Text

theses

Over the last few years, the proliferation of personal mobile computing devices like tablets and smartphones along with a plethora of data-intensive mobile applications has resulted in a tremendous increase in demand for ubiquitous and high data rate wireless communications. However, the system capacity is limited by the radio interference, which makes it difficult to improve the spectral efficiency and consequently the data rate. Current practice to enhance spectral efficiency and data rate is to increase the number of Base Stations (BSs) and go for smaller cells so as to increase the band reuse factor. However, performing additional deployment and maintenance of a large number of cellular BSs is highly inefficient due to excessive capital and operational expenditures. Moreover, with smaller cells the interference problem becomes even more challenging. It is also studied that increasing the BS density or the number of transmit antennas will decrease the energy efficiency due to the dynamic traffic variation. This is because the current cellular architecture is over 40 years old and was not originally designed for high spectral and energy efficiency performance but for coverage and mobility considerations. Cloud Radio Access Network (C-RAN) is a new paradigmatic architecture for wireless cellular networks that allows for dynamic reconfiguration of computing and spectrum resources while keeping the cost of delivering services to the users low. C-RAN consists of three main parts: 1) Remote Radio Heads (RRHs) plus antennae, which are located at the remote site and are controlled by Virtual Base Stations (VBSs) housed in a centralized processing pool, 2) the Base Band Unit (BBU) (known as VBS pool) composed of high-speed programmable processors and real-time virtualization technology to carry out the digital processing tasks, and 3) low-latency high-bandwidth optical fibers, which connect the RRHs to the VBS pool. In a centralized VBS pool, since all the information from the BSs resides in a common place, the VBSs can exchange control data at Gbps. This centralized characteristic along with virtualization technology and low-cost relay-like RRHs provides a higher degree of freedom in order to make optimized decisions; all these features combined have made C-RAN a promising technology candidate to be incorporated into the 5G wireless network standard. The overarching goal of the research presented in this thesis is to design new techniques for increasing the spectral and energy efficiency of the next generation wireless cellular networks. In order to increase the spectral efficiency and energy efficiency, we leverage the C-RAN architecture and propose four solutions, namely 1) Cloud-BSS, 2) DJP, 3) Cloud-CFFR, and 4) Elastic-Net. In Cloud-BSS, we study the performance of Blind Source Separation (BSS) in order to separate the interference from the desired signal and explore how the performance changes in different topologies. Since Cloud-BSS does not take any action to mitigate the inter-cluster interference, we propose DJP to decrease both the intra- and inter-cluster interference. Moreover, in order to improve the performance of Fractional Frequency Reuse (FFR), we propose Cloud-CFFR, which is able to reject the intra-cluster interference and decrease the inter-cluster interference. Finally, in order to increase the energy efficiency, we propose Elastic-Net, where the network parameters are optimized and adapted based on the traffic fluctuation so that the power consumption is minimized while the resource utilization is maximized.

ETD_8790

Ph.D.

Includes bibliographical references

by Abolfazl Hajisami

doi:10.7282/T30G3PKZ

ETD doctoral

The author owns the copyright to this work.