Signal-to-Noise Ratio Determination Using Unused Channelization Codes
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Solution Overview
Problem
In WCDMA systems, cross-finger interference causes significant power leakage between channels from different multipaths, leading to inaccurate signal-to-noise ratio (SIR) measurements and power control loop divergence, especially in high-speed uplink packet access environments where the interference can be stronger than noise power, severely impacting throughput.
Innovation Solution
A method involving despreading received signals using an unused channelization code to create a virtual noise channel, canceling noise power from signal power, and determining SIR based on noise and signal power estimates, which excludes cross-finger interference, allowing for accurate noise and signal power estimation and improved power control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional correlation function is used for SIR measurement, then measurement process is simple, but cross-finger interference causes huge offset in noise power estimation and SIR measurement
Solution Approach 1:
The patent segments the received signal into multiple components by applying different channelization codes: used codes extract signal components while unused codes extract noise components. This segmentation allows separate estimation of signal power and noise power, eliminating cross-finger interference from the noise measurement.
Solution Approach 2:
The patent introduces an intermediary approach by using unused channelization codes as a mediator to isolate and measure only the noise component. This intermediary method creates a clean separation between signal and noise measurements, preventing interference contamination.
2Productivity
If cross-finger interference is strong (e.g., E-DPDCH power 100s of times stronger than DPCCH), then system throughput may increase, but power control loop diverges and cannot set correct power gain factor
Solution Approach 1:
The patent implements accurate feedback by providing true noise power estimation to the power control loop. By eliminating cross-finger interference from the noise measurement, the feedback signal accurately reflects the actual channel conditions, enabling the power control loop to converge to correct power settings even when interference is strong.
3Measurement precision
If noise power is estimated from received signal including cross-finger interference, then noise power estimation includes huge offset, but if interference is removed then accurate noise power can be obtained
Solution Approach 1:
The patent segments the received signal into signal components and noise components by applying different channelization codes. Used channelization codes process signal components while unused codes process only noise components, enabling clean separation and accurate noise power estimation without interference contamination.
Data Source
AI summary
In one embodiment, the method includes despreading the received signals by applying an unused channelization code, determining noise power based on output of the despreading, and determining a signal-to-noise ratio, SIR, based on the noise power and at least one of the received signals.