Research on interference coordination techniques in heterogeneous cellular networks

In this letter, the user association problem in conjunction with almost blank subframe (ABSF) based interference coordination (IC) technique is considered in heterogeneous cellular networks. First, we formulate the combinatorial optimization problem as a network-wide utility maximization problem, whose solution is NP-hard. Fortunately, we reveal that the optimal ABSF density is the ratio of the number of vulnerable users and total users. Based on this relationship, the original problem is reduced to a pure optimal user association problem. Then, we propose a marginal utility based user association algorithm for the reformulated problem. Simulation results show the efficiency of our proposed scheme.

In this paper, a joint control method for the user association and almost blank sub-frame (ABSF) based interference coordination (IC) technique in heterogeneous cellular networks is proposed. The optimization objective is simultaneously improving system throughput and guaranteeing proportionally fairness. Usually, user and base station (UE-BS) association is performed before ABSF rate determination, which is suboptimal with respect to UE- BS association. We formulate the joint optimization of UE-BS association and ABSF rate as a combinatorial optimization problem. To deal with it, we proposed an iterative method to discover the ABSF rate, the optimal association and the optimal resource blocks(RBs) allocation that can maximum long-term average throughput. Besides, as we cannot know the interference before user-association and resource allocation, we proposed a graph-based BS clustering method to estimate the interference before user-association and resource allocation. Simulation results show the efficiency of our proposed scheme.

Embedding pico/femto base-stations and relay nodes in a macro-cellular network is a promising method for achieving substantial gains in coverage and capacity compared to macro-only networks. These new types of base-stations can operate on the same wireless channel as the macro-cellular network, providing higher spatial reuse via cell splitting. However, these base-stations are deployed in an unplanned manner, can have very different transmit powers, and may not have traffic aggregation among many users. This could potentially result in much higher interference magnitude and variability. Hence, such deployments require the use of innovative cell association and inter-cell interference coordination techniques in order to realize the promised capacity and coverage gains. In this paper, we describe new paradigms for design and operation of such heterogeneous cellular networks. Specifically, we focus on cell splitting, range expansion, semi-static resource negotiation on third-party backhaul connections, and fast dynamic interference management for QoS via over-the-air signaling. Notably, our methodologies and algorithms are simple, lightweight, and incur extremely low overhead. Numerical studies show that they provide large gains over currently used methods for cellular networks.

In a Poisson Point Process (PPP) network model, in which the locations of Base Stations (BSs) are randomly distributed according to a Spatial Poisson Process, has been recently used as a tractable stochastic model to analyse the performance of downlink Heterogeneous Cellular Networks (HCNs). The HCN is modelled as a multi-tier cellular network where each tier is characterised by the transmission power level, propagation path loss exponent and density of BSs. The current works on HCN enabling Intercell Interference Coordination (ICIC) technique usually deal with Strict Frequency Reuse (FR) or Soft FR with a reuse factor of $\Delta=1$ in a Rayleigh fading channel. It has been assumed that all Base Stations (BSs) transmit continuously which leads to a reduction on the impact of number of users and RBs on network performance. In this paper, the performance of Soft FR with a reuse factor of $\Delta>1$ in Rayleigh-Lognormal fading channel is evaluated. The impact of the number of users and Resource Blocks (RBs) on Intercell Interference (ICI) are presented for Round Robin scheduling and indicator functions. The results show that there are opposite trends between coverage probability of Cell-Center User (CCU) and Cell-Edge User (CEU).

As a mainstream technology in the 4G TDD (Time Division Duplex) systems, TD-LTE (Long Term Evolution) introduces heterogeneous network topology, utilizing a diverse set of base stations, to improve spectral efficiency per unit area. In heterogeneous network deployment comprised of macrocell and picocell, inter-cell interference coordination (ICIC) is very important to significantly improve the system and cell-edge throughput. Moreover, variety of complex situation of inter-cell interference (ICI) occurs in heterogeneous TDD LTE cellular networks due to different downlink/uplink (DL/UL) sub-frame configurations of macrocell and picocell. Therefore, this paper proposes an efficient ICIC scheme consisting of four sub-schemes according to relevant interference scenarios based on different sub-frame configurations. The scheme first analyzes interference level and finds out strong interference for each scenario. The basic idea of ICIC is that only primary interfering sources of each scenario avoid using the same frequency resource occupied by interfered victim, and other interfering sources can reuse frequency resource. Numerical results show that our proposed ICIC scheme can not only improve performance of whole region including macrocell area and picocell area, but also significantly achieve higher throughput for cell edge users.

The evolution of cellular networks from one generation to another has led to the deployment of multiple radio access technologies (such as 2G/2.5G/3G/4G) in the same geographical area. This scenario is termed heterogeneous cellular networks. In heterogeneous cellular networks, radio resources can be jointly or independently managed. When radio resources are jointly managed, joint call admission control algorithms are needed for making radio access technology selection decisions. This chapter gives an overview of joint call admission control in heterogeneous cellular networks. It then presents a model of load-based joint call admission control algorithm. Four different scenarios of call admission control in heterogeneous cellular networks are analyzed and compared. Simulations results are given to show the effectiveness of call admission control in the different scenarios. The coexistence of different cellular networks in the same geographical area necessitates joint radio resource management (JRRM) for enhanced QoS provisioning and efficient radio resource utilization. The concept of JRRM arises in order to efficiently manage the common pool of radio resources that are available in each of the existing radio access technologies (RATs) (Perez-Romero et al, 2005). In heterogeneous cellular networks, the radio resource pool consists of resources that are available in a set of cells, typically under the control of a radio network controller or a base station controller. There are a number of motivations for heterogeneous wireless networks. These motivations are (1) limitation of a single radio access technology (RAT), (2) users’ demand for advanced services and complementary features of different RATs, and (3) evolution of wireless technology. Every RAT is limited in one or more of the following: data rate, coverage, security-level, type of services, and quality of service it can provide, etc. (Vidales et al, 2005). A motivation for heterogeneous cellular networks arises from the fact that no single RAT can provide ubiquitous coverage and continuous high QoS levels across multiple smart spaces, e.g. home, office, public smart spaces, etc. Moreover, increasing users’ demand for advanced services that consume a lot of network resources has made network researchers developed more and more spectrally efficient multiple access and modulation schemes to support these services. Consequently, wireless networks have evolved from one generation to another. However, due to huge investment in existing RATs, operators do not readily discard their existing RATs when they acquire new ones. This situation has led to coexistence of multiple RATs in the same geographical area.

The cell range expansion (CRE) is encouraged to be applied in the heterogeneous cellular networks (HCNs), to enhance the capacity by offloading macro users to small cells. However, the enhanced inter-cell interference coordination (eICIC) techniques are supposed to be used for mitigating the strong cross-tier interference suffered by the offloaded users and small cell edge users. To address this, a novel soft frequency reuse (SFR) scheme is adopted in this paper. We analyze multichannel downlink scenarios for the SFR scheme using the tools of stochastic geometry. In consideration of the random resource allocation and practical cell load model, the analytical results of coverage probability and average user rate are derived and validated through Monte Carlo methods. Furthermore, our results can reduce to simple closed-form under reasonable special case for modern urban cellular networks. The main evaluation of the performance in terms of average user rate is presented, and the optimal combination of association bias and parameters of the SFR scheme is also investigated. Numerical results show that the SFR scheme outperforms the frequency resource partitioning (FRP) scheme in any load condition. Moreover, the CRE with SFR scheme can improve the average user rate significantly.

This chapter aims to jointly study and optimize unmanned aerial base stations (UABSs) placement and interference coordination in air–ground heterogeneous cellular network (AG–HetNet). It begins by reviewing unmanned aerial vehicles placement and interference coordination techniques in the literature, and then discusses several use cases of UABSs for cellular networks. Next, the chapter introduces the optimal placement problem of UABS in an AG‐HetNet using the genetic algorithm. Then, it describes the UABS‐based AG‐HetNet model, different path‐loss models, and the definition of 5th percentile spectral efficiency (5pSE) as a function of network parameters. The Rayleigh fading channel is considered while presenting AG‐HetNet design guidelines. Finally, the chapter analyzes and compares the 5pSE of the HetNet using extensive computer simulations for various inter‐cell interference coordination techniques.

Heterogeneous networks (HetNets) are considered a promising cellular network architecture to provide services to the massive number of subscribers. However, in heterogeneous networks, as cell size becomes smaller, the number of handovers and handover failure increase significantly. Therefore, mobility management becomes an important issue in HetNets. In this research, we analyzed the handover parameters, and proposed a novel handover method for heterogeneous cellular networks to minimize the number of handovers and handover failure. In the proposed method, we considered dual connectivity with control and data plane split and Coordinated Multipoint (CoMP) transmission to optimize the handover parameters. The reduction of handover improves the network performance and the handover failure reduction improves the user experience. The simulation results show that the proposed handover process significantly reduces the number of handovers in heterogeneous cellular networks.

We propose a unified static framework to study the interplay of user association and resource allocation in heterogeneous cellular networks. This framework allows us to compare the performance of three channel allocation strategies: Orthogonal deployment, Co-channel deployment, and Partially Shared deployment. We have formulated joint optimization problems that are non-convex integer programs, are NP-hard, and hence it is difficult to efficiently obtain exact solutions. We have, therefore, developed techniques to obtain upper bounds on the system's performance. We show that these upper bounds are tight by comparing them to feasible solutions. We have used these upper bounds as benchmarks to quantify how well different user association rules and resource allocation schemes perform. Our numerical results indicate that significant gains in throughput are achievable for heterogeneous networks if the right combination of user association and resource allocation is used. Noting the significant impact of the association rule on the performance, we propose a simple association rule that performs much better than all existing user association rules.

How many small cell (SC) access points (APs) are required to guarantee a chosen quality of service in a heterogeneous network? In this chapter, we answer this question considering two different network models. The first is the downlink of a finite-area SC network where the locations of APs within the chosen area are uniformly distributed. A key step in obtaining the closed-form expressions is to generalize the well-accepted moment matching approximation for the linear combination of lognormal random variables. For the second model, we focus on a two-layer downlink heterogeneous network with frequency reuse-1 hexagonal macro cells (MCs), and SC APs that are placed at locations that do not meet a chosen quality of service from macro base stations (BSs). An important property of this model is that the SC AP locations are coupled with the MC coverage. Here, simple bounds for the average total interference within an MC makes the formulation possible for the percentage of MC area in outage, as well as the required average number of SCs (per MC) to overcome outage, assuming isolated SCs. Introduction Heterogeneous cellular networks (HCNs) are being considered as an efficient way to improve system capacity as well as effectively enhance network coverage [1, 2]. Comprising multiple layers of access points (APs), HCNs encompass a conventional macro cellular network (first layer) overlaid with a diverse set of small cells (SCs) (higher layers). Cell deployment is an important problem in heterogeneous networks, both in terms of the number and positioning of the SCs. Traditional network models are either impractically simple (such as the Wyner model [3]) or excessively complex (e.g., the general case of random user locations in a hexagonal lattice network [4]) to accurately model SC networks. A useful mathematical model that accounts for the randomness in SC locations and irregularity in the cells uses spatial point processes, such as Poisson point process (PPP), to model the location of SCs in the network [5–10]. The independent placement of SCs from the MC layer, has the advantage of analytical tractability and leads to many useful SINR and/or rate expressions. However, even assuming that wireless providers would deploy SCs to support mobile broadband services, the dominant assumption remains that SCs are deployed randomly and independent of the MC layer [11].

SummaryThe use of small base stations (SBSs) to improve the throughput of cellular networks gave rise to the advent of heterogeneous cellular networks (HCNs). Still, the interleave division multiple access (IDMA) performance in sleep mode active HCNs has not been studied in the existing literature. This research examines the 24‐h throughput, spectral efficiency (SE), and energy efficiency (EE) of an IDMA‐based HCN and compares the result with orthogonal frequency division multiple access (OFDMA). An energy‐spectral‐efficiency (ESE) model of a two‐tier HCN was developed. A weighted sum modified particle swarm optimization (PSO) algorithm simultaneously maximized the SE and EE of the IDMA‐based HCN. The result obtained showed that the IDMA performs at least 68% better than the OFDMA on the throughput metric. The result also showed that the particle swarm optimization algorithm produced the Pareto optimal front at moderate traffic levels for all varied network parameters of SINR threshold, SBS density, and sleep mode technique. The IDMA‐based HCN can improve the throughput, SE, and EE via sleep mode techniques. Still, the combination of network parameters that simultaneously maximize the SE and EE is interference limited. In sleep mode, the performance of the HCN is better if the SBSs can adapt to spatial and temporal variations in network traffic.

Next generation cellular network is expected to overcome the issues like demand for high data rates, better network coverage, energy, and spectrally efficient system. In this paper, femto based heterogeneous cellular network (HCN) with cognitive approach is considered to address these issues. This paper investigates two tier cognitive based HCN for overlay, underlay, and mixed overlay-underlay spectrum sharing schemes (SSSs). Macro base station (MBS) and cognitive femto base station (CFBS) are considered as a primary user network (PUN) and cognitive user network (CUN), respectively. Outage probability is a fundamental performance measure in HCN design. In this work, stochastic geometry is used for deriving the probability density function (pdf) of the signal-to-interference ratio (SIR) and the outage probability of the HCN for different SSSs. Furthermore, energy efficiency (EE) of the HCN and single tier network (MBS only) are also calculated for different SSSs. Numerical results show that outage performance of HCN in mixed overlay-underlay scheme outperforms other schemes. Moreover, it is observed that the effect of BSs density on outage probability is lower for the CFBSs as compared to MBSs.

As discussed in Chapter 1, heterogeneous cellular networks (HCNs) with low-power nodes (LPNs) are important for improving the capacity and coverage of next generation broadband wireless communication systems. However, interference problems in HCNs pose an important challenge, and thus efficient interference management techniques are required to fully benefit from their deployments. The main contribution of this chapter is to review interference problems and interference management techniques for HCNs. A general notion of macrocell base stations (MBSs) and LPNs is adopted, but the simulations are based on Long Term Evolution (LTE) scenarios with macro eNBs and pico eNBs or femto HeNBs. More specifically, cell-selection and interference coordination methods are discussed, including mechanisms recently proposed in the 3rd Generation Partnership Project (3GPP) LTE, and their performances are evaluated through system-level simulations. In such simulations, LTE-specific notation is used, and macrocell user equipment (MUE) and picocell user equipment (PUE) denotes UEs served by macro eNBs and pico eNBs, respectively. This chapter is organized as follows. First, Section 7.1 reviews the main reasons for excessive intercell interference in HCNs. In Section 7.2, due to its significance, range expansion (RE) for HCNs is treated in more detail. Some example simulation results that demonstrate the downlink (DL)/ uplink (UL) coverage imbalance in heterogeneous deployments are also provided. Section 7.3 gives a high-level overview of intercell interference coordination (ICIC) methods that are applicable to HCNs, and the next three sections are dedicated to specific ICIC approaches: frequency-domain, power-based, and time-domain ICIC techniques are discussed in Section 7.4, Section 7.5, and Section 7.6, respectively.

In this paper, statistical Quality of Service provisioning in next generation heterogeneous mobile cellular networks is investigated. To this aim, any active entity of the cellular network is regarded as a queuing system, whose statistical QoS requirements depend on the specific application. In this context, by quantifying the performance in terms of effective capacity, we introduce a lower bound for the system performance that facilitates an efficient analysis. We exploit this analytical framework to give insights about the possible improvement of the statistical QoS experienced by the users if the current heterogeneous cellular network architecture migrates from a Half Duplex to a Full Duplex mode of operation. Numerical results and analysis are provided, where the network is modeled as a Matern point processes with a hard core distance. The results demonstrate the accuracy and computational efficiency of the proposed scheme, especially in large scale wireless systems.