Packet Receiver Channel Equalization Using Midamble Segmentation
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Solution Overview
Problem
In packet communication systems using π/4-DQPSK modulation, the midamble binary data string varies for every packet, making it difficult to apply general adaptive channel equalizers, as the midamble is located in the middle of the packet and its symbol strings are shifted in phase, complicating channel equalization and differential demodulation.
Innovation Solution
An apparatus and method that includes an input interface to receive packet samples with midamble location information, a sample divider to separate the samples into sub-strings, and a channel equalizer unit that performs equalization using a channel equalizing algorithm, rearranging the sub-strings to use a reference midamble symbol string for training and determining transmission symbols by separating odd and even-numbered symbols in the π/4-DQPSK constellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a general adaptive channel equalizer is used, then channel equalization can be performed using known symbol strings, but it cannot be applied when the midamble is located in the middle of a packet with varying binary data
Solution Approach 1:
The reception sample string is divided into first and second sub sample strings using the midamble location information. The channel equalizer processes each sub sample string separately, with the first sub sample string containing data before the midamble and the second sub sample string containing data after the midamble. This segmentation allows the equalizer to handle the midamble structure properly while maintaining equalization capability.
Solution Approach 2:
The system performs preliminary identification and separation of the midamble portion from the reception samples before equalization. By using the known midamble location information and binary data string, the receiver prepares the sample strings in advance for proper equalization processing, treating the midamble as a known reference signal for training the equalizer.
2Reliability
If the midamble symbol string is used for training, then channel equalization can be performed, but the varying phase due to π/4-DQPSK modulation complicates the process
Solution Approach 1:
The system generates a reference midamble symbol string based on the known midamble binary data string and π/4-DQPSK modulation rules. This reference symbol string serves as a template for comparing against the actual received midamble symbols, allowing the equalizer to account for phase shifts while maintaining accurate training.
Solution Approach 2:
The system adjusts the reference symbol generation to account for the varying phase characteristics of π/4-DQPSK modulation. By dynamically generating the reference midamble symbol string according to the specific packet's binary data and modulation phase, the equalizer adapts to phase changes without increasing structural complexity.
3Loss of information
If differential demodulation is performed after equalization, then transmitted data can be determined, but the process becomes more complex with phase-shifted symbols
Solution Approach 1:
The system uses the determined transmission symbols from differential demodulation as feedback for subsequent equalization processes. The equalizer utilizes the already-determined symbols to refine its coefficients, creating a feedback loop that improves equalization accuracy while simplifying the overall processing by reusing extracted information.
Data Source
AI summary
Provided is an apparatus for equalizing a channel and determining reception data of a packet communication receiver. The apparatus includes: an input interface unit which receives a reception sample string of a packet having a midamble and location information of the midamble; a sample dividing unit which divides the reception sample string into a first sub sample string and a second sub string stream using the location information of the midamble; and a channel equalizing unit which performs channel equalization on the first sub sample string and the second sub sample string, respectively, using a channel equalizing algorithm of the channel equalizer.