Wireless Signal Subframe Alignment for Interference Cancellation
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Solution Overview
Problem
In wireless communication systems, full duplex or TDD/FDD eIMTA environments face interference cancellation challenges due to carrier frequency offset differences between uplink and downlink signals, which degrade channel estimation and interference cancellation performance.
Innovation Solution
A method is implemented where a first device transmits system information and a downlink signal in a prescribed subframe, indicating whether a frequency shift or time shift is applied, based on uplink transmission parameters, to align the subframe for interference cancellation, using a time offset of 624 Ts, and informs the second device through physical or higher layer signaling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If downlink signal is transmitted in uplink subframe without frequency/time shift, then transmission simplicity is maintained, but interference cancellation performance degrades due to carrier frequency offset mismatch
Solution Approach 1:
The patent applies frequency shift and time shift parameters to the downlink signal transmitted in uplink subframes. The frequency shift aligns the carrier frequency with the uplink carrier frequency, while the time shift (624 Ts) aligns the subframe boundary with the uplink subframe boundary. These parameter changes enable the received uplink signal to match the transmitted downlink signal characteristics, thereby improving interference cancellation performance without requiring complex additional hardware.
2Reliability
If frequency shift and time shift are applied to align subframes, then interference cancellation performance improves, but system complexity increases due to additional signaling and processing
Solution Approach 1:
The patent performs preliminary frequency shift and time shift adjustments on the downlink signal before transmission in uplink subframes. By pre-aligning the carrier frequency and subframe boundary, the system eliminates the need for complex real-time interference cancellation processing at the receiver. The frequency shift is applied by tuning the oscillator based on uplink transmission CFO, and the time shift uses a predetermined offset of 624 Ts, both of which are configured in advance to simplify overall system processing.
3Productivity
If uplink subframe is used for downlink transmission, then spectrum efficiency improves, but interference from adjacent cell uplink transmissions increases without proper alignment
Solution Approach 1:
The patent employs a copying approach where the downlink signal transmitted in the uplink subframe is made to replicate the characteristics of the uplink signal. By applying the same frequency shift (CFO) and time shift (624 Ts offset) that are used for uplink transmission, the downlink signal becomes a copy of what the uplink receiver expects to receive. This allows the receiver to effectively cancel the interference by subtracting the copied signal from the received signal, thereby enabling spectrum reuse in uplink subframes without suffering from adjacent cell interference.
Data Source
AI summary
According to one embodiment of the present invention, a method by which a first device transmits and receives a signal in a wireless communication system comprises the steps of: transmitting system information; and transmitting a downlink signal in a predetermined subframe on the basis of the system information, wherein, when the predetermined subframe is indicated as a subframe for an uplink transmission in the system information, the first device transmits, to a second device, information indicating that a frequency shift has been applied and/or information indicating that a time shift has been applied.