What exactly is behind the term MIMO?
MIMO stands for Multiple Input Multiple Output. This refers to the use of multiple antennas at both the transmitter and receiver for wireless communications. This is the basis for special coding techniques, which use not only the temporal but also the spatial dimension of information transfer (space-time coding).
This delivers significant improvements in the quality (bit error rate) and data rates of a wireless connection. MIMO systems achieve more bits per second per hertz of bandwidth, and therefore higher spectral efficiency, than conventional SISO or SIMO systems. Thanks to these properties, MIMO systems are increasingly being used in telecommunications.
It is important to clearly distinguish between the transmitter and receiver – from the mobile devices to the base station or in the opposite direction.
Scalable, adaptive MIMO-OFDM wireless transmission system
The aim of the project was the development and implementation of testbeds for the evaluation of future wireless standards based on the OFDM transmission technology. The 3G-LTE standard developed by the 3rd Generation Partnership Project (3GPP) establishes MIMO/OFDMA transmission for the downlink. For the uplink, the SC/FDMA scheme is used.
The MIMO/OFDMA method permits optimal utilization of available frequency resources with a high degree of scalability and flexibility.
The OFDMA method offers a flexible allocation of frequency resources for a variety of users. For this, the available spectrum is divided into resource blocks. A resource block contains 12 adjacent subcarriers in the frequency direction for the duration of one sub-frame (1 ms). Ten sub-frames form a radio frame.
Each resource block may be modulated and coded differently, and assigned to different users. The scheduling of resources is based on the channel quality information (CQI) transmitted by the user equipment (UEs) to the base station.
Tested and implemented.
The baseband signal processing was implemented on the in-house prototyping platform FFP Basic +. The programming was done primarily in VHDL. Additional digital signal processors (DSP) were used for floating point operations. Thanks to the use of programmable hardware, it is possible to continuously adapt and extend the testbed and to implement new functions.
The testbed is used for measurements in real radio channels as well as for demonstration purposes. IP-based applications such as mobile streaming of video at high data rates have been achieved.
Specially developed analysis software allows the recording of measurements and real-time monitoring of essential system parameters. The Microsoft Windows-based software reads the data periodically from a built-in USB interface on the testbed.
„At first it sounds incredible, but it is going to expand capacity for the dramatic rise in mobile Internet traffic on our wireless network.“
The Heinrich Hertz Institute in Berlin.