Integrated Access and Backhaul (IAB) has been considered by the 3GPP as a New Radio (NR) Release 16 study item for 5G networks. The purpose of IAB is to realize low cost 5G deployments in millimeter wave bands using wireless relaying. The main benefit is to reduce the cost of backhaul by using wireless NR links between the infrastructure nodes. In this paper, we study the throughput performance of wireless relaying in 5G millimeter wave bands in the 3GPP Urban Micro scenario. We characterize the upper bound on the IAB performance using centralized scheduling and flexible time division duplex (TDD) switching, and also consider appropriate backhaul and uplink access power levels. Simulation results are presented for a scenario with multiple base stations deployed, each with multiple transmit-receive antenna array panels, and with a large number of users deployed in the system.

Flexible time division duplex (TDD) is expected to be one of the key technologies for 5G flexible air interface. The main benefit of flexible TDD is to allow for better radio resource utilization based on instantaneous user traffic demands. To boost network capacity, one could thus, utilize flexible TDD along with a dense deployment of small cells. Flexible TDD systems can be designed to benefit from strong-interference cancellation of the cross-link interference along with advanced inter-cell coordination. In this paper, we propose a centralized coordination scheme with joint uplink/downlink (UL/DL) user scheduling, rate, and MIMO rank adaptation. To reduce the complexity of coordinated scheduling, we propose a cluster-based scheduling scheme where joint UL/DL selection and joint user scheduling are performed within a cluster. MIMO rank and rate adaptation are performed across the clusters using inter-cluster rate and rank adaptation. Simulation based results are evaluated in an outdoor urban micro scenario with bursty traffic and assuming realistic channel estimation. It is observed that the proposed flexible TDD scheme with joint UL/DL scheduling, interference cancellation, and coordination provides over 120% gain in the fifth percentile and over 29% gain in the average end-to-end UL throughput as compared to flexible TDD standalone scheduling without coordination. Our results show that successive interference cancellation receivers provide over 20% UL throughput gain for flexible TDD systems as compared to Interference Rejection Combining (IRC) receivers. We also find that fully flexible TDD with interference cancellation significantly outperforms fully synchronized TDD for different cell sizes.

5G systems are expected to utilize frequency bands above 6 GHz in the so-called millimeter-wave (mmWave) spectrum because of large bandwidths. It is well know that higher carrier frequency bands suffer from higher path loss attenuation. It addition, dynamic blockages can be a challenge for achieving good coverage. Therefore, millimeter-wave deployments require cell densification to achieve high data rates. However, densification further leads to challenges in the system design because of the need for low cost backhaul. The concept of wireless self-backhauling (sBH) aims to provide a provide a backhaul solution at reduced cost. Self-backhaul solution makes use of integrated access and backhaul (IAB) at each base station to realize on-demand flexible backhaul and access. In this paper, we investigate the performance of in-band self-backhauling with integrated access and backhaul in a real-life street canyon scenario. We consider centralized scheduling which can effectively allocate radio resources for backhaul and access on a time slot basis with half duplex constraint. The centralized scheduler further mitigates cross-interference between backhaul and access using a beam coordination and interference cancellation. Our results show that the proposed relaying concept offers good user throughput gains for cell edge users and is also robust to offloading of users to relay cells. Results also show that interference cancellation receivers can improve the uplink and backhaul spectral efficiency in IAB deployment by around 10%.

Flexible time division duplex (TDD) is one of a key enablers of 5G systems which allows for instantaneous adaptation to the user traffic demands. 5G systems are also expected to benefit from user-specific beamforming using massive MIMO deployment. However, flexible TDD can lead to severe cross-link interference even with beamforming because of overlapping beams, side lobes and backlobes. In this paper we consider standalone scheduling with semi-static coordination for interference awareness in flexible TDD system. The proposed standalone scheduling schemes exploit interference measurement and SIC receivers to mitigate cross- link interference. We further propose a novel partially distributed scheduling scheme based on limited information exchange in terms of packet delays. Simulations results are shown in a multi- site scenario with multiple panels at each site. Results show that our proposed standalone schemes significantly benefit from semi-static slot coordination and achieve high median throughput in uplink and downlink. The proposed low complexity partially distributed scheduling scheme is observed to achieve good throughput gains as compared to the fully standalone scheduling.

In this paper we study the performance of centralized joint user scheduling in a dynamic TDD system with beamforming.

5G systems are expected to utilize flexible time division duplex (TDD) to cater for instantaneous user traffic demands. 5G systems are also expected to benefit from user-specific beamforming using massive MIMO deployment. In this paper we study the performance of flexible TDD system with massive MIMO deployment and inter-cell coordination. We propose a centralized scheduling approach, where joint user scheduling and beamforming is performed taking into account interference cancellation receivers. Simulations results are shown in a multi-site scenario with multiple panels at each site. Results show that flexible TDD with per site standalone scheduling provides a significant 175% median uplink throughput gain over a fixed UL/DL TDD split. Advanced inter-site coordination based on IC receivers is seen to further improve uplink and downlink median throughput by around 85% and 65% respectively as compared to intra-site standalone scheduling.

Millimeter wave frequency bands are expected to be used in future 5G networks to provide high data rates. However, higher frequency bands are characterized with high path loss attenuation and sensitivity to the blockages. Thus, deployment of dense networks using smaller cell sizes is important for coverage. To this end, in-band wireless relaying can be used to realize smaller cell sizes at reduced backhaul cost. Wireless relaying may however sacrifice capacity because of half-duplex constraint. In this paper, we investigate the performance of the millimeter wave (mmWave) network employing self-backhaul relay nodes and centralized transmission coordination. In particular, we look at the usage of interference cancellation (IC) receivers to enable backhaul uplink multiple access channel (BU-MAC) and full-duplex (FD) access/backhaul transmission which can boost capacity of relaying. Through simulation results we show, that the 5th% E2E throughput is improved by around 90% with BU-MAC scheme and over 120% in FD scheme. The average throughput of relay downlink increases by around 50% and 80% with BU-MAC and FD schemes resnectively.

The continuing growth in traffic demands impose the need for the use of frequency bands in the centimeter-wave (cmWave) and millimeter-wave (mmWave) spectrum to increase the throughput. However, this leads to challenges in the system design because of the need for higher cell densification as well as cost-effective deployment. To overcome these challenges the concept of wireless self-backhauling can be used to provide high-capacity network at reduced cost. In this paper, we investigate the performance of self-backhauling with flexible reuse of the resources for access and backhaul in a real-life street canyon scenario with dynamic blockages. The simulation results show that highly flexible access/backhaul and uplink/downlink scheduling with centralized coordination achieves significant throughput gain in median and 5 th percentile of uplink (UL) and downlink (DL). Simulation based results also show that with the limitation of TDD flexibility, self-backhauling mainly provides uplink 5 th percentile throughput gain.

The provision of very high capacity is one of the big challenges of the 5G cellular technology. This challenge will not be met using traditional approaches like increasing spectral efficiency and bandwidth, as witnessed in previous technology generations. Cell densification will play a major role thanks to its ability to increase the spatial reuse of the available resources. However, this solution is accompanied by some additional management challenges. In this article, we analyze and present the most promising solutions identified in the METIS project for the most relevant network layer challenges of cell densification: resource, interference and mobility management.

This paper presents a novel user plane framework, tailored for different 5G services with diverse and conflicting key performance indicators. Initially, this paper identifies the major challenges in the legacy user-plane approaches and highlights the up-to-date 5G standardization activities in this area. It further analyzes new functional requirements related to service-oriented design and the introduction of new mechanisms to address them. Subsequently, this paper discusses how various user plane design decisions related to the control/user plane split options, network slicing, and radio access network (RAN)core network (CN) interfacing can potentially impact the overall 5G architecture. For the latter, some key RAN/CN interface considerations and the interactions with CN given different protocols and quality of service models are investigated.

5G is expected to operate in a wide frequency range to support new challenging use-cases. Multi-RATs (Radio Access Technologies): NR (New Radio) and evolved LTE (Long Term Evolution) will together constitute 5G. Utilizing NR at high frequencies will have a significant impact on radio propagation conditions with e.g. unfavorable higher path loss and increased outdoor-to-indoor penetration losses. In order to provide a reliable communication from the outset of 5G deployment and to minimize the standardization and implementation complexity, 5G UP (User Plane) instances of 5G AIs (Air Interface) related to evolved LTE and NR need to be aggregated on a certain layer of the protocol stack. This paper sheds light on how to integrate 5G AIs into a single 5G AI framework and explores which protocol stack layer could be used as aggregation layer. Inter-RAT hard handover is the state of the art technique to integrate multiple RATs in order to support mobility and reliability across different RATs. However, the hard handover incurs a transmission interruption which stands as an obstacle along the way of accomplishing 5G design. According to simulation results, a common PDCP (Packet Data Convergence Protocol) layer improves the hard handover functionality and stands out as a basis for tight interworking between evolved LTE and NR. By means of simulation, it is shown that the multi-RAT UP aggregation can achieve three times higher user throughput, when NR is using 28 GHz and LTE 2 GHz, compared to standalone NR.

Flexible UL/DL TDD can be used for efficient spectrum utilisation in 5G small cells. In this paper, we consider fully coordinated (centralized) scheduling which exploits interference cancellation in a cluster of small cells using flexible TDD. We study joint uplink-downlink scheduling, with coordinated link adaptation and/or muting in the flexible TDD system with successive interference cancellation receiver. This coordinated link adaptation is called rate allocation. The novelty is that a scheduler may purposely schedule strong interference situations, with muting and rate allocation decisions in the small cell cluster to facilitate effective interference cancellation. Simulation based packet delay performance is shown in an indoor small cell scenario, where high base station-to-base station interference impacts the uplink. Ideal and non-ideal channel estimation cases are considered. Comparison is made to the baseline centralized scheduling where muting is used for interference mitigation without interference cancellation. Results show that with ideal channel estimation, at a system load of 55% interference cancellation aware scheduling, muting with rate allocation outperforms other schemes. It achieves high gain of 67% in terms of packet delay reduction as compared to the baseline. Interference cancellation aware scheduling and muting with uncoordinated rate adaptation also achieves high gain around 62% at the same load using realistic channel estimation.

This paper investigates block error rate (BLER) performance and computational complexity of candidate channel coding schemes for ultra-reliable low latency communication (URLLC) in 5G. The considered candidates are the same as those identified in 3GPP: turbo, LDPC, polar, and convolutional codes. Details of code constructions and decoding algorithms are provided with computational complexity analysis. Code construction parameters, number of iterations, and list sizes are selected to provide a fair comparison among candidate coding schemes. Simulation results on BLER are shown for several code rates and small-to-moderate block sizes. The results reveal that polar and LDPC codes outperform turbo codes for short block sizes of 40 bits, while the opposite is true for medium block sizes of 200 bits. None of the schemes is a clear winner at all considered block sizes and coding rates. Other aspects like implementation complexity, latency, and flexibility will also be important when deciding the URLLC coding scheme.

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.

This paper proposes a unified way of describing 5G air interface (AI) design proposals using a 5G service/frequency map based on work carried out as part of 5G-PPP/H2020 project “METIS-II”. It then crucially proposes a design framework and suitability assessment process for 5G AI candidates. The proposed assessment methodology focuses on “harmonization Key Performance Indicators, or KPIs” and how to measure them (qualitatively / quantitatively). The paper proposes that evaluation of 5G AI candidates should, in addition to performance, include the “extent of harmonization”, which is defined in this paper. The case is argued that these harmonization KPIs are essential when assessing new 5G AI technologies. Additionally, an initial overview of different User Plane aggregation approaches is provided. We then discuss the types of Application Program Interfaces (APIs) which may need to be offered to higher layers, as well as a broad set of 5G Control Plane features and how AI considerations could take these into account.

This paper describes the approach adopted by EU H2020 / 5G-PPP project “METIS-II” for a harmonized 5G air interface (AI) design, based on a suitability assessment framework for 5G AI candidates. The assessment focuses on “harmonization KPIs” and how to measure them (qualitatively / quantitatively). The paper proposes that evaluation of 5G AI candidates should, in addition to performance, include the “extent of harmonization”, which is defined in this paper. Keywords—5G air interface, User Plane design, RAN architecture, multi-connectivity, 3GPP, METIS-II, 5G-PPP

5G systems can use time division duplex (TDD) small cells employing interference cancellation (IC) receivers. IC-aware scheduling can be used to exploit strong interference cancellation with coordination. The novelty of the approach is that a scheduler purposely schedules strong interference situations in TDD instead of avoiding the interference. In this paper, we propose centralized multiple input multiple output (MIMO) joint rank adaptation for IC-aware coordinated scheduling. This is also called IC-aware joint rank allocation. The performance upper bound is evaluated in an indoor small-cell bursty traffic scenario assuming imperfect channel estimation. This is compared to a baseline of centralized scheduling with standalone rank adaptation and without interference cancellation. Numerical results show that IC-aware joint rank allocation achieves approximately 42% packet delay reduction as compared to the baseline. We further propose a low complexity approach called successively paired rank allocation (SPARK) for joint rank allocation. This heuristic is also seen to achieve around 42% packet delay reduction for the same scenario. We have also compared the benefit of IC-aware joint rank allocation to joint rank allocation without any interference cancellation and with and without downlink power reduction. Results show that IC-aware joint rank allocation outperforms joint rank allocation without interference cancellation in median packet delay by around 24%.

Mobile communication technology has been rapidly evolving ever since its first introduction in the late 1980s. The development witnessed is not just in the refinement of the radio access techniques, but also in the progression towards offering sophisticated features and services to the mobile phone users. To fulfill this ever-growing user demand and market trends, frequency ranges in millimeter wave bands are envisioned for wireless radio transmission. To respond to this trends, the EU-funded mmMAGIC project has been launched and its main objective is to design and develop radio access techniques operating in 6-100 GHz bands. When it comes to developing technologies for systems operating these frequency ranges, a major challenge encountered will be in terms of its radio access network integration. Unquestionably, issues at various aspects of physical layer design, channel modelling, architecture, network functions and deployment will be encountered; problems in multi-node and multi-antenna transceiver designs will surface as well. The work carried in this project will address those challenges and propose solutions; but additionally, measure its efficiency against the project specific KPIs set to meet the requirements of the operational future 5G systems. The main intention of this paper is to outline some of the challenges, more specifically to highlight the network integration challenges, and discuss some of its technical solutions. The primary purpose here is to focus towards integrated 5G technology, thereby opening further research avenues for the exploration of new and alternate frequency bands in the electromagnetic spectrum.