Let me take a look at just how modern-day sound transmission technologies which are employed in nowaday’s cordless speakers operate in real-world situations having a great deal of interference from other cordless devices.
The popularity of cordless gizmos such as wireless speakers is mainly responsible for a rapid increase of transmitters which transmit in the preferred frequency bands of 900 MHz, 2.4 GHz as well as 5.8 Gigahertz and thus cordless interference has become a major problem.
The least expensive transmitters normally transmit at 900 MHz. They operate similar to FM stereos. Considering that the FM transmission has a small bandwidth and thereby just uses up a tiny part of the free frequency space, interference can be prevented by changing to another channel. Digital audio transmission is generally utilized by more contemporary sound systems. Digital transmitters normally function at 2.4 Gigahertz or 5.8 GHz. The signal bandwidth is higher than 900 MHz transmitters and thus competition in these frequency bands is high.
Frequency hopping devices, on the other hand, will continue to lead to further problems since they are going to disrupt even transmitters using transmit channels. Real-time audio has pretty rigid requirements regarding stability and low latency. To be able to offer those, additional mechanisms will be required.
One of these strategies is referred to as forward error correction or FEC in short. The transmitter is going to transmit extra information besides the sound data. From this supplemental information, the receiver can easily restore the original information even if the signal was damaged to a certain extent. FEC is unidirectional. The receiver doesn’t send back any data to the transmitter. Thus it is often used for equipment including radio receivers where the quantity of receivers is big.
One more technique makes use of receivers that transmit data packets to the transmitter. The data packets incorporate a checksum from which every receiver may decide if a packet was received correctly and acknowledge proper receipt to the transmitter. If a packet was corrupted, the receiver will inform the transmitter and request retransmission of the packet. As a result, the transmitter must store a great amount of packets in a buffer. Equally, the receiver will have to have a data buffer. Employing buffers brings about a delay or latency in the transmission. The amount of the delay is proportional to the buffer size. A bigger buffer size improves the reliability of the transmission. A big latency can generate problems for many applications however. Particularly if video is present, the sound must be synchronized with the movie. In addition, in multichannel audio applications in which several loudspeakers are cordless, the wireless loudspeakers should be synchronized with the corded loudspeakers. One limitation is that systems where the receiver communicates with the transmitter usually can merely transmit to a small number of cordless receivers. Furthermore, receivers need to add a transmitter and generally use up additional current
In order to steer clear of congested frequency channels, several wireless speakers watch clear channels and can change to a clear channel when the current channel becomes occupied by another transmitter. This method is also referred to as adaptive frequency hopping.
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