Showing papers presented at "European Wireless Conference in 2017"

Performance of mobile networks with UAVs: Can flying base stations substitute ultra-dense small cells?

Abstract: A crucial challenge for future mobile networks is to enable wide range of scenarios and use cases for different devices spanning from simple sensors to advanced machines or users devices. Such requirements call for highly flexible and scalable radio access network (RAN). To provide high flexibility and scalability in dynamic scenarios, flying base stations (FlyBSs), i.e., base stations mounted on general unmanned aerial vehicles, can be integrated into RAN. In this paper, implementation and operational issues related to the FlyBSs are discussed. Additionally scenarios where the FlyBS can be profitable are outlined. Furthermore, we define the architecture of a flying RAN (FlyRAN) encompassing the FlyBSs and enabling real-time control of whole RAN so that it can dynamically adapt to users' movement and changes in their communication activity. Our results show the superior efficiency of FlyBSs comparing to an ultra-dense deployment of static base stations (BSs) for a realistic scenario with moving users. Our simulations suggest that one FlyBS can provide throughput comparable to static BSs deployed with density corresponding to inter-site distance of 45 meters. At the same time, energy efficiency of the communication for the user equipment can be improved more than 5-times. This indicates that integration of the FlyBSs into mobile networks can be an efficient alternative to ultra-dense small cell deployment, especially in scenarios with users moving in crowds.

Internet of Radio-Light: 5G Broadband in Buildings

Abstract: Wireless networks in buildings suffer from congestion, interference, security and safety concerns, restricted propagation and poor in-door location accuracy. The Internet of Radio-Light (IoRL) project develops a safer, more secure, customizable and intelligent building network that reliably delivers increased throughput (greater than 10 Gbps) from access points pervasively located within buildings, whilst minimizing interference, power consumption and harmful EM exposure and providing location accuracy of less than 10 cm. It thereby shows how to solve the problem of broadband wireless access in buildings and promotes the establishment of a global standard in ITU and 5GPPP. Building landlords will be incentivized to find funding to realize this solution for their properties to increase their value resulting in a stimulated market for broadband networking products in buildings, benefiting society and stimulating the world Gross Domestic Product. IoRL project provides solutions to develop this broadband networking solution in buildings using the existing joint VLC demonstrator at Tsinghua University & ISEP, the mmWave at Cobham Wireless and the NFV/SDN at NCSRDemocratos. The challenges are to develop broadband communication solutions for buildings by integrating these technologies to exploit the pervasiveness and accessibility of the existing electric light access points, the broadband capacities of mmWave and VLC technologies and the flexibility of SDN/NFV and to industrially design a radio-light solution that can be integrated into the myriad of form factors of existing electric light systems and consumer products.

A Precoding-based PAPR Reduction Technique for UF-OFDM and Filtered-OFDM Modulations in 5G Systems

Abstract: The universal filtered-orthogonal frequency division multiplexing (UF-OFDM) (also called universal filtered multicar- rier (UFMC)) and the filtered-OFDM (F-OFDM) are candidates to be alternative to the OFDM modulation in the upcoming 5G systems thanks to their improved spectral occupation and resistance to the carrier frequency offset. However, like the majority of the multicarrier modulations, UF-OFDM and F- OFDM have a high peak-to-average power ratio (PAPR). This influences the operation mode of radio frequency components such as the power amplifier and the digital-to-analog converter. In this paper, a precoding-based PAPR reduction technique is proposed for both the UF-OFDM and the F-OFDM cases. A similar technique has been proposed in the literature for OFDM. The principle of this method is to transform the UF-OFDM signal to a lower order summation of single carrier signals and the F-OFDM signal to single carrier signal. The relevance of the proposed PAPR reduction technique is confirmed by simulation results. The latter show a PAPR reduction of at least 2.5 dB. Moreover, the proposed technique does not impact the bit error rate performance and lowers down the power spectral density tails at the power amplifier output.

WiPLUS: Towards LTE-U Interference Detection, Assessment and Mitigation in 802.11 Networks

Abstract: We propose WiPLUS - a system that enables WiFi to deal with the stealthy invasion of LTE-U into the frequency bands used by WiFi. Using solely MAC layer information extracted passively, during runtime, out of the hardware registers of the WiFi NIC at the WiFi access point, WiPLUS is able to: i) detect interfering LTE-U signals, ii) compute their dutycycles, and iii) derive the effective medium airtime available for each WiFi link in a WiFi Basic Service Set (BSS). Moreover WiPLUS provides accurate timing information about the detected LTE-U ON and OFF phases enabling advanced interference mitigation strategies such as interference-aware scheduling of packet transmissions, rate adaptation and adaptive channel bonding. WiPLUS does not require any modifications to the WiFi client stations and works with commodity WiFi APs where it has a simple software installation process. We present the design, the implementation details and the evaluation of the WiPLUS approach. Evaluation results reveal that it is able to accurately estimate the effective available medium airtime for each link in a WiFi BSS under a wide range of LTE-U signal strengths with a root-mean-square error of less than 3% for the downlink and less 10% for the uplink.

SCMA Codebooks Optimization Based on Genetic Algorithm

Abstract: Sparse code multiple access (SCMA) is a nonorthogonal multiple access scheme based on joint modulation and spread spectrum procedure. This scheme allows to increase the number of active users inside a given time-frequency resource. Design of SCMA codebooks is a challenging problem. The paper considers the design of SCMA codebooks based on Genetic Algorithm (GA). In general case, mother constellation is not required for GA, and optimization is performed directly on the codebooks. We present the obtained structured codebooks containing two antipodal codeword pairs. Optimization was carried out to improve SCMA signal performance in additive white Gaussian noise (AWGN) channel by constraining the average energy of codewords. The obtained codebooks have minimum Euclidean distance equal to 0.87 (at unit average power of SCMA signal) and outperform known codebooks in AWGN channel with both Maximum Likelihood (ML) receiver or Message Passing Algorithm (MPA) detection. The comparison of existing and proposed codebooks is performed using computer simulation and union bounds. The asymptotic gain over the best known codebooks is 0.8 dB. As a result of the simulation, proposed codebooks demonstrate similar performance for ML and MPA detection algorithms. The proposed method is suitable for codebook design for other non-orthogonal schemes, e. g., Pattern Division Multiple Access (PDMA).

Cell discovery based on historical user's location in mmWave 5G

Abstract: By 2020, the global mobile data traffic will reach 30.6 exabytes per month. Hence, microwave bands will become saturated and insufficient to deliver that increment of data. Millimeter wave (a.k.a. mmWave) is a promising band, from 30 to 300 GHz, to allocate that data. A drawback is the high attenuation in non-line-of-sight scenarios because the millimeter wavelengths are blocked by common obstacles. Opposite to Long Term Evolution (LTE) networks which transmit in an isotropic manner, mmWave small base stations (SBS) have to transmit through directional antennas to achieve a sufficient signal to noise ratio within a radius of up to 200 meters. Moreover, current SBSs do not adapt to the environment to increase their efficiency, since they are configured manually. In this paper, we propose a learning Weight-based Algorithm to decrease the delay of finding UEs by autonomously prioritizing those sectors where more users are expected to be found according to previous experience. Our results show an increment of the number of UEs found in the first scan by over 19% and a delay reduction by over 84%, on average for all SBS-UE distances, with respect to comparable state-of-the-art approaches.

Resource Sharing for a 5G Multi-tenant and Multi-service Architecture

Abstract: As the next generation networks (5G) move into a direction of virtualization and softwarization, using technologies like Software-Defined Networking (SDN) and Network Function Virtualization (NFV), one of the main benefits is the possibility of network resource sharing among different tenants and service providers. This paper focuses on how the architecture of the 5G NORMA project will tackle the issue of resource sharing. Two main areas will be explored: how to achieve efficient resource sharing among network slices, and specific solutions used by the architecture to allow for resource sharing.

A Trade-off Between Unnecessary Handover and Handover Failure for Heterogeneous Networks

Abstract: With fast growing traffic, high-density small cells (SC) deployment is envisioned in 5G network under the macrocell (MC) coverage area. This will improve the capacity and the cellular coverage, however, it will also introduce unnecessary handovers (UHO) and handover failures (HOF) due to user mobility and, in turn, degrades the user's quality of service (QoS). This paper aims to reduce the UHOs in a SC heterogeneous networks (HetNets) and to maintain the HOF to an acceptable level specified by the operator. Time metric is used to find a trade-off between UHO and HOF. In order to reduce the target SC list for handover, the estimated time of stay is used to avoid long neighbour list. Interference from different base stations is taken into account through the use of signal to interference plus noise ratio (SINR) metric. Simulations are performed to evaluate the performance of the proposed method. Results show that the proposed method outperformed the competitive methods presented in the literature with a lower level of UHOs and HOFs.

Implementation of a Hybrid Optical-RF Wireless Network with Fast Network Handover

Abstract: Visible light communication (VLC) is a highly attractive choice for short-range communications, particularly in indoor scenarios. There are many reasons for this mainly, high achievable data rates, no interference to existing radio frequency (RF) systems, security and most importantly, an increasingly pervasive lighting infrastructure based on solid-state lighting. But there is an inherited challenge that light-based communication links need strict line-of-sight (LOS) and can easily be blocked. Researchers are proposing to exploit this property to make atto-cells in pico and micro-cellular architectures for indoor communications. Therefore, this technology seems promising to play its part in a heterogeneous environment. The proof-of-concept for such hybrid systems capable of vertical handover (VHO) between two technologies is of great value. In this paper, we present implementation details of a hybrid communication system which can efficiently monitor its primary link, i.e., VLC link and quickly switch to radio frequency (RF) whenever VLC link is failed. We define our decision-making and link-monitoring scheme in between network and data-link layers of communication protocol stack. To the best of our knowledge, this novel implementation allowing a fast handover is the first of its kind in the field of hybrid optical-RF systems.

Hybrid Precoding for Multi-Group Physical Layer Multicasting

Abstract: Next generation of wireless networks will rely on large-scale antenna systems, either in the form of massive multiple-input-multiple-output (MIMO) or millimeter wave (mmWave) systems. As digital precoders require a dedicated radio frequency (RF) chain per antenna element, the conventional fully-digital precoding schemes are not suitable for physical layer multicasting in these systems. To address this problem, in this paper we present a hybrid precoding structure for multi-group physical layer multicasting that significantly reduces the number of required RF chains. More specifically, we show that in a multi-group multicasting system with N transmit antennas, G multicasting groups, and an arbitrary number of users in each group, one can achieve the performance of any fully-digital precoder with just G radio frequency chains using the proposed hybrid multi-group multicasting structure, given N >G.

Control-aware Uplink Resource Allocation for Cyber-Physical Systems in Wireless Networks

Abstract: Cellular networks beyond LTE must address the requirements of Machine Type Communications (MTC). Many MTC applications fall into category of the cyber-physical systems, i.e., feedback systems with the physical processes integrated with networks and computation. The challenge of CPS is to design the communication network to support the underlying feedback control loop. To address this challenge, we adopt a cross-layer approach to scheduling in wireless networks. We formulate the resource allocation problem with the objective of maximizing the control performance in terms of the network-induced error. Following that, we devise a Maximum Predicted Error First (MPEF) scheduler, which provides a close to optimal performance while only relying on offline information about the control loops. In a case study of LTE cell, we compare MPEF with state-ofthe-art scheduling algorithms.

Symbol Error Outage Performance Analysis of MCIK-OFDM over Complex TWDP Fading

Abstract: This paper investigates the instantaneous symbol error outage probability (ISEOP) of a Multicarrier Index Keying with Orthogonal Frequency Division Multiplexing (MCIK-OFDM) system using greedy detection, over Two-Way with Diffused Power (TWDP) fading channels. The closed-form expressions for the upper and lower bound on the ISEOP are derived to analyze the effects of TWDP and MCIK parameters on the outage performance of MCIK-OFDM. Through the numerical analysis and asymptotic case studies, we provide a new insight on the performance of MCIK-OFDM in a complex wireless propagation environment such as in Device-to-Device (D2D) communications that face a variety of fading conditions.

Consistency-guaranteed and energy efficient sleep scheduling algorithm with data aggregation for IoT

Abstract: In data acquisition (DAQ)-based services of Internet of things (IoT), IoT devices sense data and transmit data to the application server through IoT gateway (GW). Due to the energy limitation of IoT devices, it is an important issue to increase energy efficiency of IoT devices. Meanwhile, when data from a huge number of IoT devices are individually transmitted, the data traffic volume can be significant. To resolve these issues, IoT devices and IoT GW can use sleep mode and data aggregation, respectively. However, when the IoT devices are in sleep mode for long time and/or data are aggregated in IoT GW for long time without any transmissions, the data can be inconsistent. In this paper, we propose a consistency-guaranteed and energy efficient sleep scheduling algorithm (CG-E2S2) with data aggregation. In CG-E2S2, the optimal sleep duration and the number of aggregated data are jointly determined by means of Markov decision process (MDP) with the consideration of energy efficiency of IoT devices, data traffic in networks, and data consistency. Evaluation results demonstrate that CG-E2S2 with the optimal policy outperforms the comparison schemes in terms of energy efficiency, data traffic volume, and data consistency.

An energy-efficient NOMA for small cells in heterogeneous CRAN under QoS constraints

Abstract: This paper investigates downlink performance of wireless backhaul in a heterogeneous cloud radio access network (HCRAN) consisting of a cloud-based central station (CCS) and multi-tier small cells. Non-orthogonal multiple access (NOMA) is adopted for the downlink from the CCS to multiple small cells of different types (e.g. microcells, picocells and femtocells). Taking into account practical power consumption at small cells operating within various propagation environment models, we first develop a power allocation for the NOMA, which allows us to derive the energy efficiency (EE) of the wireless backhaul in the practical HCRAN downlink. It is shown that the NOMA is superior to the conventional OFDMA scheme achieving a higher EE of up to six times with the deployment of small cells. The propagation environment is also shown to have a significant impact on the EE performance with a big gap between different cell types when the number of cells is large. Particularly, the EE of the NOMA is shown to not always increase or decrease as a function of the number of cells, while the throughput performance at the cloud edge is strikingly degraded as the number of cells increases. This accordingly motivates us to propose a two-stage algorithm for determining the optimal number of various cells that maximises the EE of the HCRAN while still maintaining the QoS requirement at the cloud edge. Simulation results show that, to meet a target cloud-edge throughput, the same number of femtocells and picocells can be used; however, the femtocells are favourable to the picocells in achieving the maximal EE.

Exploiting D2D Communications at the Network Edge for Mission-Critical IoT Applications

Abstract: The advent of the Internet of Things (IoT) is boosting a wide range of new multimedia applications driven by an ecosystems of "smart" and highly heterogeneous devices. This introduces new challenges for industries and network operators in the design of next-to-come fifth generation (5G) wireless systems, where stringent performance requirements in terms of high data rate, improved reliability, and ultra-low latency are to be met. A viable way of development is the integration of local clouds at the edge of the network as part of the recent Edge Computing paradigm. However, poor channel conditions experienced by the devices towards the serving edge node may impede the effectiveness of managing mission-critical IoT applications. In this context, Device-to-Device (D2D) communications represent a key enabling technology, which offers decisive benefits for future mobile 5G scenarios. As proposed in this paper, edgebased IoT applications may rely on D2D transmissions between the IoT devices also in the presence of mobility. In particular, a forwarding scheme is proposed showing that whenever collaborating IoT devices fall under the coverage of neighboring cellular edge nodes, D2D communications can guarantee a significant reduction in delay and traffic load across the network. The proposed solution is validated through simulations that indicate significant improvements in terms of latency, percentage of served tasks, energy efficiency, and traffic load w.r.t. the case where all communications are forwarded over the edge nodes.

Sum Power Minimization for TDD-Enabled Full-Duplex Bi-Directional MIMO Systems Under Channel Uncertainty

Abstract: In this paper we address a sum power minimization problem for a bi-directional and full-duplex (FD) communication system, where the required rate constraints are imposed on the guaranteed communication rates in each direction. In this regard, the impact of channel-state information (CSI) error, as well as the signal distortion due to hardware impairments are jointly taken into account. In order to ensure backwards compatibility to an equivalent half-duplex setup, we assume a time-division-duplex capable system where the FD communication process takes place in multiple independent time segments. Due to the intractable structure of the resulting optimization problem, a weighted minimum mean squared-error based method is applied to cast the power minimization problem into a separately convex structure, which can be iteratively solved with a guaranteed convergence. The resulting computational complexity of the algorithm is then discussed analytically. Finally, the performance of the proposed algorithm is numerically evaluated over different levels of rate demand, CSI error and transmitter/receiver dynamic range.

From Radio Design to System Evaluations for Ultra-Reliable and Low-Latency Communication

Abstract: Ultra-reliable and low-latency communication is the enabler for many new use cases, including wireless industrial automation. Fulfilling varying requirements of these use cases demands a flexible r ...

Downlink Data Rate Analysis of 5G-U (5G on Unlicensed Band): Coexistence for 3GPP 5G and IEEE802.11ad WiGig

Abstract: The enormous proliferation of mobile and personal telecommunications data traffic has brought severe challenges to the current mobile telecommunications system. Regarding the perspectives of both users and operators, the main obstacle is the licensing cost and scarcity of available spectrum. According to recent industrial and academic works, millimetre-wave (mmW) is a potential solution for next fifth generation (5G) mobile telecommunications. 5G on Unlicensed band (5G-U) technology, is an extension of the long-term evolution (LTE) on unlicensed band (LTE-U), which opportunistically transmits LTE signals in the unlicensed spectrum, a viable solution to deal with spectrum scarcity and increased data rates. In particular, 5G-U will aggregate carriers in the mmW band, 28 GHz or 38 GHz licensed spectrum, both candidates of 5G frequency band, and 60 GHz unlicensed spectrum, namely Wireless Gigabit (WiGig). Both systems, 5G and WiGig need to coexist without jeopardising each other. In this work, we study the coexistence of both systems in terms of downlink data rate, comparing three different scenarios: WiGig only, the coexistence of WiGig and 5G-U and 5G-U only. Results show, it is practical to operate 28 GHz licensed signal on the 60 GHz unlicensed frequency band, 5G-U can be coexisted with WiGig, and it is a good neighbourhood to current networks.

Wireless M-BUS in Industrial IoT: Technology Overview and Prototype Implementation

Abstract: During the past 15 years, the Internet revolution has redefined the industry landscape. The advent of the Internet of Things (IoT) is changing our lives by provisioning a wide range of novel applications that leverage the ecosystem of "smart" and highly heterogeneous devices. This is expected to dramatically transform manufacturing, energy, agriculture, transportation, and other industrial sectors. The Industrial Internet of Things (IIoT) brings along a new wave of Internet evolution and will offer unprecedented opportunities in Machine Type Communications (MTC) - intelligent industrial products, processes, and services that communicate with each other and with people over the global network. This paper delivers a technology overview of the currently utilized Wireless M-Bus communication protocol within the IIoT landscape together with describing a demonstration prototype development. In our trial implementation, the IQRF modules are utilized to be compatible with the protocol of interest. The constructed WM-Bus receiver is further integrated as part of a complex MTC Gateway, which receives the MTC data via a secure communication channel from various types of smart-metering devices.

On the asymptotic behavior of ultra-densification under a bounded dual-slope path loss model

Abstract: In this paper, we investigate the impact of networkdensification on the performance in terms of downlink signal-tointerference(SIR) coverage probability and network area spectralefficiency (ASE). A ...

Clustering and subband allocation for CoMP-based MIMO-OFDMA networks with soft frequency reuse

Abstract: Coordinated multi-point (CoMP) and soft frequency reuse (SFR) schemes are effective techniques to improve the performance of users located in the cell-edge, typically exhibiting very poor signal-to-interference plus noise ratios (SINR). While the optimization of CoMP and SFR is relatively straightforward in deployments where base stations (BSs) are regularly positioned, their use in networks with an irregular topology is far from trivial, specially since the operation of these two mechanisms is not independent. This work tackles the joint design of the CoMP and SFR parameters by proposing a two-step strategy: firstly, a clusterization stage is conducted that, taking into account the frequency reuse, leads to the formation of the cooperative clusters. Secondly, a subband allocation stage takes care of assigning frequency bands to the different clusters while trying to minimize intercluster interference (ICI). Simulation results serve to confirm the benefits of sensibly combining both interference cancellation techniques in realistic as well as idealized network topologies.

Non-Orthogonal Multiple Access with Multi-carrier Index Keying

Abstract: In this paper a novel transmission scheme that combines non-orthogonal multiple access (NOMA) and multi-carrier index keying (MCIK) is proposed. This scheme is proposed as a mechanism to enable multiple access for dense wireless device-to-device (D2D) systems that require high energy efficiency and effective interference management. The performance of the proposed scheme is analyzed in terms of the pairwise error probability (PEP) of user m. Novel closed-form expressions for the instantaneous and average pairwise error probability (PEP) over Rayleigh fading are derived. These expressions are used to investigate the detection performance of the proposed scheme over different configurations. Furthermore, a closed-form expression that approximates the overall average PEP is derived. This expression enables the performance analysis of NOMAMCIK within acceptable accuracy levels. The performance of the proposed scheme is assessed through numerical and simulation results.

Robust geometry-based user scheduling for large MIMO systems under realistic channel conditions

Abstract: The problem of user scheduling with reduced overhead of channel estimation in the uplink of Massive multiple-input multiple-output (MIMO) systems has been considered. A geometry-based stochastic channel model (GSCM), called the COST 2100 channel model has been used for realistic analysis of channels. In this paper, we propose a new user selection algorithm based on knowledge of the geometry of the service area and location of clusters, without having full channel state information (CSI) at the base station (BS). The multi-user link correlation in the GSCMs arises from the common clusters in the area. The throughput depends on the position of clusters in the GSCMs and users in the system. Simulation results show that although the BS does not require the channel information of all users, by the proposed geometry-based user scheduling algorithm the sum-rate of the system is only slightly less than the well-known greedy weight clique scheme. Finally, the robustness of the proposed algorithm to the inaccuracy of cluster localization is verified by the simulation results.

Modeling of Power Consumption by Wireless Transceivers for System Level Simulations

Abstract: The green communications concept becomes a leading paradigm in the design of modern communications systems. It requires accurate modeling of energy consumption in the wireless communications nodes to be used, e.g., for system level optimization, and this practical problem is addressed in the paper. The mean consumed power of a number of commercially available wireless transceivers has been measured and characterized as a function of throughput. This allows for realistic and simple energy consumption modeling by means of first-order polynomials.

A Coordination Architecture for Wireless Industrial Automation

Abstract: Wireless communication offers higher flexibility, and reduced deployment and maintenance costs compared to traditional fieldbus technologies for industrial automation applications. Unfortunately, existing wireless solutions are neither able to satisfy the communication nor the scalability requirements of realistic industrial automation deployments. In this paper, we propose a two-tier architecture for radio resource coordination and management to support mission-critical wireless communication and scalability in industrial automation scenarios. In particular, our architecture supports both exclusive spectrum and shared spectrum paradigms. It allows spectral interference mitigation among multiple radio cells as well as coexistence among different operating technologies in order to achieve the required high reliability and low latency communication. Furthermore, it entails the essential functionalities to achieve efficient and scalable radio resource coordination.

Reliable IoT storage for sensor monitoring applications: Trading off early redundancy injection costs and repair costs

Abstract: Providing reliable storage for sensor monitoring in IoT systems is key to manage nodes unavailability and lack of connectivity between the sensor devices and outside networks. Although reliable distributed storage systems typically assume that new devices are available to cope with disk, node or rack losses, this is not generally the case in monitoring systems. This paper proposes a data protection scheme based on network coding for monitoring networks that considers the cost of repair and the cost of setting up the initial protection for the data. We provide a theoretical characterization of the data protection problem with different operating regimes. We also analyze the mechanisms to trade-off network costs of the initial protection phase and the repair phases. Our numerical results show that a judicious choice between the preparation and repair phase costs can result in a reduction of protection cost as high as four times with respect to a naive selection, e.g., only focused on the repair costs.

Random Linear Network Coding Schemes for Reduced Zero-Padding Overhead: Complexity and Overhead Analysis

Abstract: The zero-padding overhead created when performing Random Linear Network Coding (RLNC) on unequal-sized packets can curb its promising benefits since it can be as high as the data to convey. The concept of macro-symbol coding was introduced recently in order to reduce the zero-padding overhead that RLNC has brought. Macro-symbols are subsets of the packets, i.e. concatenated bytes. They allow performing coding mainly on the payload and they proved to be efficient against the naive padding. This paper studies the properties of macro-symbols and provides a characterization of their impact on the computational complexity as well as the overall overhead. Furthermore, we provide a theoretical framework for the encoding and decoding complexity for the state-of-the-art schemes for unequal-sized packets. Our simulations results performed on a series of benchmark video traces show that small macro-symbols guarantee a dramatic reduction of padding overhead, whilst it results on a higher decoding complexity on the other hand compared with RLNC in the worst case.