DC Offset Degradation in Massive MIMO Receiver Branches
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Solution Overview
Problem
In massive MIMO systems, the DC offset generated by zero-IF receivers degrades signal quality and affects demodulation, particularly in LTE networks, due to its impact on FFT operations and SNR, especially when combined across multiple receiver branches.
Innovation Solution
Configuring local oscillators in each receiver branch with different frequencies, positioned at the center of subcarriers or offset by (N+0.5) times the subcarrier spacing, to distinguish and separate DC offsets in frequency, allowing for alignment of digital baseband signals and reduction of DC offset impact through FFT and beamforming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a high pass filter is used to filter DC offset from the baseband signal, then DC offset can be removed, but the filtering mechanism requires monitoring DC offset to generate FIR filter coefficients, increasing system complexity
Solution Approach 1:
The patent applies preliminary action by pre-configuring different local oscillator frequencies for each receiver branch before signal processing. This frequency differentiation is established in advance to ensure DC offsets fall into different frequency locations, eliminating the need for real-time monitoring and dynamic filter coefficient generation. The frequency separation strategy is prepared beforehand, converting a complex adaptive filtering problem into a simple frequency domain separation.
2Reliability
If DC offset is not equal to subcarriers frequency points, then each sample for FFT will be impacted, but using frequency differentiation strategy allows DC offsets to be isolated to specific subcarriers, reducing overall impact
Solution Approach 1:
The patent applies local quality by making each receiver branch have a distinct local oscillator frequency, causing DC offsets to be localized to specific frequency positions (specific subcarriers) rather than uniformly distributed. This frequency differentiation ensures that only certain subcarriers are affected by DC offsets while others remain clean, improving overall FFT accuracy by preserving unaffected subcarriers for reliable signal processing.
3Ease of operation
If local oscillators in multiple receiver branches use the same frequency, then DC offsets cannot be distinguished between branches, but using different frequencies allows DC offsets to be distinguished and separated in frequency domain
Solution Approach 1:
The patent applies parameter changes by modifying the frequency parameter of local oscillators in different receiver branches. Each branch is assigned a distinct frequency offset from the carrier frequency, which directly changes the frequency domain characteristics of the received signals and their associated DC offsets. This parameter differentiation enables straightforward frequency domain separation and identification of DC offsets without requiring complex identification algorithms.
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 effectively mitigates the impact of DC offsets across receiver branches, improving signal sensitivity and throughput by isolating DC offsets to specific subcarriers, thereby reducing their adverse effects on beamforming and overall system performance.
Implementation Method 1
The local oscillation signal may be transmitted to the mixer via the amplifier and the RF filter 2, and then may be mixed with the local oscillation signal directly from the local oscillator to generate the DC offset
Data Source
AI summary
Embodiments of the present disclosure provide a method, apparatus and computer program products for DC offset degradation. A method implemented in a massive multi-input multi-output (MIMO) system, which comprises a plurality of receiver branches, includes receiving a radio frequency (RF) signal in the plurality of receive branches. The method further includes configuring different local frequencies of a plurality of local oscillators respectively in the plurality of receiver branches according to a carrier frequency of the RF signal, to enable direct current (DC) offsets in the plurality of receiver branches to be distinguishable from each other in frequency.