OFDM Receiver Frequency Offset Estimation via Cyclic Prefix Correlation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In synchronous digital communication systems, particularly those using Orthogonal Frequency Division Multiplexing (OFDM), carrier frequency offsets cause Inter-Carrier Interference (ICI), deteriorating receiver performance due to Doppler Frequency offset and local carrier errors, which are challenging to address effectively in consumer-oriented receivers.
Innovation Solution
A receiver and method that utilize Pseudo Noise (PN) sequences in the guard intervals of OFDM frames for carrier frequency recovery, involving correlation between delayed and non-delayed PN sequences to estimate and compensate for carrier frequency offsets, enhancing precision and orthogonality of sub-carriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional frequency offset estimation methods (using pilots and cyclic prefixes) are used in OFDM systems, then the system can achieve basic frequency synchronization, but the precision of carrier frequency estimation is insufficient leading to Inter-Carrier Interference
Solution Approach 1:
The patent applies preliminary action by using the cyclic prefix (which is already present in the OFDM signal structure) as a preamble for frequency offset estimation before the main data transmission. The method performs correlation between the cyclic prefix and the corresponding end portion of the OFDM symbol to estimate frequency offset in advance, allowing compensation to be applied before data reception, thereby preventing ICI without requiring additional signal resources
Solution Approach 2:
The invention applies self-service by making the cyclic prefix serve dual purposes: its original function of protecting against multipath interference and an additional function of enabling frequency offset estimation. The receiver uses its own transmitted signal (via the cyclic prefix) to perform autocorrelation and estimate frequency offset, eliminating the need for separate pilot signals or external reference signals for this purpose
2Reliability
If Doppler Frequency offset and local carrier errors are present in synchronous digital communication systems, then the received signal frequency shifts occur, but the receiver performance seriously deteriorates due to additional phase rotation
Solution Approach 1:
The patent implements feedback by using the estimated frequency offset to generate a compensation signal that is applied to the received signal. The process forms a closed loop where the receiver continuously estimates frequency offset from the cyclic prefix, calculates the phase rotation caused by this offset, and applies compensating phase correction to the received signal, thereby counteracting the harmful effects of Doppler offset and local carrier errors
Solution Approach 2:
The invention uses the cyclic prefix as an intermediary element that mediates between the transmitted and received signals for frequency offset estimation. By correlating the cyclic prefix with the corresponding end portion of the OFDM symbol, the system extracts frequency offset information without directly processing the data-carrying portion of the signal, thus protecting data integrity while achieving accurate frequency synchronization
3Productivity
If OFDM systems use multiple sub-carriers to transmit high-rate data streams, then the data transmission capacity increases, but carrier frequency offset introduces Inter-Carrier Interference reducing orthogonality
Solution Approach 1:
The patent applies preliminary action by performing frequency offset estimation and compensation using the cyclic prefix before the main OFDM data symbols are processed. This preliminary frequency synchronization ensures that the orthogonality between sub-carriers is maintained throughout data transmission, preventing ICI while preserving the high data transmission capacity enabled by multiple sub-carriers
Solution Approach 2:
The invention makes the OFDM signal structure itself (specifically the cyclic prefix) serve the dual purpose of maintaining orthogonality protection and enabling frequency offset estimation. The cyclic prefix, which is already part of the OFDM signal structure required for multipath protection, is utilized to estimate and compensate frequency offset, thereby maintaining sub-carrier orthogonality without adding separate pilot signals that would reduce data transmission efficiency
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 significantly improves the accuracy of carrier frequency estimation and recovery, reducing Inter-Carrier Interference and maintaining high precision, even in multipath channel environments, thereby enhancing the consumer perceived quality of OFDM systems.
Implementation Method 1
it will usually include two parts: an integer frequency offset (IFO, multiple of subcarrier interval) and a fraction frequency offset (FFO, less than half of subcarrier interval). The IFO can be determined through cross correlation using pilots in the frequency domain, while the FFO can be determined through auto correlation using cyclic prefixes in time domain.
Implementation Method 2
In a synchronous digital communication or broadcasting system, owing to the influence of Doppler Frequency offset and the local carrier error, the frequency of the received signal will be shifted.
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The present invention provides a receiver for receiving digital signals including frames with a binary modulated cyclic preamble, comprising: means for correlating at least a part of a first cyclic preamble in a first frame and at least a part of a second cyclic preamble in a second frame, and for determining a carrier frequency offset based on the result of said correlation.