Beatriz Soret

Multicell cooperation for LTE-advanced heterogeneous network scenarios

In this article we present two promising practical use cases for simple multicell cooperation for LTE-Advanced heterogeneous network scenarios with macro and small cells. For co-channel deployment cases, we recommend the use of enhanced interference coordination, or eICIC, to mitigate cross-tier interference and ensure sufficient offload of users from macro to small cells. It is shown how the eICIC benefit is maximized by using a distributed inter-base station control framework for dynamic adjustment of essential parameters. Second, for scenarios where macro and small cells are deployed at different carriers an efficient use of the fragmented spectrum can be achieved by using collaborative inter-site carrier aggregation. In addition to distributed coordination/collaboration between base station nodes, the importance of explicit terminal assistance is highlighted. Comprehensive system-level simulation results illustrate the performance benefits of the presented techniques.

Interference coordination for dense wireless networks

The promise of ubiquitous and super-fast connectivity for the upcoming years will be in large part fulfilled by the addition of base stations and spectral aggregation. The resulting very dense networks (DenseNets) will face a number of technical challenges. Among others, the interference emerges as an old acquaintance with new significance. As a matter of fact, the interference conditions and the role of aggressor and victim depend to a large extent on the density and the scenario. To illustrate this, downlink interference statistics for different 3GPP simulation scenarios and a more irregular and dense deployment in Tokyo are compared. Evolution to DenseNets offers new opportunities for further development of downlink interference cooperation techniques. Various mechanisms in LTE and LTE-Advanced are revisited. Some techniques try to anticipate the future in a proactive way, whereas others simply react to an identified interference problem. As an example, we propose two algorithms to apply time domain and frequency domain small cell interference coordination in a DenseNet.

eICIC Functionality and Performance for LTE HetNet Co-Channel Deployments

Different technical solutions are enabling the move from macro-only scenarios towards heterogeneous networks with a mixture of different base station types. In this paper we focus on multi-layer LTE-Advanced networks, and especially address aspects related to co-channel interference management. The network controlled time-domain enhanced inter-cell interference coordination (eICIC) concept is outlined by explaining the benefits and characteristics of this solution. Extensive system level performance results are presented with bursty and non-bursty traffic to demonstrate the eICIC concepts ability to dynamically adapt according to the traffic conditions.

Fundamental tradeoffs among reliability, latency and throughput in cellular networks

We address the fundamental tradeoffs among latency, reliability and throughput in a cellular network. The most important elements influencing the KPIs in a 4G network are identified, and the inter-relationships among them is discussed. We use the effective bandwidth and the effective capacity theory as analytical framework for calculating the maximum achievable rate for a given latency and reliability constraint. The analysis is conducted in a simplified LTE network, providing baseline - yet powerful - insight of the main tradeoffs. Guidelines to extend the theory to more complex systems are also presented, including a semi-analytical approach for cases with intractable channel and traffic models. We also discuss the use of system-level simulations to explore the limits of LTE networks. Based on our findings, we give some recommendations for the imminent 5G technology design phase, in which latency and reliability will be two of the principal KPIs.

CRS interference cancellation in heterogeneous networks for LTE-Advanced downlink

Enhanced Inter-Cell Interference Coordination (eICIC) for co-channel deployment of pico-cells throughout a macro-cell layout is a promising solution to increase system capacity and network coverage in Long Term Evolution (LTE)-Advanced systems. The use of both pico-cell Range Extension (RE) and time domain eICIC (TDM muting) in this scenario has been proved to provide high gains compared to the traditional homogeneous network. Nevertheless, performance results in literature assume ideal Common Reference Signals (CRS) interference cancellation in the pico-UEs during Almost Blank Subframes (ABS), i.e., receivers are capable of perfectly suppressing all CRS interference from all neighbour cells. In this paper we investigate the impact of non-ideal CRS Interference Cancellation (IC) in eICIC systems. We propose a simple RSRP-based CRS IC criterion not requiring any extra signaling. The performance is evaluated and compared to the ideal case in the downlink by means of extensive system level simulations that follow the 3GPP guidelines. Results confirm that TDM eICIC can still provide significant gains when realistic CRS IC is considered.

Macro transmission power reduction for HetNet co-channel deployments

Enhanced Inter-Cell Interference Coordination (eICIC) techniques are targeted to improve the system and cell-edge throughput of Heterogeneous Networks (HetNets) in LTE-Advanced systems. In order to protect pico UEs from the strong macro interference, the macro eNB can either stop data transmission or simply reduce the transmission power during certain subframes. In this paper, we investigate the impact of reducing the transmission power in LTE HetNets. We evaluate the tradeoff among macro transmission power, cell load and system and cell-edge throughput, with bursty and non-bursty traffic. Moreover, we address some of the technical and standardization challenges related to having a time-varying transmission power. Based on the results, we provide guidance on how to best configure the network to achieve the full potential of the eICIC concept in dynamically changing environments.

Sensitivity study of optimal eICIC configurations in different heterogeneous network scenarios

Heterogeneous Networks (HetNet) have been recognized as a key enabler for providing high data rates. However, co-channel deployed HetNet will experience inter-layer interference, and hence calls for use of enhanced Inter-Cell Interference Coordination (eICIC) to solve such interference problems. In order to achieve the full performance benefits of eICIC, its corresponding configuration parameters shall be carefully adjusted. In this paper we study how sensitive the HetNet performance is for different eICIC parameters in different HetNet scenarios, and provide guidelines on how to set them. Among others, it is concluded how the spatial UE distribution, the used propagation models, and pico eNB transmit power settings influence the performance and the optimal eICIC parameter choice.

Centralized and Distributed Solutions for Fast Muting Adaptation in LTE-Advanced HetNets

Enhanced intercell interference coordination (eICIC) is known to provide promising performance benefits for Long-Term Evolution Advanced heterogeneous networks (LTE-Advanced HetNets). The use of eICIC facilitates more flexible interlayer load balancing by means of small-cell range extension (RE) and almost blank subframes (ABSs). Although the eICIC configuration (RE and ABS) ideally should be instantaneously adapted to follow the fluctuations of the traffic and the channel conditions over time, previous studies have focused on slow intercell coordination. In this paper, we investigate fast-dynamic eICIC solutions for centralized and distributed radio resource management (RRM) architectures. The centralized RRM architecture assumes macrocells and remote radio heads (RRHs) interconnected via high-speed fronthaul connections, whereas the distributed architecture is based on traditional macrocell and picocell deployments with an X2 backhaul interface. Two different fast muting adaptation algorithms are derived, and it is shown how those can be applied to both the centralized and distributed architectures. Performance results with bursty traffic show that the fast-dynamic adaptation provides significant gains, both in fifth-percentile and 50th-percentile user throughputs, and improvements in user fairness. The best performance is naturally obtained for the centralized architecture, although the performance of the distributed architecture is comparable for the cases where enhanced X2 intercell information exchange is exploited.

Signal Quality Outage Analysis for Ultra-Reliable Communications in Cellular Networks

Ultra-reliable communications over wireless will open the possibility for a wide range of novel use cases and applications. In cellular networks, achieving reliable communication is challenging due to many factors, particularly the fading of the desired signal and the interference. In this regard, we investigate the potential of several techniques to combat these main threats. The analysis shows that traditional microscopic multiple-input multiple-output schemes with 2×2 or 4×4 antenna configurations are not enough to fulfil stringent reliability requirements. It is revealed how such antenna schemes must be complemented with macroscopic diversity as well as interference management techniques in order to ensure the necessary SINR outage performance. Based on the obtained performance results, it is discussed which of the feasible options fulfilling the ultra-reliable criteria are most promising in a practical setting, as well as pointers to supplementary techniques that should be included in future studies.

Automation for On-Road Vehicles: Use Cases and Requirements for Radio Design

The support of mission-critical communication (MCC) opens the possibility to implement a broad range of novel applications. V2X communication for traffic safety and automation is, among others, one of these innovative applications expected to bring big benefits to society: accidents are prevented, driving times are reduced, and carbon dioxide is saved. In this regard, we first present a system model and fundamental definitions of reliability, latency and availability. Relying on these definitions, a systematic review of requirements for the huge variety of V2X applications is provided, including insights into the expected evolution towards autonomous driving. The many challenges introduced by V2X use cases are emphasized and compared to todays wireless system capabilities. Finally, we give our vision on the design of future radio technologies for the support of this kind of communications.