Adaptive Coded Modulation Systems Based On Turbo Codes

Adaptive Coded Modulation (ACM) is a powerful technique to approach Shannon capacity and achieve high throughput on fading channels. With fast development of multimedia applications and 3G mobile communication systems, adaptive coded modulation technique has received much attention and considered as a key for the future communication systems.Continuous phase modulation (CPM) is a commonly used method for data modulation in wireless communication systems. It is used primarily because continuous phase modulation provides good spectral efficiency. Furthermore, CPM is typically implemented as a constant-envelope waveform. Therefore, CPM is attractive because the phase continuity yields high spectral efficiency, and the constant-envelope yields excellent power efficiency. The primary drawback is the high implementation complexity required for an optimal receiver. With the fast development of hardware technology, an optimal receiver for CPM becomes not difficult to carry out . As the OFDM technology, CPM is an attractive development in wireless communications and satellite communications.In this dissertation, we mainly study adaptive serially concatenated systems with QAM and CPM modulations based on Turbo codes. First we introduce the encoding and iterative decoding principles of Turbo codes, and then we present the modulation and two demodulation methods for CPM, Simulation results are provided for different modulation parameters (including different modulation levels).After introducing the basic idea of ACM systematically, we depict the models of adaptive serially concatenated systems with fixed threshold shifting. Finally, we investigate bit-error-probability (BER) and throughput of the system under different channel models. At the same time,the fixed threshold shifting is divided according to different combination modes of coding rate and modulation format. The most efficient combination of coding rate and modulation format is chosen from a set of modes according to the average signal-to-noise rate (SNR). In this way, the improved spectral efficiency can be achieved for an ACM system.