Dynamic TPC Power Offset for Soft Handover Reliability
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Solution Overview
Problem
Existing methods for transmitting and using Transmission Power Control (TPC) commands in CDMA systems during soft handover can lead to unreliable power control, resulting in unbalanced uplink and downlink conditions, which may cause high Rise Over Thermal (RoT) peaks and system instability due to the discarding of unreliable TPC commands.
Innovation Solution
Adjusting the TPC power offset for each radio base station based on measurements reflecting the quality of the downlink channel carrying the uplink TPC command, such as estimated uplink DPCCH SINR, number of TPC 'up' and 'down' commands, and aggregated UE receiver power, and implementing selective TPC command discarding based on the number and reliability of simultaneously received commands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If TPC commands are discarded when SINR falls below threshold, then reliability of power control is improved, but uplink quality deteriorates due to unnecessary power decreases
Solution Approach 1:
The patent applies dynamics by making the TPC power offset adjustable rather than fixed. The offset is dynamically adapted based on channel conditions and handover states, allowing the system to optimize between reliability and quality in different operational scenarios. This resolves the contradiction by enabling the system to maintain higher offsets during soft handover to prevent unnecessary power decreases while keeping lower offsets during stable connections.
Solution Approach 2:
The patent changes the parameter of TPC power offset based on different operational states. By monitoring whether the UE is in soft handover or not, and adjusting the offset accordingly, the system can prevent the harmful effect of discarding reliable TPC commands during handover while maintaining the benefit of discarding unreliable commands during stable connections. This parameter adaptation resolves the contradiction between reliability improvement and quality preservation.
2Reliability
If TPC power offset is increased to improve reliability, then TPC command reliability is improved, but system stability deteriorates due to excessive uplink power increases
Solution Approach 1:
The patent applies local quality by differentiating the TPC power offset for different radio base stations and different operational states. Instead of using a single uniform offset for all TPC commands, the system assigns specific offset values based on the serving cell, non-serving cell, and handover status. This localized approach allows high reliability where needed (during handover) while preventing excessive power increases that would harm stability during normal operation.
Solution Approach 2:
The patent dynamically changes the TPC power offset parameter based on the UE's operational state. When the UE is in soft handover, a higher offset is applied to ensure reliable TPC reception. When the UE is not in handover, a lower or zero offset is used to prevent excessive power increases. This conditional parameter change resolves the contradiction between reliability and stability.
3Reliability
If selective TPC discarding is implemented, then reliability of power control is improved, but device complexity increases due to additional processing requirements
Solution Approach 1:
The patent applies segmentation by dividing the TPC processing into different paths based on handover state. The system segments the decision logic: during soft handover, TPC commands are generally accepted with adjusted offset; during normal operation, standard discarding rules apply. This segmentation simplifies the overall complexity compared to implementing full selective discarding analysis in all scenarios, while still improving reliability where it matters most.
Data Source
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AI summary
In a cellular radio system Transmission Power Control (TPC) power offset is set sothat it is adjusted for each transmitting radio base station based on available relevant measurements that reflect the quality of the downlink channel carrying the uplink TPC command whereby an improved performance is obtained. The TPC power offset can for example be based on an estimated uplink Dedicated Physical Control CHannel (DPCCH) SINR, the number of TPC "up" and the number of TPC "down" sent bya radio base station and aggregated UE receiver power or UE transmit power over a number N slots. Also a mobile station used in a cellular radio system supporting soft handover may be adapted to apply TPC discarding thresholds based on the number and the quality of simultaneously received TPC commands. The discarding procedure in the mobile station may also be carried out selectively such that TPC commands that are determined to be unreliable are not discarded but selectively discarded based on how reliable they are determined to be.