HetNet Environment Research Articles

An Overview on Interference Management in 3GPP LTE-Advanced Heterogeneous Networks

The increasing demand for mobile data traffic brings new challenges on cellular networks in terms of network capacity and increased data throughput. In order to fulfill these demands, Heterogeneous Networks (HetNets) has been considered as a promising solution. On the other hand, Inter-Cell Interference Coordination (ICIC) is a big challenge toward HetNet deployments; in particular users in edge area of low power small cell are mostly vulnerable to stronger interference signals from high power macro cell. To resolve ICIC problem, 3GPP released some technologies based on TDM resource partitioning, FDM resource allocation along with power control, and still continue to find out the more suitable solutions. However, to date, a common platform of all possible solutions, particularly in TDM and FDM based, is not available to readers. In this context, this paper provides a holistic overview of ICIC strategies in this emerging wireless system. Towards this objective, the evolution of inter-cell interference management techniques is thoroughly investigated from TDM based enhanced inter-cell interference coordination (eICIC) techniques to more advanced Coordinated Multi-Point (CoMP) transmission/reception, while comparing and contrasting their common features and differences. Finally, Carrier Aggregation (CA) is explored in detail as an advanced and challenging mechanism in order to have an efficient resource allocation and inter-cell interference mitigation in LTE-Advanced HetNet environments.

QoS priority-based dynamic frequency band allocation algorithm for load balancing and interference avoidance in 3GPP LTE HetNet

Abstract A 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system uses the concept of two-tier heterogeneous networks (HetNets), where low-power and short-range femtocells are laid under macrocells to fulfill the quality of service (QoS) requirements of users and to boost overall network capacity. However, co-channel interference is one of the major issues that need to be resolved for the successful deployment of HetNets. To overcome this problem, fractional frequency reuse (FFR) schemes have been proposed that can efficiently utilize the available spectrum. Nevertheless, these schemes waste limited frequency resources owing to their static allocation and lack of following QoS requirements, network loading conditions, and service priority of users. In this paper, a QoS-based dynamic FFR (QoS-DFFR) scheme is proposed that efficiently allocates the non-occupied center-zone frequency bands, i.e., bonus bandwidth (BBW), to cell-edge users by considering their QoS requirements. Consequently, the proposed QoS-DFFR scheme can optimize cell-edge user throughput and sector throughput and reduce co-channel interference by dynamically allocating the BBW to the most demanding cell-edge users. The proposed QoS-DFFR scheme improves performance because of its ability to dynamically allocate the limited portion of the frequency bands based on the service priorities of users. The system-level simulation results show that the proposed QoS-DFFR scheme performs remarkably well in a HetNet environment. Compared with the usual FFR schemes, the proposed scheme almost doubles the cell-edge user's throughput and reduces the user's packet loss rate.

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.

A context-aware framework for the efficient integration of femtocells in IP and cellular infrastructures

In today’s heterogeneous networking (HetNet) environments, where end users are provided with universal connectivity opportunities, femtocell deployments can become key players in the enhancement of critical performance indicators such as capacity, coverage, QoS, etc. In order to confront the up-to-date LTE femtocell challenges, we propose a context-aware framework that provides a controlled environment from the femtocell point of view, which is required for applicable functionality. More specifically, we aim to (a) control the local environment where the femtocell is placed within, by efficiently managing the total incoming traffic load and by continuously adjusting the distribution of the backhaul capacity among the coexisting networks and (b) control the macro–femto interference caused by macrocell users transmitting close to the femtocell by investigating the “femtocell as a relay” concept. Finally, the performance of the proposed framework is evaluated via simulation results showing that the overall performance of a HetNet environment can be leveraged in terms of QoS requirements, energy saving and data rate enhancement.

Hierarchical Interference Alignment for Downlink Heterogeneous Networks

This paper focuses on interference issues arising in the downlink of a heterogeneous network (HetNet), where small cells are deployed within a macrocell. Interference scenario in a HetNet varies based on the type of small cell access modes, which can be classified as either closed subscriber group (CSG) or open subscriber group (OSG) modes. For these two types of modes, we propose hierarchical interference alignment (HIA) schemes, which successively determine beamforming matrices for small cell and macro base stations (BSs) by considering a HetNet environment in which the macro BS and small cell BSs have different numbers of transmit antennas. Unlike prior work on interference alignment (IA) for homogeneous networks, the proposed HIA schemes compute the beamforming matrices in closed-form and reduce the feedforward overhead through a hierarchical approach. By providing a tight outer bound of the degrees-of-freedom (DoF), we also investigate the optimality of the proposed HIA schemes with respect to the number of antennas without any time expansion. Furthermore, we propose a new optimization process to maximize the sum-rate performance of each cell while satisfying the IA conditions. The simulation results show that the proposed HIA schemes provide an additional DoF compared to the conventional interference coordination schemes using a time domain-based resource partitioning. Under multi-cell interference environments, the proposed schemes offer an approximately 100% improvement in throughput gain compared to the conventional coordinated beamforming schemes when the interference from coordinated BSs is significantly stronger than the remaining interference from uncoordinated BSs.