Constellation Inversion for ACK NACK Interference Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In radio communication systems, the error rate performance of NACK signals is compromised due to inter-code interference from ACK signals during code-multiplexing, leading to increased error rates and potential delays in downlink data transmission.
Innovation Solution
A radio communication apparatus and method that employs first and second spreading sections using sequences with different cyclic shift values and orthogonal sequences, respectively, and an inverting section to rotate the constellations of response signal groups, thereby reducing inter-code interference between ACK and NACK signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If code-multiplexing is performed by spreading response signals using ZAC sequences with different cyclic shift values, then the number of multiplexed signals increases, but inter-code interference between ACK and NACK signals occurs leading to increased error rates
Solution Approach 1:
The patent inverts the constellation of NACK signals by 180 degrees relative to ACK signals. Specifically, ACK signals use constellation points at phases 0 and π, while NACK signals use constellation points at phases π/2 and 3π/2. This inversion separates the signal spaces of ACK and NACK, preventing inter-code interference when both signal types are multiplexed using the same ZAC sequence resources.
Solution Approach 2:
The patent applies different constellation configurations to different signal types (ACK vs. NACK) within the same code-multiplexing framework. By assigning distinct constellation points and phases to ACK and NACK signals locally, the system maintains high multiplexing capacity while ensuring reliable differentiation between signal types even when transmitted on overlapping resources.
2Productivity
If the same ZAC sequences are used for both ACK and NACK signals, then resource utilization improves, but interference between ACK and NACK signals increases causing detection errors
Solution Approach 1:
The patent enables reuse of the same ZAC sequences for both ACK and NACK by inverting the constellation of one signal type. This allows full resource utilization while maintaining signal integrity through the 180-degree phase inversion that creates orthogonal signal spaces for detection.
Solution Approach 2:
The patent creates a composite signaling scheme that combines code-multiplexing (using ZAC sequences) with constellation differentiation (phase inversion). This composite approach leverages both code division and signal space division to achieve high resource efficiency while preventing interference between signal types.
3Device complexity
If constellation points for ACK and NACK are not separated, then signaling simplicity is maintained, but inter-code interference causes increased NACK error rates leading to unnecessary retransmissions
Solution Approach 1:
The patent introduces constellation inversion as a simple yet effective mechanism to separate ACK and NACK signal spaces. This approach maintains signaling simplicity by using the same sequence resources while adding only a phase transformation layer, avoiding complex signaling overhead.
Solution Approach 2:
The patent changes the phase parameter of constellation points to differentiate between ACK and NACK signals. By rotating the constellation by 180 degrees for NACK signals, the system achieves reliable signal differentiation without altering the underlying code-multiplexing structure or adding significant complexity.
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
Provided is a radio communication device which can improve the NACK error rate characteristic. The device includes: a scrambling unit (214) which multiplies a response signal after modulated, by a scrambling code "1" or "-1" so as to inverse a constellation for each of response signals on a cyclic shift axis; a spread unit (215) which performs a primary spread of the response signal by using a ZAC sequence set by a control unit (209); and a spread unit (218) which performs a secondary spread of the response signal after subjected to the primary spread, by using a block-wise spread code sequence set by the control unit (209).