Which Transmission Protocols Are Being Used By Wireless Speakers?

There are three primary frequency bands in which today’s cordless speakers work: 900 MHz, 2.4 GHz and 5.8 GHz. Because the quantity of wireless devices which work in these frequency bands has been growing continuously, those frequency bands have become increasingly crowded to a point in which devices trigger apparent degradation to the performance of other equipment. I will reveal one of several approaches which modern wireless speakers makers use as a way to tolerate other cordless products as well as to reduce the impact on other products.

Adaptive frequency hopping is one of the most recent methods which functions by scanning the whole frequency band for channels which are occupied by other transmitters. From all free channels, several channels are picked and put together into a hop set. In the course of the cordless transmission, the transmitter utilizes one of several unoccupied channels for a brief time period, commonly for as much as 10 milliseconds. After that it switches to the next frequency channel within the hop set. The hop set has to be communicated to each and every receiver to ensure that both transmitter as well as receiver are at all times working on the exact same frequency channel.

Besides the current hop set, the transmitter continues scanning all of the available channels and keeps a collection of backup frequency channels. One of these backup channels is used in the case another transmitter starts transmitting on one of the current hop-set frequency channels in order to change the hop-set frequency channel that has become occupied. The list of back-up frequency channels allows the transmitter to substitute an occupied frequency channel with a free frequency channel in a short amount of time. For that reason, adaptive frequency hopping works well in avoiding transmission on busy frequency channels and in avoiding interference from other devices.

You can find more techniques which are often used on top of adaptive frequency hopping. They further improve the robustness of the cordless audio transmission. Data buffering is a frequently used technique. The most important function of data buffering is compensating for lost or broken data packets. Data packets might be misplaced or damaged for a number of good reasons such as multipath fading, interference or poor reception. The transmitter adds a cyclic redundancy check (CRC) to each and every packet and also maintains a certain quantity of packets in a storage buffer. In the event that a packet has been broken or dropped, the receiver will transmit a request to the transmitter for retransmission of the lost or impaired packet. For this reason, the receiver has to be prepared to send information to the transmitter. In the instance of several cordless receivers, the protocol needs to have an adequate amount of time slots so that every receiver can request packets from the transmitter. Due to the fixed quantity of time slots in the back channel, these kinds of cordless loudspeakers have a restriction for how many wireless speakers are able to function from one transmitter.

Source by Gunter Fellbaum

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