WiBro Frequency Synchronization Without GPS
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Solution Overview
Problem
In WiBro systems, precise frequency synchronization is challenging due to interference from other base stations or repeaters, making it difficult to estimate a frequency offset accurately without using a GPS receiver, especially in environments with multiple interfering signals.
Innovation Solution
A method that measures the spread degree of received adjacent subcarrier signals using orthogonality of Pseudo-Noise (PN) sequences to estimate frequency offset, involving despreading and calculating correlation ratios to determine the frequency offset, allowing for precise synchronization without a GPS receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS receiver is used for frequency synchronization, then frequency offset estimation precision is improved, but system cost and installation complexity increase
Solution Approach 1:
The patent extracts the frequency synchronization function from the GPS receiver dependency by using only the frame signal received through wireless channel. The system separates the synchronization task from external GPS infrastructure and implements it using internal signal processing resources, thereby reducing device complexity while maintaining precision.
Solution Approach 2:
The system performs frequency synchronization using its own received frame signal without requiring external GPS infrastructure. The base station or repeater uses the preamble and training symbols already present in the received signal to estimate frequency offset, making the system self-sufficient and reducing overall system complexity.
2Measurement precision
If GPS receiver is used for frequency synchronization, then frequency offset estimation precision is improved, but indoor installation becomes difficult
Solution Approach 1:
The patent removes the requirement for GPS signal reception by extracting frequency synchronization capability from external satellite signals and implementing it through processing of the frame signal already received through the wireless channel, enabling indoor installation.
Solution Approach 2:
The system achieves frequency synchronization using only the frame signal it receives through its wireless interface, without requiring external GPS infrastructure that cannot be accessed indoors. This self-service approach enables deployment in indoor environments.
3Device complexity
If general OFDM synchronization method is used without GPS, then system cost is reduced, but frequency offset estimation precision deteriorates in interference environments
Solution Approach 1:
The patent converts the harmful effect of interference signals into a beneficial filtering mechanism. By using correlation processing with known preamble and training symbols, the system selectively enhances the desired signal while suppressing interference, achieving precise frequency offset estimation even in interference environments without requiring GPS.
Solution Approach 2:
The system changes the processing parameters by using correlation-based frequency offset estimation with known training sequences instead of simple OFDM synchronization methods. This parameter change enables the system to distinguish desired signals from interference, maintaining precision while avoiding GPS dependency.
4Measurement precision
If correlation-based frequency offset estimation is used, then frequency synchronization precision is improved, but computational complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-processing the received frame signal to extract the preamble and training symbols before performing correlation-based frequency offset estimation. This preliminary extraction and organization of known sequences simplifies the subsequent correlation process and reduces computational complexity while maintaining precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables precise frequency synchronization with a standard deviation lower than 48 Hz, meeting WiBro system requirements, even in environments with significant interference, and supports reliable data transmission and hand-off operations.
Implementation Method 1
measuring a spread degree of a received adjacent subcarrier signal, using orthogonality of Pseudo-random Noise (PN) sequences
Data Source
AI summary
Provided is a fine frequency synchronization method of a WiBro system, and particularly, a fine frequency synchronization method which measures a spread degree of a received signal of an adjacent subcarrier using orthogonality of PN sequences and thereby estimates a frequency offset, in a base station or a wireless repeater without using a GPS receiver. The fine frequency synchronization method includes: (a) performing despreading on received adjacent subcarrier sequences, using a PN sequence transmitted from a transmitting party; (b) obtaining ratios of correlative values obtained by the despreading; and (c) estimating a frequency offset on the basis of the ratio of correlative values. Accordingly, fine frequency offset estimation with relatively low complexity is possible without using a GPS receiver in a WiBro environment where interference signals of other base stations or repeaters exist.