Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

MIMO Overview 305SinglestreamSpace–timecoding(STC)OptionalSpace–timedecodingSinglestreamFigure 6-3General principle of space–time coding (STC)The principle of STC is illustrated in Figure 6-3. The basic idea is to provide throughcoding constructive superposition of the signals transmitted from different antennas.Constructive combining can be achieved, for instance, by modulation diversity, whereorthogonal pulses are used in different transmit antennas. The receiver uses the respectivematched filters, where the contributions of all transmit antennas can be separated andcombined with MRC.The simplest form of modulation diversity is delay diversity, a special form ofspace–time trellis codes. The other alternative of STC are space–time block codes. Bothspatial coding schemes are described in the following.6.2.2.1 Space–Time Trellis Code (STTC)The simplest form of STTCs is the delay diversity technique (see Figure 6-4). The idea isto transmit the same symbol with a delay of iT s from transmit antenna i = 0,...,M − 1.SinglestreamRepetitioncode rate1/MT sOptionalDetectionSinglestream(M − 1)T sFigure 6-4Space–time trellis code with delay diversity technique