Gunnar Mildh

Design aspects of network assisted device-to-device communications

Device-to-device (D2D) communications underlaying a cellular infrastructure has been proposed as a means of taking advantage of the physical proximity of communicating devices, increasing resource utilization, and improving cellular coverage. Relative to the traditional cellular methods, there is a need to design new peer discovery methods, physical layer procedures, and radio resource management algorithms that help realize the potential advantages of D2D communications. In this article we use the 3GPP Long Term Evolution system as a baseline for D2D design, review some of the key design challenges, and propose solution approaches that allow cellular devices and D2D pairs to share spectrum resources and thereby increase the spectrum and energy efficiency of traditional cellular networks. Simulation results illustrate the viability of the proposed design.

Ultra-dense networks in millimeter-wave frequencies

Demands for very high system capacity and end-user data rates of the order of 10 Gb/s can be met in localized environments by Ultra-Dense Networks (UDN), characterized as networks with very short inter-site distances capable of ensuring low interference levels during communications. UDNs are expected to operate in the millimeter-wave band, where wide bandwidth signals needed for such high data rates can be designed, and will rely on high-gain beamforming to mitigate path loss and ensure low interference. The dense deployment of infrastructure nodes will make traditional wire-based backhaul provisioning challenging. Wireless self-backhauling over multiple hops is proposed to enhance flexibility in deployment. A description of the architecture and a concept based on separation of mobility, radio resource coordination among multiple nodes, and data plane handling, as well as on integration with wide-area networks, is introduced. A simulation of a multi-node office environment is used to demonstrate the performance of wireless self-backhauling at various loads.

Evolving Wireless Communications: Addressing the Challenges and Expectations of the Future

The wireless-access networks of today will have to evolve in several ways in order to address the challenges and expectations of the future. New technology components will be introduced as part of the evolution of current wireless-access technologies, such as high-speed packet access (HSPA) and long-term evolution (LTE). However, additional components may also constitute future new wireless-access technologies, which may complement the evolved technologies. Examples of such new technology components are new ways of accessing spectrum and substantially higher frequency ranges, the introduction of massive antenna configurations, direct device-to-device communication, and ultradense deployments.

Tight Integration of New 5G Air Interface and LTE to Fulfill 5G Requirements

Integration of new radio technologies to legacy ones has always been an important feature in any wireless communication generation shift and it is envisioned that for the transition to 5G this will be even more critical. Different 5G research projects have acknowledged the demand for a new air interface that will be designed to operate in higher frequency bands (compared to the ones currently allocated to LTE) where propagation is more challenging and coverage is spotty. This paper proposes a radio access network (RAN) architecture that realizes a tight integration of this new air interface with LTE to enable cross-air interface optimizations such as common resource management, faster mobility and simultaneous multi-connectivity features. The tight integration also aims at leveraging both the better coverage of LTE and the higher capacity of the higher frequency bands. In order to realize this integration, a common protocol layer (also called integration layer) lying on the top of lower layer protocols specified per air interface is proposed. The paper analyzes the alternatives for this integration layer, having the LTE protocol stack specified by 3GPP as a reference model. A recommendation is issued and, based on that, potential multi-connectivity features are presented.

Impact of network slicing on 5G Radio Access Networks

Network slicing addresses the deployment of multiple logical networks as independent business operations on a common physical infrastructure. The concept has initially been proposed for the 5th Generation (5G) core network (CN) however, it has not been investigated yet what network slicing would represent to the design of the 5G radio access network (RAN). The paper explains how network slicing may impact several aspects of the 5G RAN design such as the protocol architecture, the design of network functions (NFs) and the management framework that needs to support both the management of the infrastructure to be shared among the slices and the slice operation.

A novel state model for 5G Radio Access Networks

With the trends towards Internet of Things (IoT) and massive Machine-Type Communications (mMTC) it is expected that the 5th Generation of mobile communications (5G) will have a significant amount of battery powered devices (e.g. sensors, baggage tags, etc.). Therefore, battery efficiency and duration will be essential, especially for those devices in remote locations and/or restricted areas. It would be difficult to predict all the 5G use cases, for example, that may arise from IoT however it is expected that for some of these the tradeoff between efficient power savings modes and low-latency system access might be essential. In order to solve this tradeoff, called herein User Equipment (UE) sleeping problem, the paper proposes a novel state model for 5G Radio Access Networks (RAN) that relies on a novel state called “connected inactive” where both the UE and the network does not throw away context information. The state is envisioned to be highly configurable in order to address unpredictable use cases possibly with different requirements. It is shown via protocol signaling diagrams that that the proposed solution enables a quick and lightweight transition from inactive to active data transmission.

Physical Cell Identity Assignment in Heterogeneous Networks

In order to meet the ever increasing demands for capacity in mobile networks, several technological solutions are being sought and one of them is heterogeneous networks. In heterogeneous networks, the pre-planned, relatively regular placed macro base stations are complemented with several low-powered base stations that might be deployed in a relatively unplanned fashion for both capacity and coverage enhancements. This can result in a large number of cells within a given area, making it difficult to assign non-conflicting cell identities from the limited number of available sets. In this paper, we analyze this problem in realistic deployment scenarios in a 3GPP LTE network that is enhanced with low power pico nodes. System level simulation results show that for deployment densities that can meet the anticipated traffic demands for up to 2020, the 504 cell identity limit in LTE is quite sufficient and cell identities can be reused efficiently among the pico nodes.