Institut EIT 3 MIMO

 

MIMO techniques in wireless communications

 

Special scientific equipment developed at our institution

MIMO Channel Sounder ARCHIMEDES

MIMO Demonstrator DeMoCRIT


Summary

Today MIMO techniques range in the most promising strategies to significantly enhance the spectral efficiencies and data rates of future mobile communication systems. On the opposite, if now improvement of data rates is required, the use of MIMO systems enables a significant power reduction at the transmitter of any communication system. Therefore, the upcoming improvement of the IEEE 802.11 Wireless Local Area Network (WLAN) standard (version IEEE 802.11-n) also includes the use of several antennas at both, the transmitter as well as the receiver.
In order to obtain maximum capacity and high data rates it is inevitable to find valid channel models, tailored for potential communication scenarios. In this context it turns out that WLAN MIMO radio channels are significantly less understood than it was necessary to obtain maximum capacity. Due to this fact we focus on such WLAN scenarios and try to establish valid channel models. Our special interest is directed towards in-room scenarios where is no obstruction between the MIMO transmitter and the receiver. For those Line-Of-Sight (LOS) channels the widely used plane-wave assumption which results in the idea that LOS channels only provide low-rank MIMO channel transfer matrices does not hold true. A spherical wave model is much more appropriate as it models the phase angle relations for the different antenna combinations exactly and hence, provides insight into the true capacity of such LOS indoor channels. In the past we were already able to show by measurements that LOS indoor MIMO channels offer distinctly higher capacities than it is widely assumed, especially if the antenna arrangement is well adapted to construct high-rank LOS channels. The results suggest he need of modified channel models than those which are discussed at the moment in the course of the WLAN standardization process. To correctly model correlated (LOS) MIMO channels is one of the key aspect of our current research.
Of course our results from the channel measurements also have crucial impact on the design of MIMO transmission systems. For correlated channels valid equalization and modulation strategies have to be developed to exploit as much of the theoretical capacity as possible. Recent results derived by our MIMO transmission demonstrator have show that there is still a large gap between the theoretical channel capacity and the capacity which can be exploited by current popular system architectures. Moreover, also in practice well adapted antenna setups in terms of the conctruction of high-rank LOS channels show higher data rates and better results regarding the channel equalization errors. By this fact, the demand for improved receiver architectures is reveald.

 


Research topics - short listing

  • MIMO channel measurements
  • MIMO capacity evaluation of correlated channels, especially with a strong LOS signal component present
  • wideband MIMO channel modeling
  • construction of low-cost MIMO channelsonders
  • MIMO transmission techniques
  • equalization strategies for correlated MIMO channels
  • MIMO adapted modulation techniques
  • construction of highly efficient MIMO transmission sytems

 

Active persons: V. Dantona, B. Lankl

Archimedes

The logo created for ARCHIMEDES MIMO channelsounder

measured channel impulse responses

The figure shows measured channel impulse responses where the second abscissa denotes different measurement intervals. The figures differ in the amount of motion within the channel as well as the strength of the LOS signal component.

CDFs

The figure shows cumulative distribution functions for the spectral efficiency of measured indoor channels. Here the positions of transmitter as well as receiver are treated as a random variable within a widely time-invariant scenario.

Capacity_Raum

If only the LOS signal component is regarded the channel's spectral efficiency across a room depends upon the antenna arrangements and their orientations towards each other.