DC Offset Cancellation Using Pilot Symbols in Wireless Receivers
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Solution Overview
Problem
Conventional wireless communication systems face challenges in efficiently canceling DC offset interference, which can lead to reduced bandwidth and increased power consumption, especially in narrowband receivers, as they often require avoiding subcarriers near the local oscillator frequency to prevent interference.
Innovation Solution
A receiver apparatus operates a local oscillator at a frequency corresponding to a pilot symbol, estimates DC interference based on the received pilot symbol, and cancels it to enable reliable data reception, potentially using multiple pilot symbols for improved cancelation performance while maintaining bandwidth efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If subcarriers near local oscillator frequency are avoided to prevent DC interference, then interference is reduced, but bandwidth is reduced
Solution Approach 1:
The patent uses the known pilot symbol at the DC frequency to estimate and cancel the DC offset interference, converting the harmful DC component into useful information for interference cancellation. This allows the system to utilize the previously avoided subcarrier while maintaining signal quality.
Solution Approach 2:
The patent introduces an intermediary processing step where the received pilot symbol is used to estimate DC offset, which then serves as a mediator to cancel the interference before data detection. This intermediary estimation process enables safe use of DC subcarriers.
2Device complexity
If analog cancelation techniques are used for DC interference, then implementation is simple, but cancelation performance is insufficient
Solution Approach 1:
The patent replaces analog/circuit-based DC cancelation with digital signal processing methods. By using digital estimation based on pilot symbols and subsequent cancellation in the digital domain, the system achieves superior cancelation performance while maintaining implementation feasibility.
3Reliability
If multiple pilot symbols are used for DC interference estimation, then cancelation performance is improved, but bandwidth utilization is reduced
Solution Approach 1:
The patent uses multiple pilot symbols for DC estimation, which is more than the single symbol minimum requirement. This excessive use of pilot symbols improves estimation accuracy and cancelation performance, accepting the trade-off of reduced bandwidth utilization for better reliability.
Data Source
AI summary
Techniques are disclosed relating to DC interference cancelation in received wireless signals. Disclosed techniques may be performed in the digital domain, in conjunction with analog cancelation techniques. In some embodiments, a receiver apparatus operates a local oscillator at a frequency corresponding to a particular pilot symbol in a received wireless signal. In some embodiments the receiver estimates DC interference at the frequency based on the received pilot symbol (this may be facilitated by the fact that the contents of pilot symbols are known, because they are typically used for channel estimation). In some embodiments, the receiver apparatus is configured to cancel the DC interference based on the estimate to determine received data in subsequently received signals at the frequency. Disclosed techniques may allow narrowband receivers to efficiently use more of their allocated frequency bandwidth, rather than wasting bandwidth near the frequency of the local oscillator.