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Gigabit MIMO OFDM Testbed
World record in radio transmission speed
The Gigabit MIMO OFDM Testbed combines both the well-known OFDM technique with innovative intelligent antenna systems. This kind of intelligent antenna systems are also called multiple antenna systems or MIMO (Multiple Input, Multiple Output)-Systems. The multiple antenna technology allows simultaneously transmission of different data streams over the same radio channel.
The OFDM transmission technique is ideally suited for combination with MIMO signal processing due to its robustness against multipath propagation and frequency selective radio channels. Just the multiple usage of the same frequency band requires space diversity caused by multipath signal propagation.
Until end of 2004 a MIMO-OFDM transmission with three Tx antennas and five Rx antennas has been realized. The testbed allows the realtime transmission of 1 GBPS via the radio channel. The RF channel bandwidth amounts to 100 MHz, therof 82 MHz are occupied by the OFDM signal. The maximum data rate of 1 GBPS is achieved with 64 QAM modulation on all subcarriers.
The project was carried out in collaboration with Siemens AG and Heinrich Hertz Institut. The extensive experience from recent projects ( for example broadband OFDM testbed) was a substantial presupposition for the succesful development of the MIMO OFDM testbed.
The system parameters of the Gigabit OFDM Testbed are listed below:
- Number of transmit antennas
- 3 (will be enhanced to 4)
- Number of receive antennas
- 5
- RF frequency
- 5,2 GHz
- RF channel bandwidth
- 100 MHz
- occupied RF bandwidth
- 82 MHz
- max. data rate
- 1 GBPS
- number of subcarriers
- 64
- Modulation
- 64QAM, 16QAM, QPSK, BPSK
- FEC Code rates
- convolutional code CR 1/2, ¾
- Data Interfaces
- Gigabit Ethernet, USB
The implementation of main signal processing was carried out in VHDL. For floating point operation an additional digital signal processor is used. The general concept of the MIMO OFDM testbed is depicted in the diagrams below. The testbed is well-suited for measurements in real radio transmission channels as well as for IP based applications with high data rates.
The testbed hardware is based upon the universal FPGA prototyping platform FFP Basic VP100. The board is equipped with two Xilinx Virtex II Pro VP100 devices. The hardware platform is extendable by several Add-On Boards (for example A/D conversion and D/A conversion) (Link). The add-on boards can be plugged in directly on the FPGA mainboard with short signal length. Therefore a clock frequency of 200 MHz between FPGA and external components can be realized.
The results of the complex MIMO signal processing are visualized with an analyse and monitoring software tool. Measurement data are read out with high update rate via the integrated USB interface. All present MIMO data streams can be displayed and analyzed separately.
In the near future the MIMO OFDM testbed development will be proceeded. For example the number of antennas will be increased and signal processing will be improved for mobile receiption.