Continuous Ultra-Dense Networks - A System Level Design for Urban Outdoor Deployments

Ultra-dense networks (UDNs) will play a critical role in the future of mobile communications. Especially within urban street canyons with an extensive amount of mobile users, the propagation environment prevents the efficient spatial densification by means of macro cell massive MIMO systems. Hence, increasing the amount of transmission and reception points (TRPs) is the key to success. In this thesis, a system level continuous UDN (C-UDN) concept is developed. In particular, a novel radio frame structure is designed to meet the low-latency, high-capacity and mobility support requirements of the future generation wireless networks. Also the time and frequency domain scheduling framework is further developed in order to support spatial domain scheduling of highly mobile users. Moreover, transmit and receive beamforming that is based on user location estimates is studied in order to increase signal-to-interference-plus-noise ratio and decrease pilot overhead caused by full-band uplink reference signals, commonly used for channel state information (CSI) in time-division-duplex TDD systems. Since one of the main challenges for wide-scale deployment of UDNs is the backhaul, also a massive MIMO based sub-6 GHz solution that exploits spatial multiple-access and TDD for UDN self-backhauling is given. This is shown to outperform self-backhauling that is based on time domain multiplexing only. What makes this study attractive is that with wireless alternatives to wired solutions, deployment costs can be lowered significantly. Furthermore, millimeter wave technologies typically require line-of-sight conditions, which significantly reduces deployment flexibility. Lastly, an approach for dealing with uplink small packet transmissions from a massive amount of machine type communication (MTC) devices in UDNs is proposed. The proposed approach exploits beamforming based distribution of uplink grants for connectionless small data transmissions. Receive beamforming is also employed for receiving subsequent small packet transmissions. It is shown that with the proposed approach, low collision and decode failure probabilities can be achieved. Additionally, the results provided show that simultaneous reception of such small packet transmissions can be dealt with low latency and low physical resource usage by utilizing spatial receive filters that maximize received power towards the directions where grants were broadcasted.; Aarimmaisen tiheilla verkoilla tulee olemaan ratkaiseva merkitys tulevaisuuden matkaviestinnassa. Erityisesti kaupunkialueilla radiokanavan etenemisominaisuudet katukuiluissa estavat tehokkaan spatiaalisen tihentamisen makro-solujen massiivisilla MIMO -jarjestelmilla. Siksi radionoodien huomattava lisaaminen on avain menestykseen. Tassa vaitoskirjassa on kehitetty uusi yhtajaksoisen peiton tarjoava tihean verkon jarjestelmatason konsepti. Uusi radion kehysrakenne on suunniteltu tayttamaan uuden sukupolven verkkojen matalan latenssin, suuren kapasiteetin ja kayttajien liikkuvuuden vaatimukset. Myos ajan ja taajuuden…