Conversation assistant for noisy environments

An infrared (IR) emitter having a broad emission pattern driven by a frequency-modulated (FM) carrier signal enables electronic communication between multiple talkers and multiple listeners. A narrow reception pattern on the listener's receiving unit combined with the inherent capture effect of FM coding provides each listener with the means of easily and naturally selecting one of many talkers from a group. A close microphone for the talking party and a close earphone for the listening party enables the system to assist conversation particularly in the case of noisy environments by improving the signal to noise ratio. A similar system of broad emission transmitters and narrow reception can be used in other systems, such as a teleconferencing unit in which users have transmitters and receivers and a teleconferencing unit has multiple receivers arranged to receive signals in multiple different sectors.

BACKGROUND

I. Field of the Invention

The present invention relates to wireless communication systems and methods, and in particular to assistive listening systems that facilitate communication in noisy environments.

II. Discussion of Related Art

To facilitate communication in noisy environments, wireless systems may be used to effectively receive and transmit audio signals. In such systems, sounds produced by an audio source are modulated and transmitted wirelessly over, for example, an infrared (IR) or radio signal. At the destination, this signal is intercepted by a receiver that reconstructs the original sounds and plays them back. This method is employed by many commercially-available headphone systems such as the Sony MDR-IF240RK Wireless Headphone System and the Koss HB60 Infrared Clip-On Wireless Headphones.

This method can be used for two-way communication as well. Headsets like the Etymotic Research Link-It and the Comlink Personal Sound Enhancer can produce audio signals using a microphone and wireless transmitter and can also receive signals using a built-in wireless receiver and earpiece speaker.

However, many-to-many communication presents complexities that do not arise in the unidirectional and bidirectional cases described above. An impediment to the development of a system for multi-way signal transmission is the problem of co-channel interference. Traditional signal transmission using amplitude, frequency, or phase modulation of radio-frequency carriers is designed to work with one carrier signal at a time. Mixing multiple carriers in a demodulator can result in badly distorted output.

SUMMARY

Systems and methods are described here for wireless communication, including multi-way wireless communication that reduces distortion caused by co-channel interference. A talker's speech is picked up by an individual body-worn microphone and transmitted wirelessly over a relatively wide angle, but short range. Each listener wears a receiver that has a narrow reception angle. The received signal can be converted to an acoustic signal by an earphone. Each person in the conversation can have both a transmitter and a receiver, enabling multi-way wireless signal transmission for speech communication in noisy settings.

The use of a directional receiver allows the use of a simple frequency modulation (FM) scheme and provides the user with a mechanism for selecting the source to be heard. The directionality of the receiver reduces the problem of signal distortion.

A directional receiver will attenuate sources outside of a limited angular range relative to those within the limited angular range, e.g., angles relative to a straight-ahead direction, but there can still be some mixing of modulated carriers. However, FM is known to be highly resistant to co-channel interference because of an effect called “FM capture.” The capture effect is responsible for the much higher quality and noise-immune reception of an FM radio broadcast compared to AM.

The high degree of directionality that can be easily achieved with an IR receiver, e.g., by use of a lens or shaped ‘blinders’, together with the strength of the FM capture effect, supports the use of FM to facilitate this multi-way application.

In other embodiments, a receiving system can have multiple directional IR receivers for dividing a room or other region into sectors, and an FM demodulator (individually, or separate circuits collectively) for receiving IR signals in each region and providing them to other equipment, such as a recording device or a transmission device, e.g., as part of a teleconferencing system.

Other features and advantages will become apparent from the following detailed descriptions and drawings.

DETAILED DESCRIPTION

FIG. 1shows a diagrammatic representation of the light and information flow in an embodiment of a wireless communication system. Multi-way signal transmission is achieved using infra-red (IR) signal transmission. As shown inFIG. 1, two talkers transmit over a wide angular range, while the listener receives over a more limited angular range, so that (as shown) the listener is substantially only receiving from one of the two talkers. In a receiver, the directionality of IR can be easily manipulated, e.g., through the use of a lens or blinders. Making the receiver directional achieves two goals: (1) it provides a natural mechanism for a listener to select the talker to be heard (for example, by attaching the system to the head, selection is effected via turning the head toward the desired talker); and (2) by reducing co-channel interference, it allows frequency modulation (FM) of a single carrier frequency to be used for all channels. The operational simplicity of this approach enables low-cost and easy-to-use assistive listening products.

A simplified block diagram of the transmitter subsystem100and the receiver subsystem200is shown inFIG. 2. In the transmitter subsystem100, a directional microphone101is coupled to a modulation input of an FM Modulator102, and can also be coupled to an input of a Voice Operated Switch (VOX)103. The FM Modulator drives an IR LED104. To save energy and battery power, the VOX can be used to enable the LED output only when speech is present; i.e., the transmitter is powered up when speech is detected and powered down when speech is not detected. In the receiver subsystem200, an optical filter201is used to admit a desired set of wavelengths, such as near IR, and reject other wavelengths of light. A photodiode202produces a signal that provides input to an FM Demodulator203that provides a Carrier Detect (CD) signal to un-mute the output. The demodulated audio is amplified in amplifier204and provided to the user, e.g., through an earphone205when a valid carrier is being received. The receiver can be made directional, e.g., by using a lens or blinders over the photodiode or over the filter and photodiode. A power source (not shown) is used to operate the system, which may be internal to any of the subcomponents, or power may be conveyed from an external source.

FIGS. 3aand3bshow an embodiment including a one-piece unit utilizing a short bifurcated boom. The boom can be constructed so as not to impede the view of and access to the mouth during eating. The boom contains a noise-canceling microphone. The photodiode receiver is located on a flexible gooseneck to accommodate situations such as automobile travel when the talker is not in front of the listener. The receiver can be provided within a tube with a geometry that defines a limited angular range of reception. The gooseneck would normally be oriented in the same direction as the IR emitter support prong in order to facilitate easy aiming by pointing the head in the general direction of the talker. An earpiece can be designed to permit left or right ear operation.

The unit can have fixed horizontal and also vertical angles of reception that receive signals in a limited angular range while substantially attenuating signals received from sources at other angles outside that range. In other embodiments, the unit can include controls that allow the user to adjust the vertical and horizontal reception angles of the receiver. Wider reception angles provide increased freedom of movement by allowing for the vertical and horizontal head motions of the user. On the other hand, using a wider reception angle can sacrifice some of the benefits of directionality. The horizontal angle can be up to +/−45° from a center line, and be variable in a range that is within a range of about +/−10° to +/−45° from a center line (e.g., in front of the user), or within a range within about +/−20° up to +/−35° from a center line. A vertical angle can be up to about +/−45°, or some smaller angle. The controls can operate in a continuous manner, such as moving a microphone continuously within a tube, or through a set of discrete steps. The control can be implemented by altering the receiver from one setting to another, or by using multiple receivers with different characteristics such that the control selects one of the receivers to use. The controls can be operated and adjusted by a user during operation, or they can be used to set angular parameters in advance for all later uses.

Testing with a talker equipped with a microphone and IR transmitter, and a listener at a distance of 1 meter equipped with an IR receiver and earphone, indicates that speech-to-noise ratio is improved by approximately 20 dB over that of the direct acoustic signals measured at the ears of the listener. This improvement can generally be maintained with a vertical reception angle of +/−45° and a horizontal reception angle of +/−20° for a full angle of about 40°. However, the ideal reception angle depends on user preferences and environmental conditions, and the user can use the angle controls to adjust the device accordingly.

FIG. 4shows another application in which up to n transmitters can communicate with a single input audio device, such as a line input of a tape recorder or a transmission system of a teleconferencing system. Transmitters551,552,553, and554, which can represent users and have substantially the same construction as subsystem100(FIG. 2), are distributed throughout the room. A multi-channel conference unit500has directional receivers501-50n, that effectively divide the area into sectors, e.g., eight sectors, and receive signals transmitted by transmitters551-554. The sectors can be designed to have little overlap between them. In cases where there is one transmitter in a sector, that transmitter is unambiguously selected. In the case where there are multiple transmitters in a sector, the strongest transmitter is automatically selected due to the capture ratio characteristics of the FM modulation. The circuitry within each directional IR receiver would include an FM demodulator. In this system, multiple transmitters operating on a single carrier frequency can be automatically selected based on their direction relative to the conference unit without recourse to manual frequency or code setting.

FIG. 4also represents a conferencing application, such as telephone conferencing, in which the users are equipped with IR receivers having relatively narrow reception patterns, as pictured inFIG. 1, in addition to broad-angle IR transmitters. The multi-channel conference unit500also has omnidirectional IR emission, in addition to the multiple narrow reception directions501-50nshown here as sectors. Each look direction of the multi-channel conference unit500will typically receive at most one valid signal from one of the individual transmitter systems551-554. Look directions containing a valid signal, as indicated internally by a carrier detect signal, will cause that signal to be switched onto a common mixing bus to be sent out to the telephone or other conferencing input.

Since each of the individual transmitter systems551-554uses a Voice Operated Switch (VOX) to switch on its omnidirectional emission, the carrier detect signals within the multi-channel conference unit500will be active only when the given look direction is in view of an individual transmitter system that is actively conveying speech sounds, thus enabling the common mixing bus to contain only active speech signals and reducing room noise from open microphones having no active speech.

In this conferencing system, the individual units551-554function as described above, with broad or omnidirectional emission and relatively narrow reception, as pictured inFIG. 1. A user merely points the unit (aims his or her head) at the user they wish to hear. They may also in the same way point their unit at the telephone unit when they wish to hear the telephone.

It will be appreciated that the scope of the present invention is not limited to the above-described embodiments, but rather is defined by the appended claims; and that these claims will encompass modifications of and improvements to what has been described. For example, different configurations of transmitter and receiver can be used on an individual.