I’ll take a look at how present day sound transmission systems which are employed in current wireless speakers work in real-world conditions having a great deal of interference from other cordless systems.
The most popular frequency bands which can be used by wireless gadgets include the 900 MHz, 2.4 GHz and 5.8 GHz frequency band. Primarily the 900 MHz and also 2.4 Gigahertz frequency bands have begun to become clogged by the ever increasing amount of devices like wireless speakers, wireless phones and so on.
FM type sound transmitters usually are the least robust when it comes to tolerating interference because the transmission doesn’t have any procedure to deal with competing transmitters. On the other hand, those transmitters use a fairly limited bandwidth and changing channels may often eliminate interference. The 2.4 GHz and 5.8 GHz frequency bands are utilized by digital transmitters and also have become rather congested recently given that digital signals occupy far more bandwidth than analogue transmitters. Simply switching channels, however, is no dependable solution for staying away from certain transmitters that use frequency hopping. Frequency hoppers such as Bluetooth gadgets as well as quite a few cordless telephones will hop throughout the full frequency spectrum. As a result transmission on channels will be disrupted for short bursts of time. For this reason modern audio transmitters incorporate special mechanisms to cope with interfering transmitters to ensure consistent interruption-free audio transmission.
One of these strategies is referred to as forward error correction or FEC in short. The transmitter is going to broadcast additional information besides the sound data. Using this additional data, the receiver may restore the original information even when the signal was corrupted to some extent. FEC is unidirectional. The receiver won’t send back any kind of information to the transmitter. Thus it is frequently employed for products such as radio receivers in which the quantity of receivers is large.
Yet another method utilizes bidirectional transmission, i.e. every receiver transmits information to the transmitter. This approach is only helpful if the number of receivers is small. Additionally, it requires a back channel to the transmitter. The data which is broadcast includes a checksum. Using this checksum the receiver may decide if any specific packet was received correctly and acknowledge. If a packet was corrupted, the receiver will notify the transmitter and request retransmission of the packet. As such, the transmitter needs to store a great amount of packets in a buffer. Likewise, the receiver must have a data buffer. Using buffers will cause a delay or latency in the transmission. The amount of the delay is directly related to the buffer size. A larger buffer size increases the stability of the transmission. A large latency can be a problem for certain applications nonetheless. Particularly if video is present, the sound must be synchronized with the video. Also, in multichannel audio applications where a few speakers are cordless, the speakers for outdoors should be in sync with the corded speakers. Systems which integrate this mechanism, however, are limited to transmitting to a small number of receivers and the receivers consume more power. Often a frequency channel can get occupied by a different transmitter. Preferably the transmitter can understand this fact and change to yet another channel. To accomplish this, a number of wireless speakers continuously monitor which channels are available so that they can instantly switch to a clean channel. Considering that the transmitter lists clean channels, there’s no delay in looking for a clean channel. It’s simply picked from the list. This approach is usually called adaptive frequency hopping spread spectrum.