OFDM Superposition Coding Signal Separation
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Solution Overview
Problem
Current superposition coding in OFDM networks faces limitations in optimizing spectral efficiency and interference cancellation, particularly in scenarios where multiple signals share the same resources, leading to suboptimal performance and varying SINR conditions.
Innovation Solution
The method involves combining OFDM-modulated signals using non-orthogonal resources after IDFT processing, with cyclic prefixes appended before combination, and utilizing pilot signals with scrambling or spreading codes to distinguish between signals, allowing for effective recovery and subtraction of interference in receivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple signals are transmitted using the same non-orthogonal resources with superposition coding, then spectral efficiency is improved, but signal interference and difficulty in signal recovery increase
Solution Approach 1:
The patent applies preliminary action by appending cyclic prefixes to signals before superposition coding and transmission. This preprocessing step establishes time alignment and enables the receiver to perform effective interference cancellation through successive interference cancellation (SIC), resolving the interference issue while maintaining spectral efficiency gains
Solution Approach 2:
The patent converts the harmful interference between superposed signals into a beneficial structure for interference cancellation. By designing the system so that the stronger signal can be decoded first and then subtracted from the composite signal, the interference that initially degrades performance becomes a manageable component in the SIC process, enabling recovery of weaker signals
2Reliability
If signals are combined after IDFT processing with cyclic prefixes, then interference cancellation effectiveness is improved, but device complexity increases
Solution Approach 1:
The patent applies segmentation by separating the processing of different signals in the time domain through cyclic prefix insertion. This segmentation allows the receiver to identify and process signals in distinct time intervals, making the successive interference cancellation process more effective while organizing the complexity into manageable stages
3Difficulty of detecting and measuring
If pilot signals with scrambling codes are used to distinguish signals, then signal distinction capability is improved, but processing complexity increases
Solution Approach 1:
The patent introduces pilot signals with scrambling codes as intermediary elements that facilitate signal distinction and channel estimation. These pilot signals act as mediators between the transmitted superposed signals and the receiver's decoding process, enabling the receiver to differentiate between signals and perform accurate SIC despite the increased processing requirements
Data Source
AI summary
Improvements are provided in an OFDM network that uses superposition coding. A broadcast signal and e.g. a unicast signal are each subjected to OFDM modulation including processing by an IDFT, combined, and transmitted using non-orthogonal transmission resources. In one approach, the respective signals are combined after instead of before the IDFT processing. In specific examples, a respective cyclic prefix is appended to each signal after the IDFT processing but before the respective signals are combined. In another approach, a broadcast pilot signal and e.g. a unicast pilot signal are transmitted concurrently with the broadcast and unicast information signals. The pilot signals are transmitted using the same time and subcarrier resources, but are made more distinguishable by combining each with a respective scrambling or spreading code. In specific examples, embodiments, the unicast pilot signal is used for estimating the data rate for transmission of further unicast information signals.