An ever expanding quantity of cordless gadgets which include wireless outdoor speakers available at amphony.com/products/wireless-speaker.htm is bringing about growing competition for the precious frequency space. I am going to check out a number of technologies which are utilized by the latest digital sound systems in order to see how well these solutions can work in a real-world situation. The popularity of cordless gizmos just like wireless speakers is mainly responsible for a quick rise of transmitters which transmit in the preferred frequency bands of 900 MHz, 2.4 Gigahertz and 5.8 GHz and thus cordless interference has turned into a serious issue.
The least expensive transmitters normally broadcast at 900 MHz. They work similar to FM radios. Since the FM signal uses a small bandwidth and thus only occupies a tiny part of the free frequency space, interference may be prevented by changing to a new channel. The 2.4 GHz and 5.8 Gigahertz frequency bands are used by digital transmitters and also are getting to be quite crowded lately because digital signals take up much more bandwidth as compared to analog transmitters.
Just changing channels, on the other hand, is no dependable solution for avoiding certain transmitters which use frequency hopping. Frequency hoppers like Bluetooth gadgets as well as several cordless telephones are going to hop throughout the whole frequency spectrum. As a result transmission on channels is going to be disrupted for brief bursts of time. Audio can be viewed as a real-time protocol. Consequently it has strict requirements regarding dependability. In addition, small latency is critical in several applications. For that reason more sophisticated strategies are required to ensure reliability. One of these methods is called forward error correction or FEC for short. The transmitter is going to transmit extra data besides the audio data. The receiver uses an algorithm which utilizes the extra information. In the event the signal is damaged during the transmission as a result of interference, the receiver can easily remove the erroneous data and restore the original signal. This approach works if the amount of interference won’t go beyond a specific threshold. FEC is unidirectional. The receiver doesn’t send back any kind of information to the transmitter. As a result it is frequently employed for systems like radio receivers in which the number of receivers is large. Yet another method utilizes receivers that transmit data packets to the transmitter. The transmitters incorporates a checksum with every data packet. Every receiver can determine whether a specific packet has been received correctly or damaged because of interference. Subsequently, each cordless receiver sends an acknowledgement to the transmitter. Since lost packets must be resent, the transmitter and receivers have to store information packets in a buffer. Using buffers brings about a delay or latency in the transmission. The amount of the delay is proportional to the buffer size. A larger buffer size increases the stability of the transmission. A big latency can be a problem for several applications however. Particularly if video exists, the audio should be synchronized with the movie. Furthermore, in multichannel surround sound applications in which a number of loudspeakers are cordless, the wireless speakers should be synchronized with the corded speakers. One limitation is that systems in which the receiver communicates with the transmitter can usually just transmit to a few wireless receivers. Also, receivers have to incorporate a transmitter and generally consume additional current
Often a frequency channel may become occupied by a different transmitter. Preferably the transmitter is going to understand this fact and change to another channel. To do this, a number of wireless speakers continuously check which channels are available so that they can quickly switch to a clean channel. Since the transmitter has a list of clear channels, there is no delay in trying to find a clear channel. It’s simply picked from the list. This technique is frequently referred to as adaptive frequency hopping spread spectrum.