|| In mobile radio systems, the bandwidth of spread spectrum signals for CDMA system is very wide. When the bandwidth exceeds the coherence bandwidth of the channel, the effect of multi-path fading become serious and the transmission signals are severely distorted. In OFDM systems, the available bandwidth is divided into a lot of small parts. By well selecting the number of sub-carriers according to the characteristics of the mobile channel will let the bandwidth of transmission signals smaller than the coherence bandwidth of channel. Then the multi-path fading problem can be overcome.|
In future mobile communications, the demand for multimedia will grow spectacularly. For example, the need of voice transmission for mobile phone and the need of high data rate transmission for wireless local area network (WLAN). Therefore, multi-rate system was developed in the recent years.
Yet, the characteristics of mobile channel vary with the moving velocity of the systems and the environment of the mobile channel. Therefore no single transmission mode owns the best performance in terms of spectrum efficiency, bit error rate, and transmission power.
In this thesis, we study coded multi-rate OFDM systems in different mobile environment and evaluate their performance by means of computer simulation. Hoping to find better transmission modes in different mobile channel.