Inter-cell Interference Coordination Research Articles

Spectrum Sharing in Satellite-Mobile Multisystem Using 3D In-Building Small Cells for High Spectral and Energy Efficiencies in 5G and Beyond Era

In this paper, we present a novel technique for sharing satellite spectrum with terrestrial-mobile 3-dimensional (3D) in-building small cells, namely femtocells. Both the space-satellite and the terrestrial-mobile systems (TMSs) operate at their respective licensed spectrums. However, due to the scarcity of the available spectrum, a huge amount of data generated indoors, and a high external wall penetration loss of a 3D building, we propose to reuse the satellite spectrum to small cells deployed only in 3D buildings of the TMS. The proposed spectrum sharing technique is detailed by identifying and addressing the major related issues. The co-channel interference generated because of the co-existence of the satellite user equipments (UEs) in the small-cell coverage is analyzed, and the handover procedures for a satellite UE toward and away from any small cell are discussed. The almost blank subframe (ABS)-based enhanced intercell interference coordination (eICIC) technique is employed to small cells in order to assure the quality-of-service (QoS) between small-cell UEs and satellite UEs. We derive the system-level capacity, spectral efficiency, and energy efficiency performance metrics for the proposed technique by varying the number of buildings over the coverage of a macrocell and deduce the condition for optimality for both the energy efficiency and the spectral efficiency. With an extensive system-level simulation and numerical analysis, we justify the impact of using the ABS-based eICIC technique toward provisioning QoS in terms of radio resource allocation. Furthermore, we show the outperformance of the proposed technique in terms of spectral efficiency and energy efficiency over the ones expected for the fifth generation (5G) network requirements as well as achieved by numerous existing techniques. Finally, we discuss the radio resource scheduler implementation as well as the significance, challenge, and future research perspective of the proposed spectrum sharing technique.

Time-domain ICIC and optimized designs for 5G and beyond: a survey

Time-domain enhanced inter-cell interference coordination (eICIC) is an effective technique to reduce the cross-tier inter-cell interference (ICI) in long term evolution (LTE)-based heterogeneous small cell networks (HetSCNs). This paper first clarifies two main communication scenarios in HetSCNs, i.e., macrocells deployed with femtocells (macro-femto) and with picocells (macro-pico). Then, the main challenges in HetSCNs, particularly the severe cross-tier ICI in macro-femto caused by femtocells with closed subscribe group (CSG) access or in macro-pico caused by picocells with range expansion are analyzed. Based on the prominent feature of dominant interference in HetSCNs, the main idea of time-domain interference coordination and two basic schemes in the eICIC standardization, i.e., almost blank subframe (ABS) and orthogonal frequency division multiplexing symbol shift are presented, with a systematic introduction to the interactions of these techniques with other network functions. Then, given macro-femto and macro-pico HetSCNs, an overview is provided on the advanced designs of ABS-based eICIC, including self-optimized designs with regard to key parameters such as ABS muting ratio, and joint optimized designs of ABS-based eICIC and other radio resource management techniques, such as user association and power control. Finally, the open issues and future research directions are discussed.

Study on Coverage of Full Frequency Reuse in FFR Systems Based on Outage Probability

A fractional frequency reuse (FFR) system is an inter-cell interference coordination scheme used in cellular networks. In FFR systems, the available bandwidth is partitioned into orthogonal subbands such that the users near the cell center adopt subbands of a frequency reuse (FR) factor equal to one (i.e., Full FR), and the users near the cell edge adopt the subbands of an FR factor greater than one (i.e., Partial FR). The proper design of Full FR coverage, which is used to distinguish Full FR regions from Partial FR regions, plays a critical role in FFR system performance. This paper studies the optimal Full FR coverage that maximizes system throughput in the downlink in multiple-input multiple-output (MIMO) cellular networks. For MIMO systems, orthogonal space–time block codes are considered. We analytically compare the outage probabilities of Full FR and Partial FR for a given user’s location, where the outage probability is evaluated through small-scale multipath fading. By doing so, subject to the constraint that a given target outage probability (quality-of-service) is satisfied, the optimal Full FR coverage is analyzed as a function of base station (BS) power. We prove that the optimal Full FR coverage is a non-increasing function of BS power when the powers of all BSs in the network are scaled up or down at the same rate. This result offers insight into the design of Full FR coverage in relation to BS power; we gain insight into the complicated relationship between crucial FFR design parameters.

A Multi-Traffic Inter-Cell Interference Coordination Scheme in Dense Cellular Networks

This paper proposes a novel semi-distributed and practical ICIC scheme based on the Almost Blank SubFrame (ABSF) approach specified by 3GPP. We define two mathematical programming problems for the cases of guaranteed and best-effort traffic, and use game theory to study the properties of the derived ICIC distributed schemes, which are compared in detail against unaffordable centralized schemes. Based on the analysis of the proposed models, we define Distributed Multi-traffic Scheduling (DMS), a unified distributed framework for adaptive interference-aware scheduling of base stations in future cellular networks which accounts for both guaranteed and best-effort traffic. DMS follows a two-tier approach, consisting of local ABSF schedulers, which perform the resource distribution between guaranteed and best effort traffic, and a lightweight local supervisor, which coordinates ABSF local decisions. As a result of such a two-tier design, DMS requires very light signaling to drive the local schedulers to globally efficient operating points. As shown by means of numerical results, DMS allows to (i) maximize radio resources reuse, (ii) provide requested quality for guaranteed traffic, (iii) minimize the time dedicated to guaranteed traffic to leave room for best-effort traffic, and (iv) maximize resource utilization efficiency for best-effort traffic.

Performance Analysis of the Idle Mode Capability in a Dense Heterogeneous Cellular Network

In this paper, we study the impact of the base station (BS) idle mode capacity (IMC) on the network performance of multi-tier and dense heterogeneous cellular networks (HCNs) with both line-of-sight (LoS) and non-line-of-sight transmissions. Different from most existing works that investigated network scenarios with an infinite number of user equipments (UEs), we consider a more practical set-up with a finite number of UEs in our analysis. Moreover, in our model, the small BSs (SBSs) apply a positive power bias in the cell association procedure, so that macrocell UEs are actively encouraged to use the more lightly loaded SBSs. In addition, to address the severe interference that these cell range expanded UEs may suffer, the macro BSs (MBSs) apply enhanced inter-cell interference coordination, in the form of almost blank subframe (ABS) mechanism. For this model, we derive the coverage probability and the rate of a typical UE in the whole network or a certain tier. The impact of the IMC on the performance of the network is shown to be significant. In particular, it is important to note that there will be a surplus of BSs when the BS density exceeds the UE density, and thus a large number of BSs switch off. As a result, the overall coverage probability, as well as the area spectral efficiency, will continuously increase with the BS density, addressing the network outage that occurs when all BSs are active and the interference becomes LoS dominated. Finally, the optimal ABS factors are investigated in different BS density regions. One of major findings is that MBSs should give up all resources in favor of the SBSs when the small cell networks go ultra-dense. This reinforces the need for orthogonal deployments, shedding new light on the design and deployment of the future 5G dense HCNs.

Machine learning algorithms for inter-cell interference coordination

The current LTE and LTE-A deployments require larger efforts to achieve the radio resource management. This, due to the increase of users and the constantly growing demand of services. For this reason, the automatic optimization is a key point to avoid issues such as the inter-cell interference. This paper presents several proposals of machine-learning algorithms focused on this automatic optimization problem. The research works seek that the cellular systems achieve their self-optimization, a key concept within the self-organized networks, where the main objective is to achieve that the networks to be capable to automatically respond to the particular needs in the dynamic network traffic scenarios.

A two-timescale graph-based resource allocation scheme combing dynamic eICIC in Heterogeneous Networks

Heterogeneous Network (HetNet) has been viewed as an effective way to meet the tremendous growth of mobile traffic, in which the cross-tier and co-tier interference are the key limitations. Most of the traditional interference management strategies only focus on addressing either cross-tier interference or co-tier interference. We in this paper propose a resource allocation scheme to systematically cope with both of them in Orthogonal Frequency Division Multiple Access (OFDMA)-based HetNets. Specifically, the proposed scheme combines the dynamic enhanced inter-cell interference coordination (eICIC) and orthogonal resource allocation (ORA), to eliminate the cross-tier and co-tier interference respectively. Furthermore, with tracking the real-time variations of the user information (e.g., locations or service requirements), the proposed scheme is separated into two timescales. At the large timescale, a centralized strategy is performed to roughly allocate resource blocks (RBs) to cells; at the small timescale, a distributed strategy is performed to further schedule RBs among users. Also, we formulate two optimization problems to maximize the minimum of users’ throughput satisfaction rate (TSR) for our proposed scheme, followed by two graph-based algorithms to solve them with low complexity. Simulation results manifest the superiority of our proposed scheme in guaranteeing the fairness of users’ TSR.

Distance-Based Inter-Cell Interference Coordination in Small Cell Networks: Stochastic Geometry Modeling and Analysis

We propose a distance-based inter-cell interference coordination (ICIC) scheme in small cell networks (SCNs). While most of the previous works focus on a randomly selected user called a typical user, we focus on an edge user because the main purpose of ICIC is to improve the performance of an edge user. Since there are many inactive small cell base stations (SBSs) in SCNs, a simple criterion for an edge user such as being located near a cell boundary is not appropriate for SCNs. To accurately detect edge users experiencing severe performance degradation, we newly define an edge user in SCNs based on the nearest active neighbor SBS. We then apply our scheme only to edge users where SBSs within so-called the cooperation radius from each edge user cooperate. With the help of the stochastic geometry we obtain a semi-closed expression for the coverage probability of an edge user with our scheme. We investigate two tradeoffs on the resource efficiency of a network and the coverage probability of an interior user. We then determine the optimal cooperation radius that maximizes the coverage probability of an edge user considering the two tradeoffs. Our analytical results are validated through simulations.

Interference Coordination for 5G New Radio

The arrival of the 5G NR provides a unique opportunity for introducing new inter-cell interference coordination (ICIC) mechanisms. The objective is twofold: to better exploit the benefits of ICIC in coherence with the rest of radio resource management (RRM) principles in 5G, and to support new services and deployment scenarios. We propose several enhanced techniques. In the uplink, inter-cell coordination of the pilot sequence configuration mitigates the inter-cell interference problem of such pilots, which is especially severe for cell-edge users. In the downlink, coordinated small cell DTX aims at network interference control and energy consumption reduction, whereas intercell rank coordination can unleash the potential of advanced receivers with minimal control overhead. Besides, on-demand power boosting and coordinated muting can be tailored to meet URLLC requirements. The simulation results quantify the performance benefits of the different techniques under heterogeneous key performance indicators (KPIs). We also discuss the standardization effort required for having each of these techniques included in the 5G NR specifications.

FdICIC: Inter-cell Interference Coordination for Full-Duplex Cellular Systems

This paper investigates the inter-cell interference coordination (ICIC) for heterogeneous networks (HetNets) with full-duplex (FD) small cell base stations to maximize the overall system throughput. To be compatible with the enhanced ICIC (eICIC) and the further enhanced ICIC (FeICIC) of existing LTE standards, the proposed FdICIC technique adopts cell range expansion and almost blank subframe to deal with the complicated interference scenario in such FD HetNets. In detail, the FdICIC includes four steps, namely, choosing the serving base station, pairing users for FD communication, resource block (RB) allocation, and power control of FD users. Through numerical simulation, we demonstrate that: (1) the overall system throughput can be improved by 10–25% with four FD small cell base stations when the residual self-interference is between − 130 to − 110 dB, (2) by carefully selecting the CRE bias, the overall system throughput can be further improved by about 30%, (3) the proposed user pairing, RB allocation, and power control steps have significant contributions to the performance improvement.

Complexity Analysis, Potential Game Characterization and Algorithms for the Inter-Cell Interference Coordination With Fixed Transmit Power Problem

We study the inter-cell interference coordination (ICIC) problem in a multicell orthogonal frequency division multiple access based cellular network employing universal frequency reuse. In each cell, only a subset of the available subchannels are allocated to mobile stations (MSs) in a given time slot so as to limit the interference to neighboring cells; also, each base station (BS) uses a fixed transmit power on every allocated subchannel. The objective is to allocate the available subchannels in each cell to the MSs in the cell for downlink transmissions taking into account the channel qualities from BSs to MSs as well as traffic requirements of the MSs so as to maximize the weighted sum of throughputs of all the MSs. First, we show that this problem is NP-complete. Next, we show that when the potential interference levels to each MS on every subchannel are above a threshold (which is a function of the transmit power and the channel gain to the MS from the BS it is associated with), the problem can be optimally solved in polynomial-time via a reduction to the matching problem in bipartite graphs. We also formulate the ICIC problem as a noncooperative game, with each BS being a player, and prove that although it is an ordinal potential game in two special cases, it is not an ordinal potential game in general. Also, we design two heuristic algorithms for the general ICIC problem: a greedy distributed algorithm and a simulated annealing (SA) based algorithm. The distributed algorithm is fast and requires only message exchanges among neighboring BSs. The SA algorithm is centralized and allows a tradeoff between quality of solution and execution time via an appropriate choice of parameters. Our extensive simulations show that the total throughput obtained using the better response (BR) algorithm, which is often used in game theory, is very small compared to those obtained using the SA and greedy algorithms; however, the execution time of the BR algorithm is much smaller than those of the latter two algorithms. Finally, the greedy algorithm outperforms the SA algorithm in dense cellular networks and requires only a small fraction of the number of computations required by the latter algorithm for execution.

Statistical Analysis and Optimization of a Fifth-Percentile User Rate Constrained Design for FFR/SFR-Aided OFDMA-Based Cellular Networks

Interference mitigation strategies are deemed to play a key role in the context of the next generation (B4G/5G) of multicellular networks based on orthogonal frequency division multiple access. Fractional and soft frequency reuse (FFR, SFR) constitute two powerful mechanisms for intercell interference coordination that have been already adopted by emerging cellular deployments as an efficient way to improve the throughput performance perceived by cell-edge users. This paper presents a novel optimal fifth-percentile user rate constrained design for FFR/SFR-based networks that, by appropriately dimensioning the center and edge regions of the cell, rightly splitting the available bandwidth among these two areas while assigning the corresponding transmit power, allows a tradeoff between cell throughput performance and fairness to be established. To this end, both the cumulative distribution function of the user throughput and the average spectral efficiency of the system are derived assuming the use of the ubiquitous proportional fair scheduling policy. The mathematical framework is then used to obtain numerical results showing that the novel proposed design clearly outperforms previous schemes in terms of throughput fairness control due to a more rational compromise between average cell throughput and cell-edge ICIC.

Energy Efficient Pico Cell Range Expansion and Density Joint Optimization for Heterogeneous Networks with eICIC.

Heterogeneous networks, constituted by conventional macro cells and overlaying pico cells, have been deemed a promising paradigm to support the deluge of data traffic with higher spectral efficiency and Energy Efficiency (EE). In order to deploy pico cells in reality, the density of Pico Base Stations (PBSs) and the pico Cell Range Expansion (CRE) are two important factors for the network spectral efficiency as well as EE improvement. However, associated with the range and density evolution, the inter-tier interference within the heterogeneous architecture will be challenging, and the time domain Enhanced Inter-cell Interference Coordination (eICIC) technique becomes necessary. Aiming to improve the network EE, the above factors are jointly considered in this paper. More specifically, we first derive the closed-form expression of the network EE as a function of the density of PBSs and pico CRE bias based on stochastic geometry theory, followed by a linear search algorithm to optimize the pico CRE bias and PBS density, respectively. Moreover, in order to realize the pico CRE bias and PBS density joint optimization, a heuristic algorithm is proposed to achieve the network EE maximization. Numerical simulations show that our proposed pico CRE bias and PBS density joint optimization algorithm can improve the network EE significantly with low computational complexity.

Interference management based on power control and MU-MIMO

Improvement of spectrum efficiency is a valuable research topic in mobile communication system, which impact cell edge user experience especially. According to current research results, three methods to improve inter-cell spectrum efficiency base on inter-cell interference management, including inter-cell interference randomization, inter-cell interference cancellation and inter-cell interference co-ordination. In this paper, one combinatorial method based on uplink power control and SINR prediction with non-ideal MU-MIMO CSI feedback is proposed for optimal management of inter-cell interference co-ordination. The simulation results show that this method performs very well in complex inter-cell interference scenario, and the average spectrum efficiency is improved more than 50%.

Adaptive Sector Coloring Game for Geometric Network Information-Based Inter-Cell Interference Coordination in Wireless Cellular Networks

Inter-cell interference coordination (ICIC) is a promising technique to improve the performance of frequency-domain packet scheduling (FDPS) in downlink LTE/LTE-A networks. However, it is difficult to maximize the performance of FDPS using static ICIC schemes because of insufficient consideration of signal-to-interference-and-noise ratio distribution and user fairness. On the other hand, dynamic ICIC schemes based on channel state information (CSI) also have difficulty presented in the excessive signaling overhead and X2 interface latency. In order to overcome these drawbacks, we introduce a new concept of ICIC problem based on geometric network information (GNI) and propose an adaptive sector coloring game (ASCG) as a decentralized solution of the GNI-based ICIC problem. Furthermore, we develop an ASCG with a dominant strategy space noted as ASCG-D to secure a stable solution through proving the existence of Nash equilibrium. The proposed scheme provides better performance in terms of system throughput gain of up to about 44.1%, and especially of up to about 221% for the worst 10% users than static ICIC schemes. Moreover, the performance of the CSI-based ICIC, which require too much computational load and signaling overhead, is only 13.0% and 5.6% higher than that of ASCG-D regarding the total user throughput and the worst 10% user throughput, respectively. The most interesting outcome is that the signaling overhead of ASCG-D is 1/144 of dynamic ICIC schemes’ one.

HICIC: Hybrid Inter-Cell Interference Coordination for Two-Tier Heterogeneous Networks With Non-Uniform Topologies

Interference coordination is regarded as one of the most significant techniques in heterogeneous networks (HetNets). In this paper, we propose a novel interference coordination framework, which is referred to hybrid inter-cell interference coordination (HICIC), for interference mitigation in HetNets with non-uniform topologies. The meaning of hybrid is two-fold: first, several techniques belong to inter-cell interference coordination (ICIC), enhanced ICIC (eICIC), and further eICIC (FeICIC) are considered simultaneously. We perform the resource partition in both the time-domain and the frequency-domain jointly. A novel dummy base station structure is designed to take full advantage of resources. Second, different subbands in the same cell can be configured with different almost blank subframe (ABS) ratios for diverse purposes. A novel concept, coordination willingness, is proposed for determining ABS ratios in a distributed manner with limited signaling overhead. We formulate HICIC parameters optimization as a logarithm utility maximization problem and provide a semi-distributed algorithm comprising three stages to solve it. Numerical results demonstrate the efficiency of HICIC over several comparative schemes in HetNets with two different non-uniform topologies. It achieves the maximal system utility among all schemes and improves the performance of user equipment’s (UEs) who have geographical disadvantages. With HICIC, sum throughput of all UEs has a significant increase with slight losses in the fairness. Our work also verifies the fact that ICIC and eICIC/FeICIC are not either-or propositions. A reasonable combination of different techniques can mitigate interference effectively making a better HetNet.

Physical Downlink Control Channel for Beyond LTE-Advanced

With the rapid deployment of LTE, the standardization activities of releases beyond LTE-Advanced (LTE-A) are recently being actively progressed in 3GPP. The emerging services and key enhancements such as Further Enhancement of Downlink Multiple-Input Multiple-Output (MIMO), Heterogeneous Networks, and Carrier Aggregation (CA) in LTE-A has revealed and motivated the standardization of an enhanced physical control channel(s) for the LTE air interface. The advanced Physical Downlink Control Channel (PDCCH) design shall be able to support increased control channel capacity, to support frequency domain Inter Cell Interference Coordination (ICIC), to achieve improved spatial reuse of control channel resource, to support beamforming and/or diversity and at the same time able to support flexible resource allocation of control channel. In this paper, we analyzed the features and capacity of enhanced control channels considered in LTE, starting with the motivations and the standardized Enhanced PDCCH (EPDCCH). The paper proceeds to consider the PDCCH design for 5G New Radio (NR) with the advantages of both PDCCH and EPDCCH while mitigating the limitations of them. Moreover, simulation results are presented to exhibit clear performance benefits of EPDCCH and NR-PDCCH.

DECCO: Deep-Learning Enabled Coverage and Capacity Optimization for Massive MIMO Systems

System capacity and service coverage are the most critical performance metrics in cellular wireless communication networks. Usually, system capacity enhancements are at the expense of service coverage degradations, and vice versa. This capacity-coverage tradeoff and the associated joint optimization problem becomes very challenging in massive multiple-input multiple-output (MIMO) wireless systems, due to a large amount of antenna tilt values to be configured and very sophisticated inter-cell interference conditions, under massive antenna scenarios. This paper proposes a novel approach, namely group alignment of user signal strength (GAUSS), to efficiently support the user scheduling for the massive MIMO system, and thus serve as an effective parameter for the coverage and capacity optimization (CCO) problem. Together with a unified threshold of Quality of Service, i.e. the minimum signal-to-interference-plus-noise ratio ( $\textit {SINR}_{min}$ ) for user satisfaction, GAUSS can effectively control the variance of signal strengths of multiple users in the neighborhood. Moreover, an intelligent and efficient deep-learning enabled coverage and capacity optimization (DECCO) algorithm is proposed and evaluated, which adopts a pre-trained deep policy gradient-based neural network to dynamically derive GAUSS and $\textit {SINR}_{min}$ during CCO. Furthermore, an inter-cell interference coordination (ICIC) is proposed to enhance the CCO performance. Analytical and simulation results show that the proposed DECCO algorithm can effectively achieve a much better performance balance between system capacity and service coverage than traditional fixed optimization (FO) and proportional fair optimization (PFO) algorithms. Specifically, DECCO significantly increases the overall spectrum efficiency by 24% and 40%, respectively, than FO and PFO in a typical massive MIMO system.

Network Capacity Optimisation in Millimetre Wave Band Using Fractional Frequency Reuse

Inter cell interference (ICI) is a major challenge that degrades the performance of mobile systems, particularly for cell-edge users. This problem arises significantly in the next-generation system, as the trend of deployment is with high densification, which yields an ultra-dense network (UDN). One of the challenges in UDN is the dramatic increase of ICI from surrounding cells. A common technique to minimize ICI is interference coordination techniques. In this context, the most efficient ICI coordination is fractional frequency reuse (FFR). This paper investigates the FFR in UDN millimeter wave network at 26-GHz band. The focus is on dense network with short inter site distance, and higher order sectorisation (HOS). The metrics used in frequency reuse is the signal to interference plus noise ratio rather than the distance, as the line of sight in millimeter wave can be easily blocked by obstacles even if they are in close proximity to the serving base station. This paper shows that FFR can improve the network performance in terms of per user cell-edge data throughput and average cell throughput, and maintain the peak data throughput at a certain threshold. Furthermore, HOS has a potential gain over default sectored cells when the interference is carefully coordinated. The results show optimal values for bandwidth split per each scenario in FFR scheme to give the best tradeoff between inner and outer zone users performance.

Exclusion Zone Assisted eICIC in Massive MIMO Enabled Cognitive HetNets

In a massive MIMO-enabled cognitive HetNet, a multi-user massive MIMO macrocell is underlaid with dense cognitive small cells. Then, a plenty of exclusion zones (EZs) are formed around co-scheduled macrocell users. Applying enhanced inter-cell interference coordination (eICIC) in each EZ separately, we propose an EZ-assisted eICIC scheme which arranges a customized eICIC configuration for each EZ independently to others. The proposed scheme can overcome potential weaknesses of current eICIC and that of cognitive HetNets. Then, the EZ-assisted eICIC configuration problem is formulated as a general optimization problem, which maximizes overall weighted sum rate of the network. Since the problem is intractable, a cluster segmentation approach is, therefore, proposed to convert the problem into a feasible version. Furthermore, we design an iterative multi-user scheduling-based algorithm to solve the problem. Numerical results demonstrate that the proposed EZ-assisted eICIC scheme significantly outperforms eICIC and further eICIC in dense HetNet.