Thomas Haustein

Performance of a MIMO system with overlay pilots

A multiple-input multiple-output (MIMO) indoor radio system is studied to identify the origin of a typical performance degradation. When the data and overlay pilot-sequences for the channel estimation are transmitted at the same time, an error floor at high signal-to-noise ratio is normally observed. The floor is caused by channel estimation errors due to the interfering data signal. The crosstalk between the data paths can be calculated, approximately, and it is shown that the shape of the bit error curves can be steered both with the amplitude ratio /spl eta/ between pilot and data signals and with the length L of the sequences. Near-optimum performance can be reached in this way. With L = 16383, for instance, an amplitude ratio of /spl eta/ /spl ges/ 0.15 (0.3) is sufficient for BPSK (16-QAM) modulation in a MIMO system with 8 transmit and 12 receive antennas.

Link adaptation in a multi-antenna system

We consider link adaptation for multi-antenna systems based on channel information also that at the transmitter. Using adaptive channel inversion (ACI), a step-wise trade-off between spatial multiplexing and diversity is realized. Due to pre- and post-processing, the channel is corrupted only by Gaussian noise in front of the detectors. By jointly optimizing the number of data streams and the common modulation, a nearly continuous adaptation of spectral efficiency is realized. Up to moderate powers, the channel capacity is approached in regular and singular MIMO channels, provided that scalar coding is applied.

A radio system with multi-element antennas

A radio hardware concept for indoor WLAN applications is described in which both the transmitter and the receiver use multi-element antennas. The system exploits the increased capacity of the multiple-input multiple-output (MIMO) indoor radio channel and it is designed especially for high data rates. A technique to measure the MIMO channel matrix is described. A weak pseudo-noise sequence out of a set of Gold codes is added to each transmitted signal from which the amplitude and phase of the carrier corresponding to that antenna is identified at each receive antenna. The data signals are reconstructed at the receiver in a weighted-signal combining network where IQ modulators steer the complex weights. Fully transparent transmission at high data rates is possible in this way.

A power and bandwidth efficient modulation for diffuse wireless infrared communication

A new coding scheme for wireless diffuse infrared links is proposed, allowing simultaneously improvements in power and bandwidth efficiency. It gives the freedom to design diffuse systems overcoming limits given by the delay spread and required transmitter power for On-Off-keying.