Algorithms, Protocols and Cloud-RAN Implementation Aspects of 5G Networks

The future fifth generation (5G) mobile networks will support a number of use cases such as extreme Mobile BroadBand (eMBB), Ultra Reliable and Low Latency Communication (URLLC) and Machine Type Communications (MTC) with massive number of connected devices. The thesis studies implementation constraints of 5G requirements and proposes practical physical layer algorithms together with protocol and architectural designs that could support the 5G use cases. Network densification and centralized/co-ordinated processing are important elements that enable reliable and high-speed Internet access. Towards this end, Distributed Antenna Systems (DAS) and Massive MIMO with centralized processing will be used to serve high data rate applications and provide uniform coverage. Massive MIMO offers huge capacity gain by exploiting spatial diversity of the radio environment and minimizing interference among users. The main limiting factor is channel estimation error due to pilot-contamination which requires novel but practically realizable algorithms. MTC is characterized by huge number of low-data-rate users per cell. In many cases, MTC applications require transmission of only small number of packets per day. The classical cellular technologies are built on complex signaling protocols which can cause excessive overhead to MTC traffic. Another major concern in current cellular networks is deployment and maintenance costs which come from growing number of radio access technologies and deployment scenarios. This calls for a new architecture that enables flexible and low-cost deployments of various use cases. The thesis tackles these problems both from theoretical and from practical implementation perspectives. First, multi-user access schemes for efficient use the radio resources are proposed and evaluated through analytical tools and simulations. The proposed techniques include signal processing techniques for DAS systems, and efficient but less complex data-aided channel estimation algorithm to combat pilot-contamination in Massive MIMO systems. Moreover, a new MAC protocols for MTC is proposed. The protocol significantly reduces the overhead and is able to support large number of simultaneous transmissions. Finally, the thesis addresses practical implementation aspects of 5G systems in a Cloud RAN infrastructure that allows coordinated/centralized processing of data across multiple cells. Virtualization of baseband processing also offers deployment flexibility and low maintenance cost