I’ll take a look at just how modern sound transmission systems which are employed in nowaday’s wireless speakers operate in real-world environments with a large amount of interference from other wireless devices. The most popular frequency bands which are used by wireless devices include the 900 MHz, 2.4 Gigahertz and 5.8 GHz frequency band. Primarily the 900 MHz and also 2.4 Gigahertz frequency bands have started to become crowded by the increasing amount of products such as wireless speakers, cordless phones and so forth. Customary FM transmitters generally operate at 900 MHz and don’t have any specific means of coping with interference yet changing the transmit channel is a strategy to cope with interfering transmitters. Digital audio transmission is generally used by modern-day sound products. Digital transmitters normally work at 2.4 Gigahertz or 5.8 Gigahertz. The signal bandwidth is higher than 900 MHz transmitters and thus competition in these frequency bands is high. Quite a few cordless systems for example Bluetooth products along with wireless telephones use frequency hopping. Hence just changing the channel won’t steer clear of these types of frequency hoppers. Real-time audio has quite rigid requirements with regards to dependability and low latency. In order to offer those, other means are required. One technique is known as FEC or forward error correction. This approach enables the receiver to repair a damaged signal. For this purpose, supplemental data is transmitted from the transmitter. From this additional data, the receiver can restore the original information whether or not the signal was corrupted to some degree. FEC is unidirectional. The receiver does not send back any kind of data to the transmitter. As a result it is often used by products just like radio receivers in which the number of receivers is large.
A different technique employs bidirectional transmission, i.e. every receiver sends data to the transmitter. This strategy is only helpful if the number of receivers is small. Additionally, it requires a back channel to the transmitter. The information which is transmit has a checksum. From this checksum the receiver may detect whether any particular packet was received correctly and acknowledge. As lost packets will have to be resent, the transmitter and receivers have to store information packets in a buffer. This will create an audio latency, often called delay, to the transmission which is often a dilemma for real-time protocols including audio. Normally, the greater the buffer is, the greater the robustness of the transmission. Video applications, however, need the audio to be in sync with the video. In such cases a large latency is a problem. Devices that incorporate this particular procedure, nevertheless, are restricted to transmitting to a small number of receivers and the receivers consume more energy.
Often a frequency channel may become occupied by another transmitter. Ideally the transmitter can realize this fact and change to a different channel. To achieve this, a few wireless speakers continuously check which channels are available so that they can instantly switch to a clean channel. Considering that the transmitter has a list of clear channels, there is no delay in trying to find a clear channel. It is simply picked from the list. This approach is frequently termed adaptive frequency hopping spread spectrum.