Venkatkumar Venkatasubramanian

On the performance gain of flexible UL/DL TDD with centralized and decentralized resource allocation in dense 5G deployments

Ultra dense small cell deployments and a very large number of applications are expected to be the essential aspects of the newly emerging 5th generation (5G) wireless communication system. To match the diverse quality of service requirements imposed by a variety of applications, dynamic TDD is proposed as a solution by enabling flexible utilization of the spectrum for uplink and downlink of each cell. In this paper, the system performance of flexible (dynamic) TDD is compared to a fixed portioning of resources for uplink and downlink. Further, the degree of centralization for resource management is investigated in the context of dynamic TDD, because multi-cell scheduling will be important for the design of 5G ultra-dense network architecture. The results show that dynamic TDD is indeed a very promising option for 5G networks, and substantially decreases packet outage delays. We find that the performance gap between centralized and decentralized scheduling is small in case of planned deployments. However, centralized scheduling may be beneficial in certain dynamic TDD deployment scenarios with a very asymmetric access point distribution.

Centralized and decentralized multi-cell D2D resource allocation using flexible UL/DL TDD

Device to device (D2D) communication is expected to be an important aspect in future 5G communication systems. To this end, D2D has been identified as an important topic in the EU flagship project METIS, wherein commercial D2D use cases are also considered. In principle, direct D2D communication offers the double benefit of low latency and high data rate at the same time. Interference mitigation and performance optimization alongside cellular users are however some of the key challenges to D2D communication. In this paper, we present a flexible D2D concept which is based on integration of D2D communication in flexible UL/DL TDD scheduling. We then compare multi-cell decentralized and centralized approaches for joint resource allocation for direct D2D and cellular links. Simulation based results are shown in a challenging indoor scenario where direct D2D users are placed among a high density of indoor cellular small cells and users. We find that centralized multi-cell resource allocation can improve overall system performance by 24 % for supporting D2D communications. Our results also show that substantial system level gains above 30% are achieved by enabling resource reuse between direct D2D and cellular users in both uplink and downlink cellular time slots. Furthermore, we see that flexible TDD provides overall better system performance as compared to fixed TDD even with a decentralized scheduler.

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.

D2D mode selection and resource allocation with flexible UL/DL TDD for 5G deployments

Network-facilitated device to device (D2D) communication is expected to play a central role in 5th generation cellular systems, as this allows to substantially reduce the end-to-end latency in mission-critical communication use cases, but also to obtain network and spectral efficiency improvements through the exploitation of proximity gains, hop gains and reuse gains in mobile broadband scenarios. The likely complement of evolved legacy standards with non-backward compatible radio interfaces in the 5G context will allow to design radio technology that natively and efficiently supports D2D from the very beginning. However, there are various fundamental design questions to be answered, focusing in this work on the question of how mode selection between D2D and device-infrastructure-device communication should ideally be conducted, as this will have a major impact on protocol stack design. We compare a fast, instantaneous SINR based mode selection (likely implemented on MAC level) against a typically assumed path-loss based slow mode selection (PDCP or RRC level). Through extensive simulation studies, it is shown that fast mode selection does allow to improve D2D performance without impairing cellular performance, but likely requires highly coordinated RRM, and it is thus needed to carefully consider whether the depicted gains would justify the likely more complicated and overhead-prone implementation of mode selection on MAC level.

Adaptive SIMO and SDMA transmission mode for single carrier FDMA uplink

This paper is dedicated to better understanding of the achievable sum rate in the single carrier FDMA (SC-FDMA) system. We investigate the achievable sum rate in a two-user SC-FDMA system, where a mix of SIMO (single input multiple output) and SDMA (space division multiple access) transmission mode is assumed for the wideband communication. The problem is formulated which appears to be non-convex. Relation to the conventional waterfilling solution is pointed out for single mode (SIMO or SDMA) transmission. We show that a mix of SIMO and SDMA transmission mode in the wideband is not favorable for any pair of the user equipments. A better strategy would be to switch to SIMO mode or SDMA mode adaptively. We also propose a simple algorithm to find the group of users for SDMA mode based on the wideband average spatial correlation. Performance improvement is shown by combining adaptive SIMO mode and SDMA mode selection with our proposed user grouping algorithm.

Resource and Mobility Management in the Network Layer of 5G Cellular Ultra-Dense Networks

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.

Performance of strong interference cancellation in flexible UL/DL TDD systems using coordinated muting, scheduling and rate allocation

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.

5G Multi-RAT Integration Evaluations Using a Common PDCP Layer

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 stand-alone NR.

A novel scheduling framework for QoS-aware OFDMA resource allocation in a network with small relay cells and macro users

AbstractRelaying is a convenient way to provide full coverage in cellular networks. In particular, small relay cells can be used as a cost-effective solution for indoor coverage in MIMO–OFDM systems. The small relay cells would need to cater for indoor users’ quality of service (QoS) expectations. One key QoS objective is delivering stable data rates for multimedia applications, which we refer to as guaranteed data rates. In this article, we consider optimization for delivering guaranteed data rates in a network with multiple relays and a macro base station, in a scenario when there are both macro users and relay users to be served. A novel scheme called cell-guaranteed bit rate by relay scheduling is proposed, with both optimal and heuristic scheduling methods. To perform the optimization we exploit resource block allocation, and parameters such as relaying duration and relay bandwidth allocation. Interference between relays and macro is avoided through time domain orthogonalization. Another key aspect of the scheme is inter-frame scheduling, wherein relay feeder links can be flexibly scheduled in any time slot along with macro users. Performance evaluation is presented using real-time indoor measurement channels and a sample test scenario. Results show the heuristic method can improve performance by 89.47% as compared to round-robin scheduling at relays and is within a 5% gap to optimal scheduling.

Service-Tailored User-Plane Design Framework and Architecture Considerations in 5G Radio Access Networks

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.