Inter-cell Interference Mitigation Research Articles

Iterative Mitigation of Intercell Interference in Cellular Networks Based on Gaussian Belief Propagation

The mitigation of 2-D intersymbol interference (ISI) has recently emerged as an important problem in the field of storage technology and wireless communications. Several solutions based on message passing have been proposed to perform equalization on 2-D channels with ISI. We present an algorithm based on Gaussian belief propagation (GaBP). We show that the proposed algorithm has interesting features compared with the corresponding message passing solutions available in the literature. First, the complexity of the proposed equalizer is independent of the size of the constellation used for modulation. Second, since the complexity is not exponential in the size of the state space, the computational burden is reduced for channels with long memory. As an application, we consider decentralized intercell interference mitigation in uplink cellular networks, where base stations communicate with their neighbors to recover their own users' signals.

Mitigation of Inter-Cell Interference Utilizing Carrier Allocation in Visible Light Communication System

It is necessary in visible light communication where different information from adjacent cells is distinguishable without inter-cell interference for indoor localization-based services and positioning systems. In order to mitigate inter-cell interference, a carrier allocation-visible light communication system, adopting various carriers among the system's respective cells, is suggested. The effects of inter-cell interference for a single channel and the proposed systems are investigated by experimentation with simultaneous transmissions of QPSK signals.

Capacity Calculation and Sub-Optimal Power Allocation Scheme for OFDM-Based Systems

For emerging cellular wireless systems, the mitigation of inter-cell interference is the key to achieve a high capacity and good user experience. This paper is devoted to the performance analysis of interference mitigation techniques for the downlink in an orthogonal frequency division multiple access (OFDMA) network, with a focus on the Long Term Evolution-Advanced (LTE-A) standard. Here we have derived a general closed-form equation of system capacity taking multiple cells into consideration and then we have investigated a coordination technique for interference mitigation. For the given interference constraint, how power should be transmitted into each OFDM sub-carrier for prevailing channel condition such that the total transmission rate of the base station can be maximized.

Intercell Interference Management in OFDMA Networks: A Decentralized Approach Based onReinforcement Learning

This paper presents a decentralized framework for dynamic spectrum assignment in multicell orthogonal frequency division multiple access (OFDMA) networks. The proposed framework allows each cell to autonomously decide the frequency resources it should use through a procedure that incorporates concepts from self-organization and machine learning in multiagent systems (MASs). Simulation results have been obtained for several scenarios, including both macrocells (MCs) and femtocells (FCs), revealing important improvements in terms of spectral efficiency and intercell interference mitigation over reference approaches, and close performance with the one obtained by a centralized strategy. Results also suggest that the framework would be practical for future FC cellular deployments where a high degree of independence of the network nodes is expected to reduce operational costs.

CoMP-CSB for ICI Nulling with User Selection

The capacity of downlink multiple-input multiple-output (MIMO) cellular networks is significantly limited by inter-cell interference (ICI), particularly at cell boundaries. Recently, two types of coordinated multiple point transmission (CoMP) technologies, joint processing and transmission (JPT) and coordinated scheduling and beamforming (CSB), were proposed. These technologies are intended for the latest cellular communication standard in order to improve the performance of cell-edge users who suffer from significant ICI. In this paper, we propose an ICI cancellation technique based on a user selection algorithm for CoMP-CSB. Under partial channel state information (CSI) and no data sharing condition, each base station (BS) concentrates more on the direction of interference to the adjacent cell's users, during the user selection process. Unlike prior concepts for a single-cell environment, in which each BS generates a precoding matrix for selected users to be served, the proposed technique considers the effects of interference to users located in adjacent cells. Although there are obvious trade-offs between ICI mitigation and the number of simultaneous scheduled users in terms of system capacity, the simulation results demonstrate that our proposed algorithm achieves higher sector throughput and is more robust against ICI if the system is limited by interference. Furthermore, through simulation we are able to obtain the preferred option for the coordination distance (R) and the number of degrees of freedom for ICI nulling (ξ).

On Collision Probabilities in Frequency-Domain Scheduling for LTE Cellular Networks

In an Orthogonal Frequency Division Multiple Access (OFDMA) wireless network, inter-cell interference (ICI) is one of the main challenges, and is of special concern for users near the cell edge. ICI arises naturally from collisions of frequency resource assignments among neighboring base stations. An important performance parameter is the probability distribution of assignment collisions. In this paper, an exact analytical expression for the collision probability is derived for an arbitrary number of base stations with non-coordinated schedulers. The expression can be used to determine conditions under which ICI mitigation techniques may be required as well as to establish a baseline for performance comparison with ICI coordination schemes. For the important case of two base stations, the expression is particularly simple. Numerical results are presented to illustrate the analytical results.

Minimising cell transmit power

With the introduction of femtocells, cellular networks are moving from the conventional centralised architecture to a distributed one, where each network cell should make its own radio resource management decisions, while providing inter-cell interference mitigation. However, realising this distributed cellular network architecture is not a trivial task. In this paper, we first introduce a simple self-organisation rule under which a distributed cellular network is able to converge into an efficient resource allocation pattern, then propose a novel resource allocation model taking realistic resource allocation constraints into account, and finally evaluate the performance of the proposed self-organisation rule and resource allocation model using system-level simulations.

Weighted Sum-Rate Maximization in Multi-Cell Networks via Coordinated Scheduling and Discrete Power Control

Inter-cell interference mitigation is a key challenge in the next generation wireless networks which are expected to use an aggressive frequency reuse factor and a high-density base station deployment to improve coverage and spectral efficiency. In this work, we consider the problem of maximizing the weighted sum-rate of a wireless cellular network via coordinated scheduling and discrete power control. We present two distributed iterative algorithms which require limited information exchange and data processing at each base station. Both algorithms provably converge to a solution where no base station can unilaterally modify its status (i.e., transmit power and user selection) to improve the weighted sum-rate of the network. Numerical studies are carried out to assess the performance of the proposed schemes in a realistic system based on the IEEE 802.16m specifications. Simulation results show that the proposed algorithms achieve a significant rate gain over uncoordinated transmission strategies for both cell-edge and inner users.

Power allocation strategies for distributed precoded multicell based systems

Multicell cooperation is a promising solution for cellular wireless systems to mitigate intercell interference, improve system fairness, and increase capacity. In this article, we propose power allocation techniques for the downlink of distributed, precoded, multicell cellular-based systems. The precoder is designed in two phases: first the intercell interference is removed by applying a set of distributed precoding vectors; then the system is further optimized through power allocation. Three centralized power allocation algorithms with per-BS power constraint and different complexity trade-offs are proposed: one optimal in terms of minimization of the instantaneous average bit error rate (BER), and two suboptimal. In this latter approach, the powers are computed in two phases. First, the powers are derived under total power constraint (TPC) and two criterions are considered, namely, minimization of the instantaneous average BER and minimization of the sum of inverse of signal-to-noise ratio. Then, the final powers are computed to satisfy the individual per-BS power constraint. The performance of the proposed schemes is evaluated, considering typical pedestrian scenarios based on LTE specifications. The numerical results show that the proposed suboptimal schemes achieve a performance very close to the optimal but with lower computational complexity. Moreover, the performance of the proposed per-BS precoding schemes is close to the one obtained considering TPC over a supercell.

Interference mitigation and avoidance in uplink OFDMA with collaborative distributed intracell scheduling

A distributed collaborative uplink scheduling model in OFDMA systems is extended to a multicell scenario. On the intercell level, the scenarios with and without base station cooperation are investigated. In the cooperative case, base stations collaborate by performing pricing-based power control based on exchanging interference information. In the absence of intercell collaboration, probabilistic transmission is applied in each cell for interference avoidance. Simulations show that the proposed intercell interference mitigation and avoidance schemes lead to enhanced results.

Research on uplink coordinated transmission schemes in LTE-advanced systems

The investigation of inter-cell interference mitigation techniques is a key area in wireless communications. Coordinated multiple points (CoMP) transmission/reception is a candidate technique for interference cancellation in 3GPP LTE-Advanced system. However, the coordination scheme in CoMP remains a key research problem to be solved, which will have a strong influence on the performance of CoMP. In this paper, a novel coordinated transmission scheme is proposed for the uplink LTE-Advanced system. In our scheme, several base transceiver stations (BTS) and users are selected as coordination partners which form a CoMP cluster. Joint processing is used at the receiver to mitigate interference. From the perspective of coordinated partner selection, our scheme can be divided into static and dynamic coordination which are both considered to fully exploit the throughput gain of CoMP. The proposed schemes are evaluated by system level simulation and compared with the conventional LTE system based upon single cell processing. Our simulation results demonstrate that the proposed schemes attain superior performance as opposed to the conventional system in terms of cell average and cell edge throughput.

Dynamic fractional frequency reuse (D‐FFR) for multicell OFDMA networks using a graph framework

ABSTRACTA graph‐based framework is proposed in this paper to implement dynamic fractional frequency reuse (D‐FFR) in a multicell Orthogonal Frequency Division Multiple Access (OFDMA) network. FFR is a promising resource‐allocation technique that can effectively mitigate intercell interference (ICI) in OFDMA networks. The proposed D‐FFR scheme enhances the conventional FFR by enabling adaptive spectral sharing as per cell‐load conditions. Such adaptation has significant benefits in practical systems where traffic loads in different cells are usually unequal and time‐varying. The dynamic adaptation is accomplished via a graph framework in which the resource‐allocation problem is solved in two phases: (1) constructing an interference graph that matches the specific realization of FFR and the network topology and (2) coloring the graph by use of a heuristic algorithm. Various realizations of FFR can easily be incorporated in the framework by manipulating the first phase. The performance improvement enabled by the proposed D‐FFR scheme is demonstrated by computer simulation for a 19‐cell network with equal and unequal cell loads. In the unequal‐load scenario, the proposed D‐FFR scheme offers significant performance improvement in terms of cell throughput and service rate as compared to conventional FFR and previous interference management schemes. Copyright © 2011 John Wiley & Sons, Ltd.

An Algorithm of LTE Inter-cell Interference Mitigation Based on Hopping SRS Sounding

An Algorithm of LTE Inter-cell Interference Mitigation Based on Hopping SRS Sounding

셀 간 협동 CSM에서 상향 링크 용량 개선을 위한 자원 할당 알고리즘

In this paper, for a uplink space division multiple access system named cooperative spatial multiplexing(CSM), radio resource management(RRM) algorithms are proposed based on sharing uplink channel information among a serving base station(BS) and interfering BSs in a uplink coordinated wireless communication system. A constrained maximum transmit power algorithm is proposed for mobile station(MS) to limit uplink inter-cell interference(ICI). And joint scheduling algorithm among coordinated BSs is proposed to enhance uplink capacity through ICI mitigation by using channel information from interfering BSs. It is shown that the proposed RRM algorithm provides a considerable uplink capacity enhancement by effective ICI mitigation only with moderate complexity.

Intercell Radio Resource Management through Network Coordination for IMT-Advanced Systems

In IMT-Advanced systems, a cross-layer approach coupling network coordination and radio resource managements enables mitigation of intercell interference and throughput improvement of cell-edge users. To facilitate coordination among base stations, we propose a new radio-resource management framework where cell-edge users and cell-interior users are separately managed by two different radio-resource managers. In the proposed framework, we address the issue of how to classify a user as cell-edge user or cell-interior user, and how much radio resource the cell-edge users may occupy. We present a solution where a user switches the user type so as to maximize overall network throughput subject to the condition that their own throughput does not decrease upon switching. We verify our solution using analysis and simulation experiments where two or three BSs are coordinated to support fractional frequency reuse or macrodiversity and demonstrate that our solution can guarantee superior cell-edge performance and achieve a high network throughput.

Cognitive-Relay-Based Intercell Interference Cancellation in Cellular Systems

This paper proposes to use a cognitive-relay technique to mitigate intercell interference (ICI) in cellular systems. In the proposed system, several relay stations (RSs) that are equipped with cognitive radio are deployed near the cell boundary. The base station (BS) and the RS in each cell operate in the same spectrum band as primary and secondary transmitters, respectively. Once an interference-limited mobile station (MS) requests an RS for assistance, the RS senses the spectrum band and accesses a spectrum hole to forward its received signal (and interference) to the MS. At the receiver of the MS, optimum combining is employed to combine the original signal that is received from the BS and the relayed signal to cancel the ICI. The system performance is analyzed in terms of the outage capacity and the average capacity considering the impact of the availability of cognitive-relay channels and the link quality between the RS and the MS. The location and the coverage radius of the RS are designed based on the requirement of the RS-MS link quality. Finally, simulation results are given to validate the theoretical analysis and to show the capacity improvement due to the ICI cancellation with the assistance of cognitive relay.

Multiuser MISO Transmitter Optimization for Intercell Interference Mitigation

The transmitter optimization (i.e., steering vectors and power allocation) for a MISO Broadcast Channel (MISO-BC) subject to general linear constraints is considered. Such constraints include, as special cases, the sum power, the per-antenna or per-group-of-antennas power, and "forbidden interference direction" constraints. We consider both the optimal dirty-paper coding and the simple suboptimal linear zero-forcing beamforming strategies, and provide numerically efficient algorithms that solve the problem in its most general form. As an application, we consider a multi-cell scenario with partial cell cooperation, where each cell optimizes its precoder by taking into account interference constraints on specific users in adjacent cells. The effectiveness of the proposed methods is evaluated in a simple system scenario including two adjacent cells, under different fairness criteria that emphasize the bottleneck role of users near the cell "boundary". Our results show that "active" Inter-Cell Interference (ICI) mitigation outperforms the conventional "static" ICI mitigation based on fractional frequency reuse.

SC-FDMA with iterative multiuser detection: improvements on power/spectral efficiency

This article outlines the basic principles of single-carrier frequency division multiple access with iterative multiuser detection, called grouped frequency division multiple access. GFDMA allows multiple users to share a common set of subcarriers and separates the signals of users by employing distinct interleavers and frequency-domain multiuser detection. Some attractive features of GFDMA are explained, including low-cost iterative multiuser detection, multiuser and frequency diversity gains, and flexibility in resource allocation. We also discuss the applications of GFDMA to spatial diversity schemes and to intercell interference mitigation in the cell edge. It is shown that GFDMA offers advantages over SC-FDMA with respect to power/spectral efficiency. Such power/spectral efficiency can provide considerable performance improvements in future wireless communication networks.

Performance of power control in inter-cell interference coordination for frequency reuse

To mitigate inter-cell interference in 3G evolution systems, a novel inter-cell interference coordination scheme called soft fractional frequency reuse is proposed in this article, which enables to improve the data rate in cell-edge. On this basis, an inter-cell power control is presented for the inter-cell interference coordination, and the inter-cell balanced signal to interference plus noise ratio (SINR) among users is established for power allocation, which enables mitigation of inter-cell interference. Especially, the power control is based on a novel exponential kernel equation at higher convergence speed than the traditional arithmetic kernel equations. Numerical results show that the proposed scheme improves the throughput and reduces the blocking rate compared to the existing power control algorithms.

Analysis of QoS-Based Band Power Allocation for Broadband Multi-Cell Forward Link Environments

ICI (Inter-Cell Interference) mitigation schemes at the cell border are frequently dealt with as a special issue in 3GPP LTE (Long Term Evolution). However, few papers have analyzed the outage performance for the ICI mitigation schemes. In this paper, we propose a generalized cell planning scheme termed QBPA (Quality of Service based Band Power Allocation). Utilizing the QBPA scheme, we measure how much increase in channel capacity can be obtained through the flexible control of bandwidth and power in multi-cell forward-link environments. In addition, the feasible performance of the conventional schemes can be evaluated as long as those schemes are specific forms of the QBPA.