A Study Of High Dimensional Constellation Rotation Based On OFDM System

The paper is based on the two-dimensional constellation rotation technique which is mentioned in the OFDM system. First, the author introduces the concept, the broadcasting methods and the advantages of digital television, studying the overview of research on the development of terrestrial digital television broadcasting technology at home and abroad. Then the author lists every mainstream digital television broadcasting transmission standard, continuing to introduce the background of the DVB-T2 system, the system structure and constellation rotation technique used in DVB-T2 system.The third part is about the existing implementation of domestic and foreign high-dimensional constellation rotation technique. There are two main methods including constructing a rotation matrix by algebraic number theory and rotating twice to realize four-dimensional constellation rotation. Algebraic number theory method that need to find the corresponding minimal polynomial depending on the conditions seems like more complex. What calls for special attention is that there is no corresponding demodulation method, but many theories mentioned in the construction process for the design and analysis of the new method helps a lot. This method minimizes the signal to noise ration providing a well starting point for the subsequent design method for high-dimensional constellation. The other scheme uses two consecutive constellation rotation operations for the constellation of QAM signals. The advantages of this scheme are relatively simple progress and relatively low complexity, but it is not suitable for complex channel conditions.Based on the derivation and analysis of the above two methods, the author propose a new scheme to achieve the four-dimensional constellation rotation. Although the new method is also rotating twice to achieve fourth-order diversity gain, the signal combinations is different from the old scheme. What’s more, the Q-cycle delay is no need in the new method. Finally, after the analysis of the new four-dimensional constellation rotation matrix, the author propose an improved maximum likelihood detection algorithm. New detection algorithm does not loss characteristics of the system meanwhile the complexity of the algorithm is not increased. The design method is not required to make real and imaginary parts experience different channel fading, so that it can avoid some of the disadvantages of the Q-cycle delay. It is helpful to improve system performance in different kinds of complex channel. In the fourth chapter the author focuses on the steps and the simulation results of the method as an example of QPSK modulation. By the analysis of the rotation matrix, the author gets the conditions of different methods achieving the maximum diversity order.