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OFDM Testbed
With the development of new standards for WLAN in the frequency range of 5 GHz, the OFMD transmission technology asserts itself more and more in areas concerned with the transmission of high data rates in time variant and frequency selective radio channels.
The European standard Hiperlan/2 as well as the IEEE802.11a standard uses the OFDM transmission technology. The Physical Layer Realisation of both standards is very similar. The Hiperlan /2 standard offers additional functions such as QoS (Quality of Service) and Radio Resource Management.
Both standards offer different ways of modulation and FEC Coderates. The maximum performable net-data rate is 54 Mbit/s (64 QAM Coderate 3/ 4).
A Flexible OFDM Testbed was developed in the context of the Coverage Project together with our project partners Siemens, TU Hamburg-Harburg and TU Dresden. The job of IAF was the realisation of the Physical Layer. The project was carried out successfully and today, an effective testbed for measurements and further optimisation is available.
In order to be able to carry out quantitative measurements numerous measurement interfaces were implemented.
The results show a very good performance of the system. It can therefore be regarded as a reference for OFDM-transmission systems in 5 GHZ frequency band.
The diagram above shows the basic setup of the testbed. Ethernet-connections as well as MAC-Protocols are implemented on the PC platform. The Physical Layer is built on FPGA-based hardware. Hence, it offers a high degree of flexibility.
The synchronisation as well as the algorithms of channel estimation work on high-capacity DSP. The powerful reserves of the DSP allow for the implementation of algorithms with an intense calculation effort.
In addition we also develop software for measurement data acquisition and analysis, e.g. for monitoring of OFDM radio transmission (constellation diagram, error vector magnitude).
