Ralf Irmer

Load & backhaul aware decoupled downlink/uplink access in 5G systems

Until the 4th Generation (4G) cellular 3GPP systems, a user equipments (UE) cell association has been based on the downlink received power from the strongest base station. Recent work has shown that - with an increasing degree of heterogeneity in emerging 5G systems - such an approach is dramatically suboptimal, advocating for an independent association of the downlink and uplink where the downlink is served by the macro cell and the uplink by the nearest small cell. In this paper, we advance prior art by explicitly considering the cell-load as well as the available backhaul capacity during the association process. We introduce a novel association algorithm and prove its superiority w.r.t. prior art by means of simulations that are based on Vodafones small cell trial network and employing a high resolution pathloss prediction and realistic user distributions. We also study the effect that different power control settings have on the performance of our algorithm.

Coordinated multipoint: Concepts, performance, and field trial results

Coordinated multipoint or cooperative MIMO is one of the promising concepts to improve cell edge user data rate and spectral efficiency beyond what is possible with MIMOOFDM in the first versions of LTE or WiMAX. Interference can be exploited or mitigated by cooperation between sectors or different sites. Significant gains can be shown for both the uplink and downlink. A range of technical challenges were identified and partially addressed, such as backhaul traffic, synchronization and feedback design. This article also shows the principal feasibility of COMP in two field testbeds with multiple sites and different backhaul solutions between the sites. These activities have been carried out by a powerful consortium consisting of universities, chip manufacturers, equipment vendors, and network operators.

5G wireless communication systems: prospects and challenges [Guest Editorial]

In the last year or so, significant momentum has started to build around the idea of a fifth generation (5G) for wireless communications technology. New research projects have started internationally, and research centers devoted to 5G technology have begun to open. At the ICC 2013 conference in Budapest, there were a number of keynote talks and special invited sessions addressing some of the key concepts around 5G technology. This Special Issue was created by IEEE Communications Magazine to help readers understand the current perspectives on 5G technology from both industry and academic standpoints.

Multisite field trial for LTE and advanced concepts

The 3GPP LTE standard is stable now in its first release (Release 8), and the question is how good its performance is in real-world scenarios. LTE is also a good base for further innovations, but it must be proven that they offer performance advantages for the price of their complexity. This article evaluates the performance of LTE Release 8 as a baseline and advanced concepts currently in discussion such as cooperative MIMO based on system-level simulations, and measurements in the laboratory and a multisite field testbed within the EASY-C project.

Downlink and Uplink Decoupling: A disruptive architectural design for 5G networks

Cell association in cellular networks has traditionally been based on the downlink received signal power only, despite the fact that uplink and downlink transmission powers and interference levels differed significantly. This approach was adequate in homogeneous networks with macro base stations all having similar transmission power levels. However, with the growth of heterogeneous networks where there is a big disparity in the transmit power of the different base station types, this approach is highly inefficient. In this paper, we study the notion of Downlink and Uplink Decoupling (DUDe) where the downlink cell association is based on the downlink received power while the uplink is based on the pathloss. We present the motivation and assess the gains of this 5G design approach with simulations that are based on Vodafones LTE field trial network in a dense urban area, employing a high resolution ray-tracing pathloss prediction and realistic traffic maps based on live network measurements.

On coverage and capacity of relaying in LTE-advanced in example deployments

Relaying as a means of in-band backhaul has the potential to extend the coverage of Beyond 3G networks, enabling the expected high data rates of these networks to be delivered without increasing the density of traditional macro base stations. Assessing the performance of relaying is not simple, since traditional metrics fail and the performance depends strongly on the actual deployment. The current literature considers usually very artificial deployment environments and propagation models. This paper shows the coverage and achievable peak data rates for an urban area in central London using three-dimensional building data and a ray-tracing simulator. The number of relays per sector is determined for different scenarios, and compared to a Macro Deployment.

Reduced and differential parallel interference cancellation for CDMA systems

Since code division multiple access systems in multipath environments suffer from multiple access interference (MAI), multiuser detection schemes should be used in the receivers. Parallel interference cancellation (PIC) is a promising method to combat MAI due to its relatively low computational complexity and good performance. It is shown that the complexity of PIC is still high for realistic scenarios in terms of the symbol rate, the number of users, spreading gain, and multipath components. However, two novel methods are introduced to reduce significantly the complexity without sacrificing performance. The first approach, called reduced PIC, takes advantage of the composition of the interference to concentrate interference cancellation only on significant terms. The second approach, called differential PIC, exploits the multistage character of PIC to avoid unnecessary double calculations of certain terms in consecutive stages. It is shown that a combination of both approaches leads to a performance very close to the single-user bound whereas the complexity can be kept on the order of the conventional RAKE receiver.

YoMoApp: A tool for analyzing QoE of YouTube HTTP adaptive streaming in mobile networks

The performance of YouTube in mobile networks is crucial to network operators, who try to find a trade-off between cost-efficient handling of the huge traffic amounts and high perceived end-user Quality of Experience (QoE). This paper introduces YoMoApp (YouTube Performance Monitoring Application), an Android application, which passively monitors key performance indicators (KPIs) of YouTube adaptive video streaming on end-user smartphones. The monitored KPIs (i.e., player state/events, buffer, and video quality level) can be used to analyze the QoE of mobile YouTube video sessions. YoMoApp is a valuable tool to assess the performance of mobile networks with respect to YouTube traffic, as well as to develop optimizations and QoE models for mobile HTTP adaptive streaming. We test YoMoApp through real subjective QoE tests showing that the tool is accurate to capture the experience of end-users watching YouTube on smartphones.

Deployment of LTE In-Band Relay and Micro Base Stations in a Realistic Metropolitan Scenario

Complementing macro-only cellular networks with low-powered base stations is a promising deployment solution to improve both network coverage and capacity, and cope with exploding data traffic in the coming years. In Beyond 3G Networks, such as LTE-Advanced, Relay Nodes and micro base stations can transmit on the same spectrum as the overlaying macro layer, and guarantee higher spatial reuse through cell splitting. Differently from previous research studies, this paper specifically aims at evaluating and comparing the potential of LTE relay and micro deployment in a realistic metropolitan scenario. A heuristic deployment algorithm which combines network coverage and realistic spatial user density information is also proposed. The results show that for the downlink, in-band relays can be deployed to improve network coverage, but not substantially the network capacity due to the limitation of the wireless backhaul link. In-band micro deployment, on the other hand, is the best solution to boost downlink network capacity (up to 5 times), while also providing full network coverage.

Global Communications Newsletter - Paving the way for gigabit networking

Wired LANs soared to the gigabit level some years ago, and terabit networks are in place for wide area networking. However, in terms of data rate, wireless short-range networks tend to lag one generation behind wired LANs. The recent second generation of wireless short-range networks offers transmission rates of up to 54 Mb/s. The third wireless LAN generation is under development and will materialize in the IEEE 802.11n standard in about two years. IEEE 802.11n WLANs will offer a few hundred megabits per second, but the performance gap from wired networks remains. The recently started project Wireless Gigabit with Advanced Multimedia (WIGWAM) aims to close this gap with a heterogeneous 1 Gb/s fourth-generation system based on high-data-rate orthogonal OFDM transmission, MIMO, and efficient MAC protocol techniques.