OFDM Receiver Equalization for Local Content Insertion
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Solution Overview
Problem
In single frequency OFDM networks, inserting local content is challenging as existing techniques struggle to differentiate between national broadcast and local broadcast signals without causing interference, especially in multi-path fading channels.
Innovation Solution
A receiver and transmitter system using two related modulation schemes, where the first modulation scheme is a lower order scheme for national broadcast and a higher order scheme for local service, with pilot symbols to estimate channels and recover local service data symbols, allowing for effective local content insertion while maintaining national broadcast signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If hierarchical modulation scheme is used to insert local data in single frequency network, then local content insertion capability is improved, but signal differentiation and interference management becomes more difficult
Solution Approach 1:
The patent segments the broadcast signal into hierarchical modulation layers (national broadcast data and local service data) transmitted on the same frequency. The receiver segments these layers through selective demodulation, allowing independent processing of national and local content without mutual interference
Solution Approach 2:
The patent applies different modulation schemes to different data layers: national broadcast data uses a first modulation scheme while local service data uses a second modulation scheme. This local quality differentiation enables the receiver to selectively process desired content while filtering out unwanted interference
2Measurement precision
If hierarchical modulation with two modulation schemes is used, then local service data recovery is improved, but channel estimation accuracy deteriorates in multi-path fading channels
Solution Approach 1:
The patent introduces pilot symbols as intermediary reference signals embedded in the transmitted signal. These pilots serve as mediators that enable accurate channel estimation and compensation for multi-path fading effects, allowing reliable recovery of local service data even in challenging channel conditions
Solution Approach 2:
The system uses pilot symbols to continuously monitor and estimate channel conditions, providing feedback information that enables dynamic compensation for multi-path fading. This feedback mechanism maintains channel estimation reliability despite the complexity of hierarchical modulation
3Measurement precision
If local pilot symbols are incorporated for channel estimation, then local service data detection is improved, but receiver processing complexity increases
Solution Approach 1:
The patent incorporates pilot symbols in advance within the transmitted signal structure, performing preliminary channel characterization before actual data transmission. This preliminary action enables the receiver to pre-compute channel compensation factors, reducing the processing complexity during active data detection phases
Data Source
AI summary
A receiver recovers local service data symbols from first Orthogonal Frequency Division Multiplexed (OFDM) symbols in the presence of second OFDM symbols. The second OFDM symbols carry national broadcast data symbols and modulated on to the sub-carriers of the second OFDM symbols using a first modulation scheme. The first OFDM symbols carry the national broadcast data symbols and the local service data symbols from a local insertion pipe and modulated on to the sub-carriers of the first OFDM symbols using a second modulation scheme. The receiver comprises an OFDM detector which includes an equalizer to recover local service modulated sub-carriers of the second modulation scheme.