Subject: Mobile Communication Systems

Topic: Emerging Technologies for 4G

Difficulty: High

Two outstanding examples of transmit diversity schemes for the multiple-antenna flat-fading channel are space-time block coding (STBC) and space-time trellis coding (STTC). Comparing the performance of STBC and STTC in terms of the frame error rate keeping the transmit power, spectral efficiency and number of trellis states fixed.

A simple concatenation of space-time block codes with traditional AWGN (additive white Gaussian noise) trellis codes outperforms some of the best-known space-time trellis codes at SNRs (signal to noise ratios) of interest. For a small number of trellis states with one or two receive antennas, and is useful for the design and implementation of multiple-antenna wireless systems.

The inherent memory of the STTC provides an additional coding gain compared to the STBC at the expense of higher computational complexity. STBC transforms the MIMO channel into an equivalent scalar AWGN channel and the concatenation of traditional channel coding with STBC shows good performance.

STBC/SFBC are of significantly less complexity than STTC and for this reason they are usually preferred, by introducing spatial and temporal correlation into the signals transmitted from different antennas, STTC achieves both diversity gain and coding gain.