EuCNC2016-TBeds&Exper 1570255548

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Integration of Broadcast and Broadband in LTE/SG (IMBS) -

Experimental Results From the eMBMS Testbeds

10 11 12 13 14 15 16 17 18 19

Thomas Heyn, Javier Morgade

Broadband and Broadcast Department Fraunhofer lIS, Erlangen, Germany

{flfstname.lastname}@iis.fraunhofer.de

Swen Petersen, Kerstin Pfaffinger

Network Technologies, Frequency Management Institut fuer Rundfunktechnik (IRT), Munich, Germany

{petersen, kerstin.pfaffinger}@irt.de

20 Abstract-This paper describes the results of the project "In-

21 tegration of Broadcast and Broadband in LTE/5G" (IMB5). The

IMB5 project explores the LTE-broadcast mode eMBMS within 22

two detailed single-frequency-network (SFN) field trial networks 23 in Erlangen and Munich, Germany and identifies potential im-24 provements of the current broadcasting feature within LTE to-

25 wards future releases of 4G and 5G. On the User Equipment

26 (UE) side, terminals from Qualcomm and Samsung based on

27 commercial chipsets have been used mainly for application layer

28 tests. For detailed physical layer tests, two different LTE soft-

29 ware-defined-radio platforms (one based on the OpenAirlnter-

face framework and one from National Instruments) have been 30 set up to support detailed field experiments with the existing and 31 future extended eMBMS beyond the state-of-the-art in LTE re-32 lease 12. On the application layer, it is shown in the project, that

33 using LTE eMBMS, a flexible service mix of unicast mobile

34 broadband and broadcast linear TV can be delivered. For coun-

35 try-wide deployment of eMBMS SFNs, physical layer waveform

36 modifications like an increased cyclic prefix compared to the

current LTE standard are recommended. 37 38 39 40 41

Keywords- eMBMS, MBSFN, LTE-Broadcast, 5G-Broadcast,

Test/acilities, Testbed, Field Trials, SDRplatform

I. INTRODUCTION 42 43 The IMB5 project consortium (IRT, Nokia Networks,

44 Fraunhofer lIS, University of Erlangen, Rohde & Schwarz, Bayerischer Rundfunk and BMW) explores how a future mo-

45 bile broadband standard could be defmed for the common 46 transmission of broadcast and mobile network services in a 47 technically and economically efficient manner. 48 49 Terrestrial broadcasting is deployed nowadays in Germany

50 by a nationwide ubiquitous network and supports stationary as well as portable and mobile reception of television programs.

51 At the same time, L TE has been deployed and is currently be-

52 ing densified in Germany and many other countries. 53 54 55 56 57 60 61 62 63 64 65

To enable broadcasters' content reception at any place and any time on any device (TV set, smartphone, tablet), a trans­mission technology that allows a common broadcast and cellu­lar radio standard would be highly beneficial. Especially for broadcasters, new applications arise with the introduction of

Ekkehard Lang

Nokia, Munich, Germany ekkehard.lang@nokia.com

Markus Hertlein, Georg Fischer

Institute for Electronics Engineering Friedrich-Alexander-University Erlangen-Nuremberg

Erlangen, Germany {flfstname.lastname} @fau.de

the LTE Broadcast Mode "eMBMS" (evolved Multimedia Broadcast Multicast Service). So far, it shares the same trans­mission parameters that are optimized for the needs of mobile unicast networks with inter-site distances of a few km. As a consequence, the usage of eMBMS according to the existing L TE standard Release 13 ([ 1], [2], [3]) is limited to local and regional implementations in the current deployments like in the US and South Korea. A converged network made up of large (High Tower - High Power transmitters) and small cells (Low Tower - Low Power transmitters) together with the return channel present in mobile networks enables new forms of inter­activity for broadcast stations and content providers, especially in conjunction with the touch screen, microphone and camera of a mobile device.

Existing literature provides mainly simulation results for the eMBMS system based on theoretical assumptions to esti­mate the spectral efficiency and coverage area (e.g. [4], [5], [6], [7]). However, current literature lacks on reporting of eMBMS experimental results either in commercial or experimental net­works. The aim of the IMB5 project is to explore the possibili­ties and limitations of Release 12 LTE eMBMS for different mixed network topologies (Low Tower and High Tower) in real experimental networks. Existing shortcomings of the standard to implement a ubiquitous television infrastructure are identified and ways to overcome them are shown. The project is structured into a theoretical and an experimental part.

The theoretical part of IMB5 comprises the set-up of prop­agation models and the simulation of the network coverage. By means of the experimental results in the eMBMS testbeds these propagation models could be verified against real measure­ments, so that they are able to create reliable predictions of the L TE eMBMS network performance. These provide sound rec­ommendations for the planning of eMBMS networks and for the further evolution of eMBMS in 3GPP for TV services. In the experimental part of the project, two field experiments are set up in the cities of Munich and Erlangen in Germany to vali­date current eMBMS capabilities. Both networks operate in MBSFN mode, the same single frequency network (SFN) prin­ciple used for broadcast standards (e.g. DVB-T / T2 and DAB / DAB+). The conclusions of the project provide a basis for the

design of a future integrated and converged unicast/broadcast/broadband network to combine the efficiency of broadcasting services with the flexibility and individuality of interactive mobile services in a single air interface.

This paper is organized as follows: Firstly, the established infrastructure of the testbeds in Munich and Erlangen are de­scribed. Secondly, the different types of testing and measure­ment devices on terminal side are introduced. Thirdly, initial trials results from the Munich trials network are compared with network simulations. The paper concludes with an outlook on future broadcast scenarios and required improvements of eMBMS towards 5G.

II. INFRASTRUCTURE OF EMBMS TESTBEDS

To enable eMBMS field trials in different network configu­rations, two complementary networks have been set up in the project, with transmitter heights ranging from 25 m to 217 m and different coverage areas (urban center, suburban, near­by/distant highways, rural areas). The inter-site distances of both networks are mostly higher than supported by the current cyclic prefix of eMBMS (16.7 f.!S, corresponding to 5 km).

The eMBMS testbed in Erlangen consists of two base sta­tion sites with 3 sector antennas each (cf. Fig. 1). The inter­site-distance between the sites is 5.3 km, interconnected by a fixed microwave link for the SI interface between eNodeB and Core network (cf. Fig. 2). The two sites in Erlangen are operat­ed in L TE band 17 (FDD, 704 to 709 MHz uplink, 734 to 739 MHz downlink). The eMBMS configuration in the network is using the standard 15 kHz carrier spacing, MBSFN mode with 16.67 f.!s cyclic prefix (CP) and the current maximum possible resource allocation of 60% of a frame for eMBMS. The trans­mit power of the eMBMS signal is 600 W EIRP per antenna. For the operation in MBSFN mode, the two eNodeBs in Erlan­gen are synchronized by the built-in GPS time reference.

Fig. 1. Topology of Erlangen eMBMS testbed comprising two transmitter sites with 3 sector antennas each. Indicated in the figure is the antenna height above ground

The testbed in Munich consists of a single base station con­nected to four sites with remote radio heads and antennas, which are interconnected by fiber optics (cf. Fig. 4). This archi­tecture was chosen to ensure a synchronization of all MBSFN

2

transmitters. One site (Freimann) is equipped with an omnidi­rectional antenna pattern and three sites with sector antennas. The inter-site-distance between the sites is in the range between 1.8 and 19.8 km (cf. Fig. 3). The four sites in Munich are oper­ated in LTE band 28 (FDD, 706 to 716 MHz uplink, 76 1 to 771 MHz downlink). The eMBMS configuration parameters in the network are identical to those in the Erlangen testbed. The transmit power of the network is 400 W EIRP per site/antenna.

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Fig. 3. Topology of Munich eMBMS testbed with 4 transmitter sites

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III. TESTING DEVICES

Within IMB5, different types of testing devices have been established for the evaluation of eMBMS on application- and physical-layer.

A. Chipset based Testing Platforms The Rohde & Schwarz drive-test software ROMES acts in

combination with the RF scanner TSMW to measure the signal coverage and identifies interference in the SFN. Furthermore, together with a smartphone, ROMES has been used to record Layer 1 to 3 parameters of the L TE Stack.

Two smartphone-based testing devices in the eMBMS testbeds have been used, the preliminary testing terminals Qualcomm MTP-8974AB as well as the commercially availa­ble smartphone Samsung Galaxy SM-G900K S5 that is pre­pared for the use of the commercial South-Korean eMBMS service. Both terminal types are equipped with an eMBMS application developed in-house, which is based on Android and provides a Hybrid Broadcast Broadband TV (HbbTV) look­and-feel. This application allows the toggling between broad­cast and unicast services (Fig. 5).

Fig. 5. Samsung Galaxy S5 with HbbTV-like app for linear/non-linear TV consumption

B. SDR Testing Platforms Beyond the detailed tests on application and physical layer

with the existing eMBMS standard, an additional aim of the IMB5 project is to test physical layer waveform extensions to improve the existing eMBMS standard (e.g. an extension of the cyclic prefix length, implying the change of the FFT length in the demodulator). However as this is not possible with UE de­vices based on commercial L TE chipsets, software-defined­radio (SDR) platforms are used instead. SDR platforms allow full access to the source code and modifications which deviate from the already implemented, standardized transmission sys­tem of today. Since no SDR platform supporting eMBMS re­ception from commercial eNodeBs existed on the UE side, two candidate platforms (to minimize the risk within the project) were chosen for applying the necessary modifications: Firstly, the open source LTE stack from OpenAirlnterface (OAI) [8] has been extended to enable eMBMS field trials with the base stations from Nokia as used in the two trial networks. Second­ly, the SDR platform from National Instruments has been em­ployed. Both SDR platforms are described in the following.

The first SDR UE within the IMB5 project is based on OpenAirInterface which is intended to support real-time SDR testing of the 4th and 5th generation of 3GPP systems. It is

3

worth to mention that eMBMS compatible system level simu­lations have already been introduced in [9], presenting an OAI based eMBMS emulation environment including a preliminary PMCH implementation for a basic eNodeB and UE. In [9], the theoretical performance of OAI has been compared against the standard requirements. Nevertheless, besides providing a soft­ware-based link-level simulation environment, OAI is compat­ible with custom-of-the-shelf hardware components, providing the ability to develop in-lab and field test real-time RF experi­ments. OAI is compatible with several SDR platforms availa­ble in the market, where among others, the expressMIM02 and National Instruments' (NI) USRP-B21O boards are being wide­ly used for different testing scenarios. Therefore, any custom implementation based on OAI could be potentially used to tar­get a variety of real time applications, hardware platforms and experiments. Within IMB5, a fully 3GPP Release 10 eMBMS compliant implementation on the UE side has been developed. Based on OAI, all related eMBMS procedures on PHY, MAC, RLC, PDCP and RRC layer have been implemented and tested against the two testbeds in IMB5 as described in chapter II. Additionally, in case of the real-time protocol (RTP), a real time video orchestrator has been implemented on top of the PDCP layer, such that in addition to the common quality-of­service (QoS) parameters as defined in the LTE specification, subjective video quality can be evaluated. Fig. 6 presents a real time RTP decoding using a regular laptop where the OAI based eMBMS stack is implemented. Using an NI B210 USRP as SDR backend, the system allows decoding an over-the-air eMBMS bearer in real time.

The second SDR UE within the IMB5 project is based on the NI hardware platforms and software tools (Fig. 7). The hardware components are part of the Embedded Wireless Lab (EWL) [10]. Two different hardware modules are used: Firstly, a powerful FlexRIO module in combination with an RF receiv­er adapter module supporting continuous frequency range from 200 MHz to 4.4 GHz and 200 MHz instantaneous bandwidth in a PXI system [11]. Secondly, a more flexible NI USRP RIO platform with a tunable frequency range of 0.4 to 4.4 GHz and 40 MHz instantaneous bandwidth [12] is used. Both systems feature digital signal processing on Xilinx Kintex-7 FPGA, having the advantage to run the same software code on both platforms without any additional changes. NI delivers the L TE application framework as software platform in the LabVIEW Communications System Design Suite. The Framework pro­vides parts of an L TE release 10 compliant physical as well as medium access control layers. For research purposes, it is im­portant to note that source code is delivered entirely open and modifiable to prototype advanced features based on the L TE standard. LabVIEW Communications is not limited to Lab­VIEW code, so implementation in other languages like matlab or C code is supported. The existing L TE framework needs approximately half of the FPGA resources, so there are suffi­cient resources for further modules and waveform modifica­tions. To receive eMBMS signals, the existing implementation of the NI framework has been modified within the project and further parts like the Secondary Synchronization Signal (SSS), MBSFN reference signal, Physical Broadcast Channel (PBCH) and Physical Multicast Channel (PMCH) [13] have been im­plemented. All settings and results of the SDR platform can be presented on the host front panel.

Fig. 6. SDR platform based on OpenAirInterface, enabling detailed eMBMS and unicast signal analysis

Fig. 7. SDR platform from National Instruments

IV. TRIALS RESULTS

The trials in Munich provide results in the areas of use cas­es and quantitative measurements.

Different L TE Broadcast use case demos have been created within the project. It has been shown that the existing eMBMS standard on application layer is able to provide an end user video experience in high quality not only on smartphones, but also on large TV screens. The demos proved the ability of eMBMS to watch TV on the smartphone and to toggle between TV service and on-demand or Internet services.

The field trials' main target was to quantify the perfor­mance and coverage of the L TE Broadcast service in the net­work by means of measurement equipment from Rohde & Schwarz. Extensive drive tests with RF scanners were per­formed to measure Reference Signal Received Power (RSRP), signal to interference plus noise ratio (SINR) and to determine areas of SFN gains and losses. The comparison of the quantita­tive drive test results with simulated network performance and coverage data allowed the verification of the theoretical model. These generated network planning models have several uses:

Applied to real operator networks, the models allow for a reliable coverage prediction during the eMBMS network planning process.

The L TE Broadcast network planning models provide means to evaluate the possible options for the further evolution of the LTE Broadcast standard and to optimize the LTE Broad­cast protocol for SFN operation by identifying parameters, which need to be optimized in the standard regarding a nation­wide TV distribution.

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Fig. 8 shows the simulated coverage obtained in the test ar­ea with the L TE system of today based on a cyclic prefix of 16.7 f..ls. The coverage map is created by means of the simula­tion tool Fransy [14]. The IRT-2D model applied for these simulations takes into account topographical and clutter data to predict the coverage probability as well as the received field strength. The simulations are based on the characteristics of the test receiver, assuming a required minimum SINR of 11 dB. Fig. 9 visualizes the prediction of the improved eMBMS cov­erage area, if a CP of 66.7 f..lS would be used. There is still a coverage hole located in the middle of the coverage area caused by areas with high density buildings in Ismaning. It has to be noted that the CP value of 33.3 f..ls is currently partly standardized in the LTE standard (Release 12) and the CP val­ue of 66.6 f..ls is not yet standardized. In the network topology of the Munich testbed, which is in-between a classical broad­cast network and a typical mobile network, higher values of the CP increase the coverage area. A simulation with a CP of 33.3 f..lS indicates areas, especially in the middle region of the map, with a significant increase of coverage. A further improvement of the coverage is achieved when using the extended CP of 66.7 f..ls. For this particular network topology in Munich and receiving conditions, the predicted coverage area increases (for a coverage probability of 95%) are 265% and 467% for the CP lengths of 33.3 f..lS and 66.7 f..lS respectively, compared to the achieved coverage area for a CP of 16.7 f..ls. Therefore, one of the project results is a recommendation towards 3GPP to standardize a CP higher than 16.7 f..ls.

To validate the above mentioned coverage simulations, measurement results from the testbed have been compared to the simulation results. The Rohde & Schwarz measurement software ROMES in combination with the TSMW RF scanner and a single measurement antenna with omnidirectional pattern (Schwarzbeck RSH 4786) was used to perform drive test in two different routes, the so called northern route (length 55. 1 km) and downtown route of Munich (length 22. 1 km). The recorded key parameters were: RSRP/field strength, SINR and delay spread/multipath fading.

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Fig. 9. : eMBMS coverage of Munich testbed with increased CP of 66,7 J.lS

The next two figures show the measured SINR along the northern route, individually for the received signals from single transmitters in unicast operation mode (Fig. 10) as well as for the combination (MBSFN operation, Fig. 11). Within some regions, the accumulated eMBMS SINR values in MBSFN operation mode indicate improvements compared to the indi­vidual SINR values of the four sites in unicast operation mode, but as well some degraded areas. The next step after measuring SINR has been the comparison of the measured values against the simulation in MBSFN mode. The result for the SINR com­parison along the northern route is given in Fig. 12. Within a certain tolerance the simulated (yellow line) and measured SINR (blue line) matches quite well. Differences due to fading effects are unavoidable since the applied clutter data is not as detailed as the real scenery. This is particularly true for urban environment. Therefore, the difference between simulated and measured SINR along the downtown route (Fig. 13) is even larger than along the northern route. High-resolution clutter data and specific building information are indispensable for precise prediction, since it will enable the consideration of all relevant objects concerning reflections and diffractions within the simulation. In the last third of the downtown route, a large deviation is visible. After taking a closer look into the meas­urement file and the city map, the discrepancy has been identi­fied to the location of a tunnel not considered in the simulation.

Nevertheless, the measurements along the northern route in Munich indicate that the IRT-2D model provides valid simula­tion results of eMBMS networks with a CP of 16.7 f.1s. As a conclusion, the simulation for higher CP values can be used as well to predict the coverage area and probability with sufficient accuracy. For field strength predictions, all signals arriving within the CP are taken into account as cumulative useful field strength. The improvement for the field strength due to higher values of CP is small in this particular network constellation, and the SINR improvement due to the extended CP is more significant. The SINR takes into account also interfering sig­nals arriving outside the CP, representing self-interference ef­fects within the MBSFN. Fig. 12 and Fig. 13 demonstrate clearly the benefit of the extended CPs concerning the SINR.

5

Fig. 10. Received SINR values of each site along the northern route

Fig. 11. Accumulated eMBMS SINR values (MBSFN operation) of the drive test along the northern route

Fig. 12. Measured and simulated SINR - northern route in Munich

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Fig. 13. Measured and simulated SINR - downtown route in Munich

V. CONCLUSIONS AND OUTLOOK

5()()()()

Two eMBMS trial networks have been established in Ba­varia, Germany, together with two eMBMS-enabled SDR plat­forms on the UE side. The testbeds allow the evaluation of the existing eMBMS standard as well as of eMBMS enhancements in the field prior to standardization in 3GPP and availability of commercial UEs. Updates of the SDR UE and base station platforms allow to experiment with the planned eMBMS wave­form enhancements like a longer cyclic prefix and support of a standalone carrier according to the 3GPP Work item descrip­tion [16]. This paper reported on the trials results focusing on the comparison between network coverage simulation and field measurement data. Further papers will present experimental result from the trials in the Erlangen testbed, focusing on the detailed analysis of the eMBMS streaming and file transfer quality in pedestrian and vehicular reception scenarios, requir­ing the SDR platforms as described in section III. Especially for the vehicular case, single antenna (as performed in the Mu­nich network) and multi antenna configurations using Maxi­mum Ratio Combining (MRC) are evaluated.

The use case demonstrations proved the ability of eMBMS to watch TV on the smartphone and thus the offer of connected TV or HbbTV can be provided on the same end user device via the same distribution channels. In addition, the smartphone can serve as a set-top-box when casting content to a TV set, which is supported by almost any smartphone via Wi-Fi or cabling. This leads to the improved situation that TV distribution tech­nology advances will not be as challenging as they are today, when each new DTT release needs significant backing from device makers to support it in their set-top-boxes and TV sets. Smartphones have much shorter innovation cycles and there­fore support for evolved standards can be provided much quicker to large audiences. The fmding that the smartphone can evolve into a mobile TV set and an intelligent remote control with integrated set top box functionality for large TV sets, all at the same time, leads to significantly improved user experience and shorter innovation cycles in TV distribution technology.

On the long term, when using 4G/5G broadcast transmis­sions in SFN mode for a nationwide service, higher inter-site distances of the transmitter networks than in typical mobile broadband networks are likely, e.g. due to the reuse of existing DVB-T(2) infrastructure with typical inter-site distances within the SFN networks ranging from 30 to 80 km. As a conse­quence, LTE eMBMS (as well as the new 5G air interface be-

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low 6 GHz as currently examined in the European H2020 pro­ject Fantastic-5G [15]) should be specified in a way to allow more flexibility with respect to the waveform transmission parameters like cyclic prefix configuration. This flexibility should allow higher CP durations than in the existing L TE specification, longer FEC code block length and physical layer time interleaving. A research topic beyond the IMB5 project is the evaluation of future dynamic broadcast/unicast mechanisms to optimize the time/frequency resources in a cell for other services than multimedia distribution, e.g. the distribution of real time traffic information to autonomous cars in vehicle-to­X (V2X) scenarios. Another application for eMBMS is possi­ble, where audiovisual content can be distributed locally during a large event like a concert. These scenarios can be evaluated in detailed trials as well, since the testbeds cover various prop­agation environments like highway and dense urban areas.

ACKNOWLEDGMENT

The IMB5 consortium wants to thank the Bavarian Re­search Foundation [17] for supporting this research through the IMB5 project.

REFERENCES

[I] 3GPP TS 36.300, 'Evolved Universal Terrestrial Radio Access and Evolved Universal Terrestrial Radio Access Network;Overall description; Stage 2 (Release 13)', V13.3.0, 2016-03

[2] 3GPP TS 36.211, 'Evolved Universal Terrestrial Radio Access; Physical channels and modulation (Release 13)', VI3.0.0, 2015-12

[3] 3GPP TS 26.346, 'Multimedia BroadcastiMulticast Service (MBMS); Protocols and codecs (Release 13), V13.3.0, 2015-12

[4] 1. Huschke, "Facilitating Convergence between Broadcasting and Mobile Services using LTE networks", p.123-128, Technical Symposium at lTU Telecom World, 2013

[5] G. Kent Walker, Jun Wang, Charles Lo, Xiaoxia Zhang, and Gang Bao, "Relationship Between L TE BroadcastieMBMS and Next Generation Broadcast Television", IEEE Transactions on Broadcasting, Vol. 60, No.2, June 2014

[6] EBU, "Delivery of Broadcast Content over LTE Networks", Technical Report TR 027, Geneva, July 2014

[7] A. Awada, M. Sfiily, and L. Kuru, "Design and performance impact of long cyclic prefixes for eMBMS in L TE networks", accepted in IEEE Wireless Communications and Networking Conference (WCNC), April 2016, unpublished

[8] OpenAirAlliance, www.openairalliance.org

[9] Ngoc-Duy Nguyen, Raymond Knopp, Navid Nikaein, Christian Bonnet., "Implementation and Validation of Multimedia Broadcast Multicast Service for L TElL TE-Advanced in OpenAirlnterface Platform", IEEE 38th Conference on Local Computer Networks Workshops (LCN Workshops), Sydney, October 2013

[10] Embedded Wireless Labs (EWL), http://ewJ.techfak.uni-erlangen.de/

[II] N15792, http://sine.ni.com/nips/cds/view/p/langlenlnid/211686

[12] USRO-2942R http://sine.ni.com/nips/cds/view/p/langlen/nid/213001

[13] LTE Framework, http://www.ni.com/white-paper/52524/en/

[14] IRT, FRANSY network planning tool, https://www. irLde/en/activities/programme-distributionifrequency­planning-software.html

[15] H2020 project "flexible air interface for scalable service delivery within wireless communication networks of the 5th Generation", http://fantastic5g.eu/

[16] Work item description "eMBMS enhancements for LTE", RP-160675, ftp://ftp.3gpp.org

[17] Bavarian Research Foundation, http://www.forschungsstiftung.de

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