COMPARISON OF STBC SYSTEM AND STTC SYSTEM USING VARIOUS DOPPLER SPECTRA

Over recent years, the requirement for multimedia applications, Internet services and high speed transmission had been rapidly increased. For high speed communication, the technique that is suitable is by the use of Orthogonal Frequency Division Multiplexing (OFDM) which reduces Inter Symbol Interference (ISI) and maximizes spectral efficiency. By using multiple transmit antenna, the reliability of data transmission can be improved by employing space time code method. Orthogonal Space Time Code is a bewitched technique for MIMO systems exploiting full spatial diversity order and symbol wise maximum likelihood decoding. Space time block code (STBC) doesn't provide coding gain but achieves diversity gain and acts on a block of data. Space time trellis code (STTC) provides both coding gain and diversity gain. This paper presents comparison of STBC and STTC system using various Doppler spectra at maximum Doppler shift for several SNR values varying from 0 dB to 20 dB and Frame Error Rate (FER). For four transmitting antenna and two receiving antenna, the STBC system is observed to have a Frame Error Rate (FER) of 0.0183 at SNR of 8 dB and the STTC system is observed to have a low Frame Error Rate (FER) of 0.0022 at SNR of 8 dB for Bell Doppler Spectrum. The performance of Space Time Trellis Code (STTC) is better than that of Space Time Block Code (STBC) as it is having low FER. However, the complexity of STTC is more due to presence of maximum likelihood (ML) decoder in the receiver.