Super-Wideband Massive MIMO

We present a unified model for connected antenna arrays with a massive (but finite) number of tightly integrated (i.e., coupled) antennas in a compact space within the context of massive multiple-input multiple-output (MIMO) communication. We refer to this system as tightly-coupled massive MIMO. From an information-theoretic perspective, scaling the design of tightly-coupled massive MIMO systems in terms of the number of antennas, the operational bandwidth, and form factor was not addressed in prior art and hence not clearly understood. We investigate this open research problem using a physically consistent modeling approach for far-field (FF) MIMO communication based on multi-port circuit theory. In doing so, we turn mutual coupling (MC) from a foe to a friend of MIMO systems design, thereby challenging a basic percept in antenna systems engineering that promotes MC mitigation/compensation. We show that tight MC widens the operational bandwidth of antenna arrays thereby unleashing a missing MIMO gain that we coin "bandwidth gain". Furthermore, we derive analytically the asymptotically optimum spacing-to-antenna-size ratio by establishing a condition for tight coupling in the limit of large-size antenna arrays with quasi-continuous apertures. We also optimize the antenna array size while maximizing the achievable rate under fixed transmit power and inter-element spacing. Then, we study the impact of MC on the achievable rate of MIMO systems under light-of-sight (LoS) and Rayleigh fading channels. These results reveal new insights into the design of tightly-coupled massive antenna arrays as opposed to the widely-adopted "disconnected" designs that disregard MC by putting faith in the half-wavelength spacing rule

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

A novel wideband dynamic directional indoor channel model based on a Markov process

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Characterization and Enhancement of Antenna System Performance in Compact MIMO Terminals

Co-band multiple-antenna implementation in compact user terminals is necessary for harvesting the full potential of diversity and multiple-input multiple-output (MIMO) technology in cellular communication systems. The recent worldwide deployment of Long Term Evolution (LTE), which requires the use of MIMO technology in the downlink, adds to the urgency of achieving both practical and optimal multiple-antenna systems in user terminals. Contrary to conventional understanding, an optimal multiple-antenna implementation does not only involve the design and placement of antenna elements in the terminals, but extends beyond the antenna elements and common antenna parameters to comprise interactions with the near field user and the propagation environment. Moreover, these interactions are non-static, which implies that the multiple-antenna system must adapt to the prevailing overall communication channel in order to assure the highest performance gains. This doctoral thesis aims to address several key issues in optimal multiple-antenna system design for compact multi-band MIMO terminals, with the first half (Papers I to III) focusing on the performance characterization of such terminals in the presence of user interaction and propagation channel, under the challenging constraint that the terminals are compact. The second half of the thesis (Papers IV to VI) considers two performance enhancement approaches suitable for compact MIMO terminals in realistic usage conditions. In particular, the potential benefits of harmonizing compact multiple-antenna systems with the propagation channel and user influence are determined with respect to reconfigurability in antenna patterns and impedance matching circuits. In Paper I, the diversity performance of internal multiple antennas with multi-band coverage in a mock-up with the size of a typical mobile handset is investigated in different user interaction scenarios. For comparison, a second mock-up with only one multi-band antenna is also evaluated in the same user cases. An ideal uniform propagation environment is assumed. The performance at frequency bands below and above 1 GHz are presented and analyzed in detail. Paper II extends the study in Paper I by evaluating the single-input multiple-output (SIMO) and MIMO capacity performance of the same antenna prototypes under the same user interaction scenarios and propagation environment. In Paper III, the impacts of gain imbalance and antenna separation on the throughput performance of a dual-dipole configuration are studied at frequencies below and above 1 GHz in a repeatable dynamic multi-path environment, using a live HSPA network. Since the compactness of a user terminal has implications on the antenna separation and gain imbalance of the multiple antennas, the focus is to gain knowledge on how these two factors affect the end user experience in practice. In Paper IV, three simple dual-antenna topologies implemented in compact smart phone prototypes of identical form factors are evaluated in MIMO channel measurements in noise-limited and interference-limited urban scenarios. Each dual-antenna topology is intentionally designed to provide a distinct set of antenna patterns. The goal is to investigate the potential of antenna system design as one of the key performance differentiators in real terminal implementations. Paper V extends the work in Paper IV by introducing user interaction to the same MIMO channel measurement setup. Furthermore, the focus of this paper is on the evaluation of both the average and local channel performances and their potential enhancements. Finally, Paper VI ascertains the potential capacity gains of applying uncoupled adaptive matching to a compact dual-antenna terminal in an indoor office environment, under a realistic user scenario. The performance gains are evaluated by means of extensive MIMO channel measurements at frequency bands below and above 1 GHz

Radio channel characterisation and system-level modelling for ultra wideband body-centric wireless communications

PhDThe next generation of wireless communication is evolving towards user-centric networks, where constant and reliable connectivity and services are essential. Bodycentric wireless network (BCWN) is the most exciting and emerging 4G technology for short (1-5 m) and very short (below 1 m) range communication systems. It has got numerous applications including healthcare, entertainment, surveillance, emergency, sports and military. The major difference between the BCWN and conventional wireless systems is the radio channel over which the communication takes place. The human body is a hostile medium from the radio propagation perspective and it is therefore important to understand and characterise the effect of the human body on the antenna elements, the radio propagation channel parameters and hence the system performance. In addition, fading is another concern that affects the reliability and quality of the wireless link, which needs to be taken into account for a low cost and reliable wireless communication system for body-centric networks. The complex nature of the BCWN requires operating wireless devices to provide low power requirements, less complexity, low cost and compactness in size. Apart from these characteristics, scalable data rates and robust performance in most fading conditions and jamming environment, even at low signal to noise ratio (SNR) is needed. Ultra-wideband (UWB) technology is one of the most promising candidate for BCWN as it tends to fulfill most of these requirements. The thesis focuses on the characterisation of ultra wideband body-centric radio propagation channel using single and multiple antenna techniques. Apart from channel characterisation, system level modelling of potential UWB radio transceivers for body-centric wireless network is also proposed. Channel models with respect to large scale and delay analysis are derived from measured parameters. Results and analyses highlight the consequences of static and dynamic environments in addition to the antenna positions on the performance of body-centric wireless communication channels. Extensive measurement i campaigns are performed to analyse the significance of antenna diversity to combat the channel fading in body-centric wireless networks. Various diversity combining techniques are considered in this process. Measurement data are also used to predict the performance of potential UWB systems in the body-centric wireless networks. The study supports the significance of single and multiple antenna channel characterisation and modelling in producing suitable wireless systems for ultra low power body-centric wireless networks.University of Engineering and Technology Lahore Pakista

Ergodic Capacity of Doubly Selective Rayleigh Fading MIMO Channels

The ergodic capacity is investigated for doubly selective (frequency selective and time varying) MIMO Rayleigh fading channels. A closed form formula is derived that quantifies the effect of the ISI fading on the ergodic capacity into an ISI degradation factor. It is discovered that, in general frequency selective MIMO channels, the inter-tap correlations of the ISI fading will reduce the ergodic capacity comparing to the frequency flat fading channel. Only in the special case when the ISI fading does not have inter-tap correlations will the ergodic capacity be the same as that of the frequency flat channel. This new formula is mathematically proved and experimentally verified via Monte-Carlo simulations