Fabian Diehm

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.

Analysis of and compensation for non-ideal RoF links in DAS [Coordinated and Distributed MIMO]

Distributed antenna systems have been found to be an elegant solution for the problems arising in high-data-rate wireless communication, particularly in large service areas. This article considers radio over fiber links as an essential part of the DAS, connecting the central unit with the remote antenna units. In particular, we analyze and discuss delays and nonlinearities stemming from the RoF links. In addition, we study the compensation for these impairments. Our studies indicate that the RoF links are a viable and cost-effective solution for implementing the DAS, although some of the RoF link non-idealities require compensation.

The FUTON Prototype: Proof of Concept for Coordinated Multi-Point in Conjunction with a Novel Integrated Wireless/Optical Architecture

The growing relevance of wireless communications has been driving the research and development to enable cost-efficient support of very high data rates to be delivered to a large number of users. The high bandwidth targets for future networks are reflected in the ITUs call for IMT-Advanced. As interference poses the main limitation in todays networks, cooperative signal processing (often referred to as coordinated multi-point, CoMP) is seen as a key enabler to achieve these targets. However, cooperation among base stations in traditional cellular infrastructures is problematic because interconnections (referred to as backhaul) are often very limited in capacity and investigations on more flexible and cost-efficient future architectures are being undertaken. A promising concept was proposed in the European research project FUTON. It is based on the use of radio-over-fiber (RoF) technology to create a distributed antenna system (DAS) that is capable of supporting the high requirements of future wireless networks. Currently, a prototype FUTON system is being built as a proof of concept. In this contribution, we describe the FUTON architecture and give insights into the demonstration that is being prepared. Results from trials with the planned setup will follow.

The FUTON prototype: Broadband communication through coordinated multi-point using a novel integrated optical/wireless architecture

The growing relevance of wireless communications has been driving research and development to enable cost-efficient support of very high data rates to be delivered to a large number of users. The high bandwidth targets for future networks are well reflected in the ITUs call for IMT-Advanced. As interference poses the main limitation in todays networks, cooperative signal processing (often referred to as coordinated multi-point, CoMP) is seen as a key enabler to achieve these targets. However, cooperation among base stations in traditional cellular infrastructures is problematic because interconnections (referred to as backhaul) are often very limited in capacity and investigations on more flexible and cost-efficient future architectures are in progress. A promising concept was proposed in the European research project FUTON. It is based on the use of radio-over-fiber (RoF) technology to create a distributed antenna system (DAS) that is capable of supporting the high requirements of future wireless networks. In the scope of the project, a prototype system was built as a proof of concept. In this contribution, we present measurement results from the prototype system that demonstrate the potential of the FUTON architecture.

On the impact of signaling delays on the performance of centralized scheduling for joint detection cooperative cellular systems

Cooperative detection involving neighboring base stations is a promising means to increase spectral efficiency in the uplink of cellular systems. To fully utilize the new degrees of freedom that come with base station cooperation, it is essential that a joint scheduler is aware of the interference conditions in all participating cells in order to perform efficient resource and rate allocation. However, joint scheduling can introduce significant delays because it requires the exchange of channel estimates and scheduling grants over a backhaul infrastructure. Due to these delays, channel information that is used for scheduling decisions is potentially outdated. In this contribution, we explore the impact of signaling delays on the performance of joint scheduling for a small cooperative cellular system. We introduce and compare different scheduling approaches inlcuding scheduling metrics that rely solely on statistical channel information and show benefits for high user mobility.

A Low-Complexity Algorithm for Uplink Scheduling in Cooperative Cellular Networks with a Capacity-Constrained Backhaul Infrastructure

Today, it is well understood that interference poses the main capacity limitation and thus challenge for future cellular networks. A promising concept that addresses interference is multi-cell cooperative signal processing, often referred to as Network MIMO. While in recent publications, it is often assumed that the required exchange of information among the base stations can be done with unlimited capacity, current network infrastructures do not necessarily support very high data rates and backhaul has been identified as a major cost driver. For the case of unlimited backhaul availability, it has been shown that large gains can be achieved through intelligent resource assignment (scheduling). In this paper, we introduce a low-complexity algorithm for uplink scheduling in cooperative cellular networks under the assumption of a capacity constrained backhaul with the target of maximizing the tradeoff between backhaul and sum rate.

Measurement and Prediction of Turbo-SIC Receiver Performance for LTE

In this contribution, we assess a performance prediction method for turbo successive interference cancellation (turbo-SIC) receivers with the help of lab measurements from a quasi-compliant LTE platform. The presented results show that the calibrated prediction method is able to predict the system performance satisfactorily for the considered modulation and coding scheme.

Cooperative interference prediction for enhanced uplink link adaptation under backhaul delays

Inter-cell Interference (ICI) in the uplink of modern cellular communication systems with high frequency reuse is hard to predict, as fast scheduling and link adaptation lead to a high interference fluctuation. This fluctuation poses a big challenge for link adaptation algorithms that need an accurate SINR estimate to assign suitable modulation and coding schemes for transmission. To enable ICI prediction it has been proposed to exchange scheduling decisions amongst base stations. However, if this exchange is subject to delays, the system performance decreases as scheduling decisions become suboptimal. In this paper we propose a new scheme that maintains scheduling optimality at the cost of reduced link adaptation accuracy when faced with backhaul delays. We compare both schemes and provide insights into the multi-user diversity / link adaptation accuracy trade-off that arises for non-stationary users if information exchange on the backhaul is subject to delays.

Centralized Scheduling for Joint Decoding Cooperative Networks Subject to Signalling Delays

Joint detection in the uplink of a cellular network involving several non-colocated base stations is a promising means to turn inter-cell interference into useful signal energy and hence dramatically increase spectral efficiency of reuse one networks. To maximize the benefits of the new degrees of freedom that come with base station cooperation, cluster centric schedulers need to be aware of the interference situation in all participating cells. Since the required exchange of information on the backhaul infrastructure can be subject to significant delays, scheduling decisions are potentially based on outdated channel state information and will thus lead to suboptimal system performance. In this contribution we extend our framework for studying the impact of these signaling delays on the system performance by allowing bigger cooperation clusters. By comparing new algorithms and introducing the possibility of channel prediction, we provide further insight into the system behavior.

Power control and scheduling for joint detection cooperative cellular systems

Cooperative joint detection in the uplink of cellular systems is a promising means to combat inter-cell interference. In fact, interference from other users in the same cooperation cluster is turned into useful signal energy in such systems. While cooperation is generally beneficial, the system behavior largely depends on the power control and scheduling strategies employed, as demonstrated in this paper. We investigate different combinations of these two mechanisms and provide insights into the system behavior considering spectral efficiency, fairness and energy efficiency.