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Power Allocation for Downlink Shared Channel in UMTS

IP.com Disclosure Number: IPCOM000008864D
Original Publication Date: 2002-Jul-18
Included in the Prior Art Database: 2002-Jul-18
Document File: 6 page(s) / 103K

Publishing Venue

Motorola

Related People

Rapeepat Ratasuk: AUTHOR [+4]

Abstract

In UMTS, the Downlink Shared Channel (DSCH) is used to transmit data packets from the Node B to the User Equipment (UE) using the fat pipe multiplexing concept. Each DSCH is associated with a Dedicated Channel (DCH) which is used for power control, channel estimation and transmission of associated control information for the DSCH. In this paper, we propose a method to determine the power allocation of the DSCH and its associated DCH such that any Service Frame Error Rate (SFER) target can be met for both the DSCH and the associated DCH subject to power availability. The proposed algorithm relies on a two-step process to accomplish this goal. First, the required Ec/Iors (based on given target SFERs) for the DSCH and DCH are determined from a reference curve plus offset factors that are based solely on the requested data rates. From these two power requirements, the gain factor of the DSCH is set relative to the associated DCH. Next, outer-loop power control is used to drive the operating SFER of the DCH to its target range regardless of channel conditions. Since power control in the DSCH is coupled with that on the DCH, its operating SFER will also converge to the target range. From simulation results, it is shown that the proposed algorithm is able to accommodate the required SFER targets with high accuracy under various fading channel conditions and service rates.

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Power Allocation for Downlink Shared

Channel in UMTS

Rapeepat Ratasuk, Weimin Xiao, Divya Muralidhar, Amitava Ghosh

Advanced Radio Technology, GTSS

Motorola Inc.

1421 W. Shure Drive, Arlington Heights, IL, 60004

1         Abstract

In UMTS, the Downlink Shared Channel (DSCH) is used to transmit data packets from the Node B to the User Equipment (UE) using the fat pipe multiplexing concept.  Each DSCH is associated with a Dedicated Channel (DCH) which is used for power control, channel estimation and transmission of associated control information for the DSCH.  In this paper, we propose a method to determine the power allocation of the DSCH and its associated DCH such that any Service Frame Error Rate (SFER) target can be met for both the DSCH and the associated DCH subject to power availability.  The proposed algorithm relies on a two-step process to accomplish this goal.  First, the required Ec/Ior’s (based on given target SFER’s) for the DSCH and DCH are determined from a reference curve plus offset factors that are based solely on the requested data rates.  From these two power requirements, the gain factor of the DSCH is set relative to the associated DCH.  Next, outer-loop power control is used to drive the operating SFER of the DCH to its target range regardless of channel conditions.  Since power control in the DSCH is coupled with that on the DCH, its operating SFER will also converge to the target range.  From simulation results, it is shown that the proposed algorithm is able to accommodate the required SFER targets with high accuracy under various fading channel conditions and service rates. 

2         Introduction

In UMTS, the Downlink Shared Channel (DSCH) is used to transmit data packets from the Node B to the mobile UE.  Each DSCH is associated with a Dedicated Channel (DCH).  The downlink shared channel is power controlled by the associated dedicated channel.  Naturally, for each user there is a Quality of Service (QoS) requirement associated with each channel.  This QoS requirement is usually expressed in term of the average Service Frame Error Rate (SFER) for the duration of the call.  For instance, the user may require the SFER on the DCH to be around 1% while requiring an SFER of 10% for the DSCH.  Thus, at the serving Node B, power must be allocated between the DCH and its associated DSCH according to this predetermined set of QoS requirements.  In UMTS, this power allocation process is accomplished by assigning an appropriate gain factor to each channel. 

In this paper, a method is proposed to address the problem of selecting the gain factors for the DSCH and its associated DCH of an UE such that any prescribed set of QoS requirements can be achieved subject to power availability.  In addition, the method aims to achieve these QoS requirements using minimal transmission power.  The outline of the paper is as follows.  In Section 3, a detailed discussion of the power allocation algorithm is given.  This is followed, in Section 4, by simulation assumptions and...