 However, an open loop transmit diversity scheme must not degrade performance for a user close to the base station where the channels may be line of sight and nearly ideal.Since STTD is an orthogonal coding system this is also guaranteed.STTD can be applied to single symbols in QAM, CDMA code words, or subcarrier symbols in OFDM and the transmit method has become standardised, especially in 3G cellular wireless [2] as described below.