Hierarchical Modulation Receiver for Local Content Insertion in SFN
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Solution Overview
Problem
In single frequency OFDM networks, inserting local content is challenging as existing techniques struggle to differentiate and recover local service data symbols from national broadcast data symbols without causing interference or losing data due to channel effects like multi-path fading.
Innovation Solution
A receiver and transmitter system using a hierarchical modulation scheme with two related modulation schemes, where the first modulation scheme is a lower order scheme and the second is a higher order scheme, allowing the receiver to estimate and recover local service data symbols by convolving channel estimates and subtracting national broadcast data symbols, and using local pilots to estimate channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If hierarchical modulation is used to transmit both national broadcast data and local service data on the same frequency, then data transmission capability is improved, but difficulty in detecting and measuring local service data symbols increases
Solution Approach 1:
The patent segments the modulation scheme into two distinct hierarchical layers: a first modulation scheme (e.g., QPSK) for national broadcast data and a second modulation scheme (e.g., 16QAM) for local service data. This segmentation allows the receiver to separately process and recover each data type by exploiting the hierarchical structure, where the constellation points of the first scheme are a subset of the second scheme's constellation points.
Solution Approach 2:
The patent applies local quality by using different modulation characteristics for different data types within the same signal. The first modulation scheme uses a coarser constellation structure suitable for robust national broadcast transmission, while the second modulation scheme uses a finer constellation structure for local service data. This allows differentiated processing at the receiver based on the specific data type being recovered.
2Adaptability or versatility
If local service data is inserted in a single frequency network, then service versatility is improved, but interference between local and national data increases
Solution Approach 1:
The patent implements nesting by embedding the first modulation scheme's constellation points within the second modulation scheme's constellation points. The hierarchical structure allows the national broadcast data (first scheme) to be nested within the local service data transmission (second scheme), enabling both data types to coexist on the same frequency without mutual interference. The receiver can extract either data type independently by exploiting the nested structure.
3Device complexity
If conventional reception techniques are used in multi-path fading channels, then device complexity is reduced, but data integrity deteriorates
Solution Approach 1:
The patent applies preliminary action by performing channel estimation and equalization specifically tailored to the hierarchical modulation structure before data recovery. The receiver first estimates the channel response using known pilot symbols, then applies equalization to compensate for multi-path fading effects specific to each modulation layer. This preliminary processing ensures that subsequent data recovery operates on already-corrected signals, improving integrity without requiring complex post-processing.
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, and 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 equaliser for recovering local service modulated sub-carriers of the second modulation scheme by generating an estimate of a combined channel ([Hn(z)+Hl(z)]) via which the first and second OFDM symbols have passed using the pilot sub-carrier symbols of the first and second OFDM symbols.