Eeva Lähetkangas

5G small cell optimized radio design

The 5th generation (5G) of mobile radio access technologies is expected to become available for commercial launch around 2020. In this paper, we present our envisioned 5G system design optimized for small cell deployment taking a clean slate approach, i.e. removing most compatibility constraints with the previous generations of mobile radio access technologies. This paper mainly covers the physical layer aspects of the 5G concept design.

Centimeter-Wave Concept for 5G Ultra-Dense Small Cells

Ultra-dense small cells are foreseen to play an essential role in the 5th generation (5G) of mobile radio access technology, which will be operating over different bands with respect to established systems. The natural step for exploring new spectrum is to look into the centimeter-wave bands as well as exploring millimeter-wave bands. This paper presents our vision on the technology components for a 5G centimeter-wave concept for ultra-dense small cells. Fundamental features such as optimized short frame structure, multi-antenna technologies, interference rejection, rank adaptation and dynamic scheduling of uplink/downlink transmission are discussed, along with the design of a novel flexible waveform and energy-saving enablers.

Achieving low latency and energy consumption by 5G TDD mode optimization

The target for a new 5G radio access technology is to support multi-Gbps and ms latency connectivity simultaneously at noticeably lower energy consumption and cost compared to the existing 4G technologies, such as LTE-Advanced. Extremely short air interface latency is required to achieve these requirements in a TDD-based local area network. In this paper, we discuss how the required short TDD latency can be achieved and further utilized in 5G physical air interface. First, we investigate the enablers and limits of TDD latency by analyzing the performance of OFDM in different channel environments and discussing on the consequent frame length limits. We then provide a description on how the achieved short TDD latency can further be utilized to enable remarkably low energy consumption. A numerical analysis comparing the battery life time of the suggested 5G TDD air interface and LTE is provided, showing remarkable gains for the 5G air interface concept.

B4G local area: High level requirements and system design

A next generation Beyond 4G (B4G) radio access technology is expected to become available around 2020 in order to cope with the exponential increase of mobile data traffic. In this paper, research motivations and high level requirements for a B4G local area concept are discussed. Our suggestions on the design of the B4G system as well as on the choice of its key technology components are also presented.

Full-duplex self-backhauling for small-cell 5G networks

We consider in-band self-backhauling for small cell 5G systems. In-band self-backhauling enables efficient usage of frequency resources. When coupled with a flexible frame format, it also enables efficient time-division duplexing of uplink, downlink, and backhaul transmissions. Self-backhauling is particularly efficient when coupled with FD relaying. Antenna design, as well as cancellation in radio frequency and digital domains at an FD relay enables reuse of the same resources for backhaul and access hops. The use of radio resources in the self-backhauling and access hops can be coordinated to maximize end-to-end performance. We evaluate FD in-band self-backhauling in indoor 5G scenarios, targeting mobile broadband and ultrareliable communication use cases. Self-backhauling shows considerable promise for reaching 5G targets in these scenarios.

On the Potential of OFDM Enhancements as 5G Waveforms

The ideal radio waveform for an upcoming 5th Generation (5G) radio access technology should cope with a set of requirements such as limited complexity, good time/frequency localization and simple extension to multi-antenna technologies. This paper discusses the suitability of Orthogonal Frequency Division Multiplexing (OFDM) and its recently proposed enhancements as 5G waveforms, mainly focusing on their capability to cope with our requirements. Significant focus is given to the novel zero-tail paradigm, which allows boosting the OFDM flexibility while circumventing demerits such as poor spectral containment and sensitivity to hardware impairments.

On the Waveforms for 5G Mobile Broadband Communications

To realize the vision of ubiquitous mobile broadband where radio access performance should not be a limiting factor for user experience, we need to access very large bandwidths, and thus consider higher frequency bands up to the millimeter wave region. Air interface design, including waveforms, is a very important component for the success of 5G mobile broadband (MBB) in terms of flexibility, energy efficiency and cost efficiency. In this paper, we compare two waveforms, orthogonal frequency division multiplexing (OFDM) and filter bank multicarrier (FBMC), in terms of these requirements. We show that OFDM is a suitable waveform for MBB due to reasonably low overhead, low cost and latency; whereas FBMC loses its spectral properties when non-linear power amplifier is used.

Numerology and frame structure for 5G radio access

5G radio access technology is envisioned to operate from sub-1 GHz to 100 GHz using a wide range of deployment options and to support diverse services. This paper proposes OFDM numerology and frame structure for 5G radio access. The numerology is proposed keeping in view realistic propagation channel measurements, mobility, effect of phase noise, and implementation complexity. The frame structure is proposed for both FDD and TDD. The proposed frame structure is flexible, scalable, and fulfills low latency requirements.

Multihop Relaying for Local Area Access

We consider multi-hop forwarding in a Beyond 4G local area network, where in addition to nodes with wired backhaul, there is a high density of self-backhauling relay nodes acting simultaneously as access points towards users. The nodes apply Time Division Duplexing, access is framed and synchronized along a multi-hop flow, and there is a corresponding reuse factor for active hops along a multihop route. Interference cancelation, as well as power and resource optimization, is performed within along a route. Simulations are performed in a local area network consisting of multiple multi-floor buildings. Multi-hop self-backhauling is found to significantly improve the coverage of high data rates in the system.

Full duplex relaying for local area

We consider full-duplex multi-hop forwarding in a Beyond 4G local area network. In the network, there is a high density of self-backhauling relay nodes that simultaneously act as access points towards the users, in addition to few nodes with wired backhaul. The access is framed and synchronized along the multi-hop flow, and the nodes apply time division duplexing. Interference cancelation as well as power optimization is performed within the multihop route. Simulations are carried out in a local area network consisting of multiple multi-floor buildings. The propagation channel is modelled using static pathloss, log-normal distributed random variable, or static pathloss with Rayleigh fading. The simulation results indicate that full-duplex relaying improves the network performance over half-duplex relaying, if self-interference channel attenuation is kept over 80 dB. The means of achieving tolerable self-interference levels in full-duplexing relays via physical design of the relay, and analog and digital interference cancellation are discussed.