A constantly growing amount of cordless products such as wireless headphones is bringing about increasing competition for the precious frequency space. Let me take a look at a few technologies which are employed by modern electronic sound gadgets to determine how well these products can operate in a real-world situation.
The growing interest in wireless consumer systems just like wireless headphones has started to cause problems with numerous devices competing for the restricted frequency space. Wireless networks, wireless phones , Bluetooth as well as some other products are eating up the valuable frequency space at 900 MHz and 2.4 Gigahertz. Cordless audio products must assure reliable real-time transmission within an environment which has a large amount of interference.
The most cost effective transmitters generally transmit at 900 MHz. They work much like FM stereos. Because the FM transmission has a small bandwidth and thus just occupies a small fraction of the free frequency space, interference may be eliminated simply by changing to an alternative channel. Digital audio transmission is normally utilized by more contemporary audio gadgets. Digital transmitters usually work at 2.4 Gigahertz or 5.8 GHz. The signal bandwidth is higher than 900 MHz transmitters and thus competition in these frequency bands is high.
A number of cordless systems like Bluetooth devices and also cordless phones incorporate frequency hopping. Hence merely changing the channel is not going to steer clear of these kinds of frequency hoppers. As a result modern audio transmitters incorporate specific mechanisms to deal with interfering transmitters to assure consistent interruption-free sound transmission.
One of these strategies is known as forward error correction or FEC for short. The transmitter is going to broadcast extra data in addition to the audio data. From this supplemental information, the receiver can recover the original data even when the signal was corrupted to some degree. FEC is unidirectional. The receiver doesn't send back any information to the transmitter. As a result it is frequently used for products just like radio receivers in which the quantity of receivers is large.
Another approach makes use of receivers which transmit data packets back to the transmitter. The information packets have a checksum from which every receiver may decide if a packet was received properly and acknowledge proper receipt to the transmitter. In cases of dropped packets, the receiver is going to notify the transmitter and the dropped packet is resent. Therefore both the transmitter and receiver require a buffer to store packets. Employing 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 improves the reliability of the transmission. Video applications, however, need the sound to be in sync with the video. In this case a big latency is difficult. Cordless systems which incorporate this approach, however, can only broadcast to a limited number of cordless receivers. Normally the receivers have to be paired to the transmitter. Given that each receiver also requires transmit functionality, the receivers are more pricey to manufacture and in addition use up more energy.
In an effort to better handle interference, a number of wireless headphones is going to monitor the available frequency band as a way to determine which channels are clear at any moment in time. If any specific channel gets crowded by a competing transmitter, these products can change transmission to a clean channel without interruption of the audio. The clean channel is chosen from a list of channels that was determined to be clear. A technology that uses this kind of transmission protocol is called adaptive frequency hopping spread spectrum or AFHSS
The growing interest in wireless consumer systems just like wireless headphones has started to cause problems with numerous devices competing for the restricted frequency space. Wireless networks, wireless phones , Bluetooth as well as some other products are eating up the valuable frequency space at 900 MHz and 2.4 Gigahertz. Cordless audio products must assure reliable real-time transmission within an environment which has a large amount of interference.
The most cost effective transmitters generally transmit at 900 MHz. They work much like FM stereos. Because the FM transmission has a small bandwidth and thus just occupies a small fraction of the free frequency space, interference may be eliminated simply by changing to an alternative channel. Digital audio transmission is normally utilized by more contemporary audio gadgets. Digital transmitters usually work at 2.4 Gigahertz or 5.8 GHz. The signal bandwidth is higher than 900 MHz transmitters and thus competition in these frequency bands is high.
A number of cordless systems like Bluetooth devices and also cordless phones incorporate frequency hopping. Hence merely changing the channel is not going to steer clear of these kinds of frequency hoppers. As a result modern audio transmitters incorporate specific mechanisms to deal with interfering transmitters to assure consistent interruption-free sound transmission.
One of these strategies is known as forward error correction or FEC for short. The transmitter is going to broadcast extra data in addition to the audio data. From this supplemental information, the receiver can recover the original data even when the signal was corrupted to some degree. FEC is unidirectional. The receiver doesn't send back any information to the transmitter. As a result it is frequently used for products just like radio receivers in which the quantity of receivers is large.
Another approach makes use of receivers which transmit data packets back to the transmitter. The information packets have a checksum from which every receiver may decide if a packet was received properly and acknowledge proper receipt to the transmitter. In cases of dropped packets, the receiver is going to notify the transmitter and the dropped packet is resent. Therefore both the transmitter and receiver require a buffer to store packets. Employing 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 improves the reliability of the transmission. Video applications, however, need the sound to be in sync with the video. In this case a big latency is difficult. Cordless systems which incorporate this approach, however, can only broadcast to a limited number of cordless receivers. Normally the receivers have to be paired to the transmitter. Given that each receiver also requires transmit functionality, the receivers are more pricey to manufacture and in addition use up more energy.
In an effort to better handle interference, a number of wireless headphones is going to monitor the available frequency band as a way to determine which channels are clear at any moment in time. If any specific channel gets crowded by a competing transmitter, these products can change transmission to a clean channel without interruption of the audio. The clean channel is chosen from a list of channels that was determined to be clear. A technology that uses this kind of transmission protocol is called adaptive frequency hopping spread spectrum or AFHSS
About the Author:
Gunter Fellbaum has been developing audio and other electronic products for over a decade. You can get additional information about wireless headphones from Amphony's website.
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