Radio channel modelling for 5G telecommunication system evaluation and over the air testing

Abstract This thesis discusses radio channel modelling for evolving radio access and of using the models in practice in a setup for radiated testing of radio devices. New telecommunication systems are constantly being developed to address continuously increasing wireless communication needs. The first pieces of intensively developed fifth generation (5G) networks and devices are planned to be available, in some form, approximately by 2020. An interesting feature of 5G concerning propagation and consequently channel modelling, is the expected utilization of frequencies clearly higher than the legacy cellular systems. This work aims to define a channel model for the simulated evaluation of the coming 5G systems. New requirements for the channel model are identified and addressed. Further, over the air (OTA) testing of 5G devices in fading conditions is examined and a new setup is proposed. The test environment aims to reconstruct a time variant electromagnetic (EM) field around a device under test (DUT) considering the spatial, polarimetric, Doppler, and delay dispersion characteristics specified by the target channel model. Components and key design parameters of the setup are designated. It was found that the proposed map-based channel model is capable of fulfilling the identified requirements. Furthermore, the simulations indicate that the state-of-the-art geometry-based stochastic channel model (GSCM) may give over-optimistic multi-user MIMO (MU-MIMO) performance in an urban micro-cellular environment. The sectored OTA concept was shown appropriate for device testing. Key parameters, such as the physical dimensions of the multi-probe anechoic chamber (MPAC) OTA configuration and the number of active probes, were determined by simulations. The 3GPP is the main forum working towards 5G standards. A channel model for 5G evaluations has recently (2016) been specified. The base-line model is a GSCM inherited from the 4G models. However, the author expects that the proposed map-based models will gain popularity in the future, despite the current widespread use of GSCMs. In the 3GPP working group RAN4 (Radio performance and protocol aspects) the test methods for 5G user equipment (UE) are currently (2017) under investigation. The proposed sectored MPAC method has been contributed to and is under consideration in 3GPP. Even if it is not approved for UE testing, the author expects it to be useful for performance testing of base stations (BSs).Tiivistelmä Tämän väitöskirjan sisältönä on radiokanavamallinnus langattomia tiedonsiirtojärjestelmiä varten ja lisäksi mallien käyttöönottoa tulevien radiolaitteiden säteilevässä testauksessa. Uusia tietoliikennejärjestelmiä kehitetään jatkuvasti, yhtä lailla jatkuvasti kasvavien tiedonsiirtotarpeiden tyydyttämiseksi. Ensimmäisten verkkojen ja päätelaitteiden pitäisi olla saatavilla tulevaan viidennen sukupolven (5G) järjestelmään vuoden 2020 tietämillä. Työn tarkoituksena on määritellä kanavamalli 5G-järjestelmän simulointeja varten ja sitä edeltäen tunnistaa kanavamallin vaatimukset. Lisäksi tutkimuksen aiheena on 5G-laitteiden säteilevä (OTA) testaus häipyvässä radiokanavassa ja uuden testijärjestelmän määrittely tätä tarkoitusta varten. Ehdotetun testijärjestelmän keskeisenä toimintona on halutun sähkömagneettisen (EM) kentän tuottaminen testattavan laitteen ympärille. EM-kentän pitää olla kanavamallin mukainen ja toteuttaa sen häipymä-, tila-, polarisaatio-, doppler- ja viiveominaisuudet. Testijärjestelmän komponentit ja tärkeimmän suunnitteluparametrit pyritään selvittämään tässä työssä. Tutkimuksessa havaittiin, että ehdotettu karttapohjainen kanavamalli toteuttaa 5G-mallille asetetut vaatimukset. Simuloinnit osoittavat myös, että tyypillisessä kaupunkiympäristössä suosittu GSCM-malli yliarvioi kanavan kapasiteetin monen käyttäjän MIMO-tekniikka käytettäessä. Lisäksi osoitettiin sektoroidun OTA-järjestelmän, jossa hyödynnetään useita antenneja, radiokanavaemulaattoria sekä radiokaiutonta huonetta (MPAC), käyttökelpoisuus 5G-laitteiden testaukseen. Kyseisen testausjärjestelmän parametrit määriteltiin. 3GPP on tärkein foorumi, jolla 5G-standardeja luodaan. Siellä on hiljattain (2016) sovittu 5G-simulointeja varten kanavamalli, joka ei ole tässä työssä ehdotetun kaltainen. Standardoitu malli on tyypiltään GSCM ja se on johdettu suoraan edellisen sukupolven (4G) kanavamallista. Kirjoittaja olettaa tästä GSCM:n nykyisestä vahvasta asemasta huolimatta, että ehdotettu karttapohjainen kanavamalli lisää suosiotaan tulevaisuudessa. Parhaillaan (2017) on 3GPP:n RAN4-työryhmässä käynnissä 5G-päätelaitteiden (UE) testimenetelmien määrittelyvaihe. Väitöskirjassa tutkittua sektoroitua MPAC-menetelmää on ehdotettu työryhmälle standardoitavaksi. Vaikka mainittua menetelmää ei siellä standardoitaisikaan UE-testaukseen, niin voidaan olettaa menetelmän olevan hyödyllinen erityisesti tukiasemien säteilevään testaukseen

Correlation of hybrid beamforming arrays in the context of OTA testing

Abstract Hybrid beamforming antenna arrays are a prominent component in communications at mm-wave frequencies. Multiple analogue beamforming arrays will be used for spatial multiplexing of signals also in hand held devices. In this work we derive the correlation coefficient for signals received by two ideal arrays in simple power angular distribution schemes. The purpose is to develop tools for evaluating over-the-air setups for testing of hybrid beamforming devices. We show a few exemplary correlation error evaluations that compare near field multi-probe OTA setups with a perfect target channel model. Results indicate that the correlation error increases with decreasing range length and channel angular spread. Moreover, larger inter-array spacing and sub-array sizes increase the correlation error

Fading channel emulation for massive MIMO testing using a conductive phase matrix setup

Abstract Functionalities, algorithms, and performances of massive MIMO base stations should be tested in versatile fading radio channel conditions. Base stations of 5G “New radio” that operate on sub 6 GHz frequency bands typically provide antenna connectors enabling RF cable connection of test devices to the device under test (DUT). Furthermore, the number of DUT antennas is high and consequently the need of fading channel emulator (CE) resources becomes high. An approach can be taken to reduce the number of independent fading channels to be emulated. This can be done by using a phase shifting and combining unit (aka phase matrix unit) in between the DUT and CE. The phase matrix concept in fading emulation, together with its capabilities and limitations, is discussed in this paper

Assessing measurement distances for OTA testing of massive MIMO base station at 28 GHz

AbstractThis paper discusses physical dimensions for a multi probe anechoic chamber based (MPAC) over-the-air (OTA) setup aiming for base station (BS) testing. The target frequency of the simulated massive multiple-input-multiple-output (MIMO) BS arrays is 28 GHz. The assessment is performed with two metrics. The first metric is a new power metric based on assumptions of a code book of fixed beams and planar waves. The second one is the multi-user (MU) MIMO sum rate capacity. The intention is to evaluate physical dimensions in metres with respect to different BS array sizes. Simulation results indicate that OTA performance of a BS array with maximum dimension of 0.15m could be measured with a setup having measurement distance of approximately 1m

Sub-terahertz channel sounder:review and future challenges

Abstract Due to the large amount of unused and unexplored spectrum resources, the so-called sub-Terahertz (sub-THz) frequency bands from 100 to 300 GHz are seen as promising bands for the next generation of wireless communication systems. Channel modeling at sub-THz bands is essential for the design and deployment of future wireless communication systems. Channel measurement is a widely adopted method to obtain channel characteristics and establish mathematical channel models. Channel measurements depend on the design and construction of channel sounders. Thus, reliable channel sounding techniques and accurate channel measurements are required. In this paper, the requirements of an ideal channel sounder are discussed and the main channel sounding techniques are described for the sub-THz frequency bands. The state-of-the-art sub-THz channel sounders reported in the literature and respective channel measurements are presented. Moreover, a vector network analyzer (VNA) based channel sounder, which supports frequency bands from 220 to 330 GHz is presented and its performance capability and limitation are evaluated. This paper also discussed the challenge and future outlook of the sub-THz channel sounders and measurements

Spatial fading channel emulation for over-the-air testing of millimeter-wave radios:concepts and experimental validations

Abstract Millimeter-wave (mmWave) communication is regarded as the key enabling component for fifth-generation (5G) cellular systems due to the large available spectrum bandwidth. To make mmWave new radio (NR) a reality, tremendous efforts have been exerted from the industry and academia. Performance evaluation of mmWave NR is a mandatory step and the key to ensuring the success of mmWave 5G deployment. Over-the-air (OTA) radiated method of testing mmWave NR in laboratory conditions is highly attractive, since it facilitates virtual field testing of mmWave devices in realistic propagation conditions. In this paper, we first discuss the need for and challenges in OTA measurement of mmWave 5G NR under fading channel conditions. After that, two promising candidate solutions, i.e., wireless cable and multi-probe anechoic chamber (MPAC), are detailed. Their principles, applicability for mmWave NR, and main challenges are discussed. Furthermore, preliminary experimental validation results in a frequency range 2 anechoic chamber are demonstrated for the wireless cable and MPAC methods at 28 GHz

Sub-THz VNA-based channel sounder structure and channel measurements at 100 and 300 GHz

Abstract Sub-THz, i.e. frequency range 100 ‐ 300 GHz, frequency bands have attracted huge interest in recent years for beyond 5G communication and high data-rate applications, due to its large available frequency bandwidth. In this work, we presented two vector network analyzer (VNA) based channel sounder systems, operating at the frequency range of 75‐GHz and 220‐330 GHz, respectively. The focus is on the channel sounder structure, link budget as well as system calibration performance. Moreover, we presented a simple wideband directional measurement in a rich scattering laboratory scenario with the two discussed channel sounders. The results showed that similar dominant multipath components (MPCs) can be observed in the two frequency bands, yet many more weak MPCs can be seen at 100 GHz, compared to results at 300 GHz

Millimeter-wave new radio test zone validation for MIMO over-the-air testing

Abstract Standardization efforts to define radiated metrics and test methods for verifying millimeter-wave (mmWave) new radio (NR) devices are currently ongoing. Multi-probe anechoic chamber (MPAC) method, which is capable of reproducing spatial fading channels in the test zone, is selected as the reference solution for NR device testing. It is of importance to ensure that the defined testing propagation environment in the test zone is correctly implemented. In this paper, a novel algorithm is proposed to determine the wideband power-angle-delay profile of the reconstructed channels in the test zone for mmWave NR. The proposed algorithm is shown to be generic (applicable for both 2D and 3D testing setup), applicable for both near-field and far-field conditions and robust (i.e. insensitive to measurement distance errors)

Multiple-screen diffraction measurement at 10-18 GHz

Abstract This letter presents analysis of diffraction over multiple shadowing screens at frequency range of 10–18 GHz. Up to ten pieces of thin metal sheets with dimensions of 130 × 100 cm at variable spacing were used as diffraction screens. The aim of this study is to investigate the total shadowing effect of multiple knife-edge diffractions at frequencies above the legacy cellular systems. The results show the necessity to adjust the Walfisch-Bertoni path loss model for the higher frequencies in the future fifth-generation systems

Map-based channel model for evaluation of 5G wireless communication Sytems

Abstract This paper presents a channel model for the fifth generation (5G) air interface evaluations. The described model covers frequency bands from typical cellular frequencies up to millimetre waves and a variety of different environments, with emphasis on the urban outdoor. The model enables assessment of single radio links with, e.g., the massive multiple-input-multipleoutput (MIMO) and very large antenna arrays, device-to-device (D2D) links with both link ends moving, up to system level evaluations with a multitude of different types of transceivers. In addition to the overview some selected model features are described in more detail. Also few exemplary model outputs are depicted and discussed. A comparison to corresponding geometry based stochastic model (GSCM) is performed in urban outdoor environment with the second moment distributions of propagation parameters and with the multi-user (MU) MIMO sum rate capacity. The simulations indicate substantial differences in MU-MIMO performances between the models