I am going to investigate exactly how contemporary audio transmission technologies that are employed in the latest wireless speakers work in real-world situations having a great deal of interference from other cordless equipment. The increasing popularity of cordless consumer gadgets just like wireless speakers has begun to cause difficulties with several products competing for the restricted frequency space. Wireless networks, cordless phones , Bluetooth and other devices are eating up the valuable frequency space at 900 MHz and 2.4 GHz. Cordless sound gadgets have to ensure reliable real-time transmission within an environment having a great deal of interference.
FM type audio transmitters usually are the least reliable relating to tolerating interference considering that the transmission doesn’t have any procedure to deal with competing transmitters. On the other hand, these kinds of transmitters use a fairly restricted bandwidth and changing channels may avoid interference. Today’s audio gadgets utilize digital sound transmission and often function at 2.4 GHz. Such digital transmitters send out a signal which takes up more frequency space than 900 MHz transmitters and so have a greater potential for colliding with other transmitters. Just switching channels, nonetheless, is no dependable remedy for steering clear of certain transmitters which use frequency hopping. Frequency hoppers which include Bluetooth gadgets as well as numerous cordless phones are going to hop through the full frequency spectrum. Thus transmission on channels will likely be disrupted for short bursts of time. Therefore modern-day audio transmitters use specific mechanisms to deal with interfering transmitters to ensure continuous interruption-free audio transmission. One strategy is known as FEC or forward error correction. This approach allows the receiver to correct a damaged signal. For this reason, supplemental information is transmitted by the transmitter. Using this supplemental information, the receiver can recover the original data whether or not the signal was damaged to a certain degree. Transmitters utilizing FEC alone normally may transmit to any number of wireless receivers. This mechanism is usually used in products where the receiver is not able to resend data to the transmitter or where the quantity of receivers is fairly big, like digital radios, satellite receivers and so forth.
Another technique uses bidirectional transmission, i.e. each receiver sends information to the transmitter. This method is only useful if the quantity of receivers is small. In addition, it requires a back channel to the transmitter. The transmitters has a checksum with each information packet. Each receiver can easily detect whether a particular packet has been acquired correctly or disrupted because of interference. Then, each wireless receiver sends an acknowledgement to the transmitter. If a packet was corrupted, the receiver is going to notify the transmitter and ask for retransmission of the packet. As a result, the transmitter needs to store a certain amount of packets in a buffer. Similarly, the receiver will need to maintain a data buffer. This buffer brings about an audio delay which is dependent upon the buffer size with a larger buffer improving the robustness of the transmission. Video applications, nevertheless, need the sound to be in sync with the video. In such cases a large latency is problematical. Wireless systems that use this method, however, are only able to broadcast to a restricted number of cordless receivers. Typically the receivers have to be paired to the transmitter. Because each receiver also requires broadcast functionality, the receivers are more expensive to produce and also use up more energy.
To be able to better overcome interference, some cordless outdoor speakers will monitor the available frequency band so as to determine which channels are clear at any given moment in time. If any specific channel gets congested by a competing transmitter, these devices can switch transmission to a clean channel without interruption of the audio. The clean channel is selected from a list of channels which has been determined to be clear. One technique that makes use of this kind of transmission protocol is referred to as adaptive frequency hopping spread spectrum or AFHSS
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