Adaptive Technology In The Mobile Communications Applications

Future mobile communications have to support the transmission of high rate data and multimedia applications in the radio spectrum, which is already extremely scarce. When the channel can be estimated and sent back to the transmitter, the transmission scheme can be adapted relative to the channel characteristics in order to improve the spectral efficiency. Most modulation and coding techniques do not adapt to fading conditions. These nonadaptive systems are effectively designed for the worst case channel conditions, resulting in insufficient utilization of the full channel capacity. Adapting to the signal fading allows the channel to be used more efficiently since power and rate can be allocated to take advantage of favorable channel conditions.The basic idea behind adaptive transmission is to maintain a constant by varying the transmitted power level, symbol transmission rate, constellation size, coding rate or any combination of these parameters. Thus, without sacrificing bit-error rate (BER), these schemes provide high average spectral efficiency by transmitting at high speeds under favorable channel conditions, and reducing throughput as the channel degrades.In this thesis, we first introduce the characteristic and the modeling of mobile channel, and then follow the concept and the principle of AMC. We study the performance of AMC combined with the channel coding, such as Punctured convolutional codes, which can provide a high spectral efficiency and meanwhile keep a given BER performance. In order to improve the spectral efficiency, we combined the AMC scheme with multi-level coded modulation technique. The simulation results show that adaptive modulation and coding technique is an efficiency methods to provide a high spectral efficiency, combined with channel coding and multi-level coded modulation, it can maintain an acceptable transmission quality and make a good advantage of the scares spectral resourse, which will play an important role in the future mobile communication system.