Jaakko Vihriälä

Moving cells: a promising solution to boost performance for vehicular users

In future wireless networks, a significant number of users accessing wireless broadband will be vehicular (i.e., in public transportation vehicles like buses, trams, or trains). The Third Generation Partnership Project has started to investigate how to serve these vehicular users cost-effectively, and several solutions have been proposed. One promising solution is to deploy a moving relay node (MRN), on a public transportation vehicle that forms its own cell inside the vehicle to serve vehicular users. By proper antenna placement, an MRN can reduce or even eliminate the vehicular penetration loss that affects communication. Moreover, MRNs can exploit various smart antenna techniques and advanced signal processing schemes, as they are less limited by size and power than regular user equipment. However, there are also challenges in using MRNs, such as designing efficient interference management techniques as well as proper mobility management schemes to exploit the benefit of group handovers for vehicular UE devices served by the same MRN. Nevertheless, initial system-level evaluation results indicate that a dedicated MRN deployment shows great potential to improve the vehicular user experience, and thereby can potentially bring significant benefits to future wireless communication systems.

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.

Providing enhanced cellular coverage in public transportation with smart relay systems

This paper introduces a notion of coordinated and cooperative relay systems (CCRS) for providing enhanced cellular coverage in highly populated public transportation such as passenger trains, cruise ships, etc. This notion considers a closed group of relay nodes and cells thereof, deployed together for particular service area of interest, as a new interconnected-and-extended network entity of advanced cellular systems — the CCRS. The CCRS may be set up on the run and connected to donor cellular network(s) with multiple mobile wireless backhaul links in a coordinated and controlled manner. This is in order to optimize, for examples, duplexing operation in relaying, load balancing and capacity sharing, as well as mobility management of the CCRS which serves a huge number of mobile users aboard of transportation. This paper addresses challenges as well as architecture alternatives and enhancements for incorporating the CCRS into advanced cellular networks such as 3GPP LTE-A systems. This paper also shows some methods to explore notable amounts of time-space and user diversities associated with the CCRS and performance gains of the CCRS.

A Cooperative Moving Relay Node System Deployment in a High Speed Train

In this paper we present system level simulation results for a cooperative moving relay node (MRN) system deployed on a high speed train (HST). Recently interest has grown in using MRNs to provide enhanced cellular coverage to users in public transport, particularly HSTs, of which the modern construction materials and techniques cause high vehicle penetration loss (VPL) when signals propagate into the train. MRNs utilising antenna arrays on the exterior and interior of the train are a promising solution to overcoming this VPL in order to provide onboard users with improved service. We show that a cooperative system of 8 MRNs onboard a HST is able to provide significant improvements to achievable throughput of onboard users when compared to direct transmission, as well as indirectly improving the throughput of other users located in cells the HST is passing through.

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.

A Preliminary Study on Waveform Candidates for 5G Mobile Radio Communications above 6 GHz

This paper provides an overview and preliminary comparison of several multi-carrier and single-carrier waveforms that are potential candidates for future 5G mobile radio communications above 6 GHz. The waveforms are assessed primarily based on the established and known results as well as recent findings keeping in view the design requirements that are relevant to using frequencies above 6 GHz, especially the millimeter wave frequencies. The Key Performance Indicators and degrees of freedom in the design of different waveforms and their potential applications for mm-wave communications are discussed. Certain features that are particularly interesting for mm-wave communication and require further investigations are also highlighted. Furthermore, a common framework for synthesizing different waveform candidates has been developed. Finally, a preliminary qualitative comparison of different multi-carrier and single carrier waveforms has been derived.

Efficient Fast-Convolution Implementation of Filtered CP-OFDM Waveform Processing for 5G

This paper investigates the use of effective and flexible fast-convolution (FC) filtering scheme for multiplexing OFDM resource blocks (RBs) in a spectrally well-localized manner. The scheme is able to effectively suppress interference leakage between adjacent RBs, thus supporting asynchronous operation and independent waveform parametrization of RBs. This is considered as an important feature in 5G waveform development for effectively supporting diversified service characteristics. Our approach is applicable for cyclic prefix or zero prefix based OFDM and the corresponding OFDM based single-carrier (SC-FDMA) waveforms. It is also possible to generate and process traditional Nyquist pulse shaping based single-carrier waveforms and filter bank multicarrier waveforms using the same FC processing engine, accommodating different waveforms simultaneously in different RBs. Our case study is based on proposed numerology for 5G cm-wave communications utilizing flexible time-division duplexing principle. While using RBs of 160 OFDM subcarriers, it is enough to deactivate 3 to 5 subcarriers out of each RB as guardbands to effectively suppress interference leakage between RBs.

Pass It on: Advanced Relaying Concepts and Challenges for Networks Beyond 4G

Relay nodes (RNs) will be a key feature of future wireless networks. RNs can extend coverage, increase network capacity, and provide more uniform quality-of-service (QoS) across the cell area in a cost-effective manner. Therefore, not surprisingly, relaying techniques have attracted a significant amount of attention from the wireless industry and standards. The Third-Generation Partnership Project (3GPP) release 10 has considered RNs that act as base stations (BSs), known as type-1 RNs, aiming only for coverage extension. However, RNs can be employed in different ways, and several challenges have to be addressed to attain the theoretical gains. This article presents an overview of the relaying concepts related to the 3GPP long-term evolution (LTE) road map, i.e., concepts related to type-1, type-2, and moving RNs. The implementation challenges are outlined, and a number of promising solutions for each RN type are discussed. More specifically, for type-1 RNs, this article focuses on the allocation of resources to the backhaul and access links. For type-2 RNs, the focus is on designing distributed hybrid automatic repeat request (HARQ) protocols that involve RNs. Moving RNs are presented as an efficient solution to the ever-growing demand for wireless broadband by vehicleborne users. Overall, the presented relaying concepts and solutions can significantly improve the user experience and can play an important role in the future.