Monday, March 10, 2014

An In-Depth Look At Advanced Wireless Speaker Products

By Mike Heller


An ever increasing quantity of wireless products for instance wireless speakers causes increasing competition for the valuable frequency space. I'm going to look at a number of systems that are utilized by the latest digital sound systems in order to determine how well these products may operate in a real-world environment.

Customary FM transmitters usually work at 900 MHz and don't possess any certain method of dealing with interference but switching the transmit channel is a method to cope with interfering transmitters. The 2.4 Gigahertz and 5.8 Gigahertz frequency bands are utilized by digital transmitters and also are becoming pretty crowded recently as digital signals occupy much more bandwidth than analog transmitters.

Only changing channels, nonetheless, is no reliable solution for avoiding specific transmitters that use frequency hopping. Frequency hoppers just like Bluetooth gadgets or several wireless phones will hop throughout the whole frequency spectrum. Hence transmission over channels is going to be disrupted for brief bursts of time. Audio can be viewed as a real-time protocol. Therefore it has stringent needs pertaining to stability. In addition, low latency is vital in several applications. As a result more sophisticated techniques are needed to assure stability.

Merely changing channels, nonetheless, is no dependable remedy for avoiding specific transmitters which use frequency hopping. Frequency hoppers such as Bluetooth devices as well as many wireless telephones will hop through the full frequency spectrum. As a consequence transmission on channels will be disrupted for brief bursts of time. Sound can be viewed as a real-time protocol. Because of this it has strict needs with regards to reliability. Additionally, small latency is essential in lots of applications. As a result more advanced techniques are required to ensure stability.

In scenarios in which there's merely a few receivers, often yet another method is utilized. The wireless receiver sends information packets back to the transmitter to confirm correct receipt of data. The transmitters has a checksum with each data packet. Each receiver may see whether a particular packet has been received properly or damaged because of interference. Then, every wireless receiver will be sending an acknowledgement to the transmitter. Considering that lost packets must be resent, the transmitter and receivers must hold data packets in a buffer. This is going to introduce an audio latency, often called delay, to the transmission which might be an issue for real-time protocols such as audio. Commonly, the larger the buffer is, the larger the robustness of the transmission. Video applications, nevertheless, need the audio to be synchronized with the video. In cases like this a large latency is problematic. Wireless systems that incorporate this approach, however, are only able to transmit to a small number of wireless receivers. Commonly the receivers have to be paired to the transmitter. Given that each receiver also requires transmit functionality, the receivers are more expensive to produce and also use up more energy.

To avoid crowded frequency channels, some wireless speakers keep an eye on clear channels and can change to a clear channel as soon as the current channel becomes occupied by a different transmitter. The clean channel is picked from a list of channels which has been identified to be clear. A technology which utilizes this kind of transmission protocol is named adaptive frequency hopping spread spectrum or AFHSS




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