Performance analysis of base station cooperation

© 2015 Dr. Rajitha SenanayakeBase station cooperation is envisioned to be a major component in future wireless network because of its potential to exploit interference and improve network performance. In this thesis we present a comprehensive and rigorous analytical investigation of cooperative cellular networks where multiple base stations process multiple user signals via a central processor. From a theoretical perspective, the challenge is to analytically evaluate the performance gains of cooperative networks when compared to traditional non-cooperative networks. The practical challenge is to design a realistic cooperative framework that strikes a balance between performance and complexity. First, we concentrate on a fully cooperative framework where the central processor has access to all the user signals. We adopt a general network scenario with arbitrary number of users transmitting to an arbitrary number of base stations and carry out optimal multiuser detection. Considering maximum likelihood (ML) estimation, we investigate the optimum error probability based on the pair wise error probability (PEP) bounds. We derive new bounds on the bit error probability (BEP) of an arbitrary network user when the channels are subjected to independent but not necessarily identically distributed Rayleigh fading with exponentially decaying path loss. We further extend our investigation to asymptotically characterize the BEP bounds at high signal-to-noise ratios (SNRs). For the fully cooperative framework, we observe that base station cooperation can significantly improve the error performance compared to a traditional non-cooperative network. In reality, however, collecting all the user signals at one central processor is not always feasible. As such, for large-scale distributed networks, we practically constrain the cooperation to a set of geographically neighboring base stations referred to as a cluster. Taking into account the effect of interference from out-of-cluster users, we contest the significant error probability gains obtained by fully cooperative networks and highlight that the error performance enters a saturation regime at high SNRs. To obtain further insights we extend our investigation to a mixed Rician-Rayleigh fading model where users experience a line-of-sight signal path to their nearest base station. Our new error probability results prove that base station cooperation cannot convert an interference limited network into a noise limited network. Next, we focus on the achievable rate of cluster-based cooperative networks. Based on linear minimum mean square error (LMMSE) estimation, we investigate two processing architectures, namely a centralized processing architecture and a decentralized processing architecture. In the centralized case, all the in-cluster user signals are processed at one central processor whereas in the decentralized case each base station locally estimates the in-cluster user signals before sending them to the central combiner. As such, the centralized architecture adds more overhead to the network compared to the decentralized architecture. Interestingly, our numerical examples show that the decentralized processing architecture can offer a comparable achievable rate performance to the centralized processing architecture. Finally, we consider the effect of equipping large numbers of antennas at each base station in a so-called distributed massive multiple-input multiple-output (MIMO) network. For this network, we consider a simple zero-forcing (ZF) receiver at the central processor to exploit the performance advantages of massive MIMO. To gain analytical insights, we derive a simple and an accurate approximation for the SNR of an arbitrary network user. Based on our SNR approximation, we evaluate the error probability and the achievable rate of distributed massive MIMO. Our theoretical results serve to underscore the practical implementation benefits of distributed massive MIMO in future generation cooperative cellular networks

The public perceptions of urban sanitation infrastructure: a cross-sectional study in Kegalle township in Sri Lanka

Improving public restroom facilities in urban areas can contribute to ensuring the overall living standards of the urban populace. Access to improved sanitation and hygiene is also considered a fundamental human right. Therefore, the present study aims to understand public perceptions of urban public restroom use based on a case study conducted in the municipality of Kegalle township in Sri Lanka. This included a questionnaire survey (N = 115) and in-depth interviews (N = 5). The analysis indicates the urgent need for adequate, accessible, and good-quality sanitary services, particularly in densely populated urban areas of the country. More than 70% of people (from N = 115) indicate that public restrooms are not of good quality due to certain reasons such as poor maintenance and uncleanliness. Despite the insalubrity of public restrooms, many respondents have used them, indicating an urgent policy intervention in operating, and properly maintaining public restrooms in densely populated urban areas of the country. A significant number of respondents indicated that the quality of public restrooms is extremely poor (39%) or poor (31.1%). Around 86.9% of respondents are not satisfied with existing public restrooms, thus, 71.4% believe in reconstructing new public restrooms that pave the way for ensuring access, affordability, quality, and safety. HIGHLIGHTS In total, 70% of respondents indicated that the quality of public restrooms is poor due to poor maintenance.; In total, 86.9% of respondents were dissatisfied with the current state of public restrooms.; In total, 71.4% were in favor of constructing new public restrooms that ensure accessibility, affordability, quality, and safety.; The study demonstrated the demand and need for high-quality sanitation services in densely populated urban areas.