Methods and criteria for performance analysis of multiantenna systems in mobile communications

Multiple-input multiple-output (MIMO) technique is one of the most promising solutions for increasing reliability and spectral efficiency of the radio connection in future mobile communication systems. The performance potential of MIMO systems is well established from theoretical point of view. However, much effort is still needed in the experimental verification of those systems using realistic antennas and channels. It is widely accepted that the antenna properties are of significant importance regarding the performance of single-input single-output (SISO) systems. However, the effect of the antennas on MIMO systems has not been thoroughly studied. Due to the complexity of MIMO systems, evaluation of MIMO antennas becomes increasingly cumbersome and time-consuming process in comparison to simpler systems. In the first part of this work an advanced antenna evaluation technique called experimental plane-wave based method (EPWBM) is generalized and validated to cover MIMO systems. This work is the extension of the previous work where the method has been used in the analysis of SISO systems. The EPWBM is based on the measured or simulated complex 3-D radiation patterns of the antennas and measured directional radio channel data. The EPWBM simplifies antenna evaluation process in comparison to traditional means since the same channel library can be utilized in the evaluation of several antenna systems without performing the same measurements for each prototype antennas separately. It is verified that the EPWBM is sufficiently reliable in comparing the performance of prototype antennas. In the second part of the work new quality factors for MIMO system evaluation enclosing traditional systems as special cases have been developed. The MIMO channel correlation matrix is formulated so that it reveals the ability of MIMO antenna systems to transfer signal power from a transmitter to a receiver and to utilize parallel spatial channels. It is also verified that correct normalization of the channel matrices is of significant importance in the MIMO antenna evaluation. This approach gives comprehensive framework for MIMO antenna evaluation, which takes into account both realistic antenna and channel properties. In the last part of the work insight into the performance of different antennas in different signal propagation environments is given. The performance of the antennas depends on the signal-to-noise-ratio and on the outage probability level considered. Although MIMO systems are based on the utilization of parallel spatial channels, the capability of the system to transfer signal power plays a significant role especially with small MIMO systems. In the realistic dynamic channels the capacity variation is larger than in the ideal channels, which are based on the identically and independently distributed (iid) channel assumption. Large performance variations occur in the realistic channels with directive antennas, when antennas are rotated in the usage environment, whereas omnidirectional ones are more robust but are difficult to realize in practice. The largest differences between the antennas are found at the low outage probability levels due to different radiation properties of the antennas. The systems with the cross-polarized antennas have smaller eigenvalue dispersion and are more robust in performance for the variations of the channel than the systems with co-polarized antennas. On the other hand, the co-polarized antennas possess better capability to transfer signal power and are more robust in performance for the antenna array orientation. From practical point of view, the dual-polarized antennas seem to be the most feasible candidates to be used in MIMO antenna systems due to compact structure, and indoor seems to be the most suitable for MIMO applications due to typically scatter-rich channel.Multiple-input multiple-output (MIMO) tekniika on yksi lupaavimmista ratkaisuista lisätä radioyhteyden luotettavuutta ja spektritehokkuutta tulevaisuuden matkaviestinjärjestelmissä. MIMO järjestelmien suorituskykypotentiaali on teoreettisesti todistettu. Paljon työtä tarvitaan kuitenkin vielä kokeelliseen järjestelmätestaukseen käyttäen realistisia antenneja ja kanavia. On laajasti hyväksyttyä että antennien ominaisuudet ovat merkityksellisiä single-input single-output (SISO) järjestelmien suorituskyvyn kannalta. Antennien vaikutusta MIMO-järjestelmiin ei ole kuitenkaan perusteellisesti tutkittu. MIMO-järjestelmien lisääntyneestä monimutkaisuudesta johtuen, verrattuna yksinkertaisempiin järjestelmiin, MIMO antennien suorituskyvyn arviointi hankaloituu ja vie enemmän aikaa. Työn ensimmäisessä osassa uusi antennien arviointitekniikka nimeltään kokeellinen tasoaaltoihin perustuva menetelmä (EPWBM) on yleistetty käsittämään MIMO järjestelmät ja sen tarkkuus on arvioitu. Tämä työ on laajennus aikaisempaan työhön jossa menetelmää on käytetty SISO-järjestelmien arviointiin. EPWBM perustuu mitattuihin tai simuloituihin antennien kompleksisiin 3-D suuntakuvioihin ja mitattuun suuntatiedon sisältämään kanavadataan. EPWBM yksinkertaistaa antennin suorituskyvyn arviointia perinteisiin menetelmiin verrattuna, koska sama kanavamittausaineisto voidaan hyödyntää usamman antennisysteemin arvioinnissa tekemättä samoja mittauksia jokaiselle antenniprototyypille erikseen. On osoitettu että EPWBM on suhteellisen luotettava prototyyppiantennien suorituskyvyn vertailussa. Työn toisessa osassa on kehitetty uusia hyvyyslukuja MIMO-järjestelmien suorituskyvyn arviointiin sisältäen perinteiset järjestelmät erikoistapauksina. MIMO-kanavamatriisi esitetään siten että se paljastaa MIMO-antennijärjestelmien kyvyn siirtää signaalitehoa lähettimen ja vastaanottimen välillä ja hyödyntää rinnakkaisia kanavia. On myös todistettu että oikeanlainen kanavamatriisien normalisointi on erittäin merkittävää MIMO-antennivertailussa. Tämä lähestymistapa antaa kattavat puitteet MIMO-antennien suorituskyvyn arviointiin ottaen huomioon todelliset antennien ja kanavan ominaisuudet. Työn viimeisessä osassa annetaan käsitys erilaisten antennien suorituskyvystä erilaisissa signaalin etenemisympäristöissä. Antennien suorituskyky riippuu signaalikohinasuhteesta ja tarkasteltavan signaalin luotettavuustasosta. Vaikka MIMO-järjestelmät perustuvat rinnakkaisten kanavien hyödyntämiseen järjestelmän signaalitehon siirto-ominaisuudet ovat merkittäviä erityisesti pienillä MIMO järjestelmillä. Realistisissa dynaamisissa kanavissa kapasiteetinvaihtelu on suurempaa kuin ideaalisissa kanavissa jotka perustuvat oletukseen että signaalit ovat riippumattomasti ja identtisesti jakautuneita (iid). Suurta suorituskykyn vaihtelua esiintyy realistissa kanavissa suuntaavilla antenneilla, kun antenneja pyöritetään käyttöympäristössä, kun taas ympärisäteilevät antennit olisivat jäykempiä suorituskyvyn kannalta mutta käytännössä vaikeampia toteuttaa. Suuremmat erot antennien välillä on löydettävissä matalalta signaalin luotettavuustasolta johtuen antennien erilaisista säteilyominaisuuksista. Kaksipolarisaatioantennijärjestelmillä on pienempi ominaisarvohaje ja niiden suorituskyky on jäykempi kanavan vaihteluille kuin yksipolarisaatioantennijärjestelmä. Toisaalta yksipolarisaatioantenneilla on paremmat signaalitehon siirto-ominaisuudet ja suorituskyky vaihtelee vähemmän antennin katselusuunnan funktiona. Käytännön näkökulmasta katsoen kaksipolarisaatioantennit näyttävät olevan kaikkein toteuttamiskelpoisin vaihtoehto käytettäväksi MIMO-systeemeissä johtuen niiden kompaktista rakenteesta, ja sisätila näyttää olevan sopivin ympäristö MIMO-sovelluksiin johtuen tyypillisesti sirontarikkaasta kanavasta.reviewe

Capacity Enhancement by Pattern-Reconfigurable Multiple Antenna Systems in Vehicular Applications

This work presents a design methodology for pattern reconfigurable antennas in automotive applications. Channel simulation is used to identify the relevant beam directions prior to the design of the antenna. Based on this knowledge several reconfigurable multiple antenna systems are designed. These antennas are evaluated by the channel capacity calculation from virtual and real-world test drives. An increase of the channel capacity by a factor of 2 compared to a conventional system is observed

Evaluation of performance of mobile terminal antennas

Fast development of new mobile communications equipment results in demand for fast and reliable evaluation methods to estimate the performance of mobile terminals because the performance of antennas located on the terminals varies in different multipath propagation environments. Two methods presented in this thesis provide new possibilities in antenna design because, from now on, the performance of new antennas can be tested already before a prototype antenna is constructed by using existing radio channel libraries and simulated radiation patterns of the antennas. The performance can be estimated by calculating the mean effective gain (MEG) of the antenna using the elevation power distribution or by a plane wave -based method using sets of incident plane waves and the radiation pattern of an antenna. In addition to different propagation environments, the effects of the user on performance can be included in the evaluation. In this thesis, estimating the MEG of different antennas using the elevation power distribution and the power patterns of the antennas is shown to be an accurate and fast method by comparing the results with direct radio channel measurements. The mean difference between the methods is −0.18 dB with standard deviation of 0.19 dB. The usefulness of the evaluation method is demonstrated by evaluating the performance of several antennas located on mobile terminals. The antenna evaluation provided important and unique knowledge of the effect of both the environment and the user on performance. Because in calculating the radiation efficiency of the antenna we assume uniform incident field, the efficiency can result in a performance estimation that does not correspond to real usage situations. Therefore, including the environmental effects in the evaluation procedure is important, although the effect of the antenna is more important than the effect of the environment on MEG. It was noticed with calculated Gaussian-shaped beams that tilting or changing the beamwidth of a mobile terminal antenna has an effect of about 2 dB on MEG in multipath environments. Matching the polarization of the antenna to that of the environment can improve the performance more. A novel incident plane wave -based tool has been developed for evaluating the performance of antenna configurations designed for diversity and Multiple-Input Multiple-Output (MIMO) systems. In this thesis, the instantaneous joint contribution of incident field consisting of a number of extracted plane waves and the complex three-dimensional radiation pattern of the antenna is shown to be accurate and extremely fast way to estimate the diversity advantages of different antenna configurations in time-variable radio channels. The difference between the diversity gains achieved by the plane wave -based method and by the direct radio channel measurements is on average less than 0.9 dB. Moreover, the radio channel can be exactly the same for all antenna configurations under test. Furthermore, this thesis includes evaluation of the performance of different MIMO antenna configurations. The studied antenna configurations have been selected from the 16×64 MIMO channel measurement data. A novel way of using one omnidirectional reference antenna in a normalization procedure is shown to be reasonable especially in cases of antenna arrays consisting of directive elements. Three different propagation environments are used as evaluation platforms. The azimuth orientation of mobile terminal antennas may influence the performance of a MIMO antenna configuration significantly. In MIMO configurations compact dual-polarized receiving antennas provide capacity performance almost equal to the arrays employing single polarization.reviewe

Simulation framework for multigigabit applications at 60 GHz

This dissertation describes the implementation of a OFDM-based simulation framework for multigigabit applications at 60 GHz band over indoor multipath fading channels. The main goal of the framework is to provide a modular simulation tool designed for high data rate application in order to be easily adapted to a speci c standard or technology, such as 5G. The performance of OFDM using mmWave signals is severely a ected by non-linearities of the RF front-ends. This work analyses the impact of RF impairments in an OFDM system over multipath fading channels at 60 GHz using the proposed simulation framework. The impact of those impairments is evaluated through the metrics of BER, CFR, operation range and PSNR for residential and kiosk scenarios, suggested by the standard for LOS and NLOS. The presented framework allows the employment of 16 QAM or 64 QAM modulation scheme, and the length of the cyclic pre x extension is also con gurable. In order to simulate a realistic multipath fading channel, the proposed framework allows the insertion of a channel impulse response de ned by the user. The channel estimation can be performed either using pilot subcarriers or Golay sequence as channel estimation sequences. Independently of the channel estimation technique selected, frequency domain equalization is available through ZF approach or MMSE. The simulation framework also allows channel coding techniques in order to provide a more robustness transmission and to improve the link budget

Pattern Reconfigurable Cubic Antenna

International audienceA new single-feed reconfigurable antenna for pattern diversity is presented in this paper. The proposed structure is based on a metallic cubic cavity which radiates through rectangular slots. The pattern reconfiguration is achieved with PIN diode switches by short-circuiting slots in their center. The designed antenna can switch between three different radiation patterns which radiate in a 4π steradian range and can receive any incident field polarizations. A prototype of the antenna, including PIN diodes and operating in the 5 GHz band, has been built to demonstrate the feasibility of the concept. Measurements have been conducted and three-dimensional radiation patterns are provided. Diversity performances are evaluated by calculating the envelope correlation coefficient

Design and Realization of Fully-digital Microwave and Mm-wave Multi-beam Arrays with FPGA/RF-SOC Signal Processing

There has been a constant increase in data-traffic and device-connections in mobile wireless communications, which led the fifth generation (5G) implementations to exploit mm-wave bands at 24/28 GHz. The next-generation wireless access point (6G and beyond) will need to adopt large-scale transceiver arrays with a combination of multi-input-multi-output (MIMO) theory and fully digital multi-beam beamforming. The resulting high gain array factors will overcome the high path losses at mm-wave bands, and the simultaneous multi-beams will exploit the multi-directional channels due to multi-path effects and improve the signal-to-noise ratio. Such access points will be based on electronic systems which heavily depend on the integration of RF electronics with digital signal processing performed in Field programmable gate arrays (FPGA)/ RF-system-on-chip (SoC). This dissertation is directed towards the investigation and realization of fully-digital phased arrays that can produce wideband simultaneous multi-beams with FPGA or RF-SoC digital back-ends. The first proposed approach is a spatial bandpass (SBP) IIR filter-based beamformer, and is based on the concepts of space-time network resonance. A 2.4 GHz, 16-element array receiver, has been built for real-time experimental verification of this approach. The second and third approaches are respectively based on Discrete Fourier Transform (DFT) theory, and a lens plus focal planar array theory. Lens based approach is essentially an analog model of DFT. These two approaches are verified for a 28 GHz 800 MHz mm-wave implementation with RF-SoC as the digital back-end. It has been shown that for all proposed multibeam beamformer implementations, the measured beams are well aligned with those of the simulated. The proposed approaches differ in terms of their architectures, hardware complexity and costs, which will be discussed as this dissertation opens up. This dissertation also presents an application of multi-beam approaches for RF directional sensing applications to explore white spaces within the spatio-temporal spectral regions. A real-time directional sensing system is proposed to capture the white spaces within the 2.4 GHz Wi-Fi band. Further, this dissertation investigates the effect of electro-magnetic (EM) mutual coupling in antenna arrays on the real-time performance of fully-digital transceivers. Different algorithms are proposed to uncouple the mutual coupling in digital domain. The first one is based on finding the MC transfer function from the measured S-parameters of the antenna array and employing it in a Frost FIR filter in the beamforming backend. The second proposed method uses fast algorithms to realize the inverse of mutual coupling matrix via tridiagonal Toeplitz matrices having sparse factors. A 5.8 GHz 32-element array and 1-7 GHz 7-element tightly coupled dipole array (TCDA) have been employed to demonstrate the proof-of-concept of these algorithms