Let me examine exactly how contemporary audio transmission systems that are utilised in today’s wireless speaker systems operate in real-world situations having a great deal of interference from other cordless devices.
The rising interest in cordless consumer gadgets including wireless speakers has begun to cause difficulties with several devices competing for the limited frequency space. Wireless networks, cordless phones , Bluetooth and also various other products are eating up the precious frequency space at 900 MHz and 2.4 Gigahertz. Cordless sound gadgets need to assure robust real-time transmission within an environment having a large amount of interference.
Common FM transmitters typically operate at 900 MHz and do not have any certain method of coping with interference but switching the broadcast channel is a solution to cope with interfering transmitters. Today’s sound systems employ digital sound transmission and frequently operate at 2.4 GHz. These digital transmitters broadcast a signal which takes up far more frequency space than 900 MHz transmitters and therefore have a greater potential for colliding with other transmitters.
Quite a few wireless products including Bluetooth products and also cordless phones incorporate frequency hopping. Thus just switching the channel will not avoid these kinds of frequency hoppers. Real-time audio has very strict requirements relating to stability and minimal latency. To be able to offer these, other means are needed.
One method is referred to as FEC or forward error correction. This approach enables the receiver to repair a corrupted signal. For this purpose, supplemental information is transmitted from the transmitter. Using this added data, the receiver can easily recover the original information even if the signal was damaged to some degree. FEC is unidirectional. The receiver will not send back any data to the transmitter. As a result it is often used by systems such as radio receivers in which the number of receivers is large.
Another method makes use of receivers which transmit information packets back to the transmitter. The information that is transmit includes a checksum. Using this checksum the receiver can determine whether any particular packet was received correctly and acknowledge. As lost packets must be resent, the transmitter and receivers must store information packets in a buffer. This is going to introduce an audio latency, also known as delay, to the transmission that could be a dilemma for real-time protocols including audio. Commonly, the larger the buffer is, the larger the robustness of the transmission. Video applications, however, require the sound to be in sync with the movie. In such cases a big latency is problematic. Wireless systems which use this approach, nonetheless, are only able to broadcast to a limited quantity of wireless receivers. Typically the receivers have to be paired to the transmitter. As each receiver also requires transmit functionality, the receivers are more pricey to make and in addition consume more power.
So as to better overcome interference, a few wireless speakers is going to monitor the available frequency band so as to decide which channels are clear at any given moment in time. If any particular channel becomes crowded by a competing transmitter, these products can switch transmission to a clean channel without interruption of the audio. The clear channel is picked out from a list of channels which has been identified to be clean. A technique that employs this kind of transmission protocol is referred to as adaptive frequency hopping spread spectrum or AFHSS
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