Research On Efficient Subband Adaptive Modulation Aglorithm In OFDM System

OFDM has been regarded as the key technology for future broadband wireless communication systems, due to its robust to multipath-fading and high frequency efficiency. Adaptive modulation technique in OFDM systems can improve system performance significantly by adaptively assigning appropriate modulation modes and signal power to different subchannels. Research on adaptive modulation techniques in OFDM systems will be much valuable for the development of future broadband wireless communication systems.Some fruitful theoretical researches and algorithms design work have been carried out with regard to the problems of loading algorithms.The thesis bring up two new calculating schemes of Subband Equivalent gain, named Minimum gain (Min) scheme and Reciprocal-Average (RA) gain scheme. Two new adaptive modulation technologies in constant-rate OFDM system , Subband Equivalent Greey Loading and Subband Equivalent Bandwith Optimized Loading, with low complexity and good performance are presented by using Greey Loading,Optimal Theoretical Loading and schemes of Subband Equivalent Gain.The optimization target of Subband Equivalent Greey Loading is to get the lowest total system power in the condition of fix target bit error rate and system bit rate. The main idea of this algorithm is taking a subband as a basic allocation unit of Greey Loading, which consists of consecutive carriers. This algorithm can reduce the required signaling overhead of modulation modes for practical implementations and complexity of the allocation. Besides, Minimum gain (Min) scheme and Reciprocal-Average (RA) gain scheme are proved to be a usable one with low complexity and good performance among all the calculating schemes of Subband Equivalent gain.