agent Q-learning (MAQL) method, to find the optimal user association and resource allocation strategy. Moreover, to overcome the state and action space explosion in MAQL and accelerate convergence, the deep Q-network (DQN) is applied. Simulation results reveal that the deployment of VSC can increase the system capacity and spectrum efficiency. The coupling solution achieves better performance than the decoupling solution under a large number of users.

Analysis of Interference Management in Heterogeneous Cellular Networks in the Presence of Wideband Jammers

In heterogeneous cellular networks, small base stations (SBSs) in the coverage area of macro base station (MBS) cause significant inter-cell-interference (ICI). Intentional jamming interference (JI), caused by wideband jammers (WBJs), further worsens the uplink (UL) communications in the MBS coverage edge area. This letter investigates uniform and clustered WBJs’ deployment scenarios, denoted by C1 and C2, respectively. We employ decoupled association (DeCA) and reverse frequency allocation (RFA) to mitigate both JI and ICI. Results indicate that C2 is more disruptive than C1, and that a significant UL coverage improvement can be achieved by using DeCA along with RFA.

Proactive Uplink Interference Management for Nonuniform Heterogeneous Cellular Networks

In homogeneous cellular networks, fractional power control (FPC) is employed to partially compensate the path-loss and, hence, improve uplink ( $U_{L} $ ) signal-to-interference ratio (SIR). However, this scheme is less effective in heterogeneous cellular networks (HetNets) because: (i) except the typical user, all other users with variable $U_{L} $ transmit power (UTP) act as interferers, (ii) FPC leads to high UTP by edge users and, hence, more interference, and (iii) small base stations (SBSs)’ densification further increases network interferences. Leveraging FPC in HetNets, we propose nonuniform SBS deployment ( $\text {NU-SBS}_{\mathcal {D}} $ ) to reduce interference and, thus, increase network performance. According to our $\text {NU-SBS}_{\mathcal {D}} $ model, SBS deployment ( $\text {SBS}_{\mathcal {D}} $ ) near macro base station (MBS) is avoided, whereas MBS coverage edge area is enriched with ultra-dense $\text {SBS}_{\mathcal {D}} $ . $\text {NU-SBS}_{\mathcal {D}} $ model leads to: (i) better SIR reception of MBS coverage edge users, (ii) fewer $\text {SBS}_{\mathcal {D}} $ requirement, and (iii) better SBS coverage in the MBS coverage edge area. Moreover, to make a model more proactive, we also consider reverse frequency allocation (RFA) to further abate both $U_{L} $ and downlink $(D_{L}) $ interferences. The coverage probability expressions are derived for both uniform SBS deployment ( $\text {U-SBS}_{\mathcal {D}} $ ) and $\text {NU-SBS}_{\mathcal {D}} $ while using RFA and FPC. Through simulation and numerical results, we characterize coverage probability for different values of SIR threshold, path loss compensation factor, SBS density, users density, and the distance between the typical user and the associated base station. The proposed $\text {NU-SBS}_{\mathcal {D}} $ model along with RFA leads to reduced network interference as compared with $\text {U-SBS}_{\mathcal {D}} $ and, thus, leverages FPC in HetNets.

Cell Throughput based Sleep Control Scheme for Heterogeneous Cellular Networks

The mobile traffic continuously grows at a rapid rate driven by the widespread use of wireless devices. Along with that, the demands for higher data rate and better coverage lead to increase in power consumption and operating cost of network infrastructure. The concept of heterogeneous networks (HetNets) has been proposed as a promising approach to provide higher coverage and capacity for cellular networks. HetNet is an advanced network consisting of multiple kinds of base stations, i.e., macro base station (MBS), and small base station (SBS). The overlay of many SBSs into the MBS coverage can provide higher network capacity and better coverage in cellular networks. However, the dense deployment of SBSs would cause an increase in the power consumption, leading to a decrease in the energy efficiency in downlink cellular networks. Another technique to improve energy efficiency while reducing power consumption in the network is to introduce sleep control for SBSs. This paper proposes cell throughput based sleep control which the cell capacity ratio for the SBSs is employed as decision criteria to put the SBSs into a sleep state. The simulation results for downlink communications demonstrate that the proposed scheme improves the energy efficiency, compared with the conventional scheme.

A Distributed Interference Alignment Approach Based on Grouping in Heterogeneous Network

To effectively mitigate interference and improve the performance, we propose a grouping-based two-stage distributed interference alignment (GTDIA) scheme for a two-layered heterogeneous network (HetNet) in multi-user multiple-input-multiple-output (MIMO) Gaussian downlink transmission scenario. In this paper, we first extend the grouping-based interference alignment (GIA) scheme, which is suitable in single-layer multi-cell scenario to a two-layered HetNet. Then, in order to improve the system performance and reduce the computational complexity, we propose a new interference alignment (IA) scheme (i.e., GTDIA) by grouping pico users (PUEs) to align inter-layer interference (inter-layer IF) and design the receive beamforming matrices of PUEs. Since the macro users (MUEs) are located randomly under the coverage of macro base station, the inter-layer IF is between some pico base stations and MUEs. Specifically, two-stage (i.e., a composite of two cascade matrices) transmit beamforming matrices of base stations are designed to cancel both of the inter-layer and intra-layer interference among MUEs. Furthermore, because of the reciprocity of time-division duplex system, a distributed algorithm is used when designing the second stage transmit beamforming matrices. Analysis and simulation results demonstrate that the proposed scheme outperforms the extended GIA and other conventional IA schemes.