Angle of Departure Estimation Using Cyclic Delay
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Solution Overview
Problem
Current methods for indoor localization using wireless network signals are inaccurate and unreliable, especially in environments where GPS signals are weak, such as indoors and in crowded urban areas, due to the reliance on satellite signals or single-antenna devices that cannot support multi-input multi-output (MIMO) transmission.
Innovation Solution
A method that estimates the angle of departure of wireless signals from multiple antennas using a single omnidirectional antenna by processing signals with a predefined cyclic delay, allowing for the derivation of phase delay and subsequent calculation of the angle of departure, even in the absence of MIMO capabilities, and constructs a map of access points based on these measurements for accurate location determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If GPS satellite signals are used for location determination, then location coordinates can be derived, but the method works poorly indoors and in crowded urban environments due to weak satellite signals
Solution Approach 1:
The patent introduces wireless access points as intermediary objects to enable location determination. Instead of directly relying on GPS satellites, the system uses locally deployed access points that transmit signals measurable by the mobile device, serving as intermediaries between the device and the location determination function.
Solution Approach 2:
The patent inverts the traditional angle of arrival approach by estimating the angle of departure from the access point's perspective. Instead of calculating where signals arrive at the access point from the device, the system determines the angle at which signals depart from the access point toward the device, enabling location calculation without requiring multiple antennas at the mobile device.
2Measurement precision
If cellular network triangulation is used, then telephone location can be determined, but the technique is inaccurate and unreliable
Solution Approach 1:
The patent changes the measurement parameter from signal strength-based triangulation to angle-based positioning. By measuring the angle of departure using phase differences between cyclically delayed signals, the system achieves higher precision location determination compared to traditional cellular triangulation methods.
3Measurement precision
If multiple receiving antennas are used to support MIMO transmission for accurate angle estimation, then angle of arrival can be determined, but this increases device complexity and is not feasible for single-antenna devices
Solution Approach 1:
The patent fundamentally inverts the problem formulation: instead of determining angle of arrival at the mobile device (requiring multiple receiving antennas), it estimates the angle of departure from the access point using a single receiving antenna. This is achieved by exploiting the known cyclic delay structure in the access point's multi-antenna transmission.
Solution Approach 2:
The patent creates a virtual multi-antenna receiving system through signal processing. By correlating the received signal with known cyclically delayed signal patterns from the access point, the single-antenna device effectively replicates the angle estimation capability of a multi-antenna system without the physical complexity.
4Measurement precision
If SpotFi's angle of arrival computation is used, then decimeter level localization can be achieved, but it requires filtering and estimation techniques to identify the direct path AoA from multipath components
Solution Approach 1:
The patent inverts the approach by estimating angle of departure from the transmitter rather than angle of arrival at the receiver. This inversion simplifies the signal processing requirements because it leverages the known transmission structure (cyclic delays) at the access point, avoiding the need for complex multipath filtering and direct path identification.
Solution Approach 2:
The access point's own transmission structure (cyclic delays between antennas) serves the dual purpose of data transmission and angle information encoding. The mobile device exploits this self-generated structure to extract angle of departure information without requiring additional training sequences or complex signal processing to separate angle information from data.
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
Enables accurate and reliable indoor localization without the need for GPS, using existing wireless access points and their signal patterns to triangulate device location, improving positioning accuracy and convenience in urban and indoor settings.
Implementation Method 1
The received first and second signals are processed in order to derive a measure of a phase delay between the first and second signals. Based on the measure of the phase delay, an angle (θ) of departure of the first and second signals from the wireless transmitter to the given location is estimated.
Data Source
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AI summary
A method for signal processing includes receiving at a given location at least first and second signals transmitted respectively from at least first and second antennas (34) of a wireless transmitter (24). The at least first and second signals encode identical data using a multi-carrier encoding scheme with a predefined cyclic delay between the transmitted signals. The received first and second signals are processed, using the cyclic delay, in order to derive a measure of a phase delay between the first and second signals. Based on the measure of the phase delay, an angle of departure (θ) of the first and second signals from the wireless transmitter to the given location is estimated.