Limited feedback for multicell cooperative systems

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Title: Limited feedback for multicell cooperative systems
Author: Bhagavatula, Ramya
Abstract: 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 .
URI: http : / /hdl .handle .net /2152 /ETD -UT -2010 -12 -2553
Date: 2011-02-11

Citation

Limited feedback for multicell cooperative systems. Doctoral dissertation, University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /ETD -UT -2010 -12 -2553 .

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