Uplink Channel Estimation Delay Compensation
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Solution Overview
Problem
Current channel estimation methods in WCDMA systems fail to accurately account for transmit power control commands, leading to poorer channel estimation quality, especially for stationary, high-rate users where long averaging periods are beneficial.
Innovation Solution
A method and device for uplink channel estimation in wireless communication systems that involves providing a channel state model, estimating the delay between transmit power control commands and their application, and adapting channel states based on these commands to improve tracking accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transmit power control commands are applied every time slot, then transmit power is adjusted to maintain signal quality, but channel estimation accuracy deteriorates due to power fluctuations being mistaken for fading
Solution Approach 1:
The invention extracts the transmit power control component from the received signal variations. By separately identifying and removing the effect of TPC commands from the channel estimation process, the tracker can focus solely on estimating fading variations, thereby improving channel estimation accuracy while maintaining signal quality control
Solution Approach 2:
The invention introduces an intermediary element - the estimated transmit power control effect - that mediates between the TPC commands and the channel estimation process. This intermediary allows the system to account for power fluctuations without mistaking them for channel fading, resolving the contradiction between power control and estimation accuracy
2Adaptability or versatility
If tracker step size is increased to account for power control variations, then adaptability improves, but channel estimation quality deteriorates due to excessive filtering reduction
Solution Approach 1:
The invention applies local quality by differentiating between different sources of signal variation. Instead of using a uniform approach to handle all variations, the system specifically identifies and separates TPC-induced variations from fading variations, applying appropriate tracking parameters to each, thereby maintaining both adaptability and estimation quality
Solution Approach 2:
The invention changes the parameters of the tracking system by incorporating TPC command information into the estimation process. By adjusting the tracker's behavior based on known TPC commands, the system achieves better channel estimation quality without sacrificing adaptability to actual channel conditions
3Measurement precision
If long averaging periods are used for channel estimation, then estimation accuracy for stationary users improves, but responsiveness to actual channel changes deteriorates
Solution Approach 1:
The invention performs preliminary action by pre-compensating for the expected effect of TPC commands on the received signal. By accounting for power control variations in advance, the system can use longer averaging periods to improve estimation accuracy without the risk of mistaking TPC effects for channel changes, thereby maintaining responsiveness to actual fading
Data Source
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AI summary
A method for uplink channel estimation comprises providing (210) of a channel state model in a channel estimator. An uplink radio signal of a present time slot is obtained (220) in the channel estimator as well as a series of transmit power control commands (230) issued for controlling a transmit power of the uplink radio signal. A delay between the time a transmit power control command is issued and the time that the transmit power control command is applied is estimated (232) based on measurements of the particular received uplink radio signal. Channel states are adapted (234) based on a transmit power control command compatible with the estimated delay. After the adaptation, channel states of the present time slot are estimated (240) in the channel estimator, by tracking the demodulated uplink radio signal with the channel state model. A channel estimator performing such method is also described.