OFDM Preamble Transmission for Frequency Offset Correction
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Solution Overview
Problem
In OFDM-based broadcast systems, receivers face challenges in obtaining complete control information due to frequency offset errors, leading to potential data reception failures, especially when preambles are segmented and require reordering.
Innovation Solution
A method and apparatus for transmitting and receiving preambles in OFDM systems that include generating a preamble block with a known sequence and repeating it in the frequency axis direction, allowing for robust frequency offset correction and eliminating the need for reordering segmented preambles by using a sequence detector to calculate the start position and length of the code block.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If preambles are segmented and transmitted across multiple frequency bands, then bandwidth utilization is improved, but frequency offset errors cause loss of control information and reception failures
Solution Approach 1:
The preamble is divided into multiple segments that are transmitted across different frequency bands. Each segment contains a portion of the control information, allowing the system to utilize wider bandwidth while maintaining the ability to recover control information even if some segments are affected by frequency offset errors.
Solution Approach 2:
The patent changes the parameter of preamble structure by inserting known sequences at specific positions within the segmented preamble. This allows the receiver to detect and correct frequency offset errors by comparing the received known sequences with the expected sequences, thereby maintaining reliable control information reception despite bandwidth segmentation.
2Measurement precision
If receivers align tuning windows with preambles to receive control information, then data reception accuracy is improved, but frequency offset errors misalign the tuning window and cause reception failures
Solution Approach 1:
Known sequences are inserted into the preamble structure in advance at predetermined positions. These known sequences serve as reference signals that enable the receiver to perform frequency offset estimation and correction before attempting to detect the control information, thereby maintaining accurate alignment even in the presence of frequency offset errors.
Solution Approach 2:
The receiver uses the known sequences embedded in the segmented preamble to detect frequency offset errors by comparing received signals with expected sequences. This feedback mechanism allows the receiver to adjust its tuning window alignment and compensate for frequency offset, maintaining reliable control information reception.
3Loss of information
If the receiver structure includes reordering functionality for segmented preambles, then complete control information can be reconstructed, but device complexity and processing latency increase
Solution Approach 1:
The preamble is segmented and transmitted across multiple frequency bands, with each segment containing identifiable portions of control information. The receiver reconstructs complete control information by collecting and properly ordering the segments based on their positions and the known sequence structures, eliminating the need for complex reordering functionality.
Solution Approach 2:
Known sequences are copied and inserted at specific positions within each preamble segment. These copied sequences serve as markers that simplify the reconstruction process, allowing the receiver to identify and assemble control information segments in the correct order without requiring complex reordering logic.
4Stability of the object's composition
If guard bands are increased to separate channels in DVB-C system, then channel separation is improved, but spectral efficiency deteriorates
Solution Approach 1:
The preamble is segmented and distributed across multiple frequency bands within the available channel bandwidth. This segmentation allows the system to achieve reliable control information transmission without requiring large guard bands, thereby improving spectral efficiency while maintaining adequate channel separation through the OFDM structure itself.
Data Source
AI summary
A method and apparatus for transmitting and receiving a preamble having sequence information for an OFDM system is provided. The preamble transmission method includes generating a preamble block including at least one frame having a header with a known sequence and a code block containing control information and transmitting the preamble block mapped to Orthogonal Frequency Division Multiplexing (OFDM) cells by repeating in frequency axis direction.