Data processing: generic control systems or specific application – Specific application – apparatus or process – Digital audio data processing system
Reexamination Certificate
1998-08-24
2002-10-15
Harvey, Minsun Oh (Department: 2644)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Digital audio data processing system
Reexamination Certificate
active
06466832
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wireless local audio transmission, and specifically to high quality wireless audio speakers.
BACKGROUND OF THE INVENTION
Wireless local transmission of audio data has become very popular in recent years. Wireless transmission eliminates the need for wires which are annoying and limiting. Local wireless transmission is used, for example, in portable home telephone systems, stereo systems, home theater systems, and sound surround systems.
U.S. Pat. Nos. 5,272,525, 5,349,386, and 5,319,716, which are incorporated herein by reference, describe wireless local transmission systems which transmit audio and/or video signals as modulated RF signals.
However, wireless transmission systems are limited in their transmission range and quality. One transmission problem is due to interference from other wireless communication systems, such as cordless telephones and remote control devices. These limitations are especially annoying in audio systems for high quality music transmission.
In order to avoid such interference and limitations U.S. Pat. No. 5,491,839 suggests having a transmitter and one or more receivers which allow a user to select a frequency band for transmission. Thus, the user may select a band which has less interference than other bands. In addition, the receivers have a muting circuit which is operated when a faulty signal is encountered in the transmitter or in the receiver.
PCT publication WO97/29550 describes transmitting audio data as digital signals. A forward error correction encoder and an interleaver are used to minimize the damage caused by noise and interference to the audio data.
However, improvement of transmission of audio data is still sought. It is particularly desirable to achieve high-fidelity audio transmission without requiring adjustments to be performed by the user.
SUMMARY OF THE INVENTION
It is an object of some aspects of the present invention to provide a system for high-fidelity local transmission of audio data.
It is another object of some aspects of the present invention to provide methods and apparatus for digital transmission of audio data in relatively narrow bands, such as, the ISM 900 MHz band.
It is another object of some aspects of the present invention to provide methods and apparatus for transmission of audio data with two-way control communications.
It is another object of some aspects of the present invention to provide low-cost apparatus for transmission of digital audio data.
It is another object of some aspects of the present invention to provide methods and apparatus for digital transmission of audio data with low transmission delay.
It is another object of some aspects of the present invention to provide systems for transmission of audio data, such that a plurality of systems may be used simultaneously in a single area without interfering each other.
In some aspects of the present invention, the systems, apparatus and methods are used to transmit video data, as well as audio data.
In preferred embodiments of the present invention, audio input data is wirelessly transmitted from a transmitter to one or more compatible receivers. The transmitter and receivers may comprise a standalone system which is used together with separate audio generators and speakers. Preferably, however, the transmitter and receivers are integrated in a stereo or surround system, in which the transmitter is connected to or is a part of a music generator such as a CD or DVD player, and the receivers are connected to, or part of, one or more wireless speakers.
The audio data is converted to digital form, if not already in digital form, and is preferably compressed and encoded to a coded form which allows high-quality, low-delay transmission of the audio data. Preferably, the compression is performed according to a standard compression scheme such as an audio MPEG compression scheme. The audio data is encapsulated together with ancillary data into packets, preferably having a fixed length determined according to transmission and delay considerations, as is known in the art. The methods and apparatus for data encoding and encapsulation, along with the use of the ancillary data, enable the system to convey sound of improved quality, and with greater user convenience, relative to wireless audio systems known in the art.
The ancillary data preferably includes audio control data, such as a volume indication and system control data. The system control data comprises indication of frequencies used and identification information which allows a receiver to easily ignore packets addressed to a different receiver, thus preventing crosstalk. Preferably, the identification includes a unique ID which identifies the transmitting system, and an indication to which receiver of the transmitting system the packet is addressed. For example, the indication to which receiver the packet is addressed may include indication of right or left, front or rear and/or main or sub-woofer.
Preferably, the ancillary data includes indication of a frequency channel at which the current packet is transmitted in order to allow the receiver to tune onto the frequency channel on which the packets are transmitted.
In some preferred embodiments of the present invention, the audio control data comprises a volume level, preferably for right and left receivers separately. Thus, when a low volume is used there is no need to lower the magnitude of the audio input to the transmitter and decrease the dynamic range of the signal. Rather, the audio input is transferred at full magnitude to the receivers which control the volume of the signal according to the volume level.
In some preferred embodiments of the present invention, each packet is transmitted in at least two copies to the receivers, preferably on two respective frequency channels. Preferably, the receivers assess the packets and assign a quantitative performance value to the received packets, generally based on an error detection code, such as CRC. Alternatively or additionally, the signal strength of the received signal is used in assigning the quantitative performance value to the received signal. Preferably, for each packet, the receivers choose the copy having the highest quantitative performance value, and this copy is used by the receiver to extract the audio data.
In one such preferred embodiment of the present invention, when the receiver receives the first copy it calculates the CRC of the received data and compares it to the transmitted CRC. If the calculated CRC is not identical to the transmitted CRC, the first copy is identified as “defective”, and the second copy is read and its CRC is calculated and compared to its transmitted CRC. If the calculated CRC in the second copy is correct, the audio data of the second copy is played by the speaker associated with the receiver. If, however, the calculated CRC of both copies is defective, then the speaker is preferably kept silent for a predetermined period of between about 0.1 and 1 seconds, preferably using a soft mute procedure described hereinbelow. Alternatively or additionally, the copy with a higher quantitative performance value is played, provided the performance value is above a predetermined threshold. If the calculated CRC in both copies is correct, then the copy with the highest quantitative performance value is chosen.
Alternatively or additionally, the receiver uses the first copy which arrives unless it is found to be defective (i.e., to include noise and/or errors beyond a predetermined level), for example by CRC calculation and comparison. Only when the first copy is defective does the receiver read the second copy and play it if it is not defective.
Preferably, as noted above, the at least two copies are transmitted on at least two respective distinct frequency bands, such that frequency dependent interference may be overcome by choosing the copy of the packet exhibiting a lower level of interference. Further preferably, the at least two frequency bands are separated by a span larger than bands typically used
Rephaeli Dan
Sussman Giora
Tirosh Oren
Zuqert Benjamin
Altec Lansing R & D Center Israel
Harvey Minsun Oh
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