Reference Signal Phase Control for CQI Interference Reduction
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Solution Overview
Problem
In 3GPP-LTE systems, the orthogonality of cyclic shift sequences is broken down due to channel delays and other factors, leading to interference between CQI signals and reference signals, which deteriorates channel estimation accuracy and CQI demodulation performance.
Innovation Solution
A radio communication terminal apparatus and method that generate and transmit reference signals with controlled phase differences based on allocated cyclic shift indices, reducing interference between adjacent cyclic shifts by associating cyclic shift indexes with complex coefficients {w1, w2} to improve signal separation and channel estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cyclic shift sequences are used to separate CQI signals from different terminals, then code multiplexing capability is improved, but orthogonality is broken down due to channel delays causing interference between adjacent cyclic shifts
Solution Approach 1:
The invention changes the phase parameter of reference signals by associating different cyclic shift indexes with specific phase differences. When a terminal uses cyclic shift index n, the reference signal applies a phase difference of n×π/4 between adjacent subcarriers. This parameter change maintains the orthogonality of cyclic shift sequences even under channel delays, preventing interference between adjacent cyclic shifts while preserving code multiplexing capability for separating CQI signals from different terminals.
2Object-affected harmful factors
If phase difference is controlled in accordance with cyclic shift index, then interference between adjacent cyclic shifts is reduced, but system complexity increases due to additional phase control mechanism
Solution Approach 1:
The system achieves self-service by having terminals automatically determine the phase difference based on their allocated cyclic shift index without requiring additional signaling or complex coordination. The base station simply assigns a cyclic shift index to each terminal, and the terminal independently applies the corresponding phase difference (n×π/4) to its reference signal, reducing interference while maintaining system simplicity.
Data Source
AI summary
It is possible to provide a radio communication terminal device and a radio transmission method which can improve reception performance of a CQI and a reference signal. A phase table storage unit stores a phase table which correlates the amount of cyclic shift to complex coefficients {w1, w2} to be multiplied on the reference signal. A complex coefficient multiplication unit reads out a complex coefficient corresponding to the amount of cyclic shift indicated by resource allocation information, from the phase table storage unit and multiplies the read-out complex coefficient on the reference signal so as to change the phase relationship between the reference signals in a slot.