Time Interleaved Unmodulated Sync Sequence for CDMA Clock Recovery
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Solution Overview
Problem
Existing CDMA systems face challenges in achieving efficient Clock and Data Recovery (CDR) due to interference and high latency in synchronizing local sampling clocks with the transmitter clock, particularly when using modulated synchronization sequences that are spread over the frequency band, leading to lower Signal to Noise Ratio (SNR) and increased cross-correlation with other signals.
Innovation Solution
Time interleaving an unmodulated synchronization sequence, such as a Barker code, within the CDMA stream to improve CDR by ensuring it occupies the entire frequency band and using early-late correlators for precise clock synchronization, thereby enhancing immunity to interference and reducing locking time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a modulated synchronization sequence is spread over the frequency band in a CDMA system, then the synchronization signal can be integrated with the CDMA stream, but the Signal to Noise Ratio (SNR) decreases and cross-correlation with other signals increases
Solution Approach 1:
The patent extracts the synchronization sequence from the modulated CDMA stream by using time interleaving to insert unmodulated synchronization chips at specific intervals. This separation allows the synchronization signal to be extracted and processed independently from the modulated data, improving SNR by eliminating the effects of modulation and spreading on the synchronization signal.
Solution Approach 2:
The CDMA stream is segmented into data portions and synchronization portions through time interleaving. The synchronization sequence is inserted as distinct unmodulated chips between data symbols, creating a segmented structure that allows separate processing of synchronization and data functions with optimized performance for each.
2Productivity
If a modulated synchronization sequence is used in CDMA transmission, then the system can maintain continuous data flow, but the synchronization latency increases
Solution Approach 1:
The unmodulated synchronization sequence is inserted at predetermined intervals before data transmission occurs. This preliminary insertion of known synchronization patterns allows the receiver to perform correlation-based timing recovery in advance, reducing the latency required to achieve and maintain synchronization compared to waiting for modulated signals to be processed.
3Reliability
If an unmodulated synchronization sequence is time interleaved with the CDMA stream, then the synchronization signal occupies the entire frequency band and immunity to interference improves, but the system complexity increases
Solution Approach 1:
The unmodulated synchronization sequence is inserted periodically at fixed intervals within the CDMA stream using time interleaving. This periodic insertion creates a regular pattern that is easy to detect and process, allowing the receiver to use simple correlation techniques to recover timing information without requiring complex processing, thus achieving improved interference immunity with minimal added complexity.
Data Source
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AI summary
A Code Division Multiple Access (CDMA) transmitter comprising a processor adapted to obtain (102) a CDMA stream comprising one or more CDMA code sequences, create (104) an adjusted CDMA stream by interleaving a time interval containing an unmodulated (non-modulated) synchronization sequence in the CDMA stream and output (106) the adjusted CDMA stream. The unmodulated synchronization sequence used by each of a plurality of receivers of the CDMA stream for clock and data recovery (CDR) is based on a code pattern having a unique autocorrelation function presenting a linear deviation error with respect to a delay offset.