Inter-cell Interference Coordination Research Articles

Cooperative Interference Mitigation Algorithm in Heterogeneous Networks

Heterogeneous hetworks (HetNets) have been introduced as an emerging technology in order to meet the increasing demand for mobile data. HetNets are a combination of multi-layer networks such as macrocells and small cells. In such networks, users may suffer significant cross-layer interference. To manage this interference, the 3rd Generation Partnership Project (3GPP) has introduced enhanced Inter-Cell Interference Coordination (eICIC) techniques. Almost Blank SubFrame (ABSF) is one of the time-domain techniques used in eICIC solutions. We propose a dynamically optimal Signal-to-Interference-and-Noise Ratio (SINR)-based ABSF framework to ensure macro user performance while maintaining small user performance. We also study cooperative mechanisms to help small cells collaborate efficiently in order to reduce mutual interference. Simulations show that our proposed scheme achieves good performance and outperforms the existing ABSF frameworks.

Intercell Interference Coordination for Control Channels in LTE and LTE-A: An Optimization Scheme Based on Evolutionary Algorithms

Intercell Interference Coordination (ICIC) encompasses techniques aiming at reducing the intercell interference at cell edges, an issue affecting not only data but also control channels in Long Term Evolution (LTE) and LTE-Advanced (LTE-A). This paper presents several ICIC-based optimization schemes to improve the performance of the control channels: the Physical Downlink Control Channel (PDCCH) in LTE and the enhanced PDCCH (ePDCCH) in LTE-A. The study is focused on realistic deployments, where the amount of intercell interference received at different cells varies considerably, making very difficult the task of homogenizing the performance of the ePDCCH in the coverage area. The PDCCH is time-multiplexed, and hence, traditional ICIC schemes such as Soft Frequency Reuse cannot be applied. As an answer to this, LTE-A introduces the ePDCCH. This new structure increases the signaling capacity and allows frequency domain ICIC. However, the optimization of the ePDCCH poses a new problem. The resources devoted to the ePDCCH need to be borrowed from the data channels. In order to address these problems, several multiobjective optimization schemes based on evolutionary algorithms are proposed to adjusts the configuration of the control channels, and consequently, to reduce the consumption of control resources. The results show that significant capacity gains, up to 30 %, are obtained in severely interfered cells with notorious savings in terms of transmitted power.

A Stochastic Geometry Analysis of Inter-Cell Interference Coordination and Intra-Cell Diversity

Inter-cell interference coordination (ICIC) and intra-cell diversity (ICD) play important roles in improving cellular downlink coverage. By modeling cellular base stations (BSs) as a homogeneous Poisson point process (PPP), this paper provides explicit finite-integral expressions for the coverage probability with ICIC and ICD, taking into account the temporal/spectral correlation of the signal and interference. In addition, we show that, in the high-reliability regime, where the user outage probability goes to zero, ICIC and ICD affect the network coverage in drastically different ways: ICD can provide order gain, whereas ICIC only offers linear gain. In the high-spectral efficiency regime where the SIR threshold goes to infinity, the order difference in the coverage probability does not exist; however, a linear difference makes ICIC a better scheme than ICD for realistic path loss exponents. Consequently, depending on the SIR requirements, different combinations of ICIC and ICD optimize the coverage probability.

Learning Based Frequency- and Time-Domain Inter-Cell Interference Coordination in HetNets

In this article, we focus on inter-cell interference coordination (ICIC) techniques in heterogeneous network (Het-Net) deployments, whereby macro- and picocells autonomously optimize their downlink transmissions, with loose coordination. We model this strategic coexistence as a multi-agent system, aiming at joint interference management and cell association. Using tools from Reinforcement Learning (RL), agents (i.e., macro- and picocells) sense their environment, and self-adapt based on local information so as to maximize their network performance. Specifically, we explore both time- and frequency domain ICIC scenarios, and propose a two-level RL formulation. Here, picocells learn their optimal cell range expansion (CRE) bias and transmit power allocation, as well as appropriate frequency bands for multi-flow transmissions, in which a user equipment (UE) can be simultaneously served by two or more base stations (BSs) from macro- and pico-layers. To substantiate our theoretical findings, Long Term Evolution Advanced (LTEA) based system level simulations are carried out in which our proposed approaches are compared with a number of baseline approaches, such as resource partitioning (RP), static CRE, and single-flow Carrier Aggregation (CA). Our proposed solutions yield substantial gains up to 125% compared to static ICIC approaches in terms of average UE throughput in the timedomain. In the frequency-domain our proposed solutions yield gains up to 240% in terms of cell-edge UE throughput.

Two‐level scheme to maximise the number of guaranteed users in downlink femtocell networks

In this study, the authors study the downlink resource allocation optimisation in femtocell networks, to maximise the number of guaranteed users whose data rate requirements are fully met. The spectral access of femtocell networks is based on orthogonal frequency division multiple access. In their work, two challenges are solved. The first is the intractable inter-cell interference coordination brought about by the transmission delay in backhaul connections, and the second is the incorporation of physical interference model into problem formulations. To solve these problems, the authors propose a novel two-level resource allocation scheme, implemented in both radio resource management controller and femtocell base stations, based on the maximisation of the number of guaranteed users. Notably, their proposed scheme is efficient and requires low overhead. Simulation results show that the proposed scheme offers significant performance improvement in both the percentage of guaranteed users and spectrum spatial reuse over existing methods proposed in the literature.

Fairness guaranteed joint CRE and eICIC scheme for capacity improvement in two‐tier heterogeneous networks

A joint cell range expansion (CRE) and enhanced inter-cell interference coordination (eICIC) scheme is proposed to enhance the capacity of two-tier heterogeneous networks. Optimal CRE bias and almost blank subframe ratio solutions are achieved by considering the fairness of users at the centre and cell edge. Capacity improvement is verified through extended results.

A Joint Game-Theoretic Interference Coordination Approach in Uplink Multi-Cell OFDMA Networks

In this paper, we present a joint game-theoretic approach to perform inter-cell interference coordination in uplink multi-cell orthogonal frequency division multiple access networks. The coordinated user scheduling and power allocation are considered simultaneously. We prove the existence of the joint-strategy Nash equilibrium (NE) in which both the user scheduling and power allocation strategy reach NE. Then, we design a distributed joint-strategy iterative algorithm to perform interference-aware resource allocation where only partial information exchange is involved. Simulation results demonstrate the effectiveness of the proposed algorithm.

Spectrum‐efficiency enhancement in small cell networks with biasing cell association and eICIC: An analytical framework

SUMMARYLoad balancing and interference management play crucial roles in small cell network (SCN) capacity and spectrum efficiency (SE) enhancement. By performing load balancing between macrocell and small cells, biasing cell association has attracted great attentions since it is proposed. Additionally, enhanced intercell interference coordination (eICIC) technology is also developed as an efficient interference mitigation method for the biasing cell association‐based SCNs. In this paper, we develop an SE enhancement framework with joint consideration of the eICIC factor and biasing factor. Using the stochastic geometry theory, the network is modeled by spatial Poisson point process. We firstly derive the downlink average rate, which is performed at a typical user. Secondly, the eICIC factor‐related network SE is analyzed by proving the existence of optimal eICIC factor, which maximizes the network SE. For the intractability of the closed‐form expression of optimal eICIC factor, a bisection search‐based algorithm is developed then. At last, numerical results confirm our analysis and show the proposed algorithm performance. Copyright © 2014 John Wiley & Sons, Ltd.

Improving the performance of cell edge users with fractional coordinated fair scheduling

In this study, the authors propose a fractional coordinated fair scheduling (FCFS) scheme for improving the performance of cell edge users in long term evolution (LTE-advanced) networks. To enhance the network spectral efficiency and reduce co-channel interference, they extend the inter-cell interference coordination technique for multi-sector cells. The sectors are coordinated in the sense that they are allowed to transmit simultaneously, if the neighbouring sectors co-channel interference is less than a threshold value. Accordingly, a coordinated scheduling scheme is proposed to transmit to a fraction of users, located in cell edges, with good channel conditions. The proposed scheme maintains fairness among the users using alpha-fair criterion. Furthermore, to reduce the computational complexity of the scheduling scheme, they propose a heuristic algorithm based on choosing an appropriate subset of users for scheduling computations. Performance evaluation of FCFS shows that the cell edge users’ throughput improves because of the spectral efficiency enhancement and interference reduction. Moreover, FCFS achieves a higher fairness index with respect to a non-coordinated fair scheme.

Optimal deployment of pico base stations in LTE-Advanced heterogeneous networks

As data traffic demand in cellular networks grows exponentially, operators need to add new cell sites to keep up; unfortunately, it is costly to build and operate macrocells. Moreover, it may not be possible to obtain the needed approvals for additional macrocell sites. Recently, the 3rd Generation Partnership Project (3GPP) introduced the concept of heterogeneous networks in Long Term Evolution (LTE) Release 10, where low-power base stations (BSs) are deployed within the coverage area of a macrocell to carry traffic. However, this new type of deployment can cause more severe interference conditions than a macro-only system, due to inter-cell interference; hence, enhanced inter-cell interference coordination (eICIC) has been actively discussed in LTE Release 10. Nevertheless, eICIC cannot completely eliminate interference and, to make matters worse, high-power transmissions of the reference signals from the BSs may increase the interference level. In this paper, we propose an algorithm for deploying low-power nodes within macrocell coverage areas in LTE heterogeneous networks, which aims to increase the system utility while minimizing the installation cost.

이종 네트워크 하향링크의 셀간 간섭 조정 및 사용자 스케줄링을 위한 저복잡도 알고리즘

이종 네트워크(HetNet)란 매크로셀 내에 소형셀이 혼재한 네트워크이다. 이종 네트워크에서는 대형셀로부터 소형셀 사용자에게 미치는 간섭이 소형셀 사용자의 성능을 열화시키는 주 원인 중 하나이며, 이 간섭을 줄이기 위해 향상된 셀간 간섭 조정기법(eICIC)이 필요하다. 기존의 eICIC 관련 연구에서는 프레임별 채널 변화를 거의 고려하지 않고 네트워크의 장기 처리율을 최대화하는 데 치중되어 성능 향상이 제한적이었다. 이 논문에서는 네트워크 전체 효용을 최대화하기 위해 매 프레임마다 동적으로 셀간 간섭을 제어하고 사용자를 스케줄링하며, 전수검색보다 계산 복잡도가 낮은 새로운 알고리즘을 제안한다. 제안된 알고리즘이 기존 알고리즘보다 네트워크 전체 처리율을 향상시키며, 사용자의 수가 많을 때 사용자간 공평성을 향상시킴을 컴퓨터 모의실험을 통해 보인다.

EICIC 가 적용된 이종 셀룰러 망을 위한 부하 분산 기법

기존의 매크로 셀룰러 망 환경은 공간 재사용의 한계로 인해 최근 급증하는 데이터 트래픽을 제대로 지원할 수 없게 되었다. 이 문제를 극복하기 위해 매크로 셀룰러 망위에 스몰 셀이 설치되어 적극적인 공간 재사용이 가능한 이종 셀룰러 망이 등장하게 되었다. 하지만, 매크로 셀과 스몰 셀 사이의 전송전력 차이로 인해 매크로 셀에 집중된 부하를 스몰 셀로 충분히 분산 시킬 수 없었다. 따라서, 프레임의 일정구간에서 매크로 셀의 전송전력을 차단하는 almost blank subframe (ABS) 와 스몰 셀 커버리지를 확장하여 사용자 부하를 스몰 셀로 강제 분산시키는 cell range expansion을 결합한 enhanced inter-cell interference coordination (eICIC) 기법이 제안되었다. 그러나, 이러한 eICIC 기법만으로는 효과적인 부하 분산을 달성하기 어렵다. 본 논문에서는 eICIC 기법이 적용된 이종 셀룰러 망 환경에서 비례공정을 향상시키는 부하 분산 기법을 제안한다. 구체적으로 제안된 기법은 탐욕 알고리즘 기반의 사용자의 소속 기지국 전환과 ABS 구간비율 갱신을 재귀적으로 결합하여 부하 분산을 실행한다. Recently, heterogeneous networks consisting of small-cells on top of traditional macro-cellular network has attracted much attention, because traditional macro-cellular network is not suitable to support more demanding mobile data traffic due to its limitation of spatial reuse. However, due to the transmit power difference between macro- and small-cells, most users are associated with macro-cells rather than small-cells. To solve this problem, enhanced inter-cell interference coordination (eICIC) has been introduced. Particularly, in eICIC, the small-cell coverage is forcibly expanded to associate more users with small-cells. Then, to avoid cross-tier interference from macro-cells, these users are allowed to receive the data during almost blank subframe (ABS) in which macro-cells almost remain silent. However, this approach is not sufficient to balance the load between macro- and small-cells because it only expands the small-cell coverage. In this paper, we propose a load balance scheme improving proportional fairness for heterogeneous networks employing eICIC. In particular, the proposed scheme combines the greedy-based user association and the ABS rate determination in a recursive manner to perform the load balance.

Autonomous Schemes for Inter-cell Interference Coordination in the Downlink of LTE Systems

Inter-cell interference (ICI) is one of the key challenges that limit the performance of Long Term Evolution and Long Term Evolution Advanced cellular systems. One approach to deal with ICI is through interference avoidance. Unlike static avoidance techniques where a-priori frequency planning and/or explicit inter-cell coordination is used, dynamic avoidance techniques rely on adapting its frequency planning and allocation based on the current state of the network. However, this improvement in performance comes with the cost of an increased complexity due to the coordination and alignments needed among the base stations (eNB) to manage and allocate channels among the users. Accordingly, autonomous ICI coordination techniques are receiving much interest among the various interference avoidance techniques. In this paper, we propose an autonomous self-adaptive scheme (SA, for short) for radio resource management and interference coordination. We then extend the proposed scheme to become self-adaptive power-aware (SAPA) in order to optimize and reduce the transmission power of the eNBs. A key feature in the proposed schemes is that all computations are independent of the number of users and cells in the network. This allows the proposed schemes to adapt to networks of any size and with an arbitrary number of users. Extensive simulation confirms that the proposed SA scheme ensures efficient frequency reuse patterns that lead to significant performance improvements in the throughput of the edge users without affecting other users. Moreover, the SAPA scheme achieves significant improvement in the power efficiency, while maintaining the throughput enhancements achieved by the SA scheme for both center and edge users.

A framework for leakage-based autonomous uplink inter-cell interference coordination in OFDMA/LTE heterogeneous networks

The inter-cell interference (ICI) problem in OFDMA wireless systems is a major impediment to attain high rates particularly for cell-edge users in reuse-1 systems. Using centralized resource allocation to combat ICI is not practical, particularly in heterogeneous networks (HetNets), as they require intensive signaling about interference and channel state information that may not always be practically available. The main contribution of this paper is devising efficient autonomous power allocation schemes such that the interference produced by each cell is below a certain limit. We develop two inter-cell interference coordination (ICIC) frameworks; the overall interference limit (OIL), and the interference limit per resource block (ILR). The first framework imposes an overall interference limit on each cell, while the second imposes different interference limits on different resource blocks in each cell. We propose a closed form solution, and an iterative solution for the OIL framework, and a closed form solution for the ILR framework which has an additional advantage of possible autonomous application at each terminal rather than at the base station. We present two semi-autonomous heuristic and optimal adaptive schemes that use the overload indicator (OI) signal in LTE to adjust the values of the interference limits in the ILR scheme. They attempt to alleviate the interference seen by overloaded cells in order to achieve fairness among different cells, which is very important especially in HetNets. A method based on the Kalman filter is introduced to predict the values of the OI in the intervals between the OI exchanges. This estimation can be applied to the adaptive schemes almost autonomously as it requires very infrequent signaling between cells. Simulations show that the proposed schemes exhibit better performance than equal power allocation. Comparison with centralized optimal allocation that uses global information shows good performance with acceptable degradation in the spectral efficiency which decreases as the interference limit increases. Simulations also show that the ILR and the OIL schemes almost have the same performance, and the adaptive schemes achieve fairness among different cells especially in a HetNet environment.

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.

SCHEDULING FOR INTERFERENCE MITIGATION USING ENHANCED INTERCELL INTERFERENCE COORDINATION

Deployment of low power base station (pico) in macro cell is a key for providing high data rates. Cell range expansion is one of the features of LTE-advanced where low power base station in a heterogeneous network can increase their coverage area and neighboring cells can offload users to low power base station to reduce overload in macro cell. This presents a very challenging multi-user communication problem. Co-channel deployed Het-Net will experience interference between pico and macro. The main challenge of pico cells embedded into a macro cell is to let more users profit from the additional bandwidth introduced into the network. Enhanced Inter-cell Interference Coordination (eICIC) has been introduced to solve interference problem. Scheduling for eICIC is used to provide best solution for interference mitigation, overload in macro cell, fairness in resource usage by users. In this paper we have analyzed Round Robin scheduling for eICIC, results prove that fairness is maintained between users and throughput has been improved.

Algorithms for Enhanced Inter-Cell Interference Coordination (eICIC) in LTE HetNets

The success of LTE Heterogeneous Networks (HetNets) with macro cells and pico cells critically depends on efficient spectrum sharing between high-power macros and low-power picos. Two important challenges in this context are, {(i)} determining the amount of radio resources that macro cells should {\em offer} to pico cells, and {(ii)} determining the association rules that decide which UEs should associate with picos. In this paper, we develop a novel algorithm to solve these two coupled problems in a joint manner. Our algorithm has provable guarantee, and furthermore, it accounts for network topology, traffic load, and macro-pico interference map. Our solution is standard compliant and can be implemented using the notion of Almost Blank Subframes (ABS) and Cell Selection Bias (CSB) proposed by LTE standards. We also show extensive evaluations using RF plan from a real network and discuss SON based eICIC implementation.

A measurement‐based study of handover improvement through range expansion and interference coordination

AbstractAlthough the range expansion and inter‐cell interference coordination (ICIC) have been shown to successfully enhance the capacity and load balancing in the Heterogeneous Network, their impacts on the handover (HO) performance are not fully understood in existing studies. In this paper, a novel measurement‐based approach is adopted to investigate these issues, where the real measured data of the reference signal received power in a macro–pico co‐channel deployment are collected. Then the mobility performance in terms of the HO failure rate and ping‐pong rate is simulated with various ICIC schemes in the same reality environment. This has been made possible by modeling the possible HO failure events based on evaluating the downlink received signal‐to‐interference‐plus‐noise ratio from reference signal received power. The simulation results indicate that range expansion together with ICIC can have positive or negative influences on macro‐to‐pico, pico‐to‐macro, pico‐to‐pico and macro‐to‐macro HOs in the Heterogeneous Network. The existing static ICIC or mobility‐based ICIC cannot handle the intra‐layer (pico‐to‐pico and macro‐to‐macro) interference, thus limiting their abilities to improve the mobility performance. Motivated by this, a dynamic‐ICIC‐aided HO procedure is proposed. The proposed HO enhancement method is more flexible and effective in mitigating both the inter‐layer and intra‐layer interference, outperforming the existing methods significantly. Copyright © 2014 John Wiley & Sons, Ltd.

셀 경계 단말의 성능 향상을 위한 회전성 빔 방향 패턴의 활용

셀룰러 이동통신 시스템의 용량과 커버리지를 향상시키기 위한 많은 연구 결과들이 시스템에 적용되었지만, 셀 경계에서의 심각한 성능 열화는 여전히 단말 전송률의 더 나은 향상을 가로막는 주요한 요인으로 남아있다. 3GPP (Third Generation Partnership Project)의 LTE-A (Long Term Evolution-Advanced) 표준에서는 협력적 전송 (CoMP, coordinated-multipoint transmission reception)과 ICIC (inter-cell interference coordination)와 같은 진보된 기술들이 셀 경계 성능 열화 문제를 해결하기 위해 소개되었다. 본 논문에서는 다수개의 빔 방향 패턴 (BDP, beam direction pattern)을 활용하여 셀 경계 단말들의 성능을 향상시킬 수 있는 방안을 제안한다. 다수개의 빔 방향 패턴은 기지국에 설치된 복수 계층 안테나 어레이를 사용해 구현될 수 있다. 고정된 빔 패턴을 갖는 기존의 3섹터 안테나와 비교해서, 제안하는 방식은 다수개의 BDP들이 시간상에서 회전하면서 신호를 전송하게 된다. 이를 통해 셀 또는 섹터 경계에 위치하는 특정 단말들이 기지국으로부터 전체 전송 시간에 걸쳐 나쁜 성능의 신호를 수신하게 되는 상황을 억제함으로써, 해당 단말들의 수신 신호 품질을 향상시킬 수 있다. 성능 평가 결과는 제안하는 방식이 기존 3섹터 전송 방식에 비해 평균 단말 전송률 측면에서 하위 5% 단말에서 약 171% 향상된 성능을 나타냄을 보여준다.

Intercell Interference Coordination for LTE Systems

Intercell interference coordination (ICIC) techniques not only help improve cellular data coverage but allow more efficient use of a valuable wireless spectrum as well. This paper investigates soft frequency reuse (SFR), which is a form of ICIC, for long-term evolution (LTE) systems. By analyzing the throughput of the SFR scheme, we find that classifying cell-edge users and cell-center users is critical. Thus, we develop low-complexity decentralized SFR scheduling algorithms that include optimal user classification and balance throughput and fairness among multiusers. We also propose suboptimal methods to reduce computational complexity. Computer simulation demonstrates that gains of the proposed SFR algorithm can improve the fifth percentile user throughput by 26% while maintaining the same cell average throughput, compared with a non-ICIC system.