Assessment of Automotive Environmental Noise on Mobile Phone Hands-Free Call Quality

Environmental noises such as wind, road, powertrain, and HVAC noise are important aspects to consider when implementing a hands-free terminal for mobile phone calling from within a car. Traditionally, these environmental noises have been exclusively considered for driver comfort; however, with the introduction of the hands-free terminals (HFT) and increasing consumer demand relative to mobile phone call quality, a broader implication of high background noise levels should be considered. HFT algorithm development and implementation can and does provide a high level of background noise suppression to mitigate these concerns, but this is often done at the expense of computational power and cumulative delay during a phone call. The more advantageous solution would be to address the problem from a source and path perspective with emphasis on reduction of noise in the frequency bands which most influence call quality performance. The assessments shown throughout this paper establish a sensitivity of HFT call quality to background noise levels based on industry-standard metrics, including those defined by International Telecommunication Union (ITU) standards. These assessments were established based on a series of experiments that include characterizing vehicle to vehicle variability with a common background noise and single vehicle sensitivity to reductions in background noise. In the background noise sensitivity investigations, filtering investigations were conducted to identify the frequency ranges which drive the most significant degradation in speech intelligibility and HFT performance. The information gained provides insight regarding the requirements for mitigating background noise in the context of both customer comfort as well as HFT performance, both of which are key factors in the perception of overall vehicle quality.