Deconvolution Filter for Channel Impulse Response Estimation
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Solution Overview
Problem
Existing communication systems face challenges in accurately estimating the impulse response of communication channels using short spreading codes, which results in distorted estimates due to significant side lobes in the autocorrelation of the spreading sequence, affecting the precision of channel equalization.
Innovation Solution
A method and apparatus that generate a data sequence with a constrained portion associated with two codes, where the correlation has a maximum value at zero and less at non-zero values, and a chip sequence spread by a spreading sequence of length N, allowing for accurate estimation of the communication channel impulse response through correlation and filtering, even with short spreading codes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a short spreading code is used for packet detection and synchronization, then the detection speed and synchronization efficiency are improved, but the channel impulse response estimate becomes distorted due to significant side lobes in the autocorrelation
Solution Approach 1:
The patent introduces a deconvolution filter as an intermediary processing step between the received signal and the channel impulse response estimate. This filter, designed based on the known spreading code sequence, acts as a mediator to remove the distortion caused by the spreading code's autocorrelation side lobes, thereby recovering the accurate channel impulse response while maintaining the benefits of short spreading codes
Solution Approach 2:
The patent extracts and removes the harmful component (side lobes) from the autocorrelation function through deconvolution processing. By applying a filter that is the inverse of the spreading code's autocorrelation function, the method extracts and eliminates the distortion introduced by the short spreading code, leaving only the desired channel impulse response
2Measurement precision
If a long spreading code sequence is used, then the channel impulse response estimate is accurate, but the packet detection and synchronization process experiences unacceptable delays
Solution Approach 1:
The patent changes the parameter of spreading code length from long to short, and compensates for the resulting distortion by introducing deconvolution processing. This parameter change allows the system to achieve both fast synchronization (benefit of short codes) and accurate channel estimation (compensated by deconvolution), effectively decoupling these two previously conflicting requirements
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 estimation of the communication channel impulse response, particularly in the limit of high signal-to-noise ratio, and effectively reduces the impact of side lobes, improving channel equalization and signal detection.
Implementation Method 1
Correlation techniques are used to identify and synchronize to its timing
Implementation Method 2
generating a chip sequence cj having a chip period Tc as the data sequence di spread by a spreading sequence Si of length N
Data Source
AI summary
A method and apparatus for estimating a communication channel impulse response h(t) is disclosed. The method comprises the steps of generating a data sequence di having a constrained portion Cdi associated with at least two codes w0, w1, wherein a correlation Acode(k) of the constrained portion Cdi with one of the codes w0, w1 is characterized by a maximum value at k=0 and less than maximum values at k≠0; generating a chip sequence cj having a chip period Tc as the data sequence di spread by a spreading sequence Si of length N; generating com(t)=co(t+mNTc) for m=0, 1, . . . , M by correlating a received signal r(t) with the spreading sequence Si, wherein the received signal r(t) comprises the chip sequence cj applied to the communication channel; and generating an estimated communication channel impulse response ĥM(t) as a combination of com(t) and dm for m=0, 1, . . . , M.