Guillermo Pocovi

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.

Dynamic Enhanced Intercell Interference Coordination for Realistic Networks

Enhanced intercell interference coordination (eICIC) is a key ingredient in boosting the performance of cochannel heterogeneous networks. eICIC encompasses two main techniques: almost blank subframes (ABS), during which the macrocell remains silent to reduce the interference; and biased user association to offload more users to the picocells. However, its application to realistic irregular deployments raises a number of research questions. In this paper, we investigate the operation of eICIC in a realistic deployment based on 3-D data from a dense urban European capital area. Rather than the classical semistatic and network-wise configuration, the importance of having highly dynamic and distributed mechanisms that are able to adapt to local environment conditions is revealed. We propose two promising cell association algorithms: one aiming at pure load balancing and an opportunistic approach exploiting the varying cell conditions. Moreover, an autonomous fast distributed muting algorithm is presented, which is simple, robust, and well suited for irregular network deployments. Performance results for realistic network deployments show that the traditional semistatic eICIC configuration leads to modest gains, whereas the set of proposed fast dynamic eICIC algorithms results in capacity gains on the order of 35%-120%, depending on the local environment characteristics. These attractive gains, together with the simplicity of the proposed solutions, underline the practical relevance of such schemes.

MAC layer enhancements for ultra-reliable low-latency communications in cellular networks

Ultra-reliable low-latency communications (URLLC) entail the transmission of sporadic and small packets, with low latency and very high reliability. Among many potential areas of optimization for URLLC, the problems of large delays during HARQ retransmissions, and inaccurate link adaptation as a consequence of the rapidly-varying interference conditions are studied. The former is addressed by reducing the TTI length and HARQ round-trip time, as compared to what is used in LTE; whereas including low-pass filtered interference information in the CQI report is also proved to have great potential. Extensive system-level simulations of the downlink performance show that the URLLC requirements, i.e. latencies below 1 ms and 99.999% reliability, are achievable at low load scenarios, whereas some performance degradation (1 – 3 ms latency) is experienced at higher loads due to the increased queuing delay and inter-cell interference.

Analysis of Heterogeneous Networks with Dual Connectivity in a Realistic Urban Deployment

Dual Connectivity (DC) has been studied and proved to be an effective solution to deal with the fragmented resources in deployment scenarios where the macro and small cells use different frequency carriers. The performance of DC has mainly been analyzed using generic network models such as those proposed by the 3GPP. However, the benefits of DC in real networks have not been proved. In this paper, we investigate the performance of DC in a realistic deployment from a big European city. Additionally, a novel opportunistic cell selection technique is also proposed. Results show that DC does improve the performance in this realistic layout. Due to the uneven load distribution observed in realistic deployments, DC is able to provide fast load balancing gains also at relatively high load - and not only at low load as typically observed in 3GPP scenarios. For the same reason, the proposed cell selection technique that aims at performing intra-layer load balancing shows promising benefits in this irregular deployment.

On the Impact of Multi-User Traffic Dynamics on Low Latency Communications

In this paper we study the downlink latency performance in a multi-user cellular network. We use a flexible 5G radio frame structure, where the TTI size is configurable on a peruser basis according to their specific service requirements. Results show that at low system loads using a short TTI (e.g. 0.25 ms) is an attractive solution to achieve low latency communications (LLC). The main benefits come from the low transmission delay required to transmit the payloads. However, as the load increases, longer TTI configurations with lower relative control overhead (and therefore higher spectral efficiency) provide better performance as these better cope with the non-negligible queuing delay. The presented results allow to conclude that support for scheduling with different TTI sizes is important for LLC and should be included in the future 5G.

Increasing Reliability by Means of Root Cause Aware HARQ and Interference Coordination

The arrival of mission critical applications in the context of vehicular, medical and industrial wireless communications calls for reliability constraints never seen before in cellular systems. Enhanced Inter-Cell Interference Coordination (eICIC) has been widely investigated in the context of LTE-A Heterogeneous Networks, but always with load balancing and resource partitioning purposes. Given the broad range of new use cases targeting ultra high reliability, we propose the use of on-demand eICIC for reducing the BLER of the retransmissions of critical users while minimizing the impact to the rest of the network. Combined with a ROot Cause Aware HARQ (ROCA-HARQ), which provides additional information when a transmission fails, the joint mechanism is relevant for any LTE/LTE-A deployment and can be easily implemented in a real network. System-level simulations show attractive BLER reductions up to 80% with little impact in throughput performance (loss in user throughput below 6%).

Ultra-reliable communications in failure-prone realistic networks

We investigate the potential of different diversity and interference management techniques to achieve the required downlink SINR outage probability for ultra-reliable communications. The evaluation is performed in a realistic network deployment based on site-specific data from a European capital. Micro and macroscopic diversity techniques are proved to be important enablers of ultra-reliable communications. Particularly, it is shown how a 4×4 MIMO scheme with three orders of macroscopic diversity can achieve the required SINR outage performance. Smaller gains are obtained from interference cancellation, since this technique does not increase the diversity order of the desired signal. In addition, failures or malfunction of the cellular infrastructure are analysed. Among different types of failures evaluated, results show that failures spanning over large geographical areas can have a significant negative performance impact when attempting to support high reliability use cases.

Study of Dynamic eICIC in a Realistic Urban Deployment

In this paper, we investigate the operation of eICIC in a realistic deployment based on site specific data from a dense urban European capital area. Rather than the classical semi-static and common network-wide configuration, the importance of having highly dynamic and distributed mechanisms that are able to adapt to local environment conditions is revealed. We propose a promising opportunistic cell association algorithm and a generalized method for fast muting adaptation. The performance results show that the traditional semi-static eICIC configuration leads to modest gains in realistic deployments, whereas the set of proposed fast dynamic eICIC algorithms leads to capacity gains on the order of 35-120% depending on the local environment characteristics. In the analysis of the performance results for the site specific use case, it is furthermore highlighted how those deviate from typical findings from 3GPP standardized HetNet scenarios.

Achieving Ultra-Reliable Low-Latency Communications: Challenges and Envisioned System Enhancements

URLLC have the potential to enable a new range of applications and services: from wireless control and automation in industrial environments to self-driving vehicles. 5G wireless systems are faced by different challenges for supporting URLLC. Some of the challenges, particularly in the downlink direction, are related to the reliability requirements for both data and control channels, the need for accurate and flexible link adaptation, reducing the processing time of data retransmissions, and the multiplexing of URLLC with other services. This article considers these challenges and proposes state-of-the-art solutions covering different aspects of the radio interface. In addition, system-level simulation results are presented, showing how the proposed techniques can work in harmony in order to fulfill the ambitious latency and reliability requirements of upcoming URLLC applications.