OFDMA Ranging Subcarrier Allocation Using Segmented Spacing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current ranging techniques in OFDMA systems face challenges in accurately estimating delays and complexity due to constraints in subcarrier allocation, particularly with uniformly spaced subcarriers leading to ambiguity and high complexity in frequency domain correlation, while randomly spaced subcarriers increase computational complexity and randomly spaced subcarriers result in higher complexity and ambiguity in delay estimation.
Innovation Solution
The method involves extracting uniformly spaced subcarriers with a predetermined spacing and starting position from the received OFDM symbol, allowing for detection of ranging CPEs using frequency domain correlation, and performing delay estimation using both uniformly and randomly spaced subcarriers, reducing complexity by using smaller IFFTs during detection and larger IFFTs during estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If uniformly spaced subcarriers are used for ranging, then the frequency domain correlation process becomes simpler, but delay estimation ambiguity increases due to repetition of correlation peaks
Solution Approach 1:
The patent segments the subcarrier set into two distinct groups: uniformly spaced subcarriers for low-complexity detection and randomly spaced subcarriers for unambiguous delay estimation. This segmentation allows each subset to serve its specific function optimally without compromising the other.
Solution Approach 2:
The patent merges both uniformly spaced and randomly spaced subcarriers into a single ranging signal transmission. The base station transmits ranging signals on both types of subcarriers simultaneously, and the receiver processes both sets to achieve both low complexity detection and unambiguous delay estimation.
2Measurement precision
If randomly spaced subcarriers are used for ranging, then delay estimation becomes unambiguous, but computational complexity increases due to longer IFFT requirements
Solution Approach 1:
The patent divides the ranging subcarriers into two segments with different spacing patterns. The uniformly spaced segment enables simple correlation processing, while the randomly spaced segment provides unambiguous delay information. This segmentation allows the system to avoid using complex IFFT processing for the entire signal.
Solution Approach 2:
The patent extracts and utilizes only the randomly spaced subcarriers for unambiguous delay estimation when needed, while relying on the uniformly spaced subcarriers for general ranging detection. This extraction approach allows the system to achieve unambiguous delay estimation without always requiring complex computational processing.
3Device complexity
If a single IFFT size is used for all ranging operations, then processing is simplified, but complexity cannot be reduced for detection operations
Solution Approach 1:
The patent implements dynamic IFFT size selection based on the processing stage: smaller IFFT size for detection operations using uniformly spaced subcarriers, and larger IFFT size for delay estimation operations using randomly spaced subcarriers. This dynamic adjustment optimizes processing efficiency at each stage.
Solution Approach 2:
The patent applies different IFFT processing qualities to different parts of the ranging signal. Local quality optimization means using computationally efficient processing for detection and more intensive processing for estimation, matching the specific requirements of each operation type.
Data Source
AI summary
A method of ranging and sub-carrier selection in an orthogonal frequency division multiple access (OFDMA) system and the OFDMA system is disclosed. An OFDM symbol is received from a customer premises equipment (CPE) at a base station. The OFDM symbol is demodulated for obtaining a plurality of subcarriers. A plurality of data subcarriers are multiplied by zeros and stored. A plurality of uniformly spaced subcarriers is extracted from the stored subcarriers. A ranging CPE is detected in uniformly spaced subcarriers. Delay estimation is performed using the stored plurality of subcarriers upon detecting presence of ranging CPE. A method of subcarrier allocation at a ranging CPE transmitter based on total number of subcarriers, subcarriers in used band, a delay spread to be supported in terms of number of samples, a required ratio of highest amplitude to second highest amplitude of the ranging signal is disclosed.