Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1998-01-23
2003-01-07
Urban, Edward F. (Department: 2685)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S575100, C455S557000
Reexamination Certificate
active
06505057
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to vehicle voice enhancement systems and hands-free cellular telephone systems using microphones mounted throughout a vehicle to sense driver and/or passenger speech. In particular, the invention relates to improvements in the selection of transmitted microphone signals and noise reduction filtering.
BACKGROUND OF THE INVENTION
A vehicle voice enhancement system uses intercom systems to facilitate conversations of passengers sitting within different zones of a vehicle. A single channel voice enhancement system has a near-end zone and a far-end zone with one speaking location in each zone. A near-end microphone senses speech in the near-end zone and transmits a voice signal to a far-end loudspeaker. The far-end loudspeaker outputs the voice signal into the far-end zone, thereby enhancing the ability of a driver and/or passenger in the far-end zone to listen to speech occurring in the near-end zone even though there may be substantial background noise within the vehicle. Likewise, a far-end microphone senses speech in the far-end zone and transmits a voice signal to a near-end loudspeaker that outputs the voice signal into the near-end zone. Voice enhancement systems not only amplify the voice signal, but also bring an acoustic source of the voice signal closer to the listener.
Microphones are typically mounted within the vehicle near the usual speaking locations, such as on the ceiling of the vehicle passenger compartment above the seats or on seat belt shoulder harnesses. Inasmuch as microphones are present when implementing a vehicle voice enhancement system, it is desirable to use the voice enhancement system microphones in combination with a cellular telephone system to provide a hands-free cellular telephone system within the vehicle.
It is important that an integrated voice enhancement system and hands-free cellular telephone system be able to transmit clear intelligible voice signals. This can be difficult in a vehicle because significant acoustic changes can occur quickly within the passenger compartment of the vehicle. For instance, background noise can change substantially depending on the environment around the vehicle, the speed of the vehicle, etc. Also, the acoustic plant within the passenger compartment can change substantially depending upon temperature within the vehicle and/or the number of passengers within the vehicle, etc. Adaptive acoustic echo cancellation as disclosed in U.S. Pat. Nos. 5,033,082 and 5,602,928 and pending U.S. patent application Ser. No. 08/626,208, can be used to effectively model various acoustic characteristics within the passenger compartment to remove annoying echoes. However, even after annoying echoes are removed, background noise within the vehicle passenger compartment can distort voice signals. Further, microphone switching can create unnatural speech patterns and annoying clicking noises.
Providing intelligible and natural sounding voice signals is important for voice enhancement systems, and is also important for hands-free cellular telephone systems. However, providing intelligible and natural sounding voice signals is typically more difficult for cellular telephone systems. This is because a listener on the other end of the line must be able to not only clearly hear speech from the vehicle but also must be able to easily detect whether the cellular telephone is on-line. That is, the line must not appear dead to the listeners when no speech is present in the vehicle. Also, the listener on the other end of the line is typically in a quiet environment and the presence of background vehicle noises during speech is annoying.
SUMMARY OF THE INVENTION
The invention is an integrated vehicle voice enhancement system and hands-free cellular telephone system that implements a voice activated microphone steering technique to provide intelligible and natural sounding voice signals for both the voice enhancement aspects of the system and the hands-free cellular telephone aspects of the system. This invention arose during continuing development efforts relating to the subject matter of U.S. Pat. Nos. 5,033,082; 5,602,928; 5,172,416; and copending U.S. patent application Ser. No. 08/626,208 entitled “Acoustic Echo Cancellation In An Integrated Audio and Telecommunication Intercom System”), all incorporated herein by reference. The invention applies to both single channel (SISO) and multiple channel (MIMO) systems.
In one aspect, the invention involves the use of a microphone steering switch that inputs echo-cancelled voice signals from the microphones within the vehicle and outputs a raw telephone input signal. Each of the microphones in the system has the capability of switching between an “off” state and an “on” state. The microphones are voice activated such that a respective microphone can switch into the “on” state only when the sound level in the microphone signal (e.g. dB) exceeds a threshold switching value, thus indicating that speech is present in a speaking location near the microphone. The microphone steering switch outputs a raw telephone input signal which is preferably a combination of 100% of the microphone output from the microphone in the “on” state, and preferably approximately 20% of the microphone output from the microphone(s) in the “off” state. In order for the telephone input signal to be intelligible by a person on the other end of the cellular telephone line, the invention allows only one of the microphones to be designated as the primary microphone (i.e. switched to the “on” state) at any given time.
The invention implements microphone steering techniques for the designation of primary microphone signals into the “on” state so that no two microphones are switched into the “on” state at the same time. Yet, microphone output between the “on” and “off” states fades out and cross-fades between microphones in a manner that is not annoying to the driver and/or passengers within the vehicle or a person on the other end of the cellular telephone line.
When generating the raw telephone input signal, it is desirable that a rather high percentage of the microphone output for the microphones in the “off” state, for example approximately 20%, be transmitted so that the cellular telephone line does not appear dead to a person on the other end of the telephone line when speech is not present within the vehicle.
In a second aspect, the invention applies noise reduction filters to filter out the background vehicle noise in the system microphone signals. In a microphone steering context, it is designed to remove the noise in the signals corresponding to the microphone(s) in the “on” state. The noise reduction filters are important for three primary reasons:
1. They generate a noise-reduced telephone input signal having improved clarity. By properly steering and switching the microphone signals, an intelligible raw telephone input signal is derived from the set of system microphone signals. However, this signal also contains a relatively large amount of background noise which in many cases severely degrades the quality of the speech signal, especially to a listener in a quiet environment on the other end of the line.
2. They reduce the background noise that is rebroadcasted to the system loudspeakers in both SISO and MIMO voice enhancement systems. The rebroadcast of the background noise is very perceivable in situations where the noise characteristics spatially vary within the vehicle. This is common in large vehicles where the amount of wind noise (i.e. open/closed window or sunroof), HVAC/fan noise, road noise, etc. vary depending on the passenger's position in the vehicle.
3. For vehicles employing voice recognition systems (for example, those that are used to interpret hands-free cellular phone commands), the background noise on the microphone signal(s) can severely degrade the performance of such systems. The noise reduction filter(s) reduce the background noise and therefore improve the performance of the voice recognition.
In its most general state, the noise reduction filte
Finn Brian M.
Nowak Michael P.
Andrus Sceales Starke & Sawall LLP
Digisonix LLC
Gesesse Tilahun
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