Browse Prior Art Database

Improvements for Uplink Power Control

IP.com Disclosure Number: IPCOM000130338D
Published in the IP.com Journal: Volume 5 Issue 11A (2005-11-25)
Included in the Prior Art Database: 2005-Nov-25
Document File: 7 page(s) / 580K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

Effective transmitter power control is essential for high-capacity cellular radio systems to provide a satisfactory quality of service (QoS). The estimated received SINR (Signal to Interference-plus-Noise Ratio) is compared to the target SINR for each user at the base station. If the received SINR is larger (lower) than the target SINR, the base station will command the mobile to reduce (increase) its power by a fixed step size (d). The target SINR is adapted very slowly by an outer loop to guarantee a certain QoS requirement. The power control commands transmitted via the downlink to the mobile terminal are corrupted by transmit power control command errors eTPC(k), so that the mobile station possibly updates its Tx power (Tx, Transmitter) differently than decided by the base station. Due to the limited transmit power the mobile can not always react as it is decided by the base station. E.g. in case the mobile transmits already with its maximal transmit power, a further power up command will not change the transmit power. As there is a logarithmical model used, the received SINR is the result of adding the channel power process A(k) to the Tx power X(k) and subtracting the interference noise power I(k). In case of fast and deep fading of the wireless channel, the performance of conventional Closed Loop Power Control (CLPC) is limited, as it can not track the channel due to the limited and fixed step size (d). Obviously in case of medium to high velocities (30-50 km/h) the standard deviation of the control error increases due to the fixed power update step size and the limited loop bandwidth.

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Improvements for Uplink Power Control

Idea: Meik Doerpinghaus, DE-Aachen; Lars Schmitt, DE-Aachen; Dr. Ingo Viering, DE-Munich; Axel

Klein, DE-Munich; Dr. Hans Dieterich, DE-Ulm; Joachim Schmid, DE-Ulm

Effective transmitter power control is essential for high-capacity cellular radio systems to provide a satisfactory quality of service (QoS). The estimated received SINR (Signal to Interference-plus-Noise Ratio) is compared to the target SINR for each user at the base station. If the received SINR is larger (lower) than the target SINR, the base station will command the mobile to reduce (increase) its power by a fixed step size (d). The target SINR is adapted very slowly by an outer loop to guarantee a certain QoS requirement. The power control commands transmitted via the downlink to the mobile terminal are corrupted by transmit power control command errors eTPC(k), so that the mobile station possibly updates its Tx power (Tx, Transmitter) differently than decided by the base station. Due to the limited transmit power the mobile can not always react as it is decided by the base station. E.g. in case the mobile transmits already with its maximal transmit power, a further power up command will not change the transmit power. As there is a logarithmical model used, the received SINR is the result of adding the channel power process A(k) to the Tx power X(k) and subtracting the interference noise power I(k).

In case of fast and deep fading of the wireless channel, the performance of conventional Closed Loop Power Control (CLPC) is limited, as it can not track the channel due to the limited and fixed step size
(d). Obviously in case of medium to high velocities (30-50 km/h) the standard deviation of the control error increases due to the fixed power update step size and the limited loop bandwidth.

At present this problem can be solved by increasing the target SINR to achieve the required BLER (Block Error Rate) on the link. Because interference of the CDMA (Code Division Multiple Access) is limited, the spectral efficiency decreases and less users with given QoS constraints can be supported. There has been also proposed a predictive power control for one step prediction, i.e. a TPC (transmit power control) command generation considering predicted channel states. However, it is assumed that the received power is estimated with no errors, and the power control feedback loop is assumed to be error free, i.e. the availability of the old and present channel states is supposed. This assumption is critical for a system concerning realistic scenarios with TPC errors and a Tx power limitation in the mobile terminal.

The following idea proposes to decrease the power control error variance by generating a TPC sequence accounting for the future channel fading states. Therefore, the following three components are necessary.

1) Nonlinear Controller

The nonlinear controller generates the transmit power control commands. A reasonable optimization crit...