OFDM Receiver Offset Compensation Using Cyclic Shifted Pilots
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Solution Overview
Problem
In OFDM communication systems, especially in MIMO-OFDM systems, the existing methods for compensating carrier and clock offsets are influenced by fading, leading to reduced reception performance due to interference and fading effects, which complicates the reception of pilot signals and subsequent offset compensation.
Innovation Solution
A receiver system that includes a reception unit for OFDM signals with cyclically shifted pilot subcarriers, an estimator for phase error calculation across multiple OFDM symbols, a weighting adder to combine estimated values, and a compensator to generate a compensated OFDM signal, which enhances offset estimation and compensation resilience against fading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If identical pilot signals are transmitted from multiple antennas in a MIMO-OFDM system, then the beam forming influence creates directional transmission patterns, but this causes mutual interference and reduces reception performance in certain directions
Solution Approach 1:
The patent applies asymmetry by using different cyclic shift amounts for pilot signals transmitted from different antennas. Instead of transmitting identical pilot signals that create symmetric beam forming patterns, each antenna transmits pilot signals with unique cyclic shifts, breaking the symmetry and eliminating the directional nulls that cause reception problems in certain directions.
Solution Approach 2:
The patent segments the pilot signal transmission by assigning different cyclic shift values to different antennas. This segmentation divides the原本 identical pilot signal into distinct versions that can be differentiated at the receiver, allowing separate estimation of carrier and clock offsets for each antenna without mutual interference.
2Measurement precision
If pilot signals are transmitted in MIMO-OFDM systems, then offset estimation can be performed, but fading effects cause the pilot signals to be buried in noise, reducing estimation accuracy
Solution Approach 1:
The patent uses feedback by iteratively estimating carrier offset and clock offset multiple times. The receiver performs initial offset estimation, then uses this information to refine subsequent estimations. This iterative feedback process improves measurement precision by progressively reducing the effects of fading and noise.
Solution Approach 2:
The patent applies preliminary action by performing carrier offset compensation before clock offset estimation. This preliminary step removes the dominant carrier offset effect first, making the subsequent clock offset estimation more accurate and less susceptible to fading effects.
3Reliability
If carrier offset and clock offset occur simultaneously, then both offsets must be compensated, but the combined phase rotations complicate the estimation process
Solution Approach 1:
The patent segments the offset compensation process into two distinct stages: first estimating and compensating carrier offset, then estimating and compensating clock offset. This segmentation breaks down the complex simultaneous compensation problem into manageable sequential steps, reducing estimation process complexity while maintaining complete offset compensation.
Solution Approach 2:
The patent applies preliminary action by performing carrier offset compensation as a preliminary step before clock offset compensation. Since carrier offset causes larger phase rotations that affect all subcarriers uniformly, removing it first simplifies the subsequent clock offset estimation, making the overall process less complex.
Data Source
AI summary
A receiver of an OFDM signal includes a reception unit to receive an OFDM signal formed by a plurality of OFDM symbols respectively including data subcarriers to which data signals are allocated and pilot subcarriers to which cyclically shifted pilot signals are allocated in frequency domain, an estimator to estimate phase errors of the pilot signals to generate first estimated values related to an offset of the OFDM symbol corresponding to each two or more OFDM symbols in the OFDM signal, a weighting adder to perform weighting additions on the first estimated values to obtain one second estimated value related to the offset, a compensator to compensate the offset by using the second estimated value to obtain a compensated OFDM signal, and a decoder to decode the compensated OFDM signal to reproduce the data signals.