The acoustics department of the EMPA performs measurements of sound transmission in buildings. For that purpose it is necessary to measure two audio signals in different rooms. These signals have to be connected with a central analyser. Until now this connection was done with cables, which shall be replaced with a wireless connection in the future.

This large project has been divided into two parts. One for coding and decoding the audio data and the other for the transmission itself.

In this part the development of the digital transmission is described. For that a radio card, working half duplex in the 2.4 GHz frequency band, was used.

The radio channel can be used in both directions but not at the same time. That's why the project is realised with a state machine implemented with a digital signal processor (DSP). First a selectable transmission time is written into the DSP at the so-called masterside and then transmitted to the slaveside. The slave responds with the transmission of the audio data during the preset transmission time. When this time is over the cycle restarts. In addition, the DSP is responsible for the programming of the radio cards.

The data transfer to the two radio cards occurs serially. This process is controlled by specific control signals from the DSP. An interface card between the DSP and the radio card, which is implemented with a GAL-chip, handles this data transfer. The interface to the audio encoder and decoder is realised with a Dual-Port-RAM on a small printed circuit board.

The system successfully transmits the data over the air. But we couldn't write the data into the Dual-Port-RAM.

The aim of this project was to design a fast synthesizer for different frequency bands.

The schematic for the frequency synthesizer was designed and the layout was drawn. The subsequent measurements for the frequency band of 440MHz - 470MHz demonstrate that the specifications, lock time of less than 2ms and channel spacings of 12,5kHz, 20kHz or 25 kHz, could be reached.

A synthesizer for the band from 146MHz to 174MHz was not built due to lack of time. The schematic would be the same as for the other band. For a later realisation the design is described in the documentation.

In order to use the PLL-chip (Phase Locked Loop) LMX2352, its registers had to be programmed. In this project the programming has been realised by a DVD-Code Free Board (supplied externally).

If you are surfing with an analog modem in the Internet, only a small part of the theoretical bandwidth of the phone cable is used. xDSL increases this bandwidth with a terminal adapter on the user and network side. Thereby much more data can be transferred over the existing phone line.

DSL means Digital Subscriber Line and the 'x' stands for a letter. xDSL is the collective term for ADSL, HDSL, SDSL, etc.

In this diploma thesis a program was implemented to simulate the transfer loop-lenght of xDSL. In principle: The longer and thinner a copper cable is, the smaller the data rate. In particular signals containing high frequencies suffer heavy losses. A further problem are the disturbances caused by neighbouring phone lines.

In the program the disturbers and cable parameters can be choosen to simulate the reality as exactly as possible. With this simulation it's possible to make a decision whether the transfer will work or not.

The program was written in Matlab and designed with the Matlab toolbox GUI.

The diploma thesis was developed on behalf of the company Schmid Telecom AG Zurich.

The department of acoustics of the EMPA performes acoustic measurements outside and inside buildings. For that acoustic signals are measured at different locations and analysed in a central unit. Until now a complex wiring was necessary, which was a laborious task especially inside buildings. This shall be bypassed by transferring the audio data with a wireless system.

The entire task was divided into two theses (diploma). This thesis deals with the audio section, the other one with the data transfer, which uses a commercial radio module in the 2.45 GHz - band.

The requirements that must be fulfilled by the audio section are high. The data transfer should be in CD-quality. This requires a minimum dynamic response of 96 dB and protective measures against transfer errors.

The main problem thereby was the error protection. A Reed-Solomon code and an interleaving was used, with which the data transfer can be protected from burst errors. The complex mathematical basis of the Reed-Solomon code is treated in the literature only very theoretically. This thesis (diploma) tries to counteract this deficiency. It contains a short theoretical paper on Reed-Solomon codes, which was complemented with concrete numerical examples.

Furthermore the interface between the audio codecs, which were available on evaluation-boards and the DSP56002 from Motorola was designed, as well as a frame for the transfer was defined. With the implementation it became quickly evident that the necessary computing time frame for the decoding and correction of the received data was a further criteria to be considered, because the processing power of the DSP is limited.

In conclusion, a system has been developed that operates with a RS(15,11) code with 4-Bit symbols and an interleaving, so that a loss of 40 data bits every 220 s can be absorbed. The system (without the transfer unit of the second thesis) could be tested and is so far operational.