AirSync: Enabling Distributed Multiuser MIMO with Full Spatial Multiplexing

The enormous success of advanced wireless devices is pushing the demand for higher wireless data rates. Denser spectrum reuse through the deployment of more access points per square mile has the potential to successfully meet the increasing demand for more bandwidth. In theory, the best approach to density increase is via distributed multiuser MIMO, where several access points are connected to a central server and operate as a large distributed multi-antenna access point, ensuring that all transmitted signal power serves the purpose of data transmission, rather than creating "interference." In practice, while enterprise networks offer a natural setup in which distributed MIMO might be possible, there are serious implementation difficulties, the primary one being the need to eliminate phase and timing offsets between the jointly coordinated access points. In this paper we propose AirSync, a novel scheme which provides not only time but also phase synchronization, thus enabling distributed MIMO with full spatial multiplexing gains. AirSync locks the phase of all access points using a common reference broadcasted over the air in conjunction with a Kalman filter which closely tracks the phase drift. We have implemented AirSync as a digital circuit in the FPGA of the WARP radio platform. Our experimental testbed, comprised of two access points and two clients, shows that AirSync is able to achieve phase synchronization within a few degrees, and allows the system to nearly achieve the theoretical optimal multiplexing gain. We also discuss MAC and higher layer aspects of a practical deployment. To the best of our knowledge, AirSync offers the first ever realization of the full multiuser MIMO gain, namely the ability to increase the number of wireless clients linearly with the number of jointly coordinated access points, without reducing the per client rate.Comment: Submitted to Transactions on Networkin

Multi-Antenna Techniques for Next Generation Cellular Communications

Future cellular communications are expected to offer substantial improvements for the pre- existing mobile services with higher data rates and lower latency as well as pioneer new types of applications that must comply with strict demands from a wider range of user types. All of these tasks require utmost efficiency in the use of spectral resources. Deploying multiple antennas introduces an additional signal dimension to wireless data transmissions, which provides a significant alternative solution against the plateauing capacity issue of the limited available spectrum. Multi-antenna techniques and the associated key enabling technologies possess unquestionable potential to play a key role in the evolution of next generation cellular systems. Spectral efficiency can be improved on downlink by concurrently serving multiple users with high-rate data connections on shared resources. In this thesis optimized multi-user multi-input multi-output (MIMO) transmissions are investigated on downlink from both filter design and resource allocation/assignment points of view. Regarding filter design, a joint baseband processing method is proposed specifically for high signal-to-noise ratio (SNR) conditions, where the necessary signaling overhead can be compensated for. Regarding resource scheduling, greedy- and genetic-based algorithms are proposed that demand lower complexity with large number of resource blocks relative to prior implementations. Channel estimation techniques are investigated for massive MIMO technology. In case of channel reciprocity, this thesis proposes an overhead reduction scheme for the signaling of user channel state information (CSI) feedback during a relative antenna calibration. In addition, a multi-cell coordination method is proposed for subspace-based blind estimators on uplink, which can be implicitly translated to downlink CSI in the presence of ideal reciprocity. Regarding non-reciprocal channels, a novel estimation technique is proposed based on reconstructing full downlink CSI from a select number of dominant propagation paths. The proposed method offers drastic compressions in user feedback reports and requires much simpler downlink training processes. Full-duplex technology can provide up to twice the spectral efficiency of conventional resource divisions. This thesis considers a full-duplex two-hop link with a MIMO relay and investigates mitigation techniques against the inherent loop-interference. Spatial-domain suppression schemes are developed for the optimization of full-duplex MIMO relaying in a coverage extension scenario on downlink. The proposed methods are demonstrated to generate data rates that closely approximate their global bounds

Over-the-air test configurations for MIMO in Long Term Evolution

One of the main challenges for the mobile industry is the growing demand for the high speed mobile data. The 3GPP (3rd Generation Partner Project) is the organization that specifies most mobile data communication standards used globally. For the demand for high data rates, 3GPP has specified LTE (Long Term Evolution). One solution included in LTE among many is the MIMO (Multiple Input Multiple Output) technology. This thesis discusses the basic features included in LTE Release 9 focusing on MIMO-technology. This thesis also discusses the MIMO-OTA (Over-the-Air) testing configurations introduced in 3GPP Technical Report 37.976. These configurations are divided into two main types: anechoic chamber-based environments and reverberation chamber-based environments. 3GPP divides these two methods into five different anechoic chamber methods and two reverberation chamber methods. Testing MIMO-technology in LTE introduces new requirements for OTA-testing. While test requirements for GSM and WCDMA networks have included TRS (Total Radiated Sensitivity) and TRP (Total Radiated Power), the LTE MIMO testing adds the requirements for throughput testing. When using MIMO-configurations, the throughput depends on power transmitted to UE (User Equipment) that depends on the position of the UE. Addition to that, the throughput also depends on used TM (Transmission Mode). So test specifications need to include throughput tests for all TMs. Performance of TMs and the overall performance of MIMO cannot be tested in traditional OTA-measurement chambers because the transmission channels in traditional OTA-chambers are configured to be as simple as possible, so that the power and sensitivity measurements could be repeatable. Suggestions for LTE testing chambers have included configuring the transmission channel to be more versatile. This has been achieved by methods such as using multiple antennas or including a channel emulator to the system. Using these methods, the UE’s MIMO performance can be tested in different channel environments in laboratory, therefore improving possibilities for research and development.Opinnäytetyössä tutkittiin LTE-teknologian perusperiaatteita keskittyen siihen sisälletyn MIMO-tekniikan toimintaan. Opinnäytetyö tutki myös 3GPP:n TR 37.976 -raportissa esiteltyjä testausympäristövaihtoehtoja. Nämä jakautuvat 2 pääkategoriaan: kaiuttoman kammion järjestelmiin ja heijastavan kammion järjestelmiin. 3GPP jakaa nämä vielä 5:een eri kaiuttoman kammion järjestelmään ja 2:een heijastamattoman kammion järjestelmään. MIMO-tekniikan testaaminen LTE-teknologiassa asettaa suuria vaatimuksia OTA-testaamiselle. GSM- ja WCDMA-verkkojen testaamiseen ovat riittäneet vain herkkyysmittaukset (Total Radiated Sensitivity, TRS) ja tehomittaukset (Total Radiated Power, TRP). LTE:n MIMO-tekniikka lisää testausvaatimuksiin tiedonsiirtonopeuden, joka on MIMO-tekniikkaa käytettäessä riippuvainen herkkyydestä ja lähetetystä sekä vastaanotetusta tehosta, jotka riippuvat puhelimen asennosta. Näiden lisäksi tiedonsiirtonopeus riippuu myös MIMO:n käyttämien siirtotapojen (Transmission Mode, TM) toiminnasta. Siirtotapojen ja MIMO:n toimintaa ei pystytä testaamaan perinteisissä OTA-mittauskammioissa, sillä näissä siirtokanava on yritetty tehdä yksinkertaiseksi, jotta tehojen ja herkkyyden mittaukset olisivat mahdollisimman toistettavia. LTE:n MIMO-testauksen vaatimissa mittauskammioissa on pyritty tekemään siirtokanavasta mahdollisimman monimuotoinen. Tähän on pyritty eri ympäristövaihtoehdoissa erilaisin menetelmin, kuten käyttäen useaa antennia tai kanavaemulaattoria. Tällöin pystytään testaamaan laitteen MIMO:n toimintaa erilaisissa reaalimaailman ympäristöissä laboratorio-olosuhteissa

Indoor Radio Measurement and Planning for UMTS/HSPDA with Antennas

Over the last decade, mobile communication networks have evolved tremendously with a key focus on providing high speed data services in addition to voice. The third generation of mobile networks in the form of Universal Mobile Telecommunications System (UMTS) is already offering revolutionary mobile broadband experience to its users by deploying High Speed Downlink Packet Access (HSDPA) as its packet-data technology. With data speeds up to 14.4 Mbps and ubiquitous mobility, HSDPA is anticipated to become a preferred broadband access medium for end-users via mobile phones, laptops etc. While majority of these end-users are located indoors most of the time, approximately 70-80% of the HSDPA traffic is estimated to originate from inside buildings. Thus for network operators, indoor coverage has become a necessity for technical and business reasons. Macro-cellular (outdoor) to indoor coverage is a natural inexpensive way of providing network coverage inside the buildings. However, it does not guarantee sufficient link quality required for optimal HSDPA operation. On the contrary, deploying a dedicated indoor system may be far too expensive from an operator\u27s point of view. In this thesis, the concept is laid for the understanding of indoor radio wave propagation in a campus building environment which could be used to plan and improve outdoor-to-indoor UMTS/HSDPA radio propagation performance. It will be shown that indoor range performance depends not only on the transmit power of an indoor antenna, but also on the product\u27s response to multipath and obstructions in the environment along the radio propagation path. An extensive measurement campaign will be executed in different indoor environments analogous to easy, medium and hard radio conditions. The effects of walls, ceilings, doors and other obstacles on measurement results would be observed. Chapter one gives a brief introduction to the evolution of UMTS and HSDPA. It goes on to talk about radio wave propagation and some important properties of antennas which must be considered when choosing an antenna for indoor radio propagation. The challenges of in-building network coverage and also the objectives of this thesis are also mentioned in this chapter. The evolution and standardization, network architecture, radio features and most importantly, the radio resource management features of UMTS/HSDPA are given in chapter two. In this chapter, the reason why Wideband Code Division Multiple Access (WCDMA) was specified and selected for 3G (UMTS) systems would be seen. The architecture of the radio access network, interfaces with the radio access network between base stations and radio network controllers (RNC), and the interface between the radio access network and the core network are also described in this chapter. The main features of HSDPA are mentioned at the end of the chapter. In chapter three the principles of the WCDMA air interface, including spreading, Rake reception, signal fading, power control and handovers are introduced. The different types and characteristics of the propagation environments and how they influence radio wave propagation are mentioned. UMTS transport, logical and physical channels are also mentioned, highlighting their significance and relationship in and with the network. Radio network planning for UMTS is discussed in chapter four. The outdoor planning process which includes dimensioning, detailed planning, optimization and monitoring is outlined. Indoor radio planning with distributed antenna systems (DAS), which is the idea and motivation behind this thesis work, is also discussed. The various antennas considered and the antenna that was selected for this thesis experiment was discussed in chapter five. The antenna radiation pattern, directivity, gain and input impedance were the properties of the antenna that were taken into consideration. The importance of the choice of the antenna for any particular type of indoor environment is also mentioned. In chapter six, the design and fabrication of the monopole antennas used for the experimental measurement is mentioned. The procedure for measurement and the equipment used are also discussed. The results gotten from the experiment are finally analyzed and discussed. In this chapter the effect of walls, floors, doors, ceilings and other obstacles on radio wave propagation will be seen. Finally, chapter seven concludes this thesis work and gives some directions for future work

Técnicas de processamento com múltiplas antenas para o sistema LTE

Mestrado em Engenharia Electrónica e TelecomunicaçõesPerformance, mobilidade e partilha podem ser consideras como as três palavras-chave nas comunicações móveis de hoje em dia. Uma das necessidades fundamentais do ser humano é a partilha de experiencias e informação. Com a evolução ao nível do hardware móvel, a crescente popularidade de smartphones, tablets e outros dispositivos moveis, fez com que a exigência em termos de capacidade e taxa de transferência por parte das redes móveis não parasse de crescer. As limitações das redes 3G fizeram com que não conseguissem corresponder a tais exigências e como tal, a transição para uma tecnologia mais robusta e eficiente passou a ser inevitável. A resposta escolhida como solução a longo prazo é a rede designada por LTE, desenvolvida pela organização 3GPP é assumido que será a rede de telecomunicações predominante no futuro. As vantagens mais sonantes são, naturalmente, elevadas taxas de transmissão, maior eficiência espectral, redução da latência e de custos de operação. As principais tecnologias em que o LTE se baseia, são o OFDM e sua variante para múltiplo acesso, OFDMA, usado para o downlink e o SC-FDMA para o uplink. Além disso, usa sistemas com múltiplas antenas para impulsionar a eficiência espectral. Apesar de já implementado em alguns países por diversas operadoras, constantes pesquisas continuam a ser realizadas com o intuito de melhorar a sua performance. Nesta dissertação é proposto um esquema duplo de codificação na frequência e no espaço (D-SFBC) para um cenário baseado em OFDM com 4 antenas de transmissão e duas antenas de recepção (4 × 2 D-SFBC) para o downlink. No cenário considerado, 4 símbolos de dados são transmitidos utilizando unicamente 2 sub-portadoras, fazendo com que, este sistema seja limitado pela interferência. Para de forma eficiente descodificar os símbolos de dados transmitidos, foi desenvolvido um equalizador iterativo no domínio da frequência. Duas abordagens são consideradas: cancelamento da interferência em paralelo (PIC) e sucessivo cancelamento de interferência (SIC). Uma vez que apenas 2 sub-portadoras são usadas para transmitir quatro símbolos de dados em paralelo, o esquema desenvolvido duplica a taxa de dados quando comparado com o esquema 2 × 2 SFBC, especificado no standard do LTE. Os esquemas desenvolvidos foram avaliados sob as especificações para LTE e usando codificação de canal. Os resultados mostram que os esquemas implementados neste trabalho utilizando um equalizador iterativo supera os convencionais equalizadores lineares na eliminação da interferência adicional introduzida, em apenas 2 ou 3 iterações.Performance, mobility and sharing can be assumed as the three keywords in the mobile communications nowadays. One of the fundamental needs of human beings is to share experiences and information. With the evolution of mobile hardware level, the growing popularity of smartphones, tablets and other mobile devices, has made that the demand in terms of capacity and throughput by mobile networks did not stop growing. Thus, the limitations of 3G stops it of being the answer of such demand, and a transition to a powerful technology has become unavoidable. The answer chosen is LTE, developed by the 3GPP organization is assumed to be the predominant telecommunications network in the future. The most relevant advantages are high transmission rates, higher spectral efficiency, reducing latency and operating costs. The key technologies in which LTE is based, are OFDM and its variant schemes for multiple access, OFDMA, used for downlink, and SC-FDMA for the uplink. It also uses multiple antennas systems in order to improve spectral efficiency. Although already implemented in some countries by several operators, continuous research is conducted in order to improve their performance. In this dissertation it is proposed a double space-frequency block coding (D-SFBC) scheme for an OFDM based scenario with 4 transmit antennas and 2 receive antennas (4×2 D-SFBC) for the downlink. In the considered scenario, 4 data symbols are transmitted by using only 2 subcarriers and thus the system is interference limited. To efficiently decode the transmitted data symbols an iterative equalizer designed in frequency domain is developed. Two approaches are considered: parallel interference cancellation (PIC) and successive interference cancellation (SIC). Since only 2 subcarriers are used to transmit 4 data symbols in parallel the developed scheme achieve the double data rate when compared with the 2×2 SFBC, specified in the LTE standard. The developed schemes were evaluated under the main LTE specifications and using channel coding. The results have show that the schemes implemented in this work using an interactive equalizer outperforms the conventional linear equalizers in the interference removal, just by using 2 or 3 iterations

Radio over fiber enabling PON fronthaul in a two-tiered cloud

Avec l’avènement des objets connectés, la bande passante nécessaire dépasse la capacité des interconnections électriques et interface sans fils dans les réseaux d’accès mais aussi dans les réseaux coeurs. Des systèmes photoniques haute capacité situés dans les réseaux d’accès utilisant la technologie radio sur fibre systèmes ont été proposés comme solution dans les réseaux sans fil de 5e générations. Afin de maximiser l’utilisation des ressources des serveurs et des ressources réseau, le cloud computing et des services de stockage sont en cours de déploiement. De cette manière, les ressources centralisées pourraient être diffusées de façon dynamique comme l’utilisateur final le souhaite. Chaque échange nécessitant une synchronisation entre le serveur et son infrastructure, une couche physique optique permet au cloud de supporter la virtualisation des réseaux et de les définir de façon logicielle. Les amplificateurs à semi-conducteurs réflectifs (RSOA) sont une technologie clé au niveau des ONU(unité de communications optiques) dans les réseaux d’accès passif (PON) à fibres. Nous examinons ici la possibilité d’utiliser un RSOA et la technologie radio sur fibre pour transporter des signaux sans fil ainsi qu’un signal numérique sur un PON. La radio sur fibres peut être facilement réalisée grâce à l’insensibilité a la longueur d’onde du RSOA. Le choix de la longueur d’onde pour la couche physique est cependant choisi dans les couches 2/3 du modèle OSI. Les interactions entre la couche physique et la commutation de réseaux peuvent être faites par l’ajout d’un contrôleur SDN pour inclure des gestionnaires de couches optiques. La virtualisation réseau pourrait ainsi bénéficier d’une couche optique flexible grâce des ressources réseau dynamique et adaptée. Dans ce mémoire, nous étudions un système disposant d’une couche physique optique basé sur un RSOA. Celle-ci nous permet de façon simultanée un envoi de signaux sans fil et le transport de signaux numérique au format modulation tout ou rien (OOK) dans un système WDM(multiplexage en longueur d’onde)-PON. Le RSOA a été caractérisé pour montrer sa capacité à gérer une plage dynamique élevée du signal sans fil analogique. Ensuite, les signaux RF et IF du système de fibres sont comparés avec ses avantages et ses inconvénients. Finalement, nous réalisons de façon expérimentale une liaison point à point WDM utilisant la transmission en duplex intégral d’un signal wifi analogique ainsi qu’un signal descendant au format OOK. En introduisant deux mélangeurs RF dans la liaison montante, nous avons résolu le problème d’incompatibilité avec le système sans fil basé sur le TDD (multiplexage en temps duplexé).With the advent of IoT (internet of things) bandwidth requirements triggered by aggregated wireless connections have exceeded the fundamental limitation of copper and microwave based wireless backhaul and fronthaul networks. High capacity photonic fronthaul systems employing radio over fiber technology has been proposed as the ultimate solution for 5G wireless system. To maximize utilization of server and network resources, cloud computing and storage based services are being deployed. In this manner, centralized resources could be dynamically streamed to the end user as requested. Since on demand resource provision requires the orchestration between the server and network infrastructure, a smart photonic (physical layer)PHY enabled cloud is foreseen to support network virtualization and software defined network. RSOAs (Reflective Semiconductor Optical Amplifier) are being investigated as key enablers of the colorless ONU(Optical Network Unit) solution in PON (Passive Optical Network). We examine the use of an RSOA in radio over fiber systems to transport wireless signals over a PON simultaneously with digital data. Radio over fiber systems with flexible wavelength allocation could be achieved thanks to the colorless operation of the RSOA and wavelength reuse technique. The wavelength flexibility in optical PHY are inline with the paradigm of software defined network (SDN) in OSI layer 2/3. The orchestration between optical PHY and network switching fabric could be realized by extending the SDN controller to include optical layer handlers. Network virtualization could also benefit from the flexible optical PHY through dynamic and tailored optical network resource provision. In this thesis, we investigate an optical PHY system based on RSOA enabling both analog wireless signal and digital On-Off Keying (OOK) transportation within WDM (Wavelength Division Multiplexing) PON architecture. The RSOA has been characterized to show its potential ability to handle high dynamic range analog wireless signal. Then the RF and IF radio over fiber scheme is compared with its pros and cons. Finally we perform the experiment to shown a point to point WDM link with full duplex transmission of analog WiFi signal with downlink OOK signal. By introducing two RF mixer in the uplink, we have solved the incompatible problem with TDD (Time Division Duplex) based wireless system

On the ergodic sum-rate performance of CDD in multi-user systems

The main focus of space-time coding design and analysis for MIMO systems has been so far focused on single-user systems. For single-user systems, transmit diversity schemes suffer a loss in spectral efficiency if the receiver is equipped with more than one antenna, making them unsuitable for high rate transmission. One such transmit diversity scheme is the cyclic delay diversity code (CDD). The advantage of CDD over other diversity schemes such as orthogonal space-time block codes (OSTBC) is that a code rate of one and delay optimality are achieved independent of the number of transmit antennas. In this work we analyze the ergodic rate of a multi-user multiple access channel (MAC) with each user applying such a cyclic delay diversity (CDD) code. We derive closed form expressions for the ergodic sum-rate of multi-user CDD and compare it with the sum-capacity. We study the ergodic rate region and show that in contrast to what is conventionally known regarding the single-user case, transmit diversity schemes are viable candidates for high rate transmission in multi-user systems. Finally, our theoretical findings are illustrated by numerical simulation results.Comment: to appear in Proceedings of 2007 IEEE Information Theory Workshop (ITW) in Lake Taho