Interference mitigation in cognitive small cell networks (original) (raw)

A Cell Based Dynamic Spectrum Management Scheme with Interference Mitigation for Cognitive Networks

2009

Future wireless systems are expected to be characterized by the coexistence of different radio access technologies (RATs) resulting in complex heterogeneous wireless environments. In parallel with this, the tremendous demand for spectrum has inspired the requirement of dynamic spectrum management (DSM). This paper aims at designing a cell based dynamic spectrum management (CBDSM) scheme to enhance the spectrum utilization and maximize the profit of operators in wireless heterogeneous networks. The system architecture and the functional modules supporting the CBDSM scheme are designed. As a fundamental issue in spectrum management, the inter-system interference issue is solved in the proposed CBDSM scheme. Furthermore, game theory, which is a potential tool for studying the distributed autonomous resource optimization algorithms, is applied to design a spectrum trading algorithm enabling the heterogeneous wireless networks to dynamically trade spectrum and to share the profit. In the algorithm, we take into account the economic value of the spectrum of wireless systems in order to guarantee the rationality for the spectrum trading. The simulation results show that the proposed CBDSM scheme effectively improves the spectrum utilization and the profit of operators while it reduces the mutual interference between wireless networks to a tolerable level.

Cognitive Interference Management in Heterogeneous Femto-Macro Cell Networks

2011 IEEE International Conference on Communications (ICC), 2011

In this work, we propose a cognitive interference management scheme for heterogeneous cellular wireless networks (LTE-A and WiMAX) with macrocells and femtocells (that operate in a closed-access mode). The scheme presented allocates resources (in time and frequency) and transmission opportunities to the macro/femtocells in the network by considering their potential to cause interference at each others associated user equipments (UEs). We study the efficacy of the proposed scheme using a LTE-A system level simulator and compare with frequency reuse techniques and no interference management scenarios. We observe that our scheme significantly enhances average cell-edge UE throughput (5%-tile throughput) with slight degradation in overall sum throughput. Also we observe that the scheme decreases the probability of cell-edge users in the system experiencing degraded SINR.

Small Cells in Cellular Networks: Challenges of Future HetNets

Due to their low cost and easy deployment, small cells provide a viable and costeffective way of improving the cellular coverage and capacity both for homes and enterprises, both in metropolitan and rural areas. Stimulated by their attractive features and advantages, the ongoing development and deployment of small cells by manufacturers and mobile network operators have seen a surge in recent years. Together with macro-cells, they form, what are called Heterogeneous Networks or HetNets. However, the successful rollout and operation of small cells are still facing significan issues. In this paper the need for, challenges and solutions of small cell deployments are analyzed. This analysis is conducted with respect to self-organizing features, interference coordination, energy efficiency and spectrum efficiency. The analysis is complemented with numerical results based on system simulations in Macroonly and HetNet scenarios and also on real measurements performed on an mobile operator network. Results show the clear improvement that a HetNet brings in term of user throughput and also the amunt of spectrum waste that is present in nowadays' operator networks.

Interference mitigation in cognitive femtocell networks

2015

Femtocells have been introduced as a solution to poor indoor coverage in cellular communication which has hugely attracted network operators and stakeholders. However, femtocells are designed to co-exist alongside macrocells providing improved spatial frequency reuse and higher spectrum efficiency to name a few. Therefore, when deployed in the two-tier architecture with macrocells, it is necessary to mitigate the inherent co-tier and cross-tier interference. The integration of cognitive radio (CR) in femtocells introduces the ability of femtocells to dynamically adapt to varying network conditions through learning and reasoning. This research work focuses on the exploitation of cognitive radio in femtocells to mitigate the mutual interference caused in the two-tier architecture. The research work presents original contributions in mitigating interference in femtocells by introducing practical approaches which comprises a power control scheme where femtocells adaptively controls its transmit power levels to reduce the interference it causes in a network. This is especially useful since femtocells are user deployed as this seeks to mitigate interference based on their blind placement in an indoor environment. Hybrid interference mitigation schemes which combine power control and resource/scheduling are also implemented. In a joint threshold power based 7 Conclusion and future work 7.1 Conclusion xviii 7.1 Future work 131 References 135 Femtocells: Deployment Scenarios Access Methods Tramsmit power Spectrum Usage Dedicated Channel Closed Access or CSG Open Access Co-channel Adaptive Downlink Fixed Downlink Hybrid Access Cognitive Interference Mitigation Power Control Centralised Power Control Decentralised Power Control Spectrum Access Frequency based Time based Joint Frequency and Time based Centralised / Decentralised Schemes Individual vs Group Channel Sensing Antenna Schemes Single Element vs Multi Element Adaptive beam forming vs Adaptive Pattern Switching Joint Schemes

Interference Modeling of Cognitive Radio Networks

VTC Spring 2008 - IEEE Vehicular Technology Conference, 2008

Cognitive radio (secondary) networks have been proposed as means to improve the spectrum utilization. A secondary network can reuse the spectrum of a primary network under the condition that the primary services are not harmfully interrupted. In this paper, we study the distribution of the interference power at a primary receiver when the interfering secondary terminals are distributed in a Poisson field. We assume that a secondary terminal is able to cease its transmission if it is within a distance of R to the primary receiver. We derive a general formula for the characteristic function of the random interference generated by such a secondary network. With this general formula we investigate the impacts of R, shadowing, and small scale fading on the probability density function (PDF) of the interference power. We find that when there is no interference region (R = 0), the interference PDFs follow heavy-tailed α-stable distributions. In case that a proper interference region is defined by a positive value of R, the tails of the interference power PDFs can be significantly shortened. Moreover, the impacts of shadowing and small scale fading on the interference PDFs are studied and the small scale fading is found to be beneficial in terms of reducing the mean value and outage probability of the interference power.

Cognitive Network Interference- Modeling and Applications

2011 IEEE International Conference on Communications (ICC), 2011

Opportunistic spectrum access creates the opening of under-utilized portions of the licensed spectrum for reuse, provided that the transmissions of secondary radios do not cause harmful interference to primary users. Therefore, it is important to characterize the effect of cognitive network interference due to such secondary spectrum reuse. In this paper, we show how a new statistical model for aggregate interference of a cognitive network, which accounts for the sensing procedure, secondary spatial reuse protocol, and environment-dependent conditions such as path loss, shadowing, and channel fading can be used to assess the aggregate interference in specific environments. Specifically, we consider scenarios like power controlled primary network, secondary network with interference avoidance mechanism, and non-circular coverage region.

Backhaul-Aware Interference Management in the Uplink of Wireless Small Cell Networks

IEEE Transactions on Wireless Communications, 2000

The design of distributed mechanisms for interference management is one of the key challenges in emerging wireless small cell networks whose backhaul is capacity limited and heterogeneous (wired, wireless and a mix thereof). In this paper, a novel, backhaul-aware approach to interference management in wireless small cell networks is proposed. The proposed approach enables macrocell user equipments (MUEs) to optimize their uplink performance, by exploiting the presence of neighboring small cell base stations. The problem is formulated as a noncooperative game among the MUEs that seek to optimize their delay-rate tradeoff, given the conditions of both the radio access network and the-possibly heterogeneous-backhaul. To solve this game, a novel, distributed learning algorithm is proposed using which the MUEs autonomously choose their optimal uplink transmission strategies, given a limited amount of available information. The convergence of the proposed algorithm is shown and its properties are studied. Simulation results show that, under various types of backhauls, the proposed approach yields significant performance gains, in terms of both average throughput and delay for the MUEs, when compared to existing benchmark algorithms. Index Terms-heterogeneous networks; capacity-limited backhaul; wired and wireless backhaul; reinforcement learning; game theory. Sumudu Samarakoon received his B. Sc. degree in Electronic and Telecommunication Engineering from the University of Moratuwa , Sri Lanka in 2009 and the M. Eng. degree from the Asian Institute of Technology, Thailand in 2011. He is currently working Dr. Tech (Hons.) degree in Communications Engineering in University of Oulu, Finland. Sumudu is also a member of the research staff of the Centre for Wireless Communications (CWC), Oulu, Finlad. His main research interests are in heterogeneous networks, radio resource management and game theory.

Coexistence of Wi-Fi and heterogeneous small cell networks sharing unlicensed spectrum

IEEE Communications Magazine, 2015

As two major players in terrestrial wireless communications, Wi-Fi systems and cellular networks have different origins and have largely evolved separately. Motivated by the exponentially increasing wireless data demand, cellular networks are evolving towards a heterogeneous and small cell network architecture, wherein small cells are expected to provide very high capacity. However, due to the limited licensed spectrum for cellular networks, any effort to achieve capacity growth through network densification will face the challenge of severe inter-cell interference. In view of this, recent standardization developments have started to consider the opportunities for cellular networks to use the unlicensed spectrum bands, including the 2.4 GHz and 5 GHz bands that are currently used by Wi-Fi, Zigbee and some other communication systems. In this article, we look into the coexistence of Wi-Fi and 4G cellular networks sharing the unlicensed spectrum. We introduce a network architecture where small cells use the same unlicensed spectrum that Wi-Fi systems operate in without affecting the performance of Wi-Fi systems. We present an almost blank subframe (ABS) scheme without priority to mitigate the co-channel interference from small cells to Wi-Fi systems, and propose an interference avoidance scheme based on small cells estimating the density of nearby Wi-Fi access points to facilitate their coexistence while sharing the same unlicensed spectrum. Simulation results show that the proposed network architecture and interference avoidance schemes can significantly increase the capacity of 4G heterogeneous cellular networks while maintaining the service quality of Wi-Fi systems.