Inter-cell Interference Cancellation Research Articles

Impact of Imperfect Channel State Information on Quasi-Decentralized Cooperative Inter-Cell Interference Cancellation with Fractional Frequency Reuse

Impact of Imperfect Channel State Information on Quasi-Decentralized Cooperative Inter-Cell Interference Cancellation with Fractional Frequency Reuse

Sparsity Enhanced Mismatch Model for Robust Spatial Intercell Interference Cancelation in Heterogeneous Networks

Performance of precoder-based spatial intercell interference cancelation in heterogeneous networks is often hampered due to lack of accurate channel state information. Performance can be augmented by modifying the design of the precoder to incorporate the channel estimate mismatch by using deterministic and probabilistic mismatch models. Previously proposed models either have been deemed too conservative (deterministic) or are prone to error due to inaccuracy in the probability distribution function and corresponding parameters (stochastic). A new deterministic mismatch model is proposed herein in an attempt to alleviate these problems. Different from all previously proposed deterministic models, the proposed model, called sparsity enhanced mismatch model (SEMM), exploits the inherent sparse characteristics of MIMO interference channels. The SEMM has two variants, i.e., SEMM (angular) and SEMM (eigenmode). The SEMM incorporates a basis expansion model to bring forth the inherent sparsity, which exists in MIMO interference channels. In the context of precoder design for heterogeneous network, it is analytically shown, and by simulation, the proposed mismatch models enable the aggressor-transmitter (A-Tx) to allocate more transmission power to the sparse elements of the interfering link so that performance in the communicating link is enhanced compared with conventional norm ball mismatch model.

Adaptive limited feedback links for cooperative multi-antenna multicell networks

The overall performance of cooperative networks is quite sensitive to channel state information (CSI) of serving and interfering base stations (BSs) and affected strongly by quality of limited feedback links. In this paper, we propose two adaptive limited feedback strategies for intercell interference cancelation in multi-antenna multicell networks. The first proposed strategy is developed to improve average multicell capacity assuming a fixed rate feedback link. This algorithm is based on adaptation of the number of bits to quantize CSI of serving and interfering BSs according to transmitter power and location of the user in its own cell. The second proposed strategy is designed in a way to increase average capacity of cell-edge users assuming an adaptive rate feedback link. This algorithm is based on the idea of allocating more bits to quantize CSI of users at cell-edge regions while allocating less bits for users near the serving BS. We illustrate performance of the proposed feedback links for downlink cooperative multi-antenna multicell networks in wireless channels.

Coordinated 3D Beamforming for Interference Management in Cellular Networks

We consider downlink transmission in a cellular network consisting of multi-antenna base stations (BSs), single-antenna mobile users, directional antennas each with a vertically adjustable beam, and control signaling delays in feedback and backhaul links. We propose a novel transmission technique in which intercell interference management is performed via coordinating the beamforming jointly in the horizontal and vertical planes of the wireless channel, denoted as coordinated 3D beamforming. In the horizontal plane, we focus on intercell interference cancelation (ICIC) and investigate its performance when the provided channel state information (CSI) is impaired due to delay/mobility. It is demonstrated that the superiority of ICIC over conventional intracell maximum ratio transmission is highly dependent on the CSI accuracy. In the vertical plane, we consider intercell interference control via coordinatively adapting the elevation angle of the BS antenna pattern, denoted as tilt, to the locations of the scheduled users. It is shown that with perfect CSI interference management should be performed in the horizontal plane using ICIC, while at high delay/mobility it should be done in the vertical plane via coordinated tilt adaptation. For intermediate values of delay/mobility, joint interference management in both planes is required.

A Simulation Framework for Evaluating Interference Mitigation Techniques in Heterogeneous Cellular Environments

Femtocells present an attractive solution for the improvement of a mobile network's services providing better data rates and coverage. Since their deployment results to a heterogeneous network where two layers must utilize the available spectrum, issues of interference arise. A method to address this challenge, is investigating the locations of the newly installed FBS, and enforcing a power controlled transmission of all FBSs that achieves optimal and fair overall performance. Another option that becomes available in inter-cell interference cancellation (ICIC) macrocell environments, is utilizing the available spectrum to complete or partly avoid co-channel operation. In this work, we provide a simulation framework that allows the creation of custom, high configurable, user defined topologies of femtocells with power control and frequency allocation capabilities. It allows the investigation of the margin of improvement in interference when these methods are applied and may work as a decision tool for planning and evaluating heterogeneous networks. To showcase the framework's capabilities, we evaluate and study the behaviour of custom deployed femtocells/macrocells networks and examine the cross-tier interference issues. Facilitated by the framework, we enforce and evaluate each interference mitigation technique for different femtocells' deployment densities. Finally, we compare the results of each method in terms of total throughput, spectral efficiency and cell-edge users' performance.

Inter-cell spectrum efficiency improvement technology

Improvement in inter-cell spectrum efficiency is a valuable research topic in mobile communication system, which affects cell edge user experience especially. According to current research results, there are three methods to deal with inter-cell interference to improve inter-cell spectrum efficiency, including inter-cell interference randomization, inter-cell interference cancellation and inter-cell interference coordination. This paper analyzes three important inter-cell spectrum efficiency improvement technologies, soft frequency reuse (SFR), uplink power control, and downlink coordinated multi-point transmission/reception (CoMP), and relative research progress.

Joint User Scheduling and Adaptive Intercell Interference Cancelation for MISO Downlink Cellular Systems

Recently, an adaptive intercell interference (ICI) mitigation technique has been proposed for downlink cellular systems as a means to increase throughput with low system complexity. However, in the prior work, the issue of intercell user scheduling has not been considered. In this paper, we study multiple-input-single-output (MISO) downlink cellular systems that jointly design adaptive ICI cancelation (ICIC) and intercell user scheduling assuming that partial channel state information (CSI) is shared among base stations (BSs). Since the optimal solution would require high complexity, we investigate a new low-complexity algorithm that selects the best users and their beamforming strategies in terms of maximizing the weighted sum rate (WSR). To this end, we first develop a simple threshold criterion for each user to decide the preferred beamforming strategy based on the derivation of the expected signal-to-interference-plus-noise ratio (SINR). Then, according to users' feedback about their decisions, a successive user and beamforming selection algorithm is performed at the BSs. From simulation results, we show that, combined with proportional fair scheduling, the proposed scheme provides excellent throughput performance with very low computational complexity and the amount of inter-BS CSI exchange. Furthermore, we discuss an extension of the proposed scheme to limited feedback systems and observe that our algorithm also provides similar advantages over conventional schemes with quantized feedback.

Spectral Efficiency Improvement of Fractional Frequency Reuse by Inter-Cell Interference Cancellation on Cooperative Base Station

Spectral Efficiency Improvement of Fractional Frequency Reuse by Inter-Cell Interference Cancellation on Cooperative Base Station

Semi-Blind HEBB-PPIC Multiuser Detection Algorithm

Inter-cell interference greatly impairs the capacity of CDMA system. 4G era is coming with much severer inter-cell inte-rference, and it's important to find a good solution to inter-cell Interference cancellation. In this paper, the semiblind Hebb-PPIC Multi-User Detection(MUD algorithm which applied in the CDMA uplink is proposed. This approach fully utilizes all known users’ information, performs Hebb-PPIC detector to suppress the int-erferers within the cell, and exploits the blind detector to suppress the inter-cell interference. Simulation results demonstrate that the proposed Hebb-PPIC semi-blind algorithm offers substantial perfo-rmance gains over the blind multi-user detection methods, and the Multiple Access Interference and Near-Far effect can be suppressed effectively in a CDMA uplink environment.

Improving network energy efficiency through cooperative idling in the multi-cell systems

Abstract Network energy efficiency (NEE) is considered as the metric to address the energy efficiency problem in the cooperative multi-cell systems in this article. At first, three typical schemes with different levels of cooperation, i.e., interference aware game theory, inter-cell interference cancellation, and multi-cell joint processing, are discussed. For both unconstrained and constrained case, efficient power control strategies are developed to maximize the NEE. During the optimization, both the optimization objects and strategies are distinct because of different levels of data and channel state information at the transmitter sharing. In order to further improve NEE, a novel cooperative idling (CI) scheme is proposed through cooperatively switching some BSs into micro-sleep and guaranteeing the data transmission with the other active BSs' cooperative transmission. Simulation results indicate that cooperation can improve both NEE and network capacity and demonstrate that CI can further improve the NEE significantly.

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).

Adaptive Spatial Intercell Interference Cancellation in Multicell Wireless Networks

Downlink spatial intercell interference cancellation (ICIC) is considered for mitigating other-cell interference using multiple transmit antennas. A principle question we explore is whether it is better to do ICIC or simply standard single-cell beamforming. We explore this question analytically and show that beamforming is preferred for all users when the edge SNR (signal-to-noise ratio) is low ( 10 dB), for example in an urban setting. At medium SNR, a proposed adaptive strategy, where multiple base stations jointly select transmission strategies based on the user location, outperforms both while requiring a lower feedback rate than the pure ICIC approach. The employed metric is sum rate, which is normally a dubious metric for cellular systems, but surprisingly we show that even with this reward function the adaptive strategy also improves fairness. When the channel information is provided by limited feedback, the impact of the induced quantization error is also investigated. The analysis provides insights on the feedback design, and it is shown that ICIC with well-designed feedback strategies still provides significant throughput gain.

Dynamic Inter-cell Interference Cancellation for Uplink in Multi-cell OFDMA Systems

Dynamic Inter-cell Interference Cancellation for Uplink in Multi-cell OFDMA Systems

Multi‐group linear turbo equalization with intercell interference cancellation for MC‐CDMA cellular systems

AbstractIn this paper, we investigate multi‐group linear turbo equalization using single antenna interference cancellation (SAIC) techniques to mitigate the intercell interference for multi‐carrier code division multiple access (MC‐CDMA) cellular systems. It is important for the mobile station to mitigate the intercell interference as the performance of the users close to cell edge is mainly degraded by the intercell interference. The complexity of the proposed iterative detector and receiver is low as the one‐tap minimum mean square error (MMSE) equalizer is employed for mitigating the intracell interference, while a simple group interference canceller is used for suppressing the intercell interference. Simulation results show that the proposed iterative detector and receiver can mitigate the intercell interference effectively through iterations for both uncoded and coded signals. Copyright © 2009 John Wiley & Sons, Ltd.

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.

Multi-Cell Cooperation with Fairness Constraint in the Downlink OFDMA Cellular Networks

SUMMARY In this letter, we study cell cooperation in the downlinkOFDMA cellular networks. The proposed cooperation scheme is based onfractional frequency reuse (FFR), where a cooperation group consists ofthree sector antennas from three adjacent cells and the subchannels of eachcooperation group are allocated coordinately to users. Simulation resultsdemonstrate the effectiveness of the proposed schemes in terms of through-put and fairness. key words: multi-cell cooperation, OFDMA, FFR, ICI coordination, fair-ness 1. Introduction As an advanced physical layer technology, OFDMA hasbeen proposed by 3GPP LTE (3rd Generation PartnershipProject Long Term Evolution) to be the multiple accesstech-nique for the downlink in B3G (Beyond 3rd Generation)systems [1]. In the OFDMA-based cellular system, the sub-channels used within a cell are orthogonal to each other suchthat the interference can be avoided. However, the users onthe border of the cell not only receive signals from the serv-ing base station (BS), but also suffer severe inter cell inter-ference (ICI) from the neighboring cells which use the sameset of subchannels. The so called ICI will degenerate thesystem performance and must be mitigated.In 3GPP LTE, three approaches have been proposed tomitigate the so-called ICI, i.e., ICI randomization, ICI coor-dination, and ICI cancelation. Among the three approaches,ICI coordination is comparatively easier to be realized andcan be used in various wide band traffics [2]. The basicidea behind ICI coordination is exploiting FFR techniqueto separate the interfering source as far as possible whileincreasing spectral efficiency as much as possible [3],[4].FFR relies on partitioning the total available frequency re-source into two sets and dividing a cell into two concentricregion, namely, interior region and exterior region. One setof the frequency is used by users in the interior region of allcells with a frequency reuse factor (FRF) of 1. While the

An Inter-Cell Interference Mitigation Method for OFDM-Based Cellular Systems Using Independent Component Analysis

Orthogonal frequency division multiplexing (OFDM) is a critical technology in 3G evolution systems, which can effectively avoid intra-cell interference, but may bring with serious inter-cell interference. Inter-cell interference cancellation is one of effective schemes taken in mitigating inter-cell interference, but for many existing schemes in inter-cell interference cancellation, various generalized spatial diversities are taken, which always bring with extra interference and blind spots, or even need to acquire extra information on source and channel. In this paper, a novel inter-cell interference mitigation method is proposed for 3G evolution systems. This method is based on independent component analysis in blind source separation, and the input signal to interference plus noise ratio (SINR) is set as objective function. By generalized eigenvalue decomposition and algorithm iterations, maximum signal noise ratio (SNR) can be obtained in output. On the other hand, this method can be worked with no precise knowledge of source signal and channel information. Performance evaluation shows that such method can mitigate inter-cell interference in a semi-blind state, and effectively improve output SNR with the condition that lower input SINR, higher input SNR and longer lengths of the processing frame.

On Intercell Interference and Its Cancellation in Cellular Multicarrier CDMA Systems

The handling of intercell interference at the cell border area is a strong demand in future communication systems to guarantee efficient use of the available bandwidth. Therefore, this paper focuses on the application of iterative intercell interference cancellation schemes in cellular multicarrier code division multiple access (MC-CDMA) systems at the receiver side for the downlink. First, the influence of the interfering base stations to the total intercell interference is investigated. Then, different concepts for intercell interference cancellation are described and investigated for scenarios with several interfering cells. The first approach is based on the use of the hard decision of the demodulator to reconstruct the received signals. This does not require the higher amount of complexity compared to the second approach which is based on the use of the more reliable soft values from the decoding process. Furthermore, the extrinsic information as a reliability measure of this soft iterative cancellation process is investigated in more detail based on the geographical position of the mobile terminal. Both approaches show significant performance gains in the severe cell border area. With the soft intercell interference cancellation scheme, it is possible to reach the single-user bound. Therefore, the intercell interference can be almost eliminated.

Inter-Cell Interference Cancellation Algorithm for Reverse Link TDD-CDMA Systems

This paper proposes a new inter-cell interference cancellation algorithm called subspace projection in order to eliminate the stronger inter-cell interference. This algorithm is designed for the reverse link of time division duplex-code division multiple access systems. The algorithm works by projecting desired users' signal vector onto the subspace orthogonal to the subspace that interfers the users' signal. Link-level simulation results show that the scheme eliminates the inter-cell interference efficiently, improves the receiver performance, and increases the system capacity.