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Wideband OFDM Testbed
Air Interface for 4G Mobile Communication
Within the last years OFDM (Orthogonal Frequency Division Multiplex) has attracted more and more interest due to its robustness against frequency selective fading radio channels. Furthermore OFDM systems are well- suited for efficient hardware realization.
Combination of OFDM transmission technique and multiple antenna systems (MIMO) will allow enormous increase of spectral efficiency. MIMO systems benefit from multipath propagation combined with multiple transmit and receive antennas.
The OFDM transmission technique is also well-suited for mobile applications. Dependent on system parameters and receiver algorithms a high robustness against doppler-shift is achievable.
The project Development of a wideband OFDM Testbed was realized in cooperation with Siemens AG Munich. It is used for research activities in the area Air Interface for 4G Mobile Communication.
The used signal bandwidth amounts to 85 MHZ and enables transmission data rates up to 300 MBPS. The system was designed for use in the wireless LAN frequency bands located at 2,4 GHz and 5,2 GHz.
To achieve a optimized adaption on radio channel characteristics, the transmission modes are adjustable in a wide range.
- Modulation:
- BPSK, QPSK, 16QAM, 64QAM
- Guard-Intervall-length:
- 1/4, 1/8
- FEC-Coderate:
- 1/2, 3/4
For connection of IP based applications a Gigabit Ethernet interface was integrated. Therewith it is now possible to run applications with a very high demand on data rate over a wireless channel.It is also possible to built a network consisting of multiple wireless terminals. The allocation of data rates to multiple users ist individual adjustable.
The baseband processing was realized completely in VHDL and impelmented on two Xilinx FPGA. Hardware-efficient algorithms for synchronisation and channel estimation were developed and integrated. Due to its flexible structure the system is well-suited for future enhancements, for example for MIMO signal processing.
As hardware platform the universal FPGA prototyping board FFP Basic is used. The board includes two Virtex II FPGA and connectors for multiple add-on boards.The hardware modules for A/D and D/A conversion and LVDS interfacing are connected directly to the FPGA. Thereby external clock frequencies up to 200 MHZ are achievable.
Measurement data can be read out via an integrated USB interface. Analysis and visualization of measurement data is processed with a customized measurement and analyzing software.
