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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Limited feedback for multicell cooperative systems

Bhagavatula, Ramya 11 February 2011 (has links)
Cellular systems are interference limited in nature. This problem is further accentuated in upcoming commercial wireless standards, which intend to use all the available spectrum in every cell in the network to improve peak data rates. This, however, could lead to considerable interference among neighboring cells, decreasing data rates and causing outages at the cell-edge. Multicell cooperation offers a solution for reducing the high levels of interference. The basic idea is that base stations coordinate transmissions by sharing user information among themselves via backhaul links. With the backhaul being bandwidth limited, cooperative strategies that involve the exchange of only user channel state information (CSI) among base stations offer the best tradeoff between complexity, backhaul load and performance gains. This dissertation focuses on these partial cooperative techniques, known as coordinated beamforming in 3GPP LTE Advanced. In existing frequency division duplex systems, users estimate and feedback the CSI of a single channel over a finite-bandwidth feedback link, using limited feedback techniques. In a multicell cooperative scenario, each user needs to transmit the CSI of multiple channels using the same feedback link. This implies that the available feedback bandwidth must be efficiently shared among different channels to maximize performance gains in the cellular network. This dissertation develops three different approaches to limited feedback in multicell cooperative systems. The first technique, separate quantization, involves each channel being fed back individually using a different codebook. Closed-form expressions are derived to partition adaptively the available feedback bits, as a function of the signal strengths and delays associated with each of the multiple channels. The second strategy is known as joint quantization, where the CSI of all the channels are quantized together as a composite vector. It is shown that though this approach yields higher data rates with smaller feedback requirements than separate quantization, it requires the design and storage of special codebooks. Finally, predictive joint quantization is proposed to exploit the temporal correlation of the wireless channel to reduce feedback requirements significantly as compared to the other two strategies, at the cost of high complexity at the user terminals. / text
2

Multicell coordination with multiple receive antennas

Hwang, Insoo 25 February 2014 (has links)
In multicell coordinated networks where multiple base stations cooperate to jointly combat interference from adjacent cells and fading to receivers, one of the outstanding questions is what is the role of receive antenna and receiver processing. Multiple receive antennas not only enable additional degrees of freedom at each receiver to combat the other-cell interference but also can change the transmitter design because transmitter and receiver beamforming design is often closely coordinated. In this dissertation, we investigate the role of the multiple receive antennas in multicell cooperative systems under different interference conditions. We then present novel non-iterative and iterative coordinated beamforming and precoding algorithms with different receiver processing. We present comprehensive performance comparison of various multicell cooperative systems and explore the feasibility of achieving much higher throughput via hyper-densification of heterogeneous and small cell networks with mandatory multicell cooperation. / text

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