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Interference based power control in local area environment
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School of Electrical Engineering |
Master's thesis
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S-72
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en
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x + 66
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Abstract
OFDM has been chosen by 3GPP as the access scheme for uplink UTRAN Long term Evolution (LTE) because of its inherent robustness against frequency selective fading and ability to remove intra-cell interference. As OFDMA provides intra-cell orthogonality, one of the main reasons for performance degradation is the inter-cell interference.
This degradation is accentuated by the frequency reuse factor of 1 deployed in the system, which makes the Power Control (PC) functionality a critical issue. Power Control aims to adjust the powers of ail mobiles so as to minimize the network interference but at the same time maximize the user data rate. The PC algorithm in LTE contains an open loop and a closed loop component. The open loop power control compensates for slow varying path loss and shadowing, while the closed loop power control aims to adjust the variations caused by fast fading.
Recently a new modification to the original LTE Uplink PC has been proposed. The new PC scheme boasts to have better performance in terms of cell edge throughput by including the path loss to the strongest interferer in the PC formula.
In this thesis, the LTE OLPC as well as the new proposed formula is studied in detail with particular focus on some of the associated parameters. To find the best possible performance values of these parameters, values other than those proposed by the standard have also been exhaustively searched. Due to large number of possible outcomes simulations are carried out first in a simple simulator and the results obtained are then further scrutinized in a complex local area office environment.
With particular focus on the cell edge performance, comparison is carried out between the two different PC schemes. The results show that in an indoor office environment the newly proposed PC scheme provides 5 % gain in average user throughput and about 8 % gain in cell edge throughput. Using curve fitting a model is developed which is general enough to predict the values of power control parameters in an indoor environment, given the required throughput.