Waveforms for sub-THz 6G: Design Guidelines

The projected sub-THz (100 - 300 GHz) part of the upcoming 6G standard will require a careful design of the waveform and choice of slot structure. Not only that the design of the physical layer for 6G will be driven by ambitious system performance requirements, but also hardware limitations, specific to sub-THz frequencies, pose a fundamental design constraint for the waveform. In this contribution, general guidelines for the waveform design are given, together with a non-exhaustive list of exemplary waveforms that can be used to meet the design requirements.Comment: Paper presented at EuCNC 2023, June 6-9 2023, Gothenburg, Swede

Towards versatile access networks (Chapter 3)

Compared to its previous generations, the 5th generation (5G) cellular network features an additional type of densification, i.e., a large number of active antennas per access point (AP) can be deployed. This technique is known as massive multipleinput multiple-output (mMIMO) [1]. Meanwhile, multiple-input multiple-output (MIMO) evolution, e.g., in channel state information (CSI) enhancement, and also on the study of a larger number of orthogonal demodulation reference signal (DMRS) ports for MU-MIMO, was one of the Release 18 of 3rd generation partnership project (3GPP Rel-18) work item. This release (3GPP Rel-18) package approval, in the fourth quarter of 2021, marked the start of the 5G Advanced evolution in 3GPP. The other items in 3GPP Rel-18 are to study and add functionality in the areas of network energy savings, coverage, mobility support, multicast broadcast services, and positionin

Virtual antenna array based MIMO radio channel measurement system at 10 GHz

In this thesis, a 10 GHz multiple-input multiple-output radio channel measurement system using four port vector network analyzer and virtual antenna arrays in both transmitter and receiver ends is presented. The channel measurement system measures each single antenna channel separately. The radio propagation environment is assumed to be static during the recordings. As an antenna element, a dual polarized patch antenna with two feeding ports is used. Linear stages and programmable stepper motors are utilized to build an XY-gantry to move the antenna element in a plane. The stepper motors and the vector network analyzer are controlled by the same measurement control software. The basic principles of the control software are also presented along the measurement system. Three channel measurement scenarios and their initial results are presented to verify the system operation and to demonstrate the system in different cases. A verification measurement is performed in an anechoic chamber to verify that the system does not cause internal spurious responses to the results. The next measurement is performed in a classroom to demonstrate the multipath propagation environment. Furthermore, an indoor wall penetration loss measurement from the classroom to another is made to show that the measurement system can also be applied for the measurements requiring an accurate antenna shifting between the measurement points. The results measured with this setup can be applied angular domain algorithms to estimate the direction of arrival and departure, respectively.Tämä diplomityö esittelee moniantenniradiokanavan mittausjärjestelmän, jossa mittauslaitteena käytetään vektoripiirianalysaattoria ja kahta virtuaalista tasoantenniryhmää. Järjestelmä mittaa jokaisen antennielementin välisen kanavan erikseen. Etenemisympäristö on oletettu staattiseksi radiokanavan tallennuksen aikana. Antennielementtinä käytetään kaksoispolaroitua mikroliuska-antennia, jossa on omat syöttöportit molemmille ortogonaalisille lineaarisille polarisaatioille. Antennielementtiä siirretään tasossa käyttämällä ohjelmoitavia askelmoottoreita ja lineaariyksiköitä. Kaikkia mittausjärjestelmän laitteita ohjataan samalla ohjausohjelmistolla, jonka toimintaperiaate on myös esitetty tässä työssä. Mittausjärjestelmän toiminta varmistetaan ja sitä demonstroidaan suorittamalla kanavamittauksia erilaisissa etenemisympäristöissä. Varmennusmittaukset suoritetaan kaiuttomassa huoneessa, jotta voidaan varmistua siitä, ettei järjestelmä tuota sisäisiä harhatoistoja, jotka vaikuttaisivat mittaustuloksiin. Monitie-etenemisympäristöä demonstroidaan kanavamittauksilla luokkahuoneessa. Myös luokkahuoneiden välistä etenemisvaimennusta mitataan. Mittaustuloksia voidaan käyttää muodostettaessa erilaisia radiokanavamalleja ja niitä voidaan soveltaa myös aallon tulo- ja lähtökulman estimointiin käyttämällä siihen tarkoitettuja algoritmeja

Concepts for radiated nonlinear distortion and spatial linearization in millimeter-wave phased arrays

Abstract This thesis presents concepts for understanding and utilizing the spatial behavior of nonlinear distortion in a millimeter-wave (mmW) multi-antenna transmitter. The work begins with an approach for radio frequency (RF) link budget and performance evaluation in a multiple-input multiple-output (MIMO) system. In the approach, the radio channel is decomposed into independent MIMO channels whose link budgets are analyzed independently using power dependent nonideal models of RF transceivers. The nonlinear distortion caused by RF power amplifiers (PAs) is studied in phased array systems that use analog beamforming. In particular, the focus is on the scenarios in which also the amplitudes of individual paths are controlled to shape the beam pattern. The differences in the nonlinear behavior of the individual paths make the beams of the signal and the distortion differ from each other. This observation is important to consider when specifying the transmitter error vector magnitude (EVM) and adjacent channel power ratio (ACPR) with over-the-air measurements. In phased array systems, multiple PAs share the same digital input and hence the PA linearization by digital predistortion (DPD) turns into an array linearization problem. The linearization of such an array can be performed by modeling, emulating, or measuring the transmitter radiated response in various ways. In particular, this thesis discusses different conductive and radiated feedback receiver approaches and proposes procedures for training the DPD objective based on the measurements. Linearizing the array in the main lobe does not mean linearization of individual PAs if the transmit paths differ from each other. In such scenarios, it is shown that linearizing the signal in the main lobe creates a notch in the training direction that is a result of OTA combining different nonlinear components. This is shown to make a tradeoff between the EVM characterized in the steering angle and ACPR integrated over the sphere. It is proposed that such a problem can be tackled by modifying the nonlinearity of individual paths by PA bias control to make the distortion of individual paths more similar. This is shown to simplify the DPD trained in a certain steering angle to be effective also in other directions thus linearizing both EVM and total radiated ACPR of the array while achieving decent power efficiency.Tiivistelmä Tässä väitöskirjatyössä esitetään menetelmiä korkean taajuuden moniantennijärjestelmän epälineaarisen vääristymän tilatason käyttäytymisen ymmärtämiseksi ja hyödyntämiseksi. Työn alkuosa käsittelee radiojärjestelmän linkkibudjettia tavalla, joka yhdistää monikeilalähetyksen ja radiokanavamallin radiolähettimen ja -vastaanottimen käyttäytymismalleihin. Loppuosa työstä keskittyy tarkastelemaan tehovahvistimista aiheutuvaa epälineaarista häiriötä vaiheistetuissa keilanmuodostusjärjestelmissä. Työssä havaitaan erojen lähetinhaarojen epälineaarisessa käyttäytymisessä luovan eroja halutun lineaarisen signaalin keilan sekä häiriön keilan välille. Tämän johdosta häiriö voi antennien avulla säteillessään muodostaa erilaisen säteilykuvion kuin lähetetty signaali. Tämä havainto on erityisen tärkeä ymmärtää, kun muodostetaan säteilevän viereisen kaistan epälineaarisen häiriön sekä signaalin virhevektorin järjestelmätason vaatimuksia moniantennilähettimille. Ilmiötä voidaan myös hyödyntää lähettimen linearisoinnissa. Vaiheistetuissa ryhmissä useat antennikohtaiset tehovahvistimet jakavat yhden yhteisen tulon, jota voidaan digitaalisesti esivääristää. Tällaisissa ryhmissä lähettimen digitaalinen esivääristys (DPD) muuttuu säteilevän keilan esivääristämiseksi, joka sisältää myös antennit sekä niiden tilatason summausvaikutuksen. Ryhmän linearisointi voidaan suorittaa käsittelemällä koko lähetinryhmää yhtenä epälineaarisena komponenttina. Työssä esitetään erilaisia havainnointivastaanotinstrategioita sekä menetelmiä DPD-objektin muodostamiseksi hyödyntäen ryhmästä eri suuntiin säteilevän aaltomuodon mallinnusta ja mittauksia. Työssä huomataan, että lähettimen linearisointi tietyssä suunnassa ei takaa linearisointia muissa suunnissa, jos haarojen epälineaariset käyttäytymiset eroavat toisistaan. Tällöin yhden suunnan linearisointi muodostaa minimin häiriölle halutussa suunnassa summaamalla epälineaarisia komponentteja tilatasossa. Tällaisissa tapauksissa haarojen epälineaarisuutta voidaan analogisesti muokata esimerkiksi tehovahvistimien toimintapisteitä muuttamalla siten, että niiden epälineaarisuus muuttuu samankaltaiseksi. Työssä näytetään simuloinnein ja mittauksin, että tällöin yhden suunnan linearisoinnilla voidaan saavuttaa lineaarinen lähtösignaali kaikissa suunnissa hyvällä hyötysuhteella tapauksissa missä tehovahvistimien lähtöamplitudeja halutaan kontrolloida

Analyzing 5G RF system performance and relation to link budget for directive MIMO

Abstract Wideband fifth generation (5G) systems utilizing high carrier frequency and multiple-input multiple-output (MIMO) raise major challenges for the system design. Wave propagation and practical hardware tradeoffs at higher frequency ranges provide new boundary conditions for the implementation. This paper addresses system performance boundaries and the analysis method towards multibeam communications at mmW. We combine analysis from antennas and propagation to the RF transceiver specifications and beamforming requirements. Realistic propagation model and antenna implementation is used to generate beam-specific path gains and provide a wide variety of user scenarios. Using this approach, system level interdependencies and RF performance boundaries can be verified with different antenna configurations in various propagation environments. As an example, we present MIMO link budget analysis targeting 10 Gbits/s for multiple devices in the office scenario at 27 GHz

Analyses of Beamspace MIMO Channels at 142GHz

| openaire: EC/H2020/101015956/EU//Hexa-X | openaire: EC/H2020/101095759/EU//Hexa-X-IIThis paper presents the analyses of a single-user beamspace MIMO on measured indoor and outdoor channels at 142 GHz. The rank is evaluated under different antenna sizes, number of beams, and thresholds. We assume a total power constraint at the transmitter which results in a decrease in signal-to-noise ratio as the link distance increases. When using spatial multiplexing, the indoor and outdoor sites demonstrate an average capacity gain of 2x and 1.5x at link distances below 60 m. Also, the rank for our measured 142 GHz channels is comparable to that at 60 GHz channels but significantly lower than the rank at 5 GHz channels reported in the literature. We also found that at 142 GHz, the indoor and outdoor sites have median ranks of 3.0 and 1.7 for the small antenna case, and 4.9 and 2.4 for the large antenna case assuming a rank threshold of 20 dB. The indoor site has a rank higher by 1.8 than the outdoor site, regardless of antenna size. The rank decreases by only 20% and 15% for indoor and outdoor scenarios when beam density is halved, allowing a significant reduction in implementation complexity of the beamspace MIMO without remarkably reducing the rank.Peer reviewe

Inter-beam interference reduction in hybrid mmW beamforming transceivers

Abstract Practical radio frequency beamforming can suffer from high sidelobe levels which cause inter-beam interference (IBI) in multibeam transceivers. IBI can be reduced by shaping the amplitude and phase excitation over the individual antenna elements. However, such methods do not exploit the available power efficiently in practical arrays, where each antenna is driven with a dedicated power amplifier. In this paper, we show a simplified approach for hybrid beam synthesis in subarray-based beamforming architecture and propose a two-stage beamforming method for cancelling the IBI. The proposed technique cancels the interference between the subarrays while it maximizes the effective isotropic radiated powers in the desired directions. Simulation show typically over 40 dB IBI rejection for randomly spread beams and more than 4 dB improvement for radiated power compared to amplitude tapering

How many beams does sub-THz channel support

| openaire: EC/H2020/101015956/EU//Hexa-XAntenna, radio frequency (RF) circuit, algorithm, and system researchers on sub-THz RF are interested in knowing characteristics of corresponding radio channels. Among other things, a relevant question is the number of beams supported by the channel. From wideband directional propagation measurements one can estimate how many significant paths are present in a measurement location, but interpreting that to separable beams is not trivial. In this letter, we introduce three methods to approximate the number of beams that a measured power angular delay profile can support. We show also example evaluations and distribution functions of beam numbers, estimated from indoor D-band measurement data.Peer reviewe

How many beams does sub-THz channel support

| openaire: EC/H2020/101015956/EU//Hexa-XAntenna, radio frequency (RF) circuit, algorithm, and system researchers on sub-THz RF are interested in knowing characteristics of corresponding radio channels. Among other things, a relevant question is the number of beams supported by the channel. From wideband directional propagation measurements one can estimate how many significant paths are present in a measurement location, but interpreting that to separable beams is not trivial. In this letter, we introduce three methods to approximate the number of beams that a measured power angular delay profile can support. We show also example evaluations and distribution functions of beam numbers, estimated from indoor D-band measurement data.Peer reviewe