In connection with the measurement of the acoustical isolation between various rooms and floors in buildings or with noise measurements along motorways, the company Norsonic has the problem of not being able to use traditional hardwired measuring links. We were successful in solving this inconvenience by applying a robust wireless digital link.

The demands for such a transmission link are high: The audio data shall meet CD?quality. In order to protect the audio data from eventual errors coming from disturbances of the wireless link, provisions are made to augment the signals with additional redundant information. With such information the receiver can recognise and subsequently correct errors up to a high degree. For the transmission of a monaural signal of CD ? quality a channel bandwidth of 1Mbit/s required. Additionally for the error correction feature the same amount of bandwidth is required. This results in a necessary bandwidth of 2Mbit/s, which will be transmitted by a wireless LAN - card (WLC). The chosen radio transmission PC card has only a physical layer and not as usual an additional MAC ? layer. The advantage of this concept is that the entire bandwidth is available for the transmission of data.

The sample rate of ordinary audio sources does not correspond exactly to the transmission rate of the radio transmission channel. For this reason the sample-rate-converter converts the signal to the given transmission rate of the WLC. With this method it is possible to transmit the data after the sample-rate-converter with the I2S?bus.

The audio data shall be protected with an error correction code, which can be implemented by means of the DSP-board. It should be possible to correct the errors of the radio link virtually up to the point of complete interruption of the signals. For this purpose the transmission link has to be precisely characterised in order to be able to choose an appropriate error correction protocol for which recommendations are given