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The Role of MEMS Speakers in Accurate Indoor Acoustic Localization
High-precision indoor positioning is revolutionizing various industries, including robotics, augmented reality, smart homes, and personal navigation, where accurate indoor positioning is essential. Acoustic Localization Positioning Systems (ALPSs) achieve this by precisely measuring the time-of-flight (ToF) or time-of-arrival (ToA) of acoustic signals. However, real-world conditions, such as multipath propagation, Doppler effects, and ambient noise, present significant challenges. To effectively address these challenges, advanced signal processing and high-performance hardware, such as wideband MEMS speakers, are crucial.
Why Use Ultrasound for Indoor Localization?
Compared to RF, IR, or vision-based systems, ultrasound offers unique advantages:
- High Precision: Due to its slower speed in air (~343 m/s), ToF measurements can achieve millimeter-level resolution.
- Low Susceptibility to Interference: Ultrasound is less affected by multipath and doesn’t penetrate walls, which minimizes inter-room interference. Additionally, it remains reliable across different lighting conditions.
- Cost & Power Efficiency: Ultrasound systems are inexpensive, energy-efficient, and ideal for mobile or embedded applications.
USound’s Conamara MEMS Speaker: Enabling the Next Generation of ALPS
USound’s Conamara series MEMS speakers bring a breakthrough: small form factor, wideband capability, and omnidirectional emission—all in one package. This enables:
- Support for complex wideband signal schemes like Zadoff–Chu and chirps.
- Enhanced spatial resolution and SNR.
- Robust performance even in dynamic, cluttered environments.
- Seamless integration into compact devices such as wearables or IoT sensors.
Advanced Techniques with wideband transducers for ALPS
Real-world deployments face challenges such as multipath interference, Doppler effects, ambient noise, and multiple access interference (MAI). To overcome these issues, ALPSs utilize advanced techniques like:
Kasami Sequences
Pseudorandom binary codes are typically modulated using Binary Phase Shift Keying (BPSK): though computationally efficient, they struggle with Doppler sensitivity, multipath, and long-distance attenuation, limiting their use in dynamic scenarios. USound Conamara wideband ultrasound speakers enhance the performance of BPSK-modulated Kasami sequences by preserving their structure despite challenges like Doppler shifts, multipath, and attenuation. Their wide frequency response and low distortion help maintain signal clarity, making them more reliable in dynamic, real-world scenarios.
Zadoff–Chu (ZC)
Sequences are complex-valued polyphase sequences known for their constant amplitude and strong autocorrelation properties, making them ideal for precise signal detection in noisy environments. When used with USound MEMS speakers, they enhance signal fidelity and improve time-of-flight measurements in challenging conditions.
Chirp-Based Signals
Highly effective in dynamic, cluttered environments due to their frequency sweeping nature, which helps distinguish direct and reflected paths. They maintain a high signal-to-noise ratio (SNR) and data availability, with strong Doppler tolerance and adaptability. USound’s wideband MEMS transducers enhance chirp-based systems by providing full spectral coverage and sharp autocorrelation peaks, improving SNR and ensuring reliable operation in complex environments with multiple users and varying signal strengths.
Chirp-Based Pulse Compression: Boosting Range and Accuracy
Chirping and pulse compression are signal processing techniques used to enhance range resolution and signal-to-noise ratio (SNR) when pulse duration is limited or when peak power and bandwidth are constrained. These techniques involve modulating transmitted pulses and correlating received signals with the transmitted waveform. By using matched filtering, pulse compression narrows the pulse width and improves resolution without increasing pulse duration, effectively increasing SNR.
Chirp signals, a common method for pulse compression, are particularly effective in environments where range resolution and SNR are critical. When paired with USound’s wideband MEMS speakers, the system can reproduce the full chirp spectrum, reducing signal distortion and improving range resolution. The result is better SNR, sharper autocorrelation peaks, and improved signal accuracy, even in noisy environments.
USound’s Conamara series MEMS speakers optimize chirp-based pulse compression by ensuring efficient energy distribution across a wide frequency range, improving the signal quality without requiring multiple measurements. The use of longer chirps further enhances SNR, and the ability to adapt to varying excitation characteristics allows for optimal performance across diverse applications, such as structural health monitoring and non-destructive evaluation.
A Different Approach: Ranging with Frequency-Dependent Attenuation
USound’s Conamara series MEMS transducers offer compact size, low power consumption, and wide isotropic emission, making them ideal for integration into portable devices like smartphones and IoT sensors.
An ultrasonic distance estimation technique can leverage the difference in air attenuation between two sinusoidal signals of distinct frequencies. As the signal travels through the air, the higher-frequency component experiences greater attenuation than the lower-frequency one. By measuring the amplitude ratio of the two components at the receiver and applying a logarithmic model, the distance between the emitter and receiver can be estimated accurately. This approach removes the need for precise time synchronization or high-speed sampling, making it significantly more computationally efficient and simpler in hardware design than traditional time-of-flight (ToF)-based methods.
Conclusion
Wideband MEMS transducers, such as USound’s Conamara series, provide a range of benefits that enhance the performance and efficiency of acoustic systems. Key advantages include:
- Compact Size: USound MEMS speakers have a reduced form factor, making them ideal for integration into small, portable devices like smartphones, wearables, and IoT sensors.
- Low Power Consumption: These speakers are energy-efficient, making them well-suited for battery-operated and embedded systems.
- Wideband Performance: USound’s MEMS technology provides broad spectral coverage, improving temporal resolution and spatial discrimination for precise localization.
- Isotropic Acoustic Emission: Their small size ensures more uniform sound emission across all directions, reducing directional bias and enhancing omnidirectional coverage.
- Enhanced Localization Accuracy: The isotropic emission and wideband performance improve time-of-flight measurements and overall localization consistency, especially in dynamic environments.
- Scalability: Due to their low power consumption and compactness, multiple USound MEMS speakers can operate simultaneously in the same space without interference, enhancing multi-user compatibility.
- Doppler and Multipath Resistance: The wideband capability helps mitigate multipath interference and ensures reliable performance in complex and dynamic environments.
Whether you’re developing a robot fleet, indoor navigation system, or wearable tech, these wideband transducers form the acoustic backbone for next-generation ALPS solutions.
Download our latest whitepaper for more insights on how USound’s wideband MEMS speakers can enable acoustic localization.
About the author
Manuel Arias Ruiz is Head of Hardware Development at USound, driving innovation in product design within the R&D department. With a solid foundation in Electrical Engineering and over 15 years of experience in electronic products and systems, Manuel leads the development of cutting-edge hardware solutions, offers key application support, and plays a central role in shaping USound’s technological advancements. LinkedIn
