Almost Blank Subframe 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.

Interference Management with Cell Selection Using Cell Range Expansion and ABS in the Heterogeneous Network Based on LTE-Advanced

Long term evolution-advanced has developed the heterogeneous network (HetNet) that consists of a mix of macrocells and low-power nodes, such as picocells, to improve the system performance. Also, to encourage data offloading in HetNet, cell range expansion has been introduced. In this paper, we propose a cell selection scheme based on signal to interference plus noise ratio for optimal offloading effect. Also, we manage interference for the user located cell range expanded region using almost blank subframe (ABS) with flexible ABS ratio, to improve the spectrum efficiency in the time domain. Simulation results show that the proposed scheme can improve the spectrum efficiency of the macrocell and picocell user. Eventually, the proposed scheme can improve overall user performance.

Exploiting an Optimal User Association Strategy for Interference Management in HetNets

Heterogeneous Cellular Network consists of low power Pico Base Stations (PBS) overlaid in high power Macro Base Station's (MBS) coverage area. Edge User Equipments (UE) of PBS are victims of interference from MBS. Almost Blank Subframes (ABS) can provide interference free communication for these UEs. However, existing techniques perform UE-BS association before ABS determination, which is suboptimal with respect to UE-BS association.We formulate the joint optimization of UE-BS association and ABS computation as a combinatorial optimization problem, which is NP-Hard. We suggest the use of Hungarian matching algorithm and iterative exploration of candidate ABS densities to discover the ABS that can minimize system blocking.

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.

Picocell based telemedicine health service for human UX/UI

Telemedicine health created from the combination of IT and BT technologies has received increased attention for improved quality of life in medically vulnerable regions. As the health care paradigm shifts to preventive management in diagnosis and treatment, the importance of prevention of chronic diseases such as obesity is growing. In this paper, we proposed a picocell-based telemedicine health service for the human UX/UI based on a BT-IT fusion technology considering user convenience. The proposed medical service is a BT-IT fusion technology based on the telemedicine health service that can overcome the spatial limitations of hospital-oriented medical services in order to improve user convenience while naturally combining life and medical service spaces. Human UX/UI technology, which is based on sensor network and biomedical technology, requires next generation wireless communication between devices that connects the inside of the human body with the outside. A heterogeneous network is composed within a single domain, as the frequency bandwidth used by the medical device in the ISM bandwidth is different. If a wireless device and low output ISM device spatially access a heterogeneous network, then an interference problem will occur between the small cells. Additionally, there can be interference as the traffic is off-loaded from the base station at the grouped region of a hotspot. A fatal problem may occur due to an information error of the patient due to interference. To solve the interference problem generated by the telemedicine health platform, the performance of the picocell-based telemedicine health service can be improved by applying scheduling using ABS(Almost Blank Subframe) in the time domain. Therefore, the human UX/UI and the provided guidelines can quickly provide patient information, thereby increasing safety of patients.

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.

이종망 환경에서의 간섭완화를 위한 전력제어와 ABSF의 혼합운용 기법

We propose joint employment of power control and almost blank subframes (ABSF) for femtocells to mitigate the interference of femto-cells to a macrocell in heterogeneous networks. We obtained improved performance in terms of both femtocells capacity and reduced interference by computer simulations while we have marginally decreased overall network capacity compared to possibly maximum capacity.

Joint User Association and Interference Coordination in Heterogeneous Cellular Networks

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

LTE-Advanced 기반 이종 네트워크에서 셀 영역 확장에 대한 셀 선택과 ABS를 통한 간섭 관리 기법

LTE(Long Term Evolution)-Advanced에서는 저전력 피코셀(picocell)과 같은 소형셀을 중첩하여 배치해 시스템 성능을 향상시키기 위한 HetNet(Heterogeneous Network)에 대한 연구가 활발히 진행되고 있다. 또한 HetNet에서 데이터 오프로딩 효과를 증대시키기 위해 셀 영역 확장(CRE: Cell Range Expansion) 기술이 소개되었다. 본 논문에서는 최적의 오프로딩 효과를 위해 SINR(Signal to Interference plus Noise Ratio) 기반 셀 선택 기법을 제안한다. 셀 확장 영역에 존재하는 사용자의 간섭 관리를 위해 ABS를 사용하며, 스펙스럼 효율을 증가시키기 위하여 동적인 ABS 비율을 사용한다. 모의실험 결과, 제안한 기법에서 피코셀뿐만 아니라 매크로셀 사용자의 스펙트럼 효율이 향상되어 전체적인 사용자의 성능이 향상 된 것을 볼 수 있다.

On Number of Almost Blank Subframes in Heterogeneous Cellular Networks

In heterogeneous cellular scenarios with macrocells, femtocells or picocells users may suffer from significant co-channel cross-tier interference. To manage this interference 3GPP introduced almost blank subframe (ABSF), a subframe in which the interferer tier is not allowed to transmit data. Vulnerable users thus get a chance to be scheduled in ABSFs with reduced cross-tier interference. We analyze downlink scenarios using stochastic geometry and formulate a condition for the required number of ABSFs based on base station placement statistics and user throughput requirement. The result is a semi-analytical formula that serves as a good initial estimate and offers an easy way to analyze impact of network parameters. We show that while in macro/femto scenario the residue ABSF interference can be well managed, in macro/pico scenario it affects the number of required ABSFs strongly. The effect of ABSFs is subsequently demonstrated via user throughput simulations. Especially in the macro/pico scenario, we find that using ABSFs is advantageous for the system since victim users no longer suffer from poor performance for the price of relatively small drop in higher throughput percentiles.

Statistical Analysis of Self-Organizing Networks With Biased Cell Association and Interference Avoidance

In this paper, we assess the viability of heterogeneous networks composed of legacy macrocells, which are underlaid with self-organizing picocells. Aiming to improve coverage, cell-edge throughput, and overall system capacity, self-organizing solutions, such as range expansion bias, an almost blank subframe (ABS), and distributed antenna systems, are considered. Herein, stochastic geometry is used to model network deployments, whereas higher order statistics through the cumulants concept is utilized to characterize the probability distribution of received power and aggregate interference at the user of interest. A comprehensive analytical framework is introduced to evaluate the performance of such self-organizing networks in terms of outage probability and average channel capacity with respect to the tagged receiver. To conduct our studies, we consider a shadowed fading channel model incorporating lognormal shadowing and Nakagami-m fading. Results show that the analytical framework matches well with numerical results obtained from Monte Carlo simulations. We also observed that by simply using ABSs, the aggregate interference at the tagged receiver is reduced by about 8 dB. Although more elaborated, interference control techniques such as downlink bitmap and distributed antennas systems become needed when the density of picocells in the underlaid tier gets high.

이종 네트워크를 위한 Almost Blank Subframes의 성능 분석

이종 네트워크 환경에서 이종셀 간 간섭 제어를 위해 Almost Blank Subframes (ABS)이 제안 되었다. ABS에서는 서브프레임에 대한 자원 할당을 하지 않음으로써 동일 채널 간섭을 줄일 수 있다. 기존 연구에서는 ABS 기술의 성능 평가를 위한 수학적 모델링이 제안되지 않았다. 본 논문에서는 ABS 기술에 대한 수학적 모델을 제시하였다. 분석을 위한 가정에서 OFDMA 기반의 다중 반송파 (multi carrier) 시스템을 가정하였고, large-scale 페이딩을 가정하였다. 성능 평가로써 effective SINR에 대한 누적분포함수를 나타낸다. 시뮬레이션과 분석에 대한 결과 비교를 통해 수학적 모델에 대한 정확도를 보인다. In heterogeneous networks, the almost blank subframes (ABS) for inter-cell interference coordination (ICIC), which can be protected from the CCI due to unutilized subframes (i.e., ABS) is proposed. However, the analytical model for ABS-based systems has not been fully studied yet. In this paper, we derive a new analytical model to evaluate the performance of ABS-based systems. In an analytic model, we assume that each carrier in multicarrier systems, such as in OFDMA, is subject to large-scale fading, which is independent of other carriers. As a performance measure, we present the cumulative distribution function (CDF) for the effective SINR. We show the accuracy of the analytical model via simulation results.

이기종 네트워크에서의 간섭 제어 분석

In this paper, we introduce the technologies to handle the interference in the heterogeneous network and evaluate the performance of enhanced Inter-Cell Interference Coordination (enhanced ICIC, eICIC) techniques that are being introduced in 3GPP Release 10. In the time-domain eICIC scheme, time-domain resources are scheduled to avoid the interference by using Almost Blank Subframe (ABS) and Cell Range Expansion (CRE). To mitigate the cross-tier interference between macro and femtocell, it is important to efficiently combine the ABS and CRE in heterogeneous network. Since it is hard to evaluate the total throughput of heterogeneous network numerically, we evaluate the total throughput by using system level simulation (SLS). As a result of evaluation, the throughputs of many different cases of combination of ABS and CRE are compared.

Analysis of Cell Range Expansion with TDM ICIC in Heterogeneous Cellular Networks

This work investigates the cell range expansion (CRE) possible with time-domain multiplexing inter-cell interference coordination (TDM ICIC) in heterogeneous cellular networks (HCN). CRE is proposed to enable a user to connect to a picocell even when it is not the cell with the strongest received power. However, the users in the expanded region suffer severe interference from the macrocells. To alleviate the cross-tier interference, TDM ICIC is proposed to improve the SIR of pico users. In contrast to previous studies on CRE with TDM ICIC, which rely mostly on simulations, we give theoretical analysis results for different types of users in HCN with CRE and TDM ICIC under the Poisson Point Process (PPP) model, especially for the users in the expanded region of picocells. We analyze the outage probability and average ergodic rate based on the connect probability and statistical distance we obtain in advance. Furthermore, we analyze the optimal ratio of almost blank subframes (ABS) and bias factor of picocells in terms of the network fairness, which is useful in the parameter design of a two-tier HCN.

Mobility management challenges in 3GPP heterogeneous networks

In this article we provide a comprehensive review of the handover process in heterogeneous networks (HetNets), and identify technical challenges in mobility management. In this line, we evaluate the mobility performance of HetNets with the 3rd Generation Partnership Project (3GPP) Release-10 range expansion and enhanced inter-cell interference coordination (eICIC) features such as almost blank subframes (ABSFs). Simulation assumptions and parameters of a related study item in 3GPP are used to investigate the impact of various handover parameters on mobility performance. In addition, we propose a mobility-based inter-cell interference coordination (MB-ICIC) scheme, in which picocells configure coordinated resources so that macrocells can schedule their high-mobility UEs in these resources without co-channel interference from picocells. MB-ICIC also benefits low-mobility UEs, since handover parameters can now be more flexibly optimized. Simulations using the 3GPP simulation assumptions are performed to evaluate the performance of MB-ICIC under several scenarios.

Investigation on Interference Coordination Employing Almost Blank Subframes in Heterogeneous Networks for LTE-Advanced Downlink

This paper investigates the application of inter-cell interference coordination (ICIC) in heterogeneous networks for the LTE-Advanced downlink where picocells are overlaid onto macrocells. In LTE-Advanced, in order to perform ICIC, almost blank subframes (ABSs) are employed, where only the cell-specific reference signal (CRS) is transmitted to protect the subframes in the picocells from severe interference from the macrocells. Furthermore, multicast/broadcast over single-frequency network (MBSFN) subframes are employed to reduce the interference of the CRS on the data channel, although the control channel still suffers from interference from the CRS. When the cell range expansion (CRE), which offload the UEs from macrocells to picocells, is used to improve the system performance, the influence from the CRS increases. In order to assess the influence, the required CRE bias to improve the data channel is investigated based on a system-level simulation under various conditions such as the number of picocells, the protected subframe ratio, and the user distribution. The simulation results show that the cell-edge user throughput is improved with the CRE bias of more than 8dB, employing ABSs. Furthermore, simulation results show that one dominant source of interference is observed for the sets of user equipment (UEs) connected to the picocells via CRE with such a bias value. Based on observation, the influence that the CRS has on the control channel, i.e., physical control format indicator channel (PCFICH), and physical downlink control channel (PDCCH) is investigated based on a link-level simulation combined with a system-level simulation. The simulation results show that protecting the PCFICH is very important compared to protecting the PDCCH, since the block error rate (BLER) performance of the PCFICH becomes worse than the required BLER of 10-3 to support various conditions, although the BLER performance of the PDCCH can exceed the required BLER of 10-2 by spanning the PDCCH over three OFDM symbols.