Peter Rost

Cloud technologies for flexible 5G radio access networks

The evolution toward 5G mobile networks will be characterized by an increasing number of wireless devices, increasing device and service complexity, and the requirement to access mobile services ubiquitously. Two key enablers will allow the realization of the vision of 5G: very dense deployments and centralized processing. This article discusses the challenges and requirements in the design of 5G mobile networks based on these two key enablers. It discusses how cloud technologies and flexible functionality assignment in radio access networks enable network densification and centralized operation of the radio access network over heterogeneous backhaul networks. The article describes the fundamental concepts, shows how to evolve the 3GPP LTE architecture, and outlines the expected benefits.

Benefits and Impact of Cloud Computing on 5G Signal Processing: Flexible centralization through cloud-RAN

Cloud computing draws significant attention in the information technology (IT) community as it provides ubiquitous on-demand access to a shared pool of configurable computing resources with minimum management effort. It gains also more impact on the communication technology (CT) community and is currently discussed as an enabler for flexible, cost-efficient and more powerful mobile network implementations. Although centralized baseband pools are already investigated for the radio access network (RAN) to allow for efficient resource usage and advanced multicell algorithms, these technologies still require dedicated hardware and do not offer the same characteristics as cloud-computing platforms, i.e., on-demand provisioning, virtualization, resource pooling, elasticity, service metering, and multitenancy. However, these properties of cloud computing are key enablers for future mobile communication systems characterized by an ultradense deployment of radio access points (RAPs) leading to severe multicell interference in combination with a significant increase of the number of access nodes and huge fluctuations of the rate requirements over time. In this article, we will explore the benefits that cloud computing offers for fifth-generation (5G) mobile networks and investigate the implications on the signal processing algorithms.

Dynamic resource assignment and cooperative relaying in cellular networks: concept and performance assessment

Relays are a cost-efficient way to extend or distribute high data rate coverage more evenly in next generation cellular networks. This paper introduces a radio resource management solution based on dynamic and flexible resource assignment and cooperative relaying as key technologies to enhance the downlink performance of relay-based OFDMA cellular networks. It is illustrated how the dynamic resource assignment is combined with beamforming in a macrocellular deployment and with soft-frequency reuse in a metropolitan area deployment. The cooperative relaying solution allows multiple radio access points to cooperatively serve mobile stations by combining their antennas and using the multiantenna techniques available in the system. The proposed schemes are compared to BS only deployments in test scenarios, which have been defined in the WINNER project to be representative for next generation networks. The test scenarios are well defined and motivated and can serve as reference scenarios in standardisation and research. The results show that the proposed schemes increase the average cell throughput and more importantly the number of users with low throughput is greatly reduced.

Fronthaul and backhaul requirements of flexibly centralized radio access networks

Cloud radio access networks promise considerable benefits compared to decentralized network architectures, but they also put challenging requirements on the fronthaul and backhaul network. Flexible centralization can relax these requirements by adaptively assigning different parts of the processing chain to either the centralized baseband processors or the base stations based on the load situation, user scenario, and availability of fronthaul links. In this article, we provide a comprehensive overview of different functional split options and analyze their specific requirements. We compare these requirements to available fronthaul technologies, and discuss the convergence of fronthaul and backhaul technologies. By evaluating the aggregated fronthaul traffic, we show the benefits of flexible centralization and give guidelines on how to set up the fronthaul network to avoid over- or under-dimensioning.

Towards a flexible functional split for cloud-RAN networks

Very dense deployments of small cells are one of the key enablers to tackle the ever-growing demand on mobile bandwidth. In such deployments, centralization of RAN functions on cloud resources is envisioned to overcome severe inter-cell interference and to keep costs acceptable. However, RAN back-haul constraints need to be considered when designing the functional split between RAN front-ends and centralized equipment. In this paper we analyse constraints and outline applications of flexible RAN centralization.

On the transmission-computation-energy tradeoff in wireless and fixed networks

In this paper, a framework for the analysis of the transmission-computation-energy tradeoff in wireless and fixed networks is introduced. The analysis of this tradeoff considers both the transmission energy as well as the energy consumed at the receiver to process the received signal. While previous work considers linear decoder complexity, which is only achieved by uncoded transmission, this paper claims that the average processing (or computation) energy per symbol depends exponentially on the information rate of the source message. The introduced framework is parametrized in a way that it reflects properties of fixed and wireless networks alike. The analysis of this paper shows that exponential complexity and therefore stronger codes are preferable at low data rates while linear complexity and therefore uncoded transmission becomes preferable at high data rates. The more the computation energy is emphasized (such as in fixed networks), the less hops are optimal and the lower is the benefit of multi-hopping. On the other hand, the higher the information rate of the singlehop network, the higher the benefits of multi-hopping. Both conclusions are underlined by analytical results.

Analysis of a Mixed Strategy for Multiple Relay Networks

Infrastructure-based wireless communications systems as well as ad hoc networks experience a growing importance in present-day telecommunications. An increased density and popularity of mobile terminals poses the question how to exploit wireless networks more efficiently. One possibility is to use relay nodes supporting the end-to-end communication of two nodes. In their landmark paper, Cover and El Gamal proposed different coding strategies for the single-relay channel. These strategies are the decode-and-forward and compress-and-forward approach, as well as a general lower bound on the capacity of a single-relay network which relies on the combined application of the previous two strategies. So far, only parts of their work-the decode-and-forward and the compress-and-forward strategy-have been applied to networks with multiple relays. In this paper a generalizing framework for multiple-relay networks is derived using a combined approach of partial decode-and-forward and the ideas of successive refinement with different side information. After describing the protocol structure, the achievable rates for the discrete memoryless relay channel as well as the Gaussian multiple-relay channel are presented and analyzed. Using these results the derived framework is compared with protocols of lower complexity, e.g., multilevel decode-and-forward and distributed compress-and-forward.

The Complexity–Rate Tradeoff of Centralized Radio Access Networks

In a centralized radio access network (RAN), the signals from multiple radio access points (RAPs) are centrally processed in a data center. A centralized RAN enables advanced interference coordination strategies while leveraging the elastic provisioning of data processing resources. It is particularly well suited for dense deployments, such as within a large building where the RAPs are connected via fiber and where many cells are underutilized. This paper considers the computational requirements of a centralized RAN with the goal of illuminating the benefits of pooling computational resources. A new analytical framework is proposed for quantifying the computational load associated with the centralized processing of uplink signals in the presence of block Rayleigh fading, a distance-dependent path loss, and fractional power control. Several new performance metrics are defined, including the computational outage probability, the outage complexity, the computational gain, the computational diversity, and the complexity-rate tradeoff. The validity of the analytical framework is confirmed by numerically comparing it with a simulator compliant with the 3GPP LTE standard. Using the developed metrics, it is shown that centralizing computing resources provides a higher net throughput per computational resource as compared with local processing.

Opportunistic Hybrid ARQ—Enabler of Centralized-RAN Over Nonideal Backhaul

Centralized radio access networks rely on transport networks with very high throughput and very low latency. In the case of nonideal backhaul, it may be necessary to only centralize parts of the radio access network. This implies several timing and protocol constraints, e.g., predefined timing of retransmissions due to hybrid ARQ. In this paper, an opportunistic hybrid-ARQ approach is introduced, which estimates the decoding error probability at the radio access points and directly provides feedback to mobile terminals, while actual decoding is performed at the central processor. Furthermore, an effective signal-to-noise ratio (SNR) is derived, which allows for the use of a single mapping curve.

A Cooperative Relaying Scheme without the Need for Modulation with Increased Spectral Efficiency

Future infrastructure based wireless systems are likely to use relaying due to energy savings, simpler roll-out of cellular networks, simpler increase of coverage and so forth. To increase the performance of relaying based systems cooperative relaying has emerged as an additional option to exploit spatial diversity. In order to allow for a fair comparison between single- hop and multi-hop schemes, an N-fold more spectrally efficient use of each link needs to be assumed for the multi-hop case. We propose a novel protocol relying on two relaying nodes which does not require the need for an increase in spectral efficiency in comparison to direct transmission. However, we achieve a better performance in the low SNR/high rate regime at the expense of a worse performance in the high SNR/low rate regime. The proposal is compared to direct transmission, conventional relaying, transmit diversity and a distinct cooperative relaying scheme considering their outage probability.